Emapalumab in pediatric relapsed/refractory hemophagocytic lymphohistiocytosis: clinical responses, attenuated efficacy upon retreatment, and role in bridging to HSCT

Emapalumab in pediatric relapsed/refractory hemophagocytic lymphohistiocytosis: clinical responses, attenuated efficacy upon retreatment, and role in bridging to HSCT | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Emapalumab in pediatric relapsed/refractory hemophagocytic lymphohistiocytosis: clinical responses, attenuated efficacy upon retreatment, and role in bridging to HSCT Min’er Gu, Shengchao Wu, Jingying Zhang, Fenying Zhao, Juan Liang, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8540730/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract Relapsed/refractory hemophagocytic lymphohistiocytosis (R/R HLH) represents a hyperinflammatory state driven largely by IFN-γ dysregulation and carries a high risk of early mortality and failure to bridge to hematopoietic stem cell transplantation (HSCT). Emapalumab, a fully human anti–IFN-γ monoclonal antibody, has emerged as a targeted option, but evidence in heterogeneous real-world pediatric populations remains limited. We retrospectively reviewed pediatric patients with R/R HLH who received emapalumab at our center from April 2023 to July 2025. Clinical responses, cytokine kinetics, virologic parameters, survival outcomes, and HSCT feasibility were assessed. Ten children were included: primary HLH (n = 3), EBV-HLH (n = 5), and malignancy-associated HLH (n = 2). Early clinical improvement was observed in most patients, with an ORR of 70% (3 pHLH, 3 EBV-HLH, and 1 M-HLH). IFN-γ, IL-6 and CXCL9 levels declined markedly among responders. Five (3 pHLH and 2 EBV-HLH) successfully proceeded to HSCT, four of whom achieved sustained remission. Patients requiring a second course of emapalumab exhibited attenuated fever resolution and reduced cytokine clearance. During a median follow-up of 3.8 months, the 6-month OS was 45.3 \(\:\text{±}\) 29.2%. Five patients (3 pHLH and 2 EBV-HLH) remained alive at the time of last follow-up. No newly emerged treatment-related toxicities were observed. In conclusion, emapalumab rapidly controls hyperinflammation in pediatric R/R HLH and enables HSCT in a substantial subset of patients. Diminished responsiveness during retreatment underscores the need for timely disease-modifying therapy. Integrated evidence supports IFN-γ blockade as a key component of multimodal HLH management. emapalumab relapsed/refractory hemophagocytic lymphohistiocytosis interferon-γ retreatment Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome characterized by uncontrolled activation of cytotoxic T cells and macrophages, leading to excessive cytokine release and progressive multiorgan dysfunction. HLH comprises primary forms driven by pathogenic variants affecting cytotoxic machinery—including PRF1 , UNC13D , STX11 , STXBP2 , RAB27A , and others—and secondary forms triggered by infections, malignancies, autoimmune conditions, immune reconstitution, or immunotherapy[ 1 , 2 ]. Despite etiologic diversity, dysregulated IFN-γ signaling represents a shared pathogenic axis. IFN-γ not only amplifies macrophage activation and hemophagocytosis but also drives key biomarkers such as CXCL9 and soluble CD25 (sCD25), which correlate with disease activity and treatment response[ 3 – 7 ]. Standard HLH-directed therapy, historically based on the HLH-94/04 regimens using dexamethasone and etoposide, can induce remission in many patients[ 8 – 10 ]; however, a substantial subset of children develop relapsed or refractory hemophagocytic lymphohistiocytosis (R/R HLH). R/R HLH is marked by persistent hyperinflammation, high early mortality, and difficulty achieving adequate disease control to bridge to hematopoietic stem cell transplantation (HSCT), the only curative option for most patients[ 11 – 13 ]. Adjunctive immunomodulatory agents—such as JAK inhibitors, IL-1 blockade, PD-1 inhibitors, and anti-CD52 therapy—have expanded treatment strategies[ 11 ], but their efficacy remains variable across HLH subtypes. Given the central role of IFN-γ in HLH pathophysiology, targeted neutralization has emerged as a rational therapeutic approach[ 14 ]. Emapalumab, a fully human monoclonal antibody that binds and neutralizes free IFN-γ, was approved in 2018 by the U.S. Food and Drug Administration for primary HLH that is refractory, recurrent, progressive or intolerant to conventional HLH therapy[ 15 ]. Early clinical studies demonstrated rapid fever resolution, cytokine downregulation, and improved transplant feasibility[ 16 ]. However, existing research evidence and real-world data in pediatric R/R HLH, particularly in EBV-HLH, malignancy-associated HLH, and post-transplant settings, remain limited[ 17 – 20 ]. Moreover, the durability of response and the effectiveness of repeated emapalumab courses have not been thoroughly examined. To address these knowledge gaps, we conducted a single-center retrospective study evaluating the clinical responses, cytokine kinetics, virologic patterns, survival outcomes, and HSCT feasibility in children with R/R HLH treated with emapalumab. This study aims to clarify the role of IFN-γ blockade in contemporary HLH management and to explore its potential positioning within multimodal treatment strategies, including sequential therapy and HSCT preparation. Methods Study design and patients This was a single-center, retrospective study conducted in the department of hematology/oncology, Children's Hospital of Zhejiang University School of Medicine, China. Consecutive pediatric patients diagnosed with R/R HLH who received emapalumab between April 2023 and July 2025 were included. All of the patients presented indication for hematopoietic stem cell transplantation. The study was approved by the institutional ethics committee (2025-IRB-0497), and the requirement for informed consent was waived due to the retrospective design. HLH diagnosis followed the HLH-2004 criteria. Refractory disease was defined as failed to achieve at least partial remission 2 weeks after initial HLH-94 regimen or other chemotherapy-contained regimens, and relapse was defined as disease reactivation after initial remission. Assessment of treatment response and monitoring Clinical and laboratory responses were assessed at baseline (prior to the first emapalumab infusion) and at days 3, 7, and 14 after the first emapalumab infusion. HLH-associated biomarkers—including ferritin, sCD25, CXCL9, IL-6, IL-10, IFN-γ, D-dimer, liver function indicators, and EBV-DNA titers—were serially monitored. Cytokine analyses used standard hospital laboratory assays. Fever resolution was defined as axillary temperature < 37.3°C for ≥ 24 hours without antipyretics. The primary endpoints were overall response rate (ORR) and event-free survival (EFS). Clinical response categories followed criteria used in prior clinical studies of HLH[ 16 , 21 ]. The ORR was defined as achieving a complete response, partial response, or improvement in measures of HLH. EFS was defined as the time from first emapalumab initiation to disease relapse, death without remission or death. Patients without an event were censored at the date of last follow-up. Secondary endpoints included overall survival (OS) and bridging to HSCT. OS was defined as the time from first emapalumab dose to death from any cause, survivors were censored at last follow-up. Safety assessment All adverse events occurring within 30 days of the first emapalumab dose were collected and graded per the Common Terminology Criteria for Adverse Events (CTCAE v5.0). Potential emapalumab-related toxicities—including myelosuppression, infections, organ dysfunction, metabolic abnormalities, infusion reactions, et al—were recorded. Because many patients received concomitant chemotherapy or targeted immunomodulators, attribution focused on identifying “possibly related” adverse events. Statistical analysis Statistical analysis was performed using SPSS 25.0. Changes in laboratory parameters from baseline to days 3, 7, and 14 were analyzed using paired tests (paired t test for approximately normally distributed differences or Wilcoxon signed-rank test for non-normally distributed differences), with analyses restricted to patients with available paired measurements at each time point. Time-to-event outcomes (EFS and OS) were estimated using the Kaplan-Meier method with 95% confidence intervals (CIs). All tests were two-sided, and p values < 0.05 were considered statistically significant. Results Patients and baseline characteristics A total of 10 pediatric patients with relapsed/refractory HLH were included in this study (Table 1). The median age was 5.7 years (range, 0.2–13.9 years), with eight male patients. According to underlying etiology, three patients were diagnosed with primary HLH (pHLH), five with Epstein–Barr virus–associated HLH (EBV-HLH), and two with malignancy-associated HLH (M-HLH). Pathogenic variants were identified in three pHLH patients (Two patients harbored compound heterozygous mutations in UNC13D , and one patient had a compound heterozygous mutation in STXBP2 ), and the two M-HLH cases were diagnosed with peripheral T-cell lymphoma (PTCL) and diffuse large B-cell lymphoma (DLBCL), respectively. Among EBV-HLH patients or presenting with concomitant EBV infection, detectable serum EBV-DNA loads were present at baseline, ranging from 3.41×10 3 to 1.42×10 5 copies/mL. The median interval from initial HLH diagnosis to emapalumab initiation was 42.5 days, ranging from 24 to 176 days. At baseline, most patients exhibited marked hyperinflammation, characterized by elevated ferritin, sCD25, CXCL9, and IFN-γ levels, with persistent high EBV-DNA titers in the EBV-HLH subgroup. Dosing, scheduling, and concomitant therapies were abstracted retrospectively from the medical records. All patients had received multiple prior therapies, including dexamethasone, HLH-94-based regimens, ruxolitinib, PD-1 inhibitors, and L-DEP combinations. At emapalumab initiation, all patients continued to receive concurrent immunochemotherapy or immunomodulatory agents, as detailed in Table 2 . Emapalumab was administered intravenously at doses ranging from 1 to 6 mg/kg every 3–4 days, and the number of doses per course was individualized according to disease activity and response. In patients who developed reactivation after an initial response, a second emapalumab course was sometimes administered at the time of reactivation. Throughout all emapalumab courses, patients concomitantly received systemic corticosteroids and ruxolitinib as part of institutional salvage regimens for R/R HLH. Table 2 Treatment exposure, response assessment, and outcomes following emapalumab therapy No. 1 2 3 4 5 6 7 8 9 10 Emapalumab exposure dose (mg/kg) 2 1 2 1 1 2 2 2.5 1.5 3 Number of doses received in first course 2 1 1 2 1 4 1 1 1 1 Treat exposure and outcomes Previous therapy HLH-94, RUX HLH-94, R-DEP, PD-1 mAb + L-DEP HLH-94, RUX, L-DEP HLH-94, RUX, L-DEP RUX, PD-1 mAb + L-DEP, DXM, L-DEP HLH-94, RUX, PD-1 mAb + L-DEP, HSCT HLH-94, PD-1 mAb + L-DEP VMLD, Hyper-CVAD, ICE, DXM, RUX R-CHOP, COP, RTX, HLH-94, RUX HLH-94, RUX Concurrent therapy HLH-94, RUX HLH-94, RUX DXM, RUX RUX, L-DEP DXM, RUX MP, RUX RUX, PD-1 mAb + L-DEP DXM, RUX RUX, L-DEP HLH-94, RUX Response PR Improvement Death PR PR NR CR NR PR PR First event Censored Relapse Death without remission Relapse Relapse Death without remission Censored Death without remission Relapse Relapse HSCT after therapy Yes Yes No Yes Yes No No No No Yes Outcome Alive Alive Death Death Alive Death Alive Death Death Alive Abbreviations: DXM, Dexamethasone; RUX, Ruxolitinib; R-DEP, Ruxolitinib - liposome doxorubicin, etoposide, and methylprednisolone; PD-1 mAb+L-DEP, Programmed Death-1 Monoclonal Antibody combined with PEG-asparaginase, liposome doxorubicin, etoposide, and methylprednisolone; VMLD, Vincristine, Mitoxantrone Liposome, L-Asparaginase and Dexamethasone; Hyper-CVAD, Cyclophosphamide, Vincristine, Epirubicin and Dexamethasone; ICE, Ifosfamide, Carbopatin and Etoposide; R-CHOP, Rituximab - Cyclophosphamide, Epirubicin, Vincristine and Prednisone; COP, Cyclophosphamide, Vincristine and Dexamethasone; RTX, Rituximab; MP, methylprednisolone. Treatment response and cytokine kinetics Rapid clinical responses were observed following emapalumab initiation. Early defervescence occurred in all febrile patients within 48–72 hours, except for one patient (EBV-HLH) who experienced fulminant disease progression with central nervous system (CNS) involvement and subsequently died after 4 days of first emapalumab administration. The ORR to emapalumab was 70% in this cohort, comprising 1 CR (EBV-HLH), 5 PR (2 pHLH, 2 EBV-HLH and 1 M-HLH), and 1 improvement of HLH (pHLH) (Table 2 ). Two patients (1 EBV-HLH and 1 M-HLH) failed to achieve response following emapalumab therapy. One patient experienced EBV reactivation-associated HLH relapse after HSCT, whereas the other developed secondary HLH in the context of peripheral T-cell lymphoma. Despite continuous concomitant treatment with systemic corticosteroids and ruxolitinib during emapalumab therapy, both patients showed persistent disease activity and ultimately died. Serial laboratory assessment showed differential biomarker dynamics (Fig. 1 ). Ferritin and IL-10 levels did not demonstrate significant early changes (Fig. 1 A, C), whereas IL-6 and IFN-γ showed reductions over time, with statistically significant improvement at selected time points (e.g., IL-6 at day 3 and 7, P = 0.02; IFN-γ at day 3 and 14, P < 0.01) (Fig. 1 B, D). sCD25 and CXCL9 decreased more prominently in most responders than in non-responders (Fig. 1 E-F), consistent with pharmacodynamic modulation of the IFN-γ axis. In contrast to inflammatory biomarkers, virological control was limited. EBV-DNA titers remained persistently elevated in most EBV-HLH patients, highlighting limited virological response despite initial clinical inflammatory improvement (Fig. 1 G). Despite initial responses, durability was limited: among 7 patients who responded to emapalumab, five (2 pHLH, 2 EBV-HLH and 1 M-HLH) experienced relapse as the first event, consistent with the swimmer plot showing early disease control followed by frequent subsequent relapse (Fig. 2 ). Only two patients (1 PR and 1 CR at initial response) achieved sustained remission at last follow-up: one pHLH patient who proceeded to successful HSCT and one R/R EBV-HLH patient who achieved prolonged remission following combined emapalumab with PD-1 inhibitor and L-DEP therapy. Among the five patients who experienced disease relapse after an initial response, subsequent management strategies varied. Four patients (1 pHLH, 2 EBV-HLH, and 1 M-HLH) were re-treated with emapalumab, either as monotherapy or in combination with chemotherapy, whereas one patient with pHLH continued treatment with the HLH-94-based regimen. One patient with EBV-HLH, who experienced multiple relapses following repeated emapalumab exposure, ultimately proceeded to HSCT during a subsequent remission phase. In contrast, the remaining four patients failed to achieve adequate disease control after relapse and were considered for urgent HSCT. Of these, three ultimately underwent transplantation, while one patient with M-HLH who had underlying immunodeficiency and severe disease-related complications, experienced failure of urgent HSCT and subsequently experienced progressive clinical deterioration and ultimately died. Comparison of treatment response between first and second Emapalumab courses For patients who achieved an initial response to emapalumab but later experienced HLH reactivation, a second course was defined as a new treatment sequence initiated after documented clinical and/or laboratory relapse. Four such patients received at least two emapalumab courses, enabling a direct comparison of treatment effects. Baseline values for each course were taken from the last assessment before initiation, and post-treatment status was defined using the best measurement within the first 7 days—specifically, the lowest value for inflammatory markers (or highest for albumin)—to capture early pharmacodynamic suppression of IFN-γ–driven inflammation. Changes in body temperature and key biomarkers (ferritin, IL-6, IL-8, IL-10, IFN-γ, D-dimer, alanine aminotransferase [ALT], and albumin [ALB]) were compared between courses. To quantify response magnitude, we calculated the log₁₀-transformed change (Δlog value) from baseline to post-treatment and visualized individual and group-level responses using radar plots, where smaller areas indicate greater overall improvement. During the first course, most patients exhibited rapid and sustained defervescence. In contrast, fever resolution was slower and more variable during the second course (Fig. 3 A). Radar plots of log₁₀(post-treatment/baseline) ratios for inflammatory and organ-function markers consistently showed reduced biomarker improvements in the second course (Figs. 3 B-C). At the group level, the composite radar area was larger during retreatment, reflecting attenuated reductions in IFN-γ, IL-6, IL-10, IL-8, ferritin, D-dimer, and ALT, along with less pronounced albumin recovery. Together, these findings indicate diminished responsiveness of the IFN-γ–driven inflammatory pathway upon emapalumab retreatment and less effective control of systemic inflammation during the second course. Safety, bridging to HSCT and survival outcomes No emapalumab-attributable severe adverse events were identified during the study period. Among 9 evaluable patients (one died for disease progression of HLH after 4 days of first emapalumab dose) the most frequent grade ≥ 3 potential adverse events included myelosuppression and secondary infections (bacterial predominance) ( Supplementary Table S1 ). Less frequent events included liver dysfunction, gastrointestinal bleeding, and electrolyte abnormalities. Overall, most observed toxicities were considered attributable to underlying disease severity, concomitant chemotherapy, or underlying immune dysregulation rather than emapalumab itself. Overall, five patients (3 pHLH and 2 EBV-HLH) were successfully bridged to HSCT. Among them, two patients proceeded to HSCT during a phase of disease control following HLH remission, whereas the remaining three underwent urgent HSCT after disease relapse with persistently uncontrolled HLH despite repeated courses of emapalumab and/or combination chemotherapy. At the time of last follow-up, four (3 pHLH and 1 EBV-HLH) among the five patients who underwent HSCT remained alive with sustained disease control, while one patient died from transplantation-related complications. During a median follow-up of 3.8 months (range, 0.1–30.3 months), five patients (3 pHLH and 2 EBV-HLH) remained alive and the 6-month OS was 45.3 \(\:\pm\:\) 29.2% (Fig. 4 ). Among the five patients who received HSCT, the median interval from HLH diagnosis to HSCT was 3 months, and from first emapalumab dose to HSCT was 33 days. Four of them achieved durable remission post-HSCT. Non-HSCT patients had poor outcomes, including rapid progression, CNS involvement, or refractory hyperinflammation. Notably, one EBV-HLH patient achieved complete virological remission after emapalumab combined with PD-1 inhibitor and L-DEP therapy, suggesting potential synergy between IFN-γ blockade and immune-checkpoint–directed regimens. When outcomes were analyzed according to HLH subtype, all three patients with pHLH ultimately underwent HSCT and achieved sustained remission. Among the five patients with EBV-HLH, clinical courses were heterogeneous: one patient experienced rapid disease progression with CNS involvement and died early; one achieved sustained remission following combined emapalumab, PD-1 inhibitor, and L-DEP therapy; one proceeded to HSCT during remission; one failed to achieve disease control and died; and one underwent urgent HSCT but died from transplantation-related complications. In contrast, both M-HLH patients experienced failure of urgent HSCT and ultimately died from progressive disease. Discussion HLH is driven by profound immune dysregulation characterized by uncontrolled activation of cytotoxic lymphocytes and macrophages, leading to excessive cytokine release and progressive multiorgan damage. For patients with relapsed or refractory disease (R/R HLH), outcomes remain poor despite intensified immunochemotherapy, and rapid control of hyperinflammation is often essential to permit definitive treatment with HSCT. Currently, there is no standardized therapeutic approach for R/R HLH. A range of targeted immunomodulatory strategies—including ruxolitinib, anakinra, alemtuzumab, and PD-1–blocking antibodies—has been explored in clinical studies in an effort to improve outcomes in this high-risk population[ 22 – 26 ]. Given the central pathogenic role of IFN-γ, targeted blockade with emapalumab has emerged as a rational therapeutic strategy. In this single-center real-world cohort, we observed that emapalumab provides rapid inflammatory control and facilitates HSCT in a subset of pediatric R/R HLH patients, while also revealing clinically relevant limitations in retreatment responsiveness. A principal observation of our cohort is the prompt improvement in systemic inflammation following emapalumab exposure, consistent with an IFN-γ–dependent disease component in many patients with R/R HLH. Clinically, early defervescence was frequently observed, accompanied by improvement in selected inflammatory biomarkers. Importantly, treatment was generally manageable from a safety standpoint; infections and myelosuppression remained common during the disease course, which is expected in heavily pretreated HLH patients and may also reflect concomitant immunosuppression and organ dysfunction rather than a drug-specific signal alone. These findings support the role of IFN-γ blockade as a rapid “inflammation-containment” strategy in critically ill patients, particularly when a narrow therapeutic window exists to stabilize patients for definitive therapy. These findings reinforce the concept that a substantial proportion of R/R HLH remains at least partially IFN-γ-dependent, even after failure of conventional therapy. A novel observation in our study is the diminished treatment responsiveness during second-course emapalumab therapy. Although retreatment produced short-term symptomatic improvement, the magnitude of fever reduction and cytokine clearance—including IL-6, IL-10, IFN-γ and IL-8—was consistently smaller than during the initial course. This attenuation suggests reduced IFN-γ pathway responsiveness, potentially reflecting disease evolution, persistent viral or malignant triggers, or alternative inflammatory circuits gaining dominance during relapse. Mechanistically, our findings support the concept that IFN-γ remains a key driver of hyperinflammation throughout the disease course[ 27 , 28 ], allowing repeated blockade to temporarily dampen cytokine peaks. However, when EBV replication or tumor burden persists, IFN-γ neutralization alone may be insufficient to fundamentally alter the disease trajectory. This interpretation is reinforced by clinical outcomes: durable remission occurred predominantly in patients who either successfully bridged to HSCT or received disease-directed immunochemotherapy (such as PD-1 inhibition plus L-DEP) in combination with emapalumab, whereas patients relying solely on repeated inflammatory control frequently experienced relapse or progression. These findings underscore that emapalumab should be viewed primarily as a rapid inflammation-containment strategy rather than a standalone disease-modifying therapy, particularly in the setting of persistent viral or malignant drivers. Subtype-specific outcomes further contextualize the role of emapalumab. Patients with malignancy-associated HLH in our cohort had poor outcomes, consistent with prior reports showing limited benefit of IFN-γ blockade in malignancy-driven hyperinflammation[ 18 ]. By contrast, patients with pHLH or EBV-HLH were more likely to achieve clinical responses and bridge to HSCT, supporting the relevance of IFN-γ-dependent pathology in these subgroups. Notably, EBV-HLH displayed particularly heterogeneous trajectories, ranging from fulminant early progression to sustained remission when emapalumab was integrated with virologically and immunologically targeted therapies. Moreover, our results highlight the emerging importance of multimodal therapeutic approaches. Combined IFN-γ blockade plus PD-1 inhibition and cytotoxic chemotherapy enabled complete virological remission and durable disease control in a EBV-HLH patient—consistent with reports suggesting synergistic benefit when emapalumab is integrated with JAK inhibition or disease-directed immunotherapy[ 21 , 29 – 31 ]. These findings suggest that IFN-γ blockade may be more effective when embedded within a broad strategy targeting both cytokine-mediated inflammation and underlying triggers. This study has several limitations. First, the retrospective single-center design and small sample size limit generalizability, and treatment regimens were not uniform due to clinical necessity. Second, the patients receiving second-course emapalumab were heterogeneous in baseline disease and concomitant therapies, making it difficult to isolate the drug-specific contribution. Third, outcome definitions and assessment time points in real-world practice may vary, and residual confounding (including infection burden, organ dysfunction, and prior immunochemotherapy exposure) is unavoidable. Finally, the absence of a comparator group restricts inference regarding the relative efficacy of emapalumab versus alternative salvage approaches or optimal sequencing. Despite these limitations, our findings indicate that emapalumab offers meaningful inflammatory control in pediatric R/R HLH and enables HSCT in nearly half of patients. However, attenuated responsiveness during retreatment and poor outcomes in M-HLH highlight the importance of rapid disease-modifying therapy, integration of trigger-directed treatments, and timely HSCT when appropriate. Our observation of an attenuated response upon retreatment with emapalumab highlights the importance of balancing disease status with the timing of HSCT. For some children with R/R HLH, urgent transplantation may be necessary in some patients even when the disease has not achieved complete remission but shows improvement, or when viral clearance is incomplete. Future prospective studies are needed to evaluate optimal sequencing, combination strategies, and biomarkers predicting sustained responsiveness to IFN-γ blockade. Declarations Author Contributions MG and SW contributed to the literature review and writing the original draft. MG, JZ, FZ and JL contributed to data collec­tion, literature review and revised the original draft. XX and YT contributed to conceptualization, investigation, reviewing and editing the draft, and supervision. Funding This study was partly supported by the grants from National Natural Science Foundation of China (Grant numbers [81970122]). Data Availability For the data that support the findings of this study, please contact the corresponding author ( [email protected] ). 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Table 1 Table 1 is available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Supplementarydata.pdf Table1.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 02 Feb, 2026 Editor assigned by journal 07 Jan, 2026 Submission checks completed at journal 07 Jan, 2026 First submitted to journal 07 Jan, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8540730","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":584646245,"identity":"6c388aea-d8a1-4f64-8183-f89f18591fd6","order_by":0,"name":"Min’er Gu","email":"","orcid":"","institution":"Children’s Hospital of Zhejiang University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Min’er","middleName":"","lastName":"Gu","suffix":""},{"id":584646247,"identity":"4f064dce-77e7-4f7b-bbfc-c22d7f0812e4","order_by":1,"name":"Shengchao Wu","email":"","orcid":"","institution":"Children’s Hospital of Zhejiang University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Shengchao","middleName":"","lastName":"Wu","suffix":""},{"id":584646248,"identity":"2298b765-a3a1-46ae-b12e-da1420d93f9a","order_by":2,"name":"Jingying Zhang","email":"","orcid":"","institution":"Children’s Hospital of Zhejiang University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Jingying","middleName":"","lastName":"Zhang","suffix":""},{"id":584646249,"identity":"c9f67bde-df5e-42a6-8b82-d87b32780aed","order_by":3,"name":"Fenying Zhao","email":"","orcid":"","institution":"Children’s Hospital of Zhejiang University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Fenying","middleName":"","lastName":"Zhao","suffix":""},{"id":584646250,"identity":"0f1cd672-d439-4773-b6df-2bf048ccee92","order_by":4,"name":"Juan Liang","email":"","orcid":"","institution":"Children’s Hospital of Zhejiang University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Juan","middleName":"","lastName":"Liang","suffix":""},{"id":584646258,"identity":"dbdc1059-f362-4913-9edc-7c2d3a3f42b2","order_by":5,"name":"Yongmin Tang","email":"","orcid":"","institution":"Children’s Hospital of Zhejiang University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Yongmin","middleName":"","lastName":"Tang","suffix":""},{"id":584646260,"identity":"92cc2df3-07c6-42aa-b0fa-0af814c76346","order_by":6,"name":"Xiaojun Xu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6ElEQVRIiWNgGAWjYJCCAwwMbAwM7A0MBkAOYwPxWngOkKAFAiQSwBRhLQY3cgwP/KjgS9wu+fxBMQ+DjeyGA8zPHuDTIjkjLeFgzxm2xJ2zExKMeRjSjDccYDM3wKeFXyL5wAHeNrbEDbcTDgC1HE7ccICHTQKfFjaJxIaDf0Fabh5sAGr5T1gLyJbDYFtuMDMAtRwgrEWy51nCYZkzbMYbzqQxGM4xSDaeeZjNDK8Wg+M5xh/fVByT3XD8+DODNxV2sn3Hm5/h1QIFx8D+MgBHJjMR6oGgBkQwPyBO8SgYBaNgFIw0AADtFEsFmxu0zgAAAABJRU5ErkJggg==","orcid":"","institution":"Children’s Hospital of Zhejiang University School of Medicine","correspondingAuthor":true,"prefix":"","firstName":"Xiaojun","middleName":"","lastName":"Xu","suffix":""}],"badges":[],"createdAt":"2026-01-07 11:23:37","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8540730/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8540730/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":101940292,"identity":"fa639158-cbef-4885-8457-c2934b952c37","added_by":"auto","created_at":"2026-02-05 09:13:36","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":546198,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDynamics of laboratory parameters following emapalumab infusion. \u003c/strong\u003eLongitudinal changes in serum levels of ferritin (A), IL-6 (B), IL-10 (C), and IFN-γ (D) were monitored in 10 patients before and at 3 days, 1 week, and 2 weeks after emapalumab treatment.Each line represents an individual patient (Patient 1–10). The statistical significance of changes over time was assessed using the Wilcoxon signed-rank test: ferritin (day 3: Z = 0.30, P = 0.767; 1 week: Z = 0.42, P = 0.678; 2 weeks: Z = 1.86, P = 0.063), IL-6 (day 3: Z = 2.29, P = 0.022; 1 week: Z = 2.31, P = 0.021; 2 weeks: Z = 0.06, P = 0.953), IL-10 (day 3: Z = 0.76, P=0.445; 1 week: t = 0.16, P = 0.878; 2 weeks: Z = 0.53, P = 0.594), IFN-γ (day 3: Z = 2.80, P = 0.005; 1 week: Z = 1.72, P=0.086; 2 weeks: Z = 2.67, P=0.008). Paired comparisons of sCD25 (E) and CXCL9 (F) levels before and after treatment are shown for responders (blue lines) and non-responders (red lines), with significant reductions observed in most responders. The serum EBV-DNA (G) levels in pediatric R/R HLH patients who tested positive for EBV is shown at various time points after emapalumab treatment.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8540730/v1/cd478efe0a47ea27b0f3e344.png"},{"id":101940269,"identity":"06ffd445-c38c-49ee-90a4-8980a34d0a3f","added_by":"auto","created_at":"2026-02-05 09:13:29","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":436259,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSwimmer plot of time on treatment for pediatric patients with relapsed/refractory HLH. \u003c/strong\u003eHSCT, hematopoietic stem cell transplantation; DEP, liposome doxorubicin, etoposide, and methylprednisolone; L/R-DEP, PEG-asparaginase / Ruxolitinib - liposome doxorubicin, etoposide, and methylprednisolone; PD-1 mAb+L-DEP, Programmed Death-1 Monoclonal Antibody combined with PEG-asparaginase, liposome doxorubicin, etoposide, and methylprednisolone.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8540730/v1/0eaa512cb0d40060b8ba2eb3.png"},{"id":101940288,"identity":"bdf3da6f-b39f-42f0-b963-38dbd7f019d9","added_by":"auto","created_at":"2026-02-05 09:13:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":558145,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of treatment responses between the first and second courses. (\u003c/strong\u003eA). Body-temperature dynamics during the first and second Emapalumab courses. (B). Patient-level comparison of inflammatory biomarker responses between treatment courses. (C). Group-level composite radar plot of biomarker changes.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8540730/v1/36374074d31f7b1a2d1504a6.png"},{"id":101940297,"identity":"0ec785e7-128f-4060-ade8-0b24ad70f956","added_by":"auto","created_at":"2026-02-05 09:13:37","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":50084,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eKaplan–Meier Analysis of Survival. \u003c/strong\u003e(A) Overall survival after Emapalumab treatment for the patients. (B) Event-free survival after Emapalumab treatment for the patients.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8540730/v1/348475236cca52b248d75ac5.png"},{"id":101944178,"identity":"9d097358-5184-43ad-a3bd-0d2ac90d0bff","added_by":"auto","created_at":"2026-02-05 09:49:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2371314,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8540730/v1/7cc5297a-cea7-47d9-804c-2eee27e56edd.pdf"},{"id":101940304,"identity":"76bdd483-fa1f-4c39-a7c1-647734124503","added_by":"auto","created_at":"2026-02-05 09:13:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":61950,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarydata.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8540730/v1/d81517cc682a015fbccd4541.pdf"},{"id":101943352,"identity":"73a44c8e-8499-42c9-8335-5d1957aa8447","added_by":"auto","created_at":"2026-02-05 09:41:44","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":19797,"visible":true,"origin":"","legend":"","description":"","filename":"Table1.docx","url":"https://assets-eu.researchsquare.com/files/rs-8540730/v1/051cf05679d1f6dc1bb5df76.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Emapalumab in pediatric relapsed/refractory hemophagocytic lymphohistiocytosis: clinical responses, attenuated efficacy upon retreatment, and role in bridging to HSCT","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome characterized by uncontrolled activation of cytotoxic T cells and macrophages, leading to excessive cytokine release and progressive multiorgan dysfunction. HLH comprises primary forms driven by pathogenic variants affecting cytotoxic machinery\u0026mdash;including \u003cem\u003ePRF1\u003c/em\u003e, \u003cem\u003eUNC13D\u003c/em\u003e, \u003cem\u003eSTX11\u003c/em\u003e, \u003cem\u003eSTXBP2\u003c/em\u003e, \u003cem\u003eRAB27A\u003c/em\u003e, and others\u0026mdash;and secondary forms triggered by infections, malignancies, autoimmune conditions, immune reconstitution, or immunotherapy[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Despite etiologic diversity, dysregulated IFN-γ signaling represents a shared pathogenic axis. IFN-γ not only amplifies macrophage activation and hemophagocytosis but also drives key biomarkers such as CXCL9 and soluble CD25 (sCD25), which correlate with disease activity and treatment response[\u003cspan additionalcitationids=\"CR4 CR5 CR6\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eStandard HLH-directed therapy, historically based on the HLH-94/04 regimens using dexamethasone and etoposide, can induce remission in many patients[\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]; however, a substantial subset of children develop relapsed or refractory hemophagocytic lymphohistiocytosis (R/R HLH). R/R HLH is marked by persistent hyperinflammation, high early mortality, and difficulty achieving adequate disease control to bridge to hematopoietic stem cell transplantation (HSCT), the only curative option for most patients[\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Adjunctive immunomodulatory agents\u0026mdash;such as JAK inhibitors, IL-1 blockade, PD-1 inhibitors, and anti-CD52 therapy\u0026mdash;have expanded treatment strategies[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], but their efficacy remains variable across HLH subtypes.\u003c/p\u003e \u003cp\u003eGiven the central role of IFN-γ in HLH pathophysiology, targeted neutralization has emerged as a rational therapeutic approach[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Emapalumab, a fully human monoclonal antibody that binds and neutralizes free IFN-γ, was approved in 2018 by the U.S. Food and Drug Administration for primary HLH that is refractory, recurrent, progressive or intolerant to conventional HLH therapy[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Early clinical studies demonstrated rapid fever resolution, cytokine downregulation, and improved transplant feasibility[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. However, existing research evidence and real-world data in pediatric R/R HLH, particularly in EBV-HLH, malignancy-associated HLH, and post-transplant settings, remain limited[\u003cspan additionalcitationids=\"CR18 CR19\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Moreover, the durability of response and the effectiveness of repeated emapalumab courses have not been thoroughly examined.\u003c/p\u003e \u003cp\u003eTo address these knowledge gaps, we conducted a single-center retrospective study evaluating the clinical responses, cytokine kinetics, virologic patterns, survival outcomes, and HSCT feasibility in children with R/R HLH treated with emapalumab. This study aims to clarify the role of IFN-γ blockade in contemporary HLH management and to explore its potential positioning within multimodal treatment strategies, including sequential therapy and HSCT preparation.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy design and patients\u003c/h2\u003e \u003cp\u003eThis was a single-center, retrospective study conducted in the department of hematology/oncology, Children's Hospital of Zhejiang University School of Medicine, China. Consecutive pediatric patients diagnosed with R/R HLH who received emapalumab between April 2023 and July 2025 were included. All of the patients presented indication for hematopoietic stem cell transplantation. The study was approved by the institutional ethics committee (2025-IRB-0497), and the requirement for informed consent was waived due to the retrospective design. HLH diagnosis followed the HLH-2004 criteria. Refractory disease was defined as failed to achieve at least partial remission 2 weeks after initial HLH-94 regimen or other chemotherapy-contained regimens, and relapse was defined as disease reactivation after initial remission.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eAssessment of treatment response and monitoring\u003c/h3\u003e\n\u003cp\u003eClinical and laboratory responses were assessed at baseline (prior to the first emapalumab infusion) and at days 3, 7, and 14 after the first emapalumab infusion. HLH-associated biomarkers\u0026mdash;including ferritin, sCD25, CXCL9, IL-6, IL-10, IFN-γ, D-dimer, liver function indicators, and EBV-DNA titers\u0026mdash;were serially monitored. Cytokine analyses used standard hospital laboratory assays. Fever resolution was defined as axillary temperature\u0026thinsp;\u0026lt;\u0026thinsp;37.3\u0026deg;C for \u0026ge;\u0026thinsp;24 hours without antipyretics.\u003c/p\u003e \u003cp\u003eThe primary endpoints were overall response rate (ORR) and event-free survival (EFS). Clinical response categories followed criteria used in prior clinical studies of HLH[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The ORR was defined as achieving a complete response, partial response, or improvement in measures of HLH. EFS was defined as the time from first emapalumab initiation to disease relapse, death without remission or death. Patients without an event were censored at the date of last follow-up. Secondary endpoints included overall survival (OS) and bridging to HSCT. OS was defined as the time from first emapalumab dose to death from any cause, survivors were censored at last follow-up.\u003c/p\u003e\n\u003ch3\u003eSafety assessment\u003c/h3\u003e\n\u003cp\u003eAll adverse events occurring within 30 days of the first emapalumab dose were collected and graded per the Common Terminology Criteria for Adverse Events (CTCAE v5.0). Potential emapalumab-related toxicities\u0026mdash;including myelosuppression, infections, organ dysfunction, metabolic abnormalities, infusion reactions, et al\u0026mdash;were recorded. Because many patients received concomitant chemotherapy or targeted immunomodulators, attribution focused on identifying \u0026ldquo;possibly related\u0026rdquo; adverse events.\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eStatistical analysis was performed using SPSS 25.0. Changes in laboratory parameters from baseline to days 3, 7, and 14 were analyzed using paired tests (paired t test for approximately normally distributed differences or Wilcoxon signed-rank test for non-normally distributed differences), with analyses restricted to patients with available paired measurements at each time point. Time-to-event outcomes (EFS and OS) were estimated using the Kaplan-Meier method with 95% confidence intervals (CIs). All tests were two-sided, and p values\u0026thinsp;\u0026lt;\u0026thinsp;0.05 were considered statistically significant.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec8\"\u003e\n \u003ch2\u003ePatients and baseline characteristics\u003c/h2\u003e\n \u003cp\u003eA total of 10 pediatric patients with relapsed/refractory HLH were included in this study (Table 1). The median age was 5.7 years (range, 0.2–13.9 years), with eight male patients. According to underlying etiology, three patients were diagnosed with primary HLH (pHLH), five with Epstein–Barr virus–associated HLH (EBV-HLH), and two with malignancy-associated HLH (M-HLH). Pathogenic variants were identified in three pHLH patients (Two patients harbored compound heterozygous mutations in \u003cem\u003eUNC13D\u003c/em\u003e, and one patient had a compound heterozygous mutation in \u003cem\u003eSTXBP2\u003c/em\u003e), and the two M-HLH cases were diagnosed with peripheral T-cell lymphoma (PTCL) and diffuse large B-cell lymphoma (DLBCL), respectively. Among EBV-HLH patients or presenting with concomitant EBV infection, detectable serum EBV-DNA loads were present at baseline, ranging from 3.41×10\u003csup\u003e3\u003c/sup\u003e to 1.42×10\u003csup\u003e5\u003c/sup\u003e copies/mL. The median interval from initial HLH diagnosis to emapalumab initiation was 42.5 days, ranging from 24 to 176 days. At baseline, most patients exhibited marked hyperinflammation, characterized by elevated ferritin, sCD25, CXCL9, and IFN-γ levels, with persistent high EBV-DNA titers in the EBV-HLH subgroup.\u003c/p\u003e\n\u003c/div\u003e \u003cp\u003eDosing, scheduling, and concomitant therapies were abstracted retrospectively from the medical records. All patients had received multiple prior therapies, including dexamethasone, HLH-94-based regimens, ruxolitinib, PD-1 inhibitors, and L-DEP combinations. At emapalumab initiation, all patients continued to receive concurrent immunochemotherapy or immunomodulatory agents, as detailed in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Emapalumab was administered intravenously at doses ranging from 1 to 6 mg/kg every 3\u0026ndash;4 days, and the number of doses per course was individualized according to disease activity and response. In patients who developed reactivation after an initial response, a second emapalumab course was sometimes administered at the time of reactivation. Throughout all emapalumab courses, patients concomitantly received systemic corticosteroids and ruxolitinib as part of institutional salvage regimens for R/R HLH.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTreatment exposure, response assessment, and outcomes following emapalumab therapy\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"11\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"11\" nameend=\"c11\" namest=\"c1\"\u003e \u003cp\u003eEmapalumab exposure\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003edose (mg/kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNumber of doses received in first course\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"11\" nameend=\"c11\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTreat exposure and outcomes\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePrevious therapy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHLH-94, RUX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHLH-94, R-DEP, PD-1 mAb\u0026thinsp;+\u0026thinsp;L-DEP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHLH-94, RUX, L-DEP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHLH-94, RUX, L-DEP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRUX, PD-1 mAb\u0026thinsp;+\u0026thinsp;L-DEP, DXM, L-DEP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eHLH-94, RUX, PD-1 mAb\u0026thinsp;+\u0026thinsp;L-DEP, HSCT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eHLH-94, PD-1 mAb\u0026thinsp;+\u0026thinsp;L-DEP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eVMLD, Hyper-CVAD, ICE, DXM, RUX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eR-CHOP, COP, RTX, HLH-94, RUX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eHLH-94, RUX\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConcurrent therapy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHLH-94, RUX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHLH-94, RUX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDXM, RUX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRUX, L-DEP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDXM, RUX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eMP, RUX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eRUX, PD-1 mAb\u0026thinsp;+\u0026thinsp;L-DEP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eDXM, RUX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eRUX, L-DEP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eHLH-94, RUX\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eResponse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eImprovement\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDeath\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eNR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ePR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003ePR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFirst event\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCensored\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRelapse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDeath without remission\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRelapse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRelapse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eDeath without remission\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCensored\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eDeath without remission\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eRelapse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eRelapse\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHSCT after therapy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOutcome\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAlive\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAlive\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDeath\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDeath\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAlive\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eDeath\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eAlive\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eDeath\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eDeath\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eAlive\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e\u003cp\u003e\u003cstrong\u003eAbbreviations:\u0026nbsp;\u003c/strong\u003eDXM, Dexamethasone; RUX, Ruxolitinib; R-DEP, Ruxolitinib - liposome doxorubicin, etoposide, and methylprednisolone; PD-1 mAb+L-DEP, Programmed Death-1 Monoclonal Antibody combined with PEG-asparaginase, liposome doxorubicin, etoposide, and methylprednisolone; VMLD, Vincristine, Mitoxantrone Liposome, L-Asparaginase and Dexamethasone; Hyper-CVAD, Cyclophosphamide, Vincristine, Epirubicin and Dexamethasone; ICE, Ifosfamide, Carbopatin and Etoposide; R-CHOP, Rituximab - Cyclophosphamide, Epirubicin, Vincristine and Prednisone; COP, Cyclophosphamide, Vincristine and Dexamethasone; RTX, Rituximab; MP, methylprednisolone.\u003c/p\u003e\n\u003ch3\u003eTreatment response and cytokine kinetics\u003c/h3\u003e\n\u003cp\u003eRapid clinical responses were observed following emapalumab initiation. Early defervescence occurred in all febrile patients within 48\u0026ndash;72 hours, except for one patient (EBV-HLH) who experienced fulminant disease progression with central nervous system (CNS) involvement and subsequently died after 4 days of first emapalumab administration. The ORR to emapalumab was 70% in this cohort, comprising 1 CR (EBV-HLH), 5 PR (2 pHLH, 2 EBV-HLH and 1 M-HLH), and 1 improvement of HLH (pHLH) (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Two patients (1 EBV-HLH and 1 M-HLH) failed to achieve response following emapalumab therapy. One patient experienced EBV reactivation-associated HLH relapse after HSCT, whereas the other developed secondary HLH in the context of peripheral T-cell lymphoma. Despite continuous concomitant treatment with systemic corticosteroids and ruxolitinib during emapalumab therapy, both patients showed persistent disease activity and ultimately died.\u003c/p\u003e \u003cp\u003eSerial laboratory assessment showed differential biomarker dynamics (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Ferritin and IL-10 levels did not demonstrate significant early changes (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA, C), whereas IL-6 and IFN-γ showed reductions over time, with statistically significant improvement at selected time points (e.g., IL-6 at day 3 and 7, P\u0026thinsp;=\u0026thinsp;0.02; IFN-γ at day 3 and 14, P\u0026thinsp;\u0026lt;\u0026thinsp;0.01) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB, D). sCD25 and CXCL9 decreased more prominently in most responders than in non-responders (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eE-F), consistent with pharmacodynamic modulation of the IFN-γ axis. In contrast to inflammatory biomarkers, virological control was limited. EBV-DNA titers remained persistently elevated in most EBV-HLH patients, highlighting limited virological response despite initial clinical inflammatory improvement (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eG).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDespite initial responses, durability was limited: among 7 patients who responded to emapalumab, five (2 pHLH, 2 EBV-HLH and 1 M-HLH) experienced relapse as the first event, consistent with the swimmer plot showing early disease control followed by frequent subsequent relapse (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Only two patients (1 PR and 1 CR at initial response) achieved sustained remission at last follow-up: one pHLH patient who proceeded to successful HSCT and one R/R EBV-HLH patient who achieved prolonged remission following combined emapalumab with PD-1 inhibitor and L-DEP therapy. Among the five patients who experienced disease relapse after an initial response, subsequent management strategies varied. Four patients (1 pHLH, 2 EBV-HLH, and 1 M-HLH) were re-treated with emapalumab, either as monotherapy or in combination with chemotherapy, whereas one patient with pHLH continued treatment with the HLH-94-based regimen. One patient with EBV-HLH, who experienced multiple relapses following repeated emapalumab exposure, ultimately proceeded to HSCT during a subsequent remission phase. In contrast, the remaining four patients failed to achieve adequate disease control after relapse and were considered for urgent HSCT. Of these, three ultimately underwent transplantation, while one patient with M-HLH who had underlying immunodeficiency and severe disease-related complications, experienced failure of urgent HSCT and subsequently experienced progressive clinical deterioration and ultimately died.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eComparison of treatment response between first and second Emapalumab courses\u003c/h3\u003e\n\u003cp\u003eFor patients who achieved an initial response to emapalumab but later experienced HLH reactivation, a second course was defined as a new treatment sequence initiated after documented clinical and/or laboratory relapse. Four such patients received at least two emapalumab courses, enabling a direct comparison of treatment effects.\u003c/p\u003e \u003cp\u003eBaseline values for each course were taken from the last assessment before initiation, and post-treatment status was defined using the best measurement within the first 7 days\u0026mdash;specifically, the lowest value for inflammatory markers (or highest for albumin)\u0026mdash;to capture early pharmacodynamic suppression of IFN-γ\u0026ndash;driven inflammation. Changes in body temperature and key biomarkers (ferritin, IL-6, IL-8, IL-10, IFN-γ, D-dimer, alanine aminotransferase [ALT], and albumin [ALB]) were compared between courses. To quantify response magnitude, we calculated the log₁₀-transformed change (Δlog value) from baseline to post-treatment and visualized individual and group-level responses using radar plots, where smaller areas indicate greater overall improvement.\u003c/p\u003e \u003cp\u003eDuring the first course, most patients exhibited rapid and sustained defervescence. In contrast, fever resolution was slower and more variable during the second course (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). Radar plots of log₁₀(post-treatment/baseline) ratios for inflammatory and organ-function markers consistently showed reduced biomarker improvements in the second course (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB-C). At the group level, the composite radar area was larger during retreatment, reflecting attenuated reductions in IFN-γ, IL-6, IL-10, IL-8, ferritin, D-dimer, and ALT, along with less pronounced albumin recovery. Together, these findings indicate diminished responsiveness of the IFN-γ\u0026ndash;driven inflammatory pathway upon emapalumab retreatment and less effective control of systemic inflammation during the second course.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eSafety, bridging to HSCT and survival outcomes\u003c/h2\u003e \u003cp\u003eNo emapalumab-attributable severe adverse events were identified during the study period. Among 9 evaluable patients (one died for disease progression of HLH after 4 days of first emapalumab dose) the most frequent grade\u0026thinsp;\u0026ge;\u0026thinsp;3 potential adverse events included myelosuppression and secondary infections (bacterial predominance) (\u003cb\u003eSupplementary Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e). Less frequent events included liver dysfunction, gastrointestinal bleeding, and electrolyte abnormalities. Overall, most observed toxicities were considered attributable to underlying disease severity, concomitant chemotherapy, or underlying immune dysregulation rather than emapalumab itself.\u003c/p\u003e \u003cp\u003eOverall, five patients (3 pHLH and 2 EBV-HLH) were successfully bridged to HSCT. Among them, two patients proceeded to HSCT during a phase of disease control following HLH remission, whereas the remaining three underwent urgent HSCT after disease relapse with persistently uncontrolled HLH despite repeated courses of emapalumab and/or combination chemotherapy. At the time of last follow-up, four (3 pHLH and 1 EBV-HLH) among the five patients who underwent HSCT remained alive with sustained disease control, while one patient died from transplantation-related complications.\u003c/p\u003e \u003cp\u003eDuring a median follow-up of 3.8 months (range, 0.1\u0026ndash;30.3 months), five patients (3 pHLH and 2 EBV-HLH) remained alive and the 6-month OS was 45.3 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\pm\\:\\)\u003c/span\u003e\u003c/span\u003e 29.2% (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Among the five patients who received HSCT, the median interval from HLH diagnosis to HSCT was 3 months, and from first emapalumab dose to HSCT was 33 days. Four of them achieved durable remission post-HSCT. Non-HSCT patients had poor outcomes, including rapid progression, CNS involvement, or refractory hyperinflammation. Notably, one EBV-HLH patient achieved complete virological remission after emapalumab combined with PD-1 inhibitor and L-DEP therapy, suggesting potential synergy between IFN-γ blockade and immune-checkpoint\u0026ndash;directed regimens. When outcomes were analyzed according to HLH subtype, all three patients with pHLH ultimately underwent HSCT and achieved sustained remission. Among the five patients with EBV-HLH, clinical courses were heterogeneous: one patient experienced rapid disease progression with CNS involvement and died early; one achieved sustained remission following combined emapalumab, PD-1 inhibitor, and L-DEP therapy; one proceeded to HSCT during remission; one failed to achieve disease control and died; and one underwent urgent HSCT but died from transplantation-related complications. In contrast, both M-HLH patients experienced failure of urgent HSCT and ultimately died from progressive disease.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eHLH is driven by profound immune dysregulation characterized by uncontrolled activation of cytotoxic lymphocytes and macrophages, leading to excessive cytokine release and progressive multiorgan damage. For patients with relapsed or refractory disease (R/R HLH), outcomes remain poor despite intensified immunochemotherapy, and rapid control of hyperinflammation is often essential to permit definitive treatment with HSCT. Currently, there is no standardized therapeutic approach for R/R HLH. A range of targeted immunomodulatory strategies\u0026mdash;including ruxolitinib, anakinra, alemtuzumab, and PD-1\u0026ndash;blocking antibodies\u0026mdash;has been explored in clinical studies in an effort to improve outcomes in this high-risk population[\u003cspan additionalcitationids=\"CR23 CR24 CR25\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Given the central pathogenic role of IFN-γ, targeted blockade with emapalumab has emerged as a rational therapeutic strategy. In this single-center real-world cohort, we observed that emapalumab provides rapid inflammatory control and facilitates HSCT in a subset of pediatric R/R HLH patients, while also revealing clinically relevant limitations in retreatment responsiveness.\u003c/p\u003e \u003cp\u003eA principal observation of our cohort is the prompt improvement in systemic inflammation following emapalumab exposure, consistent with an IFN-γ\u0026ndash;dependent disease component in many patients with R/R HLH. Clinically, early defervescence was frequently observed, accompanied by improvement in selected inflammatory biomarkers. Importantly, treatment was generally manageable from a safety standpoint; infections and myelosuppression remained common during the disease course, which is expected in heavily pretreated HLH patients and may also reflect concomitant immunosuppression and organ dysfunction rather than a drug-specific signal alone. These findings support the role of IFN-γ blockade as a rapid \u0026ldquo;inflammation-containment\u0026rdquo; strategy in critically ill patients, particularly when a narrow therapeutic window exists to stabilize patients for definitive therapy. These findings reinforce the concept that a substantial proportion of R/R HLH remains at least partially IFN-γ-dependent, even after failure of conventional therapy.\u003c/p\u003e \u003cp\u003eA novel observation in our study is the diminished treatment responsiveness during second-course emapalumab therapy. Although retreatment produced short-term symptomatic improvement, the magnitude of fever reduction and cytokine clearance\u0026mdash;including IL-6, IL-10, IFN-γ and IL-8\u0026mdash;was consistently smaller than during the initial course. This attenuation suggests reduced IFN-γ pathway responsiveness, potentially reflecting disease evolution, persistent viral or malignant triggers, or alternative inflammatory circuits gaining dominance during relapse. Mechanistically, our findings support the concept that IFN-γ remains a key driver of hyperinflammation throughout the disease course[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], allowing repeated blockade to temporarily dampen cytokine peaks. However, when EBV replication or tumor burden persists, IFN-γ neutralization alone may be insufficient to fundamentally alter the disease trajectory. This interpretation is reinforced by clinical outcomes: durable remission occurred predominantly in patients who either successfully bridged to HSCT or received disease-directed immunochemotherapy (such as PD-1 inhibition plus L-DEP) in combination with emapalumab, whereas patients relying solely on repeated inflammatory control frequently experienced relapse or progression. These findings underscore that emapalumab should be viewed primarily as a rapid inflammation-containment strategy rather than a standalone disease-modifying therapy, particularly in the setting of persistent viral or malignant drivers.\u003c/p\u003e \u003cp\u003eSubtype-specific outcomes further contextualize the role of emapalumab. Patients with malignancy-associated HLH in our cohort had poor outcomes, consistent with prior reports showing limited benefit of IFN-γ blockade in malignancy-driven hyperinflammation[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. By contrast, patients with pHLH or EBV-HLH were more likely to achieve clinical responses and bridge to HSCT, supporting the relevance of IFN-γ-dependent pathology in these subgroups. Notably, EBV-HLH displayed particularly heterogeneous trajectories, ranging from fulminant early progression to sustained remission when emapalumab was integrated with virologically and immunologically targeted therapies.\u003c/p\u003e \u003cp\u003eMoreover, our results highlight the emerging importance of multimodal therapeutic approaches. Combined IFN-γ blockade plus PD-1 inhibition and cytotoxic chemotherapy enabled complete virological remission and durable disease control in a EBV-HLH patient\u0026mdash;consistent with reports suggesting synergistic benefit when emapalumab is integrated with JAK inhibition or disease-directed immunotherapy[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan additionalcitationids=\"CR30\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. These findings suggest that IFN-γ blockade may be more effective when embedded within a broad strategy targeting both cytokine-mediated inflammation and underlying triggers.\u003c/p\u003e \u003cp\u003eThis study has several limitations. First, the retrospective single-center design and small sample size limit generalizability, and treatment regimens were not uniform due to clinical necessity. Second, the patients receiving second-course emapalumab were heterogeneous in baseline disease and concomitant therapies, making it difficult to isolate the drug-specific contribution. Third, outcome definitions and assessment time points in real-world practice may vary, and residual confounding (including infection burden, organ dysfunction, and prior immunochemotherapy exposure) is unavoidable. Finally, the absence of a comparator group restricts inference regarding the relative efficacy of emapalumab versus alternative salvage approaches or optimal sequencing.\u003c/p\u003e \u003cp\u003eDespite these limitations, our findings indicate that emapalumab offers meaningful inflammatory control in pediatric R/R HLH and enables HSCT in nearly half of patients. However, attenuated responsiveness during retreatment and poor outcomes in M-HLH highlight the importance of rapid disease-modifying therapy, integration of trigger-directed treatments, and timely HSCT when appropriate. Our observation of an attenuated response upon retreatment with emapalumab highlights the importance of balancing disease status with the timing of HSCT. For some children with R/R HLH, urgent transplantation may be necessary in some patients even when the disease has not achieved complete remission but shows improvement, or when viral clearance is incomplete. Future prospective studies are needed to evaluate optimal sequencing, combination strategies, and biomarkers predicting sustained responsiveness to IFN-γ blockade.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u0026nbsp;\u003c/strong\u003eMG and\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eSW contributed to the literature review and writing the original draft. MG, JZ, FZ and JL contributed to data collec\u0026shy;tion, literature review and revised the original draft. XX and YT contributed to conceptualization, investigation, reviewing and editing the draft, and supervision.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003eThis study was partly supported by the grants from National Natural Science Foundation of China (Grant numbers [81970122]).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e For the data that support the findings of this study, please contact the corresponding author ([email protected]).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDisclosure of Conflicts of Interest\u0026nbsp;\u003c/strong\u003eThe authors declare no competing financial interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eHenter JI. Hemophagocytic Lymphohistiocytosis. N Engl J Med. 2025;392(6):584\u0026ndash;98.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eToumeh N, Abu-Zeinah KF, Godby RC. 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Pediatric Hemophagocytic Lymphohistiocytosis \u0026mdash; A Single Center Study. Indian Pediatr. 2022;59(4):283\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJacqmin P, Laveille C, Snoeck E, et al. Emapalumab in primary haemophagocytic lymphohistiocytosis and the pathogenic role of interferon gamma: A pharmacometric model-based approach. Br J Clin Pharmacol. 2022;88(5):2128\u0026ndash;39.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAl-Salama ZT, Emapalumab. First Global Approval Drugs. 2019;79(1):99\u0026ndash;103.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLocatelli F, Jordan MB, Allen C, et al. Emapalumab in Children with Primary Hemophagocytic Lymphohistiocytosis. N Engl J Med. 2020;382(19):1811\u0026ndash;22.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChandrakasan S, Jordan MB, Baker A, et al. Real-world treatment patterns and outcomes in patients with primary hemophagocytic lymphohistiocytosis treated with emapalumab. Blood Adv. 2024;8(9):2248\u0026ndash;58.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJohnson WT, Epstein-Peterson ZD, Ganesan N et al. Emapalumab as salvage therapy for adults with malignancy-associated hemophagocytic lymphohistiocytosis. Haematologica, 2024.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChandrakasan S, Allen CE, Bhatla D, et al. Emapalumab Treatment in Patients With Rheumatologic Disease\u0026ndash;Associated Hemophagocytic Lymphohistiocytosis in the United States: A Retrospective Medical Chart Review Study. Volume 77. Arthritis \u0026amp; Rheumatology; 2025. pp. 226\u0026ndash;38. 2.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang W, Yuan X, Yu L, et al. Emapalumab as a therapeutic intervention for Epstein\u0026ndash;Barr virus-associated hemophagocytic lymphohistiocytosis: A case series. Medicine. 2024;103(39):e39880.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSong Y, Zhou F, Du F et al. Combined emapalumab and ruxolitinib in patients with haemophagocytic Lymphohistiocytosis. Blood Cancer J, 2024, 14(1).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSong Y, Li X, He X, 等. Dose-escalating ruxolitinib for refractory hemophagocytic lymphohistiocytosis. Front Immunol. 2023;14:1211655.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee BJ, Cao Y, Vittayawacharin P, et al. Anakinra versus etoposide-based therapy added to high‐dose steroids for the treatment of secondary hemophagocytic lymphohistiocytosis. Eur J Haematol. 2023;111(3):477\u0026ndash;84.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMarsh RA, Allen CE, McClain KL, et al. Salvage therapy of refractory hemophagocytic lymphohistiocytosis with alemtuzumab. Pediatr Blood Cancer. 2013;60(1):101\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu P, Pan X, Chen C, et al. Nivolumab treatment of relapsed/refractory Epstein-Barr virus\u0026ndash;associated hemophagocytic lymphohistiocytosis in adults. Blood. 2020;135(11):826\u0026ndash;33.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuo S, Wang J, Fang J, et al. Treatment of pediatric refractory or relapsed Epstein\u0026ndash;Barr virus-associated hemophagocytic syndrome with PD‐1 inhibitors. Pediatr Blood Cancer. 2024;71(12):e31340.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePrencipe G, Caiello I, Pascarella A, et al. Neutralization of IFN-γ reverts clinical and laboratory features in a mouse model of macrophage activation syndrome. J Allergy Clin Immunol. 2018;141(4):1439\u0026ndash;49.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIvashkiv LB. IFNγ: signalling, epigenetics and roles in immunity, metabolism, disease and cancer immunotherapy. Nat Rev Immunol. 2018;18(9):545\u0026ndash;58.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhu W, Zhou F, Song Y, et al. Low-dose emapalumab combined with chemotherapy for adult patients with Epstein\u0026ndash;Barr virus-associated hemophagocytic lymphohistiocytosis. Transpl Immunol. 2025;88:102162.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSong Y, Li W, Wu D, et al. Successful Treatment of Refractory EBV-Associated Hemophagocytic Lymphohistiocytosis with Combined Emapalumab and PD-1 Blockade. J Clin Immunol. 2024;44(3):70.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiang J, Xu X, Chen Z, et al. Combined Use of Emapalumab With Ruxolitinib and Dexamethasone as an Effective Treatment for Epstein-Barr Virus\u0026ndash;associated Hemophagocytic Lymphohistiocytosis Complicated With Multiorgan Damage and Severe Infection. J Pediatr Hematol Oncol. 2024;46(5):e360\u0026ndash;2.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Table 1","content":"\u003cp\u003eTable 1 is available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-clinical-immunology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"joci","sideBox":"Learn more about [Journal of Clinical Immunology](https://www.springer.com/journal/10875)","snPcode":"10875","submissionUrl":"https://submission.nature.com/new-submission/10875/3","title":"Journal of Clinical Immunology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"emapalumab, relapsed/refractory hemophagocytic lymphohistiocytosis, interferon-γ, retreatment","lastPublishedDoi":"10.21203/rs.3.rs-8540730/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8540730/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRelapsed/refractory hemophagocytic lymphohistiocytosis (R/R HLH) represents a hyperinflammatory state driven largely by IFN-γ dysregulation and carries a high risk of early mortality and failure to bridge to hematopoietic stem cell transplantation (HSCT). Emapalumab, a fully human anti\u0026ndash;IFN-γ monoclonal antibody, has emerged as a targeted option, but evidence in heterogeneous real-world pediatric populations remains limited. We retrospectively reviewed pediatric patients with R/R HLH who received emapalumab at our center from April 2023 to July 2025. Clinical responses, cytokine kinetics, virologic parameters, survival outcomes, and HSCT feasibility were assessed. Ten children were included: primary HLH (n\u0026thinsp;=\u0026thinsp;3), EBV-HLH (n\u0026thinsp;=\u0026thinsp;5), and malignancy-associated HLH (n\u0026thinsp;=\u0026thinsp;2). Early clinical improvement was observed in most patients, with an ORR of 70% (3 pHLH, 3 EBV-HLH, and 1 M-HLH). IFN-γ, IL-6 and CXCL9 levels declined markedly among responders. Five (3 pHLH and 2 EBV-HLH) successfully proceeded to HSCT, four of whom achieved sustained remission. Patients requiring a second course of emapalumab exhibited attenuated fever resolution and reduced cytokine clearance. During a median follow-up of 3.8 months, the 6-month OS was 45.3 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{\u0026plusmn;}\\)\u003c/span\u003e\u003c/span\u003e 29.2%. Five patients (3 pHLH and 2 EBV-HLH) remained alive at the time of last follow-up. No newly emerged treatment-related toxicities were observed. In conclusion, emapalumab rapidly controls hyperinflammation in pediatric R/R HLH and enables HSCT in a substantial subset of patients. Diminished responsiveness during retreatment underscores the need for timely disease-modifying therapy. Integrated evidence supports IFN-γ blockade as a key component of multimodal HLH management.\u003c/p\u003e","manuscriptTitle":"Emapalumab in pediatric relapsed/refractory hemophagocytic lymphohistiocytosis: clinical responses, attenuated efficacy upon retreatment, and role in bridging to HSCT","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-05 09:11:04","doi":"10.21203/rs.3.rs-8540730/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2026-02-02T23:25:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-07T23:25:00+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-01-07T23:24:49+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Clinical Immunology","date":"2026-01-07T11:08:59+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-clinical-immunology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"joci","sideBox":"Learn more about [Journal of Clinical Immunology](https://www.springer.com/journal/10875)","snPcode":"10875","submissionUrl":"https://submission.nature.com/new-submission/10875/3","title":"Journal of Clinical Immunology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"16d17578-d0ac-49c5-a688-dbf2308fdbf0","owner":[],"postedDate":"February 5th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-02-05T09:11:04+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-05 09:11:04","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8540730","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8540730","identity":"rs-8540730","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}