Low-dose interleukin-2 for recurrent early pregnancy loss: a proof-of-concept study

Low-dose interleukin-2 for recurrent early pregnancy loss: a proof-of-concept study | 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 Brief Communication Low-dose interleukin-2 for recurrent early pregnancy loss: a proof-of-concept study David Klatzmann, Arsene Mekinian, NOEMIE ABISROR, CHLOE MCAVOY, and 9 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7093926/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Regulatory T cells (Tregs) are essential for maternal-fetal tolerance, and their deficiency is implicated in unexplained recurrent early pregnancy loss (uREPL). Low-dose interleukin-2 (IL-2 LD ) selectively activates Tregs. In the FACIL-2 open-label trial (NCT03970954), 15 women with ≥5 uREPLs received a 5-day IL-2 LD treatment, starting 10 days after menses onset. Nine additional patients received similar treatment under compassionate use. IL-2 LD significantly expanded Tregs at 8 days post-treatment initiation (p<0.001; primary endpoint met). Of eight pregnancies in FACIL-2, four progressed beyond 14 weeks, yielding three live births. Remarkably, compared to pregnancy losses, these successful pregnancies were associated with a significantly greater Treg expansion (p= 0.008). In the compassionate group, two of five pregnancies resulted in live births. Thus, a short-course IL-2 LD expanded Tregs and achieved an almost 50% viable pregnancy rate in this high-risk population. These results support further investigation of IL-2 LD for uREPL, with regimens extending through early pregnancy. Health sciences/Medical research/Clinical trial design/Clinical trials/Phase II trials Health sciences/Diseases/Immunological disorders/Autoimmune diseases Figures Figure 1 Figure 2 Main text Unexplained recurrent early pregnancy loss (uREPL), defined as ≥ 3 miscarriages before 14 weeks of gestation (WG) without identifiable cause, affects 3–5% of women 1 . After five losses, the likelihood of causal chromosomal anomalies drops to ~ 39%, suggesting maternal immune dysfunction, notably insufficient regulatory T cells (Tregs), as a plausible mechanism 2 – 4 . Tregs are essential for maternal-fetal tolerance; in murine models, their depletion results in fetal rejection, while their expansion promotes tolerance and fetal survival 5 – 10 . In humans, normal pregnancy has been associated with their elevation 11 and accumulation at the maternal-fetal interface 12 , while pregnancy loss has been associated with endometrial and decidual Tregs reduction 12 . Low-dose interleukin-2 (IL-2 LD ) selectively expands and activates Tregs in humans 13 – 16 and prevents miscarriage in mice 6 , 17 . We hypothesized that IL-2 LD could restore maternal-fetal immune tolerance and improve pregnancy outcomes in women with uREPL. FACIL-2 was an open-label, single-center, proof-of-concept study (NCT03970954). Women aged 18–40 with ≥ 5 uREPLs and no anatomical, chromosomal, infectious, or hormonal abnormalities were eligible. Key exclusion criteria included thrombophilia, autoimmune disorders, and diminished ovarian reserve (Extended Data Table 1 ). Table 1 Demographic, clinical and biological characteristics FACIL-2 (n = 15) Compassionate (n = 9) Age (years) (mean ± sd) (range) 34.5 ± 3.85 (26–39) 36.8 ± 4.9 (26–41) BMI 29.1 ± 5.5 (20–41) 24.0 ± 3.5 (19–31) Diabetes (n; %) 0 (0%) 0 (0%) Active tobacco (n; %) 3 (20%) 1 (11%) Alcohol (n;%) 0 (0%) 0 (0%) Obstetric history Nulliparity (n;%) 12 (80%) 4 (44%) Number of previous miscarriages (mean ± sd) (range) 6.4 ± 1.9 (5–10) 7.4 ± 3.24(5–15) History of live birth (n; %) 3 (20%) 5 (56%) Anti-mullerian hormone level at baseline (ng/mL) (mean ± sd) (range) 2.85 ± 2.0 (1-8.2) 4.98 ± 7.14 (1.1–23.6) Antral follicular counts at baseline(ng/mL) (mean ± sd) (range) 20.85 ± 13.92 (7–55) 14.67 ± 8.40 (6–34) Number of previous treated pregnancies Progesterone Steroids LMWH and aspirin 1 1 2 2 1 2 IL-2 LD treatment Number of cycles of IL2 received: mean (range) 2 ± 1.19 (1–5) 2.3 ± 10 (1–4) Total dose of IL2 received (MIU): mean (range) 23.3 ± 13.24 (9–54) 33.06 ± 19.41 (7.5–69) Pregnancy outcomes 8 (53%) 5 (55%) Pregnancies ending before 14 WG (n;%) 4 (26%) 3 (33%) Pregnancies continuing after 14WG (n;%) 4 (26%) 2 (22%) Late miscarriages (14-20WG) (n;%) 1 (0.6%) 0 (0%) Lives births (n;%) 3 (20%) 2 (22%) Biology % Treg/CD4 (mean, range) 8.01 (6.37–10.11) NA Treg/mm3 (mean, range) 77.38 (49.41–153.9) NA NA: Not Available Participants first underwent an untreated baseline hormonal cycle for immunophenotyping, then received a first course of 3 million international units (MIU) of subcutaneous IL-2 daily for 5 consecutive days per hormonal cycle, starting ten days after menses onset. Up to five IL-2 LD courses were administered if pregnancy was not achieved (Fig. 1 A). The study was approved by the local institutional review board (Comité de protection des personnes Ile de France III) and was conducted in accordance with the Declaration of Helsinki and good clinical practice guidelines. Written, informed consent was obtained from all participants before enrolment in the study. The primary endpoint was Treg expansion at day-17, 8 days post-treatment initiation, measured as FoxP3 + Tregs within CD4 + T cells. Secondary endpoints included pregnancy outcomes and safety. Nine additional women with similar clinical profiles received compassionate-use IL-2 LD using the same therapeutic scheme but were not followed immunologically (Extended Table 1 ). All 15 FACIL-2 participants completed at least one treatment cycle; nine received two cycles, three received three, two received four, and one completed five. Two participants exceeding the permitted interval between cycles were withdrawn and continued treatment under compassionate use (Fig. 1 B). At baseline (day 10 of the untreated cycle), mean Treg frequency was 7.93%, rising modestly to 8.49% by day 14 (p = 0.016) (Extended Fig. 1 ), consistent with a preimplantation Treg increase supporting maternofetal tolerance 11 . During IL-2LD treatment, Tregs transiently decreased over the first 5 days reflecting recirculation 18 , then significantly increased at day 14 with a mean 1.14 fold rise (p = 0.17), peaking at day-17 with a mean 2.01-fold rise (p < 0.001), meeting the primary endpoint (Fig. 2 A & Extended Fig. 2 ). This effect persisted through day-29 (1.33-fold increase, p < 0.001). The second cycle induced a stronger response (2.47-fold at day-17; 1.55-fold at day-29). Similar trends were observed in the third cycle, although participant numbers were too low for robust conclusions (Fig. 2 A). Treg activation (CD25 MFI) increased during treatment (Fig. 2 B) without expansion of effector T cells (Teffs), resulting in an elevated Treg/Teff ratio (Fig. 2 C). Of eight pregnancies in FACIL-2, four progressed beyond 14 WG, resulting in three live births and one late miscarriage at 20 WG due to premature rupture of membranes (Fig. 1 B). In the compassionate-use group, five pregnancies occurred, with two resulting in live births (Fig. 1 B). All newborns were healthy (APGAR ≥ 9 at 5 and 10 minutes). Noteworthily, successful pregnancies in FACIL-2 were associated with significantly greater Treg expansion (2.87-fold vs 1.64-fold at day-17, p = 0.03; 1.71-fold vs 1.24-fold at day-29, p = 0.008) (Fig. 2 D). Baseline Treg levels and number of prior miscarriages did not predict outcome (Extended Table 2). IL-2 LD was generally well tolerated (Extended Table 3). Seventeen serious adverse events (SAEs), all at the 3 MIU dose, prompted dose reductions to 1.5 or 1 MIU in four patients and discontinuation in one due to EKG changes (negative T waves). Among 149 non-serious adverse events (NSAEs), 127 were deemed IL-2-related (93 Grade 1, 33 Grade 2, 1 Grade 3), mostly at 3 MIU (105 events). No adverse fetal events or neonatal complications were reported up to 6 months post-birth. In summary, IL-2 LD robustly and safely expanded Tregs in women with severe uREPL. The association between pregnancy success and greater Treg expansion supports a causal role and validates Tregs as a therapeutic target. Our conservative 5-day regimen, establish to avoid potential embryo exposure due to lack of IL-2 genotoxicity data, resulted in a treatment effect lasting ~ 4 weeks, shorter than the 14-week period during which uREPLs occur. Despite this, we observed an almost 50% viable pregnancy rate in a population with repeated prior failures, suggesting that extended IL-2 LD regimens covering the first trimester of pregnancy may yield greater benefits. Although limited by its open-label design and lack of a control group, this study provides compelling proof-of-concept evidence warranting a randomized controlled trial of IL-2 LD for uREPL extending through the first pregnancy trimester. Declarations Declaration of interests MR and DK are inventors of patent applications related to the therapeutic use of IL-2 LD , which belongs to their academic institutions. No other potential conflicts of interest relevant to this article were reported. Funding: Assistance Publique-Hôpitaux de Paris and the French National Research Agency (ANR-16-RHUS-0001,RHU IMAP). Acknowledgement We thank the patients for their participation in the trial and the personnel of the Pitié-Salpêtrière Clinical Investigation Center for Biotherapies (CIC-BTi), Michèle Barbié, Natalie Féry, Catherine Ferrapie, Nadia Graffin, Aurélie Marc, for their excellent technical assistance. References Mekinian, A. et al. Unexplained Recurrent Miscarriage and Recurrent Implantation Failure: Is There a Place for Immunomodulation? American J Rep Immunol 76, 8–28 (2016). Lee, S. K. et al. An imbalance in interleukin-17-producing T and Foxp3 + regulatory T cells in women with idiopathic recurrent pregnancy loss. Human Reproduction 26, 2964–2971 (2011). Nakashima, A. et al. SHORT COMMUNICATION: Circulating and Decidual Th17 Cell Levels in Healthy Pregnancy. American J Rep Immunol 63, 104–109 (2010). Wang, W.-J. et al. Increased prevalence of T helper 17 (Th17) cells in peripheral blood and decidua in unexplained recurrent spontaneous abortion patients. Journal of Reproductive Immunology 84, 164–170 (2010). Darrasse-Jèze, G. et al. CD4 + CD25 + regulatory/suppressor T cells prevent allogeneic fetus rejection in mice. Immunol. Lett. 102, 106–109 (2006). Chen, T. et al. Self-specific memory regulatory T cells protect embryos at implantation in mice. J Immunol 191, 2273–81 (2013). Churlaud, G. et al. Sustained stimulation and expansion of Tregs by IL2 control autoimmunity without impairing immune responses to infection, vaccination and cancer. Clinical Immunology 151, 114–126 (2014). Aluvihare, V. R., Kallikourdis, M. & Betz, A. G. Regulatory T cells mediate maternal tolerance to the fetus. Nat Immunol 5, 266–271 (2004). Shima, T. et al. Regulatory T cells are necessary for implantation and maintenance of early pregnancy but not late pregnancy in allogeneic mice. Journal of Reproductive Immunology 85, 121–129 (2010). Nehar-Belaid, D. et al. Regulatory T Cells Orchestrate Similar Immune Evasion of Fetuses and Tumors in Mice. The Journal of Immunology 196, 678–690 (2016). Somerset, D. A., Zheng, Y., Kilby, M. D., Sansom, D. M. & Drayson, M. T. Normal human pregnancy is associated with an elevation in the immune suppressive CD25 + CD4 + regulatory T-cell subset. Immunology 112, 38–43 (2004). Tilburgs, T. et al. Evidence for a selective migration of fetus-specific CD4 + CD25bright regulatory T cells from the peripheral blood to the decidua in human pregnancy. J Immunol 180, 5737–5745 (2008). Saadoun, D. et al. Regulatory T-cell responses to low-dose interleukin-2 in HCV-induced vasculitis. N Engl J Med 365, 2067–77 (2011). Koreth, J. et al. Interleukin-2 and regulatory T cells in graft-versus-host disease. N Engl J Med 365, 2055–66 (2011). Rosenzwajg, M. et al. Immunological and clinical effects of low-dose interleukin-2 across 11 autoimmune diseases in a single, open clinical trial. Ann. Rheum. Dis. 78, 209–217 (2019). Raeber, M. E., Sahin, D., Karakus, U. & Boyman, O. A systematic review of interleukin-2-based immunotherapies in clinical trials for cancer and autoimmune diseases. EBioMedicine 90, 104539 (2023). Churlaud, G. et al. Sustained stimulation and expansion of Tregs by IL2 control autoimmunity without impairing immune responses to infection, vaccination and cancer. Clin Immunol 151, 114–26 (2014). Rosenzwajg, M. et al. Low-dose interleukin-2 fosters a dose-dependent regulatory T cell tuned milieu in T1D patients. J. Autoimmun. 58, 48–58 (2015). Additional Declarations Yes there is potential Competing Interest. MR and DK are inventors of patent applications related to the therapeutic use of IL-2LD, which belongs to their academic institutions. No other potential conflicts of interest relevant to this article were reported. 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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-7093926","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Brief Communication","associatedPublications":[],"authors":[{"id":485313076,"identity":"e837f182-b1ca-44b0-8b37-29f821863827","order_by":0,"name":"David 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14:20:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7093926/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7093926/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":88226463,"identity":"3a3df894-8f9d-4d79-8566-7838e2c00039","added_by":"auto","created_at":"2025-08-04 08:40:22","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":72626,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA)Study design; B) Trial profile showing FACIL-2 and compassionate use cohort recruitment and outcomes\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7093926/v1/e76c155b1b40c060a0a65b60.png"},{"id":88226443,"identity":"9d5a1a24-0cc8-4a79-909c-5d231fe06071","added_by":"auto","created_at":"2025-08-04 08:40:16","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":120732,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eChanges in Regulatory (Treg) and Effector T cells (Teff) during IL-2LD treatment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTreg cells were identified within the CD4⁺ T cell population as CD25^hiCD127\u003csup\u003elo/-\u003c/sup\u003eFoxp3⁺ cells. (A–D) Changes from baseline are shown as mean ± SEM: \u003cstrong\u003e(A) \u003c/strong\u003eTreg percentages among CD4⁺ T cells over the full follow-up period under IL-2\u003csub\u003eLD\u003c/sub\u003e treatment; \u003cstrong\u003e(B\u003c/strong\u003e) CD25 MFI in Tregs; \u003cstrong\u003e(C)\u003c/strong\u003e Tregs to Teffs ratio; \u003cstrong\u003e(D)\u003c/strong\u003e Treg expansion by pregnancy outcome: successful pregnancy (\u0026gt;14 WG, red, n = 4), early pregnancy loss (\u0026lt;14 WG, blue, n = 4), and no pregnancy (green, n = 7).Statistical comparisons during follow-up were conducted using t-tests or Mann–Whitney tests, depending on data distribution (*p\u0026lt;0.05; **p\u0026lt;0.01; ***p\u0026lt;0.001).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7093926/v1/0c6b1d1622b307b4bb790d69.png"},{"id":94985359,"identity":"76774a0f-9288-4eba-80f5-c0d6af91205c","added_by":"auto","created_at":"2025-11-03 06:58:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":770379,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7093926/v1/1539f195-e3f3-425b-a993-e914f11ed4be.pdf"},{"id":88226441,"identity":"ad1d2bc9-6176-45af-8332-ed45904d0a6a","added_by":"auto","created_at":"2025-08-04 08:40:16","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":168676,"visible":true,"origin":"","legend":"Supplemental data","description":"","filename":"MethodsExtendeddata.docx","url":"https://assets-eu.researchsquare.com/files/rs-7093926/v1/8b202b68ce6b8a429e46e891.docx"}],"financialInterests":"\u003cb\u003eYes\u003c/b\u003e there is potential Competing Interest.\nMR and DK are inventors of patent applications related to the therapeutic use of IL-2LD, which belongs to their academic institutions. No other potential conflicts of interest relevant to this article were reported.","formattedTitle":"Low-dose interleukin-2 for recurrent early pregnancy loss: a proof-of-concept study","fulltext":[{"header":"Main text","content":"\u003cp\u003eUnexplained recurrent early pregnancy loss (uREPL), defined as \u0026ge;\u0026thinsp;3 miscarriages before 14 weeks of gestation (WG) without identifiable cause, affects 3\u0026ndash;5% of women\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. After five losses, the likelihood of causal chromosomal anomalies drops to ~\u0026thinsp;39%, suggesting maternal immune dysfunction, notably insufficient regulatory T cells (Tregs), as a plausible mechanism\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Tregs are essential for maternal-fetal tolerance; in murine models, their depletion results in fetal rejection, while their expansion promotes tolerance and fetal survival\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. In humans, normal pregnancy has been associated with their elevation\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e and accumulation at the maternal-fetal interface\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e, while pregnancy loss has been associated with endometrial and decidual Tregs reduction\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Low-dose interleukin-2 (IL-2\u003csub\u003eLD\u003c/sub\u003e) selectively expands and activates Tregs in humans\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e and prevents miscarriage in mice\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. We hypothesized that IL-2\u003csub\u003eLD\u003c/sub\u003e could restore maternal-fetal immune tolerance and improve pregnancy outcomes in women with uREPL.\u003c/p\u003e\n\u003cp\u003eFACIL-2 was an open-label, single-center, proof-of-concept study (NCT03970954). Women aged 18\u0026ndash;40 with \u0026ge;\u0026thinsp;5 uREPLs and no anatomical, chromosomal, infectious, or hormonal abnormalities were eligible. Key exclusion criteria included thrombophilia, autoimmune disorders, and diminished ovarian reserve (Extended Data Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDemographic, clinical and biological characteristics\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFACIL-2\u003c/p\u003e\n \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;15)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCompassionate\u003c/p\u003e\n \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;9)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAge (years)\u003c/strong\u003e (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;sd)\u003c/p\u003e\n \u003cp\u003e(range)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e34.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.85\u003c/p\u003e\n \u003cp\u003e(26\u0026ndash;39)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e36.8\u0026thinsp;\u0026plusmn;\u0026thinsp;4.9\u003c/p\u003e\n \u003cp\u003e(26\u0026ndash;41)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBMI\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e29.1\u0026thinsp;\u0026plusmn;\u0026thinsp;5.5\u003c/p\u003e\n \u003cp\u003e(20\u0026ndash;41)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e24.0\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u003c/p\u003e\n \u003cp\u003e(19\u0026ndash;31)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eDiabetes (n; %)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eActive tobacco (n; %)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3 (20%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (11%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAlcohol (n;%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eObstetric history\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNulliparity \u003cstrong\u003e(n;%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12 (80%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4 (44%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNumber of previous miscarriages (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;sd)\u003c/p\u003e\n \u003cp\u003e(range)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9\u003c/p\u003e\n \u003cp\u003e(5\u0026ndash;10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.24(5\u0026ndash;15)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHistory of live birth (n; %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3 (20%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5 (56%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAnti-mullerian\u0026nbsp;hormone\u0026nbsp;level at\u0026nbsp;baseline\u0026nbsp;(ng/mL) (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;sd)\u003c/p\u003e\n \u003cp\u003e(range)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.85\u0026thinsp;\u0026plusmn;\u0026thinsp;2.0\u003c/p\u003e\n \u003cp\u003e(1-8.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.98\u0026thinsp;\u0026plusmn;\u0026thinsp;7.14\u003c/p\u003e\n \u003cp\u003e(1.1\u0026ndash;23.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAntral\u0026nbsp;follicular\u0026nbsp;counts\u0026nbsp;at\u0026nbsp;baseline(ng/mL)\u003c/p\u003e\n \u003cp\u003e(mean\u0026thinsp;\u0026plusmn;\u0026thinsp;sd)\u003c/p\u003e\n \u003cp\u003e(range)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20.85\u0026thinsp;\u0026plusmn;\u0026thinsp;13.92\u003c/p\u003e\n \u003cp\u003e(7\u0026ndash;55)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.67\u0026thinsp;\u0026plusmn;\u0026thinsp;8.40\u003c/p\u003e\n \u003cp\u003e(6\u0026ndash;34)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNumber of previous treated pregnancies\u003c/p\u003e\n \u003cp\u003eProgesterone\u003c/p\u003e\n \u003cp\u003eSteroids\u003c/p\u003e\n \u003cp\u003eLMWH and aspirin\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eIL-2\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eLD\u003c/strong\u003e\u003c/sub\u003e \u003cstrong\u003etreatment\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNumber of\u0026nbsp;cycles\u0026nbsp;of\u0026nbsp;IL2\u0026nbsp;received: mean\u003c/p\u003e\n \u003cp\u003e(range)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.19\u003c/p\u003e\n \u003cp\u003e(1\u0026ndash;5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.3\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003c/p\u003e\n \u003cp\u003e(1\u0026ndash;4)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTotal\u0026nbsp;dose\u0026nbsp;of\u0026nbsp;IL2\u0026nbsp;received (MIU): mean\u003c/p\u003e\n \u003cp\u003e(range)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23.3\u0026thinsp;\u0026plusmn;\u0026thinsp;13.24\u003c/p\u003e\n \u003cp\u003e(9\u0026ndash;54)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e33.06\u0026thinsp;\u0026plusmn;\u0026thinsp;19.41\u003c/p\u003e\n \u003cp\u003e(7.5\u0026ndash;69)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003ePregnancy outcomes\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8 (53%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5 (55%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePregnancies ending before 14 WG (n;%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4 (26%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3 (33%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePregnancies continuing after 14WG (n;%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4 (26%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2 (22%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLate miscarriages (14-20WG) (n;%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (0.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLives births (n;%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3 (20%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2 (22%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBiology\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e% Treg/CD4 (mean, range)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.01\u003c/p\u003e\n \u003cp\u003e(6.37\u0026ndash;10.11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTreg/mm3 (mean, range)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e77.38\u003c/p\u003e\n \u003cp\u003e(49.41\u0026ndash;153.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\"\u003eNA: Not Available\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eParticipants first underwent an untreated baseline hormonal cycle for immunophenotyping, then received a first course of 3\u0026nbsp;million international units (MIU) of subcutaneous IL-2 daily for 5 consecutive days per hormonal cycle, starting ten days after menses onset. Up to five IL-2\u003csub\u003eLD\u003c/sub\u003e courses were administered if pregnancy was not achieved (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eA). The study was approved by the local institutional review board (Comit\u0026eacute; de protection des personnes Ile de France III) and was conducted in accordance with the Declaration of Helsinki and good clinical practice guidelines. Written, informed consent was obtained from all participants before enrolment in the study. The primary endpoint was Treg expansion at day-17, 8 days post-treatment initiation, measured as FoxP3\u0026thinsp;+\u0026thinsp;Tregs within CD4\u0026thinsp;+\u0026thinsp;T cells. Secondary endpoints included pregnancy outcomes and safety. Nine additional women with similar clinical profiles received compassionate-use IL-2\u003csub\u003eLD\u003c/sub\u003e using the same therapeutic scheme but were not followed immunologically (Extended Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eAll 15 FACIL-2 participants completed at least one treatment cycle; nine received two cycles, three received three, two received four, and one completed five. Two participants exceeding the permitted interval between cycles were withdrawn and continued treatment under compassionate use (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eB).\u003c/p\u003e\n\u003cp\u003eAt baseline (day 10 of the untreated cycle), mean Treg frequency was 7.93%, rising modestly to 8.49% by day 14 (p\u0026thinsp;=\u0026thinsp;0.016) (Extended Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e), consistent with a preimplantation Treg increase supporting maternofetal tolerance\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. During IL-2LD treatment, Tregs transiently decreased over the first 5 days reflecting recirculation\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, then significantly increased at day 14 with a mean 1.14 fold rise (p\u0026thinsp;=\u0026thinsp;0.17), peaking at day-17 with a mean 2.01-fold rise (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), meeting the primary endpoint (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA \u0026amp; Extended Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). This effect persisted through day-29 (1.33-fold increase, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The second cycle induced a stronger response (2.47-fold at day-17; 1.55-fold at day-29). Similar trends were observed in the third cycle, although participant numbers were too low for robust conclusions (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA). Treg activation (CD25 MFI) increased during treatment (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eB) without expansion of effector T cells (Teffs), resulting in an elevated Treg/Teff ratio (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eC).\u003c/p\u003e\n\u003cp\u003eOf eight pregnancies in FACIL-2, four progressed beyond 14 WG, resulting in three live births and one late miscarriage at 20 WG due to premature rupture of membranes (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eB). In the compassionate-use group, five pregnancies occurred, with two resulting in live births (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eB). All newborns were healthy (APGAR\u0026thinsp;\u0026ge;\u0026thinsp;9 at 5 and 10 minutes).\u003c/p\u003e\n\u003cp\u003eNoteworthily, successful pregnancies in FACIL-2 were associated with significantly greater Treg expansion (2.87-fold vs 1.64-fold at day-17, p\u0026thinsp;=\u0026thinsp;0.03; 1.71-fold vs 1.24-fold at day-29, p\u0026thinsp;=\u0026thinsp;0.008) (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eD). Baseline Treg levels and number of prior miscarriages did not predict outcome (Extended Table\u0026nbsp;2).\u003c/p\u003e\n\u003cp\u003eIL-2\u003csub\u003eLD\u003c/sub\u003e was generally well tolerated (Extended Table\u0026nbsp;3). Seventeen serious adverse events (SAEs), all at the 3 MIU dose, prompted dose reductions to 1.5 or 1 MIU in four patients and discontinuation in one due to EKG changes (negative T waves). Among 149 non-serious adverse events (NSAEs), 127 were deemed IL-2-related (93 Grade 1, 33 Grade 2, 1 Grade 3), mostly at 3 MIU (105 events). No adverse fetal events or neonatal complications were reported up to 6 months post-birth.\u003c/p\u003e\n\u003cp\u003eIn summary, IL-2\u003csub\u003eLD\u003c/sub\u003e robustly and safely expanded Tregs in women with severe uREPL. The association between pregnancy success and greater Treg expansion supports a causal role and validates Tregs as a therapeutic target. Our conservative 5-day regimen, establish to avoid potential embryo exposure due to lack of IL-2 genotoxicity data, resulted in a treatment effect lasting\u0026thinsp;~\u0026thinsp;4 weeks, shorter than the 14-week period during which uREPLs occur. Despite this, we observed an almost 50% viable pregnancy rate in a population with repeated prior failures, suggesting that extended IL-2\u003csub\u003eLD\u003c/sub\u003e regimens covering the first trimester of pregnancy may yield greater benefits. Although limited by its open-label design and lack of a control group, this study provides compelling proof-of-concept evidence warranting a randomized controlled trial of IL-2\u003csub\u003eLD\u003c/sub\u003e for uREPL extending through the first pregnancy trimester.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eDeclaration of interests\u003c/h2\u003e\u003cp\u003eMR and DK are inventors of patent applications related to the therapeutic use of IL-2\u003csub\u003eLD\u003c/sub\u003e, which belongs to their academic institutions. No other potential conflicts of interest relevant to this article were reported.\u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e\u003cp\u003eAssistance Publique-H\u0026ocirc;pitaux de Paris and the French National Research Agency (ANR-16-RHUS-0001,RHU IMAP).\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe thank the patients for their participation in the trial and the personnel of the Piti\u0026eacute;-Salp\u0026ecirc;tri\u0026egrave;re Clinical Investigation Center for Biotherapies (CIC-BTi), Mich\u0026egrave;le Barbi\u0026eacute;, Natalie F\u0026eacute;ry, Catherine Ferrapie, Nadia Graffin, Aur\u0026eacute;lie Marc, for their excellent technical assistance.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMekinian, A. \u003cem\u003eet al.\u003c/em\u003e Unexplained Recurrent Miscarriage and Recurrent Implantation Failure: Is There a Place for Immunomodulation? \u003cem\u003eAmerican J Rep Immunol\u003c/em\u003e 76, 8\u0026ndash;28 (2016).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLee, S. K. \u003cem\u003eet al.\u003c/em\u003e An imbalance in interleukin-17-producing T and Foxp3\u0026thinsp;+\u0026thinsp;regulatory T cells in women with idiopathic recurrent pregnancy loss. \u003cem\u003eHuman Reproduction\u003c/em\u003e 26, 2964\u0026ndash;2971 (2011).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNakashima, A. \u003cem\u003eet al.\u003c/em\u003e SHORT COMMUNICATION: Circulating and Decidual Th17 Cell Levels in Healthy Pregnancy. \u003cem\u003eAmerican J Rep Immunol\u003c/em\u003e 63, 104\u0026ndash;109 (2010).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang, W.-J. \u003cem\u003eet al.\u003c/em\u003e Increased prevalence of T helper 17 (Th17) cells in peripheral blood and decidua in unexplained recurrent spontaneous abortion patients. \u003cem\u003eJournal of Reproductive Immunology\u003c/em\u003e 84, 164\u0026ndash;170 (2010).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDarrasse-J\u0026egrave;ze, G. \u003cem\u003eet al.\u003c/em\u003e CD4\u0026thinsp;+\u0026thinsp;CD25\u0026thinsp;+\u0026thinsp;regulatory/suppressor T cells prevent allogeneic fetus rejection in mice. \u003cem\u003eImmunol. Lett.\u003c/em\u003e 102, 106\u0026ndash;109 (2006).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChen, T. \u003cem\u003eet al.\u003c/em\u003e Self-specific memory regulatory T cells protect embryos at implantation in mice. \u003cem\u003eJ Immunol\u003c/em\u003e 191, 2273\u0026ndash;81 (2013).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChurlaud, G. \u003cem\u003eet al.\u003c/em\u003e Sustained stimulation and expansion of Tregs by IL2 control autoimmunity without impairing immune responses to infection, vaccination and cancer. \u003cem\u003eClinical Immunology\u003c/em\u003e 151, 114\u0026ndash;126 (2014).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAluvihare, V. R., Kallikourdis, M. \u0026amp; Betz, A. G. 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Rheum. Dis.\u003c/em\u003e 78, 209\u0026ndash;217 (2019).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRaeber, M. E., Sahin, D., Karakus, U. \u0026amp; Boyman, O. A systematic review of interleukin-2-based immunotherapies in clinical trials for cancer and autoimmune diseases. \u003cem\u003eEBioMedicine\u003c/em\u003e 90, 104539 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChurlaud, G. \u003cem\u003eet al.\u003c/em\u003e Sustained stimulation and expansion of Tregs by IL2 control autoimmunity without impairing immune responses to infection, vaccination and cancer. \u003cem\u003eClin Immunol\u003c/em\u003e 151, 114\u0026ndash;26 (2014).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRosenzwajg, M. \u003cem\u003eet al.\u003c/em\u003e Low-dose interleukin-2 fosters a dose-dependent regulatory T cell tuned milieu in T1D patients. \u003cem\u003eJ. Autoimmun.\u003c/em\u003e 58, 48\u0026ndash;58 (2015).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"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":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7093926/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7093926/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRegulatory T cells (Tregs) are essential for maternal-fetal tolerance, and their deficiency is implicated in unexplained recurrent early pregnancy loss (uREPL). Low-dose interleukin-2 (IL-2\u003csub\u003eLD\u003c/sub\u003e) selectively activates Tregs. In the FACIL-2 open-label trial (NCT03970954), 15 women with ≥5 uREPLs received a 5-day IL-2\u003csub\u003eLD\u003c/sub\u003e treatment, starting 10 days after menses onset. Nine additional patients received similar treatment under compassionate use. IL-2\u003csub\u003eLD\u003c/sub\u003e significantly expanded Tregs at 8 days post-treatment initiation (p\u0026lt;0.001; primary endpoint met). Of eight pregnancies in FACIL-2, four progressed beyond 14 weeks, yielding three live births. Remarkably, compared to pregnancy losses, these successful pregnancies were associated with a significantly greater Treg expansion (p= 0.008). In the compassionate group, two of five pregnancies resulted in live births. \u0026nbsp;Thus, a short-course IL-2\u003csub\u003eLD\u003c/sub\u003e expanded Tregs and achieved an almost 50% viable pregnancy rate in this high-risk population. These results support further investigation of IL-2\u003csub\u003eLD\u003c/sub\u003e for uREPL, with regimens extending through early pregnancy.\u003c/p\u003e","manuscriptTitle":"Low-dose interleukin-2 for recurrent early pregnancy loss: a proof-of-concept study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-04 08:38:59","doi":"10.21203/rs.3.rs-7093926/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"eaa9d621-5094-490a-b68c-3f0009ef9fe4","owner":[],"postedDate":"August 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":51520145,"name":"Health sciences/Medical research/Clinical trial design/Clinical trials/Phase II trials"},{"id":51520146,"name":"Health sciences/Diseases/Immunological disorders/Autoimmune diseases"}],"tags":[],"updatedAt":"2025-12-02T12:00:21+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-04 08:38:59","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7093926","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7093926","identity":"rs-7093926","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}