Recent advances in understanding the immune microenvironment in ovarian cancer.

Chemotherapy is a widely employed medical treatment for cancer, involving the use of one or more chemical agents to eradicate or curb the proliferation and division of cancer cells. These chemotherapeutic agents function by damaging the DNA of cancer cells, obstructing crucial phases of cell division, suppressing necessary hormones or signals for cell growth, and facilitating the programmed death of the cancer cells themselves. Given that cancer cells often divide more rapidly than normal cells, chemotherapeutic agents are particularly effective at targeting these swiftly multiplying cells, although they may also impact other rapidly dividing healthy cells in the body, such as those in hair follicles, blood, and the digestive tract, leading to various side effects ( 152 ). Chemotherapy is critical in treating OC, with systemic administration being typical, allowing the drugs to circulate through the bloodstream and target both the primary tumor and any microscopic metastatic foci elsewhere in the body ( 153 ). Treatment usually involves a combination of drugs, predominantly those containing platinum and paclitaxel, which impede tumor growth by various mechanisms that damage the DNA of cancer cells; thus, preventing their replication and division. Chemotherapy may serve as a primary treatment (neoadjuvant or postoperative adjuvant chemotherapy) to lessen tumor size and reduce recurrence risk, or as palliative care for advanced or recurrent OC to extend survival and enhance the quality of life. Despite chemotherapy’s role in treating OC, its side effects and the impact on patient quality of life must be considered. Common side effects include nausea, vomiting, hair loss, fatigue, low white blood cell count, and anemia. Thus, the selection and management of chemotherapy regimens should consider the tumor characteristics, overall patient condition, and patient preferences. The influence of TME on the therapeutic outcomes of chemotherapy has been thoroughly investigated. Immune cells within tumors can suppress growth by disrupting immune regulatory tumor cells, yet they may also foster tumor resistance to treatment by affecting tumor immunogenicity and selecting tumor clones that contribute to immune evasion ( 154 ). Furthermore, immune cells in the TME play a dual role in cancer development and metastasis. Cells such as Type 1 helper T cells (Th1), cytotoxic T lymphocytes (CTL), and natural killer cells (NK cells) contribute to an immune-stimulating environment. Conversely, the regulatory cells of the TME, including Type 2 helper T cells (Th2), TAMs, regulatory T cells (Tregs), and myeloid-derived suppressor cells (MDSCs), create an immunosuppressive environment and are linked with adverse outcomes ( 155 ). These cells either support tumor eradication or promote tumor escape by removing immunogenic tumor cells or modifying tumor immunogenicity ( 156 ). Additionally, chemokines and cytokines are significant components of the tumor immune microenvironment (TIME), playing a pivotal role in balancing oncogenic and anti-tumor immune responses. The intricate interactions between cancer cells and immune niches influence immunotherapy and various other anti-cancer treatments. With advancements in personalized medicine and targeted therapeutic approaches, integrating chemotherapy with other treatments like targeted therapy and immunotherapy offers more options and hope for OC patients. It also highlights that combining agents targeting TME and chemotherapeutics may overcome drug resistance and yield synergistic effects. Radiotherapy is a medical procedure that employs high-energy radiation, such as X-rays, gamma rays, or proton beams, to address cancer and certain non-cancerous conditions. This method functions by damaging the DNA of cancer cells, inhibiting their ability to divide and multiply, and ultimately resulting in their death. Radiotherapy is typically localized to the tumor area, which minimizes harm to the adjacent healthy tissue. It can be applied as an independent treatment or combined with other therapeutic strategies, such as surgery, chemotherapy, or immunotherapy, to develop a comprehensive cancer treatment plan tailored to the specific objectives and modalities of treatment. The primary limitation of radiotherapy in treating OC lies in its general indication for localized conditions, whereas OC frequently affects multiple locations on the peritoneal surface and within the abdominal cavity. Furthermore, the tissues within the abdominal cavity are particularly prone to radiation-induced damage, which restricts the safe dosage of radiation that can be administered ( 157 ). Therefore, radiotherapy, such as palliative treatment against a single residual tumor or treatment for the recurrence of OC, is mainly used in specific cases of OC, especially if multiple lines of chemotherapy are used. Nevertheless, radiotherapy continues to be an option for selected OC patients. In advanced stages of OC, radiotherapy can alleviate pain, control bleeding, or manage other symptoms; thus, enhancing the quality of life for patients. Recent advancements in radiotherapy techniques, such as intensity-modulated radiotherapy (IMRT), stereotactic radiotherapy (SBRT), and proton therapy, have significantly enhanced the precision and safety of treatments. These improvements may broaden the application of radiotherapy in OC treatment in the future. Immunotherapy has emerged as a significant treatment modality for tumors in recent years ( 158 ). Rather than directly targeting tumor cells, immunotherapy engages the body’s immune system to recognize and eliminate tumors. This category includes ICIs, immunomodulators, cancer vaccines, and cellular therapies like CAR-T therapy. ICIs are particularly crucial as they enhance the immune response by blocking checkpoint proteins within the immune system, such as PD-1, PD-L1, and CTLA-4. These proteins typically maintain immune balance and prevent the immune system from attacking normal cells, but many cancer cells exploit these mechanisms to evade immune detection and destruction. By inhibiting these checkpoints, the suppression is removed, allowing the immune system to target cancer cells effectively. The use of immunotherapy in managing OC is increasing, although its role is less defined compared to other cancers due to the immunosuppressive microenvironment of OC, which hampers the ability of immune cells to infiltrate and eliminate cancer cells. However, initial clinical trials and studies have indicated benefits for certain OC patients, particularly those who express PD-L1 or have a high mutational burden. Research is also ongoing in utilizing cancer vaccines and cellular therapies in OC treatment. These vaccines aim to prime the immune system to recognize and attack cancer cells bearing specific antigens. While still in the early stages for OC, immunotherapy has shown promise and offers an alternative for patients who respond poorly to conventional treatments like surgery and chemotherapy. As understanding of the immune microenvironment of OC deepens and immunotherapy strategies are optimized, it is anticipated that more effective treatment options will be provided and outcomes for OC patients will improve. PD-1 is expressed on the surfaces of immune cells, such as T cells and B cells, with two ligands, PD-L1 (B7-H1, CD274) and PD-L2 (B7-DC, CD273) ( 159 ). PD-L1 is found on subsets of activated T cells, B cells, and macrophages, while PD-L2 is primarily on antigen-presenting cells ( 160 ). In physiological conditions, the PD-1/PD-L1 axis reduces inflammation-induced tissue damage and T-cell responses, playing a role in maintaining homeostasis to prevent autoimmune diseases ( 161 ). However, when activated T cells express PD-1 combined with tumor cells expressing PD-LI, the PD-1/PD-LI axis promotes immune escape from tumor cells through a variety of mechanisms ( 162 ). The PD-1/PD-LI axis induces T-cell tolerance by inhibiting TRC signaling ( 163 ). They can also inhibit the proliferation of CD8+ T lymphocytes to promote the death of antigen-specific T cells and tumor-infiltrating T lymphocytes, thereby suppressing the antitumor immune response ( 164 ). In addition, the PD-1/PD-LI axis can inhibit the PI3K/ALK and RAS/MEK/ERK signaling pathways to hinder the normal proliferation cycle of T lymphocytes, and the PD-1/PD-LI axis can downregulate the phosphorylation of mTOR, AKT, and ERK2 to upregulate the expression of PTEN, which promotes the transformation of CD4+ T cells into Tregs and inhibits the activity of effector T cells ( 165 ). An overview of PD-1/PD-L1 interaction-mediated T-cell inhibition is displayed in Figure 2 . The immune checkpoint inhibitors used for the treatment of ovarian cancer in randomized clinical trials are summarized in Table 2 . PD-1/PD-L1 interaction-mediated T-cell inhibition. Many mechanisms, such as genomic aberrations, oncogenic transcription factors and pathways, and post-translational regulation and transport, are involved in the regulation of PD-L1 expression. In addition, anti-PD-1/PD-L1 antibodies can block the activation of PD-1/PD-L1. APCs can absorb tumor antigens and regulate T-cell responses through interactions between the main MHC and TCR. APC can also regulate T-cell activity by regulating the interaction between PD-L1/PD-L2 and PD-1, as well as the interaction between B7 and CD28. The figure was generated by Biorender.com . Immune checkpoint inhibitors used related agents for ovarian cancer in randomized clinical trials. Fukumoto et al. found that the combination of HDAC6 inhibition and anti-PD-L1 ICB exhibited a synergistic effect in OCs with ARID1A inactivation. This therapeutic strategy notably suppressed the transcription of CD274, the gene responsible for PD-L1 encoding. In preclinical mouse models treated with ACY1215, an HDAC6 inhibitor, and anti-PD-L1 ICB, there was a significant reduction in tumor burden and an improvement in survival rates. These favorable outcomes were linked to the activation and increase of IFNγ-positive CD8 T cells. These findings suggest that targeting HDAC6 in conjunction with ICB could represent a promising approach for treating cancers with ARID1A mutations ( 166 ). Shang et al. observed that transcript at the distal tip (HOTTIP), interleukin-6 (IL-6), and PD-L1 were all highly expressed in OC tissues. There was a positive correlation between IL-6 and PD-L1 levels; furthermore, HOTTIP was found to enhance IL-6 expression by binding to c-jun. This interaction subsequently promoted PD-L1 expression and facilitated immune escape in neutrophils, while inhibiting T cell proliferation and tumor immunotherapy effectiveness. The study suggests that HOTTIP’s role in increasing IL-6 secretion leads to enhanced PD-L1 expression in neutrophils, impairing T cell activity and promoting immune evasion by OC cells. Thus, targeting HOTTIP may offer a potential therapeutic strategy for OC ( 167 ). Cai et al. reported that PD-L1 was not significantly expressed in the TME of human OC. In contrast, B7-H3 was found to be highly expressed in both tumor cells and antigen-presenting cells within the tumor. This discrepancy highlights the complexity of immune responses in OC and suggests that other targets like B7-H3 may be crucial in developing effective therapies. Experiments conducted on mice with ID8 OvCa tumors revealed that B7-H3 expressed by tumor cells strongly inhibited the immune response against tumors, while its expression on host cells did not have the same effect. Blocking B7-H3 has been found to prolong survival in mice with ID8 tumors, indicating that B7-H3 expressed by tumors may inhibit the function of CD8+ T cells. This suggests that B7-H3 could be a potential therapeutic target for patients who do not respond effectively to PD-L1/PD-1 inhibitors ( 168 ). Lampert et al. observed varied responses among some OC patients, where a lower overall response rate (ORR) and a higher disease control rate (PRþSD) were reported. Treatment was associated with enhanced expression of several factors, increased systemic production of IFNγ and TNFα, and an increase in tumor-infiltrating lymphocytes, indicative of an immunostimulatory environment. Notably, higher IFNγ levels were linked to improved PFS, whereas elevated levels of VEGFR3 were associated with reduced PFS. These observations suggest that the combination of PARP inhibition (PARPi) and anti-PD-L1 therapy has modest clinical activity in recurrent OC. The use of olaparib/duvalizumab demonstrated an immunomodulatory effect in patients, highlighting the necessity of blocking the VEGF receptor pathway to enhance the efficacy of this combination treatment ( 169 ). Zhang et al. reported that the use of abcetinib as monotherapy significantly increased CD8+ T-cell and B-cell infiltration in an ID8 mouse model of OC, indicating potential benefits of this approach in enhancing anti-tumor immunity. The analysis showed that abercetinib induced proinflammatory immune responses in the TME. Compared with control cells, abciximab-treated ID8 cells secreted more CXCL10 and CXCL13. The synergistic antitumor effect of abemaciclib and anti-PD-1 combination therapy depended on CD8+ T cells and B cells. The research argues that the combination of cyclin-dependent kinases 4 and 6 inhibitors (CDK4/6i) with anti-PD-1 antibodies enhances the effectiveness of anti-PD-1 therapies and holds significant potential for the treatment of OC characterized by poor immune infiltration ( 170 ). Wan et al. identified that bivalent antibodies activate T cells and natural killer (NK) cells, leading to NK cells transitioning from an inactive to a more active cytotoxic state. This transformation suggests a substantial role of NK cells in the immune response induced by ICB in HGSC, highlighting the involvement of previously uncharacterized CD8 T cells in mounting an immune response. The observed alterations were partially attributed to the downregulation of the bromodomain-containing protein BRD1 by double-stranded antibodies. These findings suggest that modifying the state of NK cells and T cell subsets could be essential for eliciting an effective anti-tumor immune response and propose that immunotherapies, such as BRD1 inhibitors, which can induce such changes, may enhance treatment efficacy against HGSC ( 171 ). Yang et al. discovered that the presence of CXC-chemokine ligand 13 (CXCL13) in culture stimulates the expansion and activation of CXCR5+ CD8+ T cells in vivo . These T cells were found to be closer to CXCL13 within tumors and showed a propensity to migrate towards it in vitro . Additionally, patients with higher levels of CD20+ B cells and the presence of CXCL13 exhibited improved survival rates. When used in conjunction with anti-PD-1 therapy, CXCL13 effectively hindered tumor growth by enhancing the influx of cytotoxic CD8+ T cells and promoting the maintenance of CXCR5+ CD8+ T-cells within tertiary lymphoid structures (TLS). These findings strongly advocate for targeting CXCL13 along with PD-1 blockade as a potential therapeutic strategy for treating high-grade serous carcinoma (HGSC) ( 172 ). Laumont et al. found that the presence of CD39, CD103, and PD-1 together identifies specific subsets of TILs, namely CD8þ T cells and CD4þ regulatory Tregs. The co-expression of these markers correlates with a reduced diversity in the T cell receptor (TCR) among triple-positive CD8þ TILs. Additionally, triple-positive CD8þ effector cells uniquely showed higher expression of TIGIT compared to CD4þ Tregs. This simultaneous expression signifies the involvement of these highly activated immune cells in cytolytic, humoral, and regulatory immune responses. Notably, triple-positive TILs have significant prognostic value and present promising targets for combination immunotherapy involving PD-1 blockade as well as targeting both CD39 and TIGIT receptors ( 173 ). Seitz et al. found that overexpression of CXCL9 leads to T cell clustering, which results in delayed ascites formation and improved survival rates. This chemokine had effects similar to anti-PD-L1 therapy in an ICB-resistant mouse model, although the impacts were less pronounced in Brca2-deficient tumors. Moreover, the clear cell subtype, known for its high responsiveness to ICB among OC patients, exhibited a significantly greater prevalence of high CXCL9 tumors compared to other subtypes. These findings underscore the crucial role of CXCL9 in enhancing the efficacy of ICB treatments for preclinical OC and suggest that CXCL9 inducers could serve as both a viable predictive biomarker and a potent co-administration partner for improving ICB effectiveness in this cancer type ( 174 ). Dong et al. reported low expression of cullin 3 in OC (CUL3) and speckle-type POZ protein (SPOP). From a functional perspective, CUL3 degrades the PD-L1 protein by forming a complex with SPOP. By degrading the PD-L1 protein, CUL3 overexpression inhibited tumor formation, enhanced the chemosensitivity of mouse OC cells and reduced the malignant features and immune escape of OC cells. The findings indicate that the CUL3/SPOP complex facilitates PD-L1 degradation, thereby suppressing immune evasion and enhancing chemosensitivity in OC cells, presenting a promising therapeutic avenue for OC treatment ( 175 ). Lv-PD1-γδ T cells, developed by Wang et al., produced humanized anti-PD-1 antibodies. These cells amplified tumor cell proliferation and cytotoxicity, resulting in enhanced therapeutic efficacy and survival rates in mice harboring ovarian tumors. There was no potential tumorigenicity in immunocompromised NOD/SCID/γ-fasted mice. In addition, Lv-PD1- γδ T cells showed excellent tolerance and safety in humanized NOD/SCID/γ-fasted mice. The experimental results suggested that Lv-PD1-γδ T cells could attenuate or eliminate immunosuppression and maximize cytotoxicity by secreting anti-PD1 antibodies locally in the tumor and thus could serve as a promising anticancer “off-the-shelf” cell therapy ( 176 ). The surface of T cells expresses CTLA-4, which is a molecule that acts as an immune checkpoint with inhibitory functions. CTLA-4 regulates T-cell activation and maintains immune system self-tolerance, preventing the immune system from attacking normal tissues ( 161 ). CTLA-4 competitively inhibits immune activation signaling and reduces T-cell activity by binding to B7 molecules (CD80 and CD86) ( 177 ). By blocking the function of CTLA-4, CTLA-4 inhibitors can inhibit T-cell activation, thereby improving the capacity of the immune system to recognize and attack cancer cells ( 178 , 179 ). Although CTLA-4 inhibitors have shown significant effects in boosting immune responses, they may also lead to overactivation of the immune system to attack normal tissues and cause immune-related side effects ( 180 ). With an improved comprehension of immune checkpoint pathways and the advancement of novel immunotherapeutic approaches, the anticipation is that CTLA-4 inhibitors and their combined therapies will offer more efficacious treatment alternatives for a broader spectrum of cancer patients. Friese et al. used a CTLA-4 blocking antibody, which was added during initial tumor-inflating lymphocyte (TIL) culture, and found that CTLA-4 blockade favored the propagation of CD8+ TILs in ovarian tumor fragments. In addition, the addition of CTLA-4 blocking antibody at the initial stage of TIL culture produced more potent antitumor TILs than did standard TIL culture. This phenotype was retained during the rapid amplification phase. These findings suggest that targeting CTLA-4 in the intact TME of a tumor fragment enriches tumor-responsive TILs and thus improves the clinical outcome of TIL-based ACT in OC ( 181 ). An investigation conducted by Swiderska et al. focused on three proteins associated with the immune response, namely, PD-1, PD-L1, and CTLA-4. To assess their effectiveness, receiver operating characteristic (ROC) curves were generated, and the area under the curve (AUC) was calculated to determine the sensitivity and specificity of these parameters. Utilizing Cox regression models, both univariate and multivariate analyses were carried out during this research endeavor. The findings from this study strongly suggest that considering CTLA-4 as a prospective biomarker could prove valuable in diagnosing OC while highlighting that elevated concentrations of PD-L1 and PD-1 serve as unfavorable prognostic indicators for this particular form of cancer ( 182 ). Chen et al. performed survival analyses on a subset of patients who were followed up. The results showed that the genotype and allele distribution frequency of the rs5742909 C/T polymorphism in cytotoxic T-lymphocyte antigen-4 (CTLA-4) differed significantly between patients and controls. Compared with the CC genotype, the CT + TT genotype significantly reduced the risk of developing EOC. However, no significant correlation was detected between the rs231775 G/A and rs3087243 G/A polymorphisms and susceptibility to EOC. The results confirmed that in women, the CTLA-4 rs5742909 C/T polymorphism may decrease the genetic predisposition to EOC ( 183 ). Tumor vaccines are a new approach to immunotherapy and are considered a highly promising therapeutic modality in the field of tumor therapy. Tumor vaccines can induce body-specific antitumor immune responses by actively delivering tumor antigens to the body. Tumor vaccines can also make use of widely distributed T cells in the body to recognize and kill tumors ( 184 ). Tumor vaccines both improve the efficiency of tumor killing and overcome the drawbacks of conventional difficulties in completely removing tumors ( 161 , 185 ). Currently, more clinical trials have been conducted in the field of tumor vaccines. However, most of the trials have small sample sizes, and a significant number of them have not achieved the expected results. Antigens, adjuvants, vectors, and the autoimmune status of the body play a dominant role in causing poor results in tumor vaccines. It is important to optimize the composition and timing of tumor vaccines with respect to these aspects to enhance the effectiveness of the vaccine. At the same time, the design of vaccines with individualized characteristics and preventive ability is highly important for improving tumor treatment and preventing tumor recurrence and metastasis. Adams et al. demonstrated the potential of isolating ascites monocytes within the ID8 model and boosting their role as genuine antigen-presenting cells (APCs) by employing Toll-like receptor (TLR) 4 LPS, TLR9 CpG-oligonucleotide, and an interleukin-10 receptor (IL-10R) blocking antibody. Activated ascites monocytes efficiently curbed tumors and malignant ascites in vivo . Similarly, human ascites monocytes exhibited tumor-associated antigens (TAAs) under steady-state conditions. Notably, activated ascites mononuclear cells preserved their capacity to activate TALs even in the presence of ascites fluid. The findings suggest that ascites monocytes inherently harbor tumor antigens and can serve as potent antigen-presenting immune cells following a brief in vivo activation. This innovative ascites APC vaccine can be swiftly prepared, is straightforward, and cost-effective, making it an appealing option for OC treatment ( 186 ). Block et al. employed a Th17 induction protocol to generate DCs and loaded them with the HLA class II epitope of folate receptor alpha (FRα). Mature antigen-presenting DCs were subcutaneously injected. The majority of patients completing the respective interventions developed Th1, Th17, and FRα antibody responses post-vaccination. Prolonged relapse-free survival was associated with the presence of antibody-dependent cell-mediated cytotoxicity targeting FRα. Among the patients evaluable for efficacy, fewer than 40% remained relapse-free at the data cutoff. The findings indicate that vaccinating DCs with Th17-induced FRα loading is safe, induces antigen-specific immunity, and extends remission ( 187 ). Tanyi et al. improved vaccine-induced immune responses by combining ASA and low-dose IL-2 with the OCDC-Bev-Cy treatment. In the ID8 ovarian model, animals that received this treatment exhibited prolonged survival, elevated levels of perforin T cells within tumors and CD8+ T cells specific to neoantigens, and decreased expression of endothelial Fas ligand and intratumoral T-regulatory cells. These findings suggest that the ID8 model holds promise for the future development of OC trials ( 188 ). Nishida et al. observed a notable increase in the proportion of highly active tetrameric WT1-CTLs within CD8+ T lymphocytes (%tet-hi WT1-CTL) and a rise in WT1235-IgG levels post-vaccination. Furthermore, the elevated WT1235-IgG levels significantly prolonged progression-free survival. Unfavorable clinical outcomes associated with the WT1 vaccine included lower serum albumin levels, multiple tumor lesions, poor performance status, and excessive ascites. These results underscore that patients with refractory OC develop antigen-specific cellular and humoral immunity following WT1 vaccine administration. Both %tet-hi WT1-CTL and WT1235-IgG levels serve as prognostic markers for evaluating WT1 vaccine efficacy ( 189 ). Zhang et al. devised a fused cell membrane (FCM) nanovaccine, termed FCM-NPs. In addition, FCM-NPs exhibited the immunogenicity of tumor cells and the antigen-presenting ability of DCs and stimulated naïve T lymphocytes to produce large numbers of tumor-specific cytotoxic CD8+ T lymphocytes. FCM-NPs demonstrated robust immune activation both in vitro and in vivo . These findings highlight the potential of FCM-NPs to impede OC growth and hinder metastasis. FCM-NPs are poised to emerge as a novel tumor vaccine for OC treatment ( 190 ). As per Fucikova et al., although a higher tumor mutational burden (TMB) and significant CD8+ T-cell infiltration have been associated with improved outcomes in EOC patients undergoing conventional chemotherapy, this correlation does not apply to female patients undergoing DCVAC treatment. Conversely, positive responses to DCVAC were observed among individuals with below-average TMB levels and an excessive presence of CD8+ T-cells. These responses were accompanied by indications of enhanced effector function and specific tumor destruction within peripheral blood samples. In conclusion, our findings suggest that while heavily infiltrated “hot” EOC cases may benefit from chemotherapy, females diagnosed with less infiltrated “cold” EOC may require a dendritic cell-based vaccine as an alternative approach to elicit a clinically significant immune response against cancer ( 191 ). Zhao et al. conducted a study comparing the efficacy of co-formulated preparations of ICC and CPMV, either naturally bonded through CPMV-cell interactions or chemically coupled, with mixtures of PEGylated CPMV and ICC. The results revealed that blocking ICC interactions by PEGylation of CPMV did not significantly affect mice inoculated with the simple mixture of ICCs and (PEGylated) CPMV adjuvant. However, when co-formulated CPMV-ICCs were administered, approximately 70% of the mice survived, and 60% of the surviving mice successfully rejected tumor growth in a re-challenge experiment. These findings underscore the necessity of delivering cancer antigens and adjuvants together for effective OC vaccine development ( 192 ). Kos et al. reported a clinical therapeutic benefit in a small number of patients, including three partial responders (PR) and three patients with stable disease (SD) for more than six months. Clinical benefit was achieved in 1/3 of immunological responders and in less than 30% of evaluated patients. High levels of mRNA for various molecules linked to terminally differentiated T cells were expressed by immunological nonresponders in pretreatment peripheral blood mononuclear cell samples. These findings suggest that the combination of p53MVA and pembrolizumab immunotherapy shows promising efficacy against tumors in individuals with intact T-cell function in their peripheral blood. The identification of markers indicative of fully differentiated T cells prior to treatment could serve as a means to predict patients who are nonresponsive to p53MVA/pembrolizumab ( 193 ). CAR-T-cell immunotherapy is one of the more established forms of cellular therapy and involves the artificial modification of T cells taken from the patient’s body. T cells are artificially modified by the addition of chimeric antigen receptors (CARs), which can recognize tumor antigens, giving T cells the ability to recognize tumor cells. The modified T cells are then infused back into the body to achieve tumor recognition and killing ( 194 ). CAR-T-cell therapy was initially developed for certain types of hematological cancers ( 195 ) and has already achieved significant therapeutic results under these conditions. The successful use of CAR-T-cell therapy has stimulated widespread interest and research into its application in the treatment of solid tumors. The rapid generation and administration of CAR-T cells are shown in Figure 3 , while the antigens used in CAR-T-cell therapy for ovarian cancer in randomized clinical trials are summarized in Table 3 . Generation of the brief and administration of CAR-T cells. The production and administration of CAR-T cells in cancer patients. (A) T cells are collected from patient blood through a single collection and genetically engineered to express CARs. After amplifying CAR-T cells in vitro , they are used in cancer patients. The reconstructed CAR-T cells are able to recognize their targets and kill tumor cells expressing that target. (B) Explanation of the basic structure of fourth-generation CAR-T cells. The figure was generated by Biorender.com . Antigen used in CAR-T-cell therapy for ovarian cancer in randomized clinical trials. Garcia et al. reported that T cells expressing a specific chimeric antigen receptor (CAR) targeting the Müllerian inhibiting substance type 2 receptor (MISIIR) demonstrated targeted responses when exposed to antigens under laboratory conditions, effectively eradicating tumors with overexpressed MISIIR receptors within living organisms. Furthermore, these MISIIR CAR-T cells recognized various types of ovarian and endometrial cancer cell lines and exhibited the ability to destroy tumor samples obtained from patients without harming normal primary human cells. These results demonstrate that MISIIR-targeted therapy for OC and other gynecological malignancies can be achieved using CAR technology. In vitro experiments conducted by Li et al. illustrated the potent capacity of chimeric antigen receptor T (CAR-T) cells to eliminate OVCAR-3 cells while releasing a plethora of cytokines. Moreover, therapeutic efficacy was observed, along with significantly prolonged survival time in OVCAR-3 tumor-bearing mice. The experimental findings revealed that the killing capability of dual CAR-T cells on OVCAR-3 cells mirrored that of single CAR-T cells in vitro . However, in vivo , the killing efficacy of dual CAR-T cells led to a noteworthy enhancement and substantial extension of the lifespan of mice harboring tumors. In vivo , PD1-anti-MUC16 CAR-T cells exhibited stronger antitumor activity than single CAR-T cells. The current experimental data may lead to clinical studies ( 196 ). Shu et al. designed a truncated CD47 CAR without intracellular signaling structural domains. The CD47 CAR facilitates binding to CD47+ cells; thus, increasing the possibility of eradicating TAG72+ cells via the TAG72 CAR. In addition, we can reduce damage to normal tissues by monopolymerizing CD47 CAR. These findings suggest that expressing both TAG-72 CAR and CD47-truncated monoclonal CAR on T cells may be an effective dual CAR-T-cell strategy for the treatment of OC and is also applicable to other adenocarcinomas ( 197 ). Schoutrop et al. discovered that administering CAR T cells expressing an MSLN CAR construct incorporating the CD28 structural domain (M28z) led to a significant extension in survival. Despite a modest response rate, MSLN-4–1BB (MBBz) CAR T cells achieved long-term remission. Intratumorally infiltrated M28z and MBBz CAR T cells exhibited upregulation of PD-1 and LAG3 in response to antigens, while the respective ligands were expressed by MSLNþ-positive tumor cells. This suggests that immunosuppressive pathways within the ovarian tumor microenvironment hinder the persistence of CAR T cells. These findings highlight the promise of MSLN-CAR T cells for OC treatment ( 198 ). Guo et al. focused on the development of 5T4 CAR-T cells, which are second-generation human CAR-T cells engineered to specifically target the 5T4 protein. These CAR-T cells not only secrete cytotoxic cytokines but also exhibit lysogenic cytotoxicity against tumor cells. Additionally, the adoptive transfer of 5T4 CAR-T cells significantly delayed tumor formation. These findings underscore the potential effectiveness and viability of employing 5T4 CAR-T cell immunotherapy for OC treatment and lay a robust theoretical groundwork for future clinical studies targeting 5T4 cells ( 199 ). Liang et al. devised an innovative strategy to enhance the efficacy of CAR-T cell therapy by designing a tandem CAR that targets two antigens, one of which exhibits secretory activity (IL-12). In vitro experiments demonstrated that compared with single-target CAR-T cells, tandem CAR-T cells efficiently killed antigen-positive OC (OV) cells and showed enhanced secretion of cytokines. More importantly, the tandem CAR-T cells prolonged the survival of mice by reducing tumor size and enhancing antitumor activity. The results demonstrated that IL-12-secreting tandem CAR-T cells can enhance immunotherapeutic efficacy by reducing tumor antigen escape and improving T-cell function, which may be a promising strategy for the treatment of OV and other solid tumors ( 200 ). Chen et al. illustrated the effectiveness of anti-MSLN CAR-T cells in treating OC by inducing programmed cell death in MSLN-positive tumor cell lines. This led to suppressed tumor growth and increased cytokine levels compared to control groups. Subsequently, an in vivo experiment targeted OC-derived xenografts, demonstrating the safety and efficacy of autologous anti-MSLN CAR-T cell therapy for patients with this condition. These findings reinforce the potential efficacy of employing an anti-MSLN CAR-T treatment strategy for OC and offer initial data for future clinical trials ( 201 ). Shen et al. developed a novel CAR-T-cell therapy that effectively targets TM4SF1 for OC treatment. In vitro experiments demonstrated that CAR-T cells can specifically eliminate TM4SF1-positive tumor cell lines, while in vivo studies revealed that these modified immune cells significantly inhibited SKOV3-derived tumor growth. Possible therapeutic options for the management of OC may involve targeting TM4SF1, which has encouraging potential. Furthermore, there is a possibility for the advancement of immunotherapy utilizing TM4SF1 as a basis ( 202 ). Schoutrop et al. evaluated the therapeutic efficacy of MSLN-CAR-T cells and the characteristics and number of different MSLN-CAR-T cells and found that M1xx CAR-T cells had greater antitumor potency and durability than conventional second-generation M28z and MBBz CAR-T cells. In addition, M1xx CAR-T cells exhibited improved in vitro generation capacity and were characterized by self-renewal genes. These findings indicate that MSLN-CAR T cells, which express a mutated CD3ζ strand containing only one immunoreceptor tyrosine-based activation motif (ITAM), demonstrate enhanced potential for treating OC. Employing CAR T cells with precisely calibrated activation potential may lead to improved clinical responses in solid tumors ( 203 ). Ranoa et al. conducted a comparative analysis on the efficacy of four Tn-dependent CARs with different affinities toward the Tn antigen. The 237 CAR and a mutant with significantly higher affinity, along with a CAR with lower affinity, effectively controlled advanced ID8Cosmc-KO tumors. Tumor regression was more pronounced with a single dose of intraperitoneal intravenous CAR. The most successful CARs were associated with the antigen possessing the highest affinity. Furthermore, less effective CARs exhibited tonic signaling, leading to cytokine expression independent of the antigen. These findings provide evidence for the potential use of affinity-enhanced CAR-T cells in treating advanced OC, where different patterns of inflammatory cytokine release were observed in vitro among successful CARs. Importantly, Tn-dependent CAR-T cells, which are considered highly effective, do not exhibit any toxicity to the immune system of tumor-bearing mice ( 204 ). Xu et al. conducted a thorough investigation into the therapeutic potential of PTK7 CAR-T cells against OC, both in vitro and in vivo . Their study unveiled significant PTK7 expression in OC tissues and cells, indicating its suitability as a target for CAR-T cell therapy. Through the TREM1/DAP12 signaling pathway, researchers observed robust cytotoxicity of PTK7-targeted CAR-T cells against OC cells expressing PTK7 in laboratory settings. Additionally, these engineered immune cells effectively eradicated tumors in animal models. These findings suggest that employing TREM1/DAP12-based PTK7 CAR-T cell therapy shows promise as an innovative approach for treating OC; however, further evaluation is necessary to determine its safety profile and clinical efficacy through rigorous clinical trials ( 205 ). Mun et al. developed Muc16-specific CAR T cells (4H11) capable of producing a bispecific T cell engager (BiTE), composed of a TCR mimetic antibody (ESK1). This BiTE selectively binds to the WT1-derived epitope RMFP, presented by the HLA-A2 molecule. Compared with 4H11 CAR-T cells alone, secreted ESK1 BiTE redirected additional T cells toward WT1 on tumor cells, resulting in improved anticancer activity against Muc16-overexpressing cancer cells. These observations were made in both laboratory experiments and a mouse model of tumors. This novel strategy of dual orthogonal cytotoxicity targets distinct surface and intracellular tumor-associated antigens, indicating potential for overcoming resistance to CAR-T cell therapies not only in EOC but also in other malignancies ( 206 ). Mondal et al. characterized an important cluster of positively charged residues known as PPCR within domain 2 of the Fas protein structure. This cluster plays a crucial role in blocking apoptotic signaling triggered by mutated forms of either FasL or Fas, thereby affecting both tumor cells and T cells. Furthermore, our study sheds light on how Fasl interacts with its receptor, Fas, at the PPCR interface through various mechanisms. These findings suggest that employing death agonists could potentially offer an effective therapeutic avenue for targeting FAS and improving cancer immunotherapy outcomes, not only for OC but also for various solid tumors ( 207 ). Biotec et al. verified the high expression and consistency of the tumor-associated antigen FOLR1 in primary OC samples. Subsequently, a range of potential CAR T cells were engineered to target the identified markers, and their efficacy against OC cell lines was validated in laboratory and animal models. Ultimately, an automated manufacturing process for these candidate CAR T cells was developed through additional laboratory tests. These results underscore the potential of utilizing anti-FOLR1 CAR T cells as a therapeutic strategy for treating OC and other tumors expressing FOLR1 ( 208 ).

Ovarian cancer (OC) is a prevalent form of gynecological cancer, recognized for its aggressive nature and tendency to metastasize ( 1 ). Its atypical presentation poses challenges for early detection and treatment, with approximately three-quarters of OC cases diagnosed at an advanced stage ( 2 ). OC includes various types, including epithelial tumors, sex cord stromal tumors, germ cell tumors, unclassified types, and metastatic secondary tumors, with epithelial ovarian cancer (EOC) accounting for over 95% of cases ( 3 ). EOC comprises diverse histological types, grades, and molecular profiles, primarily classified into type I and type II. Type I OC typically includes endometrioid carcinoma, low-grade serous carcinoma, clear cell carcinoma, and mucinous carcinoma, often arising from atypical proliferative (borderline) tumors ( 4 ). Type I OC is associated with mutations in genes such as K-Ras and PTEN, tends to present at early stages, exhibits slow growth, and carries a favorable prognosis. Conversely, type II OC originates from serous intraepithelial carcinoma of the fallopian tube, featuring high-grade serous carcinoma (HGSC), carcinosarcoma, and undifferentiated carcinoma subtypes ( 5 ). Research indicates that inflammation and endometriosis stemming from repeated ovarian cycles contribute to the development of type II OC. This type is frequently linked to mutations in the p53 and BRCA genes, HER2 overexpression, and is often diagnosed late, leading to a poor prognosis. It tends to be highly invasive and carries a high mortality rate ( 6 ). Currently, the primary approach to treating OC involves surgical resection alongside systemic radiotherapy and chemotherapy ( 7 ). In recent years, increased understanding of tumor immunity has led to the recognition of immunotherapy as a promising therapeutic option ( 8 , 9 ). Despite the effectiveness of many treatments in managing OC, the disease still exhibits high rates of recurrence and low survival rates, underscoring the need for the development of new or enhanced therapeutic strategies.Tumor development is a complex process that unfolds in multiple stages. The tumor microenvironment (TME) plays a crucial role in facilitating the uncontrolled survival and growth of tumor cells, from initial carcinogenesis to fully developed cancer. Comprising various cell types and their driver molecules, such as immune cells, interstitial cells, endothelial cells, adipocytes, extracellular matrix, cytokines, and chemokines, the TME orchestrates diverse intracellular signaling pathways ( 10 ). Recent investigations underscore the significance of both the primary site TME and the microenvironment formed by distant metastasis in driving tumor proliferation, metastasis, invasion, drug resistance, and the preservation of tumor cell stemness ( 11 ). Immune checkpoints (ICs) are molecules expressed on immune cells that modulate immune system activation. Immune checkpoint inhibitors (ICIs) act by blocking the interaction between ICs and their ligands; thus, preventing T lymphocyte inactivation and exerting an anti-tumor effect. In the past two decades, targeting the TME has become a key therapeutic strategy for solid tumors ( 12 ). The first successful pathway involved the programmed death 1 (PD-1)/programmed death ligand 1 (PD-L1) and cytotoxic T lymphocyte-associated protein 4 (CTLA-4) pathways, which are key mediators through which cancer cells evade antitumor T-cell-mediated cytotoxicity ( 13 ). Immune checkpoint inhibitors (ICIs) targeting PD-1/PD-L1 and CTLA-4 were the earliest developed, showing remarkable benefits in specific patients and revolutionizing the treatment landscape for numerous cancers ( 14 ). While these ICIs were also trialed in OC patients, phase III trials demonstrated that ICIs, either as monotherapy or combined with chemotherapy, did not yield statistically significant survival advantages ( 15 , 16 ). The strong immunosuppressive environment and the number of participants involved in the OC TME are likely reasons for these disappointing results. Current data suggests that targeting the OC TME remains a challenging endeavor. However, within the context of the OC TME, concentrating solely on T cell activity and the PD-1/PD-L1 pathway might be overly restrictive. Achieving a broader characterization and a more thorough comprehension of the intricate interactions between OC tumor cells and their microenvironment is imperative to altering this trend. This review summarized the related studies of different cell populations that combined the TME and immunotherapy challenge in OC.

The TME is the cellular milieu in which neoplastic cells or cancer stem cells reside. These include the blood vessels surrounding tumor cells, immune cells, other nontumor cells, the extracellular matrix, and signaling molecules ( 17 , 18 ). The interactions between these components and tumor cells have a significant impact on tumor progression ( 19 , 20 ). The TME consists of cancer cells, the extracellular matrix (ECM), cancer-associated fibroblasts (CAFs), a complex network of blood vessels, and diverse immune cells, including T-cells, B-cells, and cells linked to tumor progression (TACs). Cancer cells recruit and activate immune cells and stromal components, like lymphocytes, tumor-associated macrophages (TAMs), natural killer (NK) cells, dendritic cells (DCs), tumor-associated neutrophils (TANs), and myeloid-derived suppressor cells (MDSCs) ( 21 – 23 ), collectively establishing an anti-tumor inflammatory microenvironment during early tumor colonization or expansion; thus, impeding tumor growth ( 24 , 25 ). However, prolonged exposure to tumor antigens and immune activation can deplete or alter effector cells, resulting in an immunosuppressive microenvironment that fosters tumor aggressiveness ( 26 , 27 ). Given that the key cellular components sustaining this immunosuppressive microenvironment also exhibit anti-cancer properties during the initial tumor phases, they represent potential intervention targets. Figure 1 illustrates the cellular constituents within the TME. The cell com ponents in the tumor microenvironment (TME). The TME is mainly composed of cancer cells, immune cells, and stromal cells. These cells interact with receptors such as the molecules they secrete, histocompatibility complex (MHC) molecules, programmed cell death protein-1 (PD-1), and others to form an evolutionary microenvironment. The figure was generated by Biorender.com . TAMs, tumor-associated macrophages; DCs, dendritic cells; MDSCs, myeloid-derived suppressor cells; CAFs, cancer-associated fibroblasts. CAFs are significant components of the tumor stroma and are primarily distributed in the perivascular or tumor peripheral fibrous mesenchyme ( 28 , 29 ). CAFs produce cytokines, ECM components, and associated enzymes ( 30 , 31 ). The ECM offers structural support to TME cells and plays a crucial role in cellular adhesion and infiltration ( 32 , 33 ). ECM deposition leads to the creation of a dense fibrous mesenchyme enveloping the tumor, making the tumor tissue stiffer and more brittle than normal tissue. The buildup of ECM results in the formation of a dense fibrous mesenchyme encircling the tumor, increasing its stiffness and fragility compared to normal tissue. This forms a physical barrier hindering immune cell penetration and obstructing the efficient delivery of anti-cancer drugs to the TME. CAFs produce matrix metalloproteinases that can modify the ECM and release chemokines, growth factors, and proangiogenic factors, thereby facilitating the malignant transformation of tumors ( 34 – 36 ). Due to the rapid growth of tumors and irregular blood flow patterns, tumors often face inadequate blood supply, leading to prolonged oxygen deprivation. Consequently, the tumor environment becomes acidic due to metabolic processes generating lactate and hydrogen ions. Vascular abnormalities and metabolic imbalances trigger signaling cascades, fostering the development of an immunosuppressive TME. This environment is infiltrated by diverse immune cells, including CD8+ or cytotoxic T lymphocytes (CTLs), crucial for tumor elimination. While CD8+ or cytotoxic T lymphocytes (CTLs) target tumor cells for destruction, regulatory T cells (Tregs) suppress the activity of effector T cells and promote immunosuppression within the TME ( 37 – 39 ). M1-type macrophages typically release Th1 cytokines, exerting pro-inflammatory and anti-tumor effects ( 40 , 41 ). However, TAMs in the TME predominantly exhibit the M2 subtype and can induce angiogenesis and tumor invasion by secreting Th2 cytokines ( 42 , 43 ). NK cells can eliminate target cells through the release of granzymes and perforin or by facilitating antibody-dependent cytotoxicity via their Fc receptors ( 44 , 45 ). Nevertheless, the killing activity of T cells is hindered by the accumulation of TGF-β in the TME, and the antigen-presenting function of DCs is impaired by the hypoxic and inflammatory conditions of the TME ( 46 , 47 ). Additionally, MDSCs, acting as negative immune regulators within the TME, suppress T-cell activation and the functions of various immune cells ( 48 , 49 ).

OC is difficult to diagnose at an early stage, and its five-year survival rate is low. Henceforth, it is crucial to develop new methods for early screening of OC and new therapeutic strategies. As the role of the TME in OC metastasis has received increasing attention, understanding the interactions between immune cell molecules in the TME and tumor cells at primary and metastatic sites and elucidating the molecular mechanisms of the TIME and tumor cells in OC metastasis are urgently needed to provide guidance for the clinical development of new diagnostic markers and therapeutic targets for OC. Since most tumor cells are weakly immunogenic, it is difficult to induce specific immune responses against these antigens in the body. Immunotherapies, such as vaccines to stimulate the host antitumor immune response, the application of genetically engineered cytokines, the infusion of immune effector cells, etc., to assist surgery, radiotherapy, and chemotherapy, in the treatment of OC, have promising application prospects. The intricate interplay between cancer genomic alterations and the complex microenvironment poses challenges to the development of effective immunotherapies. Successful immunotherapy for OC hinges on stimulating antigen-presenting cells, mitigating the suppressive immune microenvironment, and enhancing effector T-cell activity. The modulation of cell-mediated immune responses entails both inhibitory and stimulatory signals. Immune checkpoint receptors play a crucial role in dampening T-cell activation to prevent hyperactivation. Figure 4 illustrates the constituents and therapeutic targets of the TME. The components and therapeutic targets of the tumor microenvironment (TME). The TME is composed of various cells, including cancer stem cells, immune cells, and stromal cells. Treatment targets and intervention measures for the TME. Drugs approved by the US Food and Drug Administration for targeting VEGF, CTLA-4, EGFR, PD-L1, and PD-1. Certain types of tumors express immune checkpoints, allowing them to evade the immune system hence blocking these checkpoints is crucial in immunotherapy. Lysovirus therapy, a novel anti-tumor strategy, triggers an immune response against tumors by rapidly proliferating and ultimately killing tumor cells in response to lysovirus infection ( 209 ). While immune checkpoint inhibitors have shown promise in various tumors, their efficacy in OC therapy is relatively low. To enhance the anti-tumor response rate, several studies are combining them with chemotherapy or small molecule inhibitors as adjuvant therapy. However, applying CAR-T cell therapy to solid tumors faces challenges like effective penetration into tumor tissues, overcoming immunosuppressive factors, and minimizing damage to normal tissues. Despite these challenges, CAR-T cell therapy holds significant potential in cancer treatment. Ongoing research explores new target antigens, improved CAR designs, novel management strategies, and combination therapies to expand CAR-T therapy’s application and efficacy. As research advances, CAR-T cell therapy is expected to offer hope to more cancer patients. Immunotherapy represents a paradigm shift in OC treatment, but effectively enhancing its efficacy remains a priority. A deeper understanding of the OC immune microenvironment and immune escape mechanisms could lead to novel therapeutic strategies. By using cutting-edge technologies, personalized immunotherapy can be implemented by considering tumor biology and the microenvironment. Therefore, investigating the integration of chemotherapy with immunotherapy or other strategies is essential to improve efficacy and mitigate immune escape in OC treatment. Given its poor prognosis and high mortality rates, OC has presented significant challenges in treatment, especially in advanced stages where options are scarce. Immunotherapy holds potential for OC treatment, offering better survival outcomes, long-lasting responses, and manageable safety profiles in advanced cases. Nonetheless, current single-agent studies have not yielded substantial survival benefits. In addition to the immunosuppressive properties of OC, this may be due to the complexity of the OC microenvironment, which prevents the activity of immune cells and should, therefore, be targeted by the TME. Temporal factors play a crucial role in modulating the suppression of the immune response and tolerance, as well as influencing the quantity and functionality of TILs. Elucidating the interplay between OC cells and the surrounding mesenchymal environment is imperative for identifying effective therapeutic approaches and reliable prognostic biomarkers. All elements of the TME must be taken into account when devising new therapeutic approaches, particularly for “variable tumors” or “cold tumors.” These strategies may involve initiating T-cell responses, utilizing vaccines and CAR-T cells targeting neoantigens in tumor cells, inducing immunogenic cell death in in situ vaccination strategies, and simultaneously targeting checkpoint inhibitors responsible for T-cell dysfunction or failure.

In this study, we conducted a thorough analysis of the diverse cellular components within the TME and their functions in controlling OC progression and treatment responses. Furthermore, we offered a detailed evaluation of the obstacles linked to ICI-based therapies in OC. Altogether, advancing our understanding of the TME will facilitate the development of precise and effective treatment approaches for OC. The tools currently employed to examine the TME include genomics to investigate gene expression features in high-grade serous ovarian cancer. Verhaak et al. identified four distinct genetic categories in a study on ovarian tumors, designated as differentiated, immune responsive, mesenchymal, and proliferative ( 210 ). It has been determined through IHC that T lymphocytes are increased in the immune-responsive group, while an increase in connective tissue proliferation associated with infiltrating stromal cells is noted in the mesenchymal group. The survival outcomes for patients in the immune-responsive group are the most favorable. Several malignant tissues exhibit more than one of these four gene clusters. These findings were corroborated using an independent dataset of 879 high-grade serous ovarian cancer expression profiles. Additional insights into survival outcomes and platinum resistance were gained using survival prediction models related to BRCA1/2 mutation status, postoperative residual disease, and disease staging ( 210 ). Therefore, the development of similar gene classification models might assist in selecting patients for targeted or immunotherapy, or in predicting patient prognosis. For instance, it has been observed that patients exhibiting mesenchymal traits may respond more effectively to therapies such as angiogenic inhibitors. Additional methods for studying the high-grade serous ovarian carcinoma TME include integrating proteomics with other genomic data ( 211 ), and employing multiple parameter analysis techniques (such as gene expression, matrix proteomics, cytokine and chemokine expression, ECM parameters, and biomechanical properties) on single biopsy samples to enhance understanding of the events occurring within the tumor tissue ( 212 ). Novel tools for investigating ovarian TME include the utilization of artificial microenvironments to monitor the progression of ovarian cancer ( 213 ). The TME is a complex and dynamic entity that may vary between primary disease and recurrence. In devising more effective treatments, it is crucial to consider existing immune suppression and emerging mechanisms of therapeutic resistance ( 214 ). Cancer treatment with immunotherapy has not achieved the same success as treatments for other types of cancer ( 215 ). Combining immunotherapy, such as PD-1 blockade, with other checkpoint inhibitory molecules like anti CTLA-4, anti TIM-3, anti LAG-3, PARP inhibitors, kinase inhibitors, chemotherapy drugs ( 216 ), dendritic cell vaccines, CAR T cell therapy ( 217 ), or other therapies have been validated to be successful measures to overcome multiple immunosuppressive mechanisms in TME. In fact, targeting complements in OC-TME is a new approach to developing effective immunotherapy. A randomized phase 2 clinical trial ( NCT04919629 ) is currently underway, investigating the combination of a complement inhibitor, anti-PD1, and anti-VEGF for recurrent ovarian cancer patients. The results of this trial may guide future strategies involving complement inhibition in ovarian cancer TME alongside other treatments.

JC: Writing – review & editing, Writing – original draft. LY: Writing – original draft, Validation. YM: Writing – review & editing, Visualization, Investigation. YZ: Writing – review & editing, Writing – original draft, Visualization, Validation.