Myeloid-derived suppressor cells modulate immune responses independently of NADPH oxidase in the ovarian tumor microenvironment in mice

VSSP abrogates murine ovarian tumor-associated myeloid cell-driven immune suppression and induces M1 polarization in tumor-associated macrophages from ovarian cancer patients

The ovarian tumor microenvironment (TME) is characterized by the accumulation of immunosuppressive tumor-associated macrophages (TAMs) and granulocytic cells. Very small size particles (VSSP), comprised of the ganglioside NAcGM3 and Neisseria meningitidis derived outer membrane vesicles, is being developed as a nanoparticulated modulator of innate immunity. Prior studies have shown that VSSP enhanced antigen-specific cytotoxic T cell responses and reduced the suppressive phenotype of splenic granulocytic cells in tumor-bearing mice. Here, we hypothesized that intraperitoneal VSSP would modify myeloid cell accumulation and phenotypes in the ovarian TME and abrogate suppressor function of TAMs and tumor-associated granulocytic cells. In the ID8 syngeneic model of epithelial ovarian cancer, VSSP reduced peritoneal TAMs and induced M1-like polarization in TAMs. In addition, VSSP stimulated peritoneal inflammation characterized by increased granulocytes and monocytes, including inflammatory monocytic cells. VSSP treatment resulted in peritoneal TAMs and granulocytic cells being less suppressive of ex vivo stimulated CD8+ T cell responses. VSSP alone and combined with anti-PD-1 modestly but significantly prolonged survival in tumor-bearing mice. In addition, ex vivo treatment with VSSP induced M1-like polarization in TAMs from patients with metastatic ovarian cancer and variably abrogated their suppressor phenotype. VSSP treatment also partially abrogated the induction of suppressor function in healthy donor neutrophils exposed to ascites supernatants from patients with ovarian cancer. Together, these results point to VSSP reprogramming myeloid responses resulting in abrogation of suppressive pathways and raise the potential for administration of VSSP into the TME to enhance anti-tumor immunity.

LYVE1+ macrophages of murine peritoneal mesothelium promote omentum-independent ovarian tumor growth

Two resident macrophage subsets reside in peritoneal fluid. Macrophages also reside within mesothelial membranes lining the peritoneal cavity, but they remain poorly characterized. Here, we identified two macrophage populations (LYVE1hi MHC IIlo-hi CX3CR1gfplo/- and LYVE1lo/- MHC IIhi CX3CR1gfphi subsets) in the mesenteric and parietal mesothelial linings of the peritoneum. These macrophages resembled LYVE1+ macrophages within surface membranes of numerous organs. Fate-mapping approaches and analysis of newborn mice showed that LYVE1hi macrophages predominantly originated from embryonic-derived progenitors and were controlled by CSF1 made by Wt1+ stromal cells. Their gene expression profile closely overlapped with ovarian tumor-associated macrophages previously described in the omentum. Indeed, syngeneic epithelial ovarian tumor growth was strongly reduced following in vivo ablation of LYVE1hi macrophages, including in mice that received omentectomy to dissociate the role from omental macrophages. These data reveal that the peritoneal compartment contains at least four resident macrophage populations and that LYVE1hi mesothelial macrophages drive tumor growth independently of the omentum.

Ovarian cancer modulates the immunosuppressive function of CD11b+Gr1+ myeloid cells via glutamine metabolism

OBJECTIVE

Immature CD11b + Gr1+ myeloid cells that acquire immunosuppressive capability, also known as myeloid-derived suppressor cells (MDSCs), are a heterogeneous population of cells that regulate immune responses. Our study's objective was to elucidate the role of ovarian cancer microenvironment in regulating the immunosuppressive function of CD11b+Gr1+ myeloid cells.

METHODS

All studies were performed using the intraperitoneal ID8 syngeneic epithelial ovarian cancer mouse model. Myeloid cell depletion and immunotherapy were carried out using anti-Gr1 mAb, gemcitabine treatments, and/or anti-PD1 mAb. The treatment effect was assessed by a survival curve, in situ luciferase-guided imaging, and histopathologic evaluation. Adoptive transfer assays were carried out between congenic CD45.2 and CD45.1 mice. Immune surface and intracellular markers were assessed by flow cytometry. ELISA, western blot, and RT-PCR techniques were employed to assess the protein and RNA expression of various markers. Bone marrow-derived myeloid cells were used for ex-vivo studies.

RESULTS

The depletion of Gr1+ immunosuppressive myeloid cells alone and in combination with anti-PD1 immunotherapy inhibited ovarian cancer growth. In addition to the adoptive transfer studies, these findings validate the role of immunosuppressive CD11b+Gr1+ myeloid cells in promoting ovarian cancer. Mechanistic investigations showed that ID8 tumor cells and their microenvironments produced recruitment and regulatory factors for immunosuppressive CD11b+Gr1+ myeloid cells. CD11b+Gr1+ myeloid cells primed by ID8 tumors showed increased immunosuppressive marker expression and acquired an energetic metabolic phenotype promoted primarily by increased oxidative phosphorylation fueled by glutamine. Inhibiting the glutamine metabolic pathway reduced the increased oxidative phosphorylation and decreased immunosuppressive markers' expression and function. Dihydrolipoamide succinyl transferase (DLST), a subunit of α-KGDC in the TCA cycle, was found to be the most significantly elevated gene in tumor-primed myeloid cells. The inhibition of DLST reduced oxidative phosphorylation, immunosuppressive marker expression and function in myeloid cells.

CONCLUSION

Our study shows that the ovarian cancer microenvironment can regulate the metabolism and function of immunosuppressive CD11b + Gr1+ myeloid cells and modulate its immune microenvironment. Targeting glutamine metabolism via DLST in immunosuppressive myeloid cells decreased their activity, leading to a reduction in the immunosuppressive tumor microenvironment. Thus, targeting glutamine metabolism has the potential to enhance the success of immunotherapy in ovarian cancer.

Stroke-Induced Modulation of Myeloid-Derived Suppressor Cells (MDSCs) and IL-10-Producing Regulatory Monocytes

Background: Stroke patients are at risk of acquiring secondary infections due to stroke-induced immune suppression (SIIS). Immunosuppressive cells comprise myeloid-derived suppressor cells (MDSCs) and immunosuppressive interleukin 10 (IL-10)-producing monocytes. MDSCs represent a small but heterogeneous population of monocytic, polymorphonuclear (or granulocytic), and early progenitor cells (“early” MDSC), which can expand extensively in pathophysiological conditions. MDSCs have been shown to exert strong immune-suppressive effects. The role of IL-10-producing immunosuppressive monocytes after stroke has not been investigated, but monocytes are impaired in oxidative burst and downregulate human leukocyte antigen—DR isotype (HLA-DR) on the cell surface.

Objectives: The objective of this work was to investigate the regulation and function of MDSCs as well as the immunosuppressive IL-10-producing monocytes in experimental and human stroke.

Methods: This longitudinal, monocentric, non-interventional prospective explorative study used multicolor flow cytometry to identify MDSC subpopulations and IL-10 expression in monocytes in the peripheral blood of 19 healthy controls and 27 patients on days 1, 3, and 5 post-stroke. Quantification of intracellular STAT3p and Arginase-1 by geometric mean fluorescence intensity was used to assess the functionality of MDSCs. In experimental stroke induced by electrocoagulation in middle-aged mice, monocytic (CD11b⁺Ly6G⁻Ly6C^high) and polymorphonuclear (CD11b⁺Ly6G⁺Ly6C^low) MDSCs in the spleen were analyzed by flow cytometry.

Results: Compared to the controls, stroke patients showed a relative increase in monocytic MDSCs (percentage of CD11b⁺ cells) in whole blood without evidence for an altered function. The other MDSC subgroups did not differ from the control. Also, in experimental stroke, monocytic, and in addition, polymorphonuclear MDSCs were increased. The numbers of IL-10-positive monocytes did not differ between the patients and controls. However, we provide a new insight into monocytic function post-stroke since we can report that a differential regulation of HLA-DR and PD-L1 was found depending on the IL-10 production of monocytes. IL-10-positive monocytes are more activated post-stroke, as indicated by their increased HLA-DR expression.

Conclusions: MDSC and IL-10⁺ monocytes can induce immunosuppression within days after stroke.

Metabolic changes and interaction of tumor cell, myeloid-derived suppressor cell and T cell in hypoxic microenvironment

It is universally acknowledged that a large number of immune cells, as well as inflammatory factors, regulatory factors and metabolites, accumulate in the tumor microenvironment to jointly promote tumor escape, development and metastasis. Hypoxia is one of the characteristics in tumor microenvironment and is a common phenomenon in all solid tumors. In tumor hypoxia response, there is a key regulator called HIF-1a, which is a key transcriptional regulatory protein that regulates many critical genes. In this paper, the effects of hypoxia on glucose metabolism of tumor cells, myeloid-derived suppressor cells and T cells in tumor microenvironment were reviewed, and the interaction among the three was also described.

A Call for Epidemiological Research on Myeloid-Derived Suppressor Cells in Ovarian Cancer: A Review of the Existing Immunological Evidence and Suggestions for Moving Forward

Recently, there have been encouraging findings suggesting that myeloid-derived suppressor cells (MDSCs) may be a good target for studying immune suppression in ovarian cancer. MDSCs are an abundance of immature myeloid cells that have demonstrated the ability to decrease tumor-infiltrating immune cells, increase the accrual of tumor-associated macrophages and regulatory T cells, as well as secrete various pro-inflammatory mediators and growth stimulating cytokines. Most studies on this topic utilized murine models, but there are limited reports in human subjects which have important limitations. With the majority of ovarian cancer patients presenting with distant metastases and a corresponding 5-year relative survival rate of < 30%, continued efforts are obligatory toward identifying potential prognostic factors. Given the difficulty of studying exposures in this patient population, as well as the existing immunologic characteristics of this cancer, there is growing interest in further identifying genetic and immunologic associations with patient survival. Furthermore, prognostic factors that may necessitate therapeutic intervention may significantly alter disease outlook. In this review paper, we address the current literature on MDSCs and their immunosuppressive behavior in ovarian cancer patients. While the previous studies on these cells in ovarian cancer have demonstrated some potential prognostic significance, there are many limitations to such studies including small sample sizes, inconsistent staging and histology, as well as inconsistent surface markers for the identification of MDSCs. Additionally, such studies include minimal patient characteristics involved with the clinical course of ovarian cancer. Here, we have proposed improving on studies analyzing MDSCs as a potential prognostic factor in ovarian cancer patients, as well as further identifying the potential of this novel prognostic factor in future care, through the use of a comprehensive epidemiologic model.

Emerging Role and Future Directions of Immunotherapy in Advanced Ovarian Cancer

Clinical progress in cancer immunotherapy has been slow; however, within the last 5 years, breakthrough successes have brought immunotherapy to the forefront in cancer therapy. Promising results have been observed in solid tumors and hematologic malignancies. Most treatment modalities have shown limited efficacy as monotherapy. The complex nature of cancer and the immunosuppressive microenvironment emphasizes the need to personalize immunotherapy by manipulating the patient's own immune system. For successful and long-lasting cure of cancer, a multimodal approach is essential, combining antitumor cell therapy with manipulation of multiple pathways in the tumor microenvironment to ameliorate tumor-induced immunosuppression.

High numbers of myeloid derived suppressor cells in peripheral blood and ascitic fluid of cirrhotic and HCC patients

BACKGROUND

Hepatocellular carcinoma (HCC) is the 3rd most common cause of cancer-related death worldwide. It has evolved different immune escape mechanisms, which might include emergence of lymphoid and myeloid regulatory cells. Aim of this work: To determine the numbers of Myeloid-derived suppressor cells (MDSCs) in peripheral blood and ascitic fluid in cirrhosis and HCC and their relation to IFN-γ and α-fetoprotein (α-FP).

PATIENTS AND METHODS

Sixty individuals were enrolled in this study; forty cirrhotic patients with ascites; twenty without HCC (Group I), and twenty with HCC (group II) as well as twenty healthy individuals as a control group (group III). The phenotype and numbers of MDSCs were analyzed in peripheral blood of all the individuals and ascitic fluid of the patients using flow cytometry. Intracellular IFN-γ and serum alfa-fetoprotein were measured.

RESULTS

Significant increases in the relative and the mean number of peripheral blood MDSCs were found in the cirrhosis and HCC groups than in the control group, with the HCC group showing the highest number. MDSC count was negatively correlated with IFN-γ levels, while α-FP was positively correlated with MDSC% in the HCC group. MDSC count was low in ascitic fluid of both HCC and cirrhosis groups with no significant difference between the 2 groups.

CONCLUSION

A high frequency of MDSCs was detected in the peripheral blood of cirrhotic and HCC patients, indicating presence of immunosuppressive arms. These cells could be targeted to develop a new effective immunotherapy or an adjuvant to current therapies.

Myeloid-derived suppressor cells in ovarian cancer: friend or foe?

Although previous decades contributed to major progress in targeted therapy of many malignancies, the treatment of gynaecological cancers remains a challenging task. In the evidence of rising cancer mortality, the search for new methods of treatment is a dire need. Exploring the mechanisms of interaction between tumour cells and host immune response may allow the introduction of new, effective therapies – not as toxic and far more efficient than conventional methods of cancer treatment. Epithelial ovarian cancer (EOC) is typically diagnosed at advanced stages. Its incidence and mortality rate is high. Powerful diagnostic tools for this kind of cancer are still under investigation. Multiple mechanisms existing in the ovarian tumour network create a specific immunosuppressive microenvironment, in which accumulation of myeloid-derived suppressor cells (MDSCs) may be a critical component for diagnosis and treatment. This review attempts to verify current knowledge on the role of MDSCs in EOC.

PRKCI promotes immune suppression in ovarian cancer

Here, Sarkar et al. report that PRKCI expression, which is a key feature of high-grade serous ovarian carcinoma (HGSOC), is also up-regulated in serous tubal intraepithelial carcinoma (STIC) and early fallopian tube (FT) lesions. Using a transgenic mouse model of ovarian cancer overexpressing PRKCI, they show that PRKCI is a deregulated ovarian cancer-specific oncogene and plays a role in early stages of cancer development.

A key feature of high-grade serous ovarian carcinoma (HGSOC) is frequent amplification of the 3q26 locus harboring PRKC-ι (PRKCI). Here, we show that PRKCI is also expressed in early fallopian tube lesions, called serous tubal intraepithelial carcinoma. Transgenic mouse studies establish PRKCI as an ovarian cancer-specific oncogene. Mechanistically, we show that the oncogenic activity of PRKCI relates in part to the up-regulation of TNFα to promote an immune-suppressive tumor microenvironment characterized by an abundance of myeloid-derived suppressor cells and inhibition of cytotoxic T-cell infiltration. Furthermore, system-level and functional analyses identify YAP1 as a downstream effector in tumor progression. In human ovarian cancers, high PRKCI expression also correlates with high expression of TNFα and YAP1 and low infiltration of cytotoxic T cells. The PRKCI–YAP1 regulation of the tumor immunity provides a therapeutic strategy for highly lethal ovarian cancer.

Impact of ascites volume on clinical outcomes in ovarian cancer: A cohort study

OBJECTIVES

To investigate the impact of ascites volume on ovarian cancer outcomes.

METHODS

Clinicopathologic features of a cohort of patients with ovarian cancer were obtained from a curated database at a single institution. Progression free survival (PFS) and overall survival (OS) were recorded. Ascites volume at primary surgery was dichotomized at 2000mL and comparisons for high and low volume ascites were made. Additionally, to elucidate interactions between ascites and ovarian tumor progression, we evaluated the effect of intraperitoneal administrations of murine cell-free ascites versus saline in a syngeneic mouse model of epithelial ovarian cancer.

RESULTS

Out of 685 patients identified, 58% had ascites present at the time of initial surgery. Considering the volume of ascites continuously, each liter of ascites was associated with shorter PFS (HR=1.12, 95% CI: 1.07-1.17) and OS (HR=1.12, 95%CI: 1.07-1.17). Patients with ascites greater than the median of 2000mL had significantly shorter PFS (14.5months vs. 22.7months; p<0.001) and OS (27.7months vs. 42.9months; p<0.001). After adjusting for stage, presence of ascites was inversely associated with ability to achieve optimal cytoreductive surgery. Consistent with these correlative results in patients, intraperitoneal administrations of murine cell-free ascites accelerated ovarian cancer progression in mice.

CONCLUSIONS

The volume of ascites at initial diagnosis of ovarian cancer correlated with worse PFS and OS. The effect of large volume on prognosis is likely to be in part related to reduced likelihood for complete resection of tumor (R0). If these findings are confirmed in independent studies, consideration should be made to add the presence of large volume ascites at diagnosis to the staging criteria for ovarian cancer.

Neutrophils in the tumor microenvironment: trying to heal the wound that cannot heal

Neutrophils are the first responders to infection and injury and are critical for antimicrobial host defense. Through the generation of reactive oxidants, activation of granular constituents and neutrophil extracellular traps, neutrophils target microbes and prevent their dissemination. While these pathways are beneficial in the context of trauma and infection, their off-target effects in the context of tumor are variable. Tumor-derived factors have been shown to reprogram the marrow, skewing toward the expansion of myelopoiesis. This can result in stimulation of both neutrophilic leukocytosis and the release of immature granulocytic populations that accumulate in circulation and in the tumor microenvironment. While activated neutrophils have been shown to kill tumor cells, there is growing evidence for neutrophil activation driving tumor progression and metastasis through a number of pathways, including stimulation of thrombosis and angiogenesis, stromal remodeling, and impairment of T cell-dependent anti-tumor immunity. There is also growing appreciation of neutrophil heterogeneity in cancer, with distinct neutrophil populations promoting cancer control or progression. In addition to the effects of tumor on neutrophil responses, anti-neoplastic treatment, including surgery, chemotherapy, and growth factors, can influence neutrophil responses. Future directions for research are expected to result in more mechanistic knowledge of neutrophil biology in the tumor microenvironment that may be exploited as prognostic biomarkers and therapeutic targets.

Chronic Recreational Physical Inactivity and Epithelial Ovarian Cancer Risk: Evidence from the Ovarian Cancer Association Consortium

BACKGROUND

Despite a large body of literature evaluating the association between recreational physical activity and epithelial ovarian cancer (EOC) risk, the extant evidence is inconclusive, and little is known about the independent association between recreational physical inactivity and EOC risk. We conducted a pooled analysis of nine studies from the Ovarian Cancer Association Consortium to investigate the association between chronic recreational physical inactivity and EOC risk.

METHODS

In accordance with the 2008 Physical Activity Guidelines for Americans, women reporting no regular, weekly recreational physical activity were classified as inactive. Multivariable logistic regression was utilized to estimate the ORs and 95% confidence intervals (CI) for the association between inactivity and EOC risk overall and by subgroups based upon histotype, menopausal status, race, and body mass index.

RESULTS

The current analysis included data from 8,309 EOC patients and 12,612 controls. We observed a significant positive association between inactivity and EOC risk (OR = 1.34; 95% CI, 1.14-1.57), and similar associations were observed for each histotype.

CONCLUSIONS

In this large pooled analysis examining the association between recreational physical inactivity and EOC risk, we observed consistent evidence of an association between chronic inactivity and all EOC histotypes.

IMPACT

These data add to the growing body of evidence suggesting that inactivity is an independent risk factor for cancer. If the apparent association between inactivity and EOC risk is substantiated, additional work via targeted interventions should be pursued to characterize the dose of activity required to mitigate the risk of this highly fatal disease. Cancer Epidemiol Biomarkers Prev; 25(7); 1114-24. ©2016 AACR.

NOX2-dependent regulation of inflammation

NADPH oxidase (NOX) isoforms together have multiple functions that are important for normal physiology and have been implicated in the pathogenesis of a broad range of diseases, including atherosclerosis, cancer and neurodegenerative diseases. The phagocyte NADPH oxidase (NOX2) is critical for antimicrobial host defence. Chronic granulomatous disease (CGD) is an inherited disorder of NOX2 characterized by severe life-threatening bacterial and fungal infections and by excessive inflammation, including Crohn's-like inflammatory bowel disease (IBD). NOX2 defends against microbes through the direct antimicrobial activity of reactive oxidants and through activation of granular proteases and generation of neutrophil extracellular traps (NETs). NETosis involves the breakdown of cell membranes and extracellular release of chromatin and neutrophil granular constituents that target extracellular pathogens. Although the immediate effects of oxidant generation and NETosis are predicted to be injurious, NOX2, in several contexts, limits inflammation and injury by modulation of key signalling pathways that affect neutrophil accumulation and clearance. NOX2 also plays a role in antigen presentation and regulation of adaptive immunity. Specific NOX2-activated pathways such as nuclear factor erythroid 2-related factor 2 (Nrf2), a transcriptional factor that induces antioxidative and cytoprotective responses, may be important therapeutic targets for CGD and, more broadly, diseases associated with excessive inflammation and injury.

Targeting myeloid cells in the tumor microenvironment enhances vaccine efficacy in murine epithelial ovarian cancer

Epithelial ovarian cancer (EOC) is typically diagnosed at advanced stages, and is associated with a high relapse rate. Patients in remission are ideal candidates for immunotherapy aimed at cure or prolonging disease-free periods. However, immunosuppressive pathways in the tumor microenvironment are obstacles to durable anti-tumor immunity. In a metastatic syngeneic mouse model of EOC, immunosuppressive macrophages and myeloid-derived suppressor cells (MDSCs) accumulate in the local tumor environment. In addition, resident peritoneal macrophages from non-tumor-bearing mice were highly immunosuppressive, abrogating stimulated T cell proliferation in a cell contact-dependent manner. Immunization with microparticles containing TLR9 and NOD-2 ligands (MIS416) significantly prolonged survival in tumor-bearing mice. The strategy of MIS416 immunization followed by anti-CD11b administration further delayed tumor progression, thereby establishing the proof of principle that myeloid depletion can enhance vaccine efficacy. In patients with advanced EOC, ascites analysis showed substantial heterogeneity in the relative proportions of myeloid subsets and their immunosuppressive properties. Together, these findings point to immunosuppressive myeloid cells in the EOC microenvironment as targets to enhance vaccination. Further studies of myeloid cell accumulation and functional phenotypes in the EOC microenvironment may identify patients who are likely to benefit from vaccination combined with approaches that deplete tumor-associated myeloid cells.

IFN-γ from lymphocytes induces PD-L1 expression and promotes progression of ovarian cancer

BACKGROUND

PD-L1 (programmed cell death 1 ligand 1) on tumour cells suppresses host immunity through binding to its receptor PD-1 on lymphocytes, and promotes peritoneal dissemination in mouse models of ovarian cancer. However, how PD-L1 expression is regulated in ovarian cancer microenvironment remains unclear.

METHODS

The number of CD8-positive lymphocytes and PD-L1 expression in tumour cells was assessed in ovarian cancer clinical samples. PD-L1 expression and tumour progression in mouse models under conditions of altering IFN-γ signals was assessed.

RESULTS

The number of CD8-positive cells in cancer stroma was very high in peritoneally disseminated tumours, and was strongly correlated to PD-L1 expression on the tumour cells (P<0.001). In mouse models, depleting IFNGR1 (interferon-γ receptor 1) resulted in lower level of PD-L1 expression in tumour cells, increased the number of tumour-infiltrating CD8-positive lymphocytes, inhibition of peritoneal disseminated tumour growth and longer survival (P=0.02). The injection of IFN-γ into subcutaneous tumours induced PD-L1 expression and promoted tumour growth, and PD-L1 depletion completely abrogated tumour growth caused by IFN-γ injection (P=0.01).

CONCLUSIONS

Interferon-γ secreted by CD8-positive lymphocytes upregulates PD-L1 on ovarian cancer cells and promotes tumour growth. The lymphocyte infiltration and the IFN-γ status may be the key to effective anti-PD-1 or anti-PD-L1 therapy in ovarian cancer.

IFN-γ from lymphocytes induces PD-L1 expression and promotes progression of ovarian cancer

BACKGROUND

PD-L1 (programmed cell death 1 ligand 1) on tumour cells suppresses host immunity through binding to its receptor PD-1 on lymphocytes, and promotes peritoneal dissemination in mouse models of ovarian cancer. However, how PD-L1 expression is regulated in ovarian cancer microenvironment remains unclear.

METHODS

The number of CD8-positive lymphocytes and PD-L1 expression in tumour cells was assessed in ovarian cancer clinical samples. PD-L1 expression and tumour progression in mouse models under conditions of altering IFN-γ signals was assessed.

RESULTS

The number of CD8-positive cells in cancer stroma was very high in peritoneally disseminated tumours, and was strongly correlated to PD-L1 expression on the tumour cells (P<0.001). In mouse models, depleting IFNGR1 (interferon-γ receptor 1) resulted in lower level of PD-L1 expression in tumour cells, increased the number of tumour-infiltrating CD8-positive lymphocytes, inhibition of peritoneal disseminated tumour growth and longer survival (P=0.02). The injection of IFN-γ into subcutaneous tumours induced PD-L1 expression and promoted tumour growth, and PD-L1 depletion completely abrogated tumour growth caused by IFN-γ injection (P=0.01).

CONCLUSIONS

Interferon-γ secreted by CD8-positive lymphocytes upregulates PD-L1 on ovarian cancer cells and promotes tumour growth. The lymphocyte infiltration and the IFN-γ status may be the key to effective anti-PD-1 or anti-PD-L1 therapy in ovarian cancer.