Abstract B63: Expression of VEGF in ovarian cancer suppresses tumor immunity through recruitment of myeloid derived suppressor cells.

Abstract

Abstract Background and Objective: High expression of VEGF in ovarian cancer is a known unfavorable prognostic factor. However, its role in tumor immunity remains unclear. In this study, the impact of VEGF on ovarian cancer local immunity, including myeloid derived suppressor cells (MDSC), was explored. Methods: High grade serous ovarian cancer (HGSOC) cases were analyzed by gene expression microarray and immunohistochemistry for VEGF and CD33. Mouse HM-1 sh-Vegfa cells were generated and inoculated into immunocompetent mice subcutaneously. The proportions of lymphocytes and MDSC in tumors and spleens were analyzed by flow cytometry. Spleen cells from these mice were stimulated with CD3/CD28 antibody and Granzyme B+ CTLs were analyzed. The effects of Vegfa on differentiation and migration of MDSC were investigated. Results: Microarray analysis of 32 clinical HGSOC samples revealed that, in VEGF-high expressing cases, several chemoattractants for myeloid cells were significantly up-regulated, whereas lymphocyte-related pathways were down-regulated. In immunohistochemical analysis of 56 HGSOC samples, the number of CD33+MDSC positively correlated with the intensity of VEGF staining (r=0.43, p<.005). Patients with high infiltration of CD33+MDSC in peritoneal metastasis demonstrated significantly shorter overall survival (p<.05). Multivariate survival analysis using the Cox regression model demonstrated that high infiltration of CD33+MDSC in peritoneal dissemination is a significant prognostic parameter. In an immunocompetent mouse ovarian cancer model, silencing Vegf resulted in diminished infiltration of CD11b+/Gr-1+MDSC (p<.05) and increased infiltration of CD8+ lymphocytes (p<.05) in tumors as well as in spleens. Tumor growth was markedly inhibited in the Vegf-silenced group (p<.05). Granzyme B+ CTLs were increased in spleen cells of sh-Vegf tumor-bearing mice compared to those of HM-1 control tumor-bearing mice (p<.05). In the mouse ex vivo assay, generation of MDSC from mouse bone marrow cells was augmented by adding recombinant VEGF, whereas this was attenuated by adding an anti-VEGF antibody. In chemotaxis assays, inhibition of VEGF signaling attenuated the migration of MDSC. Conclusion: High expression of VEGF correlates with infiltration of MDSC and poor prognosis in ovarian cancer clinical samples. VEGF promotes the generation, migration, and immunosuppressive function of MDSC in mouse models. It is likely that VEGF expressed in ovarian cancer inhibits local immunity through recruitment of MDSC and thus contributes to poor prognosis. Citation Format: Naoki Horikawa, Kaoru Abiko, Noriomi Matsumura, Junzo Hamanishi, Susan Murphy, Tsukasa Baba, Ken Yamaguchi, Masafumi Koshiyama, Ikuo Konishi. Expression of VEGF in ovarian cancer suppresses tumor immunity through recruitment of myeloid derived suppressor cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr B63.