Abstract A50: Chemoimmunotherapy with PD-1 blockade and paclitaxel induce a potent antitumor immunity in ovarian cancers.
Authors: Hamanishi Junzo , Peng Jin , Matsumura Noriomi , Abiko Kaoru , Baba Tsukasa , Yamaguchi Ken , Konishi Ikuo , Mandai Masaki 
Published: May 2016

Some chemotherapeutic agents are known to enhance both systemic immunosuppressive changes and local immunogenicity of tumor cells at the tumor site. To evaluate how chemotherapeutic agents commonly used for ovarian cancer could influence on the immune system, we analyzed the number of CD8+ TILs in ovarian cancer tissues from 21 patients who received operation before and after chemotherapy by immunohistochemistry and found that CD8+ TILs significantly increased after chemotherapy (p&lt;0.05).

Because the expansion of CD8+ TILs is generally related to the overexpression of PD-L1 (programmed cell death ligand 1) on cancer cells, we collected cancer cells from massive ascites of a stage IIIc ovarian cancer patient both before and after paclitaxel (PTX) plus carboplatin (CBDCA), and analyzed the expression PD-L1 expression on the tumor cells. These ascites cells expressed about 5-fold higher expression of PD-L1 after chemotherapy than before chemotherapy.

To confirm overexpression of PD-L1 by chemotherapy, we next conducted in vitro experiments using four human ovarian cancer cell lines and two mouse ovarian cancer cell lines. We treated the cell lines with several dose of paclitaxel (PTX) or gemcitabine (GEM) for 24 hours, each. These chemotherapeutic agents increased protein expression of PD-L1, detected by Western blotting, in all the cell lines tested to a varying level in dose dependent manner. Increased expression of PD-L1 was also confirmed with flow cytometry in HM1 and ID8 treated with PTX or GEM.

We next assessed alterations in CD8+ TILs following their encounter with PTX-induced PD-L1 using cytotoxic T cell assay. Following co-culture with CD8+ T cells, PTX-pretreated ID8-control cells show a lower lysis percentage than non-pretreated ID8-control cells, indicating that T-cell activation may be inhibited by PTX (p&lt;0.05). Additionaly, PTX-pretreated ID8-pdl1KO, co-cultured with CD8+ T cells show the highest lysis percentage (p&lt;0.01). This suggests that depletion of PD-L1 in ovarian cancer cells induces activation of CD8+ T cells.

Lastly, to evaluate whether blocking PD-L1 in tumor cells reversed the decline in T cell immunity and promoted tumor rejection after chemotherapy, we conducted a combined immunochemotherapy in a mouse ovarian cancer model. We injected ID8 cells intraperitoneally into syngeneic mice following treatment with PTX alone, anti-PD-1 antibody (αPD-1) alone, the combination of PTX and αPD-1, or saline and IgG intraperitoneal injection (control). Combined treatment of PTX with αPD-1 resulted in the best survival among the four groups. ID8 tumor-bearing mice that received either αPD-1 or PTX alone showed significantly better survival than the no treatment control group (p&lt;0.05). In place of anti-PD-1 antibody, we also treated these mice model with anti-PD-L1 antibody (αPD-L1) and found that the combined treatment of PTX with αPD-L1 also resulted in the best survival (p&lt;0.05).

In summary, combined chemoimmunotherapy with PD-1 signal blocking may improve the antitumor response and offer a promising new treatment against ovarian cancer.

Citation Format: Junzo Hamanishi, Jin Peng, Noriomi Matsumura, Kaoru Abiko, Tsukasa Baba, Ken Yamaguchi, Ikuo Konishi, Masaki Mandai. Chemoimmunotherapy with PD-1 blockade and paclitaxel induce a potent antitumor immunity in ovarian cancers. [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 A50.