Analysis of chemotherapy-related modulation of the immune microenvironment in muscle invasive bladder cancer.

5049 Background: Novel immune checkpoint inhibitors provide significant clinical benefits for patients with metastatic bladder cancer. It is known that chemotherapy administered to muscle invasive patients prior to radical cystectomy (neoadjuvant chemotherapy) improves survival. However, it is unknown whether immune checkpoint inhibitor therapy in combination with chemotherapy can provide further clinical benefits as neoadjuvant therapy. Here, we test the hypothesis that treatment of bladder cancer with certain chemotherapy agents can modulate bladder tumor immune microenvironment (TIME) for optimal combination with immune checkpoint therapy. Methods: Time course and dose response experiments were performed using eight human bladder cancer cell lines (UMUC3, RT4, 253J, RT112, J82, HT1376, T24, and HT1197) and two murine bladder cancer cell lines (MB49, MBT2). Conventional chemotherapy agents and combinations (MVAC, GemCis, PemVin) were used to treat bladder cancer cell lines. Flow cytometry analysis was used to measure immune cell subsets and PD-L1 expression. For in vivo studies, the subcutaneous MB49 murine bladder cancer model was used to evaluate responses to chemotherapy and anti-PD-L1 combinations. Pre- and post-treatment bladder tumors from patients who received neoadjuvant MVAC and GemCis are selected to evaluate changes in TIME. Results: Our data demonstrate that chemotherapy agents varies in their ability to up-regulate PD-L1 expression on bladder cancer cell lines. Vinblastine, gemcitabine, and pemetrexed treatment each resulted in significant upregulation of PD-L1 expression. Combination regimens with GemCis or PemVin demonstrated induction of PD-L1 across different cell lines. In in-vivo studies, GemCis + anti-PD-L1 had a synergistic activity in causing tumor regression. We also found that sequential versus concurrent treatment with chemotherapy and anti-PD-L1 had a similar outcome. Tissue analyses show that combination chemotherapies increased CD4 Th cell infiltration while decreasing Treg cells in TIME. Consistent with the in vitro data, PD-L1 expression was also up-regulated with combination treatment. The evaluation of TIME modulation in human bladder tumors treated with neoadjuvant MVAC or GemCis is ongoing. Conclusions: Our data suggest that chemotherapy could favorably modulate TIME and thus, may be combined with immune checkpoint inhibitor to improve anti-tumor responses in the neoadjuvant setting for patients with muscle invasive bladder cancer.