The immunosuppressive effects of chemotherapy present a challenge for designing effective cancer immunotherapy strategies. We hypothesized that although systemic chemotherapy (SC) exhibits negative immunologic effects, local chemotherapy (LC) can potentiate an antitumor immuneresponse.We showthat LC combinedwith anti-programmed cell death protein 1 (PD-1) facilitates an antitumor immune response and improves survival (P < 0.001) in glioblastoma. LC-treated mice had increased infiltration of tumor-associated dendritic cells and clonal expansion of antigen-specific T effector cells. In comparison, SC resulted in systemic and intratumoral lymphodepletion, with decreased immune memory in long-term survivors. Furthermore, adoptive transfer of CD8+ cells from LC-treated mice partially rescued SC-treated mice after tumor rechallenge. Last, the timing of chemo-and immunotherapy had differential effects on anti-PD-1 efficacy. This study suggests that both mode of delivery and timing have distinct effects on the efficacy of anti-PD-1. The results of thiswork could help guide the selection and scheduling of combination treatment for patients with glioblastoma and other tumor types.
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