Abstract 609: Neutrophils play a critical role in mediating antitumor activity of a combination therapy of radiation and immunotherapy

Abstract

Abstract The goal of cancer immunotherapy is to elicit robust tumor-specific immune responses that can generate durable tumor regression and/or eradication. Recent clinical trials using immune checkpoint blockades specific to programmed cell death-1/ligand-1 (PD-1/PD-L1) have shown durable clinical responses in various cancer types but benefit only a small portion of patients. We previously demonstrated that combination of radiation and immunotherapy of interleukin 12 (IL-12) and granulocyte macrophage colony-stimulator factor (GM-CSF) greatly improved the therapeutic efficacy than either single therapy alone. In analysis of the tumor-infiltrating leukocytes post combination therapy, we found that the number of CD11b+F4/80-/Ly6G+ neutrophils were greatly increased. In this study, we characterized these tumor-associated neutrophils (TANs) before and after treatment and investigated their role in mediating the antitumor activity of the combination therapy. We isolated TANs from the regressing tumors and demonstrated that these TANs were impaired in their immunosuppressive activities. Flowcytometric analysis revealed that several co-stimulatory molecules, including class II major histocompatibility complex, CD40 and CD86, were increased on these TANs. Accordingly, these TANs gained the ability to stimulate T cell proliferation. Antibody-depletion experiments showed that TANs were required for tumor regression in RT/12GM combination therapy. Together, our data demonstrate that combination of radiotherapy and IL-12/GM-CSF improved antitumor immunity through enhancing antigen presentation activity and reduced immunosuppressive functions of TANs. Citation Format: Mi-Hua Tao, Chia-Jen Wu, Yi-Ting Tsai, Ping-Yi Wu. Neutrophils play a critical role in mediating antitumor activity of a combination therapy of radiation and immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 609.