Chemoradiation Combined with Phosphatidylserine-Targeting Antibody Enhances Systemic Anti-tumor Immune Responses

Abstract

Recent advances in cancer immunotherapy have sparked significant interest in harnessing the body’s immune system to fight cancer. However, the response rates of cancer immunotherapies, including immune checkpoint blockade, remain low. Strategies to enhance anti-tumor immune responses by targeting different steps along the immune activation cascade that can complement T cell-based immunotherapies are clearly needed. Here, we examine whether the addition of an antibody that targets extracellular phosphatidylserine (PS), a molecule that is recognized by myeloid derived cells, can enhance anti-tumor immune responses of chemoradiation for non-small cell lung cancer (NSCLC). Chemoradiation (CRT) was combined with a murine monoclonal antibody (mch1N11). PS is highly expressed in both orthotopically and ectopically implanted 393P murine NSCLC models. Radiation dose was 2 Gy/day, given for 5 days. Chemotherapy consists of carboplatin and paclitaxel at a dose of 30 mg/kg and 10 mg/kg, respectively. PS-targeting antibody (mch1N11) was given at 3mg/kg for 2 weekly doses. For ectopic tumor models, bilateral tumors were established in the legs. Radiation was directed to the R leg and tumor on the L side was shielded. Tumor growth was measured either with CT imaging or digital caliper. Tumor infiltrating immune cell profiles were analyzed using immunohistochemistry. Survival analyses were performed using Kaplan-Meier method and compared using Log-rank test. CRT + mch1N11 treatment significantly inhibited growth and improved survival in mice implanted with orthotopic 393P tumors as compared to CRT alone (median: 21 vs. 15 days, HR: 2.77, P = 0.006). Tissue analyses showed that CRT significantly increased the expression of PD-L1 within the tumor and drastically reduced the number of tumor infiltrating CD8 T cells. For the CRT + mch1N11 group, a similar up-regulation of PD-L1 expression was noted. However, the addition of mch1N11 re-populated the infiltrating CD8 T cells within the tumor. In the bilateral tumor model, the addition of mch1N11 antibody to CRT resulted in tumor regression in ∼40% of the non-irradiated tumors in the contralateral side as compared to 0% in the CRT alone or chemotherapy + mch1N11 groups. We showed that PS-targeting combined with standard CRT can significantly prolong survival in preclinical models of NSCLC and generate enhanced systemic anti-tumor immunity against lesions outside of the irradiated field. CRT up-regulated PD-L1 expression within the tumor and depleted tumor infiltrating cytotoxic CD8 T cells. The addition of mch1N11 antibody to CRT, however, was able to re-populate this critical immune effector cell population. Together, our results demonstrate that PS-targeting antibodies may be combined with CRT to enhance intrinsic tumor immunogenicity, activate systemic anti-tumor immune responses, and act as a priming strategy to sensitize the tumor to immune checkpoint inhibition with PD-1 or PD-L1 antibodies.