Abstract 1478: Anti-EMP2 IgG1 combined with anti-PD1/PDL1 antibodies synergistically reduce tumor load in animal models of breast cancer

Purpose: Despite significant advances in detection and medicine, the incidence and mortality due to breast cancer world-wide is still unacceptably high. Our recent work reveals that tetraspan protein epithelial membrane protein-2 (EMP2) is up-regulated in up to 70% of patients with invasive breast cancer and its expression is further augmented in metastatic lesions. New data suggests that EMP2 expression correlate with an increase in tumor associated PDL1 expression. We thus hypothesized that EMP2 expression regulated tumor immunogenicity through either direct control of PDL1 expression or MHC Class I processing. Recently, to determine the therapeutic potential of EMP2, our group created a panel of anti-EMP2 antibodies and new data shows that tumors treated with anti-EMP2 IgG1 show an increase in immune infiltrates. We thus proposed that EMP2 positive tumors will be amendable to anti-PD1/PDL1 therapy. Methods:A panel of breast cancer cell lines, both TNBC as well as hormone positive cell lines, were transfected with a vector to overexpress EMP2 or to reduce its levels. To determine if EMP2 expression influenced the expression of immune associated genes, RNAseq was performed. In addition, PDL1 protein expression was measured using standard immunohistochemistry or western blot analysis. Immune cell populations in various xenografts models were quantitated using standard immunohistochemistry. To determine the efficacy of combination anti-EMP2 and anti-PD1 therapy, syngeneic 4T1/firefly luciferase mouse models were created in BALB/c mice. Briefly, cells were injected into the mammary fat pad of female BALB/c mice, and once they approached 100 mm3, were injected IP with a)10 mg/kg dose twice a week of anti-EMP2 antibody, b) 5mg/kg twice a week with anti-PD-1 antibody (BioXCell), c) 10mg/kg ant-EMP2 and 5mg/kg of anti-PD-1 antibody twice a week, or d) saline control. Results: In multiple breast cell lines, EMP2 levels correlated with an increase in PDL1 expression, and treatment with anti-EMP2 IgG1 increased the number of infiltrating leukocytes. Using syngeneic mouse models, tumors treated with a combination of anti-EMP2 and anti-PD-1 antibodies grew slowly and had the smallest total volume compared to all other treatment groups. Anti-EMP2 IgG1 treatment was superior in reducing overall tumor volume compared to anti-PD-1 antibody treatment alone. Conclusions: Our preliminary data strongly supports the synergistic efficacy of anti-EMP2 IgG1 and anti-PD-1 antibody in reducing tumor load, suggesting that using anti-EMP2 treatment with an anti-PD1/PDL1 antibody may improve survival without inducing systemic toxicity as seen with chemotherapy. We predict that this is the direct result of EMP2 expression altering the immunogenicity of the tumor and in support of this, RNAseq data and western blot data suggest that EMP2 levels regulate PDL1 and MHC associated gene expression. Citation Format: Negin Ashki, Jessica Tsui, Madhuri Wadehra. Anti-EMP2 IgG1 combined with anti-PD1/PDL1 antibodies synergistically reduce tumor load in animal models of breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1478.