We recently reported that the mRNA expression of genes in the Major Histocompatibility Complex class II (MHCII) antigen processing and presentation pathway in breast tumor tissues was strongly prognostic of good clinical outcome in triple negative breast cancer (TNBC) patients (J Clin Oncol 33, 2015 suppl; abstr 1066). Although MHCII expression is most often observed on antigen-presenting cells, such as dendritic cells, macrophages and B cells, we observed MHCII protein expression on TNBC tumor cells. These observations suggested that TNBC cells expressing MHCII may have the ability to directly stimulate CD4 T cells and promote anti-tumor immune responses. To test this hypothesis, we transfected murine TS/A tumor cells (syngeneic, non-immunogenic, and metastatic breast cancer model) with a vector encoding the human MHCII Transcriptional Activator (hCIITA) under the control of a doxycycline (Dox)-inducible promoter. We found that TS/A-hCIITA cells did not express MHCII or CD74 until exposed to Dox, whereupon they expressed MHCII and CD74 mRNA and protein in a dose-dependent fashion. We also found that TS/A-hCIITA cells injected into the mammary fat pad expressed MHCII genes and cell surface MHCII proteins on tumor cells if mice received Dox in their drinking water. Importantly, tumor-bearing, Dox-exposed mice exhibited significantly impaired tumor growth compared to mice that were not exposed to Dox. We also found that tumor-bearing, Dox-exposed mice had a significantly enhanced tumor-specific CD8 T cell response in both the tumor-draining lymph node and tumor bed. Thus, breast cancer tumor cells expressing MHCII proteins promote anti-tumor immune responses, which likely contribute to the control of tumor growth in vivo.

Citation Format: Mei Li, Tyler R. McCaw, Selene Meza-Perez, Troy D. Randall, Amy Weinmann, Donald J. Buchsbaum, Andres Forero, Albert F. LoBuglio. MHCII-expressing breast cancer cells can induce anti-tumor immune response. [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 1461.