Abstract 6043: Role of Rab11 family interacting proteins in immune recognition of breast cancer

Abstract Breast cancer is the second leading cause of death for American women, with the majority of morbidity attributable to metastatic disease. Breast cancer brain metastases (BCBM) account for 30% of breast cancer mortality and treatment options remain limited. While immunotherapy holds great promise, objective response rates for metastatic disease are poor. To improve these outcomes, we must understand the context-specific mechanisms used by cancer cells to suppress and evade the immune system. Successful T cell interaction with cancer cells requires proper surface localization of proteins such as MHC complexes and co-activators, all of which are localized within the cell via endosomal protein trafficking. Immunotherapy also relies on CTLA-4 or PD-1/PD-L1 on the cell surface to remove inhibition of T cells and improve the anti-tumor response. How molecular trafficking controls localization of activating and inhibitory proteins to the surface in order to facilitate cancer-immune cell interaction is a key knowledge gap. We previously showed that Rab11b-mediated endosomal trafficking is required for BCBM. Here we investigate how trafficking-mediated control of the cell surface dictates immune recognition and response. Using a targeted CRISPR screen, we found that Rab11 family interacting proteins Rab11fip2 and Rab11fip3 are required for highly immunogenic ovalbumin (OVA) expressing breast cancer cells to be recognized by OT-I CD8+ T cells. Flow cytometry analysis revealed that the decrease in recognition is not due to surface localization of PD-L1 or the MHC/SIINFEKL complex (SIINFEKL is the OVA peptide presented for OT-I recognition). Knockout of Rab11fip2 or 3 did not change cell proliferation or tumor burden in immunocompromised animals, but led to significantly increased tumor growth in immunocompetent animals. This suggests that non-targeting control cells are partially restrained by the immune system, and knockout of either Rab11fip causes loss of immune recognition to allow faster tumor growth. Immunohistochemical analysis revealed a significant decrease of tumor infiltrating T cells in Rab11fip knockout tumors. Cytotoxic CD8+ T cells exhibited the most extreme decrease in infiltration, with CD4+ helper T cells decreasing in only the Rab11fip3 knockout condition. These results indicate that Rab11 may play a role in immune cell recruitment in addition to recognition and activation. We are currently focused on characterizing Rab11 control of the T cell-cancer cell interaction in human breast cancer cell lines. Dissecting the role of Rab11 in tumor cell antigen presentation, immune cell recruitment, T cell cytotoxicity and activation will help determine if inhibition of Rab11-mediated recycling can be used to increase the efficacy of immunotherapy for patients with BCBM. Citation Format: Oly Khowash, Paras Sahani, Christopher Kywe, Kathleen Conway, Khushi Tekale, Jessica Contreras, Erin Howe. Role of Rab11 family interacting proteins in immune recognition of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6043.