Purpose Adoptive T-cell therapy using autologous tumor-infiltrating lymphocytes (TIL) has shown an overall clinical response rate 40–50% in metastatic melanoma patients. BTLA (B-and-T lymphocyte attenuator) expression on transferred CD8+ TIL was associated with better clinical outcome. The suppressive function of the ITIM and ITSM motifs of BTLA is well described. Here, we sought to determine the functional characteristics of the CD8+BTLA+TIL subset and define the contribution of the Grb2 motif of BTLA in T cell co-stimulation. Experimental Design We determined the functional role and downstream signal of BTLA in both human CD8+ TIL and mouse CD8+ T cells. Functional assays were used including single cell analysis, Reverse Phase Protein Array (RPPA), antigen-specific vaccination models with adoptively transferred TCR-transgenic T cells as well as Patient-Derived Xenograft (PDX) model using Immunodeficient NOD-scid IL2Rgammanull (NSG) tumor-bearing mice treated with autologous TIL. Results CD8+BTLA− TIL could not control tumor growth in vivo as well as their BTLA+ counterpart and antigen-specific CD8+BTLA− T cells had impaired recall response to a vaccine. However CD8+BTLA+ TIL displayed improved survival following the killing of a tumor target and heightened “serial killing” capacity. Using mutants of BTLA signaling motifs we uncovered a costimulatory function mediated by Grb2 through enhancing the secretion of IL-2 and the activation of Src after TCR stimulation. Conclusions Our data portrays BTLA as a molecule with the singular ability to provide both co-stimulatory and co-inhibitory signals to activated CD8+ T cells, resulting in extended survival, improved tumor control and the development of a functional recall response.

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Metastatic breast cancer is the most dreadful malignant disease that accounts for the majority of cancer-related deaths worldwide among women. A number of studies have shown that the tumor microenvironment (TME) plays a crucial role in regulating metastasis. It is therefore imperative to understand the dynamic interactions between cancer cells and their microenvironment to examine the molecular interaction and to effectively target cancer cells. TME comprises a variety of cells including immune cells which can influence tumor survival, growth and metastasis. Tumor-infiltrating lymphocytes (TILs), in particular, the CD8 T lymphocytes, has emerged as a promising prognostic marker for immunotherapy in a variety of cancers. However, the key molecular factors that regulate the cross-talk between tumor cells and CD8 T lymphocytes and its impact on metastatic traits in breast cancer is still inconclusive. Platelets are crucial components of the tumor microenvironment that are known to modulate tumor promotion and metastasis. The contribution of platelets and platelet secreted molecules are also carefully examined in metastasis of various cancers. The primary objective of this study is to investigate the role of CD8 T lymphocytes and platelets in breast tumor progression using isogenic tumor lines that form identical primary tumors but differ in their ability to develop metastasis. Citation Format: Robiya Joseph, Rama Soundararajan, Suhas Vasaikar, Fei Yang, Sevinj Isgandarova, Lin Tian, Monika Haemmerle, Barbara Mino, Tieling Zhou, Geraldine Vidhya Raja, Esmeralda Ramirez Pena, Petra Den Hollander, Neeraja Bhangre, Crystal Shin, Melisa Martinez, Jaime Rodriguez Canales, Jeffrey Chang, Anil Sood, Ignacio Ivan Wistuba, Don L. Gibbons, Jeffrey M. Rosen, Ghanashyam Acharya, Navin Varadarajan, Xiang H. Zhang, Sendurai A. Mani. Regulation of metastasis by CD8 T lymphocytes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3761.