Abstract B056: Thrombospondin-1:CD47 Signaling Contributes to the Development of T Cell Exhaustion in Cancer

Introduction: Multiple suppressive mechanisms within the tumor microenvironment (TME) contribute to blunt anti-tumor T cell responses. Among them, tumor-associated T cells have been phenotypically described to be functionally exhausted (or dysfunctional), reflecting to a hyporesponsive state of chronically stimulated T cells that express multiple inhibitory receptors (or immune checkpoint molecules), such as programmed cell death protein 1 (PD-1), T-cell immunoglobulin and mucin-domain containing-3 (TIM-3), lymphocyte-activation gene 3 (LAG-3), 2B4 (also known as CD244), and T cell immunoreceptor with Ig and ITIM domains (TIGIT), and exhibit a compromised cellular cytotoxicity. While immune checkpoint blockade therapies aimed at reversing the dysfunctional state T cell effector function have demonstrated clinical effectiveness, not all cancer patients achieve long-term disease control. This is due, at least in part, to the refractory nature of what are categorized as terminally exhausted CD8+ T cells to PD-1/PD-L blockade, for example. Considering that CD8+ T cell exhaustion and/or dysfunction is one of the major therapeutic challenges, we aim to uncover pathways that contribute to program T cells toward exhaustion/dysfunction during cancer progression. Methods and experimental procedures: CD47 (a.k.a. integrin-associated protein, IAP) is known for its role as a ‘‘don’t-eat-me’’ signal in malignant, transformed cells. Our recent study found that both human and murine tumor-associated CD8+ T cells derived from lesions of human and murine melanoma, and ovarian cancers exhibit a significant elevation of surface CD47. Surprisingly, the population of tumor-associated CD8+ T cells that express high level of CD47 also express high levels of TOX, the critical factor that drives differentiation of exhausted T (Tex) cells, as well as other known immune checkpoint molecules. Through naïve T cell adoptive transfer experiments paired with single cell-RNA sequencing analysis, we demonstrated that CD47 plays a key role in driving T cell exhaustion. We demonstrated that extracellular matrix protein thrombospondin-1 (TSP-1) is the ligand for CD47-mediated T cell exhaustion during tumor progression by selectively disrupting the interaction between TSP-1 and CD47. Mechanistically, we demonstrate through immunoblot experiments that engagement of TSP-1:CD47 results in activation of calcineurin-NFAT axis, a key modulatory pathway upstream of TOX that drives T cell exhaustion and dysfunction. Summary of new, unpublished data: Our study uncovered a novel role of TSP-1:CD47 interaction, besides chronic antigen stimulation, in driving CD8 T cells exhaustion via the calcineurin-NFAT pathway. Our findings have implications for the mechanism of action in CD47 targeting therapies. Concluding statement: Extracellular matrix protein thrombospondin-1 and CD47 expressed on T cells contributes to promote TOX-driven T cell exhaustion program in cancer. Citation Format: Chien-Huan Weng, Anais Assouvie, Lauren Dong, Jean-Christophe Beltra, Sadna Budhu, Levi Mangarin, Yacine Marouf, Lucia Morgado-Palacin, Cailian Liu, Sébastien Monette, Jonathan Khan, Isabell Schulze, Dmitriy Zamarin, Linda Hamadene, Fadi Samaan, Daniel Hirschhorn, Stephane Pourpe, David Schroder, Roberta Zappasodi, Pamela Holland, Niroshana Anandasabapathy, John Wherry, Jedd D Wolchok, Taha Merghoub. Thrombospondin-1:CD47 signaling contributes to the development of T cell exhaustion in cancer [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr B056.