Abstract B026: Regulation of CTLA-4 and PD-1 blockade immunotherapy by distinct subpopulations of CD4 and CD8 tumor-resident memory T cells

Abstract Accumulating evidence indicates that the clinical benefits of anti-PD-1 immunotherapy are dependent on tumor infiltration by specific CD8 T lymphocytes, whereas the response to anti-CTLA-4 blocking antibodies is associated with a reactivation of CD4 T lymphocytes. However, whether these T-cell subpopulations belong to tissue-resident memory T (TRM) cells, and the signaling pathways involved in their differentiation within the tumor microenvironment (TME) are only partially known. Using mouse tumor models and human tumor cohorts and cellular models, our results show that while CD8+CD103+ TRM cells are associated with response to PD-1 blockade, CD4+CD49a+ TRM promote the response to anti-CTLA-4 neutralizing antibodies. The benefits of anti-PD-1 treatment, but not of anti-CTLA-4, are compromised in mice challenged with anti-CD8 and anti-CD103 blocking antibodies, and in CD8- and CD103-knockout mice, unless wild-type CD8 T cells are also transferred. By contrast, the benefits of CTLA-4 blockade are decreased by anti-CD4 and anti-CD49a neutralizing antibodies. Single-cell RNA sequencing on mouse tumor-infiltrating T lymphocytes (TIL) revealed different CD4 and CD8 TRM subsets that accumulate in the tumor and are affected differently by anti-CTLA-4 and anti-PD-1 therapies. Anti-PD-1 treatment induced changes in CD8 T-cell clusters by increasing the proportions of two TRM clusters, whereas anti-CTLA-4 induced a decrease in the proportion of a third CD8 TRM cluster. By contrast, CTLA-4 blockade resulted in exacerbation of a CD4+CD49a+ TRM signature enriched in Ctla-4, Icos and Runx, and residency-linked transcripts. Functionally, anti-CTLA-4 therapy leads to intratumoral expansion of CD4+CD49a+ TRM cells and an increase in CD4 TIL-mediated cytotoxicity toward tumor target cells. A CD4+CD49a+ TRM signature enriched in CTLA-4 and cytotoxicity-linked transcripts is identified in TIL from human lung tumors and melanomas. Multiplex fluorescence immunohistochemistry on cohorts of anti-CTLA-4-plus-anti-PD-1-treated melanomas shows that an increase in the density of CD4+CD49a+ TIL is associated with higher rates of progression-free survival. Our more recent results indicate that the differentiation and persistence of CD4+CD49a+ and CD8+CD103+ TRM cells in tumors involve distinct transcription factors and signaling molecules. The formation of CD8+CD103+ TRM cells is dependent on TGF-beta, at least in part via induction of CD103 integrin in T-cell receptor (TCR)-engaged T cells, with the transcription factors Smad2/3 and NFAT-1 as two critical regulators of this process. The molecular mechanisms and cytokines involved in CD4 TRM-cell development and maintenance in the tumor will be presented as well as the cellular interactions of CD4+CD49a+ and CD8+CD103+ TRM cells within the TME. Our results support the conclusion that different CD4 and CD8 TRM subpopulations participate to antitumor immunity and response to immune checkpoint blockade, and that their differentiation at the tumor site relies on specific cellular interactome and distinct signaling pathways. Citation Format: Fathia MAMI-CHOUAIB, Isabelle Damei, Stéphanie Corgnac. Regulation of CTLA-4 and PD-1 blockade immunotherapy by distinct subpopulations of CD4 and CD8 tumor-resident memory T cells [abstract]. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr B026.