Abstract 7536: CD4+T cell exhaustion in the tumor microenvironment and antitumor immunity

Abstract Background: Immune checkpoint inhibitors (ICIs) exert clinical efficacy against various types of cancer through reinvigoration of exhausted CD8+ T cells that attack cancer cells directly in the tumor microenvironment (TME). However, compared to CD8+ T cell exhaustion, the role of CD4+ T cell exhaustion in antitumor immunity remains unclear. Methods and Results: From single-cell sequencing for tumor-infiltrating lymphocytes (TILs) from patients with melanoma and mouse models, we found that CXCL13, which is highly expressed in tumor-infiltrating exhausted CD8+ T cells, induces PD-1+CXCR5+CD4+ follicular helper T (TFH)-like cell infiltration, which could contribute to antitumor immunity. Furthermore, a part of the TFH-like cells in the TME exhibits cytotoxicity and directly attacks MHC-II-expressing tumors. RNA velocity and latent time analysis in single-cell sequencing for melanoma TILs showed that the differentiation of TFH-like cells from the naive CD4+ T cells were different from that of other CD4+ T cells. In addition, the TFH-like cytotoxic CD4+ T cells were at the late stage of differentiation and some non-cytotoxic TFH-like cells might differentiate into TFH-like cytotoxic CD4+ T cells. We additionally found considerable overlapped clonotypes between the cytotoxic and non-cytotoxic clusters. TFH-like cytotoxic CD4+ T cells have high LAG-3/BLIMP1 and low TCF1 expression without self-renewal ability, whereas non-cytotoxic TFH-like cells express low LAG-3/BLIMP1 and high TCF1 with self-renewal ability, closely resembling the relationship between terminally differentiated and stem-like progenitor exhaustion in CD8+ T cells, respectively. Conclusion: Our findings provide novel insights into TFH-like CD4+ T cell exhaustion with helper progenitor and cytotoxic differentiated functions, which mediates antitumor immunity orchestrally with CD8+ T cells. Citation Format: Joji Nagasaki, Wenhao Zhou, Shusuke Kawashima, Takamasa Ishino, Katsushige Kawase, Youki Ueda, Kazuo Yamashita, Tomofumi Watanabe, Takashi Inozume, Yosuke Togashi. CD4+T cell exhaustion in the tumor microenvironment and antitumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7536.