Abstract A006: Clonal dynamics of tumor-infiltrating CD4+ T cells in response to immune checkpoint and Shp-1 inhibition

Abstract CD4+ T cells are important contributors to anti-tumor responses but remain understudied and less well characterized than CD8+ T cells. For example, CD4+ T cells enhance CAR-T and ACT therapies, and that addition of MHC Class II-restricted epitopes improves cancer vaccine efficacy. However, CD4+ T cells can also acquire regulatory functions that promote increased tumor growth. We previously reported that inhibition of the TCR-regulatory phosphatase SHP-1 (SHP-1i) enhanced the therapeutic efficacy of immune checkpoint inhibitors (ICI), particularly in ICI-resistant tumors with low mutation burden. While treatment efficacy was associated with the recruitment of low affinity effector CD8+ T cells specific for tumor self-antigens, CD4+ T cell frequencies remained unchanged. The goal of this study was to examine whether immunotherapy affected the function and clonal makeup of the CD4+ T cell response in response to treatment and to identify MHC Class II-restricted TCRs associated with either therapeutic or regulatory function. To accomplish this, we performed single cell RNA and V(D)J sequencing on CD4+ T cells specific for the tumor self-antigen tyrosinase protein 1 (TRP-1) isolated from Yale University mouse melanoma 1.1 (Yumm1.1) tumors. We compared clonal dominance and diversity in mice receiving no treatment to those receiving combined ICI and SHP-1 inhibitor treatment (SHP-1i+ICI). We found that tumor growth resulted in clonally distinct populations of effector cells (characterized by expression of Tbx21, Ifng, and Pdcd1) and regulatory T cells (expressing FoxP3). Moreover, SHP-1i+ICI resulted in a decrease in overall repertoire diversity and selective outgrowth of clones expressing effector, regulatory, or stem-like (Tcf7, Slamf6) transcriptional programs. We propose that SHP-1i+ICI dramatically reshapes the anti-tumor CD4+ T cell response through selective expansion of clones with anti-tumor effector functions. Future studies will be directed towards determining whether treatment-selected TCRs specific for tumor self-antigens demonstrate immunotherapeutic efficacy in settings of low mutation burden. Citation Format: Kaitlyn A. Flint, Joseph G . Matous, Christopher H. Hanson, Yohichi Kumaki, Matthew A . Williams. Clonal dynamics of tumor-infiltrating CD4+ T cells in response to immune checkpoint and Shp-1 inhibition 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 A006.