Single-cell profiling of tumor-reactive CD4+ T-cells reveals unexpected transcriptomic diversity

Most current tumor immunotherapy strategies leverage cytotoxic CD8 + T cells. Despite evidence for clinical potential of CD4 + tumor-infiltrating lymphocytes (TILs), their functional diversity has limited our ability to harness their activity. To address this issue, we have used single-cell mRNA sequencing to analyze the response of CD4 + T cells specific for a defined recombinant tumor antigen, both in the tumor microenvironment and draining lymph nodes (dLN). Designing new computational approaches to characterize subpopulations, we identify TIL transcriptomic patterns strikingly distinct from those elicited by responses to infection, and dominated by diversity among T-bet-expressing T helper type 1 (Th1)-like cells. In contrast, the dLN response includes follicular helper (Tfh)-like cells but lacks Th1 cells. We identify a type I interferon-driven signature in Th1-like TILs, and show that it is found in human liver cancer and melanoma, in which it is negatively associated with response to checkpoint therapy. Our study unveils unsuspected differences between tumor and virus CD4 + T cell responses, and provides a proof-of-concept methodology to characterize tumor specific CD4 + T cell effector programs. Targeting these programs should help improve immunotherapy strategies.