T cell-intrinsic VISTA expression promotes resistance to CTLA-4 blockade by restricting CD8+ T cell responses.

V-domain immunoglobulin suppressor of T cell activation (VISTA) is an immune checkpoint protein that impairs antitumor T cell responses. While broadly expressed on myeloid cells and T cells, the specific contribution of T cell-intrinsic VISTA to antitumor immunity remains undefined. This study investigated the phenotypic and functional consequences of T cell-specific VISTA deletion in tumor-specific CD8+ T cells. Single-cell transcriptomic analysis, TCR repertoire profiling, and flow cytometry revealed that loss of T cell-intrinsic VISTA enhanced early priming and short-term expansion of CD8+ T cells, yet this initial advantage failed to confer durable tumor control. Persistent dysfunction in VISTA-deficient T cells was in part driven by trans-VISTA on myeloid cells, while CTLA-4 upregulation further constrained T cell responses. T cell-intrinsic VISTA deficiency cooperated with CTLA-4 blockade to improve T cell survival and broaden TCR repertoire diversity, resulting in more robust tumor regression than CTLA-4 inhibition alone. A transcriptional signature enriched in VISTA-deficient cytotoxic T cells correlated with favorable outcomes in cancer patients treated with existing immune checkpoint inhibitors. These findings collectively define T cell-intrinsic mechanisms by which VISTA enforces T cell dysfunction and underscore its potential as both a therapeutic target and a biomarker of resistance to current immunotherapies.