VISTA as a myeloid-centered checkpoint axis in cancer: biology, tumor microenvironment, and therapeutic implications.

VISTA (V-domain Ig suppressor of T-cell activation; gene symbol VSIR) has emerged as a distinct immune checkpoint with increasing relevance in cancer biology and immunotherapy. Unlike classical checkpoint pathways that are predominantly interpreted through T cell-centered suppression, accumulating evidence indicates that VISTA exerts broader and highly context-dependent immunoregulatory functions, frequently centered on myeloid cells within the tumor microenvironment. In many malignancies, VISTA is preferentially enriched in tumor-associated macrophages, myeloid-derived suppressor cells, and dendritic cells rather than being uniformly expressed by tumor cells. This compartment-specific distribution has been linked to suppressive myeloid differentiation, impaired antigen presentation, altered inflammatory cytokine programs, T-cell dysfunction, and immune exclusion. Recent studies further suggest that VISTA biology is shaped by ligand context, tissue compartment, tumor acidity, and therapy-induced adaptation, supporting its role in resistance to conventional immune checkpoint blockade in selected settings. In this review, we summarize the structural and functional features of VISTA, its expression patterns in physiological and tumor contexts, its mechanistic role in shaping the tumor microenvironment, and the current landscape of VISTA-targeted therapeutic strategies. Key unresolved questions include which VISTA binding partners dominate in vivo, how cellular source and spatial localization determine biological and prognostic meaning, and whether early pharmacodynamic target engagement will translate into durable clinical benefit. Collectively, current evidence supports the view that VISTA should be considered not simply as another inhibitory receptor, but as a dynamically regulated, myeloid-centered checkpoint axis with translational relevance in checkpoint-refractory and immune-excluded tumors. A compartment-resolved understanding of VISTA expression and function may improve prognostic interpretation, biomarker development, and patient selection for VISTA-directed therapies.