Background <p>V-domain Ig-containing suppressor of T cell activation (VISTA) is an immune checkpoint molecule predominantly expressed on myeloid cells and has recently been recognised as a key mediator of immunosuppression within the tumour microenvironment (TME). However, its expression pattern in gastric cancer and the functional characteristics of the VISTA-high TME remain poorly understood.</p> Methods <p>We conducted multiplex immunohistochemistry on tumour samples from 172 patients to characterise the immune landscape of the VISTA-high tumour microenvironment. Additionally, single-cell RNA sequencing (<i>n</i> = 17) and spatial transcriptomics (<i>n</i> = 3) were employed to delineate the cellular expression patterns of VISTA and investigate the potential immunomodulatory functions of VISTA-expressing macrophages.</p> Results <p>High VISTA expression was associated with an immunosuppressive TME characterised by increased infiltration of exhausted CD8⁺ T cells, regulatory T cells (Tregs), M2-like macrophages, and cancer-associated fibroblasts (CAFs). Moreover, elevated VISTA levels in the tumour region were linked to worse immune-related progression-free survival (irPFS) in patients treated with immune checkpoint inhibitors (ICIs). Mechanistically, VISTA⁺ monocyte-macrophage (MoMac) populations promoted T cell exhaustion via the LGALS9-PTPRC signalling axis and exhibited enhanced antigen-presenting capacity.</p> Conclusions <p>Our findings establish VISTA as a central immunoregulatory checkpoint in gastric cancer, suggesting its potential as a promising therapeutic target for combination immunotherapeutic approaches.</p> <p></p>