VISTA: Targeted combination immunotherapy for suppression of breast cancer metastasis and recurrence.

1137 Background: Triple-negative breast cancer (TNBC) has limited treatment options and poor outcomes, with ~12% 5-year overall survival in stage IV. In early-stage TNBC (II/III), recurrence remains substantial among patients without pathological complete response after chemo-immunotherapy. Current PD-1/PD-L1 inhibitors show limited efficacy in metastatic TNBC (median OS ~23 months) and infrequent durable responses. Novel immune targets are urgently needed to overcome resistance and prevent metastasis. V-domain Ig suppressor of T-cell activation (VISTA) is a next-generation checkpoint with distinct biology, enriched in tumor-infiltrating immune cells in TNBC. Methods: Comprehensive bioinformatic analyses of VSIR (VISTA) and ligands were performed across multi-cohort TNBC datasets spanning early and advanced stages, including pre-treatment, post-treatment, and progression samples. Spatial single-cell profiling of stage III TNBC tumors with recurrence versus non-recurrence was conducted using NanoString CosMx. VISTA expression in tumor tissue and circulating tumor cells (CTCs) was assessed by optimized immunofluorescence and digital pathology. Clinically relevant TNBC mouse models evaluated VISTA-mediated immune modulation alone and combined with chemo- or immunotherapy. Results: Single-cell bioinformatic analyses revealed enrichment of VSIR and ligands SELPLG/LGALS9 in post-treatment and progression-stage TNBC versus pre-treatment, observed in tumors and liquid biopsies. VSIR/SELPLG were enriched in progenitor and terminally exhausted immune subsets, whereas early-stage TNBC showed broader immune distribution. Digital pathology identified VISTA in metastasis-initiating tumor cells and dysfunctional immune cells, with induction following anti–PD-1 therapy in TNBC mouse models. Spatial profiling of recurrence-associated tumors showed co-enrichment of VSIR/SELPLG with inhibitory receptors TIM3, LAG3, and TIGIT across immune niches in recurrence-associated tumors. VISTA targeting with a novel antibody, HMBD-002, enhanced anti-tumor immunity, synergized with chemo- and immunotherapy, and suppressed recurrence and metastatic burden in preclinical models. Conclusions: VISTA is a treatment-emergent checkpoint associated with T-cell exhaustion, recurrence, and metastasis in TNBC. Its enrichment in exhausted T-cell niches, metastasis-initiating tumor cells, and CTCs post–chemo-immunotherapy supports its role in adaptive resistance. VISTA expression in tissue and liquid biopsy CTCs represents a clinically actionable biomarker for patient selection and response monitoring. These data provide strong rationale for early-phase clinical trials of combination VISTA blockade with ICIs in high-risk early-stage TNBC with residual disease and metastatic TNBC after prior ICI exposure.