VISTA immune-checkpoint blunts radiotherapy induced anti-tumor immune response

Radiotherapy (RT) is a cornerstone treatment for cancers like head and neck cancer (HNC), but it can also unintentionally activate immune-suppressive myeloid cells, which may limit its effectiveness. This study explores the role of the immune checkpoint protein VISTA, which is found at high levels on myeloid cells in both mouse and human HNC tumors. RT further increases the number of VISTA-positive myeloid cells in the tumor and bloodstream. Mice lacking VISTA responded better to RT, with their immune cells–especially macrophages and neutrophils–shifting toward anti-tumor behavior, as revealed by single-cell RNA sequencing. Importantly, combining RT with anti-VISTA antibodies significantly shrank tumors in several cancer models (HNC, breast, colorectal), more so than either treatment alone. This combination also boosted the overall immune response, improving T cell activity through reprogramming of myeloid cells. These findings suggest that blocking VISTA could make RT more effective by counteracting immune suppression in the tumor environment. To investigate how VISTA modulates the immune microenvironment after radiotherapy, we performed single-cell RNA sequencing on MOC2 tumors implanted in VSIR wild-type (WT) and knockout (KO) mice. Tumors were harvested two days after the last dose of radiation (3 Gy 5 fractions). Eight libraries were generated from four experimental groups (WT, KO, WT + RT, KO + RT) with two biological replicates per group. Single-cell suspensions were prepared and sequenced using the 10x Genomics Chromium Single Cell 3 v3.1 platform on an Illumina NovaSeq 6000.