'Ex vivo staining of patient tumour tissue shows the formation of an acid wall below pH 5.3 at the stromal–tumour tissue interface with exclusion of CD8+ T cells (Fig. 4c). We theorize that polarized secretion of lactic acid creates exclusionary zones that exterminate CD8+ T cells upon cell–cell contact, which offers a survival advantage for cancer cells with strong acidotic properties'
https://www.nature.com/articles/s41551-024-01178-7#Sec10