GPR68 and melanoma: To understand the direct consequences of pH alterations on T cells mediated by Ogr1 in regulating tumor protection, T cells isolated from the spleens of B16-F10 tumor-bearing mice (Supplementary Fig. 3A) were cultured for 12 h in the presence of the inorganic acid HCL, which mimics the low pH characteristic of melanomas, with magnetic beads and recombinant IL-2.