In preclinical models of melanoma, Slamf6 was identified as a cell-surface marker that distinguished progenitor-exhausted CD8+ T cells from terminally exhausted CD8+ T cells, and CD8+ T cells co-expressing TCF1 and SLAMF6 retained polyfunctionality, produced IFN-γ, TNF, and/or IL-2 and persisted long term upon adoptive transfer, thereby contributing to long-term tumor control compared to terminally-exhausted T cells8. The gene discussed is TCF7; the disease is melanoma.