XCL1 and neoplasm: Then, rare tumor-specific TOX-low EM TILs driven by persistent antigenic stimulation differentiate into TOX-high XCL1-high quiescent (Tpex) cells which, following interaction with XCR1+ APCs, give rise to highly proliferative terminally exhausted/dysfunctional (Tex) CD8+ TILs that engage in tumor cell killing (Fig. 9).