Second, given the low levels of CXCR3 expression in CX3CR1+ CD8+ T cells (Fig. 2b), which is required to traffic to tumors41, it is possible that CX3CR1+ CD8+ T cells remain in circulation, and might not actively traffic to the tumor unless fractalkine (CX3CL1), the ligand of CX3CR1 is produced from the TME. Here, CX3CL1 is linked to neoplasm.