TCF7 and neoplasm: CX3CR1 was also found to be a marker of T-cell differentiation, where functionally distinct viral and tumor-specific CX3CR1− CD8+ T cells expressing high levels of TCF-1, CD62L, CD27, and/or CD127 can give rise to CX3CR1+ subsets via unidirectional differentiation upon activation in vivo (14, 15).