Here, we provide evidence in tumor-bearing mice that: (1) effective ICI therapy correlates with the increased frequency and TCR clonality of peripheral CX3CR1+ CD8+ T cells that identify an enriched repertoire of neoantigen- and TAA-specific CD8+ T cells; (2) the frequency of CX3CR1+ but not Ki-67+ PB CD8+ T cells remained elevated during ICI therapy; and (3) there is a high degree of TCR sequence overlap and similarity between CD8+ TILs and the peripheral CX3CR1+ subset during ICI therapy. This evidence concerns the gene CX3CR1 and neoplasm.