CX3CR1 and neoplasm: The efficacy of anti-PD-1 immunotherapy can be predicted according to the degree of immune cells infiltration, determined by two main factors: (1) chemokines (e.g., CCR5, CXCR3, CX3CR1, and CXCR6 are related to the migration of CTLs to tumor sites) and (2) entry through tumor blood vessels.