CX3CR1 and neoplasm: Except for the capacity to generate naive-like T cells, IL-21 is also required for the formation of the CX3CR1+ cytolytic subset, therefore promoting the cytotoxicity of CD8+ T cells with enhanced Granzyme B and IFN-γ expression.35,36 The defect in effector transition from low-differentiated memory T cell subsets inside the tumor may dampen the antitumor function of tumor-infiltrating T cells,36 indicating that strategies that only maintain T cells low differentiated state are unsuitable for transferred T cells inside the tumor microenvironment.