Cytokine IFN-γ secreted by T cell boosts the tumor-repopulating cells that exhibit high tumorigenicity and self-renews to release more kynurenine, which is transferred into T cells via SLC7A8 and PAT4 to increase PD-1 expression, accompanied by impaired anti-tumor immunity of T cells [43]. This evidence concerns the gene SLC36A4 and neoplasm.