XCL2 and neoplasm: As the key players in anti-tumor immunity, the impaired amino acid metabolism in CD8-GNLY effector T cells and CD8-XCL2 memory T cells was found in high tumor cell microenvironment, including Arginine, Proline, Glycine, Serine, Threonine, Valine, Leucine, Isoleucine and Histidine metabolism shown in Figure 6A.