Moreover, studies have shown that, in the highly dynamic tumor-immune system, the expression of PD-L1 in tumor microenvironment can also be induced by CD8-positive T cells, as well as cytokines such as interferon γ, IL-2, IL-7, IL-15, and IL-21 in a positive feedback mechanism [27, 31, 32]. This evidence concerns the gene IL15 and neoplasm.