PDCD1 and neoplasm: Studies have shown that serial cytokine measurements with serum cytokine signatures may be used as a predictive factor for ICIs therapies, but even though exposure to interferons is critical for PD-1/PD-L1 targeting cancer treatment, pro-inflammatory cytokines such as IL-2 or IFN-γ showed no significance in this respect (29, 67, 69). IFN-γ was reported to be produced by tumor infiltrating lymphocytes (TILs) in solid tumors and shown to upregulate PD-L1 expression on tumor cells (70).