TNF and neoplasm: Although an abundance of IFN-γ and TNF-α will be produced during the differentiation of monocytes into macrophages, in vitro experiments confirmed that certain cytokines would be produced when tumor cells are co-cultured with monocytes, which could promote the secretion of TNF-α by monocytes along with the expression of PD-L1 on the surface of monocytes [84].