CD4 and neoplasm: More specifically, evasion of the immune system and tumor development by Kupffer cells and other monocyte-derived tumor-associated macrophages can occur through different routes, such as the release of immunosuppressive cytokines (e.g., interleukin-10 (IL-10), transforming growth factor-β (TGF-β)), the expression of programmed cell death ligand 1 (PD-L1), the downregulation of class II major histocompatibility complex (MHC-II) and costimulatory markers (e.g., CD80, CD86), the recruitment of CD4+ T helper cells expressing IL-17 and regulatory T cells, and the triggering of angiogenesis.