HOXD13 and neoplasm: Functional studies of sPD-1 have been performed both in vitro and in mice, with most of these studies, in contrast to membrane-bound PD-1, reporting sPD-1 to exhibit pro-inflammatory and anti-tumor effects; sPD-1 activated T lymphocytes [98–101], upregulated the expression of IFN-γ and tumor necrosis factor alpha (TNF-α) [98], and reduced expression of IL-10 [98].