CTLA4 and neoplasm: Clostridium IV is able to participate in the modulation of the intestinal immune microenvironment, and an animal study found that Clostridium IV colonisation of the mouse intestine significantly up-regulated the level of intestinal Tregs [60], Clostridium IV was able to provide bacterial antigens and a transforming growth factor-β (TGF-β)-rich environment, which promoted the proliferation and differentiation of Tregs [61], and Tregs expressed the immune checkpoint receptor for cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), which promotes tumour immune tolerance [62].