CD4 and neoplasm: IL-33 initiates a type 2 immune response by activating mast cells or other immune cells, including T cells; Mast cells can release IL-2 via the IL-33 and ST2 pathway, which facilitates the differentiation of CD4+ T cells into ICOS+ regulatory T cells while suppressing the activity of CD8+ T cells, thus fostering tumor progression [56], but the mechanism of interaction of these molecules between mast cells and Treg and whether there is a lack of studies on other immune cells is ambiguous.