CTLA4 and neoplasm: A previous study found that CD4 + T cells regulate other immune cells, such as CD8+ T cells, where activated CD8+ T cell subsets produce various cytokines that affect the tumor microenvironment.33 Interestingly, SP2509 attenuated the immunosuppressive CD25+ CTLA4+ T cells (a subset of CD4+ T cells) (Fig. 3b).