CD4 and neoplasm: However, in established tumors M1 promote Th1 (T helper type 1; CD4+ effector T cells) responses such as proliferation of cytotoxic (CD8+) T cells, and are involved in tumor rejection via release of pro-inflammatory cytokines and reactive oxygen species, while M2 promote tissue remodeling, immune regulation, tumor progression and metastasis (15–17).