CD4 and neoplasm: Tomasz Ahrends et al, using anti-tumor vaccine mouse models, have shown at the molecular level that CD4+ T cells promote the migration and recognition of cytotoxic T cells towards tumor cells, and thus kill tumor cells, by down-regulating the expression of co-inhibitory receptors that affect cytotoxic T cell activity and by up-regulating the expression of multiple chemokine receptors on cytotoxic T cells [28].