CD4 and leishmaniasis: We predict that this difference is due to the absence of regulatory T cells (Tregs) since in tumor models Tregs control the cytotoxicity of CD8+ T cells in a TGF-β dependent manner [41], [54], and in leishmaniasis both CD4+ Th1 cells and CD4+ T regulatory cells (Treg) dampen the immune response [55], [56], [57].