CD4 and cancer: A number of different cells can participate in the interactions of the tumor microenvironment, including cancer cells, cancer stem-like cells, macrophages, NK cells, CD8+ t cells, CD4+ t cells, dendritic cells, mesenchymal stem cells, γδ t cells, neutrophils, myeloid-derived suppressor cells (MDSCs), endothelial cells and platelets as well as quiescent or partially transformed resident cells in a given tissue [6].