Most, but not all, Tregs are characterized by the expression of the transcriptional regulator FoxP3, and although CD4+, CD8+, FoxP3+, and FoxP3- Tregs have been described, the one receiving most attention in cancer is the CD4+CD25+FoxP3+ subset which is associated with a poor prognosis in many cancers [21]. This evidence concerns the gene CD4 and cancer.