Studies in rheumatoid arthritis (RA) have shown that infliximab (a chimeric anti-TNFα) and methotrexate may lead to a significant rise in the number of peripheral blood Tregs in patients responding to this therapy [19] and induce in vitro the differentiation of a population of Tregs expressing FOXP3 through conversion of CD4+CD25− T cells [20]. Here, CD4 is linked to rheumatoid arthritis.