FOXP3 and B-cell acute lymphoblastic leukemia: However, activin A also contributes to the switching of CD4+CD25-Foxp3- (Foxp3: forkhead box P3) cells to CD4+CD25+Foxp3+ T-regulatory (Treg) cells, which correlates with immunosuppression in patients with B-cell acute lymphoblastic leukemia [11,13,15,26,63,64,103,125].