FOXP3 and polyendocrinopathy: For example, a vector was recently described for the treatment of the PID Immunodysregulation, Polyendocrinopathy, Enteropathy X-Linked (IPEX) that restricts expression of FOXP3 to regulatory T cells after transducing and transplanting HSC by controlling the FOXP3 gene with transcriptional regulatory elements from the endogenous gene (89).