Our findings support active involvement of the B cell population in naïve Treg selection and homeostasis, and imply a possible link between susceptibility to the development of autoimmune and inflammatory diseases in XLA patients (15, 16) and the proportional reduction of naïve Treg cells, combined with the alteration of naive CD4+ and naïve Treg TCR repertoires and naïve Treg transcriptional programs. The gene discussed is CD4; the disease is Bruton-type agammaglobulinemia.