CD19 and Wiskott-Aldrich syndrome: The B-cell compartment of patients with WAS is also characterized by the presence of an unusual population phenotypically identified as CD19+CD21−CD38− (referred to as CD21low)18 that were enriched in autoreactive and unresponsive B cells that could be involved in the breakdown of B-cell tolerance.32-34 Before treatment, patients with WAS presented with an increased frequency of CD21low B cells, which diminished 3 months after GT, becoming nearly absent starting at 18 months after treatment (Fig 4, C and D).