BM samples of RAG-deficient SCID patients contained increased numbers of the most immature CD22⁺/CyCD79a⁻ pro-B cells.

CyCD79a expression of the precursor B-cell compartment was analyzed within a lymphocyte gate and a CD22⁺ gate, which was “purified” by exclusion of cells with expression of CD3, CD16, or CD33. In healthy children the CD22⁺/CyCD79a⁻pro-B-cell subset represented a minor fraction of the total precursor B-cell compartment. In most RAG-deficient SCID patients this CyCD79a⁻ subset was relatively large but variable in size. Furthermore, the level of CyCD79a expression in the SCID patients (mainly pre–B-I cells) was lower than in the healthy controls (mainly pre–B-II cells and immature B cells). The age at BM sampling is indicated.