Composition of the precursor B-cell compartment in RAG-deficient SCID patients compared with healthy children.

The precursor B-cell compartment was set at 100% after exclusion of CD10⁻/SmIgM⁺/SmIgD⁺ mature B cells.28 All RAG-deficient SCID patients showed a similar differentiation arrest with approximately 99% of the precursor B cells in the pro-B and pre–B-I stages (stages 1-5), thereby revealing an arrest at the transition from CyIgμ⁻ pre–B-I (stages 4 and 5) to CyIgμ⁺ pre–B-II-cells (stages 6 and 7, white bars). Only in SCID-3 was some leakiness observed with more than 3% Ig⁺ B cells. These Ig⁺ B cells were mainly SmIgM⁺ immature B cells (stage 8, dark bar), which is also shown in Figure 2B. The age of BM sampling is indicated.