Bone marrow-CD34⁺ and CD34⁻ cells were sorted for their CD19 respective subsets using CD34 FITC- and CD19 PE-conjugated antibodies. To increase the sensitivity of our PCR method at the lymphoid progenitor cell level, only cells with a lymphoblastoid appearance were sorted. The FACS setting of one representative patient (K.A.) is shown. Isotype control for CD34⁺ cells (A) and for CD34⁻ cells (C) were included. Sorting gates for CD34⁺ cells (B) and CD34⁻ cells (D) were set to clearly separate between CD19⁺ and CD19⁻ cells.