The reduction in the B-cell compartment and the persistence of the Sca-1 antigen on myeloid cells because of ectopic TAL-1 expression are cell autonomous phenomena.

(A) Peripheral blood cells of NOD/SCID mice transplanted withhtal-1 transgenic (Tg) or wild-type BM were analyzed 6 weeks after transplantation for antigen expression using monoclonal anti–Sca-1–PE, anti-CD11b (MAC-1)–FITC, anti-B220–FITC, and anti-IgM–PE antibodies. Transgenic CD11b⁺ cells show persistence of the Sca-1 antigen. NOD/SCID mice engrafted withhtal-1 transgenic BM cells are deficient in B cells compared with mice transplanted with wild-type cells. Percentages refer to myeloid and lymphoid gates, respectively. (B) Phenotypic analysis of BM cells of NOD/SCID mice 8 weeks after transplantation. Cells were stained with monoclonal anti-B220–FITC and anti-CD19–PE. Percentages refer to the lymphoid gate defined by forward and side light scatter. R2 comprises mature B cells, R3 the immature B220^low cells. NOD/SCID mice not receiving transplants normally show accumulation of B220^low CD19⁺ cells as shown in the first scatter. This population disappears in NOD/SCID mice receiving transplants and is replaced by donor cells.