A transgenic marker for mouse B lymphoid precursors

Three lines of transgenic mice have been generated which express human CD25 under the control of the 722-base pair region located immediately 5' of the precursor (pre)-B-cell-specific lambda 5 gene. All three strains express human CD25 in parallel to endogenous lambda 5 on pre-B cells, but not on mature B lymphocytes or other blood cell lineages. High expression of human CD25 on B lineage cells of transgenic mice has allowed the identification of a new B220(+)CD19(-)lambda 5(+) precursor of the B220(+)CD19(+)lambda 5(+) c-kit(+) pre-BI cells. Both types of precursors are clonable on stromal cells in the presence of interleukin-7. The CD19(-) precursors have a sizeable part of their immunoglobulin heavy chain gene loci in germline configuration, while the CD19(+) pre-BI cells are predominantly DJ(H) rearranged. The results indicate that random integration of the 722-bp 5' region of the lambda 5 gene into the mouse genome confers tissue and differentiation stage-specific expression of a transgene.