Differential in vitro maturation of hematopoietic stem cells from wild-type and immunoglobulin transgenic mice

During B-cell lymphopoiesis, hematopoietic stem cells commit to the B cell lineage as monitored by the expression of phenotypic cell surface antigens and the production of immunoglobulin chains. Two cytokines, interleukin-7 ( IL-7) and Flt-3 ligand (FL), appear to act in conjunction to drive this dev elopment process. Using an in vitro, stroma-free culture system and these c ytokines, the commitment of murine Sca(+) Lin- bone marrow cells to the B-c ell lineage was examined with stem cells from immunoglobulin (Ig) transgeni c and wild-type mice. After 12 days of culture in IL-7 and FL, stem cells f rom wild-type animals had matured to express surface B220, CD19, CD43, Bp-1 and heat-stable antigen (HSA). These cells lacked detectable intracellular mu chains while exhibiting partial D-J rearrangement. In contrast, Sca(+)L in(-) cells from 18 transgenic mice that were cultured similarly expressed B220, CD19, IgD, intracellular and surface mu, HSA but not CD43 or BP-1. Th ese results suggest that expression of the Ig transgene during in vitro dev elopment overcame a block in B-cell lymphopoiesis and recapitulated in vivo events. Thus, IL-7 and FL treatment allowed uncommitted stem cells to prog ress to the early pre-B-cell stage while similarly treated 18 transgenic ce lls progressed completely to the mature B-cell stage.