CHARACTERIZATION AND DIFFERENTIATION OF AN EARLY MURINE YOLK SAC-DERIVED IL-7-INDEPENDENT PRE-PRO-B CELL-LINE

We describe a unique, stable pre-pro-B cell line (YS-PPB) derived from AA4.1(+) yolk sac cells from day 10 mouse embryos, This cell line, di scovered fortuitously during the course of studies of in vitro B cell differentiation, is independent of IL-7 supplementation for long term expansion in vitro. E'S-PPB cells as well as clonal sublines expressed AA4.1, CD43, B220, Sca-1, CD19, heat stable antigen, MHC class I, IL- 7R, and Fc gamma R, but did not express cytoplasmic mu-chain, surface IgM (sIgM), or MHC class II molecules. PCR analysis showed that the ce lls expressed TdT, lambda 5, and RAG-1 genes, but that their Tg genes were still in germline configuration, The cell line was dependent on d irect contact with S17 stromal cells for growth, but, in contrast to b one marrow stem cells, required no additional growth factors for maint enance and expansion. When stimulated with IL-7 and LPS, YS-PPB cells and cells from all tested clonal sublines differentiated into sIgM(+) B cells in vitro. Irradiated mice reconstituted with YS-PPB cells yiel ded spleens containing 38% sIgM(+) donor-derived B cells, demonstratin g that YS-PPB cells, although stably arrested in development at the bo undary between pre-pro-B and pro-B stages of B cell differentiation, s till retain their competence to differentiate into mature, Ig-producin g B cells when transferred to a normal host environment. Thus, this ne w cell line can pro,ide a reproducible source of B cell precursors arr ested at that critical time in B cell differentiation when the machine ry for Ig gene rearrangement is in place but rearrangement has not yet occurred.