Generation of precursor, immature, and mature murine B1-cell lines from c-myc/bcl-xL-overexpressing pre-BI cells.

Deregulated expression of c-myc and bcl-xL is long known to generate transformed B cells in humans and mice. We overexpressed these genes to induce in vitro and in vivo differentiation of fetal liver-derived mouse pre-BI cells to B1-lineage pre-BII-like, immature and mature B-cell lines, and to Ig-secreting cells. In vitro, doxycycline-controlled c-myc/bcl-xL-overexpressing CD19 CD93 c-kikt IgM pre-BI cells differentiate to and survive as CD19 CD93 c-kit IgM immature B1 cells. Timed CpG stimulation of these oncogene-overexpressing pre-B or immature B1 cells generates either CD19 CD93 c-kit IgM SLC pre-BII-like or IgM MHCII CD73 CD80 CD40 mature B1-cell lines and IgM-secreting B1 cells in vitro and fixes their state of differentiation. All cell lines are clonable, but a majority of immature and mature B1-cell clones eventually reach a nonproliferating, surviving G -state. Transplanted in vivo, c-myc/bcl-xL-overexpressing pre-B cells expand to mature B1 cells, and to IgM- and IgA-secreting plasmablasts and plasma cells. Within 2 months, plasmablasts have expanded most prominently in BM and spleen, indicating that the host selectively expanded development of these transformed plasma cells. The sIgM B1-cell lines and clones offer the possibility to study their roles in the development of B1-Ab repertoires, of B1-cell-mediated autoimmune diseases and of B1-cell malignancies.