Production of antigen-specific human monoclonal antibodies: comparison of mice carrying IgH/kappa or IgH/kappa/lambda transloci

Here we compare human monoclonal antibody (MAb) production from mouse strains that carry disruptions of their endogenous mouse IgH/IgK loci and harbor human IgM + Igkappa(BABkappa) or human IgM + Igkappa + IgA transloci (BABkappa,lambda). We found that whereas both strains proved effective for the isolation of antigen-specific IgM antibodies, many of the IgM MAbs elicited from BABkappa comprise human mu chains that are associated with mouse lambda chains. In contrast, BABkappa,lambda mice gave rise to fully functional, polymeric human IgM antibodies comprising both human IgH and human IgL chains. Therefore, the inclusion of a human Iglambda translocus (in addition to the human IgH + Igkappa transloci) not only diminishes problems of endogenous mouse Iglambda expression but also provides a strain of mice that yields fully human MAbs to a wide range of antigens, as witnessed by the isolation of MAbs to human blood cells, tumor cell lines, and an immunoglobulin idiotype.     

Spi-B can functionally replace PU.1 in myeloid but not lymphoid development

Mature macrophages, neutrophils and lymphoid cells do not develop in PU.1(-/-) mice. In contrast, mice lacking the highly related protein Spi-B generate all hematopoietic lineages but display a B-cell receptor signaling defect. These distinct phenotypes could result from functional differences between PU.1 and Spi-B or their unique temporal and tissue-specific expression (PU.1: myeloid and B cells; Spi-B: B cells only). To address this question, we introduced the Spi-B cDNA into the murine PU.1 locus by homologous recombination. In the absence of PU.1, Spi-B rescued macrophage and granulocyte development when assayed by in vitro differentiation of embryonic stem cells. Adherent, CD11b(+)/F4/80(+) cells capable of phagocytosis were detected in PU.1(Spi-B/Spi-B) embryoid bodies, and myeloid colonies were present in hematopoietic progenitor assays. Despite its ability to rescue myeloid differentiation, Spi-B did not rescue lymphoid development in a RAG-2(-/-) complementation assay. These results demonstrate an important difference between PU.1 and Spi-B. Careful comparison of these Ets factors will delineate important functional domains of PU.1 involved in lymphocyte lineage commitment and/or maturation.