Kenneth Dorshkind

Generation of purified stromal cell cultures that support lymphoid and myeloid precursors

Treatment of Dexter-type long-term bone marrow cultures with the antibiotic mycophenolic acid (MPA) eliminates all hemopoietic cells from the cultures, while a morphologically intact, adherent stromal cell layer is retained. The ability of these MPA treated stromal cell cultures to support long-term hemopoiesis was tested by seeding them with fresh bone marrow cells that had been passed through nylon wool. This procedure yields a relatively stromal cell depleted population of hemopoietic cells. An aliquot of 5 X 10(5) or 2.5 X 10(5) nylon wool passed bone marrow cells bearing the T6 chromosomal marker was seeded onto replicate MPA-treated stromal cell layers. The stromal cells stimulated the proliferation of the bone marrow cells, and nonadherent cells were present for up to 8 weeks of culture. Progenitors of granulocytes and macrophages (CFU-GM) were also present for this period of time despite weekly demi-depopulation, during culture feeding. Karyotypic analysis confirmed that the CFU-GM were derived from the reseeded population. Nylon wool-passed bone marrow cells seeded alone into empty flasks under identical conditions did not survive past 1 week. Cells from the reseeded cultures were also tested for early myeloid precursors (CFU-S) and injected into immunodeficient CBA/N mice to test for the presence of primitive B cell precursors. CFU-S were present in mice killed 11 days following injection of cells, and high levels of B cell colony-forming units (CFU-B) were present in mice 4 weeks post reconstitution. Further studies demonstrated that factors present in medium conditioned by the stromal cells could support the growth of CFU-GM. These data indicate that treatment of long-term bone marrow cultures with MPA results in a population of functional stromal cells.

Human, rat or mouse hybridomas secrete high levels of monoclonal antibodies following transplantation into mice with severe combined immunodificiency disease (SCID)

Mice with severe combined immunodeficiency disease (SCID) have been investigated for their ability to grow xenogenic hybridomas of mouse, rat and human origin. Two rat X mouse hybridoma lines (187.1.10 and 3B9) and 1 mouse X mouse hybridoma (2D9) grown in pristane-treated SCID mice as ascites tumors showed a 100-200-fold increase in monoclonal antibody levels over the amount produced in vitro with a total yield up to 0.5 g of antibody per animal. A human X human hybridoma, CLL-11-D1, exhibited a 1000-fold increase in human immunoglobulin levels in ascites (1.3 mg/ml) as compared to that obtained in tissue culture. Analyses of the antibody protein in the SCID ascites produced by these hybridomas using protein electrophoresis, SDS polyacrylamide gel electrophoresis and high resolution isoelectric focusing indicated the antibodies were monoclonal and free from any contaminating immunoglobulins. Yields of monoclonal antibodies of over 90% purity could be obtained from the ascites by a single ammonium sulfate precipitation step. This study indicates that SCID mice provide several significant advantages over other in vivo methods for the production of pure monoclonal antibodies of human, rat, or mouse origin.

Morphologic analysis of long-term bone marrow cultures that support B-lymphopoiesis or myelopoiesis

SummaryA comparative morphological analysis of the Whitlock-Witte long-term B-cell culture and the predominantly myeloid Dexter long-term bone marrow culture demonstrates that similarities and differences exist between the two systems. Cells from the long-term B-cell cultures have a characteristic lymphoid morphology, whereas those from the Dexter cultures are predominantly granulocytes and macrophages along with a few undifferentiated blast cells. A multilayered stromal cell layer is a common feature of both systems. Scanning electron micrographs show the cells in this layer to be large, irregularly shaped and flattened. The data further indicate that there are unique features in the relationship between developing B cells and stromal cells in the long-term B-cell cultures. Large, mononuclear cells are present that have numerous membrane infoldings within which numerous lymphoid cells lie. The relationship of these cells to macrophages and epithelial/reticular cells is discussed.

A colony assay system that detects B cell progenitors in fresh and cultured bone marrow

This report describes a colony assay system, based on methods used to grow myeloid precursors in semisolid medium, in which B cell progenitors can be grown. The formation of these B cell progenitor colonies is dependent upon soluble mediators from a stromal cell line known to support B lymphopoiesis. In initial experiments a double layer culture system was employed in which target cells in methylcellulose medium were separated from an adherent layer of S17 stromal cells by an agar interface. Target cells were harvested from Dexter type long-term bone marrow cultures at a time after transfer to the lymphoid Whitlock-Witte conditions, when myeloid progenitors were depleted and mature B cells had not yet appeared. On day 15 of culture a colony could be identified that contained several hundred tightly clustered lymphoid cells. There was a linear relationship between the number of cells plated and the number of colonies that developed. Identically appearing colonies were also observed in agar using fresh bone marrow cells as targets with either an underlayer of S17 cells or S17 conditioned medium to potentiate colony growth. Lymphoid colonies derived from fresh bone marrow appeared on days 6 and 14 of growth. A proportion of the cells from the fresh or cultured marrow derived colonies expressed the B220 antigen and cytoplasmic mu heavy chains, but surface IgM was never observed. Cell depletion experiments on antibody coated plates demonstrated the colony forming unit to be B220 antigen positive, surface IgM negative, and replating experiments indicated the colonies were lymphoid restricted in their differentiative potential.

Bone marrow cells from young and old New Zealand Black mice can reconstitute B lymphocytes in Severe Combined Immunodeficient recipients

The formation of B lymphocytes in young New Zealand Black (NZB) mice proceeds at an accelerated rate, resulting in a deficiency of B lineage progenitors in mice of 15 weeks of age and older. Multiple studies have indicated that intrinsic defects in B lineage cells as well as in the hemopoietic microenvironment in which they develop contribute to these cellular abnormalities. To determine whether the B-cell hyperactivity observed in young mice could be observed in a normal environment, bone marrow cells from young (4 weeks or less) NZB donors were transplanted into Severe Combined Immunodeficient (SCID) mice that have a marked deficiency of lymphocytes but an apparently normal hemopoietic microenvironment. Engraftment of donor lymphoid cells can occur without pretransplant conditioning regimens, thus minimizing the chances of transferring microenvironmental elements. Marrow from young NZB donors reconstituted surface IgM-expressing B cells and CFU-B (B-cell colony-forming unit) in the marrow of SCID mouse recipients to levels comparable to that observed with donor NZB.xid marrow. The latter mice carry the xid gene that ameliorates the defects exhibited by B lineage cells of NZB mice. Both the number of surface IgM-expressing B cells and CFU-B were higher in the spleen of SCID mice that received NZB grafts than marrow cells from donor BALB/c or NZB.xid mice. Marrow from young NZB donors also reconstituted Thy-1, L3T4 and Lyt2-expressing cells in the spleen to levels higher than observed with young NZB.xid donor cells. The transplantation of marrow from 6-month-old NZB donors made it possible to test whether B lineage cells were present in that tissue and could mediate reconstitution in the normal SCID environment. Marrow from old NZB donors did reconstitute B cells in the marrow and spleen of SCID recipients. The level of reconstitution was comparable to that mediated by young BALB/c cells and twice that of old NZB.xid donor cells. The absolute number of splenic CFU-B was also higher in recipients of old NZB marrow as compared to young BALB/c cells. Old NZB.xid donor marrow reconstituted splenic Thy-1, L3T4 and Lyt2 T cells to levels less than observed with NZB donor cells. Analysis of serum Ig in recipients of old NZB cells indicated higher levels of total IgM as compared to mice engrafted with NZB.xid cells, and anti-single stranded DNA antibodies were detected.