ID Bernstein

The CD34 antigen is expressed by 1% to 4% of human and baboon marrow cells, including virtually all hematopoietic progenitors detectable by in vitro assays. Previous work from our laboratory has shown that CD34+ marrow cells can engraft lethally irradiated baboons. Because the CD34 antigen has not been detected on most solid tumors, positive selection of CD34+ cells may be used to provide marrow cells capable of engraftment, but depleted of tumor cells. In seven patients with stage IV breast cancer and two patients with stage IV neuroblastoma, 2.5 to 17.5 x 10(9) marrow cells were separated by immunoadsorption with the anti-CD34 antibody 12-8 and 50 to 260 x 10(6) positively selected cells were recovered that were 64 +/- 16% (range 35% to 92%) CD34+. The patients received 1.0 to 5.2 x 10(6) CD34-enriched cells/kg after marrow ablative therapy. Six patients engrafted, achieving granulocyte counts of greater than 500/mm3 at 34 +/- 10 (range 21 to 47) days and platelets counts of greater than 20,000/mm3 at 46 +/- 14 (range 28 to 66) days posttransplant. Five of these patients showed durable engraftment until the time of death 82 to 386 days posttransplant. One patient failed to sustain engraftment associated with metastatic marrow disease. Three patients died at days 14, 14, and 17 posttransplant, two of whom had evidence of early engraftment. These studies suggest that CD34+ marrow cells are capable of reconstituting hematopoiesis in humans.

A monoclonal antibody, 12-8, prepared against KG-1a cells, recognizes an approximately 115-kd cell surface antigen and reacts with 3% to 4% of bone marrow cells, including most of the blast cells. The antigen is not expressed on peripheral blood cells. Marrow cells expressing 12-8 collected by fluorescence-activated cell sorting contained nearly all of the unipotent (CFU-GM, BFU-E) and multipotent (CFU-MIX) colony-forming cells. The isolated 12-8 positive marrow population also contained precursors of these colony-forming cells. In a two-stage long-term marrow culture system employing irradiated allogeneic marrow adherent cells, 12-8 positive cells produced both unipotent and multipotent colony-forming cells for ten weeks. Moreover, the output of colony forming cells substantially exceeded the input. Antibody 12-8 appears useful for analysis and possibly enrichment of hematopoietic progenitor cells that include colony-forming cell precursors.

We tested the ability of recombinant human stem cell factor (SCF) to stimulate isolated marrow precursor cells to form colonies in semisolid media and to generate colony-forming cells (CFC) in liquid culture. SCF, in combination with interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), or granulocyte colony-stimulating factor (G-CSF) caused CD34+ cells to form increased numbers of granulocyte-macrophage colonies (CFU-GM), and to form macroscopic erythroid burst-forming units (BFU-E) in the presence of IL-3, erythropoietin (Epo), and SCF. We tested isolated CD34+lin- cells, a minor subset of CD34+ cells that did not display antigens associated with lymphoid or myeloid lineages, and CD34+lin+ cells, which contain the vast majority of CFC, and found that the enhanced colony growth was most dramatic within the CD34+lin- population. CD34+lin- cells cultured in liquid medium containing SCF combined with IL-3, GM-CSF, or G-CSF gave rise to increased numbers of CFC. Maximal numbers of CFU-GM were generated from CD34+lin- cells after 7 to 21 days of culture, and required the presence of SCF from the initiation of liquid culture. The addition of SCF to IL-3 and/or G-CSF in cultures of single CD34+lin- cells resulted in increased numbers of CFC due to the proliferation of otherwise quiescent precursors and an increase in the numbers of CFC generated from individual precursors. These studies demonstrate the potent synergistic interaction between SCF and other hematopoietic growth factors on a highly immature population of CD34+lin- precursor cells.

Within the hematopoietic system, monoclonal antibodies reactive with antigenic determinants, expressed in a lineage- and stage-restricted fashion, can be used to map myeloid differentiation. We have generated a series of monoclonal antibodies that reacts with myeloid-associated determinants on committed myeloid stem cells and their progeny. Their reactivity with peripheral blood cells was identified by immunofluorescence assays, with bone marrow cells by fluorescence-activated cell sorting, and with committed hematopoietic progenitor cells by both cytotoxic assays and fluorescence-activated cell sorting. Antibody 1G10, which has previously been reported to react with cells of the granulocytic lineage and with a minor subset of mature monocytes, was shown to react with granulocyte-macrophage colony-forming units (CFU-GM). Three antibodies not previously characterized (T5A7, L4F3, L1B2) were shown to react with both granulocytic and monocytic cells and in fluorescence-activated cell sorting studies to detectably stain granulocytic cells at different stages of maturation. These three antibodies also react with CFU-GM, two (L4F3 and L1B2) reacting with all CFU-GM, while T5A7 reacts with only a portion of the day 7 CFU-GM. Antibody L4F3 also reacts with a portion of erythroid burst-forming units (BFU-E). In contrast, the previously reported antibody 5F1, which reacts with monocytic cells, nucleated erythroid cells, and platelets, was shown to react with erythroid colony-forming units (CFU-E). Potential applications of these antibodies to studies of normal and malignant hematopoiesis are discussed.

Recombinant human granulocyte-macrophage (GM) colony-stimulating factor (GM-CSF), G-CSF, and interleukin-3 (IL-3) labeled with 125I were used to study the characteristics and distribution of receptors for these factors on in vitro cell lines and on cells from patients with acute nonlymphocytic leukemia (ANL) and acute lymphocytic leukemia (ALL). Receptors for GM-CSF and G-CSF were restricted to a subset of myelomonocytic cell lines whereas IL-3 receptors were also found on pre-B- or early B-cell lines. Receptors for all three CSFs were broadly distributed on ANL cells, with considerable variability in levels of expression. Measurement of the colony-forming ability of ANL cells in response to the CSFs showed that there was no direct correlation between the ability of the cells to respond to a growth factor and the absolute number of receptors expressed for that growth factor. Binding of radiolabeled IL-3 and GM-CSF to ANL cells produced complex biphasic curves. Further analysis showed that both IL-3 and GM-CSF were able to partially compete for specific binding of the heterologous radiolabeled ligand to cells from several ANL patients, suggesting that heterogeneity may exist in human CSF receptors. These results provide new insights into the complex role that CSFs may play in ANL.