Human erythropoietin-specific sites of monoclonal antibody-mediated neutralization.

Recombinant human erythropoietin (rhuEpo)-specific mouse monoclonal antibodies (MoAbs) have been produced and characterized. All antibodies were specifically reactive with rhuEpo in enzyme-linked immunosorbent assay (ELISA). Epitope exclusion studies showed three distinct epitope regions, A, B, and C, recognized by neutralizing MoAbs. An additional epitope region D was recognized by non-neutralizing MoAbs. Antibodies defining an epitope region competed with each other for binding sites, but did not compete with antibodies defining a different epitope region. Group B antibodies were able to compete for the receptor binding site on rhuEpo with a soluble human Epo-receptor-lg fusion protein. No single peptide sequences were found to specifically interact either with group B MoAbs or with the rhuEpo-receptor. Therefore, it is suggested that epitope region B and the receptor binding site share binding determinants that are primarily composed of conformational epitopes. Because group A and group C antibodies did not compete with the receptor for binding to the receptor binding site of the rhuEpo molecule, it is suggested that neutralization via epitope regions A and C is mediated through binding inhibition caused by conformational changes, transmuting the binding site(s) for the receptor. Conversely, binding to the receptor seems to induce conformational changes in the hormone molecule, eliminating epitopes for group A and C antibodies.

Haematological effects of rhGM-CSF in dogs exposed to total-body irradiation with a dose of 2.4 Gy.

It was the specific aim of this study to test the stimulatory effects of recombinant human GM-CSF (rhGM-CSF) on haemopoietic regeneration in dogs which had received total-body irradiation (TBI) with a dose of 2.4 Gy. In normal dogs rhGM-CSF given subcutaneously at 10 microgram/kg per day or 30 microgram/kg per day for 21 days caused strong but transient increases in the peripheral blood neutrophils. The monocyte counts also showed a transient rise during treatment in a dose-dependent fashion, whereas the lymphocyte counts increased only at the higher dose of rhGM-CSF and the platelet counts were transiently depressed during the course of the treatment. In the irradiated animals treatment with rhGM-CSF decreased the severity and shortened the duration of neutropenia but had no significant influence on monocyte or lymphocyte recovery. The granulocyte values showed a characteristic pattern of fluctuations with the first peak occurring at the same time (day 10 to day 13) when the abortive rise was observed in the untreated dogs. In contrast the GM-CFC in the peripheral blood remained depressed during the whole treatment course, similar to the untreated irradiated controls. These results indicate that treatment with GM-CSF can be an effective biological monotherapy for radiation-induced bone marrow failure, but that for higher radiation doses the number of GM-CSF responsive target cells will become a critical determinant of therapeutic efficacy.

Studies on the efficacy of mast cell growth factor (c-kit ligand) in vitro as well as in vivo.

We tested the ability of recombinant human (rhu) mast cell growth factor (MGF), also known as c-kit ligand, to stimulate the colony formation of human bone marrow cells in semisolid medium alone and in combination with rhu erythropoietin (EPO), rhu Interleukin 3 (IL-3), rhu granulocyte colony stimulating factor (G-CSF) and rhu granulocyte-macrophage colony stimulating factor (GM-CSF). The addition of MGF to cultures containing EPO or EPO + IL-3, GM-CSF and G-CSF, resp., resulted in macroscopic erythroid burst-forming units (BFU-E). Multipotential (colony-forming unit granulocyte, erythroid, monocyte, megakaryocyte [CFU-GEMM]) progenitors were stimulated by MGF in the presence of EPO. Colony-forming unit granulocyte-macrophage (CFU-GM) were activated by MGF only in combination with GM-CSF. The combination of MGF with EPO was used for synergism studies in healthy cynomolgus monkeys. In the chosen concentration MGF alone had no effect on white blood cell (WBC) counts and on platelets, but a slight effect on reticulocytes. EPO by itself increased reticulocyte counts with no effects on WBC or platelets. The combination of both factors resulted in a significant increase of reticulocytes. No other effects were seen. These studies demonstrate the potent synergistic interaction of MGF and other hematopoietic growth factors.

Bone marrow obtained during hip surgery: a novel source for studies of hemopoiesis in human long-term bone marrow culture (LTBMC).

Studies with human bone marrow cells are often impaired by the poor quality of sternal aspirates due to varying numbers of contaminating blood cells before enrichment procedures and insufficient progenitor cell yields. In this study we report on experiments performed with human bone marrow cells isolated from a) spongiose bone fragments collected during hip surgery in patients with osteoarthritis or b) sternal aspirates. After Ficoll-Histopaque density gradient centrifugation absolute cell numbers were always lower in the samples obtained from sternal aspirates. However, both sources proved to yield the same proportions of the respective myeloid cell populations. Human long-term bone marrow cultures (LTBMC), semi-solid agar assays (CFU-GM day 14), and 3H-thymidine incorporation assays proved the comparability of the two bone marrow sources.

Development of a rapid, highly sensitive, non-radioactive assay system for hematopoietic growth factors.

The aim of this study was to develop non-radioactive cell line proliferation assays. The human leukemic cell line TF1 (Kitamura et al., 1989) was used for the determination of the specific biological activity of recombinant human (rhu) granulocyte-macrophage colony-stimulating factor (GM-CSF) and rhu Interleukin 3 (IL-3) by a simple and economical fluorometric assay with a sensitivity similar to the measurement of 3H-thymidine uptake. The TF1 cell line responds to rhu IL-3, rhu GM-CSF and to a lesser extent to rhu Erythropoietin (EPO) and mast cell growth factor (MGF), but not to rhu G-CSF. It is dependent upon rhu GM-CSF for survival in culture. For the proliferation assay 1 x 10(4) TF1 cells were incubated with 20 ng - 0.256 pg rhu GM-CSF or rhu IL-3 at 37 degrees C and 5% CO2 in humidified atmosphere. After 48 h the cells were washed twice with PBS and were incubated with 4-Methylumbelliferyl-heptanoate for 60 min. Fluorescence was determined on a Titertek Fluoroskan II (Flow Lab.), and results were given as fluorescence units using a 355 nm excitation filter and a 480 nm emission filter. The developed assay showed an interassay variability lower than 15%. The sensitivity of the proliferation assays in the same range as the thymidine incorporation assays.

Evidence for the location of the receptor-binding site of human erythropoietin at the carboxyl-terminal domain.

Five different peptides (P1: 84-95; P2: 152-166; P3: 52-63; P4: 7-23; P5: 110-123) homologous to relatively hydrophilic regions of human erythropoietin (huEpo) have been synthesized to identify biologically active domains of the hormone. All peptides were able to induce high titers of peptide-specific antibodies in rabbits. Antisera from rabbits induced by recombinant huEpo (rhuEpo) contained a relatively high amount of antibodies preferentially directed against three peptides (P2, P4, and P5), of which P4 comprised the amino-terminal region, P2 the carboxyl-terminus, and P5 an interior region previously described as the receptor-binding site. The same three peptides were able to induce rhuEpo-specific antibodies, whereas P1 and P3 lacked this activity. Only peptide-P2-induced antisera inhibited the biologic activity of rhuEpo in a cell proliferation assay, indicating that the carboxyl-terminal region of the molecule is essentially involved in the biologic function of rhuEpo.