Hemopoietic precursor cells in human peripheral blood

Interferon-gamma-mediated suppression of erythroid progenitor growth by a HLA-DR- and CD4-positive subset of T lymphocytes in acute myeloid leukemia

In this study, we examined the effects of peripheral blood T lymphocytes from patients with acute myeloid leukemia (AML) on marrow-derived erythroid progenitors (BFU-DE and CFU-DE) growth in an in vivo culture by using the plasma clot diffusion chamber (DC) technique. The application of double-compartment chambers (each compartment separated by a membrane filter) makes the investigations of humoral effects of T lymphocytes upon marrow erythroid progenitors proliferation possible. T lymphocytes of AML-patients in the absence of a statistically significant number of monocytes suppressed the growth of BFU-DE and CFU-DE from T lymphocyte- and adherent cell-depleted marrows. The inhibition ability was restricted to the CD4-positive enriched fraction obtained from T cells by using the negative selection technique. In contrast, the CD8-positive enriched fraction had no effect on erythroid colony formation. Autologous and allogeneic BFU-DE and CFU-DE were similarly affected by the CD4-positive T cells. Treatment of T cells with monoclonal antibodies against HLA-DR before cocultures, completely abrogated the suppression of BFU-DE and CFU-DE-derived colony formation. Suppressive activity detected in the CD4-positive T cells was also totally abolished by treatment with anti-interferon-gamma antibodies; whereas the inhibition was retained after 30 Gy radiation. Under these experimental conditions, resting T lymphocytes from healthy subjects did not affect the erythroid colony formation. Our data show that in AML-patients, a circulating HLA-DR-positive, less radiosensitive subset within the CD4-positive T cells is capable of inducing an interferon-gamma-mediated suppression of erythropoiesis, at least in DC culture.

Impaired release of colony stimulating activity by monocytes from Hodgkin's disease in response to phorbol myristate acetate activation

We assessed the humoral effect of resting and phorbol esters preincubated monocytes from Hodgkin's disease patients (HDMo) and healthy subjects (nMo), on granulocyte progenitors (CFU-dG) growth using a double diffusion chamber technique. The release of colony stimulating activity and indomethacin-dependent inhibitors by resting HDMo and nMo was found to be cell-concentration dependent. However, phorbol myristate acetate preincubated HDMo (PMA-HDMo) in contrast to nMo at low concentrations (2.5 x 10(4] were unable to increase the CFU-dG growth stimulation. On the other hand, at a higher cell number (5 x 10(4], phorbol treated HDMo stimulated the myeloid colony formation, whereas nMo suppressed the CFU-dG proliferation. Further enhancement of HDMo and nMo concentrations induced a pronounced inhibition of CFU-dG-derived colony formation, caused by an increased PGE2 production. After incubation with the cyclooxygenase inhibitor-indomethacin, PMA-HDMo showed considerably more granulocyte colony formation than nMo. Our results suggest that the observed abnormalities in the function of HDMo could be associated with an excessive production of PGE2 and a general dysfunction of these cells in Hodgkin's disease.

Diffusion chamber colony-forming unit (CFU-d): a primitive stem cell

Assay of hematopoietic precursor cells in diffusion chambers (DCs) implanted intraperitoneally in experimental animals provides a powerful tool for studying stem cell kinetics in vivo. In this system, the effect of cell migration (which complicates whole animal studies) is eliminated because the membranes utilized in the construction of the chambers are impermeable for cells, while permitting free passage of molecules present in the humoral phase of the host. As judged by light microscopy, conditions in the DC cultures primarily favor macrophage and granulocyte growth. However, the use of in vitro and in vivo subculture to further analyze chamber contents has demonstrated that the system supports proliferation of early hematopoietic progenitors. Additionally, cells capable of rescuing lethally irradiated mice proliferate in DC cultures. Development of the plasma clot DC technique has revealed that most of the growth occurs in colonies which are derived from single cells (CFU-d). Characterization of these cells indicates that they are at least as primitive as other colony-forming cells and, also based on subculture studies, can differentiate along several hematopoietic lineages. In addition to normal CFU-d, both embryonal and leukemic cells can give rise to granulocytes, macrophages, megakaryocytes and erythroid cells in the DC cultures. Evaluation of the effects of humoral factors on hematopoietic cell proliferation and differentiation in the system has led to the identification of both stimulators and inhibitors that may be different from the well-characterized cytokines. Thus, the system seems to be useful for detecting molecules controlling the most primitive stages of hematopoiesis. We believe that the DC culture technique holds enormous potential in the study of stem cell proliferation and differentiation in vivo.

Granulocyte progenitors (CFU-D) in neutrophilic leukemoid reaction are hyporesponsive to macrophage-induced inhibition

The responsiveness of marrow granulocyte progenitors (CFU-D) to macrophage-derived stimulatory and inhibitory factors has been studied using diffusion chamber technique in 12 patients with neutrophilic leukemoid reaction (with granulocyte count in the range between 10-40 G/l) and ten healthy subjects. CFU-D from patients with neutrophilic leukemoid reaction (NLR) revealed a normal reactivity to colony-stimulating activity, whereas they were hyporesponsive to macrophage-derived indomethacin-sensitive inhibition. This altered response was correlated both with the concentration of granulocyte progenitors in the S phase and with blood neutrophilic leukocytosis. In patients with higher granulocyte count and increased concentration of CFU-D during active DNA synthesis a more pronounced hyporesponsiveness of granulocyte progenitors to macrophage-induced inhibition has been found.

Separation by velocity sedimentation of human haemopoietic precursors forming colonies in vivo and in vitro cultures

Cells which give rise to granulocyte-macrophage colonies under the influence of peripheral blood white cells (CFU-c (WBC] and Mo T cell conditioned medium (CFU-c (Mo] sedimented at a faster rate than the cells which form mixed erythroid-granulocytic colonies in methylcellulose in vitro (CFU-mix) and granulocytic (CFU-dg) and megakaryocytic (CFU-dm) colonies in diffusion chambers in mice. Despite identical peak sedimentation rate for the two CFU-c populations, sedimentation profiles suggest that they are heterogeneous with respect to size. A proportion of CFU-c (Mo) may be identical with CFU-dg and CFU-mix. Sedimentation profiles for cells which give rise to mixed colonies in vitro (CFU-mix) and to granulocytic colonies in diffusion chambers in cyclophosphamide pretreated mice (CFU-dg (CY] and in Mo conditioned medium treated mice (CFU-dg (Mo] were similar. On the average CFU-dm sedimented somewhat slower than CFU-dg. These and other observations suggesting a close relationship between CFU-dg and multipotential haemopoietic precursors are discussed.

Density distribution of chronic myeloid leukaemia and normal colony-forming cells in diffusion chambers (CFU-D) and agar (CFU-GM)

The density distribution in Percoll gradients of clonogenic cells forming colonies in diffusion chambers (CFU-D) or in agar culture (CFU-GM) was studied in chronic myeloid leukaemia (CML). The density distribution of CFU-GM in CML was homogeneous with peaks within 1.058-1.061 g/ml, which is slightly lower than normal. CFU-D, on the other hand, showed heterogeneous distributions both in CML and in normal controls. Two separable populations of CFU-D were recognized, one with the same or lower density than CFU-GM that formed almost exclusively neutrophilic colonies in diffusion chambers, and a second population concentrating in the density range 1.068-1.075 g/ml which primarily formed macrophage colonies. The second population contained colony-forming cells derived from both Fc-receptor positive and Fc-receptor negative precursor cells, suggesting that at least some colonies in diffusion chambers arise from Fc-receptor positive granulopoietic cells of intermediate maturity and/or monocytes. The concentration of CFU-D in peripheral blood was increased 40- to 100-fold in 2 patients currently off treatment who had increased WBC counts.

Granulopoietic precursors in chronic neutropenia

11 patients with chronic neutropenia were evaluated. In 6 patients low numbers of CFU-DG were observed. Only 3 of these patients also had low CFU-C numbers, suggesting that these two precursors are not identical. Bone marrow samples from 2 patients were restudied a year later. The number of CFU-DG remained low while CFU-C numbers increased to control range in 1 patient. Studies for serum inhibitors were negative. No cytogenetic abnormalities were observed. This study suggests that abnormalities at different levels in the haemopoietic precursor cell hierarchy can be detected either simultaneously or independently in patients with chronic neutropenia.

Effect of cooling rate on human and murine hemopoietic precursor cell recovery

The effect of cooling rate on recovery of human and murine hemopoietic precursor cells was studied. In the presence of 10% Me2SO, a cooling rate of 7 degrees C/min from -4 to -30 degrees C was optimal for recovery of both human and murine precursor cells which give rise to colonies in diffusion chambers implanted in mice (CFU-DG). Cooling of human marrow at a rate between 3 and 7 degrees C/min resulted in the best CFU-C recovery, although no good correlation between the cooling rate and murine CFU-C recovery was demonstrated. These data suggest that recovery of the primitive hemopoietic precursor cells can be improved by changing the standard cryopreservation programs used presently. However, improved recovery of CFU-DG does not necessarily translate into faster reconstitution of hemopoiesis. No significant difference was observed in overall recovery of bone marrow cellularity in lethally irradiated mice following injection of untreated marrow and marrow cooled at a rate of 1 and 7 degrees C/min.

Expression of common acute lymphoblastic leukaemia antigen and terminal deoxynucleotidyl transferase in normal mononuclear blood cells during diffusion chamber culture

Peripheral mononuclear blood cells of 2 healthy individuals were cultured over a 13 d period in diffusion chambers. A high percentage of cALL antigen positive cells and later on TdT containing cells appeared during culture. The cALL+ cells could be clearly distinguished into 2 groups: a population with weak and diffuse fluorescence and a small number of ring-like brightly dyed cells. The first group develops into TdT+ cells and therefore resembles immature T-cells. The interpretation of the ring-like stained cells is still preliminary, but it cannot be excluded, that these cells represent a cell population with more than lymphatic differentiation capacity.