HIGH-DOSE THERAPY WITH PERIPHERAL BLOOD STEM CELL TRANSPLANTATION RESULTS IN A SIGNIFICANT REDUCTION OF THE HaEMOPOIETIC PROGENITOR CELL COMPARTMENT

In order to study the effect of high-dose therapy with peripheral blood stem cell transplantation (PBSCT) on the haemopoietic reserve in man, the number and composition of bone marrow (BM) and peripheral blood (PB)-derived progenitor cells were examined in 137 cancer patients. In 45 patients, paired samples from BM and PB were obtained before PBSC mobilization and 6–27 months after transplantation. Following PBSCT, the proportion of CD34⁺ cells was significantly smaller than before mobilization (BM 1.99±0.24 versus 0.8±0.09, P <0.001), and no change was observed at several follow-up visits thereafter.
The reduction was most pronounced for the primitive BM progenitor subsets such as the CD34⁺/DR⁻ and CD34⁺/Thy-1⁺ cells. The impairment of hematopoiesis was also reflected by a significant reduction in the plating efficiency of BM and PB samples.
No relationship was found between the decrease in the proportion of CD34⁺ cells and any particular patient characteristics, kind of high-dose therapy or the CD34⁺ cell content in the autograft.
In conclusion, high-dose therapy with PBSC transplantation is associated with a long-term impairment of the haemopoietic system. The reduction in the number of haemopoietic progenitor cells is not associated with a functional deficit, as peripheral blood counts post-transplantation were normal in the majority of patients.     

High levels of circulating haemopoietic stem cells in very early remission from acute non-lymphoblastic leukaemia and their collection and cryopreservation

S ummary . Circulating myeloid progenitor cells (PB CFU-GM) were measured in the peripheral blood of 13 patients with acute non-lymphoblastic leukaemia (ANLL) as they entered first remission. The mean of the recorded peak levels was 2796 × 10⁵ CFU-GM/1, representing a 2 5-fold increase above the mean value in normal subjects. These elevated levels of PB CFU-GM occurred regularly during the very early remission phase when platelet counts rose rapidly. Five of the patients had PB mononuclear cells collected by continuous-flow leukapheresis during this early recovery phase. CFU-GM were assayed as a measure of the number of haemopoietic stem cells in each collection. The cells were concentrated and then cryopreserved in liquid nitrogen. Leukapheresis was also performed on five normal subjects for comparison. Low numbers of CFU-GM were harvested from normal subjects, mean 033 ± 0-06 × 10⁴ CFU-GM/kg body weight for each leukapheresis. In ANLL patients entering remission, however, very large numbers of CFU-GM were regularly harvested. A mean of 11 ± 2 × 10⁴ CFU-GM/kg body weight were cryopreserved after each leukapheresis, representing 5 times the number of CFU-GM considered necessary for successful autologous haemopoietic reconstitution. Haemopoietic stem cell viability was assessed after varying periods of cryopreservation. There was no significant stem cell loss after up to 24 months storage. Thus, it is possible to collect and cryopreserve large numbers of CFU-GM and by inference pluripotent haemopoietic stem cells from the peripheral blood of patients with ANLL during very early remission. The possible biological and therapeutic implications are discussed.     

A comparative study of bone marrow and peripheral blood CD34+ myeloblasts in acute myeloid leukaemia

To examine the differences between primitive bone marrow (BM) and peripheral blood (PB) myeloblasts in acute myeloid leukaemia (AML), we compared CD34⁺ myeloblasts of paired BM and PB samples from 14 AML patients in terms of surface phenotype, homing and engraftment in a xenogeneic transplantation model, and gene expression, based on microarray studies and quantitative polymerase chain reaction. While there was no significant difference in surface phenotypes between these two populations, in vivo assay showed significantly better homing potential of PB CD34⁺ cells than BM CD34⁺ cells. Significant correlation between homing and engraftment in AML samples was also noted. In addition, gene expression profiling of CD34⁺ cells from five paired BM and PB leukaemic samples showed that genes involved in G-protein and prostaglandin signalling, chemotaxis and stress response, cell proliferation and apoptosis were down-regulated in PB CD34⁺ myeloblasts. These data suggested that circulating primitive myeloblasts in AML are functionally different from those residing in the marrow compartment, and such differences may be partly regulated by the BM microenvironment.     

The effect of interleukin-12 in ex-vivo expansion of human haemopoietic progenitors

Summary. We evaluated progenitor cell proliferation in cultures supplemented by different cytokine combinations in the presence or absence of IL-12. In cultures of low density cells, cytokine combinations including IL-12 were associated to a greater proliferation (up to 6.7 ± 2.5 CFU-GM fold expansion). However, in cultures of purified CD34⁺ cells the more efficient cytokine combination (147 ± 49 CFU-GM fold expansion) was SCF, IL-3, IL-11 and MlP-la, and the addition of IL-12 did not further enhance expansion of progenitors.
These results indicate that accessory cells, lost in CD34⁺ cell purification, could be in part responsible for IL-12 effect on progenitor cell proliferation. In CD34⁺ cell cultures the addition of IL-12 led to CD19 mRNA generation, suggesting that IL-12 acts on haemopoietic cells with both myeloid and lymphoid potential.     

In utero transplantation of human fetal haemopoietic cells in NOD/SCID mice

We have previously demonstrated that high levels of allogeneic, donor-derived mouse haemopoietic progenitor cells engraft following in utero transplantation in NOD/SCID mice. To evaluate whether the fetal NOD/SCID haemopoietic microenvironment supports the growth and development of human fetal haemopoietic progenitor cells, we injected fetal liver mononuclear cells (FL) or fetal bone marrow (FBM) derived CD34⁺ cells into NOD/SCID mice on day 13/14 of gestation. At 8 weeks of age 12% of FBM recipients and 10% of FL recipients were found to have been successfully engrafted with CD45⁺ human cells. CD45⁺ cells were present in the BM of all chimaeric animals; 5/6 recipients showed engraftment of the spleen, and 4/6 recipients had circulating human cells in the peripheral blood (PB). The highest levels of donor cells were found in the BM, with up to 15% of the nucleated cells expressing human specific antigens. Multilineage human haemopoietic engraftment, including B cells (CD19), myelomonocytic cells (CD13/33) and haemopoietic progenitor cells (CD34), was detected in the BM of chimaeric mice. In contrast, no human CD3⁺ cells were detected in any of the tissues evaluated. When the absolute number of engrafted human cells in the PB, BM and spleens of chimaeric mice was determined, a mean 16-fold expansion of human donor cells was observed. Although multilineage engraftment occurs in these fetal recipients, both the frequency and the levels of engraftment are lower than those previously reported when human cells are transplanted into adult NOD/SCID recipients.     

Thrombopoietin alone stimulates the early proliferation and survival of human erythroid, myeloid and multipotential progenitors in serum-free culture

We examined the effects of recombinant human thrombopoietin (TPO, c-Mpl ligand) on the proliferation and differentiation of human haemopoietic progenitors other than megakaryocytic progenitors using serum-free cultures. TPO alone supported the generation of not only megakaryocytic (MK) but also blast cell (blast) colonies from cord blood CD34⁺ cells. Delayed addition of a cytokine cocktail (cytokines; interleukin (IL)-3, IL-6, stem cell factor, erythropoietin, granulocyte-macrophage colony-stimulating factor, and TPO) to cultures with TPO alone on day 7 induced various colonies including granulocyte-macrophage (GM) colonies, erythroid bursts (E), granulocyte-erythrocyte-macrophage-megakaryocyte (GEMM) colonies. Replating experiments of blast colonies supported by TPO alone for culture with cytokines revealed that approximately 60% of the blast colonies contained various haemopoietic progenitors. Single cell cultures of clone-sorted CD34⁺ cells indicated that TPO supported the early proliferation and/or survival of both primitive and committed haemopoietic progenitors. In serum-free suspension cultures, TPO alone significantly stimulated the production of progenitors for MK, GM, E and GEMM colonies as well as long-term culture-initiating cells. These effects were completely abrogated by anti-TPO antibody. These results suggest that TPO is an important cytokine in the early proliferation of human primitive as well as committed haemopoietic progenitors, and in the ex vivo manipulation of human haemopoietic progenitors.     

Evaluation of 'discordant maturation' in chronic myeloid leukaemia using cultures of primitive progenitor cells and their production of clonogenic progeny (CFU-GM)

The 'discordant maturation hypothesis' proposes that the most mature proliferating cells in chronic-phase chronic myeloid leukaemia (CML) are responsible for the expansion of the Ph-positive population. To evaluate this hypothesis we used a delta assay for primitive haemopoietic cells (PΔ assay for PΔ cells) which allows investigation of the kinetics of granulocyte-macrophage progenitor (CFU-GM) production. The frequencies of these primitive (PΔ) cells were similar in CML blood (14.5/10⁵ mononuclear cells), CML marrow (17.3/10⁵) and normal marrow (11.6/10⁵) The average frequency in normal blood is only 0.58/10⁶. The absolute numbers of PΔ cells in CML patients are therefore greatly increased. The average numbers of CFU-GM produced by individual PΔ cells were reduced in CML blood (8.1) and marrow (11.6) compared with normal marrow (28.5). This is consistent with a reduced probability of differentiation at the single cell level in CML. Although the absolute number of CFU-GM produced by individual CML PΔ cells was subnormal there was a relative increase in the number of day 7 CFU-GM compared with the number of day 14 and 21 CFU-GM, which agrees with the 'discordant maturation hypothesis'. This bias towards day 7 colony formation could reflect accelerated maturation by the CFU-GM produced by PΔ cells or, alternatively, the production of CFU-GM with shorter than normal maturation pathways. Overall, these results suggest that discordant maturation does not by itself account for myeloid expansion in CML. It is more likely that myeloid expansion in CML is due mainly to an increase in the number of primitive haemopoietic progenitor cells.     

Rat liver biliary epithelial cells support long-term production of haemopoietic progenitors from human CD34+ cells

In this study we report the supportive activity of rat liver epithelial cells (RLEC) on human haemopoiesis in the absence of exogeneously supplied growth factors. RLEC is a rat cell line derived from primitive biliary cells with epithelial characteristics which induce the long-term differentiation of hepatocytes through cell–cell contacts. We have established the ability of these cells to sustain long-term survival and multilineage differentiation of human haemopoietic progenitors from unfractionated bone marrow and growth-factor mobilized peripheral blood cells, and from human CD34⁺ and CD34⁺ CD38⁻ haemopoietic cells, with a higher efficiency than the murine MS-5 stromal cell line: the numbers of committed progenitors recovered from RLEC cocultures after 8 weeks were 3-fold higher than from MS-5 cocultures, with an unusually high BFU-E production. Furthermore, using diffusible insert cultures, we demonstrated that, despite the lack of strong adhesive interaction between haemopoietic cells and RLEC, physical proximity was absolutely required for optimum stimulation of LTC-IC by RLEC. Taken together, these results show that biliary epithelial cells support human haemopoiesis and cause speculation that common mechanisms might be used by RLEC to regulate both the hepatocyte and the haemopoietic progenitors differentiation.     

Identification of early plasma cells in peripheral blood and their clinical significance

In the peripheral blood (PB) we detected so-called early plasma cells that might already be committed to entering the bone marrow (BM). By two-colour staining with FITC–anti-CD38 antibody, their intensity (CD38⁺⁺) of expression of CD38 antigen was between that of germinal centre (GC) B cells (low expression (CD38⁺)) and that of BM plasma cells (high expression (CD38⁺⁺⁺)), and their phenotype was CD38⁺⁺ CD19⁺ CD10⁻ CD20⁻ CD21⁺ CD24⁻ CD39⁺ CD5⁻ VLA-4⁺ VLA-5⁻ MPC-1⁻ without expression of surface membrane IgM (SmIgM). Morphological and immunological examination of the sorted cells confirmed that they were plasmacytoid cells with expression of cytoplasmic IgG (cIgG). Variations of these early plasma cells were examined in various diseases. In active systemic lupus erythematosus, bacterial septicaemia and liver cirrhosis, early plasma cell levels were significantly increased in PB, and after subsidence of such inflammation (inactive states) these cells returned to normal levels. In contrast, normal early plasma cells were significantly suppressed in myelomas, whilst normal or slightly increased numbers of early plasma cells was found in benign monoclonal gammopathy (BMG). In addition, the number of normal early plasma cells returned to a normal level in myeloma cases with complete responses. Therefore, early plasma cells were identified phenotypically, and an increase and decrease in these cells in PB may reflect mobilization and suppression, respectively, of activated B cells into BM plasma cells.     

A flow cytometric assay of CD34-positive cell populations in the bone marrow

Summary CD34⁺ BM cells form a heterogenous population of primitive stem cells and more mature progenitors committed to different lineages of differentiation. By combining CD45 expression with SSC, it is possible to separate immature cells from more diferentiated BM cells, and, by three-colour flow cytometry, analyse the antigens expressed in various subsets of cells. In this paper we show that in the normal BM at least four distinct CD34⁺ cell populations can be identified by their different patterns of CD45 expression and SSC. The most immature CD34⁺ cell population (0.1% of the BM cellularity) lacked all signs of lineage commitment and was CD45RA negative and only weakly CD45 positive. With increasing expression of the CD45 antigens, a second CD34⁺ population (0.2% of the BM cellularity) was formed expressing mainly primitive lymphatic antigens. However. 30% of the cells co-expressed B-cell line antigens and myeloid antigens. Cells committed to the myeloid cell line lost B-cell line antigens, gained CD45 antigen expression and SSC and formed two CD34⁺ cell population (0.2% and 0.1% of the BM cellularity. respectively) differing only with respect to the pattern of myeloid antigen expression and SSC characteristics. Similarly, differentiation along the lymphatic pathway implicated down-regulation of myeloid antigens, loss of the stem cell antigen and immature lymphatic antigens and gain of CD45 expression and mature lymphatic antigens.     

Early suppressive effects of chemotherapy and cytokine treatment on committed versus primitive haemopoietic progenitors in patient bone marrow

These studies investigated the effectiveness of in vivo administration of cytokines in ameliorating potential marrow damage induced by chemotherapy. Breast cancer patients received 5-fluorouracil, leucovorin, doxorubicin and cyclophosphamide (FLAC) followed by either GM-CSF, PIXY321, or no cytokine. Marrow was obtained before and after one or two cycles of FLAC once blood cell counts had recovered. Colony-forming units for granulocytes and macrophages (CFU-GM) were used to indicate the effect of therapy on recovery of committed progenitor cells responsible for early blood cell recovery. The frequency and number of CFU-GM in marrow obtained after FLAC + PIXY321 were significantly lower than in marrow obtained after FLAC + GM-CSF or FLAC without cytokine. CD34⁺ cell numbers were also reduced after FLAC + PIXY321. CFU-GM production in marrow long-term cultures (LTC) was used to assess the effect of therapy on primitive progenitors. After 5 weeks the number of CFU-GM in LTC of post-therapy marrow from all three treatment arms was < 15% of the number in pre-therapy LTC. Suppressive effects of FLAC on primitive progenitors were observed even when committed progenitors and CD34⁺ cells had recovered to pre-therapy levels. These results demonstrate that cytokine treatment did not ameliorate suppressive or toxic effects of FLAC on the functional integrity of the marrow.     

Comparative study of peripheral blood progenitor cell collection in patients with multiple myeloma after single-dose cyclophosphamide combined with rhGM-CSF or rhG-CSF

Summary. Patients suffering from high-risk multiple myeloma (MM) were randomized to receive single high-dose cyclophosphamide followed by either rhGM-CSF or rhG-CSF in order to harvest circulating peripheral blood progenitor cells. The safety of the procedure, the mobilization kinetics, the relative efficacy of rhGM-CSF and rhG-CSF to mobilize progenitor cells and their relative toxicity were studied. Special attention was paid to the antigenic profile of CD34⁺ progenitor cells.
Group I patients (n=ll) were treated with cyclophosphamide 4 g/m² i.v. followed by rhGM-CSF at 10 /ig/kg/d by subcutaneous administration. Group II (n=ll) patients received rhG-CSF s.c. at 10/zg/kg/d after the same dose cyclophosphamide. Both mobilization regimens appeared to be equally effective. No significant differences in absolute numbers of circulating progenitors, determined by CD34 expression or in yields of MNC, CFU-GM, BFU-E and CD34 subsets were observed. rhGM-CSF administration resulted however in delayed haemopoietic recovery and an increased complication rate.
We conclude that rhG-CSF may be preferred because of its markedly lower toxicity and lower in-hospital costs.     

Separation of G-CSF-mobilized PBSC transplants by counterflow centrifugal elutriation: modest enrichment of CD34+ cells but no loss of primitive haemopoietic progenitors

The suitability of counterflow centrifugal elutriation (CCE) for reduction of the number of non-stem cells in autologous G-CSF-mobilized peripheral blood stem cell (PBSC) transplants was investigated. By cell size-monitored CCE, small cells could be rapidly separated from the haemopoietic progenitor cells present in leukapheresis product (LP) samples. The large cell fraction contained an average 86 ± 25% of the CD34⁺ cells and 76 ± 20% of the granulocyte-macrophage progenitors (CFU-GM) loaded into the separation chamber, and was depleted of 75 ± 18% of the lymphocytes, 89 ± 7% of the erythrocytes and 98 ± 2% of the platelets ( n  = 21). Due to the presence of high numbers of large immature myeloid cells, which co-elutriated with progenitor cells, enrichment of CD34⁺ cells in the large cell fraction was only modest (average 1.8 times). No indication of preferential co-elutriation of primitive stem cells with the small cells was obtained. There was no difference in expression of CD38 or Thy-1 on CD34⁺ cells between the two elutriation fractions. Frequencies of cobblestone-area-forming cells (CAFC) week 6, which are considered to represent cells with long-term repopulating ability, were reduced in the small cell fractions as compared to those in the unseparated samples and the large cell fractions. On average, 100% of CAFC week 6 were recovered in the large cell fractions ( n  = 5). In conclusion erythrocytes, platelets and 40–50% of leucocytes can be depleted from G-CSF-mobilized PBSC samples by CCE with an almost complete recovery of both clonogenic and primitive stem cells.     

In vitro growth of human fetal CD34+ cells in the presence of various combinations of recombinant cytokines under serum-free culture conditions

Summary. CD34⁺ cells were purified from midtrimester human fetal blood and adult bone marrow samples and seeded in serum-free fibrin-clot cultures in order to evaluate the number and the responsiveness to recombinant cytokines of pluripotent (CFU-GEMM), erythroid (BFU-E), megakaryocyte (BFU-meg and CFU-meg) and granulocyte/macrophage (CFU-GM) haemopoietic progenitor cells.
The number of the different haemopoietic progenitors/1 × 10³ CD34⁺ cells, except CFU-meg, was significantly higher in fetal blood than in adult bone marrow in cultures stimulated by any combination of cytokines including interleukin-3 (IL-3), granulocyte/macrophage colony stimulating factor (GM-CSF) or stem cell factor (SCF) plus erythropoietin (Epo). Nevertheless, whereas adult BFU-E showed a maximal growth in the presence of Epo plus IL-3 or Epo plus SCF, fetal BFU-E showed an optimal growth in the presence of Epo alone, the sensitivity of fetal BFU-E to suboptimal concentrations of Epo being approximately 10–15-fold higher than that of adult BFU-E. Addition of optimal concentrations of IL-3, GM-CSF or SCF, alone or in various combinations, to Epocontaining cultures induced a significant increase in both the number and size of fetal CFU-GEMM, and CFU-GM, and a parallel decrease of fetal BFU-E. Finally, SCF potently syner-gized with IL-3 in increasing the growth of both classes of fetal megakaryocyte progenitors, BFU-meg and CFU-meg.     

The Labelling Index of Primitive Plasma Cells Determines the Clinical Behaviour of Patients with Myelomatosis

For patients with multiple myeloma the most important laboratory correlate of prognosis and disease activity is the bromodeoxyuridine (BrdUrd) plasma cell labelling index (LI). However, the traditional immunofluorescent microscope LI technique, like other manual enumeration assays, can suffer from poor precision and accuracy. In this study the LI of different subpopulations of plasma cells (CD38⁺⁺) as determined by flow cytometry was correlated with disease state. The mean LI of the total CD38⁺⁺ population was significantly higher (2.7±0.4%) than the LI determined by the traditional slide technique (0.6±0.1%) for 65 samples tested. Primitive plasma cells (CD38⁺⁺, CD45⁺⁺) had a higher labelling index than mature plasma cells (CD38⁺⁺, CD45⁻) (7.0±1.3% v 1.8%±0.3%) and in one patient the LI of the primitive plasma cells was 46%. In addition, the LI of the mature plasma cells was lower than the total plasma cell population. As expected, there was a significant difference between the LI of patients in plateau phase and progressive disease but this difference was greatest when the LI of the primitive plasma cells was studied (9.2±2.9% v 2.2±0.7%; z =19.9, P <0.001). This study has raised some concerns about the sensitivity and accuracy of the traditional labelling index and has shown that the increased LI associated with progressive disease is almost entirely attributable to an increase in the LI of the primitive plasma cell subpopulation and that the LI of primitive plasma cells provides a more clinically significant correlation with disease status than the traditional assay.     

Peripheral blood stem cell mobilization using high-dose cyclophosphamide and G-CSF in pretreated patients with lymphoma

Summary. Peripheral blood stem cell (PBSC) mobilization for autologous transplantation is more difficult in treated patients and those with bone marrow involvement. In 17 pretreated lymphoma patients, cyclophosphamide (4 g/m²) and G-CSF mobilized a median circulating peak of 1959 CFU-GM/ml on day 12.5. PBSC harvesting commenced when WBC was 1×10⁹/l at day 10.5 collected a median of 21.2 × 10⁴/CFU-GM/kg. 13/17 (76%) patients exceeded the 10 × 10⁴ CFU-GM/kg threshold for engraftment. The CFU-GM yield was significantly higher in patients whose WBC recovered from 1–5 × 10⁹/1 in less than 3 days and correlated with the maximum WBC pre and post the cyclophospharnide induced nadir. This regime safely mobilized adequate PBSC in the majority of pretreated lymphoma patients.     

A novel surface marker (B203.13) of human haemopoietic progenitors, preferentially expressed along the B and myeloid lineages

We used a monoclonal antibody (mAb) (B203.13, IgM) generated from a mouse immunized with the human B/myeloid bi-phenotypic B1b cell line, to analyse haemopoietic cells. The antigen recognized by this mAb is expressed on most adult and umbilical cord blood CD21⁺ B cells, at minimal density on mature monocytes, and is undetectable on granulocytes, T, natural killer (NK) cells, and erythrocytes. Within umbilical cord blood and adult bone marrow haemopoietic progenitor cells, the B203.13 mAb recognized a surface marker, present on progenitor cells of several haemopoietic lineages, that was transiently expressed on early erythroid and T/NK progenitors, and was preferentially maintained on cells of the B and myeloid lineages. Within the CD34⁺ cells, B203.13 was expressed on early committed myeloid (CD33⁺) and erythroid (CD71^dim) progenitor cells, as confirmed in colony formation assays. The mAb also reacted with cells of B and myeloid chronic leukaemias and cell lines. These data define B203.13 mAb as a novel reagent useful for the characterization of haemopoietic progenitors and leukaemias.     

Selective enrichment in human megakaryocyte progenitors by the B203.13 surface differentiation antigen

The B203.13 monoclonal antibody specifically recognizes a subset (8–18.5%) of human CD34⁺ haemopoietic progenitors, which are significantly ( P  < 0.05) enriched in megakaryocyte progenitors (CFU-meg). Moreover, B203.13 expression was progressively lost as maturation proceeded along the megakaryocytic lineage. In fact: (i) CFU-meg derived from CD34⁺/B203.13⁺ showed a greater number of cells/colony with respect to CD34⁺/B203.13⁻; (ii) after 10 d of liquid cultures with 100 ng/ml of thrombopoietin, only a minority of CD34-derived cells positive for CD41 coexpressed B203.13; (iii) in situ immunocytochemical staining revealed that B203.13 was expressed exclusively on immature megakaryoblasts; (iv) circulating platelets did not express B203.13.     

Increased number of peripheral blood CD34+ cells in lithium-treated patients

Eight adult patients with bipolar disorder were prospectively examined to find whether lithium carbonate increased their peripheral blood CD34⁺ haemopoietic stem cells. Following lithium therapy for 3–4 weeks their neutrophil counts increased by a mean of 88% (from 4625 ± 1350 × 10⁹/l, mean ± SD pretreatment, to a peak of 8300 ± 3910 × 10⁹/l). Concommitantly, there was a significant increment in their CD34⁺ cells (from 0.11 ± 0.01% to a peak of 0.18 ± 0.08%). There was a significant correlation between the rise in neutrophil count and that of the CD34⁺ cells ( r  = 0.795, P  = 0.019). Lithium therapy may be used to mobilize peripheral blood CD34⁺ cells for marrow transplantation.     

Effect of hepatocyte growth factor on early human haemopoietic cell development

Hepatocyte growth factor (HGF) stimulates cell proliferation, differentiation and migration by binding to its receptor, MET R. Whether the HGF/MET R axis plays an important regulatory role in human haemopoietic cell growth is an unresolved issue. To investigate this situation, we employed several complementary strategies including RT-PCR, FACS analysis, and mRNA perturbation with oligodeoxynucleotides (ODN). We found that very primitive, FACS sorted, CD34⁺ Kit⁺ marrow mononuclear cells (MNC) failed to express RT-PCR detectable MET R mRNA. In contrast, MET R expression was easily detectable by RT-PCR in marrow stroma fibroblasts, in cells isolated from BFU-E and CFU-GM colonies, and in unselected normal MNC. Subsequent FACS analysis revealed that MET R protein was detectable on ∼5% of the latter cells. HGF, at concentrations of 1–50 ng/ml, had no demonstrable effect on survival or cloning efficiency of normal CD34⁺ MNC in serum-free cultures. Antisense ODN mediated perturbation of MET R mRNA expression in normal CD34⁺ MNC, with FACS documented decline in protein expression, had no effect on the ability of these cells to give rise to haemopoietic colonies of any lineage. We also examined the biology of HGF/MET R expression in malignant haemopoietic cells. Using the strategies described above, we found that MET R mRNA was expressed in many human haemopoietic cell lines, and that the protein was expressed at high levels on HTLV transformed T lymphocytes. Wild-type CML and AML blast cells also expressed MET mRNA, and HGF was able to co-stimulate CFU-GM colony formation in ∼20% of cases studied. Therefore, although the HGF/MET R axis appears to be dispensable for normal haemopoietic cell growth, it may play a role in the growth of malignant haemopoietic progenitor cells.