Evidence for absence of toxicity of T101 immunotoxin on human hematopoietic progenitor cells prior to bone marrow transplantation.

T101-ricin A-chain immunotoxin is a hybrid molecule made up of the T101 monoclonal antibody bound to the A-chain of ricin. It specifically destroys cells expressing the cell surface T65 antigen. We have designed a preclinical study to evaluate its possible use for the in vitro treatment of T-cell hematological cancers prior to autologous bone marrow transplantation. The data presented here show that conditions previously defined to produce high tumor cell killing, i.e., a 20-hr incubation at 37 degrees in the presence of T101-ricin A-chain immunotoxin up to 10(-7) M in a 10 mM ammonium chloride solution, do not affect the in vitro proliferative capacity of human hematopoietic stem cells studied by means of semisolid medium cultures (granulocyte-macrophage progenitors, burst-forming units-erythrocyte) and continuous liquid cultures (pre-granulocyte-macrophage progenitors). Therefore, autologous bone marrow transplantation with T101-ricin A-chain immunotoxin-treated graft should be feasible.

Hemoglobin Cochin-Port-Royal: consequences of the replacement of the beta chain C-terminal by an arginine.

Hemoglobin Cochin Port-Royal beta 146 (HC3) His yields Arg is the second example in which the beta C-terminal residue is replaced. Owing to the known importance of His beta 146 in the co-operative effects of hemoglobin, the functional properties of this variant were carefully studied. It had a normal Hill coefficient but a reduced alkaline Bohr effect. However, the reduction in Bohr effect is less than the halving predicted from previous mutants and modified hemoglobins.

The role of autologous bone marrow transplantation in 46 adult patients with non-Hodgkin's lymphomas.

Forty-six patients with non-Hodgkin's lymphoma (NHL) were treated with autologous bone marrow transplantation (ABMT) in two different institutions. All patients were pretreated with conventional chemotherapy. Three different conditioning regimens were used, and 20 patients underwent bone marrow purging. Twelve patients were treated in first complete remission (CR); eight are in unmaintained CR 8 to 104 months after ABMT. Five patients were grafted in first partial remission (PR) after conventional therapy; all achieved CR, and all remain in prolonged CR (first CR for four patients, second CR for one patient). Of 21 patients with chemosensitive relapses, 13 patients are in prolonged unmaintained CR 8 to 94 months after ABMT. Eight patients with resistant disease remained uncured by ABMT; all eight died, six from progressive illness and two from toxicity. The current 3-year disease-free probability is 60% for all patients, 0% for refractory disease; 82% for first PR or CR, and 60% for sensitive relapses (SRs). These results confirm the efficacy of ABMT in the treatment of chemosensitive NHL with bad prognosis.

Autologous stem-cell transplantation for non-Hodgkin's lymphomas: the role of graft purging and radiotherapy posttransplantation--results of a retrospective analysis on 120 patients autografted in a single institution.

PURPOSE: To analyze retrospectively survival and prognostic factors of patients with non-Hodgkin's lymphoma (NHL) autografted from 1979 to 1995 in a single institution. PATIENTS AND METHODS: A total of 120 patients, 64 with aggressive and 56 with low-grade NHL, were autografted. The carmustine (BCNU), etoposide, cytarabine, and melphalan (BEAM) regimen was used in 104. The autograft was marrow in 101 patients. Marrow was purged in vitro by mafosfamide for 63 patients (adjusted dose [AD] in 32; unique dose [UD] in 31); 27 patients received a CD34+-selected graft. Following intensification, 45 patients received additional radiotherapy on previous sites of involvement. RESULTS: Outcome at 5 years for patients transplanted with low-grade NHL in first complete remission (CR1), in first partial remission (PR1), and in second complete remission (CR2) or beyond showed an event-free survival (EFS) of 75% +/- 12%, 46% +/- 18%, and 57% +/- 24%, a relapse incidence (RI) of 21% +/- 12%, 49% +/- 19%, and 43% +/- 25%, and a transplant-related mortality (TRM) of 5% +/- 5%, 10% +/- 7%, and 0%, respectively. For patients with aggressive NHL transplanted in CR1, in PR1, in CR2 or beyond, and in resistant relapse or in primary refractory disease, the EFS was of 73% +/- 9%, 58% +/- 19%, 29% +/- 16%, and 10% +/- 9%, the RI 22% +/- 9%, 14% +/- 9%, 77% +/- 18%, and 66% +/- 20%, and the TRM 6% +/- 6%, 32% +/- 21%, 11% +/- 10%, and 71% +/- 22%, respectively. In patients autografted upfront in first remission, additional radiotherapy was associated with a higher EFS, in univariate (P = .03) and multivariate analysis (P = .02, relative risk [RR] = .021). The role of graft purging with mafosfamide on the outcome reflected by the dose of colony-forming unit-granulocyte-macrophage (CFU-GM) per kilogram infused postpurging was assessed by univariate analysis: patients in first remission who received lower doses of CFU-GM had a lower RI and a higher EFS. CONCLUSION: This retrospective analysis suggests that marrow purging and posttransplant radiotherapy improve the outcome of patients with NHL autografted in first remission.

Autologous bone marrow transplantation with marrow purged by mafosfamide in seven patients with myelodysplastic syndromes in transformation (AML-MDS): a pilot study.

Seven patients with acute myeloblastic leukemia (AML) occurring on myelodysplastic syndromes (MDS) were consolidated while in complete remission (CR) by autologous bone marrow transplantation (ABMT) with a marrow purged in vitro by mafosfamide. The median age of population was 44 years (range 39-55). MDS FAB diagnosis was established before progression to AML in five patients: refractory anaemia with excess of blast (RAEB) in three patients, RAEB in transformation (RAEB-t) in one patient, and chronic myelomonocytic leukemia (CMML) in one patient. In the remaining two patients, the diagnosis of MDS (as a secondary malignancy in one) was made retrospectively at time of overt AML. Three out the seven patients had karyotypic abnormalities. The median interval between the obtention of CR and ABMT was 7 months (range 6-18). One patient died from transplant related toxicity. Engraftment occurred at a median of 41 days (range 27-60), for white blood cells (> 10(9)/l) and 120 days (range 60-180) for platelets (> 50 x 10(9)/l). Four patients relapsed at 2.5, 6.8, and 25 months post-ABMT. Two patients are alive and well at 10 and 28 months, respectively. ABMT with marrow purged by mafosfamide is feasible in patients with AML following MDS with a prospect of cure. However, further studies are needed to assess the real value of this approach.

A long-term follow-up of 33 patients with non-Hodgkin's lymphoma who received the BEAM high-dose intensification regimen with cytokine support only and no transplant.

High-dose intensification and autologous stem-cell transplantation (ASCT) is widely used to consolidate patients with non-Hodgkin's lymphoma (NHL), who have reached a stage of minimal residual disease. However, patients with persisting marrow and/or blood involvement and those who fail peripheral blood hemopoietic progenitor mobilization are excluded from ASCT. For such patients with no available graft to infuse, we developed 15 years ago, before the anti-CD20 monoclonal antibody therapeutic era, the use of the BEAM pretransplant regimen followed only by the administration of three cytokines (erythropoietin, granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor). We report here on the long-term follow-up of 33 patients treated with this approach. In all, 33 NHL patients underwent the BEAM (carmustine, VP-16, cytosine-arabinoside, melphalan) followed by the administration of the three cytokines from January 1994-2000. A backup marrow, albeit infiltrated by tumor cells, had been collected earlier and stored in all. A total of 30 patients (91%) recovered normal hematopoiesis. In total, 32 patients (97%) recovered neutrophils (>500/microl) at a median of 19 days and 30 patients (91%) recovered platelets (>20,000/microl) at a median of 26 days. Age, richness of backup graft and blood-hemoglobin level at intensification had an impact on the time for hematopoietic recovery (P=0.014, P=0.014, P=0.048). The median follow-up was 62 months. Five patients died from toxicity related to the procedure. Eight patients relapsed and died. A total of 20 patients (61%) are alive, 16 (49%) in complete remission. A 5-year disease-free survival was 52+/-9%, relapse incidence 35+/-16%, mortality due to the procedure 12+/-12% and overall survival 61+/-10%. The BEAM regimen is not myeloablative. The BEAM+3CK procedure is a feasible therapeutic option that has shown efficacy in poor risk NHL patients who were not eligible for autografting because of persisting marrow/blood tumor contamination, or poor hemopoietic progenitor harvesting. It is unclear today whether some of these patients would have cleared their marrow/peripheral blood with the additional use of anti-CD20 treatment, thereby making the classical approach (BEAM followed by the infusion of a clean autograft) feasible.

Multiple chromosome abnormalities in patients with acute leukemia after autologous bone marrow transplantation using total body irradiation and marrow purged with mafosfamide.

Cytogenetic follow-up studies such as those reported after allogeneic bone marrow transplantation are not available in patients submitted to an autologous bone marrow transplantation (ABMT). Of 114 patients with acute leukemia (69 acute myelocytic AML, 43 acute lymphocytic ALL, 2 undifferentiated) who underwent an ABMT in our institution in the period from February 1983 to December 1989, 66 had evaluable cytogenetic data post-transplant. They all received a pretransplant regimen consisting of cyclophosphamide (CY) and total body irradiation (TBI) followed by reinfusion of marrow purged with mafosfamide. Twenty patients showed chromosomal damage at some time; of these, six relapsed early post-ABMT, one died while in persisting remission at 81 months post-ABMT from overwhelming pneumococcal sepsis related to a previous splenectomy, and 13 are still alive and well at 13 to 88 months post-transplant. The bone marrow cytogenetic abnormalities were complex: they included various numbers of clonal aberrations or variations or combination of those; they affected all but the Y chromosome, with a predominance however for chromosomes 1, 3, 6, and 7; they were often transitory and in some instances became modified with time. None of these chromosomal abnormalities was connected with the initial leukemia, even in the 6 patients who relapsed early. In the other 14 patients, these abnormalities have so far had no detectable unfavourable implication. The origin of these abnormalities is unknown: both the pretransplant regimen (CY and/or TBI) and/or marrow purging with mafosfamide can be incriminated. Additional studies in patients autografted with pretransplant regimen not containing TBI and/or with unpurged marrow are necessary to discriminate between these two possibilities.

Comparison of the inhibitory effect of AcSDKP, TNF-alpha, TGF-beta, and MIP-1 alpha on marrow-purified CD34+ progenitors.

The aim of this study was to compare the inhibitory effect of the tetrapeptide AcSDKP, tumor necrosis factor-alpha (TNF-alpha), which contains the sequence of the peptide, transforming growth factor-beta (TGF-beta), and macrophage inflammatory protein-1 alpha (MIP-1 alpha) on sorted CD34+ cells using both proliferation and clonogenic assays. Although a short treatment with any of the molecules decreased the growth of colony-forming unit granulocyte/macrophage (CFU-GM) and burst-forming unit-erythroid (BFU-E) progenitors (except for TNF-alpha as it is a greater inhibitor for CFU-GM), further experiments using a 6-day liquid culture in the presence of a combination of growth factors (recombinant human interleukin-3 [rhIL-3], IL-6, IL-1 beta, GM colony-stimulating factor [GM-CSF], G-CSF, erythropoeitin [Epo], and stem cell factor [SCF]) allowed us to determine a number of differences between their effects: 1) TGF-beta and TNF-alpha induced a stronger decrease in the proliferation and clonogenicity of CD34+ subsets than MIP-1 alpha and AcSDKP, 2) the dose-response curves appeared different, and 3) contrary to TGF-beta and TNF-alpha, AcSDKP and MIP-1 alpha required repeated addition to induce inhibition. Therefore, our data clearly show that while the inhibitory effect of TNF-alpha and AcSDKP appeared to be different, there is a close similarity in the effect of AcSDKP and MIP-1 alpha on normal human progenitor response to the combination of growth factors used.

Study of granulocyte-macrophage progenitor (CFUc) preservation after slow freezing of bone marrow in the gas phase of liquid nitrogen.

Storage of human hematopoietic stem cells has been made possible through effective preservation of viability by freezing technique. We have studied the quantitative and qualitative aspects of granulocyte-macrophage precursor (CFUc) recovery from 29 bags of frozen bone marrow stored at - 160 degree C in the gas phase of liquid nitrogen for several months or years. it has been shown that with the freezing and preservation technique used, over 75% of the proliferative capacity of the cryopreserved CFUc was recovered. The influence of various factors on the quality of bone marrow preservation was studied and showed that dimethylsulfoxide (DMSO) appeared to cause substantial loss of CFUc at 4 degree C. Evaluation of CFUc in vitro is essential for determining the quality and richness of cryopreserved bone marrow with a view to using such marrow for autologous grafting intensive chemotherapy or total body irradiation in patients with hematological malignancies or solid tumors. No correlation was found between the number of nucleated bone marrow cells and CFUc content.

Human granulocyte colony growth: differences between serum-free and serum-dependent cultures.

Human granulocyte colony formation has been observed in serum-free methylcellulose cultures with Iscove medium, delipidated bovine serum albumin, iron-saturated transferrin, alpha-thioglycerol, oleylpalmitoyl lecithin, cholesterol, and linoleic acid using serum-free human placental-conditioned medium (SF-HPCM) as the source of colony stimulating factor (CSF). Dose-response curves for SF-HPCM indicated a lower sensitivity to colony-stimulating activity in serum-free cultures than in serum-dependent cultures. Gel filtration of SF-HPCM revealed that CSF fractions with molecular weights in the range of 30 kD are inefficient in serum-free cultures, while fractions with molecular weights in the range of 40 kD stimulate granulocyte colony formation in both types of cultures. These results demonstrate that serum constituents modulate the effects of one of the stimulating factors for granulocyte colony formation, and that serum-free culture conditions are essential for establishing the growth factor requirements of the granulocyte lineage.

Tumor necrosis factor alpha in human long-term bone marrow cultures: distinct effects on nonadherent and adherent progenitors.

Although tumor necrosis factor alpha (TNF alpha) exerts a variety of activities on hematopoietic cells, suggesting it may have some potential therapeutic applications, its long-term effects on hematopoiesis are not well defined. Therefore, we took the advantage of long-term bone marrow cultures (LTBMCs) to evaluate the long-term role of TNF alpha on both the microenvironment and the hematopoietic progenitors. LTBMCs were inoculated with 100 U/ml of recombinant human TNF alpha (rhTNF alpha) either at the onset of the cultures (d0) or at day 21 (d21) when the adherent layer (AL) was already established. Then TNF alpha was added at each weekly medium change. The cellularity and the content of progenitors in both the nonadherent layer (NAL) and AL, the formation of the AL, and the presence of various cytokines in the supernatants were examined weekly. The data showed 1) a strong and durable inhibitory effect on total nonadherent cells; 2) a rapid and transient inhibition of NA progenitors, whereas adherent progenitors were lately affected; and 3) microenvironmental changes consisting of the disappearance of adipocytes and the secretion of high levels of interleukin 6. The results suggest that the inhibitory effects of TNF alpha on the NAL are in part counterbalanced by stromal modifications that in turn lead to a faster exhaustion of hematopoiesis.

Reversible inhibitory effects and absence of toxicity of the tetrapeptide acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) in human long-term bone marrow culture.

The effects of acetyl-N-Ser-Asp-Lys-Pro (Ac-SDKP) in human long-term bone marrow cultures (LTBMCs) were assessed by measuring the number of progenitors and the development of stromal cells over a 6-week course. In a first set of experiments, AcSDKP was added weekly at each medium change. Under these conditions, no significant effect of the peptide was observed. In contrast, by adding AcSDKP daily at 10(-10) M, the growth of the progenitors of the non-adherent (NA) compartment was inhibited by about 35%. This inhibition was entirely reversible; after stopping the addition of the peptide at the fourth week, the number of progenitors returned to control level within 2 weeks. Conversely, AcSDKP did not significantly change the number of the progenitors present in the adherent layer. In addition, AcSDKP did not affect the formation of the stromal layer nor induce the secretion of cytokines, such as tumor necrosis factor alpha (TNF-alpha), interleukin 1 beta (IL-1 beta), granulocyte colony-stimulating factor (G-CSF), interleukin 3 (IL-3), or interleukin 6 (IL-6). Our results indicate that AcSDKP has inhibitory but reversible effects on NA progenitors and does not induce long-term modifications of the microenvironment, both of particular interest for its clinical application.

Establishment of a reliable experimental procedure for bone marrow purging with mafosfamide (ASTA Z 7557).

Bone marrow purging with cyclophosphamide derivatives (Mafosfamide) requires the establishment of a defined experimental procedure for reliable leukemic cell destruction while sparing normal hematopoietic stem cells to ensure engraftment. We previously defined the granulocyte-macrophage colony-forming unit (CFU-GM) LD95 as being the maximum tolerable dose of drug to use. We now report, in 20 patients with acute non-lymphoblastic leukemia (n = 5), acute lymphoblastic leukemia (n = 5), chronic myelogenous leukemia (n = 5), and non-Hodgkin's lymphoma (n = 5), that the nature of the cells treated (i.e., buffy coat cells or mononuclear cells) significantly influences the accuracy of the LD95 determination, whereas other parameters such as hematocrit or nucleated cell concentration do not. We subsequently define the most reliable experimental procedure for in vitro purging with Mafosfamide: incubation of 2 x 10(7) buffy coat cells/ml with a hematocrit of 5%. We show that the wide individual susceptibility to the drug is not related to any incubation procedure. In a series of 163 patients with hematological malignancies, we confirm the large variation of sensitivity to the drug according to patient susceptibility and diagnosis. These data favor the adjustment of the dose of Mafosfamide on an individual basis, prior to bone marrow purging for autologous bone marrow transplantation.

Inhibition of human bone marrow progenitors by the synthetic tetrapeptide AcSDKP.

The purpose of this work was to study the effects of a tetrapeptide, acetyl-N-Ser-Asp-Lys-Pro (AcSDKP), an inhibitor of spleen colony-forming unit (CFU-S) entry into DNA synthesis, on human progenitor cells. Normal human mononuclear cells were incubated with concentrations of the synthetic tetrapeptide ranging from 10(-12) to 10(-7) M for 1.5 and 24 h and then plated in methylcellulose in the presence of human placenta-conditioned medium and recombinant human erythropoietin. The proportion of progenitors in DNA synthesis was determined by the thymidine suicide assay. Incubation with AcSDKP for 24 h leads to a significant inhibition of granulocyte-macrophage colony-forming unit (CFU-GM) and erythroid burst-forming unit (BFU-E) growth and in some cases of erythroid colony-forming unit (CFU-E) growth. The inhibition, which was never greater than 50%, was obtained with 10(-10)-10(-9) M AcSDKP, whereas no effect was seen at higher concentrations. The percentage of CFU-GM, BFU-E, and CFU-E in DNA synthesis was significantly reduced in five consecutive patients after incubation of cells for 24 h with inhibitory doses of the peptide, indicating that it is active on cycling cells. Therefore, these studies provide the first evidence that the tetrapeptide AcSDKP, originally obtained from bovine marrow and now chemically synthesized, is able to inhibit the in vitro growth of human progenitors and to decrease their proportion in cell cycle.

Stimulatory effects of plasma from patients with acute nonlymphoblastic leukemia on early erythroid progenitors and pluripotent stem cells.

To examine mechanisms of cytopenia in acute nonlymphoblastic leukemia (ANLL), we determined whether leukemic plasma (LP) contains growth-promoting factors that support mammalian erythroid progenitor and pluripotential stem cell proliferation in vitro. When added to serum-free cultures of human bone marrow and peripheral blood cells, LP from anemic patients with ANLL stimulated erythroid burst formation to greater levels than did normal human plasma (p less than 0.05 for each). While LP also enhanced erythroid burst development in murine bone marrow cells, preincubation of marrow cells with LP did not alter the formation of splenic colonies (CFU-S-derived colonies) in irradiated mice (p greater than 0.10). To determine whether erythropoietin or other growth factors (functionally similar to burst-promoting activity, BPA) are important in mediating the erythropoietic effects observed in vitro, LP was preabsorbed with monospecific IgG raised against human erythropoietin or human BPA. Although elevated erythropoietin levels were found in each LP, preabsorption with antierythropoietin IgG did not alter its capacity to enhance human burst formation. In contrast, preabsorption with antimembrane IgG capable of recognizing human BPA abrogated the stimulatory effects of LP (p less than 0.05). In addition, LP was found to increase the percentage of murine CFU-S that are synthesizing DNA by the (3H) Tdr suicide technique, an effect which was not abrogated by preabsorption of LP with monospecific IgG raised against human BPA. We conclude that both erythropoietin and BPA are appropriately increased in ANLL. In addition, a factor is present in LP which induces DNA replication in murine pluripotential stem cells.

The role of methylcellulose on colony growth of human myeloid leukemic progenitors (AML-CFU).

The use of a semisolid support like methylcellulose (MC) in a clonogenic assay prevents cell migration and nonspecific aggregation. However, the inhibitory effect of MC on myeloid cell lines has been reported. To assess the effect of MC on human leukemic progenitor cell growth (acute myeloblastic leukemia colony-forming units, AML-CFU), increasing concentrations of MC (0.36%, 0.72%, and 1.44%) were added in a double-feeder culture system. T-lymphocyte-depleted leukemic cells from 12 patients with AML were cultured in the presence of 2.5% phytohemagglutinin (PHA) in a liquid and a semisolid (MC) medium over a leukocyte feeder layer. The leukemic nature of the colonies was confirmed by cytogenetic studies. The median cloning efficiency in the optimal MC assay system was significantly higher (217 leukemic colony-forming units [CFU-L]/5 x 10(4) cells) than the one obtained in the liquid assay system (72.5 CFU-L/5 x 10(4) cells). However, three patterns of growth were observed: 1) colony formation was significantly better in MC than in the liquid assay system (seven of ten cases), 2) there was no difference in growth response (three of ten cases), and 3) colony formation was significantly better in the liquid assay system (one of ten cases). In the semisolid assay system, colony growth was dependent on MC concentration and varied among individual patients. A striking feature was the partial reduction of AML-CFU growth at 1.44% MC, with complete inhibition in 4/11 cases. This phenomenon was not observed for normal progenitors cultured under the same conditions. Cytological evaluation of AML-CFU showed an incomplete maturation to the myelocyte state, accompanied occasionally by macrophagic differentiation. In contrast, maturation of the granulocyte-macrophage colony-forming unit (CFU-GM) clones was harmonious, resulting in greater than 40% polynuclear cells, even from a 7-day culture. Despite a variable clonal response of leukemic progenitors from individual patients, we conclude that 0.72% MC is the optimal concentration of MC in our system, allowing clonal growth of AML-CFU.

The tetrapeptide AcSDKP, an inhibitor of the cell-cycle status for normal human hematopoietic progenitors, has no effect on leukemic cells.

The tetrapeptide acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) inhibits the entry into DNA synthesis of murine spleen colony-forming units (CFU-S) and protects these cells during chemotherapy. This synthetic peptide also inhibits the growth of normal human marrow progenitors granulocyte-macrophage colony-forming units (CFU-GM) and erythroid burst-forming units (BFU-E) and decreases their percentage in DNA synthesis at nanomolar concentration. In view of its clinical application as a marrow protector, we have investigated its effects on malignant cells. Studies were carried out on HL-60 cells and on fresh leukemic cells from patients with either chronic myeloid leukemia (CML) or acute myeloid leukemia (AML). Results showed that AcSDKP, whatever the doses used, did not modify the proliferation of both HL-60 cells and AML cells even when enhanced by stimulating factors such as interleukin 3 or granulocyte-macrophage colony-stimulating factor (GM-CSF). In addition, no change in the number and the percentage in S-phase of both HL-60 clonogenic cells and CML progenitors was observed. Our data clearly demonstrate that the tetrapeptide AcSDKP was ineffective on leukemic cells and therefore by acting selectively on normal progenitors represents a potent therapeutical agent for the protection of normal bone marrow progenitors during chemotherapy.

The role of serum lipoproteins on the in vitro proliferative potential of human hematopoietic progenitors CFUC and CFUE.

The influence of various lipoprotein fractions on the proliferation of normal human hematopoietic progenitors, CFUC and CFUE, was studied in vitro. The lipoprotein fractions, very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL), low density lipoproteins (LDL), high density lipoproteins (HDL2 and HDL3), were isolated by sequential ultracentrifugation. The addition of each subfraction to lipoprotein deficient medium allowed us to distinguish two categories of lipoproteins: firstly, those with density d greater than 1.030, LDL, HDL2 and HDL3 which showed a marked inhibitory activity on CFUC and CFUE proliferation and, secondly, those with density d less than 1.030, VLDL and IDL which did not show any inhibitory activity. The regulatory role of lipoproteins on progenitor cell proliferation is discussed.

Thymosin beta4, inhibitor for normal hematopoietic progenitor cells.

Thymosin beta4 (Tbeta4), isolated from the calf thymus fraction 5, has a ubiquitous localization and plays a pleiotropic role in both the immune and nonimmune systems. Because it contains at its N-terminal end the sequence of a known inhibitor of hematopoiesis, the acetylated tetrapeptide Ac-N-Ser-Asp-Lys-Pro (AcSDKP, Goralatide), we have assayed Tbeta4 on human hematopoietic cells. We demonstrate that it inhibits normal bone marrow progenitor cell growth; indeed, it decreased the growth of both granulo-macrophagic and erythroid progenitors and reduces their percentage in S phase. Furthermore, we show that Tbeta4 reduces both the clonogenicity and the cell proliferation of purified CD34+ cells induced by a combination of seven growth factors. Although Tbeta4's inhibitory effect is very similar to that of AcSDKP, we demonstrate, using neutralizing antibodies and a truncated form of Tbeta4 devoid of the AcSDKP sequence, that the inhibitory effect of Tbeta4 is not mediated by the sequence AcSDKP. These data indicate that Tbeta4 is a novel inhibitor for human normal hematopoietic progenitors.

B-lymphocytes as a source of cell surface growth-promoting factors for hematopoietic progenitors.

Although B cells reside in the bone marrow, little is known concerning their functional role in hematopoiesis. We have measured the effects of surface membrane factors released from unstimulated, circulating B cells of normal donors and patients with chronic lymphocytic leukemia on human hematopoiesis in vitro. Leukemic cells augment erythroid burst formation by allogeneic blood cells (p less than 0.05). The stimulatory effect is increased in cultures containing a high B-cell seeding density, and is decreased in those with a high peripheral blood mononuclear cell seeding density. Medium conditioned by B cells (CM) from the circulation or bone marrow stimulates the formation of erythroid bursts, granulocyte-macrophage colonies, and mixed colonies containing granulocytes, erythroblasts, monocytes, and megakaryocytes (GEMM) in serum-free cultures of allogeneic and autologous marrow (p less than 0.05). This effect is localized primarily to surface membrane vesicle-rich pellets of CM. Screening of several hematopoietic and nonhematopoietic cell types reveals that membrane vesicle-associated activity is released from B cells and mitogen-stimulated, circulating T cells. In contrast, vesicles shed from freshly isolated, resting T cells, continuous T-cell leukemia cell lines, erythrocytes, and endothelial cells do not express the activity (p greater than 0.10). The stimulatory activity is augmented in cultures of marrow cells that are depleted of B4 antigen-positive lymphocytes but not of T-lymphocytes, suggesting that endogenous release of the factor(s) occurs during incubation. Furthermore, membranes partially purified from leukemic B cells also express the activity. Together with our findings that (1) the growth enhancing factor(s) is solubilized by octylglucoside, and that (2) the factor can be immunoprecipitated with BPA-neutralizing, antimembrane IgG, our results suggest that the erythropoietic activity is an integral membrane protein that may be immunologically related to BPA. The relationship of the erythroid burst stimulatory factor to other hematopoietic activities found in CM pellets is unknown.