Recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) shortens the period of neutropenia after autologous bone marrow transplantation in a primate model

Filgrastim improves survival in lethally irradiated nonhuman primates

Treatment of individuals exposed to potentially lethal doses of radiation is of paramount concern to health professionals and government agencies. We evaluated the efficacy of filgrastim to increase survival of nonhuman primates (NHP) exposed to an approximate mid-lethal dose (LD(50/60)) (7.50 Gy) of LINAC-derived photon radiation. Prior to total-body irradiation (TBI), nonhuman primates were randomized to either a control (n = 22) or filgrastim-treated (n = 24) cohorts. Filgrastim (10 μg/kg/d) was administered beginning 1 day after TBI and continued daily until the absolute neutrophil count (ANC) was >1,000/μL for 3 consecutive days. All nonhuman primates received medical management as per protocol. The primary end point was all cause overall mortality over the 60 day in-life study. Secondary end points included mean survival time of decedents and all hematologic-related parameters. Filgrastim significantly (P < 0.004) reduced 60 day overall mortality [20.8% (5/24)] compared to the controls [59.1% (13/22)]. Filgrastim significantly decreased the duration of neutropenia, but did not affect the absolute neutrophil count nadir. Febrile neutropenia (ANC <500/μL and body temperature ≥ 103°F) was experienced by 90.9% (20/22) of controls compared to 79.2% (19/24) of filgrastim-treated animals (P = 0.418). Survival was significantly increased by 38.3% over controls. Filgrastim, administered at this dose and schedule, effectively mitigated the lethality of the hematopoietic subsyndrome of the acute radiation syndrome.

Pegfilgrastim administered in an abbreviated schedule, significantly improved neutrophil recovery after high-dose radiation-induced myelosuppression in rhesus macaques

Conventional daily administration of filgrastim is effective in reducing the duration of severe neutropenia and enhancing survival following lethal radiation, myelosuppressive cytotoxic therapy or myeloablation and stem cell transplantation. A sustained-duration form of filgrastim, pegfilgrastim has significantly simplified scheduling protocols after chemotherapy-induced neutropenia to a single injection while maintaining the therapeutic effectiveness of daily administration of filgrastim. We examined the ability of a single or double (weekly) administration of pegfilgrastim to significantly improve neutrophil recovery in a rhesus macaque model of severe radiation-induced myelosuppression. Animals were exposed to potentially lethal 6 Gy total-body X radiation. After irradiation all animals received supportive care and were administered either pegfilgrastim at 300 μg/kg on day 1 or day 1 and day 7 post exposure, or filgrastim at 10 μg/kg/day initiated on day 1 post exposure and continued daily through neutrophil recovery. Pharmacokinetic parameters and neutrophil-related values for duration of neutropenia, neutrophil nadir, time to recovery to an absolute neutrophil count ≥500/μL or ≥2000/μL, and days of antibiotic support were determined. Effective plasma concentrations of pegfilgrastim were maintained in neutropenic animals until after the onset of hematopoietic recovery, which is consistent with neutrophil-dependent properties of elimination. Administration of pegfilgrastim at day 1 and day 7 was most effective at improving neutrophil recovery compared to daily administration of filgrastim or a single injection of pegfilgrastim on day 1, after severe, radiation-induced myelosuppression in rhesus macaques.

The potential role of recombinant hematopoietic colony-stimulating factors in preventing infections in the immunocompromised host

Hematopoietic colony-stimulating factors coordinate the proliferation and maturation of bone marrow and peripheral blood cells during normal hematopoiesis. Most of these factors are now available as recombinant human colony-stimulating factors, and preclinical and clinical testing is proceeding rapidly. Granulocyte and granulocyte/macrophage colony-stimulating factors have been the most extensively studied to date. In human clinical trials, granulocyte colony-stimulating factor improves neutrophil counts and function, reduces episodes of febrile neutropenia, improves neutrophil recovery after disease- or treatment-induced myelosuppression, and reduces the number of serious infections in several neutropenic disease states. Granulocyte/macrophage colony-stimulating factor has similar biological properties but may also improve eosinophil proliferation and function, and platelet cell recovery after myelotoxic bone marrow injury, Interleukin-1 boosts the effects of granulocyte colony-stimulating factor and granulocyte/macrophage colony-stimulating factor, but also may promote the resolution of established infections in conjunction with antibiotics. The therapeutic realities and future therapeutic implications of these agents for the therapy of infections, cancer and hemopoietic disorders are discussed.

Endurance exercise training promotes medullary hematopoiesis

Endurance exercise is a poorly defined yet powerful mediator of hematopoiesis. The purpose of this study was to directly investigate the effects of endurance exercise training on hematopoiesis and to identify potential mechanisms responsible for any observed changes. Four-week-old male C57Bl/6 mice were trained on a treadmill at progressive speeds over a 10-wk period. Tissues were harvested 2 d following the final training session. Flow cytometry, the cobblestone area-forming cell assay, and the methycellulose colony-forming unit assay were used to assess medullary and mobilized hematopoietic stem and progenitor cells. Quantitative real-time PCR and Western blots were used to measure hematopoietic cytokine production. Histochemistry was also used to assess adaptations to exercise in the bone marrow niche. Depending on the cell type, endurance training increased medullary and mobilized hematopoietic stem and progenitor cell content from 50 to 800%. Training also reduced marrow cavity fat by 78%. Skeletal muscle hematopoietic cytokine expression was also increased at least 60% by training. Sedentary mice served as controls for the above experiments. In conclusion, endurance exercise training greatly promotes hematopoiesis and does so through improvements in medullary niche architecture as well as increased skeletal muscle hematopoietic cytokine production.

Rapid myeloid recovery as a possible mechanism of whole-body radioadaptive response

We investigated the mechanism underlying the radioadaptive response that rescues mice from hematopoietic failure. C57BL/6 mice were irradiated with low-dose acute X rays (0.5 Gy) for priming 2 weeks prior to a high-dose (6 Gy) challenge irradiation. Bone marrow cells, erythrocytes and platelets in low-dose-preirradiated mice showed earlier recovery after the challenge irradiation than those in mice subjected only to the challenge irradiation. This suggests that hematopoiesis is enhanced after a challenge irradiation in preirradiated mice. The rapid recovery of bone marrow cells after the challenge irradiation was consistent with the proliferation of hematopoietic progenitors expressing the cell surface markers Lin-, Sca-1- and c-Kit+ in low-dose-preirradiated mice. A subpopulation of myeloid (Mac-1+/Gr-1+) cells, which were descendants of Lin-, Sca-1- and c-Kit+ cells, rapidly recovered in the bone marrow of low-dose-preirradiated mice, whereas the number of B-lymphoid (CD19+/B220+) cells did not show a statistically significant increase. Plasma cytokine profiles were analyzed using antibody arrays, and results indicated that the concentrations of several growth factors for myelopoiesis after the challenge irradiation were considerably increased by low-dose preirradiation. The rapid recovery of erythrocytes and platelets but not leukocytes was observed in the peripheral blood of preirradiated mice, suggesting that low-dose preirradiation triggered the differentiation to myelopoiesis. Thus the adaptive response induced by low-dose preirradiation in terms of the recovery kinetics of the number of hematopoietic cells may be due to the rapid recovery of the number of myeloid cells after high-dose irradiation.

The molecular regulators of macrophage and granulocyte development. Role of MGI-2/IL-6

The development of a cell culture system for the in vitro cloning and clonal differentiation of normal hematopoietic cells made it possible to identify the proteins that regulate growth and differentiation of different hematopoietic cell lineages and the change in normal controls that produce leukemia. A model system with myeloid cells has identified different myeloid cell colony-inducing proteins, which we called MGI-1 (= CSF, including IL-3). There is another protein that we first described in 1976 and called MGI-2 in 1980 that induces differentiation of myeloid cells to macrophages or granulocytes without inducing the clonal growth of myeloid cells. The four CSF proteins and IL-1 induce the production of MGI-2 in myeloid cells and MGI-2 induces the production of GM-CSF. This shows the participation of MGI-2 in the network of interactions with different myeloid regulatory proteins. Using a monoclonal antibody to MGI-2, amino acid sequencing, and recombinant protein, we have shown in collaboration with the Genetics Institute that the major form of MGI-2 (MGI-2A) is IL-6. This shows that IL-6 is a myeloid cell differentiation inducing protein. The results also suggest new clinical potentials for MGI-2/IL-6.

Cloning and Functional Analysis of the Rhesus Macaque ABCG2 Gene

Hematopoietic cells can be highly enriched for repopulating ability based upon the efflux of the fluorescent Hoechst 33342 dye by sorting for SP (side population) cells, a phenotype attributed to expression of ABCG2, a member of the ABC transporter superfamily. Intriguingly, murine studies suggest that forced ABCG2 expression prevents hematopoietic differentiation. We cloned the full-length rhesus ABCG2 and introduced it into a retroviral vector. ABCG2-transduced human peripheral blood progenitor cells (PBPCs) acquired the SP phenotype but showed significantly reduced growth compared with control. Two rhesus macaques received autologous PBPCs split for transduction with the ABCG2 or control vectors. Marking levels were similar between fractions with no discrepancy between bone marrow and peripheral blood marking. Analysis for the SP phenotype among bone marrow and mature blood populations confirmed ABCG2 expression at levels predicted by vector copy number long term, demonstrating no block to differentiation in the large animal. In vitro studies showed selective protection against mitoxantrone among ABCG2-transduced rhesus PBPCs. Our results confirm the existence of rhesus ABCG2, establish its importance in conferring the SP phenotype, suggest no detrimental effect of its overexpression upon differentiation in vivo, and imply a potential role for its overexpression as an in vivo selection strategy for gene therapy applications.

Direct comparison of RD114-pseudotyped versus amphotropic-pseudotyped retroviral vectors for transduction of rhesus macaque long-term repopulating cells

Recently, RD114 (feline endogenous retrovirus envelope protein)-pseudotyped retroviral particles have been shown to transduce human NOD/SCID repopulating cells efficiently. In this study, we compared directly transduction of repopulating cells with RD114-pseudotyped vector to that with standard amphotropic vector in the rhesus macaque model. G-CSF/SCF-mobilized CD34(+) rhesus peripheral blood cells were cultured in the presence of SCF, Flt-3 ligand, and MGDF on Retronectin-coated flasks. To assess directly the ability of the two pseudotypes to transduce primitive cells, both vectors were added simultaneously to the target cells every 24 h, for a total of four exposures in 96 h. The cells were reinfused after the animals received 1000 cGy total body irradiation. At the end of transduction, gene marking efficiency of CFU was higher with amphotropic LNL6 vector (mean 88.4%) vs RD114-G1Na vector (mean 18.5%). After long-term engraftment in three animals, total neo gene marking levels were 4-5% in PBMNCs and 1.5-4% in granulocytes. The RD114-G1Na marking levels were consistently higher in granulocytes than in mononuclear cells, while amphotropic LNL6 marking levels were higher in PBMNCs than in granulocytes. The differential gene marking patterns suggest that RD114 and amphotropic vectors may target distinct progenitor or stem cell populations. There was no clear advantage for RD114-pseudotyped vectors in this predictive preclinical model in terms of overall long-term marking levels; however, optimization of transduction conditions by increasing m.o.i. or inducing the receptor could potentially improve results with this novel vector system.

Hematopoietic recovery following autologous bone marrow transplantation in a nonhuman primate: effect of variation in treatment schedule with PEG-rHuMGDF

Mathematical modeling of pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) pharmacokinetics (PK) and pharmacodynamics (PD) suggest that variations in the PEG-rHuMGDF treatment schedule could reduce the severity and duration of thrombocytopenia following myeloablation and bone marrow transplant (BMT). We tested this hypothesis in a rhesus monkey model of autologous (Au) bone marrow-derived mononuclear cell (BM-MNC) transplantation following lethal myeloablation. On day 0, animals were myeloablated by total body exposure to 920 cGy, 250 kVp x-irradiation (TBI). Four cohorts of animals were infused with 1 x 10(8) AuBM-MNC/kg body weight within 2 hours of TBI. The AuBMT-alone cohort received no cytokine, the daily dosage cohort received PEG-rHuMGDF (2.5 micro g/kg/day, s.c.) post TBI and AuBMT, and the pre/post-transplant cohort received PEG-rHuMGDF (2.5 micro g/kg/day, s.c.) pre (day -9 to day -5) and post TBI and AuBMT. The post-transplant PEG-rHuMGDF administration in the above cohorts was begun on day 1 post TBI and continued until platelet counts reached 200,000 micro l (range, 15-31 days). Another group received PEG-rHuMGDF (300 micro g/kg/day, s.c.) on days 1 and 3 only following TBI and AuBMT. The TBI controls received neither AuBMT nor cytokine therapy. In this model of AuBMT, with regard to the PEG-rHuMGDF administration schedule, the daily dosage of the post-transplant cohort did not significantly improve platelet recovery; the pre/post-transplant schedule and an abbreviated high-dosage, post-transplant schedule (days 1 and 3) significantly improved the duration and nadir of thrombocytopenia and platelet recovery. These data confirm predictions from PK/PD modeling of PEG-rHuMGDF that thrombocytopenia is preventable following AuBMT.

Pegfilgrastim, a sustained-duration form of filgrastim, significantly improves neutrophil recovery after autologous marrow transplantation in rhesus macaques

Daily administration of filgrastim decreases the duration of severe neutropenia in the clinical setting. A sustained-duration form of filgrastim, pegfilgrastim, significantly reduces scheduling protocols to a single injection per chemotherapy cycle while maintaining therapeutic efficiency. We examined the ability of a single injection of pegfilgrastim to significantly improve neutrophil recovery following autologous bone marrow transplantation (AuBMT) in rhesus macaques. On day 1, postmyeloablation (920 cGy x-irradiation) and AuBMT, animals received either 0.1% autologous serum for 18 consecutive days (n=13), or single doses of pegfilgrastim via the subcutaneous (s.c.) or intravenous (i.v.) route (300 or 100 micro g/kg), or a single dose of filgrastim at 300 micro g/kg via the s.c. or i.v. route, or filgrastim at 10 micro g/kg via the s.c. route (n=4) on a daily basis (range=days 12-17). Pharmacokinetic parameters and neutrophil recovery were assessed. A single dose of pegfilgrastim via the i.v. or s.c. route was as effective as daily filgrastim administration, resulting in significant improvement of neutrophil recovery after myeloablation and ABuMT. Effective pegfilgrastim plasma concentrations were maintained in neutropenic animals until after the onset of hematopoietic recovery. Enhanced pharmacokinetics in AuBMT cohorts are consistent with self-regulating, neutrophil-mediated clearance.

Retroviral transduction and engraftment ability of primate hematopoietic progenitor and stem cells transduced under serum-free versus serum-containing conditions

The ability to efficiently transduce hematopoietic stem and progenitor cells under serum-free conditions would be desirable for safety and standardization of clinical gene therapy protocols. Using rhesus macaques, we studied the transduction efficiency and engraftment ability of CD34-enriched SCF/G-CSF mobilized progenitor cells (PBSC) transduced with standard amphotropic marking vectors under serum-free and serum-containing conditions. Supernatants were collected from producer cells 16 hours after serum-free medium or medium containing 10% fetal calf serum was added. Vector titers were approximately two- to threefold higher when producer cells were cultured in serum-containing medium. However, retroviral transduction of rhesus CFU-GM was improved using serum-free vector-containing medium. For analysis of engraftment with transduced cells, three macaques had CD34+ peripheral blood stem cells split into two fractions for transduction. One fraction was transduced using serum-free vector-containing medium, and the other fraction was transduced using standard serum-containing medium. The two fractions were re-infused simultaneously following total body irradiation. In all three animals, there was equivalent marking from both vectors for 7-9 months post-transplantation. These data are encouraging regarding the removal of serum-containing medium from clinical hematopoietic cell transduction protocols, given the lack of a detrimental effect on transduction and engraftment with transduced cells.

Avoidance of stimulation improves engraftment of cultured and retrovirally transduced hematopoietic cells in primates

Recent reports suggest that cells in active cell cycle have an engraftment defect compared with quiescent cells. We used nonhuman primates to investigate this finding, which has direct implications for clinical transplantation and gene therapy applications. Transfer of rhesus CD34(+) cells to culture in stem cell factor (SCF) on the CH-296 fibronectin fragment (FN) after 4 days of culture in stimulatory cytokines maintained cell viability but decreased cycling. Using retroviral marking with two different gene transfer vectors, we compared the engraftment potential of cytokine-stimulated cells versus those transferred to nonstimulatory conditions (SCF on FN alone) before reinfusion. In vivo competitive repopulation studies showed that the level of marking originating from the cells continued in culture for 2 days with SCF on FN following a 4-day stimulatory transduction was significantly higher than the level of marking coming from cells transduced for 4 days and reinfused without the 2-day culture under nonstimulatory conditions. We observed stable in vivo overall gene marking levels of up to 29%. This approach may allow more efficient engraftment of transduced or ex vivo expanded cells by avoiding active cell cycling at the time of reinfusion.

The efficacy of recombinant TPO in murine And nonhuman primate models for myelosuppression and stem cell transplantation

Radiation-induced pancytopenia proved to be a suitable model system in mice and rhesus monkeys to study thrombopoietin (TPO) target cell range and efficacy. TPO was highly effective in rhesus monkeys exposed to the midlethal dose of 5-Gy (300 kV x-rays) TBI, a model in which it alleviated thrombocytopenia, promoted red cell reconstitution, accelerated reconstitution of immature CD34+ bone marrow (BM) cells and potentiated the response to growth factors such as GM-CSF and G-CSF. The accelerated reconstitution of BM CD34+ cells appeared to be reflected by a similar rise in peripheral blood CD34+ cells, both being augmented by concomitant GM-CSF. However, TPO was ineffective following transplantation of limited numbers of autologous BM or highly purified stem cells in monkeys conditioned with 8-Gy TBI. In the 5-Gy model, a single dose of TPO 24 h after TBI was effective in preventing thrombocytopenia and was augmented by GM-CSF. The strong erythropoietic stimulation may result in iron depletion and TPO treatment should be accompanied by monitoring of iron status. In mice, similar observations were made and the importance of dose and dose schedule for stimulation of multilineage repopulating cells versus the lineage-dominant thrombopoietic response studied in detail.

Many multipotential gene-marked progenitor or stem cell clones contribute to hematopoiesis in nonhuman primates

Retroviral insertion site analysis was used to track the contribution of retrovirally transduced primitive progenitors to hematopoiesis after autologous transplantation in the rhesus macaque model. CD34-enriched mobilized peripheral blood cells were transduced with retroviral marking vectors containing the neo gene and were reinfused after total body irradiation. High-level gene transfer efficiency allowed insertion site analysis of individual myeloid and erythroid colony-forming units (CFU) and of highly purified B- and T-lymphoid populations in 2 animals. At multiple time points up to 1 year after transplantation, retroviral insertion sites were identified by performing inverse polymerase chain reaction and sequencing vector-containing CFU or more than 99% pure T- and B-cell populations. Forty-eight unique insertion sequences were detected in the first animal and also in the second animal, and multiple clones contributed to hematopoiesis at 2 or more time points. Multipotential clones contributing to myeloid and lymphoid lineages were identified. These results support the concept that hematopoiesis in large animals is polyclonal and that individual multipotential stem or progenitor cells can contribute to hematopoiesis for prolonged periods. Gene transfer to long-lived, multipotent clones is shown and is encouraging for human gene therapy applications.

Lack of efficacy of thrombopoietin and granulocyte-macrophage colony-stimulating factor after total body irradiation and autologous bone marrow transplantation in Rhesus monkeys

OBJECTIVE

If administered in a sufficiently high dose to overcome receptor-mediated clearance and in a well-scheduled manner, thrombopoietin (TPO) prominently stimulates hematopoietic reconstitution following myelosuppressive treatment and potentiates the efficacy of both granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF). However, TPO alone is not effective after bone marrow transplantation. Based on results of GM-CSF and TPO treatment after myelosuppression that resulted in augmented thrombocyte, reticulocyte, and leukocyte regeneration, we evaluated TPO/GM-CSF treatment after lethal irradiation followed by autologous bone marrow transplantation.

MATERIALS AND METHODS

Young adult Rhesus monkeys were subjected to 8-Gy total body irradiation (TBI) (x-rays) followed by transplantation of 10(7)/kg unfractionated bone marrow cells. TPO 5 microg/kg was administered intravenously at day 0 to obtain rapidly high levels. Animals then were treated with 5 microg/kg Rhesus TPO and 25 microg/kg GM-CSF given SC on days 1 to 14 after TBI.

RESULTS

The grafts shortened the profound pancytopenia induced by 8-Gy TBI from 5-6 weeks to 3 weeks. The combination of TPO and GM-CSF did not significantly influence the recovery patterns of thrombocytes (p = 0.39), reticulocytes (p = 0.08), white blood cells (p = 0.08), or bone marrow progenitors compared to TPO alone.

CONCLUSIONS

The present study demonstrates that, after high-dose TBI and transplantation of a limited number of unfractionated bone marrow cells, simultaneous administration of TPO and GM-CSF after TBI is ineffective in preventing pancytopenia. This result contrasts sharply with the prominent stimulation observed in a 5-Gy TBI myelosuppression model, despite a similar level of pancytopenia in the 8-Gy model of the present study. The discordant results of this growth factor combination in these two models may imply codependence of the hematopoietic response to TPO and/or GM-CSF on other factors or cytokines.

Many multipotential gene-marked progenitor or stem cell clones contribute to hematopoiesis in nonhuman primates

Retroviral insertion site analysis was used to track the contribution of retrovirally transduced primitive progenitors to hematopoiesis after autologous transplantation in the rhesus macaque model. CD34-enriched mobilized peripheral blood cells were transduced with retroviral marking vectors containing the neo gene and were reinfused after total body irradiation. High-level gene transfer efficiency allowed insertion site analysis of individual myeloid and erythroid colony-forming units (CFU) and of highly purified B- and T-lymphoid populations in 2 animals. At multiple time points up to 1 year after transplantation, retroviral insertion sites were identified by performing inverse polymerase chain reaction and sequencing vector-containing CFU or more than 99% pure T- and B-cell populations. Forty-eight unique insertion sequences were detected in the first animal and also in the second animal, and multiple clones contributed to hematopoiesis at 2 or more time points. Multipotential clones contributing to myeloid and lymphoid lineages were identified. These results support the concept that hematopoiesis in large animals is polyclonal and that individual multipotential stem or progenitor cells can contribute to hematopoiesis for prolonged periods. Gene transfer to long-lived, multipotent clones is shown and is encouraging for human gene therapy applications.

Prolonged high-level detection of retrovirally marked hematopoietic cells in nonhuman primates after transduction of CD34+ progenitors using clinically feasible methods

Low-level retroviral transduction and engraftment of hematopoietic long-term repopulating cells in large animals and humans remain primary obstacles to the successful application of hematopoietic stem cell (HSC) gene transfer in humans. Recent studies have reported improved efficiency by including stromal cells (STR), or the fibronectin fragment CH-296 (FN), and various cytokines such as flt3 ligand (FLT) during ex vivo culture and transduction in nonhuman primates. In this work, we extend our studies using the rhesus competitive repopulation model to further explore optimal and clinically feasible peripheral blood (PB) progenitor cell transduction methods. First, we compared transduction in the presence of either preformed autologous STR or immobilized FN. Long-term clinically relevant gene marking levels in multiple hematopoietic lineages from both conditions were demonstrated in vivo by semiquantitative PCR, colony PCR, and genomic Southern blotting, suggesting that FN could replace STR in ex vivo transduction protocols. Second, we compared transduction on FN in the presence of IL-3, IL-6, stem cell factor (SCF), and FLT (our best cytokine combination in prior studies) with a combination of megakaryocyte growth and development factor (MGDF), SCF, and FLT. Gene marking levels were equivalent in these animals, with no significant effect on retroviral gene transfer efficiency assessed in vivo by the replacement of IL-3 and IL-6 with MGDF. Our results indicate that SCF/G-CSF-mobilized PB CD34+ cells are transduced with equivalent efficiency in the presence of either STR or FN, with stable long-term marking of multiple lineages at levels of 10-15% and transient marking as high as 54%. These results represent an advance in the field of HSC gene transfer using methods easily applied in the clinical setting.

No discrepancy between in vivo gene marking efficiency assessed in peripheral blood populations compared with bone marrow progenitors or CD34+ cells

Reports of 1- to 2-log higher gene transfer levels in purified CD34+ cells or marrow CFU compared with levels in mature circulating blood cells after transplantation of retrovirally transduced primitive human hematopoietic cells have resulted in concern that transduced progenitors do not contribute proportionally to ongoing hematopoiesis (Kohn et al., 1995; Brenner, 1996). To study the issue in a relevant large animal, we analyzed samples of mature blood cells, marrow CD34-enriched cells and marrow CD34-depleted cells, and marrow CFU from a cohort of 11 rhesus transplanted with retrovirally transduced cells and followed for up to 5.5 years. They were transplanted with CD34-enriched bone marrow (BM) or G-CSF/SCF-mobilized peripheral blood (PB) cells transduced with vectors containing either neo, human glucocerebrosidase, or murine adenosine deaminase genes. There were no significant differences between the levels of vector sequences found in BM CD34+ cells, BM CD34- cells, PB granulocytes, or PB mononuclear cells (MNCs) in any animal. In four animals transplanted with SCF/G-CSF-primed BM cells and analyzed 3-6 months posttransplantation, the percentage of CFU containing the neo vector appeared to be 1 log higher than the representation of marked cells in the PB of these animals, but this discrepancy did not persist at time points greater than 6 months posttransplantation. The level of CFU marking was no higher than PB granulocyte or MNC marking at any time points in the other animals. Low levels of mature gene-modified cells probably reflect poor transduction of repopulating stem cells, not a block in differentiation or specific immune rejection of mature cells. This study represents the longest follow-up of primates transplanted with transduced hematopoietic cells, and it is encouraging that the levels of vector-containing cells appear stable for up to 5 years.

The efficacy of recombinant thrombopoietin in murine and nonhuman primate models for radiation-induced myelosuppression and stem cell transplantation

Radiation-induced pancytopenia proved to be a suitable model system in mice and rhesus monkeys for studying thrombopoietin (TPO) target cell range and efficacy. TPO was highly effective in rhesus monkeys exposed to the mid-lethal dose of 5 Gy (300 kV x-rays) TBI, a model in which it alleviated thrombocytopenia, promoted red cell reconstitution, accelerated reconstitution of immature CD34+ bone marrow cells, and potentiated the response to growth factors such as GM-CSF and G-CSF. In contrast to the results in the 5 Gy TBI model, TPO was ineffective following transplantation of limited numbers of autologous bone marrow or highly purified stem cells in monkeys conditioned with 8 Gy TBI. In the 5 Gy model, a single dose of TPO augmented by GM-CSF 24 h after TBI was effective in preventing thrombocytopenia. The strong erythropoietic stimulation may result in iron depletion, and TPO treatment should be accompanied by monitoring of iron status. This preclinical evaluation thus identified TPO as a potential major therapeutic agent for counteracting radiation-induced pancytopenia and demonstrated pronounced stimulatory effects on the reconstitution of immature CD34+ hemopoietic cells with multilineage potential. The latter observation explains the potentiation of the hematopoietic responses to G-CSF and GM-CSF when administered concomitantly. It also predicts the effective use of TPO to accelerate reconstitution of immature hematopoietic cells as well as possible synergistic effects in vivo with various other growth factors acting on immature stem cells and their direct lineage-committed progeny. The finding that a single dose of TPO might be sufficient for a clinically significant response emphasizes its potency and is of practical relevance. The heterogeneity of the TPO response encountered in the various models used for evaluation points to multiple mechanisms operating on the TPO response and heterogeneity of its target cells. Mechanistic mouse studies made apparent that the response of multilineage cells shortly after TBI to a single administration of TPO is quantitatively more important for optimal efficacy than the lineage-restricted response obtained at later intervals after TBI and emphasized the importance of a relatively high dose of TPO to overcome initial c-mpl-mediated clearance. Further elucidation of mechanisms determining efficacy might very well result in a further improvement, e.g., following transplantation of limited numbers of stem cells. Adverse effects of TPO administration to myelosuppressed or stem cell transplanted experimental animals were not observed.

Ex Vivo Expansion of Genetically Marked Rhesus Peripheral Blood Progenitor Cells Results in Diminished Long-Term Repopulating Ability

The possibility of primitive hematopoietic cell ex vivo expansion is of interest for both gene therapy and transplantation applications. The engraftment of autologous rhesus peripheral blood (PB) progenitors expanded 10 to 14 days were tracked in vivo using genetic marking. Stem cell factor (SCF)/granulocyte colony-stimulating factor (G-CSF)–mobilized and CD34-enriched PB cells were divided into two equal aliquots and transduced with one of two retroviral vectors carrying the neomycin-resistance gene (neo) for 4 days in the presence of interleukin-3 (IL-3), IL-6, and SCF in the first 5 animals, IL-3/IL-6/SCF/Flt-3 ligand (FLT) in 2 subsequent animals, or IL-3/IL-6/SCF/FLT plus an autologous stromal monolayer (STR) in the final 2. At the end of transduction period, one aliquot (nonexpanded) from each animal was frozen, whereas the other was expanded under the same conditions but without vector for a total of 14 days before freezing. After total body irradiation, both the nonexpanded and expanded transduced cells were reinfused. Despite 5- to 13-fold higher cell and colony-forming unit (CFU) doses from the expanded fraction of marked cells, there was greater short- and long-term marking from the nonexpanded cells in all animals. In animals receiving cells transduced and expanded in the presence of IL-3/IL-6/SCF/FLT, engraftment by the marked expanded cells was further diminished. This discrepancy was even more pronounced in the animals who received cells transduced and expanded in the presence of FLT and autologous stroma, with no marking detectable from the expanded cells. Despite lack of evidence for expansion of engrafting cells, we found that the addition of FLT and especially STR during the initial brief transduction period increased engraftment with marked cells into a clinically relevant range. Levels of marked progeny cells originating from the nonexpanded aliqouts were significantly higher than that seen in previous 4 animals receiving cells transduced in the presence of IL-3/IL-6/SCF, with levels of 10% to 20% confirmed by Southern blotting from the nonexpanded IL-3/IL-6/SCF/FLT/STR graft compared with 0.01% in the original IL-3/IL-6/SCF cohort. These results suggest that, although expansion of PB progenitors is feasible ex vivo, their contribution towards both short- and long-term engraftment is markedly impaired. However, a brief transduction in the presence of specific cytokines and stromal support allows engraftment with an encouraging number of retrovirally modified cells.

This is a US government work. There are no restrictions on its use.

Ex Vivo Expansion of Genetically Marked Rhesus Peripheral Blood Progenitor Cells Results in Diminished Long-Term Repopulating Ability

The possibility of primitive hematopoietic cell ex vivo expansion is of interest for both gene therapy and transplantation applications. The engraftment of autologous rhesus peripheral blood (PB) progenitors expanded 10 to 14 days were tracked in vivo using genetic marking. Stem cell factor (SCF)/granulocyte colony-stimulating factor (G-CSF)–mobilized and CD34-enriched PB cells were divided into two equal aliquots and transduced with one of two retroviral vectors carrying the neomycin-resistance gene (neo) for 4 days in the presence of interleukin-3 (IL-3), IL-6, and SCF in the first 5 animals, IL-3/IL-6/SCF/Flt-3 ligand (FLT) in 2 subsequent animals, or IL-3/IL-6/SCF/FLT plus an autologous stromal monolayer (STR) in the final 2. At the end of transduction period, one aliquot (nonexpanded) from each animal was frozen, whereas the other was expanded under the same conditions but without vector for a total of 14 days before freezing. After total body irradiation, both the nonexpanded and expanded transduced cells were reinfused. Despite 5- to 13-fold higher cell and colony-forming unit (CFU) doses from the expanded fraction of marked cells, there was greater short- and long-term marking from the nonexpanded cells in all animals. In animals receiving cells transduced and expanded in the presence of IL-3/IL-6/SCF/FLT, engraftment by the marked expanded cells was further diminished. This discrepancy was even more pronounced in the animals who received cells transduced and expanded in the presence of FLT and autologous stroma, with no marking detectable from the expanded cells. Despite lack of evidence for expansion of engrafting cells, we found that the addition of FLT and especially STR during the initial brief transduction period increased engraftment with marked cells into a clinically relevant range. Levels of marked progeny cells originating from the nonexpanded aliqouts were significantly higher than that seen in previous 4 animals receiving cells transduced in the presence of IL-3/IL-6/SCF, with levels of 10% to 20% confirmed by Southern blotting from the nonexpanded IL-3/IL-6/SCF/FLT/STR graft compared with 0.01% in the original IL-3/IL-6/SCF cohort. These results suggest that, although expansion of PB progenitors is feasible ex vivo, their contribution towards both short- and long-term engraftment is markedly impaired. However, a brief transduction in the presence of specific cytokines and stromal support allows engraftment with an encouraging number of retrovirally modified cells.

This is a US government work. There are no restrictions on its use.

Cytokines in hematopoiesis

Hematopoiesis is the process by which mature, functional progeny of the eight major lineages of blood cells are produced from a hierarchy of progressively less mature progenitor and stem cells. The control of hematopoiesis involves intimate cellular interactions between developing blood cells and stromal elements as well as regulation by soluble cytokines, that may act locally in the bone marrow environment or at remote tissue sites. In excess of twenty cytokines that stimulate the production and/or function of hematopoietic cells have now been cloned and are available in purified, recombinant form. The colony-stimulating factors, erythropoietin and the recently discovered thrombopoietin are key regulators of granulocyte/macrophage, erythroid and megakaryocyte/platelet production respectively. The activities of these cytokines have been extensively studied, both in vitro and in vivo, and recent analysis of mice genetically engineered to lack these regulators or their cell surface receptors have provided profound insights into their essential physiological roles. These studies have culminated in the development of these cytokines as valuable clinical reagents.

The Efficacy of Single-Dose Administration of Thrombopoietin With Coadministration of Either Granulocyte/Macrophage or Granulocyte Colony-Stimulating Factor in Myelosuppressed Rhesus Monkeys

Thrombopoietin (TPO) was evaluated for efficacy in a placebo-controlled study in rhesus monkeys with concurrent administration of either granulocyte/macrophage colony-stimulating factor (GM-CSF) or granulocyte CSF, (G-CSF). Rhesus monkeys were subjected to 5 Gy total-body irradiation (TBI), resulting in 3 weeks of profound pancytopenia, and received either TPO 5 μg/kg intravenously (IV) at day 1 (n = 4), GM-CSF 25 μg/kg subcutaneously (SC) for 14 days (n = 4), TPO and GM-CSF (n = 4), G-CSF 10 μg/kg/d SC for 14 days (n = 3), TPO and G-CSF (n = 4), or placebo (carrier, n = 4; historical controls, n = 8). Single-dose IV treatment with TPO 1 day after TBI effectively counteracted the need for thrombocyte transfusions (provided whenever thrombocyte levels were <40 × 109/L) and accelerated platelet reconstitution to normal levels 2 weeks earlier than placebo controls. TPO/GM-CSF was more effective than single-dose TPO alone in stimulating thrombocyte regeneration, with a less profound nadir and a further accelerated recovery to normal thrombocyte counts, as well as a slight overshoot to supranormal levels of thrombocytes. Monkeys treated with TPO/GM-CSF uniformly did not require thrombocyte transfusions, whereas those treated with GM-CSF alone needed two to three transfusions, similar to the placebo-treated monkeys, which required, on average, three transfusions. Also, reticulocyte production was stimulated by TPO and further augmented in monkeys treated with TPO/GM-CSF. TPO alone did not stimulate neutrophil regeneration, whereas GM-CSF shortened the period of neutrophil counts less than 0.5 × 109/L by approximately 1 week; TPO/GM-CSF treatment elevated the neutrophil nadir, but did not further accelerate recovery to normal values. TPO also augemented the neturophil response to G-CSF, resulting in similar patterns of reconstitution following TPO/G-CSF and TPO/GM-CSF treatment. TPO/GM-CSF resulted in significantly increased reconstitution of CD34+ bone marrow cells and progenitor cells such as GM-CFU and BFU-E. Adverse effects of combining TPO with the CSFs were not observed. It is concluded that (1) a single IV administration of TPO is sufficient to prevent severe thrombocytopenia following myelosuppression, (2) TPO/G-CSF and TPO/GM-CSF treatment result in distinct response patterns, with TPO/GM-CSF being superior to TPO/G-CSF in stimulating thrombocyte and erythrocyte recovery while being equivalent in stimulating neutrophil recovery; and (3) TPO significantly improves the performance of CSFs in alleviating severe neutropenia.

The Efficacy of Single-Dose Administration of Thrombopoietin With Coadministration of Either Granulocyte/Macrophage or Granulocyte Colony-Stimulating Factor in Myelosuppressed Rhesus Monkeys

Thrombopoietin (TPO) was evaluated for efficacy in a placebo-controlled study in rhesus monkeys with concurrent administration of either granulocyte/macrophage colony-stimulating factor (GM-CSF) or granulocyte CSF, (G-CSF). Rhesus monkeys were subjected to 5 Gy total-body irradiation (TBI), resulting in 3 weeks of profound pancytopenia, and received either TPO 5 μg/kg intravenously (IV) at day 1 (n = 4), GM-CSF 25 μg/kg subcutaneously (SC) for 14 days (n = 4), TPO and GM-CSF (n = 4), G-CSF 10 μg/kg/d SC for 14 days (n = 3), TPO and G-CSF (n = 4), or placebo (carrier, n = 4; historical controls, n = 8). Single-dose IV treatment with TPO 1 day after TBI effectively counteracted the need for thrombocyte transfusions (provided whenever thrombocyte levels were <40 × 109/L) and accelerated platelet reconstitution to normal levels 2 weeks earlier than placebo controls. TPO/GM-CSF was more effective than single-dose TPO alone in stimulating thrombocyte regeneration, with a less profound nadir and a further accelerated recovery to normal thrombocyte counts, as well as a slight overshoot to supranormal levels of thrombocytes. Monkeys treated with TPO/GM-CSF uniformly did not require thrombocyte transfusions, whereas those treated with GM-CSF alone needed two to three transfusions, similar to the placebo-treated monkeys, which required, on average, three transfusions. Also, reticulocyte production was stimulated by TPO and further augmented in monkeys treated with TPO/GM-CSF. TPO alone did not stimulate neutrophil regeneration, whereas GM-CSF shortened the period of neutrophil counts less than 0.5 × 109/L by approximately 1 week; TPO/GM-CSF treatment elevated the neutrophil nadir, but did not further accelerate recovery to normal values. TPO also augemented the neturophil response to G-CSF, resulting in similar patterns of reconstitution following TPO/G-CSF and TPO/GM-CSF treatment. TPO/GM-CSF resulted in significantly increased reconstitution of CD34+ bone marrow cells and progenitor cells such as GM-CFU and BFU-E. Adverse effects of combining TPO with the CSFs were not observed. It is concluded that (1) a single IV administration of TPO is sufficient to prevent severe thrombocytopenia following myelosuppression, (2) TPO/G-CSF and TPO/GM-CSF treatment result in distinct response patterns, with TPO/GM-CSF being superior to TPO/G-CSF in stimulating thrombocyte and erythrocyte recovery while being equivalent in stimulating neutrophil recovery; and (3) TPO significantly improves the performance of CSFs in alleviating severe neutropenia.

Recombinant cytokines and hematopoietic growth factors in allogeneic and autologous bone marrow transplantation

Use of recombinant hematopoietic growth factors in the course of bone marrow transplantation has revolutionized this modality by significantly improving the safety of the procedure. It is anticipated that use of cytokines in combination and the introduction of newer agents will further reduce costs and improve antitumor responses as well.

Improved retroviral gene transfer into murine and Rhesus peripheral blood or bone marrow repopulating cells primed in vivo with stem cell factor and granulocyte colony-stimulating factor

In previous studies we showed that 5 days of treatment with granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF) mobilized murine repopulating cells to the peripheral blood (PB) and that these cells could be efficiently transduced with retroviral vectors. We also found that, 7-14 days after cytokine treatment, the repopulating ability of murine bone marrow (BM) increased 10-fold. In this study we examined the efficiency of gene transfer into cytokine-primed murine BM cells and extended our observations to a nonhuman primate autologous transplantation model. G-CSF/SCF-primed murine BM cells collected 7-14 days after cytokine treatment were equivalent to post-5-fluorouracil BM or G-CSF/SCF-mobilized PB cells as targets for retroviral gene transfer. In nonhuman primates, CD34-enriched PB cells collected after 5 days of G-CSF/SCF treatment and CD34-enriched BM cells collected 14 days later were superior targets for retroviral gene transfer. When a clinically approved supernatant infection protocol with low-titer vector preparations was used, monkeys had up to 5% of circulating cells containing the vector for up to a year after transplantation. This relatively high level of gene transfer was confirmed by Southern blot analysis. Engraftment after transplantation using primed BM cells was more rapid than that using steady-state bone marrow, and the fraction of BM cells saving the most primitive CD34+/CD38- or CD34+/CD38dim phenotype increased 3-fold. We conclude that cytokine priming with G-CSF/SCF may allow collection of increased numbers of primitive cells from both the PB and BM that have improved susceptibility to retroviral transduction, with many potential applications in hematopoietic stem cell-directed gene therapy.

Gene transfer into hematopoietic stem cells of nonhuman primates

Nonhuman primates provide an appropriate preclinical large-animal model to test the efficacy of bone marrow gene therapy procedures. Successful retroviral vector-mediated gene transfer into monkey pluripotent hematopoietic stem cells (PHSC) has closed the gap between gene transfer experiments in mouse models and clinical application of bone marrow gene therapy. After initial bone marrow transplant failures, ex vivo bone marrow culture conditions were found that sufficiently supported maintenance of the long-term repopulating ability of genetically modified autologous monkey grafts. The efficiency of gene transfer into primate PHSC has, however, remained at least one order of magnitude lower than has been achieved in mice. Similar gene transfer efficiencies have been obtained with total bone marrow grafts, CD34+ bone marrow grafts, and mobilized peripheral blood progenitor cell grafts; however, various attempts to increase the transduction efficiency have been without significant success. Primate PHSC seem to require quite different culture conditions for their maintenance and transduction than mouse PHSC, in particular regarding hematopoietic growth factor addition. In contrast to observations in other species, some form of conditioning appeared essential for engraftment of transduced PHSC in monkeys. Although it has been shown that mouse retroviruses can replicate in monkeys and are capable of inducing neoplasms, experiments in monkeys have sufficiently confirmed the safety of current gene transfer procedures to allow their clinical application.

Clinical role of GM-CSF in neutrophil recovery in relation to health care parameters

Recombinant growth factors, particularly granulocyte-macrophage colony-stimulating factor (GM-CSF), have been only available for a few years. Since their introduction they have affected the management of drug-induced neutropenia, the use of dose intensive chemotherapy regimens and in the setting of autologous stem cell transplantation. This review addresses the clinical role of GM-CSF, using the data available, in neutrophil recovery in relation to various health care parameters.

Hematopoietic growth factors in cancer treatment

The introduction of hematopoietic growth factors during the past five years has changed the scenery of antitumor treatment. Growth factors following high-dose chemotherapy or bone marrow transplantation have become established as part of many treatment protocols. The main benefits are earlier recovery of neutrophils resulting in fewer days with fever, antibiotics and hospitalization. Growth factors were found to reduce the treatment-related morbidity and to improve the practicability of therapeutic regimens. First studies on a prospective chemotherapy dose intensification supported by growth factors are underway. As a further effect of growth factors, an attempted enhancement of antitumor cytotoxicity by recruitment of tumor cells to chemosensitivity or by modulation of antitumor drug metabolism appears realistic based on first data on growth factor priming in AML. New ways to support high-intensity and myeloablative antitumor strategies are opened by the autologous transplantation of peripheral blood progenitor cells mobilized by growth factors and also by the use of new factors like SCF and the synergistic combination of growth factors as part of future strategies against malignant disorders.

The effect of rGM-CSF on neutrophil and eosinophil regeneration after ABMT as monitored by circulating levels of granule proteins

In order to further evaluate the effects of rGM-CSF on the reconstituting granulopoiesis, plasma and serum levels of myeloperoxidase (MPO) and lactoferrin (LF), as well as serum levels of eosinophil cationic protein (ECP), were monitored daily during a period of 3-4 weeks following ABMT in a group of 22 patients treated with either rGM-CSF (n = 11) or placebo (n = 11). Despite faster increase in the neutrophil counts in the rGM-CSF group, we did not observe any difference either in P-MPO or in P-LF during the period of early engraftment (days 11-19). This finding indicates that the proliferative effect of rGM-CSF on the neutropoiesis may be overestimated when neutrophil counts alone are taken into consideration, and suggests that other mechanisms may have contributed to the increase in the number of circulating neutrophils. The ratio of the serum to plasma level of LF, but not of MPO, was higher in the rGM-CSF group, probably reflecting a specific in vivo neutrophil priming effect. In the rGM-CSF group there was a clear increase of S-ECP during the second and third week post transplant, corresponding to an increase in eosinophil counts, which indicates that rGM-CSF stimulated eosinophil reconstitution without causing excessive activation of the mature eosinophils.

Analysis of radiolabeled CHO cell-derived rHuGM-CSF pharmacokinetics and biodistribution in rhesus monkeys following intravenous and subcutaneous injection

The purpose of these studies was to examine the biodistribution and pharmacokinetics of radiolabeled human CHO cell-derived rHuGM-CSF in normal Rhesus monkeys (Macaca mulatta) following intravenous (i.v.) and subcutaneous (s.c.) injection. A dual radioisotope tracer technique was utilized to monitor the behavior of rHuGM-CSF in vivo. Recombinant HuGM-CSF was radiolabeled with I-123 (a 13.2 h half-life, 140 KeV pure gamma emitting radionuclide detected using gamma scintigraphic imaging) using a mild chloramine T reaction. A separate preparation of rHuGM-CSF radiolabeled with S-35 methionine by bioincorporation in tissue culture was mixed with the I-123-labeled protein, permitting comparison of data obtained from the two radiolabels. Two dose levels of rHuGM-CSF were used for i.v. bolus (15 and 300 micrograms/kg) and s.c. (10 and 100 micrograms/kg) studies. The results of these studies demonstrated that the co-administered I-123 rHuGM-CSF and S-35 rHuGM-CSF followed similar blood elimination kinetics after i.v. or s.c. injection. Following i.v. bolus injection, rHuGM-CSF was found to rapidly distribute to all central body cavity high blood flow organs, followed by rapid uptake in the kidneys and elimination in the urine. There were no differences in the pharmacokinetic values obtained for I-123- and S-35-labeled rHuGM-CSF nor for the two dose levels examined. Following, s.c. injection, I-123- and S-35-labeled rHuGM-CSF were found to reach maximal plasma levels after approximately 16 h. The primary route of elimination was the urine. Monkeys previously exposed to rHuGM-CSF were found to have circulating antibodies to rHuGM-CSF. Studies in these animals revealed a significantly altered distribution and clearance of radiolabeled rHuGM-CSF, with the majority of the injected activity being cleared by the liver.

Prediction of the role of granulocyte-macrophage colony-stimulating factor in animals and man from in vitro results

The possibility of predicting the clinical effects of cytokines from in vitro data is discussed, using GM-CSF as an example. GM-CSF incubated with bone marrow cells has been shown to induce proliferation and colony formation, predominantly of the colony-forming unit granulocyte and granulocyte-macrophage types. Daily treatment of normal monkeys with GM-CSF resulted in transient neutropenia followed by neutrophilia. After withdrawal of GM-CSF the neutrophil levels returned to baseline. Predictably, GM-CSF administration results in accelerated neutrophil recovery in patients with chemotherapy-induced neutropenia. GM-CSF has also been shown to induce microbial killing by neutrophils and monocytes in vitro. This activity translated into a dose-related protection of GM-CSF-pretreated mice infected with lethal doses of micro-organisms. Interleukin-3 (IL-3) increases the cellularity of the bone marrow and GM-CSF can induce mobilization of bone marrow cells into the peripheral blood. Therefore, it was predicted and subsequently proved that a combination of these cytokines is synergistic, increasing the yields of peripheral blood progenitor cells which could be collected and then retransplanted into patients undergoing myeloablative chemotherapy. Monkeys injected with recombinant human IL-3 and GM-CSF had increased antibody titres to human IL-3 compared with monkeys given IL-3 alone, suggesting a potential use of GM-CSF which was not predicted from its in vitro results, that of vaccine adjuvancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Helper virus induced T cell lymphoma in nonhuman primates after retroviral mediated gene transfer

Moloney Murine Leukemia Virus (MoMuLV) causes T cell neoplasms in rodents but is not known to be a pathogen in primates. The core protein and enzyme genes of the MoMuLV genome together with an amphotropic envelope gene are utilized to engineer the cell lines that generate retroviral vectors for use in current human gene therapy applications. We developed a producer clone that generates a very high concentration of retroviral vector particles to optimize conditions for gene insertion into pluripotent hematopoietic stem cells. This producer cell line also generates a much lower concentration of replication-competent virus that arose through recombination. Stem cells from rhesus monkeys were purified by immunoselection with an anti-CD34 antibody, incubated in vitro for 80-86 h in the presence of retroviral vector particles with accompanying replication-competent virus and used to reconstitute recipients whose bone marrow had been ablated by total body irradiation. The retroviral vector genome was detected in circulating cells of five of eight transplant recipients of CD34+ cells and in the circulating cells of two recipients of infected, unfractionated bone marrow mononuclear cells. Three recipients of CD34+ cells had a productive infection with replication-competent virus. Six or seven mo after transplantation, each of these animals developed a rapidly progressive T cell neoplasm involving the thymus, lymph nodes, liver, spleen, and bone marrow. Lymphoma cells contained 10-50 copies of the replication-competent virus, but lacked the retroviral vector genome. We conclude that replication-competent viruses arising from producer cells making retroviral vectors can be pathogenic in primates, which underscores the importance of carefully screening retroviral producer clones used in human trials to exclude contamination with replication-competent virus.

The biology of granulocyte-macrophage colony-stimulating factor: effects on hematopoietic and nonhematopoietic cells

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is one of a family of glycoprotein cytokines that have potent effects in stimulating the proliferation, maturation, and function of hematopoietic cells. Deriving its name from its ability to stimulate the formation of macroscopic colonies containing neutrophils, eosinophils, macrophages, or mixtures of these cell types, GM-CSF stimulates the proliferation and maturation of myeloid progenitors, as well as functionally activating mature neutrophils, eosinophils, and macrophages. As most of the effects observed using GM-CSF in vitro have been shown to occur in vivo either in animal models or in human subjects, it is important to consider that GM-CSF may also exert some biological effects on nonhematopoietic cells. In response to immunologic stimuli, immunologic surveillance cells and cells of the microenvironment are capable of producing GM-CSF. In vitro experiments indicate that GM-CSF production is tightly regulated. In that regard, GM-CSF is not present in measurable quantities in normal serum, but little is known about the in vivo process of GM-CSF production and regulation. The biologic capabilities of GM-CSF have triggered its widespread clinical use in situations where hematopoiesis is compromised. GM-CSF can act as a potent growth factor in vivo, increasing the number and enhancing the function of hematopoietic progenitors and mature cells. However, the precise in vivo effect that GM-CSF may have on normal and neoplastic cells of nonhematopoietic origin remains undefined. The full range of GM-CSF bioactivity is mediated following binding to its receptor. The presence of specific receptors for GM-CSF has been demonstrated in all responsive cells of hematopoietic lineage, as well as in nonhematopoietic cells, both responsive and unresponsive. In conclusion, a large body of work from a number of laboratories has defined the biology of GM-CSF. Currently available reagents and technology will provide additional insights into the biology of this molecule, thereby expanding our present definition and allowing us to explore the mechanisms regulating hematopoiesis.

Therapeutic evaluation of interleukin-1 for stimulation of hematopoiesis in primates after autologous bone marrow transplantation

A multiple dose IL-1 therapy was evaluated for its capability to stimulate hematopoiesis in normal primates and to restore hematopoiesis after autologous bone marrow transplantation. The administration of IL-1 to normal animals over a dose range of 0.5 to 10 micrograms/kg/d led to a 7-12 fold increase in peripheral blood neutrophil and monocyte counts after 24 hours. This increase in the mature peripheral blood myeloid cells was followed by changes in the myeloid composition of the bone marrow, where the percentage of myeloid elements increased along with a transient increase in myeloid progenitor cell activity. IL-1 treatment also led to an initial decrease in platelet counts of 10-30% during the first 3 days of treatment. However, a striking finding was a significant and long lasting stimulation of increased platelet production with platelet counts increasing to 77% of baseline 3 days after cessation of treatment and remaining elevated for the next 10 days. The therapeutic potential of the IL-1 regimen to restore hematopoiesis was further evaluated in an established autologous bone marrow transplantation model. In monkeys receiving IL-1 doses, 1.0 and 5.0 ug/kg/d, neutrophil counts recovered to greater than 0.5 x 10e9/1 on day 16, one day earlier than control, but the recovery to baseline neutrophil counts occurred 5 days sooner than control. IL-1 therapy had its greatest effect on the restoration of platelet counts after transplantation, reaching greater than 100 x 10e9/1 by day 21, two weeks earlier than control. This work demonstrates that IL-1 therapy stimulates myelopoiesis but its most promising clinical application is the stimulation of platelet production.

Haemopoietic cell kinetics in humans treated with rGM-CSF

We have investigated the kinetics of myeloid cell proliferation in the marrow of patients with small-cell lung cancer and treated with 10 daily subcutaneous injections of granulocyte/macrophage colony-stimulating factor (GM-CSF). Bone marrow, obtained before and during treatment with the growth factor, was labelled in vitro with tritiated thymidine (3H-TdR). A 3rd bone-marrow sample was obtained 1 hr following an intravenous injection of 3H-TdR. Subsequent daily blood samples were also collected, and 3H-TdR labelling was assessed on these and the marrow preparations by autoradiography. GM-CSF treatment increased the peripheral granulocytic cells nearly 5-fold, but this included significant eosinophilia, so that the neutrophilic granulocytes increased only 3.3-fold. These cells were released from the marrow over a normal time scale, but their peripheral half-life was about 6 times longer than normal and they were probably functionally defective. Furthermore, significant numbers of immature cells were released from the marrow. Neutrophil production stimulated by GM-CSF was thus overestimated by measurement of the apparent peripheral granulocytosis. Increased labelling indices and grain counts in the proliferating granulocytic cells of the marrow indicate shortened cell-cycle times, and the excess granulocyte production appears to be the result of extra amplification divisions in the proliferative compartments.

Effect of erythroid differentiation factor on megakaryocytic differentiation of L8057, a murine megakaryoblastic leukemia cell line

To assess the potent effect of erythroid differentiation factor (EDF) on megakaryocytopoiesis, effect of EDF on megakaryocytic differentiation of L8057, a murine megakaryoblastic cell line, was examined. EDF potentiated AchE induction of L8057 in a dose dependent manner. The potency of EDF on megakaryocytic differentiation is comparable to that on erythroid differentiation reported previously. The present results suggest that EDF may play a regulatory role in megakaryocytopoiesis as well as in erythropoiesis.

Preclinical studies and future directions in the development of new hematologic growth factors

Normal hematopoiesis is controlled by a cascade of interacting hormones collectively referred to as cytokines. These growth factors have been studied both individually and in specific combinations to determine their optimal clinical use. In some cases, the combination of certain cytokines produces a synergistic effect enhancing their efficacy. Granulocyte-macrophage colony-stimulating factor (GM-CSF) has demonstrated the ability to stimulate early- and late-phase granulocyte and macrophage progenitor cells, activate mature neutrophils and macrophages, and enhance their peripheral infection fighting performance. Interleukin-3 (IL-3), currently undergoing clinical evaluation, acts early in the development of multiple types of white blood cells and, when used in combination with GM-CSF, also produces a synergistic effect in raising white blood cell and platelet levels. A recombinant protein, PIXY321, has recently been developed that contains both IL-3 and GM-CSF domains. The development of this molecule was supported by the discovery of a dual IL-3-GM-CSF receptor on the surface of hematopoietic progenitor cells. PIXY321 provides a significantly enhanced biologic effect (10-fold greater proliferation) via multiple cross-linking of GM-CSF, IL-3, and dual receptor binding sites. PIXY321 has the same molecular weight as the equivalent molar concentrations of GM-CSF and IL-3 combined and offers the advantage of combination therapy in an easy-to-administer regimen. Another recombinant cytokine, mast cell growth factor (MGF), has shown profound hematopoietic activity in vitro and has the ability to enhance proliferation of hematopoietic stem cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The mechanism responsible for diminished neutrophil production in neonates delivered of women with pregnancy-induced hypertension

The neonatal neutropenia after pregnancy-induced hypertension is a function of diminished neutrophil production. These studies test the hypothesis that this diminution is due to decreased production of neutrophilic growth factors, reduced responsiveness of neutrophil progenitors to these factors, or the presence of an inhibitor. While the concentrations of placentally derived colony-stimulating factors were similar in normotensive and hypertensive gestations, bioassay demonstrated less colony-stimulating activity in placental conditioned media from hypertensive gestations. Evaluation of the responsiveness of progenitors to recombinant factors revealed no differences between those from normotensive and hypertensive gestations. However, neutrophilic colony formation in vitro was significantly inhibited after the addition of conditioned media or sera from hypertensive gestations, whereas the addition of these from normotensive gestations had no inhibitory effect. Thus this common maternal-fetal disorder is associated with an inhibitor of neutrophil production, which is elaborated by the placenta and present in cord blood serum.

In vitro modulation of canine polymorphonuclear leukocyte function by granulocyte-macrophage colony stimulating factor

Granulocyte-macrophage colony stimulating factor (GMCSF) promotes the growth of granulocytes and macrophages from undifferentiated bone marrow cells and modulates the oxidative responses of polymorphonuclear leukocytes (PMN) to endogenous chemoattractants. We found that, in vitro, naturally occurring glycolsylated human GMCSF does not disturb the resting canine PMN membrane potential, may attentuate PMN oxidative responses to PMA, and is, to a small degree, chemotaxigenic. GMCSF, however, inhibits PMN chemotaxis to zymosan-activated plasma (ZAP). Compared to temperature controls, GMCSF (1-100 U/ml) produced up to 1.5-fold increases in H2O2 production after 15 minutes, while phorbol myristate acetate (PMA) treated cells increased H2O2 production 8-12-fold after 15 minutes. Preincubation of cells with GMCSF (1-100 U/ml) prior to PMA stimulation significantly reduced the H2O2 levels induced by PMA. H2O2 production was inhibited up to 15% after 15 minutes of GMCSF preincubation and up to 40% after 60 minutes of preincubation. As a chemotaxigenic agent, GMCSF (10-1000 U/ml) was able to elicit 49%-102% increases in quantitative cellular migration, compared to random migration. Total cellular chemotaxis to GMCSF was less than 30% of the response to ZAP. Preincubation of PMNs with GMCSF for 15 minutes significantly inhibited ZAP-induced cellular migration. Human GMCSF does not appear to activate canine PMN in vitro and may actually down-regulate PMN inflammatory responses.