Persistence of human multilineage, self-renewing lymphohematopoietic stem cells in chimeric sheep

We have previously reported the ability of uncharacterized human bone marrow (BM) cells to engraft into preimmune fetal sheep, thereby creating sheep-human chimera suitable for in vivo examination of the properties of human hematopoietic stem cells (HSC). Adult human bone marrow CD34+ HLA-DR- cells have been extensively characterized in vitro and have been demonstrated to contain a number of primitive hematopoietic progenitor cells (PHPC). However, the capacity of such highly purified populations of human marrow CD34+ HLA-DR- cells to undergo in vivo self-renewal and multipotential lymphohematopoietic differentiation has not been previously demonstrated. To achieve that, human CD34+ HLA-DR- cells were transplanted in utero into immunoincompetent fetal sheep to investigate the BM-populating potential of these cells. Long-term chimerism, sustained human hematopoiesis, and expression of human cells belonging to all human blood cell lineages were demonstrated in two animals for more than 7 months' posttransplantation. Chimeric BM contained erythroid, granulocytic/monocytic, and megakaryocytic hematopoietic progenitor cells, as well as the primitive high proliferative potential colony-forming cell (HPP-CFC). Under a variety of in vitro experimental conditions, chimeric BM cells gave rise to human T cells expressing T-lymphocyte-specific markers, human natural killer (NK) cells, and human IgG-producing B cells. In vivo expansion and possibly self-renewal of transplanted PHPC was confirmed by the detection in chimeric BM 130 days' posttransplantation of CD34+ HLA-DR- cells, the phenotype of human cells constituting the stem-cell graft. These studies demonstrate not only the BM-populating capacity, multipotential differentiation, and most likely self-renewal capabilities of human CD34+ HLA-DR- cells, but also that this BM population contains human HSC. Furthermore, it appears that this animal model of xenogeneic stem-cell transplantation is extremely useful for in vivo examination of human hematopoiesis and the behavioral and functional characteristics of human HSC.

A novel 37-Kd adhesive membrane protein from cloned murine bone marrow stromal cells and cloned murine hematopoietic progenitor cells

The adhesion of hematopoietic progenitor cells to bone marrow stromal cells is critical to hematopoiesis and involves multiple effector molecules. Stromal cell molecules that participate in this interaction were sought by analyzing the detergent-soluble membrane proteins of GBI/6 stromal cells that could be adsorbed by intact FDCP-1 progenitor cells. A single-chain protein from GBI/6 cells having an apparent molecular weight of 37 Kd was selectively adsorbed by FDCP-1 cells. This protein, designated p37, could be surface-radiolabeled and thus appeared to be exposed on the cell membrane. An apparently identical 37-Kd protein was expressed by three stromal cell lines, by Swiss 3T3 fibroblastic cells, and by FDCP-1 and FDCP-2 progenitor cells. p37 was selectively adsorbed from membrane lysates by a variety of murine hematopoietic cells, including erythrocytes, but not by human erythrocytes. Binding of p37 to cells was calcium-dependent, and was not affected by inhibitors of the hematopoietic homing receptor or the cell-binding or heparin-binding functions of fibronectin. It is proposed that p37 may be a novel adhesive molecule expressed on the surface of a variety of hematopoietic cells that could participate in both homotypic and heterotypic interactions of stromal and progenitor cells.

Effect of xenogeneic chimerism in a human/sheep model on natural antibody

Xenogeneic transplantation is a potential solution to the severe shortage of donor organs for clinical transplantation. The primary limitation to xenogeneic transplantation between widely disparate species is hyperacute rejection, which is triggered by the recipient's natural antibodies reacting against the donor's endothelial cells. Natural antibodies react between widely disparate species but do not react between closely related species. Specific tolerance for xenogeneic transplantation between closely related species can be induced by creating hematopoietic chimerism between donor and recipient. However, whether specific xenograft tolerance can be induced by the creation of chimerism between widely disparate species, where natural antibody reacts, is unknown. We previously have established a model of hematopoietic chimerism between widely disparate species by the in utero transplantation of human fetal hematopoietic stem cells into early gestation fetal lambs. In the present study, we determined whether long-standing hematopoietic chimerism in this human/sheep model reduces the level of natural antibody directed against human endothelial cells. To answer this question, we measured the reactivity of serum from five chimeric sheep, five sheep controls, and five human controls in an in vitro enzyme-linked immunoabsorbance assay directed against human umbilical vein endothelial cells. Unexpectedly, we found that long-standing hematopoietic chimerism in the human/sheep model did not reduce the reactivity of serum against human endothelial cells compared to age-matched sheep controls. These results suggest that the induction of hematopoietic chimerism between widely disparate species will not control the problem of natural antibody and hyperacute rejection.

Suppression of normal human hematopoiesis by cytomegalovirus in vitro

Human cytomegalovirus (HCMV) infection is associated with marrow suppression in immunocompromised patients. To examine the mechanism(s) underlying this suppression, the effect of a laboratory strain of HCMV (AD169) and a clinical isolate of HCMV on colony formation by normal human marrow (BMC) hematopoietic progenitors in the presence and/or absence of monocyte/macrophages (MO) and T cells was studied. Direct addition of HCMV at multiplicity of infection (MI) of 0.1 to 5 to BMC produced dose-dependent inhibition of colony forming unit-mix (CFU-Mix) (30-82%), CFU granulocyte, macrophage (CFU-GM) (15-98%), and burst forming unit-erythroid (BFU-E) (23-86%); no consistent effect of CFU-erythroid (CFU-E) was noted. This inhibition occurred both with the direct addition of HCMV to the culture plates as well as by the preincubation of BMC with HCMV followed by washing of the cells; significant inhibition (p < 0.01) of colony formation occurred after 1 hour of incubation at MI of 5. No suppression of colony formation occurred when UV-irradiated virus was used. The inhibitory effect of HCMV was reduced when MO and T cells were removed prior to exposure of marrow to virus at MI of 1 to 5. At MI of 20, however, HCMV suppressed colony formation by BMC depleted of MO and T cells by about 40%. Coculture of autologous or allogeneic T cells, but not MO, exposed to HCMV with intact or depleted marrow resulted in inhibition of CFU-Mix (51%), CFU-GM (40%), and BFU-E (37%). The inhibitory effect of virus-exposed T cells did not appear to be mediated through a soluble factor. T cells expressing CD8 antigen were most active in this process; natural killer (NK) cells were not active. These results suggest that the suppressive effect of HCMV on hematopoiesis may be mediated in part through T lymphocytes.

Liver-derived fetal hematopoietic stem cells selectively and preferentially home to the fetal bone marrow

In the course of ontogeny, the homing site for the hematopoietic stem cells (HSC) moves with certain predictability from the yolk sac to the liver/spleen and then to the marrow. The pattern of this migration has thus far been established mostly on a morphologic basis. To delineate further the course of this migration and to gain insight into its possible mechanism, we used in utero transplantation of allogeneic or xenogeneic HSC in preimmune sheep fetuses. Sex chromosome, type of hemoglobin, and species-specific surface markers were used to follow the path of transplanted cells in the fetus. Before the development of the bone marrow, transplanted HSC (liver- or marrow-derived) homed exclusively to the liver/spleen. With the development of marrow, around day 60 of gestation (term, 145 days), homing occurred also in the nascent marrow and by day 80 transplanted cells homed exclusively to the marrow. This suggests that there may be a hierarchy in homing sites, with those of the marrow having higher affinity than those of liver/spleen. Interestingly, despite a change in homing that was followed by the expansion of the marrow compartment of HSC (ie, HSC proliferation), these cells did not participate actively in blood cell formation during most of the prenatal period. Liver remained the major hematopoietic organ throughout the gestation. It was only during the perinatal period that this organ assumed the function of hematopoiesis from the liver. This lack of expression of HSC in fetal marrow can possibly be attributable to the immaturity of marrow stroma required for differentiation and maturation of progenitors and the orderly egress of mature cells into the blood stream. The availability of this model allows us to begin studies in the molecular mechanism of stem cell homing in vivo during ontogeny.

Erythropoietin does not cross the placenta into the fetus

Erythropoiesis in the fetus is controlled by erythropoietin (Ep). To determine the role of maternal Ep in this process, we used catheterized preparations of sheep and monkey fetuses to assess the ability of Ep administered to the mother to cross the placental barrier into the fetus. Ep was injected into pregnant sheep (3,600 IU/sheep) or monkeys (800-2,000 IU/animal) as a single intravenous dose, or into sheep in intravenous doses of 2,000 IU once every 12 h for a total of 4 injections. Maternal and fetal blood samples for Ep and reticulocyte determinations were obtained before and at intervals after Ep injections. The administration of Ep resulted in significant increases in maternal circulating Ep levels in sheep and monkeys. Despite the presence of high levels of maternal Ep, however, no increase in fetal plasma Ep levels was detected. The administration of Ep to the mother caused significant increases in reticulocyte production in the mother but not the fetus; injection of Ep directly to the fetus stimulated fetal erythropoiesis. These results demonstrate that Ep does not cross the placenta into the fetus even under conditions of chronically elevated maternal Ep levels, and suggest that red cell production in the fetus is regulated by Ep produced from sites within the fetus.

Ex vivo incubation with growth factors enhances the engraftment of fetal hematopoietic cells transplanted in sheep fetuses

Hematopoietic stem cells (HSC) transplanted in utero are in competition with endogenous HSC; thus, ultimately the graft constitutes a relatively small fraction of total HSC pool. To enhance the engraftment of donor cells in sheep fetuses, we preincubated these cells, ex vivo, for 16 hours at 37 degrees C with the conditioned medium from phytohemagglutinin-stimulated lymphocytes (PHA-LCM) before in utero transplantation. PHA-LCM is a rich source of hematopoietic growth factors in sheep. Subsequent engraftment was significantly higher in cells preincubated with PHA-LCM compared with fresh cells or those incubated with control medium only. This was reflected in all markers of the donor cells (hemoglobin type, karyotype, and progenitor cell assays). Brief ex vivo incubation with PHA-LCM also increased viability of all marrow cells as well as total numbers of progenitors. Similar enhancement of engraftment was also noted in monkeys after a brief preincubation of donor cells with interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF). We conclude that brief (16 hours) ex vivo incubation of donor cells with a source of such growth factors as IL-3 and GM-CSF enhances the subsequent engraftment of transplanted cells.

Engraftment and long-term expression of human fetal hemopoietic stem cells in sheep following transplantation in utero

Hemopoietic stem cells from human fetal liver were transplanted in utero into preimmune fetal sheep (48-54 days of gestation). The fate of donor cells was followed using karyotype analysis, by immunofluorescence labeling with anti-CD antibodies, and by fluorescent in situ hybridization using human-specific DNA probes. Engraftment occurred in 13 of 33 recipients. Of five live born sheep that exhibited chimerism, all expressed human cells in the marrow, whereas three expressed them in blood as well. Engraftment was multilineage (erythroid, myeloid, and lymphoid) and human hemopoietic progenitors (multipotent colony-forming units, colony-forming units-granulocyte, macrophage, and erythroid burst-forming units) capable of forming colonies in vitro were detected in all five lambs for greater than 2 yr. These progenitors responded to human-specific growth factors both in vitro and in vivo. Thus the administration of recombinant human IL-3 and granulocyte macrophage-colony-stimulating factor to chimeric sheep resulted in a 2.1-3.4-fold increase in the relative expression of donor (human) cells. These results demonstrate that the permissive environment of the preimmune fetal sheep provides suitable conditions for the engraftment and long-term multilineage expression of human hemopoietic stem cells in a large animal model. In this model, donor human cells appear to retain certain phenotypic and functional characteristics that can be used to manipulate the size of donor cell pool.

Sustained human hematopoiesis in sheep transplanted in utero during early gestation with fractionated adult human bone marrow cells

Sheep were transplanted in utero during early gestation with subpopulations of adult human bone marrow (BM) cells enriched for human progenitor and hematopoietic stem cells (HSC). Chimerism was documented in three of seven transplanted fetuses using monoclonal antibodies against human-specific hematopoietic cell lineages and/or cytogenetic analysis of BM and peripheral blood cells of recipients. Only chimeric sheep BM cells expressing CD45 (6.0% of total BM cells) formed human hematopoietic colonies in response to human recombinant cytokines as determined by cytogenetic analysis. Sorted CD45+ BM cells developed human T-cell colonies containing CD3+, CD4+, and CD8+ cells. DNA from chimeric BM cells obtained 3 months after birth displayed a finger printing pattern identical to that of DNA from the human donor of the HSC graft. These studies indicate that first trimester sheep fetuses are tolerant of adult human HSC grafts, thus permitting the creation of xenogeneic chimera expressing human myeloid and lymphoid lineages. The present findings also suggest that HSC grafts from immunologically competent, HLA-mismatched adult donors may be useful for correcting human genetic diseases in utero during early gestation.

Effect of erythropoietic stress on donor hematopoietic cell expression in chimeric rhesus monkeys transplanted in utero

We have previously reported the successful development of hematopoietic chimerism after the in utero transplantation of fetal hematopoietic stem cells (HSC) in rhesus monkeys (Macaca mulatta). These animals exhibit sustained engraftment without immunosuppression or graft-versus-host disease (GVHD). To assess the functional response of the donor-derived erythropoietic population, we assayed the relative expression of donor and recipient hematopoietic progenitors in chimeric monkeys before and after anemic stress. Anemia in our chimeric animals resulted in increased erythropoietin (EPO) production comparable to controls. This was accompanied by changes in erythroid progenitor profiles, again similar to controls. Chimeric animals demonstrated normal reticulocytosis and reconstituted their hematocrit after hemorrhage at the same rate as controls. The donor-derived erythropoietic population exhibited normal responses to recipient regulatory signals and did not seem to expand at the expense of other hematopoietic lineages. Thus the proportions of engraftment for the myeloid and erythroid precursors in bone marrow and for blood lymphocytes remained stable. Our results demonstrate that the in utero transplantation of fetal HSC results in stable engraftment of donor erythropoietic progenitors, which appear to be fully integrated within the recipient's regulatory system. The abnormalities reported in the postnatal transplantation setting can then be attributed to immunologic reactions requiring conditioning myeloablative regimens. Fetal transplantation bypasses all these factors.

Induction of upmodulation of homing receptors in cloned hemopoietic progenitors by growth factors

Recognition and selective seeding of hemopoietic cells to the marrow after intravenous transplantation is a function of membrane protein known as homing receptor (HR), which is a lectin with galactosyl and mannosyl specificities. We have previously shown that ex vivo incubation of marrow cells with IL-3 or GM-CSF enhances the seeding efficiency and that this enhancement may be the result of upmodulation of homing receptors. In the present work, we have shown that incubation of two cloned progenitor cell lines, FDCP-1 and FDCP-mix, with IL-3 or GM-CSF resulted in a dose-dependent increase in the number of HR per cell. Interferon-gamma did not have such an effect. The upmodulation of receptors was the result of enhanced de novo synthesis and transport of the protein as it was ablated by cyclohexamide, monensin or NH4Cl. On the other hand, degradation of the protein was not affected by the growth factors. The possible mechanisms whereby a brief exposure to growth factor ex vivo could lead to enhancement of homing efficiency are discussed. Induction of upmodulation of HR by ex vivo incubation of donor cells with certain hemopoietic growth factors, could be a useful strategy for enhancing marrow reconstitution after bone marrow transplantation. This could reduce the cost and prevent the side effects of in vivo growth factor therapy.

Homing of liver-derived hemopoietic stem cells to fetal bone marrow

Tissue distribution of HSC in fetal sheep was studied by in utero transplantation during the period when a switch in the site of hemopoiesis occurs from liver/spleen to the bone marrow. At day 50 of gestation, transplanted cells exclusively homed to the liver/spleen. By day 60, some HSC also homed to the marrow and, between days 60-80, their proportion in the marrow increased. By day 100 almost all engrafted donor HSC homed to the marrow. Nonetheless, expression of these stem cells did not occur in the blood until birth (day 145) when marrow assumed the function of hemopoiesis from liver/spleen. During this latter part of gestation, although homing sites in the marrow are available to transplanted HSC, the marrow does not contribute to the function of hemopoiesis. The significance of these observations in the context of in utero gene therapy via stem cell transplantation is discussed.

The fetus as an optimal donor and recipient of hemopoietic stem cells

In the present work we used allogeneic in utero transplantation of fetal stem cells in sheep and monkeys. Thus, both the donor and recipient cells had preimmune status. We showed engraftment of allogeneic stem cells in the tolerant environment of the host. The engrafted cells showed trilineage (lymphoid, erythroid and myeloid) expression of differentiation. Long term maintenance of these engrafted cells was observed. We also demonstrated that ex vivo incubation of donor cells with growth factor can enhance the engraftment. Moreover, we have shown that the engrafted cells respond to phlebotomy in the same manner as endogenous cells. We, therefore, conclude that (a) Preimmune fetuses are highly suitable for stem cell transplantation both as donors and recipients. (b) Engraftment can be modulated by brief maneuvers such as ex vivo manipulation. (c) Functionally, the engrafted cells can respond to hemopoietic stimuli in a similar manner as the endogenous cells. Implications of this transplantation system in clinical medicine is discussed. Everyone who is involved in organ transplantation must, sooner or later, come to grips with immunological barriers which establishes the individuality of each organism by recognizing "self" from "non-self". Transplanters must overcome this barrier, if allogeneic organ transplantation is to be successful. In the case of hemopoietic stem cells (HSC), where immunocompetent cells are transplanted, graft-vs-host disease (GVHD) may also be expected. Tolerance can be expected when the recipient is genetically immunodeficient, thus being unable to mount an immunological barrier.(ABSTRACT TRUNCATED AT 250 WORDS)

Anemia of inflammation: role of T lymphocyte activating factor

Varied conditions associated with immune activation (rheumatic, infectious and malignant) are associated with a syndrome characterized by selective erythropoietic suppression. The pathogenesis of this anemia is unknown. We have cultured intact marrows from 11 patients and found decreased erythroid colony forming activity (CFU-E: colony forming unit-erythroid; p < 0.01). We analyzed sera from 23 patients with infectious, rheumatic and malignant disorders for their ability to render normal human T lymphocytes inhibitory to autologous CFU-E and burst forming unit-erythroid in vitro. Following exposure to serum from some anemic patients, normal T cells were observed to inhibit autologous CFU-E when compared to the effect elicited by T cells incubated with heterologous normal serum. Pooled data from 19 (7 not anemic, 12 anemic) serum samples using 8 different normal T cell and marrow donors revealed a significant correlation (r = 0.65, p < 0.01) between each patient's hemoglobin level and the ability of his/her serum to render T cells suppressive to CFU-E in vitro. The suppression mediated by patient serum exposed T cells on autologous CFU-E could be ameliorated by increased concentrations of erythropoietin. The serum factor was heat stable (56 degrees C) and could not be eliminated by neutralizing antibody to either gamma-interferon or tumor necrosis factor-alpha. We conclude that some patients with anemia of inflammation may have a circulating factor(s) which renders normal T lymphocytes suppressive to autologous CFU-E in vitro. The presence of a circulating serum factor in these patients may help explain how inflammatory events distant from the marrow mediate the erythropoietic suppression characteristic of this syndrome.

Human-ovine xenogenic transplantation of stem cells in utero

The preimmune status of the early gestational age fetus provides a permissive environment that bypasses the immunological barrier and permits the engraftment and expression of hemopoietic stem cells (HSC). We used in utero approach to establish long term (greater than 2 years) engraftment and expression of human fetal liver HSC in sheep. Engraftment occurred in 40% (13 of 33) of the recipients. Of 5 live born sheep, all were chimeric. Engraftment was multilineage, involving lymphoid, myeloid and erythroid donor (human) cells. Interestingly, these progenitors have continued to exhibit responsiveness to human specific growth factors both in vitro and in vivo. Therefore, the integration of human HSC into the hemopoietic framework of the host appeared to be incomplete, with donor progenitors retaining certain phenotypic characteristics that may be exploited to preferentially manipulate the donor (human) cell population in these animals. Donor HSC primarily seeded the host bone marrow. Since the donor cells were of liver origin and the host liver at the time of transplantation was the major hemopoietic organ, this near exclusive seeding to the marrow indicates the greater affinity of marrow for the homing HSC. Nonetheless, no cells of donor origin appeared in the host circulation until the perinatal period, suggesting that donor HSC expand with the developing marrow spaces, but do not undergo terminal differentiation. The absence of a significant immunological barrier and the availability of expanding marrow homing sites render the fetus an excellent host (and donor) for HSC transplantation.

Enhancement of the grafting efficiency of transplanted marrow cells by preincubation with interleukin-3 and granulocyte-macrophage colony-stimulating factor

To improve the grafting efficiency of transplanted murine hematopoietic progenitors, we briefly preincubated mouse bone marrow cells with interleukin-3 (IL-3) or granulocyte-macrophage colony-stimulating factor (GM-CSF) ex vivo before their transplantation into irradiated recipients. This treatment was translated into an increase in the seeding efficiency of colony-forming unit-spleen (CFU-S) and CFU-GM after transplantation. Not only was the concentration of CFU-S in the tibia increased 2 and 24 hours after transplantation, but the total cell number and CFU-S and CFU-GM concentrations were persistently higher in IL-3- and GM-CSF-treated groups 1 to 3 weeks after transplantation. In addition, the survival of animals as a function of transplanted cell number was persistently higher in IL-3- and GM-CSF-treated groups compared with controls. The data indicate that the pretreatment of marrow cells with IL-3 and GM-CSF before transplantation increases the seeding efficiency of hematopoietic stem cells and probably other progenitor cells after transplantation. This increased efficiency may be mediated by upward modulation of homing receptors. Therefore, ex vivo preincubation of donor marrow cells with IL-3 and GM-CSF may be a useful tactic in bone marrow transplantation.

Transplantation of fetal cells

Cellular transplantation is an attractive alternative to whole-organ transplantation when only a discrete function of the organ is deficient. Early fetal donor cells have an advantage because they engraft readily and do not cause graft-versus-host disease. Similarly, the fetus is an ideal recipient of allogeneic fetal cells as it is incapable of rejecting them early in gestation. This review presents the theoretical rationale, recent research advances, and clinical implications for adults with diabetes mellitus and Parkinson's disease; we also describe in utero transplantation of fetal hematopoietic stem cells and hepatocytes for the treatment of inherited hematologic and hepatic deficiencies, as well as the use of fetal islet cells and dopamine-producing cells to treat postnatal conditions.

Erythropoietin. Biology and clinical applications

Erythropoietin is a glycoprotein hormone that plays a vital role in erythropoiesis. It is mainly produced in the fetal liver till the third trimester of pregnancy. At that point, the kidney interstitium takes over this function and becomes the main source of erythropoietin. Hypoxia stimulates erythropoietin production by a mechanism that may require a heme protein as a second messenger. Erythropoietin stimulates the maturation of erythroid precursors (colony-forming unit-erythroid and burst-forming unit-erythroid) via at least two types of cell surface receptors. The higher-affinity receptors appear to be more important in modulating the effects of erythropoietin in vivo. Changes in intracellular calcium may ultimately mediate the action of erythropoietin on erythroid precursors. A specific and sensitive radioimmunoassay is now available for accurately measuring erythropoietin levels. All forms of erythrocytosis except polycythemia vera are associated with elevated erythropoietin levels. Levels are also high in cord blood obtained following fetal asphyxia. Reduced levels are seen in patients with anemia due to renal diseases. The response of erythropoietin to the degree of anemia appears to be attenuated in patients with cancer, chronic diseases, and human immunodeficiency virus (HIV) infection. Erythropoietin has been successfully used for treating patients with anemia due to renal failure. Its use has also been approved for the treatment of anemia patients receiving zidovudine for HIV infection. Encouraging results have been observed when erythropoietin was used to treat anemia due to rheumatoid arthritis, hematological malignancies, and prematurity. It has also been used to increase the yield of autologous blood collected prior to an elective surgical procedure. However, it has not proved to be useful in sickle cell anemia and myelodysplastic syndromes.

Retroviral vector-mediated transfer of the bacterial neomycin resistance gene into fetal and adult sheep and human hematopoietic progenitors in vitro

We compared the efficiency of retroviral vector (N2)-mediated transfer of the bacterial neomycin resistance gene (NeoR) into adult and fetal hematopoietic progenitors of sheep and humans by assessing their ability to form colonies in the presence of lethal doses of the neomycin analogue G418 in vitro. Fetal cells from both sheep and humans exhibited a higher degree of NeoR transfer than adult cells. The overall level of NeoR expression was significantly higher for sheep than human cells. The transfer/expression of NeoR into adult human bone marrow hematopoietic progenitors was not affected by the presence or absence of T cells and monocyte/macrophages. The efficiency of NeoR transfer into both adult and fetal human cells, however, was improved when transduction was carried out in the presence of recombinant human interleukin-3 and granulocyte-macrophage colony-stimulating factor. These results demonstrate the greater efficiency of NeoR gene transfer into fetal hematopoietic progenitors, which may provide a basis for the relatively higher efficiency of the in utero approach to gene therapy.

In-utero transplantation of fetal liver haemopoietic stem cells in monkeys

To evaluate the potential of in-utero transplantation of fetal haemopoietic stem cells (HSCs) for permanent engraftment as a treatment of congenital haemoglobinopathies, fetal rhesus monkeys were transplanted with HSCs derived from fetal livers. Five pregnant monkeys (60-62 days' gestation) were given an in-utero intraperitoneal injection of fetal liver cells (10(8)-10(9) cells/kg estimated fetal recipient body weight) derived from opposite sex donors at 59-68 days' gestation. Engraftment was confirmed by karyotype analysis of peripheral blood leucocytes and bone marrow; cells of donor sex were found among the recipient cells. Donor cell engraftment was apparent in four of five in-utero HSC transplant recipients at birth. Engraftment involved lymphoid (2.9-8.0% donor cells), erythroid (5.3-12.5%), and myeloid (8.5-15.4%) lineages and has persisted for up to 2 years without evidence of graft-versus-host disease.

Tumor-associated erythrocytosis in a dog with nasal fibrosarcoma

Erythrocytosis (hematocrit, 79%) was diagnosed in an 8-year-old, neutered female, mixed-breed dog with an intranasal fibrosarcoma. Both serum and tumor erythropoietin (Ep) activities were elevated, as determined by the polycythemic exhypoxic mouse model, and the Ep activity was neutralized in that model by rabbit anti-Ep antibodies. Tumor resection normalized the hematocrit.