Mary Nelson

Mesenchymal stem cells are capable of homing to the bone marrow of non-human primates following systemic infusion

OBJECTIVE The human bone marrow contains mesenchymal stem cells capable of differentiating along multiple mesenchymal cell lineages. Using a non-human primate model, we sought to determine whether the systemic infusion of baboon-derived mesenchymal stem cells was associated with toxicity and whether these cells were capable of homing to and persisting within the bone marrow. MATERIALS AND METHODS Five baboons (Papio anubis) were administered lethal irradiation followed by intravenous autologous hematopoietic progenitor cells combined with either autologous (n = 3) or allogeneic (n = 2) mesenchymal stem cells that had been expanded in culture. In four of these baboons, the mesenchymal stem cells were genetically modified with a retroviral vector encoding either the enhanced green fluorescent protein gene (n = 3) or the human placental alkaline phosphatase gene (n = 1) for tracking purposes. A sixth animal received only intravenous gene marked autologous mesenchymal stem cells but no hematopoietic stem cells or conditioning irradiation. RESULTS Following culture, baboon mesenchymal stem cells appeared morphologically as a homogeneous population of spindle-shaped cells that were identified by the monoclonal antibodies SH-3 and SH-4. These cells did not express the hematopoietic markers CD34 or CD45. Baboon mesenchymal stem cells isolated from primary culture were capable of differentiating along both adipogenic and osteogenic lineages. There was no acute or chronic toxicity associated with the intravenous infusion of mesenchymal stem cells. In all five recipients of gene marked mesenchymal stem cells, transgene was detected in post-transplant bone marrow biopsies. In two animals receiving autologous mesenchymal stem cells, including the one non-conditioned recipient, transgene could be detected over 1 year following infusion. In one recipient of allogeneic gene marked mesenchymal stem cells, transgene was detected in the bone marrow at 76 days following infusion. CONCLUSION These data demonstrate that baboon mesenchymal stem cells: 1) are not associated with significant toxicity when administered intravenously, 2) are capable of homing to the bone marrow following intravenous infusion, and 3) have the capacity to establish residence within the bone marrow for an extended duration following systemic administration.

Baboon Mesenchymal Stem Cells Can Be Genetically Modified to Secrete Human Erythropoietin In Vivo

Human mesenchymal stem cells (MSCs) are capable of differentiating into multiple mesenchymal lineages including chondrocytes, osteocytes, adipocytes, and marrow stromal cells. Using a nonhuman primate model, we evaluated nonhuman primate MSCs as targets for gene therapy. Baboon MSCs (bMSCs) cultured from bone marrow aspirates appeared as a homogeneous population of spindle-shaped cells. bMSCs were capable of differentiating into adipocytes and osteocytes in vitro and chondrocytes in vivo. bMSCs were genetically modified with a bicistronic vector encoding the human erythropoietin (hEPO) gene and the green fluorescent protein (GFP) gene. Transduction efficiencies ranged from 72 to 99% after incubation of MSCs with retroviral supernatant. Transduced cells produced from 1.83 x 10(5) to 7.12 x 10(5) mIU of hEPO per 10(6) cells per 24 hr in vitro before implantation. To determine the capacity of bMSCs to express hEPO in vivo, transduced bMSCs were injected intramuscularly in NOD/SCID mice. In a separate experiment, transduced bMSCs were loaded into immunoisolatory devices (IIDs) and surgically implanted into either autologous or allogeneic baboon recipients. Human EPO was detected in the serum of NOD/SCID mice for up to 28 days and in the serum of five baboons for between 9 and 137 days. NOD/SCID mice experienced sharp rises in hematocrit after intramuscular injection of hEPO-transduced bMSCs. The baboon that expressed hEPO for 137 days experienced a statistically significant (p < 0.04) rise in its hematocrit. These data demonstrate that nonhuman primate MSCs can be engineered to deliver a secreted and biologically active gene product. Therefore, human MSCs may be an effective target for future human gene therapy trials.

Ex Vivo Expansion and Genetic Marking of Primitive Human and Baboon Hematopoietic Cells

Abstract: The achievement of positive outcomes in many clinical protocols involving hematopoietic stem cells (HSCs) has been handicapped by the limited numbers of marrow repopulating cells available to actually bring about therapy. This insufficiency has been especially problematic in stem cell transplantation and gene therapy. A number of studies have been initiated to attempt expansion of HSCs, mainly by manipulation of key cytokines in cell suspension cultures. Unfortunately, these expansion methods usually lead to altered properties in the amplified cells, mainly by reducing their self‐renewal and multilineage differentiative potentials. Here we discuss our ongoing work, utilizing a unique endothelial cell line that supports primitive hematopoiesis, to attempt to generate expansion of primate HSCs that retain their elementary properties. Genetic marking of early hematopoietic cells to facilitate tracking will be mentioned as will the development and employment of assay systems designed to evaluate the long‐term functional attributes of the expanded cells.

Ex Vivo Expansion of Human Hematopoietic Stem Cells: Implications for The Modern Blood Bank

Pluripotent hematopoietic stem cells (PHSC) are rare cells within the marrow that are capable of self‐renewal and differentiation into multiple hematopoietic lineages. Following myeloablative chemotherapy and radiation therapy and marrow transplantation, hematological reconstitution occurs after a period of 2‐ 3 weeks. Recently, a number of laboratories have shown that both early and delayed phases of engraftment are mediated by PHSC within a graft and that engraftment can be accelerated by transplanting greater numbers of PHSC. Increasing efforts have been directed, therefore, towards developing methods to expand PHSC ex vivo. In this report, we describe an endothelial cell‐based culture system to which exogenous cytokines are added which appears to permit the ex vivo expansion of PHSC. Refinement of these technologies will potentially have a major impact on the ability of blood banks to improve the quality of hematopoietic stem cell grafts.

Interleukin 10-induced thrombocytopenia in normal healthy adult volunteers: evidence for decreased platelet production: IL-10-induced Thrombocytopenia: Decreased Platelet Production

Recombinant human interleukin 10 (rhuIL‐10) inhibits the production of proinflammatory cytokines and has shown promise in the treatment of inflammatory bowel disease. Clinical trials have been accompanied by a reversible decline in platelet counts. We conducted a randomized, double‐blinded, placebo‐controlled, parallel group trial in 12 healthy volunteers to investigate the aetiology of rhuIL‐10‐induced thrombocytopenia. Eight volunteers received 8 μg/kg/d of rhuIL‐10 subcutaneously, while four subjects received a placebo alone for 10 d. A reversible decline in the platelet counts from a mean of 275 × 109/l to 164 × 109/l was observed in the IL‐10‐treated cohort (P = 0·012). A fall in the haemoglobin mean levels was also observed in the IL‐10‐treated cohort from 13·7 to 11·7 g/dl (P = 0·011). No significant change was observed in the bone marrow cellularity or myeloid/erythroid ratio or in the number of megakaryocytes per high‐powered field (HPF). A fall was observed in the number of megakaryocyte colony‐forming units (CFU‐MKs) after the administration of IL‐10 compared with those receiving the placebo (P = 0·068). No difference in the change in granulocyte–macrophage CFUs (CFU‐GMs), mixed lineage CFUs (CFU‐GEMMs) or erythroid burst‐forming units (BFU‐Es) was observed when comparing the IL‐10‐ vs. placebo‐treated groups (P > 0·465). Serum cytokine levels of thrombopoietin (TPO), IL‐6 and granulocyte–macrophage colony stimulating factor (GM‐CSF) were not decreased following IL‐10 administration. In fact, both TPO and GM‐CSF appeared to be slightly increased in the serum. All subjects underwent In111‐labelled platelet survival studies with liver/spleen scans to assess splenic sequestration prior to and then on day 7 of treatment. A significant reduction in splenic sequestration of platelets (P = 0·012) was observed in the IL‐10‐treated group, but not in the placebo‐treated subjects.

Comparability of gene expression between human and baboon CD34+ marrow cells

Abstract Nonhuman primates are a useful model system for hematopoietic stem cell (HSC) research because they are closely related to humans. We asked whether human-based cDNA arrays could be used to study hematopoiesis in the baboon. Our objective was to compare the human and baboon transciptosome, using cDNA filter arrays surveying 25,920 human genes (Unigene), to determine if the expression patterns were similar, and to identify the commonly-expressed genes. Bone marrow mononuclear cells from a normal adult human and an adult baboon were sorted using magnetic beads, to obtain CD34+ cells of 90% and 77% purity, respectively. Total RNA was 33 P-labeled by oligo-dT primed reverse-transcription, hybridized sequentially in the presence of human Cot1 DNA and poly dA to GeneFilters releases 200–204 (Research Genetics), phospho-imaged and analyzed with Pathways software. The baboon-derived probes had a slightly higher background than human (3-fold) so the expression of low abundance cDNAs was less reliable. Overall, the relative expression of individual genes was comparable between the species, with a correlation coefficient which varied by experiment, but was between 0.86–0.90. A total of 5,474 genes showed comparably high expression in both species (≥ 10-fold above baseline) of which 1,123 were ≥ 100-fold. These highly-expressed cDNAs (67 genes, 956 ESTs) included genes such as IL-3 receptor, HLA class II, and CSF3 receptor. Only a few genes/ESTs showed species-restricted expression (75 in human and 59 in baboon). We conclude that human cDNA arrays are a reliable method to study baboon marrow. The genes/ESTs identified here represent a useful set for generating a cDNA microarray chip to study baboon stem cell function, which will facilitate the study of HSC gene expression during steady state hematopoiesis and following a variety of stimuli.