High-Level in Vivo Gene Marking after Gene-Modified Autologous Hematopoietic Stem Cell Transplantation without Marrow Conditioning in Nonhuman Primates

A simple and safe technique for longitudinal bone marrow aspiration in cynomolgus and rhesus macaques

Longitudinal bone marrow aspirates were obtained aseptically from the humerus of 36 rhesus and 6 cynomolgus macaques by using a 20G spinal needle, introduced through the bone close to the greater tuberosity. All samplings were performed without complications, and the animals showed no signs of pain or infections. The amount of total bone marrow cells obtained from each aspiration varied, in part due to animal-to-animal variation, but the yields were not affected by the sampling frequency or the length of time between each aspiration. The frequency of plasma cells in the bone marrow of each animal was also fairly stable over several longitudinal samplings while a greater, age-dependent, variation was observed between different animals.

Cotransplantation with MSCs improves engraftment of HSCs after autologous intra-bone marrow transplantation in nonhuman primates

OBJECTIVE

Hematopoietic stem cells (HSCs) reside in the osteoblastic niche, which consists of osteoblasts. Mesenchymal stromal cells (MSCs) have an ability to differentiate into osteoblasts. Here, using nonhuman primates, we investigated the effects of cotransplantation with MSCs on the engraftment of HSCs after autologous intra-bone marrow transplantation.

MATERIALS AND METHODS

From three cynomolgus monkeys, CD34-positive cells (as HSCs) and MSCs were obtained. The former were divided into two equal aliquots and each aliquot was genetically marked with a distinctive retroviral vector to track the in vivo fate. Each HSC aliquot with or without MSCs was autologously injected into the bone marrow (BM) cavity of right or left side, enabling the comparison of in vivo fates of the two HSC grafts in the same body.

RESULTS

In the three monkeys, CD34(+) cells transplanted with MSCs engrafted 4.4, 6.0, and 1.6 times more efficiently than CD34(+) cells alone, as assessed by BM colony polymerase chain reaction. In addition, virtually all marked cells detected in the peripheral blood were derived from the cotransplantation aliquots. Notably, colony-forming units derived from the cotransplantation aliquots were frequently detected in BM distant sites from the injection site, implying that cotransplantation with MSCs also restored the ability of gene-marked HSCs to migrate and achieve homing in the distant BM.

CONCLUSION

Cotransplantation with MSCs would improve the efficacy of transplantation of gene-modified HSCs in primates, with enhanced engraftment in BM as well as increased chimerism in peripheral blood through migration and homing.

Hematopoietic stem cell transduction and amplification in large animal models

Progress in retroviral gene transfer to large animal hematopoietic stem cells (HSCs) has led to efficient, reproducible long-term marking in both canine and nonhuman primate models. Successes for HSC gene therapy have occurred in the severe combined immunodeficiency setting, in which transduced cells have a selective advantage. However, for most diseases, the therapeutic transgene does not confer a sufficient survival advantage, and increasing the percentage of gene-marked cells in vivo will be necessary to observe a therapeutic effect. In vivo amplification should expand the potential of HSC gene therapy, and progress in this area has benefited greatly from the use of large animal models where efficacy and toxicity have often not correlated with results in murine models. To date, the best results have been observed with O(6)-methylguanine-DNA methyltransferase (MGMT) selection, with which increases in gene-marked repopulating cells have been maintained long-term, likely because of the toxicity of 1,3-bis-(2-chloroethyl)-1-nitrosourea and temozolomide to quiescent HSCs. Using MGMT selection, long-term marking levels exceeding 50% can now be routinely attained with minimal toxicity. There is cause to be optimistic that HSC gene therapy with in vivo amplification will soon allow the treatment of several genetic and infectious diseases.

Prevention of Immune Responses to Human Erythropoietin in Cynomologus Monkeys (Macaca fascicularis)

Genes and proteins of human origin are often administered to monkeys for research purposes, however, it can be difficult to obtain sufficient levels of the products in vivo due to immunological clearance. In this study, we showed that human erythropoietin (hEPO) induces generation of anti-hEPO antibody in cynomolgus macaques (n=2), although 92% of amino acid residues are common between the human and macaque EPO. The administered hEPO was thus eliminated from the animals. On the other hand, when an immunosuppressant, cyclosporin A (CyA), was administered (6 mg/kg) intramuscularly every other day in combination with hEPO (n=2), no anti-hEPO antibody was generated and high serum levels of hEPO were obtained during administration of hEPO, resulting in an increase in serum hemoglobin levels. No adverse effects associated with CyA were observed. Thus, CyA treatment is useful for prevention of immune responses associated with the administration of human proteins in monkeys.

Intra-bone Marrow-Bone Marrow Transplantation: A New Strategy for Treatment of Stem Cell Disorders

We have established new bone marrow transplantation (BMT) methods for the treatment of stem cell disorders such as autoimmune diseases. The methods include the perfusion method (PM) and intra-bone marrow (IBM)-BMT. PM, in comparison with the conventional aspiration method, can minimize the contamination of bone marrow cells (BMCs) with T cells from the peripheral blood. Therefore, without removing T cells, no graft-versus-host disease develops in the case of PM. Because BMCs collected using the PM contain not only hemopoietic stem cells (HSCs) but also mesenchymal stem cells (MSCs), the injection of both cells directly into the bone marrow cavity (IBM-BMT) facilitates the engraftment of donor hemopoietic cells. With IBM-BMT, no graft failure therefore occurs even if the radiation dose is reduced. IBM-BMT is applicable to regeneration therapy and various age-associated diseases such as osteoporosis, because it can efficiently recruit donor-derived normal MSCs into the bone marrow. We believe that this strategy heralds a revolution in the field of transplantation and regenerative therapy.

How do stem cells find their way home?

Migration of hematopoietic stem cells through the blood, across the endothelial vasculature to different organs and to their bone marrow (BM) niches, requires active navigation, a process termed homing. Homing is a rapid process and is the first and essential step in clinical stem cell transplantation. Similarly, homing is required for seeding of the fetal BM by hematopoietic progenitors during development. Homing has physiological roles in adult BM homeostasis, which are amplified during stress-induced recruitment of leukocytes from the BM reservoir and during stem cell mobilization, as part of host defense and repair. Homing is thought to be a coordinated, multistep process, which involves signaling by stromal-derived factor 1 (SDF-1) and stem cell factor (SCF), activation of lymphocyte function-associated antigen 1 (LFA-1), very late antigen 4/5 (VLA-4/5) and CD44, cytoskeleton rearrangement, membrane type 1 (MT1)-matrix metalloproteinase (MMP) activation and secretion of MMP2/9. Rolling and firm adhesion of progenitors to endothelial cells in small marrow sinusoids under blood flow is followed by trans-endothelial migration across the physical endothelium/extracellular matrix (ECM) barrier. Stem cells finalize their homing uniquely, by selective access and anchorage to their specialized niches in the extravascular space of the endosteum region and in periarterial sites. This review is focused on mechanisms and key regulators of human stem cell homing to the BM in experimental animal models and clinical transplantation protocols.

Safe And Efficient Collection of Cytokine-Mobilized Peripheral Blood Cells From Cynomolgus Monkeys (Macaca fascicularis) with Human Newborn-Equivalent Body Weights

Hematopoietic stem cells in bone marrow can be mobilized into peripheral blood by cytokine administration. Cytokine-mobilized peripheral blood stem cells are of great use in clinical applications. We previously established a modified procedure for the collection of cytokine-mobilized peripheral blood cells from rhesus monkeys (Macaca mulata) using a commercially available apparatus originally developed for human subjects. In this study, we examined the efficacy and safety of this method with even smaller macaques, cynomolgus monkeys (Macaca fascicularis), which are equivalent to human newborns in body weight (mean = 3.3 kg). Using the manufacturer's unmodified protocol (n=6), one monkey died of cardiac failure and three developed severe anemia. In contrast, using our modified procedure (n=6), no such complication was observed in any animal. In addition, the harvested nuclear cell, mononuclear cell and CD34(+) cell counts were significantly higher with the modified method. The modified method should allow safe and efficient collection of cytokine-mobilized peripheral blood cells from non-human primates as small as human newborns in a non-invasive manner.