Gene transfer into nonhuman primate hematopoietic stem cells: implications for gene therapy

The Cynomolgus Macaque MHC Polymorphism in Experimental Medicine

Among the non-human primates used in experimental medicine, cynomolgus macaques (Macaca fascicularis hereafter referred to as Mafa) are increasingly selected for the ease with which they are maintained and bred in captivity. Macaques belong to Old World monkeys and are phylogenetically much closer to humans than rodents, which are still the most frequently used animal model. Our understanding of the Mafa genome has progressed rapidly in recent years and has greatly benefited from the latest technical advances in molecular genetics. Cynomolgus macaques are widespread in Southeast Asia and numerous studies have shown a distinct genetic differentiation of continental and island populations. The major histocompatibility complex of cynomolgus macaque (Mafa MHC) is organized in the same way as that of human, but it differs from the latter by its high degree of classical class I gene duplication. Human polymorphic MHC regions play a pivotal role in allograft transplantation and have been associated with more than 100 diseases and/or phenotypes. The Mafa MHC polymorphism similarly plays a crucial role in experimental allografts of organs and stem cells. Experimental results show that the Mafa MHC class I and II regions influence the ability to mount an immune response against infectious pathogens and vaccines. MHC also affects cynomolgus macaque reproduction and impacts on numerous biological parameters. This review describes the Mafa MHC polymorphism and the methods currently used to characterize it. We discuss some of the major areas of experimental medicine where an effect induced by MHC polymorphism has been demonstrated.

In vivo manipulation of gene expression in non-human primates using lentiviral vectors as delivery vehicles

Non-human primates (NHPs) are an invaluable resource for the study of genetic regulation of disease mechanisms. The main disadvantage of using NHPs as a preclinical model of human disease is the difficulty of manipulating the monkey genome using conventional gene modifying strategies. Lentiviruses offer the possibility of circumventing this difficulty because they can infect and transduce either dividing or nondividing cells, without producing an immune response. In addition, lentiviruses can permanently integrate into the genome of host cells, and are able to maintain long-term expression. In this article we describe the lentiviral vectors that we use to both express transgenes and suppress expression of endogenous genes via RNA interference (RNAi) in NHPs. We also discuss the safety features of currently available vectors that are especially important when lentiviral vectors are used in a species as closely related to humans as NHPs. Finally, we describe in detail the lentiviral vector production protocol we use and provide examples of how the vector can be employed to target peripheral tissues and the brain.

Quantitative real-time polymerase chain reaction (qRT-PCR) restriction fragment length polymorphism (RFLP) method for monitoring highly conserved transgene expression during gene therapy

Evaluation of the transfer efficiency of a rat heme oxygenase-1 (HO-1) transgene into mice requires differentiation of rat and mouse HO-1. However, rat and mouse HO-1 have 94% homology; antibodies and enzyme activity cannot adequately distinguish HO-1. We designed a quantitative real-time polymerase chain reaction (qRT-PCR) method to monitor HO-1 transcription relative to a housekeeping gene, GAPDH. The ratio of rat and mouse HO-1 mRNA could be estimated through restriction fragment length polymorphism (RFLP) analysis of the PCR products. In vitro, murine AML12 hepatocytes were transfected with rat HO-1. After 40 h, the total HO-1 mRNA was enriched 2-fold relative to control cells, and rat HO-1 comprised 84% of HO-1 cDNA. In vivo, the rat HO-1 transgene was cloned into a Sleeping Beauty transposase (SB-Tn) construct and was injected hydrodynamically into a mouse model of sickle cell disease (SCD). After 21 days, there was a 32% enrichment of HO-1 mRNA relative to control mice and the rat transgene comprised 88% of HO-1 cDNA. After 21 days, HO-1 protein expression in liver was increased 2.5-fold. In summary, qRT-PCR RFLP is a useful and reliable method to differentiate the transgene from host gene transcription, especially when the host and transgene protein are identical or highly homologous. This method has translational applications to the design, delivery, and monitoring of gene-therapy vectors.

Modulation of biodistribution and expression of plasmid DNA following mesenchymal progenitor cell-based delivery

Although therapeutic applications of mesenchymal progenitor cells (MPCs) have been studied, the in vivo fate of genes delivered by the MPCs has received little attention. We report here the in vivo kinetics, tissue distribution, and duration of gene expression after systemic administration of plasmid DNA delivered by MPCs. Murine MPCs were isolated from bone marrow, cultured, and transfected with plasmid DNA using polyethylenimine. The gene-modified MPCs or naked plasmid DNA was administered intravenously to mice. Injected MPCs incorporating plasmid DNA yielded elevated serum concentrations when compared with the group treated with plasmid DNA alone, a 280-fold higher level measured at 5-min post-administration. Moreover, plasmid DNA delivered in MPCs was detected in several organs, lymph nodes, and bone marrow. The highest levels of distribution were observed in the liver, followed by lung and spleen at 4 days post-dose. Similar to the distribution of DNA, significant expression levels of the exogenous gene were observed only after delivery of the DNA in MPCs, demonstrating the sustained expression at the liver, lung, and kidney for 4 days after tail vein injection. This study provides perspectives regarding the in vivo fate and target tissue distribution of genes following MPC-based delivery.

Direct development of functionally mature tryptase/chymase double-positive connective tissue-type mast cells from primate embryonic stem cells

Conditions that influence the selective development or recruitment of connective tissue-type and mucosal-type mast cells (MCs) are not well understood. Here, we report that cynomolgus monkey embryonic stem (ES) cells cocultured with the murine aorta-gonad-mesonephros-derived stromal cell line AGM-S1 differentiated into cobblestone (CS)-like cells by day 10-15. When replated onto fresh AGM-S1 with the addition of stem cell factor, interleukin-6, and Flt3 ligand, these CS-like cells displayed robust growth and generated almost 100% tryptase/chymase double-positive MCs within 3 weeks. At all time points, the percentage of tryptase-positive cells did not exceed that of chymase-positive cells. These ES-derived MCs were CD45+/Kit+/CD31+/CD203c+/HLA-DR- and coexpressed a high-affinity IgE receptor on their surface, which was upregulated after IgE exposure. Electron microscopy showed that they contained many electron dense granules. Moreover, ES-derived MCs responded to stimulation by via IgE and substance P by releasing histamine. These results indicate that ES-derived MCs have the phenotype of functionally mature connective tissue-type MCs. The rapid maturation of ES-derived MCs suggests a unique embryonic pathway in primates for early development of connective tissue-type MCs, which may be independent from the developmental pathway of mucosal-type MCs.

Lentiviral Gene Delivery of vMIP-II to Transplanted Endothelial Cells and Endothelial Progenitors Is Proangiogenic In Vivo

Therapies that stimulate angiogenesis show promise in revascularization of transplanted or ischemic tissues. Viral macrophage inflammatory protein-II (vMIP-II) is encoded by human herpesvirus 8, and it can be both immunosuppressive and proangiogenic. However, little has been done to characterize the potential of vMIP-II-induced angiogenesis. We engineered a vMIP-II lentiviral gene vector, transduced both mature endothelial cells and progenitors, and transplanted these in Matrigel templates as an in vivo angiogenesis model. Our results show that vMIP-II promotes new, functional, branching, and segmented vessels associated with smooth muscle cells and connected with the host vasculature. Angiogenesis is enhanced through host cells as well as through transplanted vMIP-expressing endothelial cells. As a proof-of-concept for using vMIP-II in clinical applications, we showed that islets co-transplanted with endothelial cells expressing vMIP-II were revascularized and survived in Matrigel templates, whereas no islets survived under control conditions. vMIP-II up-regulates the expression of multiple proangiogenic factors that can have a synergistic effect. These include vascular endothelial growth factor (VEGF), kinase insert domain receptor, neuropilin 2, carcinoembryonic antigen-related cell adhesion molecule 1, interleukin-1alpha, fibronectin, and integrins alpha3, alpha4, and alpha5. These results provide the first demonstration that vMIP-II is proangiogenic in vivo and can deliver this function to endothelial progenitors as well as to mature endothelial cells through vector-mediated gene delivery.

RNAi in combination with a ribozyme and TAR decoy for treatment of HIV infection in hematopoietic cell gene therapy

Combinatorial therapies for the treatment of HIV infection have changed the course of the AIDS epidemic in developed nations where the antiviral drug combinations are readily available. Despite this progress, there are many problems associated with chemotherapy for AIDS including toxicities and emergence of viral mutants resistant to the drugs. Our goal has been the development of a hematopoietic gene therapy treatment for HIV infection. Like chemotherapy, gene therapy for treatment of HIV infection should be used combinatorially. We have thus combined three different inhibitory genes for treatment of HIV infection into a single lentiviral vector backbone. The inhibitory agents engage RNAi via a short hairpin RNA targeting HIV tat/rev mRNAs, a nucleolar localizing decoy that binds and sequesters the HIV Tat protein, and a ribozyme that cleaves and downregulates the CCR5 chemokine receptor used by HIV for cellular entry. This triple combination has proven to be highly effective for inhibiting HIV replication in primary hematopoietic cells, and is currently on track for human clinical application.

Bone morphogenetic protein-4 enhances cardiomyocyte differentiation of cynomolgus monkey ESCs in knockout serum replacement medium

Despite extensive research in the differentiation of rodent ESCs into cardiomyocytes, there have been few studies of this process in primates. In this study, we examined the role of bone morphogenic protein-4 (BMP-4) to induce cardiomyocyte differentiation of cynomolgus monkey ESCs. To study the role of BMP-4, EBs were formed and cultured in Knockout Serum Replacement (KSR) medium containing BMP-4 for 8 days and subsequently seeded in gelatin-coated dishes for 20 days. It was found that ESCs differentiated into cardiomyocytes upon stimulation with BMP-4 in KSR medium, which resulted in a large fraction of beating EBs ( approximately 16%) and the upregulation of cardiac-specific proteins in a dose and time-dependent manner. In contrast, the addition of BMP-4 in FBS-containing medium resulted in a lower fraction of beating EBs ( approximately 6%). BMP-4 acted principally between mesendodermal and mesoderm progenitors and subsequently enhanced their expression. Ultrastructural observation revealed that beating EBs contained mature cardiomyocytes with sarcomeric structures. In addition, immunostaining, reverse transcription-polymerase chain reaction, and Western blotting for cardiac markers confirmed the increased differentiation of cardiomyocytes in these cultures. Moreover, electrophysiological studies demonstrated that the differentiated cardiomyocytes were electrically activated. These findings may be useful in developing effective culture conditions to differentiate cynomolgus monkey ESCs into cardiomyocytes for studying developmental biology and for regenerative medicine.

Targeted killing effect of lentivirus-mediated CD/TK suicide genes on colorectal carcinoma cells

AIM: To investigate the killing effect of lentivirus-mediated double suicide genes under the regulation of kinase domain-containing receptor (KDR) promoter targeted on colorectal carcinoma cells.

METHODS: 293FT packaging cells were transfected by the constructed plasmids pLenti6/V5-D-KDR-CDglyTK and pLenti6/V5-D-GFP. After blasticidin selection and cell cloning, the infectious viruses were generated. Then SW620 (with KDR expression) and LS174T cells (without KDR expression) were transfected with the obtained viruses by lipofectamin 2000. The transfection efficacy was evaluated by the fluorecence microscopy. The expression of CDglyTK was detected by reverse transcription-polymerase chain reaction (RT-PCR). After treatment with 5-FC and GCV, the killing effects and bystander effect of CD/TK suicide genes on the two kinds of cell lines were assessed.

RESULTS: The transfection efficacy was not significantly different between SW620 and LS174T cells, and elevated with the increase of virus titer. RT-PCR demonstrated that CDglyTK was expressed only in SW620 cells infected by pLenti6/V5-D-KDR-CDglyTK but not in LS147T cells. For the transfected SW620 cells, the survival rate was 32.34% ± 2.42% or 30.56% ± 2.14% when GCV (100 mg/L) or 5-FC (2.0 g/L) was used alone, respectively, and it was 5.36% ± 1.55% when GCV and 5-FC were used in combination. For the transfected LS174T cells, the survival rate was 95.48% ± 1.70% when GCV and 5-FC were used in combination. SW620 cells had a higher sensitivity to the prodrugs than LS174T cells did (P < 0.001), and the effects of double suicide genes were markedly stranger than that of either single gene (P < 0.001). Considerable bystander effect was also observed. When the infected cells covered a percentage of 40%, the survival rate of SW620 cells was 11.42% ± 2.66%, while that of LS174T cells was 99.54% ± 2.61% after treatment with GCV and 5-FC. There was significant difference between the two kinds of cells (P < 0.001).

CONCLUSION: Lentivirus-mediated CD/TK suicide genes driven by KDR promoter have specific killing effect on colorectal carcinoma cells with KDR expression.

Identification and characterization of hemoangiogenic progenitors during cynomolgus monkey embryonic stem cell differentiation

We identified intermediate-stage progenitor cells that have the potential to differentiate into hematopoietic and endothelial lineages from nonhuman primate embryonic stem (ES) cells. Sequential fluorescence-activated cell sorting and immunostaining analyses showed that when ES cells were cultured in an OP9 coculture system, both lineages developed after the emergence of two hemoangiogenic progenitor-bearing cell fractions, namely, vascular endothelial growth factor receptor (VEGFR)-2(high) CD34(-) and VEGFR-2(high) CD34(+) cells. Exogenous vascular endothelial growth factor increased the proportion of VEGFR-2(high) cells, particularly that of VEGFR-2(high) CD34(+) cells, in a dose-dependent manner. Although either population of VEGFR-2(high) cells could differentiate into primitive and definitive hematopoietic cells (HCs), as well as endothelial cells (ECs), the VEGFR-2(high) CD34(+) cells had greater hemoangiogenic potential. Both lineages developed from VEGFR-2(high) CD34(-)or VEGFR-2(high) CD34(+) precursor at the single-cell level, which strongly supports the existence of hemangioblasts in these cell fractions. Thus, this culture system allows differentiation into the HC and EC lineages to be defined by surface markers. These observations should facilitate further studies both on early developmental processes and on regeneration therapies in human.

Current status of gene therapy strategies to treat HIV/AIDS

Progress in developing effective gene transfer approaches to treat HIV-1 infection has been steady. Many different transgenes have been reported to inhibit HIV-1 in vitro. However, effective translation of such results to clinical practice, or even to animal models of AIDS, has been challenging. Among the reasons for this failure are uncertainty as to the most effective cell population(s) to target, the diffuseness of these target cells in the body, and ineffective or insufficiently durable gene delivery. Better understanding of the HIV-1 replicative cycle, host factors involved in HIV-1 infection, vector biology and application, transgene technology, animal models, and clinical study design have all contributed vastly to planning current and future strategies for application of gene therapeutic approaches to the treatment of AIDS. This review focuses on the newest developments in these areas and provides a strong basis for renewed optimism that gene therapy will have an important role to play in treating people infected with HIV-1.

Repair of infarcted myocardium mediated by transplanted bone marrow-derived CD34+ stem cells in a nonhuman primate model

Rodent and human clinical studies have shown that transplantation of bone marrow stem cells to the ischemic myocardium results in improved cardiac function. In this study, cynomolgus monkey acute myocardial infarction was generated by ligating the left anterior descending artery, and autologous CD34(+) cells were transplanted to the peri-ischemic zone. To track the in vivo fate of transplanted cells, CD34(+) cells were genetically marked with green fluorescent protein (GFP) using a lentivirus vector before transplantation (marking efficiency, 41% on average). The group receiving cells (n = 4) demonstrated improved regional blood flow and cardiac function compared with the saline-treated group (n =4) at 2 weeks after transplant. However, very few transplanted cell-derived, GFP-positive cells were found incorporated into the vascular structure, and GFP-positive cardiomyocytes were not detected in the repaired tissue. On the other hand, cultured CD34(+) cells were found to secrete vascular endothelial growth factor (VEGF), and the in vivo regional VEGF levels showed a significant increase after the transplantation. These results suggest that the improvement is not the result of generation of transplanted cell-derived endothelial cells or cardiomyocytes; and raise the possibility that angiogenic cytokines secreted from transplanted cells potentiate angiogenic activity of endogenous cells.

Harnessing HIV for therapy, basic research and biotechnology

First described about a decade ago, lentiviral vectors ('lentivectors') have emerged as potent and versatile tools of gene transfer for basic and applied research and offer exciting perspectives for the field of gene therapy. In the clinic, HIV-based vectors are showing particular promise for delivering therapeutic genes to hematopoietic stem cells (HSCs) and terminally differentiated targets in the central nervous system (CNS). Their flexible design facilitates the accommodation of sophisticated elements of control for the precise tuning of transgene expression. The delivery of small interfering RNAs (siRNAs) and genomic or cDNA libraries and the creation of transgenic animals are the most recent and exciting applications of HIV-based vectors that will help to tackle fundamental issues across wide areas of biology.

Modification of the leukapheresis procedure for use in rhesus monkeys (Macaca mulata)

One of the most serious problems in applying leukapheresis to human infants is the large extracorporeal blood volume (ECV), resulting in substantial loss of platelets and red blood cells (RBCs). In this study, we developed a safe and effective modified procedure to collect peripheral blood stem cells (PBSCs) from rhesus monkeys (Macaca mulata) using a Baxter CS3000+ Blood Cell Separator (Baxter, Deerfield, IL) with several devices that reduced chamber size and shortened the standard apheresis kit to decrease ECV from 130 to 70 ml. Pump speed was controlled by monitoring hematocrit values and platelet counts during leukapheresis. This system makes it possible to perform safe and effective leukapheresis in rhesus monkeys whose body weight is similar to that of human infants. A total of 12 leukapheresis procedures were performed in nine monkeys and resulted in the collection of sufficient numbers of white blood cells (mean, 1.38 x 10(9) cells/kg), CD34(+) cells (mean, 17.80 x 10(6) cells/kg), mononuclear cells (mean, 3.67 x 10(8) cells/kg), and colony forming units (mean, 75.02 x 10(6) cells/kg) in all cases. In addition, no complications, such as anemia or thrombocytopenia, occurred after leukapheresis. This modified leukapheresis procedure will be useful to test new approaches in gene therapy, perform organ transplantation using nonhuman primates, and collect PBSCs from human infants in a noninvasive manner. Our nonhuman primate model provides an important framework for such future clinical studies.

Optimization of human erythropoietin secretion from MLV-infected human primary fibroblasts used for encapsulated cell therapy

BACKGROUND

The transplantation of encapsulated cells genetically engineered to secrete human erythropoietin (hEpo) represents an alternative to repeated injections of the recombinant hormone for the treatment of Epo-responsive anemia. In the present study, the ability of primary human foreskin fibroblasts to secrete high levels of hEpo and the importance of cis-acting elements and infection conditions on transgene expression level were assessed.

METHODS

The transduction efficiency was first evaluated with beta-galactosidase (LacZ)-encoding retroviral vectors derived from the murine leukemia retrovirus (MLV) pseudotyped either with an amphotropic envelope or with the G glycoprotein of vesicular stomatitis virus (VSV-G). Human fibroblasts were then infected with an amphotropic hEpo-expressing retroviral vector, which was modified by insertion of a post-transcriptional regulatory element from the woodchuck hepatitis virus (WPRE) and a Kozak consensus sequence (KZ). Human Epo production was further optimized by increasing the multiplicity of infection and by selecting high producer cells. The survival and the transgene expression of these fibroblasts were finally evaluated in vivo. The cells were encapsulated into microporous hollow fibers and subcutaneously implanted in nude mice.

RESULTS

A secretion level of approximately 5 IU hEpo/10(6) cells/day was obtained with the basal vector. A 7.5-fold increase in transgene expression was observed with the insertion of WPRE and KZ elements. Finally, according to the optimization of infection conditions, we obtained a 40-fold increase in hEpo secretion, reaching approximately 200 IU hEpo/10(6) cells/day. The in vivo experiments showed an increase in the hematocrit during the first 2 weeks and elevated levels exceeding 60% were maintained over a 6-week period.

CONCLUSIONS

These results indicate that primary human fibroblasts represent a promising source for encapsulated cell therapy.

In vivo selective expansion of gene-modified hematopoietic cells in a nonhuman primate model

A major problem limiting hematopoietic stem cell (HSC) gene therapy is the low efficiency of gene transfer into human HSCs using retroviral vectors. Strategies, which would allow in vivo expansion of gene-modified hematopoietic cells, could circumvent the problem. To this end, we developed a selective amplifier gene (SAG) consisting of a chimeric gene composed of the granulocyte colony-stimulating factor (G-CSF) receptor gene and the estrogen receptor gene hormone-binding domain. We have previously demonstrated that primary bone marrow progenitor cells transduced with the SAG could be expanded in response to estrogen in vitro. In the present study, we evaluated the efficacy of the SAG in the setting of a clinically applicable cynomolgus monkey transplantation protocol. Cynomolgus bone marrow CD34(+) cells were transduced with retroviral vectors encoding the SAG and reinfused into each myeloablated monkey. Three of the six monkeys that received SAG transduced HSCs showed an increase in the levels of circulating progeny containing the provirus in vivo following administration of estrogen or tamoxifen without any serious adverse effects. In one monkey examined in detail, transduced hematopoietic progenitor cells were increased by several-fold (from 5% to 30%). Retroviral integration site analysis revealed that this observed increase was polyclonal and no outgrowth of a dominant single clonal population was observed. These results demonstrate that the inclusion of our SAG in the retroviral construct allows selective in vivo expansion of genetically modified cells by a non-toxic hormone treatment.

C-terminal cyclization of an SDF-1 small peptide analogue dramatically increases receptor affinity and activation of the CXCR4 receptor

In an effort to improve the activities and bioavailabilities of stromal cell-derived factor-1 (SDF-1, CXCL12) sdf-(1-67)-OH (1), we have prepared a linear peptide analogue [sdf-(1-31)-NH(2) (2)] and two lactam analogues [cyclo(Lys(20)-Glu(24))-sdf-(1-31)-NH(2) (3) and cyclo(Glu(24)-Lys(28))-sdf-(1-31)-NH(2) (4)], consisting of the N-terminal region (amino acids 1-14) joined by a four-glycine linker to the C-terminal region (amino acids 56-67) of 1. Analogues 2 and 4 had eight residues of alpha-helix, as estimated from its circular dichroism (CD) spectra, in contrast to 10 residues in analogue 3. Cyclization of analogue 2 at residues 20 and 24 to give analogue 3 resulted in only a slight change to the theta;(222)/theta;(209) ratio (0.81 to 0.86, where 1.09 is considered a perfect alpha-helix), although an increase in the alpha-helix length of analogue 3 was observed. In contrast, cyclization between residues 24 and 28 by lactamization to give analogue 4 only slightly affected the helical content but clearly resulted in a more classical alpha-helical structure (theta;(222)/theta;(209) = 0.98). Cyclization of the linear analogue 2 enhanced the SDF-1 receptor CXCR4 binding approximately 114-fold, where the IC(50) values derived from (125)I-SDF-1 competitive binding assays with CEM cells were found to be 39.5 +/- 5.9 nM, 28.9 +/- 6.3 microM, 225.8 +/- 11.8 nM, and 254.1 +/- 5.4 nM for analogues 1-4, respectively. Intracellular calcium mobilization ([Ca(2+)](i)) induced after interaction with CXCR4, as measured by EC(50), was significantly reduced in analogue 4 compared to 3, and approached the EC(50) of native SDF-1, indicating a correlation between the degree of alpha-helix and biological activity. Therefore, the biological activity of small peptide SDF-1 analogues is highly dependent on the conformation of its C-terminal region.