Hematopoietic stem cell gene therapy for the treatment of SYNGAP1-related non-specific intellectual disability.

BACKGROUND: Synaptic Ras GTPase activating protein 1 (SYNGAP1)-related non-specific intellectual disability is a neurodevelopmental disorder caused by an insufficient level of SynGAP1 resulting in a dysfunction of neuronal synapses and presenting with a wide array of clinical phenotypes. Hematopoietic stem cell gene therapy has the potential to deliver therapeutic levels of functional SynGAP1 to affected neurons upon transduction of hematopoietic stem and progenitor cells with a lentiviral vector. METHODS: As a novel approach toward the treatment of SYNGAP1, we have generated a lentiviral vector expressing a modified form of SynGAP1 for transduction of human CD34+ hematopoietic stem and progenitor cells. The gene-modified cells were then transplanted into adult immunodeficient SYNGAP1+/- heterozygous mice and evaluated for improvement of SYNGAP1-related clinical phenotypes. Expression of SynGAP1 was also evaluated in the brain tissue of transplanted mice. RESULTS: In our proof-of-concept study, we have demonstrated significant improvement of SYNGAP1-related phenotypes including an improvement in motor abilities observed in mice transplanted with the vector transduced cells because they displayed decreased hyperactivity in an open field assay and an increased latency to fall in a rotarod assay. An increased level of SynGAP1 was also detected in the brains of these mice. CONCLUSIONS: These early-stage results highlight the potential of this stem cell gene therapy approach as a treatment strategy for SYNGAP1.

Functional rescue in an Angelman syndrome model following treatment with lentivector transduced hematopoietic stem cells.

Angelman syndrome (AS) is a rare neurodevelopmental disorder characterized by impaired communication skills, ataxia, motor and balance deficits, intellectual disabilities, and seizures. The genetic cause of AS is the neuronal loss of UBE3A expression in the brain. A novel approach, described here, is a stem cell gene therapy which uses lentivector-transduced hematopoietic stem and progenitor cells to deliver functional UBE3A to affected cells. We have demonstrated both the prevention and reversal of AS phenotypes upon transplantation and engraftment of human CD34+ cells transduced with a Ube3a lentivector in a novel immunodeficient Ube3amat-/pat+ IL2rg-/y mouse model of AS. A significant improvement in motor and cognitive behavioral assays as well as normalized delta power measured by electroencephalogram was observed in neonates and adults transplanted with the gene modified cells. Human hematopoietic profiles observed in the lymphoid organs by detection of human immune cells were normal. Expression of UBE3A was detected in the brains of the adult treatment group following immunohistochemical staining illustrating engraftment of the gene-modified cells expressing UBE3A in the brain. As demonstrated with our data, this stem cell gene therapy approach offers a promising treatment strategy for AS, not requiring a critical treatment window.

Improvement of motor and behavioral activity in Sandhoff mice transplanted with human CD34+ cells transduced with a HexA/HexB expressing lentiviral vector.

BACKGROUND: Tay-Sachs and Sandhoff disease are debilitating genetic diseases that affect the central nervous system leading to neurodegeneration through the accumulation of GM2 gangliosides. There are no cures for these diseases and treatments do not alleviate all symptoms. Hematopoietic stem cell gene therapy offers a promising treatment strategy for delivering wild-type enzymes to affected cells. By genetically modifying hematopoietic stem cells to express wild-type HexA and HexB, systemic delivery of functional enzyme can be achieved. METHODS: Primary human hematopoietic stem/progenitor cells and Tay-Sachs affected cells were used to evaluate the functionality of the vector. An immunodeficient and humanized mouse model of Sandhoff disease was used to evaluate whether the HexA/HexB lentiviral vector transduced cells were able to improve the phenotypes associated with Sandhoff disease. An immunodeficient NOD-RAG1-/-IL2-/- (NRG) mouse model was used to evaluate whether the HexA/HexB vector transduced human CD34+ cells were able to engraft and undergo normal multilineage hematopoiesis. RESULTS: HexA/HexB lentiviral vector transduced cells demonstrated strong expression of HexA and HexB and restored enzyme activity in Tay-Sachs affected cells. Upon transplantation into a humanized Sandhoff disease mouse model, improved motor and behavioral skills were observed. Decreased GM2 gangliosides were observed in the brains of HexA/HexB vector transduced cell transplanted mice. Increased peripheral blood levels of HexB was also observed in transplanted mice. Normal hematopoiesis in the peripheral blood and various lymphoid organs was also observed in transplanted NRG mice. CONCLUSIONS: These results highlight the potential use of stem cell gene therapy as a treatment strategy for Tay-Sachs and Sandhoff disease.

Safety and efficacy of a tCD25 preselective combination anti-HIV lentiviral vector in human hematopoietic stem and progenitor cells.

The successful suppression of human immunodeficiency virus (HIV) in the "Berlin Patient" has highlighted the ability of HIV-resistant hematopoietic stem cells to offer a potential functional cure for HIV-infected patients. HIV stem cell gene therapy can mimic this result by genetically modifying a patient's own cells with anti-HIV genes. Previous attempts of HIV gene therapy have been hampered by a low percentage of transplanted HIV-resistant cells which has led to minimal clinical efficacy. In our current study, we have evaluated the in vitro and in vivo safety and efficacy of a truncated/mutated form of human CD25 preselective anti-HIV lentiviral vector in human hematopoietic stem cells. This preselective vector allows us to purify vector-transduced cells prior to transplantation so an increased percentage of gene-modified cells can be delivered. Here, we demonstrate the safety of this strategy with successful engraftment and multilineage hematopoiesis of transduced cells in a humanized NOD-RAG1-/-IL-2rγ-/- knockout mouse model. Efficacy was also demonstrated with significant protection from HIV-1 infection including maintenance of human CD4+ cell levels and a decrease in HIV-1 plasma viremia. Collectively, these results establish the utility of this HIV stem cell gene therapy strategy and bring it closer to providing a functional cure for HIV-infected patients.

Generation of an HIV-1-resistant immune system with CD34(+) hematopoietic stem cells transduced with a triple-combination anti-HIV lentiviral vector.

HIV gene therapy has the potential to offer an alternative to the use of current small-molecule antiretroviral drugs as a treatment strategy for HIV-infected individuals. Therapies designed to administer HIV-resistant stem cells to an infected patient may also provide a functional cure, as observed in a bone marrow transplant performed with hematopoietic stem cells (HSCs) homozygous for the CCR5-Δ32-bp allele. In our current studies, preclinical evaluation of a combination anti-HIV lentiviral vector was performed, in vivo, in humanized NOD-RAG1(-/-) IL2rγ(-/-) knockout mice. This combination vector, which displays strong preintegration inhibition of HIV-1 infection in vitro, contains a human/rhesus macaque TRIM5α isoform, a CCR5 short hairpin RNA (shRNA), and a TAR decoy. Multilineage hematopoiesis from anti-HIV lentiviral vector-transduced human CD34(+) HSCs was observed in the peripheral blood and in various lymphoid organs, including the thymus, spleen, and bone marrow, of engrafted mice. Anti-HIV vector-transduced CD34(+) cells displayed normal development of immune cells, including T cells, B cells, and macrophages. The anti-HIV vector-transduced cells also displayed knockdown of cell surface CCR5 due to the expression of the CCR5 shRNA. After in vivo challenge with either an R5-tropic BaL-1 or X4-tropic NL4-3 strain of HIV-1, maintenance of human CD4(+) cell levels and a selective survival advantage of anti-HIV gene-modified cells were observed in engrafted mice. The data provided from our study confirm the safety and efficacy of this combination anti-HIV lentiviral vector in a hematopoietic stem cell gene therapy setting for HIV and validates its potential application in future clinical trials.

Generation of HIV-1 resistant and functional macrophages from hematopoietic stem cell-derived induced pluripotent stem cells.

Induced pluripotent stem cells (iPSCs) have radically advanced the field of regenerative medicine by making possible the production of patient-specific pluripotent stem cells from adult individuals. By developing iPSCs to treat HIV, there is the potential for generating a continuous supply of therapeutic cells for transplantation into HIV-infected patients. In this study, we have used human hematopoietic stem cells (HSCs) to generate anti-HIV gene expressing iPSCs for HIV gene therapy. HSCs were dedifferentiated into continuously growing iPSC lines with four reprogramming factors and a combination anti-HIV lentiviral vector containing a CCR5 short hairpin RNA (shRNA) and a human/rhesus chimeric TRIM5α gene. Upon directed differentiation of the anti-HIV iPSCs toward the hematopoietic lineage, a robust quantity of colony-forming CD133(+) HSCs were obtained. These cells were further differentiated into functional end-stage macrophages which displayed a normal phenotypic profile. Upon viral challenge, the anti-HIV iPSC-derived macrophages exhibited strong protection from HIV-1 infection. Here, we demonstrate the ability of iPSCs to develop into HIV-1 resistant immune cells and highlight the potential use of iPSCs for HIV gene and cellular therapies.

A novel Huntington's disease mouse model to assess the role of neuroinflammation on disease progression and to develop human cell therapies.

Huntington's disease (HD) is a fatal autosomal-dominant neurodegenerative disease caused by a trinucleotide CAG repeat expansion of the huntingtin gene (HTT) that affects 1 in every 10 000 individuals in the United States. Our lab developed a novel immune deficient HD mouse strain, the YACNSG, from a commonly used line, the YAC128 mouse, to enable transplantation studies using engineered human cells in addition to studying the impact of the immune system on disease progression. The primary goal of this project was to characterize this novel immune deQficient HD mouse model, using behavioral assays and histology to compare this new model to the immune competent YAC128 and immune deficient mice that had engraftment of a human immune system. Flow cytometry was used to confirm that the YACNSG strain lacked immune cells, and in vivo imaging was used to assess human mesenchymal stem/stromal cell (MSC) retention compared with a commonly used immune deficient line, the NSG mouse. We found that YACNSG were able to retain human MSCs longer than the immune competent YAC128 mice. We performed behavioral assessments starting at 4 months of age and continued testing monthly until 12 months on the accelerod and in the open field. At 12 months, brains were isolated and evaluated using immunohistochemistry for striatal volume. Results from these studies suggest that the novel immune deficient YACNSG strain of mice could provide a good model for human stem-cell based therapies and that the immune system appears to play an important role in the pathology of HD.

Preintegration HIV-1 inhibition by a combination lentiviral vector containing a chimeric TRIM5 alpha protein, a CCR5 shRNA, and a TAR decoy.

Human immunodeficiency virus (HIV) gene therapy offers a promising alternative approach to current antiretroviral treatments to inhibit HIV-1 infection. Various stages of the HIV life cycle including pre-entry, preintegration, and postintegration can be targeted by gene therapy to block viral infection and replication. By combining multiple highly potent anti-HIV transgenes in a single gene therapy vector, HIV-1 resistance can be achieved in transduced cells while prohibiting the generation of escape mutants. Here, we describe a combination lentiviral vector that encodes three highly effective anti-HIV genes functioning at separate stages of the viral life cycle including a CCR5 short hairpin RNA (shRNA) (pre-entry), a human/rhesus macaque chimeric TRIM5 alpha (postentry/preintegration), and a transactivation response element (TAR) decoy (postintegration). The major focus on designing this anti-HIV vector was to block productive infection of HIV-1 and to inhibit any formation of provirus that would maintain the viral reservoir. Upon viral challenge, potent preintegration inhibition of HIV-1 infection was achieved in combination vector-transduced cells in both cultured and primary CD34(+) hematopoietic progenitor cell (HPC)-derived macrophages. The generation of escape mutants was also blocked as evaluated by long-term culture of challenged cells. The ability of this combination anti-HIV lentiviral vector to prevent HIV-1 infection, in vitro, warrants further evaluation of its in vivo efficacy.

Derivation of normal macrophages from human embryonic stem (hES) cells for applications in HIV gene therapy.

BACKGROUND: Many novel studies and therapies are possible with the use of human embryonic stem cells (hES cells) and their differentiated cell progeny. The hES cell derived CD34 hematopoietic stem cells can be potentially used for many gene therapy applications. Here we evaluated the capacity of hES cell derived CD34 cells to give rise to normal macrophages as a first step towards using these cells in viral infection studies and in developing novel stem cell based gene therapy strategies for AIDS. RESULTS: Undifferentiated normal and lentiviral vector transduced hES cells were cultured on S17 mouse bone marrow stromal cell layers to derive CD34 hematopoietic progenitor cells. The differentiated CD34 cells isolated from cystic bodies were further cultured in cytokine media to derive macrophages. Phenotypic and functional analyses were carried out to compare these with that of fetal liver CD34 cell derived macrophages. As assessed by FACS analysis, the hES-CD34 cell derived macrophages displayed characteristic cell surface markers CD14, CD4, CCR5, CXCR4, and HLA-DR suggesting a normal phenotype. Tests evaluating phagocytosis, upregulation of the costimulatory molecule B7.1, and cytokine secretion in response to LPS stimulation showed that these macrophages are also functionally normal. When infected with HIV-1, the differentiated macrophages supported productive viral infection. Lentiviral vector transduced hES cells expressing the transgene GFP were evaluated similarly like above. The transgenic hES cells also gave rise to macrophages with normal phenotypic and functional characteristics indicating no vector mediated adverse effects during differentiation. CONCLUSION: Phenotypically normal and functionally competent macrophages could be derived from hES-CD34 cells. Since these cells are susceptible to HIV-1 infection, they provide a uniform source of macrophages for viral infection studies. Based on these results, it is also now feasible to transduce hES-CD34 cells with anti-HIV genes such as inhibitory siRNAs and test their antiviral efficacy in down stream differentiated cells such as macrophages which are among the primary cells that need to be protected against HIV-1 infection. Thus, the potential utility of hES derived CD34 hematopoietic cells for HIV-1 gene therapy can be evaluated.

Allele-Specific Reduction of the Mutant Huntingtin Allele Using Transcription Activator-Like Effectors in Human Huntington's Disease Fibroblasts.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by an abnormal expansion of CAG repeats. Although pathogenesis has been attributed to this polyglutamine expansion, the underlying mechanisms through which the huntingtin protein functions have yet to be elucidated. It has been suggested that postnatal reduction of mutant huntingtin through protein interference or conditional gene knockout could prove to be an effective therapy for patients suffering from HD. For allele-specific targeting, transcription activator-like effectors (TALE) were designed to target single-nucleotide polymorphisms (SNP) in the mutant allele and packaged into a vector backbone containing KRAB to promote transcriptional repression of the disease-associated allele. Additional TALEs were packaged into a vector backbone containing heterodimeric FokI and were designed to be used as nucleases (TALEN) to cause a CAG-collapse in the mutant allele. Human HD fibroblasts were treated with each TALE-SNP or TALEN. Allele-expression was measured using a SNP-genotyping assay and mutant protein aggregation was quantified with Western blots for anti-ubiquitin. The TALE-SNP and TALEN significantly reduced mutant allele expression (p < 0.05) when compared to control transfections while not affecting expression of the nondisease allele. This study demonstrates the potential of allele-specific gene modification using TALE proteins, and provides a foundation for targeted treatment for individuals suffering from Huntington's or other genetically linked diseases.

Hallmarks of HIV-1 pathogenesis are modulated by Nef's Secretion Modification Region.

CD4+ T cell depletion and immune activation are hallmarks of HIV infection. Despite extensive studies, the mechanisms underlying immune modulation remain elusive. HIV-1 Nef protein is secreted in exosomes from infected cells and is abundant in the plasma of HIV+ individuals. Exosomal Nef (exNef) was also shown to induce apoptosis in bystander CD4+ T cells. We hypothesized that exNef contributes to HIV pathogenesis. A HIV-1 NL4-3 virus containing alanine substitutions in the secretion modification region (SMR; amino acids 66 to 70; HIVNefsmr5a) was developed. Nef protein containing this modified SMR was shown to be deficient in exNef secretion in nef-transfected cells. Using both HIV-1 NL4-3 wild type (HIVwt) and HIVNefsmr5a, correlates of pathogenesis were evaluated in cell-lines, human peripheral blood mononuclear cells, and humanized NOD-RAG1-/- IL2r-/- double mutant (NRG) mice. Disruption of the SMR did not affect viral replication or exNef secretion from infected cell cultures as compared with nef-transfected cells. However, T cell apoptosis was reduced in HIVNefsmr5a infected cell cultures and CD4+ T cell depletion was reduced in the spleen and peripheral blood of similarly infected NRG mice. Inflammatory cytokine release was also decreased in the sera of HIVNefsmr5a infected mice relative to HIVwt infected controls. These findings demonstrate the importance of Nef and the SMR motif in HIV pathogenesis and suggest a potential role for exNef in HIV-driven immune modulation.

Stem cell transplantation in the context of HIV--how can we cure HIV infection?

All HIV target cells are derived from hematopoietic stem cells. More than two decades ago, a hypothesis was postulated that a cure for HIV may be possible by performing a transplant with HIV-resistant hematopoietic stem cells that would allow for an HIV-resistant immune system to arise. HIV-resistant stem cells could be generated by genetically modifying them with gene therapy vectors transferring anti-HIV genes. First attempts of stem cell gene therapy for HIV were carried out in the USA in the 1990s demonstrating safety, but also little efficacy at that time. The first demonstration that the postulated hypothesis was correct was the cure of an HIV-infected individual in Berlin in 2009 who received an allogeneic bone marrow transplant from a donor who lacked the CCR5 chemokine receptor, a naturally arising mutation rendering HIV target cells resistant to infection with macrophage tropic strains of HIV. In 2013, reports were published about a possible cure of HIV-infected individuals who received allogeneic bone marrow transplants with cells not resistant to HIV. We will review these stem cell transplant procedures and discuss their utility to provide a cure for HIV infection, including efficacious future stem cell gene therapy applications.

Canine epidermal neural crest stem cells: characterization and potential as therapy candidate for a large animal model of spinal cord injury.

The discovery of multipotent neural crest-derived stem cells, named epidermal neural crest stem cells (EPI-NCSC), that persist postnatally in an easy-to-access location-the bulge of hair follicles-opens a spectrum of novel opportunities for patient-specific therapies. We present a detailed characterization of canine EPI-NCSC (cEPI-NCSC) from multiple dog breeds and protocols for their isolation and ex vivo expansion. Furthermore, we provide novel tools for research in canines, which currently are still scarce. In analogy to human and mouse EPI-NCSC, the neural crest origin of cEPI-NCSC is shown by their expression of the neural crest stem cell molecular signature and other neural crest-characteristic genes. Similar to human EPI-NCSC, cEPI-NCSC also expressed pluripotency genes. We demonstrated that cEPI-NCSC can generate all major neural crest derivatives. In vitro clonal analyses established multipotency and self-renewal ability of cEPI-NCSC, establishing cEPI-NCSC as multipotent somatic stem cells. A critical analysis of the literature on canine spinal cord injury (SCI) showed the need for novel treatments and suggested that cEPI-NCSC represent viable candidates for cell-based therapies in dog SCI, particularly for chondrodystrophic dogs. This notion is supported by the close ontological relationship between neural crest stem cells and spinal cord stem cells. Thus, cEPI-NCSC promise to offer not only a potential treatment for canines but also an attractive and realistic large animal model for human SCI. Taken together, we provide the groundwork for the development of a novel cell-based therapy for a condition with extremely poor prognosis and no available effective treatment.

Using TRIM5α as an HIV therapeutic: the alpha gene?

INTRODUCTION: As HIV continues to spread worldwide, new therapies which have the potential to treat and cure infected patients need to be developed. The results observed with the "Berlin patient" who received a bone marrow transplant with HIV-resistant hematopoietic stem cells highlight the potential of HIV gene therapy to be used as an alternative treatment. With the discovery of TRIM5α, an HIV inhibitor and species-specific restriction factor, a new molecule can be evaluated as an HIV gene therapeutic. Nonhuman primate TRIM5α orthologs restrict HIV infection, whereas human TRIM5α does not. However, upon genetic modification, variations to human TRIM5α have been made which are capable of potent HIV restriction. AREAS COVERED: This review seeks to cover the discovery and biology of various HIV-restrictive nonhuman primate TRIM5α orthologs, modifications made to human TRIM5α to enable HIV restriction, and the use of these molecules in an HIV gene therapy setting. EXPERT OPINION: Engineered human TRIM5α molecules, demonstrated to be strong inhibitors of HIV infection, have the potential of being used as new HIV therapeutics in human gene therapy clinical trials. By combining TRIM5α with other highly potent anti-HIV molecules, the generation of an HIV-resistant immune system and potential cure for infected patients may be accomplished.

CD25 preselective anti-HIV vectors for improved HIV gene therapy.

As HIV continues to be a global public health problem with no effective vaccine available, new and innovative therapies, including HIV gene therapies, need to be developed. Due to low transduction efficiencies that lead to low in vivo gene marking, therapeutically relevant efficacy of HIV gene therapy has been difficult to achieve in a clinical setting. Methods to improve the transplantation of enriched populations of anti-HIV vector-transduced cells may greatly increase the in vivo efficacy of HIV gene therapies. Here we describe the development of preselective anti-HIV lentiviral vectors that allow for the purification of vector-transduced cells to achieve an enriched population of HIV-resistant cells. A selectable protein, human CD25, not normally found on CD34+ hematopoietic progenitor cells (HPCs), was incorporated into a triple combination anti-HIV lentiviral vector. Upon purification of cells transduced with the preselective anti-HIV vector, safety was demonstrated in CD34+ HPCs and in HPC-derived macrophages in vitro. Upon challenge with HIV-1, improved efficacy was observed in purified preselective anti-HIV vector-transduced macrophages compared to unpurified cells. These proof-of-concept results highlight the potential use of this method to improve HIV stem cell gene therapy for future clinical applications.

Specific transduction of HIV-susceptible cells for CCR5 knockdown and resistance to HIV infection: a novel method for targeted gene therapy and intracellular immunization.

HIV-1 gene therapy offers a promising alternative to small molecule antiretroviral treatments and current vaccination strategies by transferring, into HIV-1-susceptible cells, the genetic ability to resist infection. The need for novel and innovative strategies to prevent and treat HIV-1 infection is critical due to devastating effects of the virus in developing countries, high cost, toxicity, generation of escape mutants from antiretroviral therapies, and the failure of past and current vaccination efforts. As a first step toward achieving this goal, an HIV-1-susceptible cell-specific targeting vector was evaluated to selectively transfer, into CCR5-positive target cells, an anti-HIV CCR5 shRNA gene for subsequent knockdown of CCR5 expression and protection from HIV-1 infection. Using a ZZ domain/monoclonal antibody-conjugated Sindbis virus glycoprotein pseudotyped lentiviral vector, here we demonstrate the utility of this strategy for HIV-1 gene therapy by specifically targeting HIV-1-susceptible cells and engineering these cells to resist HIV-1 infection. CCR5-positive human cells were successfully and specifically targeted in vitro and in vivo for transduction by a lentiviral vector expressing a highly potent CCR5 shRNA which conferred resistance to HIV-1 infection. Here we report the initial evaluation of this targeting vector for HIV-1 gene therapy in a preexposure prophylactic setting.

Roles of human parainfluenza virus type 3 bases 13 to 78 in replication and transcription: identification of an additional replication promoter element and evidence for internal transcription initiation.

The genomic promoter of human parainfluenza virus type 3 (HPIV3) contains multiple cis-elements controlling transcription and replication. Previous work showed that regions 1 to 12 and 79 to 96 were critical in promoting replication of an HPIV3 minireplicon, while the intergenic sequence and N gene start signal (IS/Ngs, bases 49 to 61) were important for transcription. Because these data were collected primarily using point mutations, not every base from position 1 to 96 was analyzed, and some important control elements may have been missed. To clarify the role of bases 13 to 78 in transcription and replication, a series of mutations were made which collectively scanned this entire region. Mutation of bases 13 to 28 resulted in markedly decreased HPIV3 minireplicon replication, indicating these bases constitute an additional cis-element involved in the synthesis of the HPIV3 antigenomic RNA. The position dependence of the IS/Ngs was also examined. Analysis of mutants in which the IS/Ngs was shifted 5' or 3' showed that this segment could be moved without significantly disrupting transcription initiation. Additional mutants which contained two successive IS/Ngs segments were created to test whether the polymerase accessed the gene start signal by proceeding along the template 3' to 5' or by binding internally at the gene start signal. Based on analysis of the double gene start mutants, we propose a model of internal transcription initiation in which the polymerase enters the template at approximately the location of the natural N gene start but then scans the template bidirectionally to find a gene start signal and initiate transcription.