Qiushi Tang

Targeting recombinant adeno-associated virus vectors to enhance gene transfer to pancreatic islets and liver

Human pancreatic islet cells and hepatocytes represent the two most likely target cells for genetic therapy of type I diabetes. However, limits to the efficiency of rAAV serotype 2 (rAAV2)-mediated gene transfer have been reported for both of these cell targets. Here we report that nonserotype 2 AAV capsids can mediate more efficient transduction of islet cells, with AAV1 being the most efficient serotype in murine islets, suggesting that receptor abundance could be limiting. In order to test this, we generated rAAV particles that display a ligand (ApoE) that targets the low-density lipoprotein receptor, which is present on both of these cell types. The rAAV/ApoE viruses greatly enhanced the efficiency of transduction of both islet cells ex vivo and murine hepatocytes in vivo when compared to native rAAV2 serotype (220- and four-fold, respectively). The use of receptor-targeted rAAV particles may circumvent the lower abundance of receptors on certain nonpermissive cell types.

DNA-dependent PK inhibits adeno-associated virus DNA integration

Recent studies have shown that recombinant adeno-associated virus (rAAV) can persist in episomal form; however, factors affecting rAAV persistence are poorly understood. DNA-dependent PK (DNA-PK) is a DNA repair enzyme, which we previously found played an important role in determining the molecular fate of the rAAV genome in mouse skeletal muscle. In the present study, we tested the effect of DNA-PK on AAV serotype 2 integration in vitro and in vivo in mouse liver. In an in vitro integration system, addition of DNA-PK decreased AAV integration, whereas antibody against DNA-PKcs increased integration. In vivo, matched doses of a recombinant AAV serotype 2 vector were injected into the portal vein of either C57BL/6 (DNA-PKcs+/+) or severe combined immunodeficient (DNA-PKcs-/-) mice. After partial hepatectomy to stimulate hepatocyte proliferation, retention of vector genomes and of transgene expression was substantially higher in severe combined immunodeficient mice, indicating that in the absence of DNA-PKcs, a greater proportion of genomes integrated into the cellular genome. In summary, we have provided evidence that DNA-PK inhibits AAV integration both in vitro and in vivo.

Recombinant adeno-associated virus-mediated alpha- 1 antitrypsin gene therapy prevents type I diabetes in NOD mice

Type I diabetes results from an autoimmune destruction of the insulin-producing pancreatic β cells. Although the exact immunologic processes underlying this disease are unclear, increasing evidence suggests that immunosuppressive, immunoregulatory and anti-inflammatory agents can interrupt the progression of the disease. Alpha 1 antitrypsin (AAT) is a multifunctional serine proteinase inhibitor (serpin) that also displays a wide range of anti-inflammatory properties. To test the ability of AAT to modulate the development of type I diabetes, we performed a series of investigations involving recombinant adeno-associated virus vector (rAAV)-mediated gene delivery of human alpha-1 antitrypsin (hAAT) to nonobese diabetic (NOD) mice. Recombinant AAV-expressing hAAT (rAAV2-CB-AT) was administered intramuscularly to 4-week-old female NOD mice (1 × 1010 i.u./mouse). A single injection of this vector reduced the intensity of insulitis, the levels of insulin autoantibodies, and the frequency of overt type I diabetes (30% (3/10) at 32 weeks of age versus 70% (7/10) in controls). Transgene expression at the injection sites was confirmed by immunostaining. Interestingly, antibodies against hAAT were present in a majority of the vector-injected mice and circulating hAAT was undetectable when assessed 10 weeks postinjection. This study suggests a potential therapeutic role for AAT in preventing type I diabetes as well as the ability of AAV gene therapy-based approaches to ameliorate disease effectively.

Human Treg responses allow sustained recombinant adeno-associated virus–mediated transgene expression

Recombinant adeno-associated virus (rAAV) vectors have shown promise for the treatment of several diseases; however, immune-mediated elimination of transduced cells has been suggested to limit and account for a loss of efficacy. To determine whether rAAV vector expression can persist long term, we administered rAAV vectors expressing normal, M-type α-1 antitrypsin (M-AAT) to AAT-deficient subjects at various doses by multiple i.m. injections. M-specific AAT expression was observed in all subjects in a dose-dependent manner and was sustained for more than 1 year in the absence of immune suppression. Muscle biopsies at 1 year had sustained AAT expression and a reduction of inflammatory cells compared with 3 month biopsies. Deep sequencing of the TCR Vβ region from muscle biopsies demonstrated a limited number of T cell clones that emerged at 3 months after vector administration and persisted for 1 year. In situ immunophenotyping revealed a substantial Treg population in muscle biopsy samples containing AAT-expressing myofibers. Approximately 10% of all T cells in muscle were natural Tregs, which were activated in response to AAV capsid. These results suggest that i.m. delivery of rAAV type 1-AAT (rAAV1-AAT) induces a T regulatory response that allows ongoing transgene expression and indicates that immunomodulatory treatments may not be necessary for rAAV-mediated gene therapy.

Sustained miRNA-mediated knockdown of mutant AAT with simultaneous augmentation of wild-type AAT has minimal effect on global liver miRNA profiles.

α-1 antitrypsin (AAT) deficiency can exhibit two pathologic states: a lung disease that is primarily due to the loss of AATs antiprotease function, and a liver disease resulting from a toxic gain-of-function of the PiZ-AAT (Z-AAT) mutant protein. We have developed several recombinant adeno-associated virus (rAAV) vectors that incorporate microRNA (miRNA) sequences targeting the AAT gene while also driving the expression of miRNA-resistant wild-type AAT-PiM (M-AAT) gene, thus achieving concomitant Z-AAT knockdown in the liver and increased expression of M-AAT. Transgenic mice expressing the human PiZ allele treated with dual-function rAAV9 vectors showed that serum PiZ was stably and persistently reduced by an average of 80%. Treated animals showed knockdown of Z-AAT in liver and serum with concomitant increased serum M-AAT as determined by allele-specific enzyme-linked immunosorbent assays (ELISAs). In addition, decreased globular accumulation of misfolded Z-AAT in hepatocytes and a reduction in inflammatory infiltrates in the liver was observed. Results from microarray studies demonstrate that endogenous miRNAs were minimally affected by this treatment. These data suggests that miRNA mediated knockdown does not saturate the miRNA pathway as has been seen with viral vector expression of short hairpin RNAs (shRNAs). This safe dual-therapy approach can be applied to other disorders such as amyotrophic lateral sclerosis, Huntington disease, cerebral ataxia, and optic atrophies.

Therapeutic level of functional human alpha 1 antitrypsin (hAAT) secreted from murine muscle transduced by adeno-associated virus (rAAV1) vector

Alpha 1 antitrypsin (AAT) is a serine proteinase inhibitor (serpin). One well‐known function of this protein is to inactivate neutrophil elastase and other neutrophil‐derived proteinases, and prevent the destruction of pulmonary extracellular matrix. Deficiency of AAT can cause emphysema due to degradation of interstitial elastin by elastase. The majority of circulating AAT is secreted from the liver. Muscle‐directed gene therapy using recombinant adeno‐associated virus 2 (rAAV2) vectors has been tested to increase the serum levels of AAT. However, inefficient transduction of rAAV2 vector makes it difficult to reach therapeutic levels of AAT in clinical trials and it remains unclear as to whether muscle‐secreted AAT is functional. In the present study, we evaluated five serotypes (1, 2, 3, 4, and 5) of rAAV vectors for transduction efficiency in mouse muscle. Results from these studies showed that rAAV1 is the most efficient vector among these serotypes and mediated at least 100‐fold higher levels of AAT secretion than the rAAV2 vector. Western blot analysis showed that this murine muscle‐secreted human AAT (hAAT) formed a complex with human neutrophil elastase in a dose‐dependent manner. An anti‐elastase activity assay showed that murine muscle‐secreted hAAT inhibited elastase with equal capacity as hAAT purified from plasma. These results provide strong support for the functionality of AAT in ongoing clinical studies of muscle‐directed AAT gene therapy. Copyright

In vivo post-transcriptional gene silencing of alpha-1 antitrypsin by adeno-associated virus vectors expressing siRNA

α-1 Antitrypsin (AAT) deficiency is one of the most common genetic diseases in North America, with a carrier frequency of approximately 4% in the US population. Homozygosity for the most common mutation (Glu342Lys, PI*Z) leads to the synthesis of a mutant protein, which accumulates and polymerizes within hepatocytes rather than being efficiently secreted. This lack of secretion causes severe serum deficiency predisposing to chronic lung disease. Twelve to fifteen percent of patients with PI*ZZ also develop liver disease, which can be severe, even in infancy. This is thought to be due to toxic effects of the accumulated mutant Z-AAT within the hepatocyte. Thus, an approach to reduce AAT-deficient liver disease will likely require some mechanism to decrease the amount of Z-AAT within hepatocytes. In this report, we describe studies of small-interfering RNAs (siRNAs) designed to downregulate endogenous AAT within hepatocytes. Three different siRNA sequences were identified and cloned into a recombinant adeno-associated virus (rAAV) backbone, either singly or as a trifunctional (3X) construct. Each had activity independently, but the levels of AAT expression in cell culture models showed the greatest decrease with the 3X construct, resulting in levels that were five-fold lower than controls. The rAAV-3X-siRNA was then packaged into AAV8 capsids and used in vivo to transduce the livers of human Z-AAT overexpressing transgenic mice. Those studies showed a decrease in total human AAT, a clearing of Z-AAT accumulation by immunohistochemistry, and a decrease in monomer Z-AAT within the liver within 3 weeks after vector injection. The rAAV8-3X-siRNA vector may hold promise as a potential therapy for patients with AAT liver disease.

The pros and cons of immunomodulatory IL-10 gene therapy with recombinant AAV in a Cftr −/− -dependent allergy mouse model

Cystic fibrosis (CF) patients have decreased levels of lung epithelial interleukin (IL)-10 and increased levels of proinflammatory cytokines (tumor necrosis factor-α, IL-4, IL-8 and IL-6). This has also been documented in Cftr (cystic fibrosis transmembrane conductance regulator)-deficient mice (Cftr 489X−/−, FABP-hCFTR+/+). Our laboratory has recently characterized a peculiar hyper-IgE phenotype in these mice, in response to Aspergillus fumigatus crude protein extract (Af-cpe). Thus, we hypothesized that sustained systemic circulating IL-10 levels achieved through skeletal muscle transduction with recombinant adeno-associated vectors expressing IL-10 (rAAV1-IL-10) would serve to downregulate Th1 and Th2 cytokine production. This in turn would dampen the allergic response in the Cftr−/−-dependent mouse model of allergic bronchopulmonary aspergillosis. After Af-cpe sensitization and airway challenge, mice treated with rAAV1-IL-10 had markedly lower IgE levels when compared to the control-treated rAAV1-GFP group. This was accompanied by a significant reduction in the levels of IL-5, IL-4 and IL-13 in the lung compartment. The lower lung cytokine profiles resulted in a near absence of eosinophil recruitment in the lung and a lower inflammatory response in the lung tissue of mice receiving rAAV1-IL-10. Unfortunately, sustained secretion of IL-10 from transduced muscle did lead to thrombocytopenia and splenomegaly in mice injected with rAAV1-IL-10. These results highlight that while IL-10 gene therapy is very effective for treating allergic responses caution must be taken with the prolonged secretion of IL-10.

Efficient and Targeted Transduction of Nonhuman Primate Liver With Systemically Delivered Optimized AAV3B Vectors

Recombinant adeno-associated virus serotype 3B (rAAV3B) can transduce cultured human liver cancer cells and primary human hepatocytes efficiently. Serine (S)- and threonine (T)-directed capsid modifications further augment its transduction efficiency. Systemically delivered capsid-optimized rAAV3B vectors can specifically target cancer cells in a human liver cancer xenograft model, suggesting their potential use for human liver-directed gene therapy. Here, we compared transduction efficiencies of AAV3B and AAV8 vectors in cultured primary human hepatocytes and cancer cells as well as in human and mouse hepatocytes in a human liver xenograft NSG-PiZ mouse model. We also examined the safety and transduction efficacy of wild-type (WT) and capsid-optimized rAAV3B in the livers of nonhuman primates (NHPs). Intravenously delivered S663V+T492V (ST)-modified self-complementary (sc) AAV3B-EGFP vectors led to liver-targeted robust enhanced green fluorescence protein (EGFP) expression in NHPs without apparent hepatotoxicity. Intravenous injections of both WT and ST-modified rAAV3B.ST-rhCG vectors also generated stable super-physiological levels of rhesus chorionic gonadotropin (rhCG) in NHPs. The vector genome predominantly targeted the liver. Clinical chemistry and histopathology examinations showed no apparent vector-related toxicity. Our studies should be important and informative for clinical development of optimized AAV3B vectors for human liver-directed gene therapy.

Long-term Correction of Very Long-chain Acyl-CoA Dehydrogenase Deficiency in Mice Using AAV9 Gene Therapy

Very long-chain acyl-coA dehydrogenase (VLCAD) is the rate-limiting step in mitochondrial fatty acid oxidation. VLCAD-deficient mice and patients clinical symptoms stem from not only an energy deficiency but also long-chain metabolite accumulations. VLCAD-deficient mice were treated systemically with 1 × 1012 vector genomes of recombinant adeno-associated virus 9 (rAAV9)-VLCAD. Biochemical correction was observed in vector-treated mice beginning 2 weeks postinjection, as characterized by a significant drop in long-chain fatty acyl accumulates in whole blood after an overnight fast. Changes persisted through the termination point around 20 weeks postinjection. Magnetic resonance spectroscopy (MRS) and tandem mass spectrometry (MS/MS) revealed normalization of intramuscular lipids in treated animals. Correction was not observed in liver tissue extracts, but cardiac muscle extracts showed significant reduction of long-chain metabolites. Disease-specific phenotypes were characterized, including thermoregulation and maintenance of euglycemia after a fasting cold challenge. Internal body temperatures of untreated VLCAD−/− mice dropped below 20 °C and the mice became lethargic, requiring euthanasia. In contrast, all rAAV9-treated VLCAD−/− mice and the wild-type controls maintained body temperatures. rAAV9-treated VLCAD−/− mice maintained euglycemia, whereas untreated VLCAD−/− mice suffered hypoglycemia following a fasting cold challenge. These promising results suggest rAAV9 gene therapy as a potential treatment for VLCAD deficiency in humans.