Adeno-Associated Virus-Mediated Gene Transfer for Lung Diseases

Genes in pediatric pulmonary arterial hypertension and the most promising BMPR2 gene therapy

Pulmonary arterial hypertension (PAH) is a rare but progressive and lethal vascular disease of diverse etiologies, mainly caused by proliferation of endothelial cells, smooth muscle cells in the pulmonary artery, and fibroblasts, which ultimately leads to right-heart hypertrophy and cardiac failure. Recent genetic studies of childhood-onset PAH report that there is a greater genetic burden in children than in adults. Since the first-identified pathogenic gene of PAH, BMPR2, which encodes bone morphogenetic protein receptor 2, a receptor in the transforming growth factor-β superfamily, was discovered, novel causal genes have been identified and substantially sharpened our insights into the molecular genetics of childhood-onset PAH. Currently, some newly identified deleterious genetic variants in additional genes implicated in childhood-onset PAH, such as potassium channels (KCNK3) and transcription factors (TBX4 and SOX17), have been reported and have greatly updated our understanding of the disease mechanism. In this review, we summarized and discussed the advances of genetic variants underlying childhood-onset PAH susceptibility and potential mechanism, and the most promising BMPR2 gene therapy and gene delivery approaches to treat childhood-onset PAH in the future.

Genetic Modification of the Lung Directed Toward Treatment of Human Disease

Genetic modification therapy is a promising therapeutic strategy for many diseases of the lung intractable to other treatments. Lung gene therapy has been the subject of numerous preclinical animal experiments and human clinical trials, for targets including genetic diseases such as cystic fibrosis and α1-antitrypsin deficiency, complex disorders such as asthma, allergy, and lung cancer, infections such as respiratory syncytial virus (RSV) and Pseudomonas, as well as pulmonary arterial hypertension, transplant rejection, and lung injury. A variety of viral and non-viral vectors have been employed to overcome the many physical barriers to gene transfer imposed by lung anatomy and natural defenses. Beyond the treatment of lung diseases, the lung has the potential to be used as a metabolic factory for generating proteins for delivery to the circulation for treatment of systemic diseases. Although much has been learned through a myriad of experiments about the development of genetic modification of the lung, more work is still needed to improve the delivery vehicles and to overcome challenges such as entry barriers, persistent expression, specific cell targeting, and circumventing host anti-vector responses.

Effect of poly(ADP-ribose) polymerase 1 on integration of the adeno-associated viral vector genome

BACKGROUND

Adeno-associated virus type 2 (AAV) has the ability to target integration of its DNA into a specific locus of the human genome. Site-specific AAV integration is mediated by viral Rep proteins, although the role of cellular factors involved in this process is largely unknown. Recent studies provide evidence showing that cellular DNA repair proteins are involved in targeted integration of AAV, although their specific roles are not well defined.

METHODS

In the present study, we investigated the interaction between Rep and proteins of the back-up nonhomologous end-joining pathway (B-NHEJ). We then analyzed the effect of one of these proteins, poly(ADP-ribose) polymerase 1 (PARP1) on AAV integration.

RESULTS

We show that AAV Rep interacts with B-NHEJ members DNA ligase III and PARP1 but does not associate with the scaffolding factor XRCC1. Moreover, PARP1 and Rep bind directly and not via DNA-protein interactions. We also found that Rep increases the enzymatic activity of PARP1 potentially through the endonuclease activity of Rep. Finally, we demonstrate that both chemical inhibition of PARP1 and PARP1 depletion using small hairpin RNA enhance integration of the AAV genome in HeLa cells.

CONCLUSIONS

The findings of the present study indicate that manipulation of PARP1 activity could be used as a tool for developing new, effective AAV-based therapies for the treatment of genetic diseases and cancer.

Phase I trial of intramuscular injection of a recombinant adeno-associated virus serotype 2 alphal-antitrypsin (AAT) vector in AAT-deficient adults

A phase I trial of intramuscular injection of a recombinant adeno-associated virus serotype 2 (rAAV2) alpha1-antitrypsin (AAT) vector was performed in 12 AAT-deficient adults, 10 of whom were male. All subjects were either homozygous for the most common AAT mutation (a missense mutation designated PI*Z) or compound heterozygous for PI*Z and another mutation known to cause disease. There were four dose cohorts, ranging from 2.1 x 10(12) vector genomes (VG) to 6.9 x 10(13) VG, with three subjects per cohort. Subjects were injected sequentially in a dose-escalating fashion with a minimum of 14 days between patients. Subjects who had been receiving AAT protein replacement discontinued that therapy 28 days before vector administration. There were no vector-related serious adverse events in any of the 12 participants. Vector DNA sequences were detected in the blood between 1 and 3 days after injection in nearly all patients receiving doses of 6.9 x 10(12) VG or higher. Anti-AAV2 capsid antibodies were present and rose after vector injection, but no other immune responses were detected. One subject who had not been receiving protein replacement exhibited low-level expression of wild-type M-AAT in the serum (82 nM), which was detectable 30 days after receiving an injection of 2.1 x 10(13) VG. Unfortunately, residual but declining M-AAT levels from the washout of the protein replacement elevated background levels sufficiently to obscure any possible vector expression in that range in most of the other individuals in the higher dose cohorts.

Cell biology of membrane trafficking in human disease

Understanding the molecular and cellular mechanisms underlying membrane traffic pathways is crucial to the treatment and cure of human disease. Various human diseases caused by changes in cellular homeostasis arise through a single gene mutation(s) resulting in compromised membrane trafficking. Many pathogenic agents such as viruses, bacteria, or parasites have evolved mechanisms to subvert the host cell response to infection, or have hijacked cellular mechanisms to proliferate and ensure pathogen survival. Understanding the consequence of genetic mutations or pathogenic infection on membrane traffic has also enabled greater understanding of the interactions between organisms and the surrounding environment. This review focuses on human genetic defects and molecular mechanisms that underlie eukaryote exocytosis and endocytosis and current and future prospects for alleviation of a variety of human diseases.

Synthetic intron improves transduction efficiency of trans-splicing adeno-associated viral vectors

Trans-splicing adeno-associated viral (AAV) vectors hold great promise in many gene therapy applications. We have shown that rational selection of the gene-splitting site in a therapeutic target gene can lead to extremely efficient trans-splicing vectors [Lai, Y., Yue, Y., Liu, M., Ghosh, A., Engelhardt, J.F., Chamberlain, J.S., and Duan, D. (2005). Nat. Biotechnol. 23, 1435-1439]. Our original strategy requires the screening of endogenous introns that are capable of overcoming the mRNA accumulation barrier. To further develop transsplicing vectors, we have tested whether the use of a generic synthetic intron can bypass the labor-intensive intron-screening process. Two previously characterized exon/intron/exon junctions (60/60/61 and 63/63/64, respectively) in the 6 kb minidystrophin gene were used as templates to represent highly efficient (60/60/61) and relatively poor (63/63/64) gene-splitting sites. We compared RNA production from the reconstituted viral genome and transduction efficiency of the trans-splicing vectors in dystrophin-null mdx mouse skeletal muscle. Our results suggest that a synthetic intron can successfully overcome the mRNA accumulation barrier at the exon 63/64 junction. Furthermore, when the gene was split at the exon 63/64 junction, the synthetic intronbased vectors performed better than the endogenous intron-based vectors. When the gene was split at the exon 60/61 junction, we observed only nominal improvement in mRNA production. Nevertheless, vectors based on the exon 60/61 junction remain the best set in transduction efficiency. Taken together, our results suggest that optimizing intron sequence may boost the transduction efficiency of trans-splicing AAV vectors.

Safety in Nonhuman Primates of Ocular AAV2-RPE65, a Candidate Treatment for Blindness in Leber Congenital Amaurosis

Leber congenital amaurosis (LCA) is a molecularly heterogeneous disease group that leads to blindness. LCA caused by RPE65 mutations has been studied in animal models and vision has been restored by subretinal delivery of AAV-RPE65 vector. Human ocular gene transfer trials are being considered. Our safety studies of subretinal AAV-2/2.RPE65 in RPE65-mutant dogs showed evidence of modest photoreceptor loss in the injection region in some animals at higher vector doses. We now test the hypothesis that there can be vectorrelated toxicity to the normal monkey, with its human-like retina. Good Laboratory Practice safety studies following single intraocular injections of AAV-2/2.RPE65 in normal cynomolgus monkeys were performed for 1-week and 3-month durations. Systemic toxicity was not identified. Ocular-specific studies included clinical examinations, electroretinography, and retinal histopathology. Signs of ocular inflammation postinjection had almost disappeared by 1 week. At 3 months, electroretinography in vector-injected eyes was no different than in vehicle-injected control eyes or compared with presurgical recordings. Healed sites of retinal perforation from subretinal injections were noted clinically and by histopathology. Foveal architecture in subretinally injected eyes, vector or vehicle, could be abnormal. Morphometry of central retina showed no photoreceptor layer thickness abnormalities occurring in a dose-dependent manner. Vector sequences were present in the injected retina, vitreous, and optic nerve at 1 week but not consistently in the brain. At 3 months, there were no vector sequences in optic nerve and brain. The results allow for consideration of an upper range for no observed adverse effect level in future human trials of subretinal AAV-2/2.RPE65. The potential value of foveal treatment for LCA and other retinal degenerations warrants further research into how to achieve gene transfer without retinal injury from surgical detachment of the retina.