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Chimeric Capsid Proteins Impact Transduction Efficiency of Haploid Adeno-Associated Virus Vectors.

ABSTRACT: Our previous studies have demonstrated that haploid AAV vectors made from capsids of two different serotypes induced high transduction and prevented serotype-specific antibody binding. In this study, we explored the transduction efficiency of several haploid viruses, which were made from the VP1/VP2 of one serotype and VP3 of another compatible serotype. After systemic injection of 2 × 1010 vg of AAV vectors into mice, the haploid AAV vectors, composed of VP1/VP2 from serotypes 8 or 9, and VP3 from AAV2, displayed a two to seven-fold increase in liver transduction compared with those of parental AAV2 vectors. Furthermore, a chimeric AAV2/8 VP1/VP2 with N-terminus of VP1/VP2 from AAV2 and C-terminus (VP3 domain) from AAV8 was constructed, and produced the haploid vector 28m-2VP3 with AAV2 VP3. The haploid 28m-2VP3 vector showed a five-fold higher transduction than that of the vectors composed solely of AAV2 VPs. Remarkably, the 28m-2VP3 vectors also induced a significant increase in transgene expression compared to the vectors composed of AAV8 VP1/VP2 with AAV2 VP3. The results suggest that the difference in the VP1/VP2 N-terminal region between AAV2 and AAV8 may allow better "communication" between the VP1/VP2 N-terminus of AAV2 with its cognate VP3. Similarly, the haploid vectors, VP1/VP2 from serotypes 8 or 9 and VP3 from AAV3, achieved higher transductions in multiple tissue types beyond typical tropism compared with those of AAV3 vectors. Consistently, higher vector genome copy numbers were detected in these tissues, indicating that an incorporation of non-cognate VP1/VP2 might influence the cellular tropism of the haploid vectors. However, there was no significant difference or even decreased transductions when compared with those of parental AAV8 or AAV9 vectors. In summary, these studies provide insight into current development strategies of AAV vectors that can increase AAV transduction across multiple tissues.

SUBMITTER: Chai Z

PROVIDER: S-EPMC6950324 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Chimeric Capsid Proteins Impact Transduction Efficiency of Haploid Adeno-Associated Virus Vectors.

Chai Zheng Z Zhang Xintao X Dobbins Amanda Lee AL Frost Ellie Azure EA Samulski R Jude RJ Li Chengwen C

Viruses 20191209 12

Our previous studies have demonstrated that haploid AAV vectors made from capsids of two different serotypes induced high transduction and prevented serotype-specific antibody binding. In this study, we explored the transduction efficiency of several haploid viruses, which were made from the VP1/VP2 of one serotype and VP3 of another compatible serotype. After systemic injection of 2 × 10<sup>10</sup> vg of AAV vectors into mice, the haploid AAV vectors, composed of VP1/VP2 from serotypes 8 or 9 ...[more]

PMID: 31835440

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Project description:Recombinant adeno-associated viruses (rAAVs) are one of the most commonly used vectors for a variety of gene therapy applications. In the last 2 decades, research focused primarily on the characterization and isolation of new cap, genes resulting in hundreds of natural and engineered AAV capsid variants, while the rep gene, the other major AAV open reading frame, has been less studied. This is due to the fact that the rep gene from AAV serotype 2 (AAV2) enables the single-stranded DNA packaging of recombinant genomes into most AAV serotype and engineered capsids. However, a major by-product of all vector productions is empty AAV capsids, lacking the encapsidated vector genome, especially for non-AAV2 vectors. Despite the packaging process being considered the rate-limiting step for rAAV production, none of the rep genes from the other AAV serotypes have been characterized for their packaging efficiency. Thus, in this study AAV2 rep was replaced with the rep gene of a select number of AAV serotypes. However, this led to a lowering of capsid protein expression, relative to the standard AAV2-rep system. In further experiments the 3' end of the AAV2 rep gene was reintroduced to promote increased capsid expression and a series of chimeras between the different AAV Rep proteins were generated and characterized for their vector genome packaging ability. The utilization of these novel Rep hybrids increased the percentage of genome containing (full) capsids approximately 2- to -4-fold for all of the non-AAV2 serotypes tested. Thus, these Rep chimeras could revolutionize rAAV production. IMPORTANCE A major by-product of all adeno-associated virus (AAV) vector production systems are "empty" capsids, void of the desired therapeutic gene, and thus do not provide any curative benefit for the treatment of the targeted disease. In fact, empty capsids can potentially elicit additional immune responses in vivo gene therapies if not removed by additional purification steps. Thus, there is a need to increase the genome packaging efficiency and reduce the number of empty capsids from AAV biologics. The novel Rep hybrids from different AAV serotypes described in this study are capable of reducing the percentage of empty capsids in all tested AAV serotypes and improve overall yields of genome-containing AAV capsids at the same time. They can likely be integrated easily into existing AAV manufacturing protocols to optimize the production of the generated AAV gene therapy products.

Project description:Adeno-associated virus (AAV) vectors have been used successfully in clinical trials for patients with hemophilia or blindness, but pre-existing neutralizing antibodies (Nab) are common in the general population and exclude many patients from clinical trials. Exploration of effective strategies to enhance AAV transduction and escape from Nab activity is still imperative. Previous studies have shown the compatibility of capsids from AAV serotypes and homology of recognition sites of AAV Nab located on different capsid subunits from one virion. In this study, we co-transfected AAV2 and AAV8 helper plasmids at different ratios (3:1, 1:1 and 1:3) to assemble haploid capsids and study both their transduction efficiency and Nab escape activity. After muscular injection, all of the haploid viruses induced higher transduction than their parental AAV vectors (2- to 9-fold over AAV2), with the highest of these being the haploid vector AAV2/8 3:1. After systemic administration, a 4-fold higher transduction in the liver was observed with haploid AAV2/8 1:3 than that with AAV8 alone. We then packaged the therapeutic factor IX cassette into haploid AAV2/8 1:3 capsids and injected them into FIX knockout mice via the tail vein. Higher FIX expression and improved phenotypic correction were achieved with the haploid AAV2/8 1:3 virus vector when compared to that of AAV8. Additionally, the haploid virus AAV2/8 1:3 was able to escape AAV2 neutralization and did not increase capsid antigen presentation capacity when compared to AAV8. To improve the Nab evasion ability of the haploid virus, we produced the triploid vector AAV2/8/9 by co-transfecting AAV2, AAV8 and AAV9 helper plasmids at a ratio of 1:1:1. After systemic administration, a 2-fold higher transduction in the liver was observed with the triploid vector AAV2/8/9 than that with AAV8. Nab analysis demonstrated that the triploid AAV2/8/9 vector was able to escape Nab activity from mouse sera immunized with parental serotypes. These results indicate that polyploid viruses might potentially acquire advantages from parental serotypes for enhancement of AAV transduction and evasion of Nab recognition without increasing capsid antigen presentation in target cells. Polyploid AAV vectors can be generated from any AAV serotype, whether natural, rational, library derived or a combination thereof, providing a novel strategy that should be explored in future clinical trials in patients with neutralizing antibodies.

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Chimeric Capsid Proteins Impact Transduction Efficiency of Haploid Adeno-Associated Virus Vectors.

Publications

Chimeric Capsid Proteins Impact Transduction Efficiency of Haploid Adeno-Associated Virus Vectors.

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