In 2003 we reported the development of a microarray based high throughput screening technique for identifying gene expression patterns that correlated with a specific phenotype (Di Pasquale et al. 2003). This approach was termed comparative gene analysis (CGA). Since our initial publication we have continued to refine the bioinformatics aspect of this approach and identified several receptors for different viruses including AAVs and filoviruses. This work has lead to a better understanding of the overall virus lifecyle of AAVs and lead to the reclassification of the family Parvoviridae (Cotmore et al. 2014). This work has also highlighted the role of protein glycosylation in the lifecycle of some viruses and suggested that alterations in host glycosylation could prevent virus attachment and maturation. In collaboration with the NIH undiagnosed diseases program, we were able to test this hypothesis in vivo by studying virus replication in cells isolated from patients with genetic defects in MOGS, the gene encoding mannosyl-oligosaccharide glucosidase (the first enzyme in the processing pathway of N-linked oligosaccharide) (Sadat et al. 2014). We evaluated virus replication and infection in two siblings with CDG-IIb. As expected both had a limited clinical history of any infectious diathesis. Our results show that these patients do not possess an altered susceptibility to Adenovirus type 5 or Poliovirus 1, non-enveloped viruses; or to Vaccinia, a glycosylation-independent for entry or egression enveloped virus. In contrast, they display a markedly reduced susceptibility to infection with HIV and influenza, two glycosylation-dependent enveloped viruses. While we cannot make broad generalizations, these data appear to suggest that altered glycosylation might modify infection susceptibility to viruses that require protein glycosylation to complete their infection cycle. As a genus, the dependoviruses use a diverse group of cell surface carbohydrates for attachment and entry. Despite the fact that a majority of adeno-associated viruses (AAVs) utilize sialic acid (SIA) for binding and transduction, this virus-carbohydrate interaction is poorly understood. Utilizing X-ray crystallography, two SIA binding regions were mapped for AAV5 (Afione et al 2015). The first site mapped to the depression in the center of the 3-fold axis of symmetry, while the second site was located under the _HI loop close to the 5-fold axis. Mutagenesis of amino acids 569 and 585 or 587 within the 3-fold depression resulted in elimination or alteration in SIA-dependent transduction, respectively. This change in SIA binding was confirmed using glycan microarrays. Mutagenesis of the second site identified a role in transduction that was SIA independent. Further studies of the mutants at the 3-fold site demonstrated a change in transduction activity and cell tropism in vivo as well as resistance to neutralization by a polyclonal antibody raised against the wild-type virus. Antigenic response is a critical component of the advancement of AAV vectors for clinical applications. The clinical utility of the adeno-associated virus (AAV) gene delivery system has been validated by the regulatory approval of an AAV serotype 1 (AAV1) vector for the treatment of lipoprotein lipase deficiency. However, neutralization from preexisting antibodies is detrimental to AAV transduction efficiency. Hence, mapping of AAV antigenic sites and engineering of neutralization-escaping vectors are important for improving clinical efficacy. We report the structures of four AAV-monoclonal antibody fragment complexes, AAV1-ADK1a, AAV1-ADK1b, AAV5-ADK5a, and AAV5-ADK5b, determined by cryo-electron microscopy and image reconstruction to a resolution of ∼11 to 12 (Tseng YS et al 2015). Pseudoatomic modeling mapped the ADK1a epitope to the protrusions surrounding the icosahedral 3-fold axis and the ADK1b and ADK5a epitopes, which overlap, to the wall between depressions at the 2- and 5-fold axes (2/5-fold wall), and the ADK5b epitope spans both the 5-fold axis-facing wall of the 3-fold protrusion and portions of the 2/5-fold wall of the capsid. Combined with the six antigenic sites previously elucidated for different AAV serotypes through structural approaches, including AAV1 and AAV5, this study identified two common AAV epitopes: one on the 3-fold protrusions and one on the 2/5-fold wall. These epitopes coincide with regions with the highest sequence and structure diversity between AAV serotypes and correspond to regions determining receptor recognition and transduction phenotypes. Significantly, these locations overlap the two dominant epitopes reported for autonomous parvoviruses. Thus, rather than the amino acid sequence alone, the antigenic sites of parvoviruses appear to be dictated by structural features evolved to enable specific infectious functions Since our first publication in 1998 on the use of gene therapy to treat radiation induced xerostomia, the sections has worked to test the safety and efficacy of this approach in animal models in anticipation of initiating a phase 1 clinical trial. In preparation for testing the safety of using serotype 2 recombinant adeno-associated vector, encoding Aquaporin-1 to treat radiation-induced salivary gland damage in a phase 1 clinical trial, we conducted a 13 week GLP biodistribution and toxicology study using Balb/c mice (Momot et al 2014). To best assess the safety of rAAV2hAQP1 as well as resemble clinical delivery, vector or saline was delivered to the right parotid gland of mice via retroductal cannulation. Long-term distribution of vector appeared to be localized to the site of cannulation as well as the right and left draining submandibular lymph nodes at levels >50 copies/μg in some animals. An expected dose-related increase in neutralizing antibodies was detected by day 29. Overall, animals appeared to thrive, with no differences in mean body weight, food or water consumption between groups. There were no significant adverse effects due to treatment noted by clinical chemistry and pathology evaluations. Hematology assessment of serum demonstrated very limited changes to the white blood cell, segmented neutrophils, and hematocrit levels and were concluded to not be vector-associated. Indicators for liver, kidney, cardiac functions and general tissue damage showed no changes due to treatment. All of these indicators suggest the treatment is clinically safe. In summary, the future directions for the AAV Biology Section will be to continue examination and development of gene transfer vectors for use in treating disease as well as refine our tools for studying interactions necessary for cellular transduction.
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