Study of Human Bocavirus Gene Expression for Development of a Parvoviral Vector



 DESCRIPTION (provided by applicant): Human bocavirus 1 (HBoV1) is a small DNA virus of the family Parvoviridae, and its natural host tissue is the lung airway tract. In an effort to harnss the tropism of this virus for the development of gene therapies and vaccines to combat airway diseases (tools that are in high demand), we have cloned a full-length HBoV1 genome, established a reverse genetics system for introducing the virus into cells, and demonstrated that it can productively infect polarized primary human airway epithelium air-liquid interface (HAE-ALI) cultures. The HBoV1 capsid shares key features of the T=1 parvovirus icosahedral capsid of adeno-associated virus (AAV), and we have discovered that this makes it possible to efficiently package the recombinant AAV2 (rAAV2) genome into HBoV1 capsid via cross-genus pseudopackaging. Taking advantage of this finding, we developed a novel parvoviral cross-genus hybrid vector, rAAV2/HBoV1, to facilitate gene transfer to the human airway. This vector combines the high apical tropism of the HBoV1 capsid with the safety and persistence of the rAAV2 genome in the human airway epithelium, and expands the capacity of the rAAV genome by 20%. We have demonstrated two key advantages of this vector. Firstly, it transduces HAE-ALI from the apical surface more efficiently than rAAV vectors do. Secondly, it is capable of delivering a 5.5-kb oversized rAAV2 genome carrying the cystic fibrosis transmembrane conductance regulator (CFTR) open reading frame behind a strong promoter, and of correcting the CFTR-specific deficiency in chloride transport that characterizes HAE derived from cystic fibrosis (CF) patients. Thus, the rAAV2/HBoV1 hybrid vector is an ideal vector for CF gene therapy. Our preliminary analyses of the first-generation HBoV1 packaging helper in 293 cells have revealed a novel gene expression profile for the genes of this virus. Increasing the capsid expression yielded the second- generation HBoV1 helper, with which the rAAV2/HBoV1 vector production has been increased by 8-fold, approaching a yield of ~50-80% that of rAAV2/2. These findings will guide us to further understand the process of parvovirus cross-genus pseudopackaging in order to produce the third-generation helper and production systems that enable significantly improved vector yield. Our long-term goal is to utilize the novel rAAV2/HBoV1 vector for gene transfer to the human airway, in particular, for use in CF gene therapy. The proposed study is designed to build on these findings and expertise by: i) determining the roles of HBoV1 proteins in parvovirus cross-genus pseudopackaging; ii) optimizing an HBoV1 packaging helper construct for rAAV2/HBoV1 vector production in 293 cells (for pre-clinical applications); and iii) establishing an efficient baculovirus/insect cell sstem for high-yield and large-scale rAAV2/HBoV1 vector production in Sf9 cells (for preclinical study with animal modes and clinical applications).