No abstract

Recombinant adeno-associated (AAV) viruses have unique properties, which make them ideal vectors for gene transfer targeting the myocardium. Numerous serotypes of AAV have been identified with variable tropisms towards cardiac tissue. In the present study, we investigated the time course of expression of eight different AAV serotypes in rat myocardium and the nature of the immunity against these serotypes. We first assessed whether neutralizing antibodies (NAb) were present for any of the serotype in the rats. We injected 100 ml of each AAV 1-8 serotype (10 12 DNAse resistant particles/ml), encoding LacZ gene, into the apical wall of rat myocardium. At 1, 4, 12 and 24 weeks after gene delivery, the animals were killed and b-galactosidase (b-gal) activity was assessed by luminometry. Additionally, LacZ genomic copies and AAV capsids copies were measured through standard polymerase chain reaction analysis and cryosections from the area of viral injection were stained for X-gal detection at the same time points. No NAbs were detected against any of AAV serotypes. At all the time points studied, AAV1, 6 and 8 demonstrated the highest efficiency in transducing rat hearts in vivo. Parallel to the results with b-gal activity, the highest levels LacZ and AAV DNA genomic copies were with AAV1, 6 and 8. The positive X-gal staining depicted by these serotypes confirmed these results. These results indicate that among the various AAV serotypes, AAV1, 6 and 8 have differential tropism for the heart unaffected by pre-existing NAb in the rat. Although AAV 1 and 6 vectors induced rapid and robust expression and reach a plateau at 4 weeks, AAV 8 continued increasing until the end of the study. AAV 2, 5 and 7 vectors were slower to induce expression of the reporter gene, but did reach levels of expression comparable to AAV1 and AAV6 vectors after 3 months. Gene Therapy (2007) 14, 989-997.

Expression from the human parvovirus B 19p6 promoter fused to the firefly luciferase (' Luc') reporter gene was evaluated in a non-erythroid human nasopharyngeal carcinoma cell line, KB, and a human megakaryocytic leukaemia cell line, MB-02, known to become permissive for B19 replication following erythroid-differentiation. The B19p6-Luc construct was introduced into KB and MB-02 cells, both in undifferentiated and differentiated states, either via DNA-mediated transfection, or via infection with recombinant adeno-associated virus 2 (AAV), a non-pathogenic human parvovirus known to possess a broad host-range. Although Luc activity was readily detected in KB cells following transfection of the B 19p6-Luc plasmid DNA, no expression from the B 19p6 promoter was observed following infection with recombinant virus. In addition, transfection of the reporter plasmid resulted in high-level expression of Luc in differentiated but not in undifferentiated MB-02 cells. However, no Luc activity was detected, even in differentiated MB-02 cells, following infection with recombinant virus. Further studies with an additional recombinant as well as wild-type (wt) AAV revealed that MB-02 cells were non-permissive for AAV infection. A second human megakaryocytic leukaemia cell line, M07e, was likewise resistant to infection by recombinant as well as wt AAV. Taken together, these studies identify the first human cell type that cannot be infected by AAV.They indicate that expression from the B 19p6 promoter, in the context of an AAV genome, is restricted to primary human haematopoietic cells, perhaps because parvoviral DNA replication and transcription are intrinsically coupled.

StlmmlryRecombinant adeno-assodated virus 2 (AAV) virions were constructed containing a gene for resistance to neomycin (neoa), under the control of either the herpesvirus thymidine kinase (TK) gene promoter (vTK-Neo), or the human parvovirus B19 p6 promoter (vB19-Neo), as well as those containing an upstream erythroid cell-specific enhancer (HS-2) from the locus control region of the human fl-globin gene cluster (vHS2-TK-Neo; vHS2-B19-Neo). These recombinant virions were used to infect either low density or highly enriched populations of CD34 + cells isolated from human umbilical cord blood. In donogenic assays initiated with cells infected with the different recombinant AAV-Neo virions, equivalent high frequency transduction of the neo p" gene into slow-cycling multipotential, erythroid, and granulocyte/macrophage (GM) progenitor cells, including those with high proliferative potential, was obtained without prestimulation with growth factors, indicating that these immature and mature hematopoietic progenitor cells were susceptible to infection by the recombinant AAV virions. Successful transduction did not require and was not enhanced by prestimulation of these cell populations with cytokines. The functional activity of the transduced neo gene was evident by the development of resistance to the drug G418, a neomycin analogue. Individual high and low proliferative colony-forming unit (CFU)-GM, burst-forming unit--erythroid, and CFU-granulocyte erythroid macrophage megakaryocyte colonies from mock-infected, or the recombinant virus-infected cultures were subjected to polymerase chain reaction analysis using a neo-specific synthetic oligonucleotide primer pair. A 276-bp DNA fragment that hybridized with a neo-spedfic DNA probe on Southern blots was only detected in those colonies cloned from the recombinant virus-infected calls, indicating stable integration of the transduced neo gene. These studies suggest that parvovirus-based vectors may prove to be a useful alternative to the more commonly used retroviral vectors for high efficiency gene transfer into slow or noncycling primitive hematopoietic progenitor cells, without the need for growth factor stimulation, which could potentially lead to differentiation of these calls before transplantation.

The adeno-associated virus 2 (AAV)-based vector system has been suggested for its potential use in human gene therapy because the wild-type (wt) AAV genome appears to integrate into the human chromosomal DNA in a site-specific manner. We systematically investigated the integration patterns of the recombinant AAV genomes lacking one or both the viral coding sequences. Four recombinant AAV genomes were constructed containing the genes for resistance to tetracycline (TcR) and the herpesvirus thymidine kinase (TK) promoter-driven gene for resistance to neomycin (neoR; vTc.Neo), the genes for resistance to ampicillin (ApR) and TK-neoR (vAp.Neo), the genes for AAV replication (rep) genes and TK-neoR (vRep.Neo), and the AAV capsid (cap) genes and TK-neoR (vCap.Neo). The integration pattern of each of the recombinant AAV genomes in individual clonal isolates of the human nasopharyngeal carcinoma cell line (KB) analyzed on Southern blots using a neo-specific DNA probe was distinctly different. In addition, in none of the clones examined was the proviral genome covalently linked to the previously described AAV right-junction (Rt.Jn.) human chromosomal DNA fragment, the putative specific-site of integration for the wt AAV genome. Furthermore, whereas a 276-bp DNA fragment could be readily amplified from each of these clones, using a neo-specific primer-pair by polymerase chain reaction (PCR), no amplified DNA product was obtained using the neo- and the Rt.Jn. primer-pair under identical conditions. Fluorescence in situ hybridization (FISH) analyses further revealed the lack of integration of the recombinant AAV into human chromosome 19, even in the presence of a functional rep gene as determined by rescue of the recombinant AAV genome in the presence of adenovirus. These data suggest that the recombinant AAV genomes integrate at sites that are different from that characterized for the wt AAV genome. These studies may have implications in the development of the AAV-based vector system for its potential use in human gene therapy.