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J. Virol., Oct 1997, 7361-7371, Vol 71, No. 10
DM Kube, S Ponnazhagan and A Srivastava
The adeno-associated virus type 2 (AAV) arrests the growth of primary human
fibroblasts in vitro at high particle-to-cell ratios. To test the role of
AAV gene expression in the observed growth inhibition, primary human cells
were infected, under identical conditions, with wild-type (wt) AAV or with
recombinant AAV that lacked all viral promoters and coding sequences.
Significant, dose-dependent growth inhibition of primary human cells was
observed with both wt and recombinant AAV at particle-to-cell ratios equal
to or exceeding 10(4). In contrast, neither virus affected the growth of
immortalized human cells even at a 10-fold-higher particle-to-cell ratio.
AAV-induced growth arrest could be overcome by reculturing cells after
treatment with trypsin. Even after reculturing, cells still harbored the
proviral AAV genome. Thus, neither integration nor expression of the AAV
genome appears to be required for the virus-induced growth-inhibitory
effect on primary human cells. The growth-inhibitory effect of AAV was
hypothesized to be mediated by virion-associated AAV Rep proteins, since
these proteins have been reported to inhibit cellular DNA synthesis. Rep
proteins tightly associated with wt as well as recombinant AAV could be
detected on Western blots. Coinfection by adenovirus was necessary and
sufficient for ample replication of recombinant AAV genomes lacking the rep
gene. Although wt AAV-like particles arose during production of the
recombinant AAV stocks, their low-titer levels were insufficient to cause
the observed growth inhibition. AAV rep gene expression from these
contaminating particles was not required for replication of the recombinant
AAV genomes, which could be detected even in the absence of de novo Rep
protein synthesis. Exposure of recombinant AAV to anti-AAV Rep protein
antibodies did not abrogate viral infectivity. These results suggest that
biologically active Rep proteins are encapsidated in mature progeny AAV
particles. AAV Rep protein-mediated growth inhibition of primary human
cells has implications in the use of AAV- based vectors in human gene
therapy.
Copyright © 1997, American Society for Microbiology
Encapsidation of adeno-associated virus type 2 Rep proteins in wild- type and recombinant progeny virions: Rep-mediated growth inhibition of primary human cells
Department of Microbiology and Immunology, Walther Oncology Center, Indiana University School of Medicine, and Walther Cancer Institute, Indianapolis 46202, USA.
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