Therapeutic level of functional human alpha 1 antitrypsin (hAAT) secreted from murine muscle transduced by adeno‐associated virus (rAAV1) vector

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Abstract
Alpha 1 antitrypsin (AAT) is a serine proteinase inhibitor (serpin). One well‐known function of this protein is to inactivate neutrophil elastase and other neutrophil‐derived proteinases, and prevent the destruction of pulmonary extracellular matrix. Deficiency of AAT can cause emphysema due to degradation of interstitial elastin by elastase. The majority of circulating AAT is secreted from the liver. Muscle‐directed gene therapy using recombinant adeno‐associated virus 2 (rAAV2) vectors has been tested to increase the serum levels of AAT. However, inefficient transduction of rAAV2 vector makes it difficult to reach therapeutic levels of AAT in clinical trials and it remains unclear as to whether muscle‐secreted AAT is functional. In the present study, we evaluated five serotypes (1, 2, 3, 4, and 5) of rAAV vectors for transduction efficiency in mouse muscle. Results from these studies showed that rAAV1 is the most efficient vector among these serotypes and mediated at least 100‐fold higher levels of AAT secretion than the rAAV2 vector. Western blot analysis showed that this murine muscle‐secreted human AAT (hAAT) formed a complex with human neutrophil elastase in a dose‐dependent manner. An anti‐elastase activity assay showed that murine muscle‐secreted hAAT inhibited elastase with equal capacity as hAAT purified from plasma. These results provide strong support for the functionality of AAT in ongoing clinical studies of muscle‐directed AAT gene therapy. Copyright © 2006 John Wiley & Sons, Ltd.

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