Prevalence of neutralizing antibodies against adeno-associated virus (AAV) types 2, 5, and 6 in cystic fibrosis and normal populations: Implications for gene therapy using AAV vectors

Adeno-associated virus ( AAV) vectors are promising candidates for gene therapy directed to the lungs, in particular for treatment of cystic fibrosis (CF). In animal models of lung gene transfer, neutralizing antibodies in serum made in response to vector exposure have been associated with a partial to complete block to repeat transduction by vectors with the same capsid type, thus transduction by AAV vectors might be inefficient in humans previously exposed to the same AAV type. AAV type 2 (AAV2) has been used in clinical trials of lung gene transfer, but AAV5 and AAV6 have been shown to mediate more efficient transduction in rodent lungs and in cultured human airway epithelia compared with that of AAV2. Here we have measured neutralizing antibodies against AAV type 2, 5, and 6 vectors in serum from children and adults with CF, and from normal adults. About 30% of adults were seropositive for AAV2, 20-30% were seropositive for AAV6, and 10-20% were seropositive for AAV5. CF children were seropositive for AAV type 2, 5, or 6 at rates of 4-15%. All individuals seropositive for AAV6 were also seropositive for AAV2, and the AAV6 titer was low compared with the AAV2 titer. AAV5-positive sera were lower both in titers and rates than those seen for AAV6. The results indicate that AAV type 2, 5 or 6 exposure is low in CF and control populations and even lower in CF children.