TOXICOLOGICAL COMPARISON OF E2A-DELETED AND FIRST-GENERATION ADENOVIRAL VECTORS EXPRESSING ALPHA(1)-ANTITRYPSIN AFTER SYSTEMIC DELIVERY

Second-generation adenoviral vectors, mutated in E2a, have been propos ed to decrease host immune responses against transduced cells, reduce toxicity, and increase duration of expression as compared with first-g eneration vectors deleted only in El. To test these hypotheses further , we have developed an E2a-deleted adenoviral vector expressing human alpha(1)-antitrypsin (hAAT). Toxicity of first-generation and E2a-dele ted vectors, as determined by hematological indices, liver function te sts, and histological analyses, was evaluated in C3H mice for 21 days after vector administration at increasing doses starting at 1 x 10(12) particles/kg. Both vectors induced dose-dependent abnormalities inclu ding transient thrombocytopenia, elevated ALT levels in serum, and inc reased hepatocyte proliferation followed by inflammation and then hype rtrophy. Differences in the ratio of particles to plaque-forming units among vector preparations led to differences in hAAT expression at si milar particle doses. There were no differences in toxicity between th e two vectors when measured at matching levels of hAAT expression. How ever, the E2a-deleted vector was demonstrated to have slightly reduced hepatocyte toxicity at an intermediate particle dose. This suggests t hat hepatocyte toxicity is related primarily to viral entry and expres sion, rather than to the presence of noninfectious particles, and impl ies that vectors with complete elimination of viral gene expression, s uch as vectors with all viral coding sequences deleted, are likely to have substantial advantages in terms of safety and toxicity.