CIRCUMVENTION OF ANTI-ADENOVIRUS NEUTRALIZING IMMUNITY BY ADMINISTRATION OF AN ADENOVIRAL VECTOR OF AN ALTERNATE SEROTYPE

Effective gene transfer and expression following repetitive administra tion of adenoviral (Ad) vectors in experimental animals is limited by anti-Ad neutralizing antibodies. Knowing that anti-Ad humoral immunity is serotype-specific, we hypothesized that anti-Ad neutralizing immun ity could be circumvented using Ad vectors of different serotypes (Ad2 , Ad5) within the same subgroup (C) to transfer and express beta-glucu ronidase (beta glu) in the lung. Sprague-Dawley rats received an intra tracheal administration of either Ad2 beta glu or Ad5 beta glu, and, 1 4 days later, repeat administration of either the same vector or a vec tor of a different serotype. Analysis of serum and bronchoalveolar lav age fluid following initial vector administration demonstrated systemi c and local serotype-specific neutralizing antibodies. For both the Ad 2 and Ad5 vectors, beta glu expression 24 hr following the second admi nistration of the same serotype was <30% of that of naive animals. In contrast, beta glu expression 24 hr following second administration of a different serotype Ad vector was similar to expression at 24 hr of naive animals receiving a single administration (Ad5 beta glu followed by Ad2 beta glu, as well as Ad2 beta glu followed by Ad5 beta glu; p > 0.2 both comparisons). Although the alternative serotype bypassed an ti-Ad neutralizing immunity, persistence of expression was reduced com pared to that following administration to naive animals. Compatible wi th this observation, systemic administration of the same vectors to C5 7B1/6 mice demonstrated induction of cytotoxic T lymphocytes directed against the beta glu transgene, as well as products of the Ad genome. Interestingly, intratracheal administration of vectors with different serotypes and different transgenes to rats resulted in longer expressi on (but still not normalized) compared to that achieved with vectors o f different serotypes but the same transgene. These observations demon strate that alternate use of Ad vectors from different serotypes withi n the same subgroup can circumvent anti-Ad humoral immunity to permit effective gene transfer after repeat administration, although the chro nicity of expression is limited, likely by cellular immune processes d irected against both the transgene and viral gene products expressed b y the vector.