No abstract

Adenoviral gene transfer has potential use to attenuate the immunogenicity of hepatic allografts. However, the clinical application of adenoviral gene therapy is currently impeded by the potent host immune response to the virus that limits the duration of its effects. In these studies, we identify the cellular and humoral immune responses to recombinant adenovirus in the liver of mice and define the immunologic barriers to the successful application of this technology to transplantation. The immunobiology of recombinant adenovirus was studied in mouse liver using vectors containing the lacZ and alkaline phosphatase marker genes. The duration of transgene expression was studied in various immunodeficient mice to determine the mechanism of viral clearance. Adoptive transfer of serum to B lymphocyte deficient mice and neutralizing antibody assays were used to define the antiviral humoral response. Hepatic adenoviral transgene expression was prolonged in animals deficient in CD4+ or CD8+ T cells indicating their importance in viral clearance. Unexpectedly, mice lacking B lymphocytes also had delayed elimination of virus suggesting that B cells play a role in the primary immune response. Effective repeat gene transfer was blocked by adenoviral-specific neutralizing antibody. Therefore, a T lymphocyte response results in viral elimination after a primary intravenous inoculation of recombinant adenovirus and a potent humoral response inhibits effective repeat adenoviral gene transfer. The immunogenicity of the vector must be overcome for adenoviral gene therapy to have therapeutic application for hepatic transplantation.

The major barrier to the clinical application of adenovirus gene therapy for diseases that require stable transgene expression is the immunogenicity of recombinant adenovirus, which ordinarily limits the duration of its effects to a period of about 2 weeks. We postulated that tolerance to adenovirus could be induced and transgene expression could be prolonged if T lymphocytes underwent thymic selection in the presence of adenovirus antigens. Mice were inoculated in the thymus with a recombinant adenovirus containing the lacZ marker gene during the neonatal period at a time before T-cell maturation had occurred. When the virus was administered intravenously to these mice in adulthood, they were found to have an impaired adenovirusspecific cytotoxic T-lymphocyte response which allowed prolonged hepatic lacZ expression, for up to 260 days. The ability to achieve unresponsiveness to a recombinant adenovirus after inoculation of the thymus in neonates extends the paradigm of intrathymic tolerance induction. Furthermore, this model will enable the study of stable adenovirus transgene expression in vivo without the use of immunosuppression and ultimately may have clinical utility.