Adenoviral Gene Delivery Elicits Distinct Pulmonary-Associated T Helper Cell Responses to the Vector and to Its Transgene

Replication-deficient adenovirus (Ad) vectors are effective to specifically target the respiratory epithelium for either corrective gene therapy such as cystic fibrosis or for mucosal immunization. As a consequence of transducing the lower respiratory tract with an E1/E3 deleted Ad5 vector, host responses have been characterized by the duration of transgene expression and by the induction of CTL responses. However, limited emphasis has been devoted to understanding the contribution of CD4⁺ T cell responses to the Ad vector. Both CD4⁺ and CD8⁺ T cells migrate into the lung following sequential intratracheal Ad5 transgene instillations. Isolated CD3⁺ T lymphocytes from the lungs were predominantly of the Th2 type, and after cell sorting, the IL-4-producing T cells were largely CD4⁺, while IFN-γ expression was associated with both CD4⁺ and CD8⁺ T cells. Ab responses to the Ad5 vector and to the expressed transgene β-galactosidase (βgal) revealed elevated bronchial and serum IgA and IgG Abs with low neutralization titers. Analysis of serum IgG subclass responses showed IgG1 and IgG2b with lower IgG2a Abs to Ad5 and IgG2a and IgG2b Ab responses to βgal. Ad5-specifc CD4⁺ T cells produced both Th1 (IFN-γ and IL-2)- and Th2 (IL-4, IL-5, IL-6)-type cytokines, while βgal-specific CD4⁺ T cells secreted IFN-γ and IL-6. This study provides direct evidence for the concomitant induction of Th2- with Th1-type responses in both the pulmonary systemic and mucosal immune compartments to the Ad5 vector as well as a Th1-dominant response to the transgene.