Repeated intratracheal instillations of nonreplicating adenovirus 2 vector attenuate CTL responses and IFN-gamma production.

The proposed usage of replication-deficient adenovirus (Ad) vectors for corrective gene therapy or for mucosal immunization has been limited in part by the host reactivity to the Ad vector, thus limiting repeated Ad instillations. We have recently shown that the reactivity to the Ad vector is in large part due to increased CD4+ Th1 and Th2 responses as well as elevated IgG and mucosal IgA responses. It has been recently proposed that the diminution of transgene expression in respiratory epithelia was due to increased CTL reactivity to expressed Ad proteins. Herein, we report that repeated intratracheal delivery of a second generation Ad2 vector into mice results in no detectable CTL activity in freshly isolated lymphoid cells from lungs, lower respiratory lymph nodes, or spleens or after in vitro restimulation. In contrast, a single dose of Ad2 vector did elicit a robust CTL response. This attenuation of CTL activity was long lived and was not affected by macrophage depletion or due to a reduction in CD4+ or CD8+ T cells. Examination of cytokine production via MHC class I or class II restimulation by lymphoid cells from three intratracheally treated mice showed an attenuation in the production of IFN-gamma by as much as 110-fold. This reduction in IFN-gamma could not be attributed to increased IL-4 or IL-10 production. Thus, this study shows that the CTL response to Ad vectors is attenuated upon repeated administration.