Adenovirus hexon protein is a potent adjuvant for activation of a cellularimmune response

The capacity of recombinant adenoviruses (rAd) to induce immunization again st their transgene products has been well documented. In the present study, we evaluated the vaccinal adjuvant role of rAd independently of its vector function. BALB/c mice received one subcutaneous injection of a mixture of six lipopeptides (LP6) used as a model immunogen, along with AdE1 degrees ( 10(9) particles), a first-generation rAd empty vector. Although coinjected with a suboptimal dose of lipopeptides, AdE1 degrees significantly improved the effectiveness of the vaccination, even in the absence of booster immun ization. In contrast to mice that received LP6 alone or LP6 plus a mock adj uvant, mice injected with AdE1 degrees plus LP6 developed both a polyspecif ic T-helper type I response and an effector CD8 T-cell response specific to at least two class I-restricted epitopes. The helper response was still ob served when immunization was performed using LP6 plus a mixture of soluble capsid components released from detergent-disrupted virions. When mice were immunized with LP6 and each individual capsid component, i.e., hexon, pent on base, or fiber, the results obtained suggested that hexon protein was re sponsible for the adjuvant effect exerted by disrupted Ad particles on the helper response to the immunogen. Our results thus have some important impl ications not only in vaccinology but also for gene therapy using rAd vector s.