Mucosal immunization with recombinant adenoviral vectors expressing murine gammaherpesvirus-68 genes M2 and M3 can reduce latent viral load

Gammaherpesviruses establish life-long latent infections in their hosts. If the host becomes immunosuppressed, these viruses may reactivate and cause severe disease, and even in immunocompetent individuals the gammaherpesviruses are presumed to have an oncogenic potential. Murine gammaherpesvirus-68 (MHV-68) is a member of the Gammaherpesvirinae subfamily and represents a useful murine model for this category of infections, in which new vaccination strategies may initially be evaluated. Two attenuated variants of MHV-68 have successfully been used as vaccines, but the oncogenic potential of the gammaherpesvirinae speaks against using a similar approach in humans. DNA immunization with plasmids encoding the MHV-68 genes M2 or M3 caused a reduction in either acute or early latent viral load, respectively, but neither immunization had an effect at times later than 14 days post-infection. Adenovirus-based vaccines are substantially more immunogenic than DNA vaccines and can be applied to induce mucosal immunity. Here we show that a significant reduction of the late viral load in the spleens, at 60 days post-infection, was achieved when immunizing mice both intranasally and subcutaneously with adenoviral vectors encoding both M2 and M3. Additionally we show that M3 immunization prevented the usual development of virus-induced splenomegaly at 2-3 weeks post-infection. This is the first time that immunization with a non-replicating vaccine has lead to a significantly reduced viral load at time points beyond 14 days post-infection, and thus demonstrates that a non-replicating vaccine may successfully be employed to reduce the viral burden during chronic gammaherpesvirus infection.