Due to their ability to activate the immune system, replication-defective Adenoviruses (Ad) are potential vaccine vectors for several pathogens. The proinflammatory response to Ad contributes to the response to vaccine antigens. We found that reactive oxygen species (ROS) are an important signal in the proinflammatory response to Ad. We identified that serotype 5 adenovirus (Ad5) elicits ROS by inducing mitochondrial membrane damage, a process that is dependent on endosomal membrane rupture and Cathepsin release. This mitochondrial dysfunction contributes to NLRP3 inflammasome- and NFκB-dependent innate immune activation. The ROS-dependent inflammatory response likely contributes to the adaptive immune response by supporting DC maturation and activation, lymphocyte recruitment, and cytokine production influencing B and T cell proliferation and differentiation.
We next exploited these immunostimulatory properties of Ad in vaccines to prevent transmission of malaria by Plasmodium falciparum. When combined with vaccines preventing infection, transmission-blocking vaccines (TBVs) could limit the spread of malaria. Our study explores how novel, Ad5-based TBVs enhance the humoral immune response to Pfs25, a vaccine antigen. Antibodies against Pfs25 can block transmission. While studies have designed Pfs25 protein-based vaccines with adjuvants, these vaccines do not efficiently elicit transmission-blocking antibodies. We hypothesized Ad5 would serve as a vaccine delivery platform and adjuvant for Pfs25 to generate a robust and prolonged Pfs25-specific antibody response. We found that Ad5-pfs25, which expresses pfs25, generated a robust Pfs25-specific antibody response characterized by a higher titer, higher relative affinity, and broader IgG subclass switching as compared to alum-adjuvanted Pfs25 protein vaccination. Ad5-specific T cell activation correlated with the observed increase in Pfs25-specific antibody titer following Ad5-pfs25 vaccination. Ad-based vectors enhance the humoral immune response to target antigens and likely do so by enhancing T cell activation.
To further improve the Pfs25-specific antibody response we combined Ad5-pfs25 with Ad vectors displaying transmission-blocking Pfs25 epitopes within the viral capsid. These prime-boost vaccinations with Ad5-Pfs25 followed by capsid-displayed Pfs25 Ad vectors increase the Pfs25-specific antibody titer as compared to homologous prime-boost with Pfs25-alum. Ad-vectored prime-boosts also block transmission to the mosquito in vitro. In conclusion, we generated novel, Ad-based TBVs that improve the Pfs25-specific antibody response and block transmission
