Replicating Single-Cycle Adenovirus Vectors Generate Amplified Influenza Vaccine Responses

Abstract

Head-to-head comparisons of conventional influenza vaccines with adenovirus (Ad) gene-based vaccines demonstrated that these viral vectors can mediate more potent protection against influenza virus infection in animal models. In most cases, Ad vaccines are engineered to be replication-defective (RD-Ad) vectors. In contrast, replication-competent Ad (RC-Ad) vaccines are markedly more potent but risk causing adenovirus diseases in vaccine recipients and health care workers. To harness antigen gene replication but avoid production of infectious virions, we developed “single-cycle” adenovirus (SC-Ad) vectors. Previous work demonstrated that SC-Ads amplify transgene expression 100-fold and produce markedly stronger and more persistent immune responses than RD-Ad vectors in Syrian hamsters and rhesus macaques. To test them as potential vaccines, we engineered RD and SC versions of adenovirus serotype 6 (Ad6) to express the hemagglutinin (HA) gene from influenza A/PR/8/34 virus. We show here that it takes approximately 33 times less SC-Ad6 than RD-Ad6 to produce equal amounts of HA antigen in vitro. SC-Ad produced markedly higher HA binding and hemagglutination inhibition (HAI) titers than RD-Ad in Syrian hamsters. SC-Ad-vaccinated cotton rats had markedly lower influenza titers than RD-Ad-vaccinated animals after challenge with influenza A/PR/8/34 virus. These data suggest that SC-Ads may be more potent vaccine platforms than conventional RD-Ad vectors and may have utility as “needle-free” mucosal vaccines.IMPORTANCE Most adenovirus vaccines that are being tested are replication-defective adenoviruses (RD-Ads). This work describes testing newer single-cycle adenovirus (SC-Ad) vectors that replicate transgenes to amplify protein production and immune responses. We show that SC-Ads generate markedly more influenza virus hemagglutinin protein and require substantially less vector to generate the same immune responses as RD-Ad vectors. SC-Ads therefore hold promise to be more potent vectors and vaccines than current RD-Ad vectors.

Single-cycle adenovirus vectors in the current vaccine landscape

“…This premise is supported by abundant data from Dr. Marjorie Guroff's group, our lab, and others (15-17, 43-55). For example, when chimpanzees were immunized twice with RD-Ads, this generated no detectable antibodies against HIV (15).…”

“…We see similar effects when comparing replicating Ads vs. RD-Ads in mice, hamsters, cotton rats, and in rhesus macaques (16, 17, 55). …”

“…SC-Ad produces 30 to 300-fold more antigen than RD-Ad (14, 16, 17). This improvement in antigen expression per unit virus by SC-Ad could translate into getting 30-300 times as many vaccine doses out of an SC-Ad GMP production than an RD-Ad production.…”

“…This can be either good or bad. The good is that these progeny viruses can go forth and infect more cells and further amplify antigen production and vaccine effects (15-17). The bad is that unchecked amplification of progeny viruses can actually cause the disease that the virus originally causes (2).…”

“…1). However, these non-replicating vectors do not replicate antigen genes and do not amplify antigen production effects (15-17). The good is that RD vaccines are safe.…”