Alpha-defensin 5 differentially modulates adenovirus vaccine vectors from different serotypes in vivo

Abstract

Adenoviral vectors have shown significant promise as vaccine delivery vectors due to their ability to elicit both innate and adaptive immune responses. α-defensins are effector molecules of the innate immune response and have been shown to modulate natural infection with adenoviruses, but the majority of α-defensin-adenovirus interactions studied to date have only been analyzed in vitro. In this study, we evaluated the role of α-defensin 5 (HD5) in modulating adenovirus vaccine immunogenicity using various serotype adenovirus vectors in mice. We screened a panel of human adenoviruses including Ad5 (species C), Ad26 (species D), Ad35 (species B), Ad48 (species D) and a chimeric Ad5HVR48 for HD5 sensitivity. HD5 inhibited transgene expression from Ad5 and Ad35 but augmented transgene expression from Ad26, Ad48, and Ad5HVR48. HD5 similarly suppressed antigen-specific IgG and CD8+ T cell responses elicited by Ad5 vectors in mice, but augmented IgG and CD8+ T cell responses and innate cytokine responses elicited by Ad26 vectors in mice. Moreover, HD5 suppressed the protective efficacy of Ad5 vectors but enhanced the protective efficacy of Ad26 vectors expressing SIINFEKL against a surrogate Listeria-OVA challenge in mice. These data demonstrate that HD5 differentially modulates adenovirus vaccine delivery vectors in a species-specific manner in vivo.

Defensin-driven viral evolution

“…However, we were unable to account for the extensive HD5 binding to the hexons of HAdV-5 in our cryoEM studies [ 9 ]. Our new results indicate that the HVR1 loop of hexon functions in cooperation with the vertex proteins as a previously unidentified determinant of HD5-mediated neutralization, which is further supported by the recent demonstration of neutralization and enhancement of HAdV-based vectors by HD5 in a mouse model [ 37 ]. If either HVR1 or both vertex determinants (four residues near the N-terminus of fiber and the C-terminal half of PB) are derived from a resistant serotype, then neutralization does not occur.…”

Defensin-driven viral evolution

“…A similar mechanism has been shown in shigella, another gastrointestinal pathogen that appropriates HD5 to facilitate infection [19, 20]. In addition, only viruses containing hexons in which all of the HVRs are from one serotype are enhanced, including a recently published HAdV-5 chimera containing all of the HVRs of HAdV-48 hexon [32]. This suggests that homotypic interactions involving hexon HVRs mediate enhancement.…”

“…Importantly, all three HAdV capsid proteins play a role in neutralization, but hexon rather than PB or fiber determines enhancement. Thus, we have extensively revised the prior model of HD5-mediated neutralization and established the feasibility of this process to shape viral evolution in vivo , which is further supported by the recent demonstration of neutralization and enhancement of HAdV-based vectors by HD5 in a mouse model [32].…”

Cytokine Responses to Adenovirus and Adenovirus Vectors

“…Upon searching for the natural mechanisms that may neutralize adenoviruses, it was found that human alpha defensin 5 (HD5), a small antimicrobial peptide, has potent inhibitory activity against species C adenovirus HAdV-C5 [ 93 ]. However, HD5 does not inhibit adenoviruses of species D and F, but rather augments the virus infection in vitro and increases adaptive responses to the virus-encoded transgene antigens in vivo [ 94 ]. Furthermore, pre-treatment of mice with HD5 prior to HAdV-D26 injection resulted in a higher cytokine response than to the virus alone.…”

“…Mechanistically, more robust cytokine production in response to the virus–HD5 complexes is thought to be due to more efficient virus entry into dendritic cells in the presence of HD5. It is plausible that HD5 functions as a polycation, and upon binding to adenovirus, it shields the negatively charged amino acids present at the surface of the virion, thus reducing repulsion between the negatively charged virus surface and plasma membrane, leading to a more efficient infection of dendritic cells [ 94 ].…”