Firewalls Prevent Systemic Dissemination of Vectors Derived from Human Adenovirus Type 5 and Suppress Production of Transgene-Encoded Antigen in a Murine Model of Oral Vaccination

Abstract

To define the bottlenecks that restrict antigen expression after oral administration of viral-vectored vaccines, we tracked vectors derived from the human adenovirus type 5 at whole body, tissue, and cellular scales throughout the digestive tract in a murine model of oral delivery. After intragastric administration of vectors encoding firefly luciferase or a model antigen, detectable levels of transgene-encoded protein or mRNA were confined to the intestine, and restricted to delimited anatomical zones. Expression of luciferase in the form of multiple small bioluminescent foci in the distal ileum, cecum, and proximal colon suggested multiple crossing points. Many foci were unassociated with visible Peyer's patches, implying that transduced cells lay in proximity to villous rather than follicle-associated epithelium, as supported by detection of transgene-encoded antigen in villous epithelial cells. Transgene-encoded mRNA but not protein was readily detected in Peyer's patches, suggesting that post-transcriptional regulation of viral gene expression might limit expression of transgene-encoded antigen in this tissue. To characterize the pathways by which the vector crossed the intestinal epithelium and encountered sentinel cells, a fluorescent-labeled vector was administered to mice by the intragastric route or inoculated into ligated intestinal loops comprising a Peyer's patch. The vector adhered selectively to microfold cells in the follicle-associated epithelium, and, after translocation to the subepithelial dome region, was captured by phagocytes that expressed CD11c and lysozyme. In conclusion, although a large number of crossing events took place throughout the intestine within and without Peyer's patches, multiple firewalls prevented systemic dissemination of vector and suppressed production of transgene-encoded protein in Peyer's patches.

Dendritic cell functions in the inductive and effector sites of intestinal immunity

“…Indeed, both Salmonella Typhimurium and Listeria monocytogenes are mainly taken up by LysoDCs and/or subepithelial macrophages but not by cDC2s 139,140 . In addition, other particulate materials have been shown to be selectively engulfed by LysoDCs and subepithelial macrophages but not cDC2s, including microspheres, adenoviral vectors, IgA-opsonized antigens, M cellreleased subepithelial vesicles, and dying M cells 13,139,[141][142][143] . All differentiation states of LysoDCs are equally able to internalize particulate antigens in vitro but mature LysoDCs are the most susceptible to encounter antigens in vivo due to their proximity to the epithelium 11 .…”

Viral vector-based vaccines against SARS-CoV-2

“…Oral tablets have been applied for vaccine development of an adenovirus vector expressing the full-length SARS-CoV-2 S and N proteins in combination with a Toll-like receptor-3 (TLR-3) agonist adjuvant [67]. Immunization of mice elicited strong neutralizing antibody responses, although in this case intranasal administration was preferred as the transgene expression in mice can be suppressed in the intestinal environment after oral administration [68]. However, the oral vaccine delivery approach has been evaluated in a phase I clinical trial for the VXA-COV2-1 vaccine candidate to assess safety and immunogenicity [69].…”

Pre-clinical studies of a recombinant adenoviral mucosal vaccine to prevent SARS-CoV-2 infection

“…The primary objective of the initial mouse immunogenicity studies was to determine which of the rAd vectors induced significant antibody responses to S, and to obtain those results rapidly enough to provide a GMP seed in time for manufacturing. We and others 17 have observed that transgene expression by vaccine vectors orally administered to mice can be suppressed in their intestinal environment, so immunogenicity was assessed following intranasal (i.n.) immunization.…”