Pathways to Antigen Expression after Oral Delivery of an Adenovirus-Based Vaccine

Recombinant adenoviruses (rAd) represent an appealing platform for the development of orally delivered vaccines. Nevertheless, the humoral and cell-mediated immune responses elicited by rAd upon oral delivery are currently unsatisfactory. To conceive strategies to optimize their administration by the oral route, a better understanding of the fate of rAd in the digestive tract is a prerequisite. In order to characterize the pathways by which the vector crosses the intestinal epithelium and is captured by sentinel cells, a fluorescent-labelled vector was introduced into ligated intestinal loops of mice. Confocal microscopy revealed that the vector preferentially adheres to M cells in Peyer’s patches, and appears to cross the epithelium by transcytosis before being taken up by cells expressing CD11c. To evaluate transgene expression, quantitative RT-PCR was performed in the intestine and in peripheral tissues after intragastric delivery of vector in mice, and revealed that antigen-encoding transcripts were largely confined to the intestine. Finally, in order to provide a global vision of transgene expression in the intestine, whole body bioluminescent imaging after intragastric administration of a rAd encoding firefly luciferase is underway in mice. Identification of the bottlenecks in expression of transgene-encoded antigen should instruct optimisation of rAd-based vaccines for oral delivery.