Optimising a vaccine carrier for delivering cargo antigen to the Peyer’s Patches

Gastrointestinal (GI) infections impact significantly on global health. With the alarming rise in multiple drug-resistant pathogens, attention is turning to oral vaccines. Nevertheless, to date, oral vaccines are licenced for targeting only 4 pathogens namely Rotavirus, Poliovirus, Vibrio cholerae and Salmonella typhi causing typhoid fever. The two main bottlenecks hampering progress in the development of oral vaccines are the need for protection from the harsh environment of the stomach and the lack of delivery systems (carriers) for antigens to cross the epithelium to lymphoid cells. A gut-stable recombinant protein has shown promise as a vaccine carrier, carried by Griffin et al (unpublished data). Two-fold aims of research were to assess new enteric capsules for release in the small intestine and compare two versions of the carrier engineered to deliver mPlum as a fluorescent surrogate antigen easily detectable in gut tissue. Recombinant mPlum was first produced, lyophilised into a dry powder and packed into S100 spray-coated size 9h capsules. The capsules were administered oro-gastrically in the hamster model for live tracking through the GI tract. IVIS imaging showed that the capsule successfully protected mPlum cargo in the stomach, and that the cargo reconstituted successfully in fluid in the terminal ileum. Next, two versions of the carrier were engineered to carry mPlum. In silico analysis was conducted to predict stability and structural integrity. Following production of the two chimeras and assessment of yield and purity, they were compared for their ability to transcytose across the ileal epithelium in an ex vivo hamster model. Washed lumens were exposed separately to the two fusion proteins, as well as to mPlum cargo alone as a control, for 2 minutes then the lumens were washed thoroughly, fixed, wax-embedded, sectioned and stained. Fluorescence microscopy showed greater transcytosis capability for one of the carriers which will now be taken forwards to develop a new gut- targeting oral vaccine against the bacterium Clostridioides difficile.