Repurposing Allergen-free Pollen Grains for Oral Vaccination: Microparticle Development, Mucoadhesive Properties, and Anthrax-vaccine Efficacy

Date

2022-12

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Abstract

Oral vaccines offer a pain- and needle-free delivery that induces both systemic and mucosal immunity. Currently, most vaccines are parentally administered which only produces systemic protection. However, most pathogens enter the body through mucosal surfaces, such as the gastrointestinal and respiratory tracts. There is a need to develop vaccines that elicit mucosal immunity to act as first line of defense. However, oral vaccines face multiple challenges while travelling through the gastrointestinal tract. Barriers in the form of acidic pH, enzymatic environments, and limited epithelia permeability can diminish vaccine bioavailability. Particle delivery systems have been engineered to protect the vaccine while in transit. They can be designed with properties that enhances delivery efficiency and immune response strength. Pollen grains have emerged as a novel biomaterial that can be repurpose as an oral delivery system. This naturally occurring microparticles carry plants male gametophyte. They are strong particles which are highly resistant to extreme weather conditions. However, allergic reaction can be triggered if these biomolecules are not removed. We developed a multi-step chemical treatment that produces intact, hollow, and biomolecule-free pollen shells. By using acetone, phosphoric acid, and potassium hydroxide we removed allergens, intine layer, and opened the pollen pore. Thus, leaving behind the tough sporopollenin shell that will be filled with our vaccine. This novel treatment can be applied to multiple pollen species which allows exploration of new applications for particle delivery systems. To overcome oral vaccine delivery challenges some particle systems are engineered with mucoadhesive properties. This will allow them to interact with mucus layer lining the stomach and intestine walls. We examined four pollen species (ragweed, sunflower, black alder, lamb’s quarter) before and after chemical treatment to determine any mucoadhesive properties. In vitro testing with pig intestine showed that treated echinate pollens had better retention on the mucus layer. Further in vivo testing confirmed that echinate pollen adhered to mucus layer and delay their removal. This demonstrate that pollen can be used in oral delivery to protect but also enhance delivery efficiency by allowing antigen presenting cells more time to sample their cargo. A technological application was investigated in order to analyze pollen grains as an effective drug delivery system for an actual disease. Hence the development of an innovative pollen-based anthrax vaccine. Anthrax is a disease that has been weaponized successfully in the past. The commercially available treatment requires five doses with annual booster to maintain systemic protection. This study explored the potential of ragweed pollen to orally deliver recombinant protective antigen (rPA) an elicit an immune response. Mice serum and bone marrow response was significantly higher compared to rPA alone. Mucosal response was comparable to our positive control group. The antibodies produce by pollen formulations with a three-dose vaccine regimen were capable of neutralizing rPA. This in turn prevented LeTx cell mediated killing indicating the potential of pollen to induce strong and long-lasting immunity against anthrax.


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Keywords

Oral vaccine, Pollen, Mucoadhesive, Chemical Treatment, Anthrax vaccine

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