Pollen grains and plant spores have emerged as a novel biomaterial for a broad range of applications including oral drug and vaccine delivery, catalyst support, and removal of heavy metals. However, before pollens can be used, their intrinsic biomolecules, which occupy a large part of the pollen inner cavity must be removed not only to create empty space but because they have potential to cause allergies when used in vivo. These intrinsic materials in the pollen core can be extracted through a chemical treatment to generate clean pollen shells. The commonly used method involves a series of sequential treatments with organic solvents, alkalis, and acids to remove the native pollen biomolecules. This method, though successful for treating lycopodium (Lycopodium clavatum) spores, fails for other species of pollens such as common ragweed (Ambrosia elatior) and thus prevents widespread investigation of different pollens. Herein, we report a new chemical treatment for obtaining clean pollen shells from multiple plant species. This new method involves sequential treatment with acetone, phosphoric acid, and potassium hydroxide. Scanning electron micrographs and protein quantification have shown that the new method can successfully produce clean, intact, and hollow shells from many pollen species including ragweed, sunflower, black alder, and lamb’s quarters. These results demonstrate the broad applicability of this method to clean pollens of different species, and paves the way to start investigating them for various applications.

Oral vaccine delivery remains an unmet goal due to biochemical and immunological barriers in the gastrointestinal tract. Sporopollenin microcapsules from natural pollen grains have recently been engineered to overcome these multifaceted challenges. Using four morphologically different sporopollenin shells and two inbred mouse strains, this study addresses three key questions regarding sporopollenin shell's application for oral vaccine delivery: i) the impact of sporopollenin shell surface morphology on the immune response, ii) the duration of the immunity, and iii) the applicability of the delivery system across a diverse genetic background population. Using ovalbumin (OVA) as a model vaccine antigen, this study demonstrates that OVA can adsorb on the sporopollenin shell surfaces. Mice orally vaccinated with a sporopollenin shell-based OVA formulation show sustained antibody responses for 454 days after the immunization that are correlated with the generation of OVA-specific plasma cells in the vaccinated mice bone marrow. Sporopollenin shell surface spikes have a greater impact on immune responses than the shell size and shape. A spiky ragweed sporopollenin formulation induces systemic and mucosal responses in C57BL/6 and BALB/c mice. Together, this study provides a framework to select sporopollenin shells based on the surface morphology to use as a microcapsule for oral vaccination.

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Vaccine delivery through the oral route is challenging due to physical, biochemical, and immunological barriers in the gastrointestinal tract. In article number 2000102, Harvinder Singh Gill and co‐workers present spikey sporopollenin microcapsules as an oral vaccine carrier and adjuvant. This vaccination approach induces a sustained humoral immune response for the entire lifespan of treated mice.