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Developing prolonged antigen delivery systems that mimic long-term exposure to pathogens appears as a promising but still poorly explored approach to reach durable immunities. In this study, we have used a simple technology by which His-tagged proteins can be assembled, assisted by divalent cations, as supramolecular complexes with progressive complexity, namely protein-only nanoparticles and microparticles. Microparticles produced out of nanoparticles are biomimetics of secretory granules from the mammalian hormonal system. Upon subcutaneous administration, they slowly disintegrate, acting as an endocrine-like secretory system and rendering the building block nanoparticles progressively bioavailable. The performance of such materials, previously validated for drug delivery in oncology, has been tested here regarding the potential for time-prolonged antigen release. This has been completed by taking, as a building block, a nanostructured version of p30, a main structural immunogen from the African swine fever virus (ASFV). By challenging the system in both mice and pigs, we have observed unusually potent pro-inflammatory activity in porcine macrophages, and long-lasting humoral and cellular responses in vivo, which might overcome the need for an adjuvant. The robustness of both innate and adaptive responses tag, for the first time, these dynamic depot materials as a novel and valuable instrument with transversal applicability in immune stimulation and vaccinology. [ABSTRACT FROM AUTHOR]

The effect of the composition and size of polymeric particles on the immunogenicity of the fibrillogenic β2-microglobulin protein immobilized on their surface was studied. For this purpose, nanoparticles (NP) based on a copolymer of L-glutamic acid and L-phenylalanine (P(Glu-co-Phe)) and a block copolymer of poly(ethylene glycol) with poly(lactic acid) (PEG-b-PLA) as well as microparticles (MP) based on poly(lactic acid) (PLA) were selected. Materials and Methods. α-L-amino acid copolymer-based nanoparticles were prepared by gradient phase inversion, and PEG-b-PLA-based nanoparticles by nanoprecipitation. Double emulsion method was used to form polymeric microparticles based on PLA. Recombinant chimeric model protein beta-2-microglobulin-green fluorescent protein (β2M-sfGFP) was used to covalently modify all types of polymeric particles followed by immunization of four groups of laboratory animals equal in number. An enzyme immunoassay method was used to evaluate the humoral immune response. Results and discussion. In three experimental groups, mice were immunized using poly(amino acid)-based (NP-PAA) and PEG-b-PLA (NP-PLA) nanoparticles as well as PLA microparticles containing immobilized β2M-sfGFP on the surface. The control group was immunized using a physical mixture of PEG-b-PLA nanoparticles and free β2M-sfGFP. The highest level of antibodies to sfGFP in blood serum was found when mice were immunized with a mixture of protein and nanoparticles. When mice were immunized with β2M-sfGFP-modified nanoparticles, the amount of antibodies to sfGFP was statistically significantly lower (p < 0.001) compared to the control group. However, the groups immunized with nanoparticles of similar size but different composition conjugated to the model proteins did not differ significantly among themselves. It was also found that the size of the particles affects the immunogenicity of the associated protein. A similar pattern of relative antibody content in the sera of mice was maintained at all steps of immunization. [ABSTRACT FROM AUTHOR]

Noroviruses (NoVs) are one of the major causes of acute viral gastroenteritis in humans. Virus-like particles (VLPs) without genomes that mimic the capsid structure of viruses are promising vaccine candidates for the prevention of NoVs infection. To produce large amounts of recombinant protein, including VLPs, the silkworm-expression vector system (silkworm-BEVS) is an efficient and powerful tool. In this study, we constructed a recombinant baculovirus that expresses VP1 protein, the major structural protein of NoV GII.4. Expression analysis showed that the baculovirus-infected silkworm pupae expressed NoV VP1 protein more efficiently than silkworm larval fat bodies. We obtained about 4.9 mg of purified NoV VP1 protein from only five silkworm pupae. The purified VP1 protein was confirmed by dynamic light scattering and electron microscopy to form VLPs of approximately 40 nm in diameter. Antisera from mice immunized with the antigen blocked NoV VLPs binding to histo-blood group antigens of pig gastric mucin and also blocked NoV infection in intestinal epithelial cells derived from human induced pluripotent stem (iPS) cells. Our findings demonstrated that NoV VLP eliciting protective antibodies could be obtained in milligram quantities from a few silkworm pupae using the silkworm-BEVS. [ABSTRACT FROM AUTHOR]