Self-adjuvanting calcium-phosphate-coated microcrystal-based vaccines induce pyroptosis in human and livestock immune cells

Corripio-Miyar, Yolanda and MacLeod, Clair Lyle and Mair, Iris and Mellanby, Richard J. and Moore, Barry D. and McNeilly, Tom N. (2023) Self-adjuvanting calcium-phosphate-coated microcrystal-based vaccines induce pyroptosis in human and livestock immune cells. Vaccines, 11 (7). 1229. ISSN 2076-393X (https://doi.org/10.3390/vaccines11071229)

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Abstract

Successful vaccines require adjuvants able to activate the innate immune system, eliciting antigen-specific immune responses and B-cell-mediated antibody production. However, unwanted secondary effects and the lack of effectiveness of traditional adjuvants has prompted investigation into novel adjuvants in recent years. Protein-coated microcrystals modified with calcium phosphate (CaP-PCMCs) in which vaccine antigens are co-immobilised within amino acid crystals represent one of these promising self-adjuvanting vaccine delivery systems. CaP-PCMCs has been shown to enhance antigen-specific IgG responses in mouse models; however, the exact mechanism of action of these microcrystals is currently unclear. Here, we set out to investigate this mechanism by studying the interaction between CaP-PCMCs and mammalian immune cells in an in vitro system. Incubation of cells with CaP-PCMCs induced rapid pyroptosis of peripheral blood mononuclear cells and monocyte-derived dendritic cells from cattle, sheep and humans, which was accompanied by the release of interleukin-1β and the activation of Caspase-1. We show that this pyroptotic event was cell–CaP-PCMCs contact dependent, and neither soluble calcium nor microcrystals without CaP (soluble PCMCs) induced pyroptosis. Our results corroborate CaP-PCMCs as a promising delivery system for vaccine antigens, showing great potential for subunit vaccines where the enhancement or find tuning of adaptive immunity is required.

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