Zymosan Particle-Induced Hemodynamic, Cytokine and Blood Cell Changes in Pigs: An Innate Immune Stimulation Model with Relevance to Cytokine Storm Syndrome and Severe COVID-19

mRNA-LNP COVID-19 Vaccine Lipids Induce Complement Activation and Production of Proinflammatory Cytokines: Mechanisms, Effects of Complement Inhibitors, and Relevance to Adverse Reactions

A small fraction of people vaccinated with mRNA-lipid nanoparticle (mRNA-LNP)-based COVID-19 vaccines display acute or subacute inflammatory symptoms whose mechanism has not been clarified to date. To better understand the molecular mechanism of these adverse events (AEs), here, we analyzed in vitro the vaccine-induced induction and interrelations of the following two major inflammatory processes: complement (C) activation and release of proinflammatory cytokines. Incubation of Pfizer-BioNTech's Comirnaty and Moderna's Spikevax with 75% human serum led to significant increases in C5a, sC5b-9, and Bb but not C4d, indicating C activation mainly via the alternative pathway. Control PEGylated liposomes (Doxebo) also induced C activation, but, on a weight basis, it was ~5 times less effective than that of Comirnaty. Viral or synthetic naked mRNAs had no C-activating effects. In peripheral blood mononuclear cell (PBMC) cultures supplemented with 20% autologous serum, besides C activation, Comirnaty induced the secretion of proinflammatory cytokines in the following order: IL-1α < IFN-γ < IL-1β < TNF-α < IL-6 < IL-8. Heat-inactivation of C in serum prevented a rise in IL-1α, IL-1β, and TNF-α, suggesting C-dependence of these cytokines' induction, although the C5 blocker Soliris and C1 inhibitor Berinert, which effectively inhibited C activation in both systems, did not suppress the release of any cytokines. These findings suggest that the inflammatory AEs of mRNA-LNP vaccines are due, at least in part, to stimulation of both arms of the innate immune system, whereupon C activation may be causally involved in the induction of some, but not all, inflammatory cytokines. Thus, the pharmacological attenuation of inflammatory AEs may not be achieved via monotherapy with the tested C inhibitors; efficacy may require combination therapy with different C inhibitors and/or other anti-inflammatory agents.

Evaluation of the Acute Anaphylactoid Reactogenicity of Nanoparticle-Containing Medicines and Vaccines Using the Porcine CARPA Model

A small fraction, up to 10%, of people treated intravenously with state-of-the-art nanoparticulate drugs or diagnostic agents develop an acute infusion reaction which can be severe or even lethal. Activation of the complement (C) system can play a causal, or contributing role in these atypical, "pseudoallergic" reactions, hence their name, C activation-related pseudoallergy (CARPA). Intravenous (i.v.) administration of the human reaction-triggering (very small) dose of a test sample in pigs triggers a symptom tetrad (characteristic hemodynamic, hematological, skin, and laboratory changes) that correspond to the major human symptoms. Quantitating these changes provides a highly sensitive and reproducible method for assessing the risk of CARPA, enabling the implementation of appropriate preventive measures. Accordingly, the porcine CARPA model has been increasingly used for the safety evaluation of therapeutic and diagnostic nanomedicines and, recently, mRNA-lipid nanoparticle vaccines. This chapter provides details of the experimental procedure followed upon using the model.