Nonclinical Safety Assessment of Lipid Nanoparticle-and Emulsion-Based Self-Amplifying mRNA Vaccines in Rats

Abstract

Vaccines containing mRNA with the capacity to self-amplify represent an alternative to the mRNA vaccines that came to prominence during the COVID-19 pandemic. To gain further insights on the safety profile of self-amplifying mRNA- (SAM-) vaccines, this preclinical toxicology study in rats evaluated the effect of (i) the type of delivery system (lipid nanoparticle [LNP] vs cationic nano-emulsion [CNE]); (ii) antigen-encoding sequence (rabies glycoprotein G vs SARS-CoV-2 Spike); and (iii) RNA amplification. Further analyses also evaluated gene expression in peripheral blood after vaccination, and the biodistribution of vaccine RNA. The SAM vaccines administered as two doses 2-weeks apart had acceptable safety profiles in rats, with respect to clinical signs, blood biochemistry, and macroscopic and microscopic pathology. A transient increase in ALT/AST ratio occurred only in female rats and in the absence of muscle and liver damage was dependent on RNA amplification and appeared related to the greater quantities of vaccine RNA in the muscle and livers of female rats vs male rats. The RNA and delivery-vehicle components, but not the nature of the antigen-coding sequence or the requirement for RNA amplification, affected aspects of the stimulation of innate-immune activity, which was consistent with the transient activation of type I and type II interferon signaling. The delivery vehicle, LNP, differed from CNE as vaccine RNA in CNE compositions appeared independently to stimulate innate-immune activity at 4 hours after vaccination. Our analysis supports further studies to assess whether these differences in innate-immune activity affect safety and efficacy of the SAM vaccine.

Evaluation of non-clinical toxicity studies of COVID-19 vaccines

“…with mRNA vaccines, but also with an adenovector vaccine and an adjuvanted vaccine. Donahue et al (2023) have described effects of mRNA vaccines on AST and ALT. In our dataset a relation could be found with the occurrence of the acute phase protein response, indicating a involvement of the liver in the innate immune response.…”

Recent advances in mRNA‐based vaccine for cancer therapy; bench to bedside

“…Given that SAM is a large, negatively charged molecule, cellular absorption as well as safeguarding from enzymatic breakdown requires a delivery method. 109,110 The most alluring aspect is that replicons immediately increase their copy numbers in target cells upon administration by encoding their own replication machinery. Because of its self-amplifying properties, patients experience fewer side effects because the initial mRNA dose is drastically reduced.…”

“…Fully synthetic SAM created following IVT is now able to be utilized as an RNA‐based vaccination without raising any possible safety issues with the viral components. Given that SAM is a large, negatively charged molecule, cellular absorption as well as safeguarding from enzymatic breakdown requires a delivery method 109,110 . The most alluring aspect is that replicons immediately increase their copy numbers in target cells upon administration by encoding their own replication machinery.…”

Self-Amplifying RNA: A Second Revolution of mRNA Vaccines against COVID-19

“…The additional effects of the RNA self-amplification and the composition of the delivery vehicle were evaluated in another study, in which LNPs were compared to a cationic nano-emulsion (CNE) [ 83 ]. This CNE, composed of the cationic lipid DOTAP, has previously been used to deliver saRNA-based vaccines in different animal models, and demonstrated to be immunogenic and well-tolerated [ 84 ].…”