Corticosteroids and cellulose purification improve respectively the in vivo translation and vaccination efficacy of self-amplifying mRNAs

Abstract

Synthetic mRNAs are an appealing therapeutic platform with multiple biomedical applications ranging from protein replacement therapy to vaccination. In comparison to conventional mRNA, synthetic self-amplifying mRNAs (sa-mRNAs) are gaining increased interest due to their higher and longer-lasting expression. However, sa-mRNAs also elicit an innate immune response, which may complicate the clinical translation of this platform. Approaches to reduce the innate immunity of sa-mRNAs have not been studied in detail. In this work we investigated the effect of several innate immune inhibitors and a novel cellulose-based mRNA purification approach on the type I interferon (IFN) response, translation and vaccination efficacy of our formerly developed sa-mRNA vaccine against Zika virus. Among the investigated inhibitors, we found that topical application of clobetasol at the sa-mRNA injection site was the most efficient in suppressing the type I IFN response and increasing the translation of sa-mRNA. However, clobetasol prevented the formation of antibodies against sa-mRNA encoded antigens and should therefore be avoided in a vaccination context. Residual dsRNA by-products of the in vitro transcription reaction are known inducers of immediate type I IFN responses. We additionally demonstrate drastic reduction of these dsRNA by-products upon cellulose-based purification, consequently reducing the innate immune response and improving sa-mRNA vaccination efficacy.

Low-dose single-shot COVID-19 mRNA vaccines lie ahead

“…Therefore, it is possible that the COVID-19 mRNA vaccines from Moderna and Pfizer/BioNTech perform better than the conventional COVID-19 mRNA vaccine used in this study, making the difference between selfamplifying and non-amplifying mRNA vaccines smaller. Nevertheless, self-amplifying RNA vaccines are just emerging and improvements, like advanced purification protocols, 3 are expected to further increase their efficiency.…”

RNA-based vaccines and innate immune activation: Not too hot and not too cold

“…In this issue of Molecular Therapy , Zhong et al. 2 show that inhibition of the type 1 interferon (IFN I) response to sa-RNA using corticosteroids and other inhibitors substantially increased production of the sa-mRNA-encoded protein antigen but, unfortunately, was detrimental to the vaccine effect. However, modification of the purification method to eliminate double-stranded RNA (dsRNA) byproducts during sa-mRNA production reduced innate immunity and improved the efficacy of a Zika virus vaccine, resulting in higher antibody titers and T cell responses against Zika target antigen.…”

“…To address this issue, Zhong et al. 2 topically applied corticosteroids at the site of vaccine administration in mice prior to intradermal electroporation. The steroids suppressed IFN I production, and the approach was ultimately successful in raising expression, as measured by a luciferase reporter coexpressed from the sa-mRNA (see Figure 1 ).…”