Immunogenicity and protective efficacy of Marburg virus glycoprotein and virus-like particle-forming mRNA-based vaccines.
Mounting evidence suggests the high immunogenicity of virus-like particle (VLPs) based vaccines. Although VLP vaccines can be effective, they have not been compared to an envelope glycoprotein (GP)-only vaccine for filoviruses. We  conducted a detailed side-by-side comparison of the immunogenicity and protective efficacy of mRNA vaccines encoding for the Marburg virus (MARV) full length GP delivered alone or as a VLP. As expected, co-formulation of the MARV GP and matrix protein VP40 resulted in the formation of VLPs readily detected by electron microscopy after purification from cell supernatants. We vaccinated guinea pigs with a two-component mRNA vaccine  encoding for GP and VP40  (from now on referred as VLP vaccine) or a monovalent mRNA vaccine encoding for GP alone. At high vaccine doses, the VLP group demonstrated reduced humoral response as compared to the GP-only group, but both mRNA vaccines fully protected guinea pigs against lethal MARV infection. However, at low doses, GP-only mRNA conferred a 100% protection, whereas the VLP exhibited only a partial protection. In mice the VLP mRNA vaccine was more efficient at inducing GP-specific CD8+ T cells co-expressing IFN-? and TNF-a, whereas the GP-only mRNA vaccine better induced CD4+ T cells expressing IFN-?, IL-2 and TNF-a. In addition, in guinea pigs, the VLP vaccine was associated with down-regulation of  genes associated with various biological and metabolic processes, including the NF-?B signaling pathway, post-transcriptional silencing of small RNAs, and upregulation of genes involved in the mitochondrial respiratory chain complex. In contrast, the GP-only vaccine upregulated genes involved in interferon signaling. Overall, the VLP mRNA vaccine was less immunogenic and protective, whereas the GP-only mRNA vaccine conferred a robust protection by as little as one µg dose in guinea pigs. Overall design: To understand transcriptional changes in the GP and VLP mRNA vaccinated groups, we performed bulk RNA sequencing (RNA-seq) of guinea pig whole blood for day 54 post-vaccination and day three post-challenge of Marburg virus (day 59 post-vaccination).