Interim results from a phase I randomized, placebo-controlled trial of novel SARS-CoV-2 beta variant receptor-binding domain recombinant protein and mRNA vaccines as a 4th dose booster

Tailored Monoacyl Poly(2-oxazoline)- and Poly(2-oxazine)-Lipids as PEG-Lipid Alternatives for Stabilization and Delivery of mRNA-Lipid Nanoparticles

The successful use of lipid nanoparticles (LNPs) for clinical development of the COVID-19 mRNA vaccines marked a breakthrough in mRNA-LNP therapeutics. As one of the vital components of LNPs, poly(ethylene glycol)-lipid conjugates (PEG-lipids) influence particle biophysical properties and stability, as well as interactions within biological environments. Reports suggesting that anti-PEG antibodies can be detected quite commonly within the human population raise concerns that PEG content in commercial LNP products could further stimulate immune responses to PEG. The presence of anti-PEG antibodies has been linked to accelerated clearance of LNPs, potentially a source of variability in the biological response to mRNA-LNP products. This motivated us to explore potential PEG alternatives. Herein, we report physicochemical and biological properties of mRNA-LNPs assembled using poly(2-oxazoline) (POx)- and poly(2-oxazine) (POz)-based polymer-lipid conjugates. Notably, we investigated monoacyl lipids as alternatives to diacyl lipids. mRNA-LNPs produced using monoacyl POx/POz-lipids displayed comparable biophysical characteristics and cytocompatibility. Delivery of reporter mRNA resulted in similar transfection efficiencies, in both adherent and suspension cells, and in mice, compared to PEG-lipid equivalents. Our results suggest that monoacyl POx/POz-lipid-containing LNPs are promising candidates for the development of PEG-free LNP-based therapeutic products.

A Gamma-adapted subunit vaccine induces broadly neutralizing antibodies against SARS-CoV-2 variants and protects mice from infection

In the context of continuous emergence of SARS-CoV-2 variants of concern (VOCs), one strategy to prevent the severe outcomes of COVID-19 is developing safe and effective broad-spectrum vaccines. Here, we present preclinical studies of a RBD vaccine derived from the Gamma SARS-CoV-2 variant adjuvanted with Alum. The Gamma-adapted RBD vaccine is more immunogenic than the Ancestral RBD vaccine in terms of inducing broader neutralizing antibodies. The Gamma RBD presents more immunogenic B-cell restricted epitopes and induces a higher proportion of specific-B cells and plasmablasts than the Ancestral RBD version. The Gamma-adapted vaccine induces antigen specific T cell immune responses and confers protection against Ancestral and Omicron BA.5 SARS-CoV-2 challenge in mice. Moreover, the Gamma RBD vaccine induces higher and broader neutralizing antibody activity than homologous booster vaccination in mice previously primed with different SARS-CoV-2 vaccine platforms. Our study indicates that the adjuvanted Gamma RBD vaccine is highly immunogenic and a broad-spectrum vaccine candidate.