Low and highly variable B cell responses were observed in the 0

Low and highly variable B cell responses were observed in the 0.015 g dose group, possibly because of the very low dose used. Further, vaccine-induced Tcell-mediated immune responses against the spike antigen were analyzed in mice YH239-EE spleens at 2wp2 by intracellular-cytokine-staining and multi-parametric flow cytometry, afterexvivorestimulation with full-length spike, S1, S2, or receptor-binding domain name (RBD) peptide mixes (Figures 3andS4). 1 clinical evaluation (NCT04758962). Keywords:self-amplifying mRNA, SARS-CoV-2 vaccine, immunogenicity, biodistribution, toxicity, efficacy, spike YH239-EE antigen == Graphical abstract == Comprehensive preclinical development of a lipid nanoparticle (LNP)-formulated SAM vaccine encoding the prefusion-stabilized SARS-CoV-2 spike full-length antigen is usually reported. Protective efficacy, immunogenicity, toxicity, and biodistribution assessment of this candidate vaccine in mice, rats, and hamsters showed a favorable safety profile and strong immune responses against SARS-CoV-2 contamination and disease. == Introduction == On March 11th, 2020, the World Health Organization declared the coronavirus disease 2019 (COVID-19) outbreak, caused by a novel coronavirus termed SARS-CoV-2, a global pandemic. Multifactorial approaches, including vaccines and therapeutics, have been developed to contain the devastating impact of the COVID-19 pandemic in the last 18 months.1In less than 2 years, an unprecedented number of vaccine candidates have been developed, with over 100 currently undergoing clinical evaluation and a few approved for emergency use or fully licensed.2Given the need to produce billions of doses to immunize the world’s population, the unknown duration of protection in most vulnerable populations, and the need to address continuously emerging variants, more than one type of vaccine will be needed. The first SARS-CoV-2 vaccine receiving emergency use authorization in several countries and later full approval in the US is a conventional optimized non-amplifying messenger RNA (mRNA)-based vaccine, validating the mRNA vaccine platforms for rapid vaccine development.3,4The utility of the mRNA platform for rapid pandemic response was first reported in preclinical models in 2013 using a self-amplifying mRNA (SAM).5 SAM is a synthetic mRNA vaccine platform using a self-amplifying mRNA derived from an alphavirus genome.6SAM encodes the antigen of interest and the viral replication machinery YH239-EE required for intracellular RNA amplification. Unlike conventional mRNA vaccines, which only encode the antigen of interest and are translated directly from the incoming RNA molecules, SAM can generate many copies of the mRNA in the target cell, leading to high and prolonged expression of the antigen and additional self-adjuvanting of innate immune responses.6,7As a result, SAM vaccines can elicit protective immune responses at lower doses,8possibly even with a single-dose regimen,9,10,11so they could represent an important platform for vaccine development to control the global spread of SARS-CoV-2. SARS-CoV-2 is an enveloped, single-stranded positive-sense RNA computer virus in the Coronaviridae family. It carries an approximately 30,000-nucleotide genome that encodes open reading frames of four major structural proteins: spike (S), envelope, membrane, and nucleocapsid.12The trimeric spike glycoprotein is located around the viral surface playing an essential role YH239-EE in virus entry and intercellular spread and is also the major target for virus neutralizing antibodies.13The spike protein is a class I fusion protein, consisting of S1 and S2 domains, and exists in a metastable prefusion conformation. The prefusion spike protein binds to the human angiotensin-converting enzyme 2 (hACE2) receptor, and enter the cells via fusion of viral and Mouse monoclonal to WIF1 host cell membranes through spike structural rearrangements,14or via clathrin-mediated endocytosis.15Introduction of two proline mutations in the C-terminal S2 fusion domain stabilizes the protein in a prefusion conformation, which exposes the receptor-binding sites and a dense cluster of neutralizing epitopes,16making it a prime vaccine candidate for SARS-CoV-2. For an effective and safe COVID-19 vaccine, type YH239-EE 1 helper (Th1) T cell responses are also highly desirable, in addition to neutralizing antibodies against the spike protein. SARS vaccines driving Th2 responses have been previously associated with enhanced lung immunopathology after challenge with SARS-CoV.17,18 In this paper, we report a comprehensive preclinical development of a lipid nanoparticle (LNP)-formulated SAM vaccine encoding the prefusion-stabilized SARS-CoV-2 spike full-length antigen. We assessed protective efficacy, immunogenicity, toxicity, and biodistribution of this candidate vaccine in mice, rats, and hamsters..