Recently, the World Health Organization confirmed 120 new human cases of avian H7N9 influenza in China resulting in 37 deaths, highlighting the concern for a potential pandemic and the need for an effective, safe, and high-speed vaccine production platform. Production speed and scale of mRNA-based vaccines make them ideally suited to impede potential pandemic threats. Here we show that lipid nanoparticle (LNP)-formulated, modified mRNA vaccines, encoding hemagglutinin (HA) proteins of H10N8 (A/Jiangxi-Donghu/346/2013) or H7N9 (A/Anhui/1/2013), generated rapid and robust immune responses in mice, ferrets, and nonhuman primates, as measured by hemagglutination inhibition (HAI) and microneutralization (MN) assays. A single dose of H7N9 mRNA protected mice from a lethal challenge and reduced lung viral titers in ferrets. Interim results from a first-in-human, escalating-dose, phase 1 H10N8 study show very high seroconversion rates, demonstrating robust prophylactic immunity in humans. Adverse events (AEs) were mild or moderate with only a few severe and no serious events. These data show that LNP-formulated, modified mRNA vaccines can induce protective immunogenicity with acceptable tolerability profiles.

Propionic acidemia (PA) is an ultrarare disorder caused by deficiency of the mitochondrial enzyme, propionyl-CoA carboxylase (PCC), composed of PCCA and PCCB subunits. An enzyme replacement therapy is being developed using dual messenger RNA (mRNA) therapy composed of lipid nanoparticles (LNPs) encapsulating mRNAs encoding PCCA and PCCB subunits of the PCC enzyme. We herein report on development of a translational semimechanistic pharmacokinetic (PK) and PK/pharmacodynamic (PD) model to quantify the relationship between the mRNA components of mRNA-3927 (an LNP encapsulating PCCA and PCCB mRNAs) and dose levels; PCCA/B mRNA PK and PD responses were assessed as circulating levels of primary disease markers 2-methyl citrate, 3-hydroxypropionate, and propionyl carnitine normalized to acetyl carnitine (C3/C2 ratio) to inform the first-in-human dose range and regimen selection. The translational PK/PD model was developed using preclinical data available in mice with PA, Sprague Dawley rats, and cynomolgus monkeys at dose levels ranging from 0.2 to 9 mg/kg. PCCA/B mRNA PK in mice, rats, and monkeys was adequately described using allometric scaling of volume and clearance parameters. The interspecies preclinical model was scaled allometrically to humans to predict the dose–response relationship in adult and pediatric patients with PA to guide selection of dose range and regimen for the Phase 1 clinical trial ( Identifier NCT04159103).