Development of an adaptable RNA vaccine against enterovirus D68 infection for the prevention of acute flaccid myelitis

Project summary: First identified in California in 2012, acute flaccid myelitis in children, associated with enterovirus D68 (EV-D68) infection, has been increasing in incidence with outbreaks detected every 2 years. Enteroviruses are well-known causes of central nervous system pathologies, ranging from aseptic meningitis to sometimes fatal brainstem encephalitis and myelitis, which can lead to permanent debilitating paralysis. Additionally, EV-D68 infects the respiratory tract, causing severe respiratory disease and facilitating person-to-person transmission via respiratory droplets. Despite EV-D68’s emergence as a major cause of severe respiratory and neurological disease, there are no vaccines or therapeutics available to combat and control the spread of this pathogen. HDT Bio has developed a self-amplifying replicon RNA (repRNA) vaccine platform delivered by a Lipid InOrganic Nanoparticle (LION) scheduled to enter phase I clinical trials in the first quarter of 2021 as a vaccine against COVID-19. These activities will enable rapid translation of other vaccine candidates, utilizing the same platform, into the clinic. Additionally, HDT has an ongoing program to develop broad-spectrum anti-EV-D68 antibody therapeutics, in which we have identified promising RNA-based vaccines that encode the necessary genes for production of divergent EV-D68 virus like particles (VLPs) in vivo upon intramuscular administration. Our preliminary data establishes that 1) we can launch VLPs of non-enveloped viruses from our repRNA platform, 2) we can rapidly adapt this approach for genotypic and/or antigenic variants of EV-D68, and 3) these antigens are very immunogenic in small and large animals, generating robust neutralizing antibody responses after a single dose. In this application, we propose to screen six vaccine candidates, which are currently being evaluated as a mixture in alpacas for antibody discovery efforts, to identify a single candidate that induces the best cross- neutralizing antibody responses. We will then characterize safety, immunogenicity and efficacy in neurological- and respiratory-disease mouse models of EV-D68 infection. Finally, we will evaluate safety and immunogenicity in pregnant mouse models and efficacy in birthed pups while characterizing maternal antibody transfer.Project narrative: Biennial outbreaks of enterovirus D68 infections, the resulting cases of acute flaccid myelitis, and the alarming rate of increasing case numbers, has prompted the development of vaccines and therapeutics against this pathogen of concern. The objective of this project is to select a broad-spectrum RNA vaccine candidate, capable of inducing cross-neutralizing antibody responses against the six sub- clades of the species/serotype, and evaluate its safety, immunogenicity, and efficacy in respiratory- and neurological-disease mouse models of enterovirus D68 infection. Also, due to the prevalence of enterovirus D68 infection in children, this project will also evaluate maternal vaccination, maternal-fetal antibody transfer, and efficacy in pups born to vaccinated mothers.