Development of an mRNA-base Universal Influenza Vaccine
Norbert Pardi, PhD, Assistant Professor of Medicine, University of Pennsylvania
At the TIDES USA conference in San Diego, Norbert Pardi, PhD, Assistant Professor of Medicine, at the University of Pennsylvania, began his presentation by discussing the nucleoside-modified, purified mRNA vaccine platform that they use for all the infectious disease studies.
In the platform, RNA is made from a plasmid DNA template, encoding not only the antigen of interest but also the regulatory elements, including 5’ cap, 5’ UTR, 3’ UTR, and poly(A) tail. Once RNA is made, it undergoes cellulose purification to eliminate dsRNA and other contaminants. Additionally, his team uses modified nucleosides in all infectious disease vaccine programs by replacing uridine with 1-methyl-pseudouridine while performing in vitro transcription reaction. Once RNA is made, it gets formulated into lipid nanoparticles (LNPs).
Advancing Vaccines
Pardi also briefly talked about existing vaccines. He said that the problem is that seasonal influenza virus vaccines provide suboptimal levels of production. Most of the vaccines contain three to four inactivated viruses. If those viruses do not match well with the circulating viruses, the effectiveness of the vaccine reduces dramatically. Therefore, there is a need for better influenza vaccines.
The mRNA-LNP platform has many advantages such as flexibility of the platform that enables formulation of more than one antigen encoding mRNA. He said that most vaccines target hemagglutinin (HA), but its head domain is highly variable across strains and immunodominant. So they focused on conserved antibody-accessible regions of influenza virus: HA stalk, some parts of neuraminidase, and matrix protein 2.
Pardi described their vaccine program against influenza A and influenza B viruses in four parts: vaccines against influenza A group 1 viruses, influenza A group 2 viruses, influenza B viruses, and final multivalent formulation containing all antigens. They showed that all four vaccine antigens induce humoral immune response in mice. They also indicated that even the monovalent vaccines induce protection against a high dose of challenge virus.
To figure out the mechanism of protection, they conducted a serum transfer study, and the results showed that protection from viral infection is primarily mediated by antibodies. They also looked at the T cell responses induced by the neuraminidase (NA) and nucleoprotein (NP) vaccine, showing that the NA and NP components induced strong CD4+ and CD8+ responses in mice. A dose de-escalation study was also conducted to determine the minimum protective dose. Indications showed that the combination mRNA-LNP vaccine provides protection from multiple influenza A viruses after a single immunization.
In the last part of his talk, Pardi touched upon mRNA vaccine development against influenza B virus. He explained that influenza B viruses have two distinct lineages, and they decided to use HA from each lineage. They generated monovalent and pentavalent vaccines. They followed a similar experimental setup as group 1 studies except that this time they tried prime only and prime boost vaccinations. They showed that there is a good immune response against each of the five components. They also indicated that the second vaccine dose very potently boosted immune responses.
Challenge studies showed that the combination of mRNA-LNP influenza vaccine provides protection from multiple influenza B viruses after a single immunization. Pardi underlined that monovalent vaccines induce protection from certain viruses but not from all viruses. Only the pentavalent combined vaccine induces protection against every virus tried in this study. The combination vaccine also induces sterilizing protection after a single immunization. As seen in the group 1 studies, the dose de-escalation studies indicated that as little as 50 ng of combination vaccine could induce protection in mice after a single immunization. Serum transfer experiments showed that protection induced by the influenza mRNA vaccine is primarily antibody-mediated.