An optimized prophylactic mRNA vaccine against coronavirus disease 2019

Background and rationale: The current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic highlights that mRNA vaccines are the fastest formulation to manufacture: the company that I co-founded in 1999, CureVac (Tuebingen, Germany), as well as two other large mRNA companies (BioNTech, Mainz, Germany, founded in 2008, and ModeRNA, Boston, USA, founded in 2008) are at the front line and have already begun human clinical studies with mRNA vaccines coding for SARS-CoV-2 proteins. A non-replicating mRNA-based format was used for our first mRNA-based anti-cancer vaccine subject to clinical studies (first patient injected in 2003 in Tuebingen) and is currently in use against coronavirus disease 2019 (COVID-19). Non-replicating mRNAs are very safe vectors that are easily and quickly produced. However, the doses required to obtain a good antibody response after intra-dermal or intra-muscular injection are relatively high and in the range of 100 micrograms per injection. Accordingly, the phase I study by ModeRNA involved two intra-muscular injections administered 28 days apart with doses of 25, 100 or 250 micrograms for both vaccinations. Based on the phase I results, the company is now doing a phase II study with two doses: 50 and 100 micrograms. Should a 100 microgram dose be required for the final vaccine, vaccinating the population of Switzerland twice would require 20 million doses, which corresponds to two kilograms of purified mRNA, i.e., at least 400 litres of transcription reaction. This cannot be achieved easily and quickly, even when conducted by a large industry such as Lonza, because the raw materials (cap analogues, nucleotides and polymerases) are not readily available in such large amounts. Accordingly, among the four different mRNA vaccines that BioNTech is testing in large phase I studies in association with Pfizer, one is self-amplifying mRNA that requires much lower amounts of material than non-replicating mRNA.Overall objective and specific aims: We aim to generate an optimal mRNA vaccine for sub-cutaneous, intra-muscular or intranasal administration that induces a strong antibody response with amounts of mRNA one thousand-fold lower than the amounts of mRNA required for the non-replicating mRNA vaccines currently being tested.Methods to be used: Replicating mRNAs are efficacious in triggering immune responses at doses 400-fold lower than those of non-replicating mRNAs. The production of five grams of mRNA is feasible (covering two injections of 10 millions people). Thus, a replicating format is best adapted to a world pandemic in which billions of vaccine doses would be required. A novel, safe, efficacious and cost-effective version of replicative mRNA could take the form of a two-component vaccine consisting of a non-replicating mRNA coding the replicase (that can be stored and used in any vaccine) and a replicating mRNA coding the antigen (to be produced according to the virus that generates the pandemic): the transreplicon. This technology was recently reported (Beisser et al. Mol Ther. 2020 Jan 8;28(1):119-128) and shown to be equivalent to a non-replicating mRNA vaccine with a dose at least 400-fold lower: in mice, intra-dermal injection of 50 ng of the transreplicon coding for influenza HA gave an antibody response and neutralizing titres similar to those of the intra-dermal injection of 20 micrograms of non-replicating mRNA coding for influenza HA. The purpose of the present grant is to implement this trans-amplifying mRNA vaccine and to optimize its formulation for sub-cutaneous, intra-muscular or intranasal vaccination. We will optimize this technology using our expertise (sequence of the antigen, of the replicase, structures of mRNAs, ratios of replicative and non-replicative mRNAs) and formulate the two mRNAs in nanoparticles (in our proprietary protamine nanoparticles as well as commercially available or innovative liposomal particles). These will be characterized and evaluated in vitro. We will then measure anti-SARS-CoV-2 Spike protein antibody and neutralizing titres induced after sub-cutaneous, intra-muscular or intranasal administration of the selected formulations in mice. As benchmark positive controls, we will use the intra-dermal injection of naked trans-amplifying mRNAs, as described in Beisser et al., and the intravenous injection of our usual spleen-targeted liposomal non-replicating mRNA formulation.Expected results and their impact: We expect to identify a nanoparticle formulation of a trans-amplifying mRNA vaccine that will induce a strong antibody response with the sub-cutaneous, intra-muscular or intranasal administration of transreplicon in the range of one nanogram per mouse. The outcome will be a safe, efficacious, versatile and inexpensive mRNA vaccine against coronavirus that can also be the basis for easily and quickly manufactured vaccines against any new viral threats.