Elsevier

Vaccine

Volume 39, Issue 8, 22 February 2021, Pages 1310-1318
Vaccine

Proof-of-concept of a low-dose unmodified mRNA-based rabies vaccine formulated with lipid nanoparticles in human volunteers: A phase 1 trial

https://doi.org/10.1016/j.vaccine.2020.12.070Get rights and content

Highlights

  • Rabies glycoprotein-G mRNA in lipid nanoparticles (mRNA-LNP) was highly immunogenic.

  • Two low (1 or 2 μg) doses of mRNA-LNP induced immunity acceptable by WHO standard.

  • Low doses were well tolerated, but 5 μg dose had unacceptable reactogenicity.

Abstract

Introduction

In a first-in-human study immune responses to rabies virus glycoprotein (RABV-G)-mRNA vaccine were dependent on the route of administration, necessitating specialized devices. Following successful preclinical studies with mRNA encapsulated in lipid nanoparticles (LNP), we tested an mRNA-LNP formulation (CV7202).

Methods

In this phase 1, multi-center, controlled study in Belgium and Germany we enrolled 55 healthy 18–40-year-olds to receive intramuscular injections of 5 μg (n = 10), 1 μg (n = 16), or 2 μg (n = 16) CV7202 on Day 1; subsets (n = 8) of 1 μg and 2 μg groups received second doses on Day 29. Controls (n = 10) received rabies vaccine, Rabipur, on Days 1, 8 and 29. Safety and reactogenicity were assessed up to 28 days post-vaccination using diary cards; immunogenicity was measured as RABV-G-specific neutralizing titers (VNT) by RFFIT and IgG by ELISA.

Results

As initially tested doses of 5 μg CV7202 elicited unacceptably high reactogenicity we subsequently tested 1 and 2 μg doses which were better tolerated. No vaccine-related serious adverse events or withdrawals occurred. Low, dose-dependent VNT responses were detectable from Day 15 and by Day 29%, 31% and 22% of 1, 2 and 5 μg groups, respectively, had VNTs ≥ 0·5 IU/mL, considered an adequate response by the WHO. After two 1 or 2 μg doses all recipients had titers ≥ 0.5 IU/mL by Day 43. Day 57 GMTs were not significantly lower than those with Rabipur, which elicited adequate responses in all vaccinees after two doses. CV7202-elicited VNT were significantly correlated with RABV-G-specific IgG antibodies (r2 = 0.8319, p < 0.0001).

Conclusions

Two 1 μg or 2 μg doses of CV7202 were well tolerated and elicited rabies neutralizing antibody responses that met WHO criteria in all recipients, but 5 μg had unacceptable reactogenicity for a prophylactic vaccine.

ClinicalTrials.gov Identifier: NCT03713086.

Introduction

Recent infectious disease outbreaks caused by Zika, Ebola, chikungunya and SARS-CoV-2 viruses have highlighted the potential global threat to human health posed by emerging human infectious diseases [1]. There are increasing risks of spread of novel pathogens through human vectors with international travel as evidenced by the 2020 Covid-19 pandemic [2], or animal vectors with climate change illustrated by the increasingly wide range of dengue, chikungunya and Zika virus endemicity [3], [4], [5]. The development of new platforms to allow rapid production of novel vaccines, preferably avoiding the use of live pathogenic viruses and chemical inactivation steps which may modify the natural epitopes, is a major priority of vaccine research [1].

One promising technology with the potential to overcome many of these limitations is the use of messenger ribonucleic acid (mRNA) coding for the required antigen [6], which offers several advantages for vaccine manufacture. Production of mRNA using well-defined manufacturing techniques allows the same facilities to be used to prepare different mRNA molecules for vaccines against various other pathogens using the same manufacturing platform. As this may lead to lower production costs this may be of particular importance for vaccines destined for low-income countries, including rabies vaccines.

CureVac has developed a proprietary mRNA platform, RNActive®, for use in the development of safe and effective prophylactic vaccines for humans [7]. Following preclinical demonstration of the feasibility of this approach the first clinical investigation assessing the potential of RNActive® for a variety of vaccine targets used the rabies virus glycoprotein (RABV-G) as a model antigen. Use of RABV-G presents several advantages in the early stages of development: the antigen has been clearly defined and characterized, and there is a WHO-defined level of immune response that is considered adequate for the assessment of new vaccines. Furthermore, the virtually 100% fatality outcome of rabies disease means that volunteers in phase 1 trials, providing they have no history of rabies vaccination, will represent an immunologically naïve population.

We demonstrated the proof-of-concept of mRNA for human vaccines in the first-ever human clinical trial of RABV-G mRNA using an initial formulation (CV7201) with the cationic protein protamine [8]. CV7201 was generally well tolerated but the induction of adequate immune responses was dependent upon the mode of administration of the vaccine, notably requiring intradermal or intramuscular administration with specialized devices. Further preclinical research in animal models has found that formulation of the mRNA in lipid nanoparticles (LNP) protects the mRNA and enhances the immune response [9]. Preclinical studies found that CV7202, a novel mRNA-LNP formulation which includes the same mRNA antigen as CV7201 encapsulated in LNP, elicits immune responses in non-human primates comparable to those induced by licensed vaccines (CureVac, data on file). We now report on the first use of this new formulation in adult human volunteers in an ongoing phase 1 study to assess the safety and immunogenic potential of this new vaccine model, which is now being applied to other novel pathogenic viruses, notably SARS-CoV-2.

Section snippets

Methods

This is a non-randomized, open-label, controlled, dose-escalation, multi-center phase 1 study done at the University Hospital LMU Munich, Germany and the University of Ghent, Belgium from October 2018. The objective was to determine the safety, reactogenicity and immunogenicity of different dosages of CV7202 when administered as intramuscular injections in one- or two-dose regimens. The study protocol was approved by the respective Ethical Committees of the two institutions and registered on

Results

A total of 69 volunteers were screened of whom 55 were enrolled, screen failures mainly being due to inability to meet all protocol requirements (Fig. 1). Two enrolled participants did not receive any vaccination, one due to non-compliance with the protocol and one who withdrew for personal reasons. The original staggered enrolment plan was followed for the 5 μg dose group, and ten volunteers were enrolled and received one 5 μg vaccination. However, concerns over the reactogenicity profile in

Discussion

Following demonstration that encapsulation of RABV-G mRNA in lipid nanoparticles improved immune responses in animal models [9], we assessed the safety, reactogenicity, and immunogenicity of CV7202, a novel mRNA-LNP formulation, in adults in comparison with a licensed rabies vaccine. Following observations of high reactogenicity when using the 5 μg dose of CV7202 we found 1 and 2 μg dosages were better tolerated, with no safety concerns and two doses elicited immune responses in terms of

Funding statement

The study was fully supported by CureVac AG.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors are grateful to all the participants in Munich and Ghent who volunteered for this study and to Dr Mirjam Schunk (Munich), Dr Cathy Maes (Ghent), and Dr Aurelio Garofano (CureVac), and the respective study teams, trial coordinators and nurses for their expert assistance. We thank Keith Veitch (keithveitch communications, Amsterdam, the Netherlands) for assistance in drafting the manuscript. This paper is dedicated to the memory of Professor Frank von Sonnenburg who passed away on 21

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    1

    Current address: Department of Molecular and Developmental Medicine, University of Siena, Italy.

    2

    In memory of Professor Frank von Sonnenburg.

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