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

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.

Keywords: Lipid nanoparticles; Rabies; Vaccine; mRNA.

Fig. 1

Trial profile.

Fig. 2

Geometric mean virus neutralizing titers (with 95% CI) in the four study groups after immunization (indicated by arrows) with CV7202 or Rabipur. Dashed line indicates level considered adequate by the WHO (0.5 IU/mL).

Fig. 3

Responder rates (percentages of each group with a VNT ≥ 0.5 IU/mL) in the four study groups after immunization with CV7202 or Rabipur. Rates represent the numbers of participants achieving the protective VNT of 0.5 IU/mL. The 1 and 2 μg CV7202 groups consisted of 16 participants each for Days 8, 15 and 29, and 8 participants each for Days 36, 43 and 57. The 5 μg CV7202 group consisted of 10 participants for Days 8 and 15, 9 participants for Days 29, 36, 43 and 57. The Rabipur group had 10 participants at each timepoint.

Fig. 4

GMTs (with 95% CI) of RABV-G-specific Ig responses assessed by ELISA. IgG concentrations after immunization with one (red arrow) or two (open arrow) doses of CV7202 or three doses of Rabipur (blue arrows). Dotted lines indicate LLOQ. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 5

Correlation of titers of RABV-G-specific neutralizing activity (VNT) and IgG antibodies after one or two doses of CV7202.