Safety and immunogenicity of a prototype recombinant alpha-like protein subunit vaccine (GBS-NN) against Group B Streptococcus in a randomised placebo-controlled double-blind phase 1 trial in healthy adult women

Abstract

Background: Group B Streptococcus (GBS) is the leading cause of life-threatening infections in new-borns and may cause invasive disease, stillbirth and preterm delivery during pregnancy. While no licensed vaccine exists, maternal immunization might protect against neonatal disease and adverse pregnancy outcomes. We assessed the safety and immunogenicity of a prototype vaccine consisting of the fused N-terminal domains of the AlphaC and Rib surface proteins of GBS (GBS-NN).

Methods: GBS-NN was tested in a randomised, double-blind, placebo-controlled, parallel group, phase I study, in healthy non-pregnant women. A dose-escalation phase, with two doses, four weeks apart, of 10, 50 or 250 µg, administered with or without aluminium hydroxide, was initially assessed (n = 60). This was followed by a dose-confirmation study, where one dose of 100 µg adjuvanted GBS-NN was compared with two doses of either 50 or 100 µg adjuvanted GBS-NN, again administered with four weeks interval between the doses (n = 180). Safety and immunogenicity were monitored for one year.

Results: GBS-NN was well tolerated with some, mostly mild, injection site reactions observed. Adjuvant significantly increased antibody concentrations and the response was boosted by a second dose. The IgG GMCs remained strongly elevated during the whole one-year duration of the study. Maximal responses occurred after two 50 µg doses, resulting in IgG GMC of 16.9 µg/ml at the primary immunological endpoint, twelve weeks after the first dose. For this regimen, 100% and 89% of the subjects achieved antibody levels above the arbitrary thresholds of 1 and 4 µg/ml, respectively. The added beneficial effect of a second dose was most pronounced for subjects with pre-existing IgG levels below the median of the entire cohort.

Conclusion: The prototype GBS-NN vaccine was found to be well tolerated and highly immunogenic with an optimal regimen of two doses of 50 µg in the presence of adjuvant. Further development of a maternal vaccine based on the N-terminal domains of the alpha-like protein family of GBS is warranted (NCT02459262).

Keywords: Antibodies; Group B Streptococcus; Maternal vaccination.

Conflict of interest statement

Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Dr. Fischer reports grants and personal fees from MinervaX ApS, during the conduct of the study; personal fees from MinervaX ApS, outside the submitted work; In addition, Dr. Fischer has a Patent Applications relating to the use of GBS-NN as a vaccine candidate pending. Dr. Johansson-Lindbom reports personal fees from MinervaX ApS, grants from MinervaX ApS, during the conduct of the study. Dr. Darsley reports personal fees from MinervaA ApS, during the conduct of the study. Dr. Kitson reports personal fees from MinervaX ApS, during the conduct of the study; personal fees from Various clients, outside the submitted work. Dr. Pawlowski, Dr. Cao and Dr. Bell have nothing to disclose.

Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.