Next generation yellow fever vaccine induces an equivalent immune and transcriptomic profile to the current vaccine: observations from a phase I randomised clinical trial.

Background: Yellow fever (YF), a mosquito-borne acute viral haemorrhagic illness, is endemic to many tropical and subtropical areas of Africa and Central and South America. Vaccination remains the most effective prevention strategy; however, as repeated outbreaks have exhausted vaccine stockpiles, there is a need for improved YF vaccines to meet global demand. A live-attenuated YF vaccine candidate (referred to as vYF) cloned from a YF-17D vaccine (YF-VAX®) sub-strain, adapted for growth in Vero cells cultured in serum-free media, is in clinical development. We report the innate and adaptive immune responses and the transcriptome profile of selected genes induced by vYF.
Methods: Healthy adults aged 18-60 years were randomised at a 1:1:1:1 ratio to receive one dose of vYF at 4, 5 or 6 Log CCID ₅₀ or YF-VAX (reference vaccine), administered subcutaneously in the upper arm (ClinicalTrials.gov identifier: NCT04142086). Blood/serum samples were obtained at scheduled time points through 180 days (D180) post-vaccination. The surrogate endpoints assessed were: serum cytokine/chemokine concentrations, measured by bead-based Multiplex assay; peripheral blood vYF-specific IgG and IgM memory B cell frequencies, measured by FluoroSpot assay; and expression of genes involved in the immune response to YF-17D vaccination by RT-qPCR.
Findings: There was no increase in any of the cytokine/chemokine concentrations assessed through D14 following vaccination with vYF or YF-VAX, except for a slight increase in IP-10 (CXCL10) levels. The gene expression profiles and kinetics following vaccination with vYF and YF-VAX were similar, inclusive of innate (antiviral responses [type-1 interferon, IFN signal transduction; interferon-stimulated genes], activated dendritic cells, viral sensing pattern recognition receptors) and adaptive (cell division in stimulated CD4+ T cells, B cell and antibody) immune signatures, which peaked at D7 and D14, respectively. Increases in vYF-specific IgG and IgM memory B cell frequencies at D28 and D180 were similar across the study groups.
Interpretation: vYF-induced strong innate and adaptive immune responses comparable to those induced by YF-VAX, with similar transcriptomic and kinetic profiles observed.
Funding: Sanofi.
Competing Interests: Declaration of interests AP, CC, MA, EC, SG, FR, EF, MV, and NM are Sanofi employees and hold shares and/or stock options in the company. PS and KM received funds from Sanofi through their institution (WRAIR) to support their work in the vYF01 trial. The opinions expressed herein are those of the authors and should not be construed as official or representing the views of the US Department of Defense or the Department of the Army.
(Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)