Immunogenicity of chimeric haemagglutinin-based, universal influenza virus vaccine candidates: interim results of a randomised, placebo-controlled, phase 1 clinical trial

Abstract

Background: Influenza viruses cause substantial annual morbidity and mortality globally. Current vaccines protect against influenza only when well matched to the circulating strains. However, antigenic drift can cause considerable mismatches between vaccine and circulating strains, substantially reducing vaccine effectiveness. Moreover, current seasonal vaccines are ineffective against pandemic influenza, and production of a vaccine matched to a newly emerging virus strain takes months. Therefore, there is an unmet medical need for a broadly protective influenza virus vaccine. We aimed to test the ability of chimeric H1 haemagglutinin-based universal influenza virus vaccine candidates to induce broadly cross-reactive antibodies targeting the stalk domain of group 1 haemagglutinin-expressing influenza viruses.

Methods: We did a randomised, observer-blinded, phase 1 study in healthy adults in two centres in the USA. Participants were randomly assigned to one of three prime-boost, chimeric haemagglutinin-based vaccine regimens or one of two placebo groups. The vaccine regimens included a chimeric H8/1, intranasal, live-attenuated vaccine on day 1 followed by a non-adjuvanted, chimeric H5/1, intramuscular, inactivated vaccine on day 85; the same regimen but with the inactivated vaccine being adjuvanted with AS03; and an AS03-adjuvanted, chimeric H8/1, intramuscular, inactivated vaccine followed by an AS03-adjuvanted, chimeric H5/1, intramuscular, inactivated vaccine. In this planned interim analysis, the primary endpoints of reactogenicity and safety were assessed by blinded study group. We also assessed anti-H1 haemagglutinin stalk, anti-H2, anti-H9, and anti-H18 IgG antibody titres and plasmablast and memory B-cell responses in peripheral blood. This trial is registered with ClinicalTrials.gov, number NCT03300050.

Findings: Between Oct 10, 2017, and Nov 27, 2017, 65 participants were enrolled and randomly assigned. The adjuvanted inactivated vaccine, but not the live-attenuated vaccine, induced a substantial serum IgG antibody response after the prime immunisation, with a seven times increase in anti-H1 stalk antibody titres on day 29. After boost immunisation, all vaccine regimens induced detectable anti-H1 stalk antibody (2·2-5·6 times induction over baseline), cross-reactive serum IgG antibody, and peripheral blood plasmablast responses. An unsolicited adverse event was reported for 29 (48%) of 61 participants. Solicited local adverse events were reported in 12 (48%) of 25 participants following prime vaccination with intramuscular study product or placebo, in 12 (33%) of 36 after prime immunisation with intranasal study product or placebo, and in 18 (32%) of 56 following booster doses of study product or placebo. Solicited systemic adverse events were reported in 14 (56%) of 25 after prime immunisation with intramuscular study product or placebo, in 22 (61%) of 36 after immunisation with intranasal study product or placebo, and in 21 (38%) of 56 after booster doses of study product or placebo. Disaggregated safety data were not available at the time of this interim analysis.

Interpretation: The tested chimeric haemagglutinin-based, universal influenza virus vaccine regimens elicited cross-reactive serum IgG antibodies that targeted the conserved haemagglutinin stalk domain. This is the first proof-of-principle study to show that high anti-stalk titres can be induced by a rationally designed vaccine in humans and opens up avenues for further development of universal influenza virus vaccines. On the basis of the blinded study group, the vaccine regimens were tolerable and no safety concerns were observed.

Funding: Bill & Melinda Gates Foundation.

Figure 1

Schematic of the chimeric HA vaccination regimens and trial design (A) Vaccination strategy. Adults have pre-existing antibodies targeting both the membrane-distal head domain (top) and the membrane-proximal stalk domain (bottom) of H1 HA (green) due to previous exposure to influenza viruses. Vaccination with a chimeric H8/1 construct is expected to elicit some antibodies against the head domain (yellow), to which humans are naive, while substantially boosting H1 stalk antibodies. An additional booster vaccination with chimeric H5/1 HA was expected to provide an additional increase in antibodies targeting the HA stalk domain. Structures were adapted from RCSB Protein Data Bank ID 1RU7 and visualised in Protein Workshop.12 (B) Vaccination and blood collection schedule. (C) A phylogenetic tree based on percentage amino acid difference was constructed to illustrate the evolutionary distance of the antigens used for the ELISA analysis. The H1 (blue) stalk domain was used in the vaccines. H2 is closely related to H1, whereas H9 and H18 (all highlighted in green) are distantly related HAs within influenza A group 1. HA subtypes that donated heads to the vaccine constructs (H5 and H8) are shown in purple. Group 1 HAs are shaded in purple and group 2 in orange. HA clades are indicated within the groups. The scale bar represents a 5% difference in amino acid sequence. IIV=inactivated influenza vaccine. LAIV=live-attenuated influenza vaccine. PBS=phosphate-buffered saline. HA=haemagglutinin.

Figure 2

Trial profile Randomisation into inpatient (LAIV8-IIV5/AS03, LAIV8-IIV5, and sterile saline placebo control) and outpatient (IIV8/AS03-IIV5/AS03 and phosphate buffered saline placebo control) groups is shown. ^*66 randomly assigned, with one ineligible participant included in error and excluded after randomisation.

Figure 3

Titres of antibodies targeting the H1 stalk domain and heterosubtypic group 1 haemagglutinins Geometric mean ELISA antibody titres (ELISA units per mL) are plotted on the y axis (log₁₀) for the timepoints indicated on the x axis. Error bars show the upper and lower limits of the 95% CIs. Vaccination timepoints for the LAIV8-IIV5/AS03, LAIV8-IIV5, IIV8/AS03-IIV5/AS03, and PBS groups are indicated below the x-axis. Group sizes are 19 for the LAIV8-IIV5/AS03 group, 14 for the LAIV8-IIV5 group, 15 for the IIV8/AS03-IIV5/AS03 group, and ten for the PBS group. IIV=inactivated influenza vaccine. LAIV=live-attenuated influenza vaccine. PBS=phosphate-buffered saline.

Figure 4

Plasmablast and memory B-cell responses to the H1 stalk and wild-type H1 haemagglutinins The error bars indicate the upper and lower limits of the 95% CIs. The lower limit of detection was four spot forming units per 10⁶ PBMCs. Plasmablasts were tested for H1 stalk-specific IgG (A), IgA (C), and Cal09 H1 IgA plus IgG (E) secretion on days 8 and 92 (7 days after vaccination). Memory B cells were tested for H1 stalk-specific IgG (B), IgA (D), and Cal09 H1 IgA plus IgG (F) secretion on days 1, 29, 85, and 113 (vaccination timepoints and 4-week post-vaccination timepoints). Group sizes are 19 for the LAIV8-IIV5/AS03 group, 14 for the LAIV8-IIV5 group, 15 for the IIV8/AS03-IIV5/AS03 group, and ten in the PBS group. IIV=inactivated influenza vaccine. LAIV=live-attenuated influenza vaccine. PBMC=peripheral blood mononuclear cells. PBS=phosphate-buffered saline.