Development of VAX128, a recombinant hemagglutinin (HA) influenza-flagellin fusion vaccine with improved safety and immune response.

BACKGROUND: We evaluated the safety and immunogenicity profiles of 3 novel influenza vaccine constructs consisting of the globular head of the HA1 domain of the Novel H1N1 genetically fused to the TLR5 ligand, flagellin. HA1 was fused to the C-terminus of flagellin in VAX128A, replaced the D3 domain of flagellin in VAX128B and was fused in both positions in VAX128C. METHODS: In a dose escalation trial, 112 healthy subjects 18-49 and 100 adults ≥65 years old were enrolled in a double blind, placebo controlled clinical trial at two centers. Vaccines were administered IM at doses ranging from 0.5 to 20 µg. VAX128C was selected for second study performed in 100 subjects 18-64 years old comparing 1.25 and 2.5 µg doses. All subjects were followed for safety and sera collected pre- and post-vaccination were tested by hemagglutination-inhibition (HAI). Serum C-reactive protein and cytokine levels were also measured. CONCLUSIONS: In the first study high HAI titers and high seroconversion and seroprotection rates were observed at doses ≥2.5 µg in adults 18-49. In adults ≥65 years, the vaccines doses of ≥4 µg were required to induce a ≥4-fold rise in HAI titer, 50% seroconversion and 70% seroprotection. Based on safety, VAX128A was tested up to 8 µg, VAX128B to 16 µg and VAX128C to 20 µg. Dose escalation for VAX128A was stopped at 8 µg because one subject had temperature 101.6°F associated with a high CRP response, VAX128B was stopped at 16 µg because of a severe AE associated with a high CRP and IL-6 response. VAX128C was not stopped before reaching the 20 µg dose. In the second study VAX128C was well tolerated among 100 subjects who received 1.25 or 2.5 µg. The peak GMT was 385 (95%CI 272-546), 79% (71-87%) seroconversion and 92% (84-96%) seroprotection. DISCUSSION: Flagellin adjuvanted vaccines can be designed to minimize reactogenicity and retain immunogenicity, thereby representing a promising next generation vaccine technology.

Induction of a potent immune response in the elderly using the TLR-5 agonist, flagellin, with a recombinant hemagglutinin influenza-flagellin fusion vaccine (VAX125, STF2.HA1 SI).

BACKGROUND: Influenza vaccines perform poorly in the elderly with reduced serological response and vaccine efficacy. We evaluated a novel influenza vaccine consisting of the globular head of the HA1 domain of the A/Solomon Islands/3/2006 (H1N1) influenza virus (VAX125) genetically fused to the TLR5 ligand, flagellin, and produced in Escherichia coli. METHODS: 120 subjects ≥ 65 years old were enrolled at three clinical centers. VAX125 vaccine was administered at doses of 0.5, 1, 2, 3, 5 or 8 µg delivered i.m. as a single dose vaccination on Day 0 using a dose-escalation with 20 subjects in each dose level. Subjects were followed for adverse events and sera were tested by hemagglutination-inhibition (HAI) against egg-grown virus on days 0, 7, 14, and 28. Serum C-reactive protein (CRP) and anti-flagellin antibody were also assessed. RESULTS: The mean age was 71 years. The vaccine was well tolerated at all dose levels, with no more than mild to moderate local or systemic symptoms. The geometric mean titers (GMT) increased in all dose groups. In the 5 µg group the day 14 post-vaccination HAI titer was 1:226 showing a 12-fold increase over baseline. The 8 µg group showed a similar post-vaccination GMT increase (∼ 8-fold). In the combined 5 and 8 µg groups, the seroconversion rate was 75% and the seroprotection rate was 98%. CONCLUSIONS: A 5 µg dose of VAX125 was safe and able to induce a greater than 10-fold increase HAI antibody levels and nearly complete seroprotection in subjects over 65 years old. The use of flagellin to adjuvant influenza vaccines via the TLR5 innate immune pathway appears to be a useful approach to overcome poor immune responses in the elderly. VAX125 is a promising new candidate for prevention of influenza A disease in both young adults and the elderly.