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.