A Randomised, Controlled, Phase 1 Study in Healthy Adults to Evaluate the Immunogenicity and Safety of a Recombinant H7 Hemagglutinin Influenza Vaccine

Because antibody responses to experimental H7 vaccine have been low even with high antigen doses, there is a need to find ways to enhance the effectiveness of H7 vaccines. Protein Sciences Corporation (PSC) produces an FDA approved seasonal recombinant trivalent influenza vaccine consisting of influenza hemagglutinin proteins (HA) which are full length uncleaved glycoproteins (rHA0) produced using baculovirus expression vectors in cultured insect cells grown in serum-free media (FluBlok®). The mechanism of action of FluBlok is the same as that of traditional inactivated seasonal influenza vaccines.

PanBlok H7 is a pandemic influenza vaccine produced by PSC in the same way as Flublok but it is directed against H7 rather than seasonal influenza virus strains. The vaccine candidate consists of a full-length recombinant monovalent hemagglutinin (rHA) derived from H7N9 virus, in a sterile solution for intramuscular injection. PanBlok H7 rHA is manufactured using the same production process as previously used for Panblok H1/2009pdm ("swine flu") and Panblok H5 pandemic vaccines, both of which vaccines have been previously successfully trialled by us in clinical protocols, FLU005 and FLU003. In both these trials the Panblok antigen was combined with Advax adjuvant formulations. In the FLU005 trial of Panblok H1N1/2009pdm vaccine, the inclusion of Advax adjuvant doubled the seroconversion rate of the vaccine and provided major antigen-sparing effects (Gordon et al, 2012). Whilst the FLU003 trial is ongoing, preliminary data again shows the importance of the Advax adjuvants to vaccine effectiveness. This provides a strong rationale for inclusion of Advax adjuvants in the Panblok H7 vaccine.

It has also been recently recognised that at least one of the reasons for the low immunogenicity of H7 vaccines in human trials to date is that the H7 antigen from this virus contains a T-cell regulatory epitope (Tregitope) in the HA stem region which suppresses the immune response to the vaccine. It was recently demonstrated in humanised animal studies undertaken by collaborators in Japan that removing this Tregitope by modifying 3 amino acids in the H7 stem was able to significantly increase the ability of the H7 vaccine to induce antibody production by human immune cells. This trial will provide the first opportunity to confirm this approach is able to enhance the immunogenicity of H7 in humans, which if confirmed would represent a major breakthough in pandemic influenza vaccine design.