Adjuvant solution for pandemic influenza vaccine production

Extensive preparation is underway to mitigate the next pandemic influenza outbreak. New vaccine technologies intended to supplant egg-based production methods are being developed, with recombinant hemagglutinin (rHA) as the most advanced program for preventing seasonal and avian H5N1 Influenza. Increased efforts are being focused on adjuvants that can broaden vaccine immunogenicity against emerging viruses and maximize vaccine supply on a worldwide scale. Here, we test protection against avian flu by using H5N1-derived rHA and GLA-SE, a two-part adjuvant system containing glucopyranosyl lipid adjuvant (GLA), a formulated synthetic Toll-like receptor 4 agonist, and a stable emulsion (SE) of oil in water, which is similar to the best-in-class adjuvants being developed for pandemic flu. Notably, a single submicrogram dose of rH5 adjuvanted with GLA-SE protects mice and ferrets against a high titer challenge with H5N1 virus. GLA-SE, relative to emulsion alone, accelerated induction of the primary immune response and broadened its durability against heterosubtypic H5N1 virus challenge. Mechanistically, GLA-SE augments protection via induction of a Th1-mediated antibody response. Innate signaling pathways that amplify priming of Th1 CD4 T cells will likely improve vaccine performance against future outbreaks of lethal pandemic flu.H5N1 is a highly pathogenic avian influenza virus that can cause severe disease and death in humans, and world health authorities agree that the potential for pandemic H5N1 infection is high. Vaccination remains the most effective mechanism for preventing influenza, but there are complex challenges in implementing a pandemic preparedness plan, including: an inability to rapidly deploy the vast numbers of safe and effective doses needed on a worldwide scale; the fact that the immunogenicity of current nonadjuvanted H5N1 vaccines are relatively weak and require large antigen doses; and the potency of stockpiled prepandemic vaccines may be severely limited given the anticipated antigenic drift/shift associated with the emergence of a novel strain of pandemic H5N1.The US government has outlined provisions for new technologies that maximize immunogenicity and manufacturing capacity of vaccines for influenza, including the use of recombinant protein-based vaccines and adjuvants, which augment immunity and dose-sparing capacity. The most advanced egg-free flu vaccine candidate is a recombinant multimeric H5 hemagglutinin protein (rH5) produced by using a baculovirus expression vector system in SF+ insect cells (1, 2). Previous clinical studies suggested that two 90-μg doses of rH5 induced modest responses equivalent to conventional subvirion-based H5N1 vaccines (3, 4). This finding has prompted efforts to test rH5 with an adjuvant. Currently, the leading H5N1 vaccine adjuvants are oil-in-water (o/w) emulsions, which augment neutralizing antibody titers, increase the breadth of cross-reactive antibodies, and possess significant dose-sparing activity (5, 6). Importantly, these adjuvants are particularly effective in priming naïve individuals in the absence of preexisting memory.Vaccine adjuvants regulate adaptive immunity by stimulating dendritic cell maturation and antigen presentation (7, 8). A leading adjuvant target on DC is the family of innate Toll-like receptors, particularly the LPS receptor, Toll-like receptor 4 (TLR4). Glucopyranosyl lipid adjuvant (GLA) is a formulated form of the synthetic TLR4 agonist PHAD (Avanti Polar Lipids), which is analogous to the detoxified LPS derivative monophosphoryl lipid A (MPL), a component of the human papillomavirus vaccine Cervarix (9). Experimental vaccines containing GLA demonstrate enhanced immunogenicity in a variety of disease models (8), and in the context of influenza, GLA formulated in a stable emulsion (GLA-SE) improved Fluzone-dependent antibody titers in mice and nonhuman primates, relative to an emulsion alone (10–13). Given the critical importance of immunological priming for pandemic vaccine preparedness, we set out to test whether adjuvanting a recombinant H5 antigen with GLA-SE would broaden protective immunity against H5N1.