Covalent conjugation of a TLR7/8 agonist to recombinant influenza A virus hemagglutinin provides enhanced immunogenicity and protection against disease from a drifted strain 9291

Description Effective immunization against a rapidly mutating pathogen such as influenza virus requires that protection extend to genetically drifted strains. Adjuvantation has the potential to provide this benefit. Toll-like receptors (TLR) 7 and 8 are homologous receptors that detect single-stranded RNA in the endosomal pathway, a hallmark of viral infections. These receptors can be engaged by synthetic, small molecule agonists that make promising adjuvant candidates, although such agents have shown unacceptable levels of toxicity when used as soluble, unbound molecules in the past. We have previously described a controlled method of covalently attaching small TLR7/8 agonists to proteins in order to enhance their immunogenicity while keeping toxicity in check. We used this technology to conjugate a TLR7/8 agonist to recombinant hemagglutinin trimers from an H7N9 strain (H7) of influenza A virus. When compared to administering the equivalent amount of agonist and protein in an admixed vaccine formulation, the conjugates enhanced the immune response, and most notably drove a Th1-mediated cellular response in mice. Although this was unnecessary for disease prevention after challenge with the homologous strain of H7N9, adjuvantation provided an advantage against a drifted strain, and only the conjugated adjuvant provided 100% survival. This establishes conjugation of a TLR7/8 agonist to protein antigen as a strategy to safely and efficiently expand protection against a viral pathogen.