Pandemic preparedness: Addition of TLR agonists CpG+MPLA to emulsified H5 confers protection against H5N1 challenge after a single dose.

Abstract

Abstract H5N1 vaccines adjuvanted in the oil-in-water emulsion MF59 are maintained in the Strategic National Stockpile for pre-pandemic preparedness. The US population are currently naïve to H5 and a prime/boost regimen will likely be needed to engender a protective response. Ideally, a rapid response to pandemic influenza would benefit from being able to induce protection from a single dose of vaccine. Here, we have used a systems immunology approach in mice to examine the effect of formulating recombinant H5 in AddaVax alone or AddaVax with CpG+MPLA. AddaVax emulsion alone does not stimulate the innate immune system, although the oil droplets do act as a nanocarrier for antigen and enhance B cell activation, presumably by BCR cross-linking. In vitro, germinal center reactions show inclusion of CpG+MPLA to the emulsion (a combination adjuvant we call IVAX-1) synergize to enhance B cell maturation and class-switching. Similarly, in vivo, the combination of H5/IVAX-1 enhances both H5-specific B and T cell responses compared to individual components. Single cell mRNA sequencing of spleen cells after a boost indicate responses to H5/CpG+MPLA and H5/IVAX-1 are more similar to each other but distinct from H5/AddaVax or H5/PBS. Unexpectedly, H5/AddaVax, H5/CpG+MPLA and H5/IVAX-1 all engendered 100% efficacy against lethal intranasal challenge of H5N1 virus, although only H5/IVAX-1 engendered 100% protection after a single dose. Our data indicate the potential for certain combination adjuvants to enhance the immunogenicity of influenza vaccines and achieve efficacy from single dose vaccination. Supported by AI160397. NIAID Grant AI160397