The TLR7/8 agonist INI-4001 enhances the immunogenicity of a Powassan virus-like-particle vaccine

Crawford, M. W.; Abdelwahab, W. M.; Siram, K.; Parkins, C. J.; Harrison, H. F.; Osman, S. R.; Schweitzer, D.; Evans, J. T.; Burkhart, D. J.; Pinto, A. K.; Brien, J. D.; Smith, J. L.; Hirsch, A. J.

doi:10.1101/2024.11.28.625832

bioRxiv · 10.1101/2024.11.28.625832

The TLR7/8 agonist INI-4001 enhances the immunogenicity of a Powassan virus-like-particle vaccine

Crawford, M. W.·Abdelwahab, W. M.·Siram, K.·Parkins, C. J.·Harrison, H. F.·Osman, S. R.·Schweitzer, D.·Evans, J. T.·Burkhart, D. J.·Pinto, A. K.·Brien, J. D.·Smith, J. L.·Hirsch, A. J.

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Abstract

Powassan virus (POWV) is a pathogenic tick-borne flavivirus that causes fatal neuroinvasive disease in humans. There are currently no approved therapies or vaccines for POWV infection. Here, we develop a POW virus-like-particle (POW-VLP) based vaccine adjuvanted with the novel synthetic Toll-like receptor 7/8 agonist INI-4001. We demonstrate that INI-4001 outperforms both alum and the Toll-like receptor 4 agonist INI-2002 in enhancing the immunogenicity of a dose-sparing POW-VLP vaccine in mice. INI-4001 increases the magnitude and breadth of the antibody response as measured by whole-virus ELISA, induces neutralizing antibodies measured by FRNT, reduces viral burden in the brain of infected mice measured by RT qPCR, and confers 100% protection from lethal challenge with both lineages of POWV. We show that the antibody response induced by INI-4001 is more durable than standard alum, and 80% of mice remain protected from lethal challenge 9-months post-vaccination. Lastly, we show that the protection elicited by INI-4001 adjuvanted POW-VLP vaccine is unaffected by either CD4+ or CD8+ T cell depletion and can be passively transferred to unvaccinated mice indicating that protection is mediated through humoral immunity. This study highlights the utility of novel synthetic adjuvants in VLP-based vaccines. Author summaryPowassan virus (POWV) is an emerging pathogenic tick-borne flavivirus for which there is no vaccine. Current tick-borne flavivirus vaccines are less than ideal and use formalin-inactivated virus adjuvanted with alum. These vaccines require thorough inactivation of the antigen and frequent boosting to maintain immunity. In this study, we describe the development of a POWV vaccine using Powassan virus-like-particles (POW-VLPs) adjuvanted with either of two novel Toll-like receptor (TLR) agonists, the TLR4 agonist INI-2002 or the TLR7/8 agonist INI-4001. We show that INI-4001 enhances the antibody response, reduces POWV neuroinvasion, and elicits full protection from lethal POWV infection in mice prime-boost vaccinated with low doses of POW-VLP. We further show that this protection is mediated by a humoral immune response which is both broader and more durable than a POW-VLP vaccine formulated with alum. These findings demonstrate the effectiveness of the novel synthetic TLR7/8 agonist INI-4001 as an adjuvant for low-dose VLP-based vaccines and the ability of this vaccine platform to improve upon current tick-borne flavivirus vaccine methodology.

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Crawford, M. W., Abdelwahab, W. M., Siram, K., Parkins, C. J., Harrison, H. F., Osman, S. R., Schweitzer, D., Evans, J. T., Burkhart, D. J., Pinto, A. K., Brien, J. D., Smith, J. L., Hirsch, A. J.. 2024-12-03. The TLR7/8 agonist INI-4001 enhances the immunogenicity of a Powassan virus-like-particle vaccine. https://doi.org/10.1101/2024.11.28.625832

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