6″-Modifed α-GalCer-peptide conjugate vaccine candidates protect against liver-stage malaria.

Self-adjuvanting vaccines consisting of peptide epitopes conjugated to immune adjuvants are a powerful way of generating antigen-specific immune responses. We previously showed that a Plasmodium -derived peptide conjugated to a rearranged form of α-galactosylceramide (α-GalCer) could stimulate liver-resident memory T (T _RM ) cells that were effective killers of liver-stage Plasmodium berghei ANKA (Pba)-infected cells. To investigate if similar or even superior T _RM responses can be induced by modifying the α-GalCer adjuvant, we created new conjugate vaccine cadidates by attaching an immunogenic Plasmodium -derived peptide antigen to 6″-substituted α-GalCer analogues. Vaccine synthesis involved developing an efficient route to α-galactosylphytosphingosine (α-GalPhs), from which the prototypical iNKT cell agonist, α-GalCer, and its 6″-deoxy-6″-thio and -amino analogues were derived. Attaching a cathepsin B-cleavable linker to the 6″-modified α-GalCer created pro-adjuvants bearing a pendant ketone group available for peptide conjugation. Optimized reaction conditions were developed that allow for the efficient conjugation of peptide antigens to the pro-adjuvants via oxime ligation to create new glycolipid-peptide (GLP) conjugate vaccines. A single dose of the vaccine candidates induced acute NKT and Plasmodium -specific CD8 ⁺ T cell responses that generated potent hepatic T _RM responses in mice. Our findings demonstrate that attaching antigenic peptides to 6″-modifed α-GalCer generates powerful self-adjuvanting conjugate vaccine candidates that could potentially control hepatotropic infections such as liver-stage malaria.
Competing Interests: The authors declare the following competing financial interest(s): G. F. P. and I. F. H. are the chief technical officer and chief scientific officer (respectively) of Avalia Immunotherapies Limited, and W. R. H. is a member of its Scientific Advisory Board. Avalia holds exclusive, worldwide license to patents related to aspects of the chemical design reported here. R. J. A., I. F. H., G. F. P., and B. J. C. are inventors on a granted patent (U.S. patent no. 10046046, granted 14 August 2018). B.J.C., R.J.A., I.F.H., G. F. P., L. E. H., and W. R. H. are named inventors on a PCT application (PCTNZ2020050048) submitted by Victoria University of Wellington, Malcorp Biodiscoveries Limited, and Victoria Link Limited that covers the production of tissue-resident memory T cells with glycolipid-peptide vaccines.
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