Poster Presentation 8th Australasian Vaccines & Immunotherapeutics Development Meeting 2020

Bile acid-based delivery system for lipopeptide vaccine against Group A Streptococcus (#310)

Armira Azuar 1 , Lili Zhao 1 , Tsui Ting Hei 1 , Reshma Nevagi 1 , Stacey Bartlett 1 , Waleed Hussein 1 , Zeinab G. Khalil 2 , Robert J. Capon 2 , Istvan Toth 1 2 3 , Mariusz Skwarczynski 1
  1. School of Chemistry and Molecular Biosciences, The University of Queensland, St. Lucia, QUEENSLAND, Australia
  2. Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QUEENSLAND, Australia
  3. School of Pharmacy, The University of Queensland, Brisbane, QLD, Australia

Introduction: Group A Streptococcus (GAS) infection causes a variety of diseases in human, ranging from a benign throat infection to life-threatening rheumatic fever (RF) and rheumatic heart disease (RHD).  However, there is no vaccines currently available on the market. Due to the autoimmune response associated with M-protein (major virulent factor of GAS), modern peptide-based vaccines approach has been widely investigated to develop safe vaccine against GAS [1].  This peptide-based vaccine requires immunostimulant (adjuvant) and/or delivery system to protect the antigenic peptide from degradation and induce the desired immunity [2]. Adjuvants in the market are either too toxic for human use (experimental adjuvants) or they are limited to particular applications (commercial adjuvants) [3]. Thus, we designed vaccine candidates that utilise J8 B-cell epitope and PADRE T-helper epitopes that were anchored to liposome via cholic acid as an adjuvant-free vaccine candidate [4].

Methods: Cholic acid-conjugates were synthesized using Fmoc-SPPS and self-assembled to form nanoparticles in water. In addition, the conjugates were also incorporated into liposomes and extruded via a 100 nm membrane to form uniform unilamellar vesicles. The size, size distribution (PDI), surface charge, morphology, and stability vaccine candidates were characterized using DLS and TEM. Immunological evaluation of cholic acid-conjugate and cholic acid-liposome was performed in C57BL/6 mice using the prime-boost vaccination strategy. The vaccine candidates were delivered intranasally.  Antibodies produced by the immunized mice were measured and tested for their ability to opsonize different strains of GAS clinical isolates.

Results: Cholic acid-conjugate was successfully synthesized with high purity (>95%) and yield. Cholic acid conjugated to peptide epitope were able to self-assemble into rod-like nanoparticles. The conjugate was also incorporated into liposome. Both cholic acid-conjugate and cholic acid-liposomes were able to induce high J8-specific IgG titer that able to opsonize different GAS strains upon intranasal immunisation. Cholic acid was able to enhance the immune response of targeted antigen and show stronger adjuvanting capacity than traditional self-adjuvanting lipid.

Conclusion/Implications: Cholic acid (a human bile acid) upon conjugation to GAS B-cell epitope self-assembled into rod-like nanoparticles, which induced opsonic antibody production in mice. Thus, we have shown for the first time that human-derived lipid, cholic acid, can act as a built-in immunoadjuvant for simple intranasal vaccination.

  1. 1. Azuar, A., Jin, W., Mukaida, S., Hussein, W. M., Skwarczynski, M., and Toth, I.; “Recent advances in the development of peptide vaccines and their delivery systems against Group A Streptococcus”, Vaccines, 2019, 7, 58.
  2. 2. Skwarczynski, M.; Toth, I., “Peptide-based synthetic vaccines.” Chemical Science 2016, 7; pp. 842-854. Nevagi, R. J.; Toth, I.; Skwarczynski, M., Peptide-based vaccines. In Peptide Applications in Biomedicine, Biotechnology and Bioengineering; S. Koutsopoulos Ed.; Woodhead Publishing, 2018; pp. 327-358.
  3. 3. Azuar, A., Zhao, L., Hei, T. T., Nevagi, R. J., Bartlett S., Hussein, W. M., Khalil, Z. G., Capon, R. J., Toth, I., and Skwarczynski, M. “Cholic acid-based delivery system for vaccine candidates against Group A Streptococcus”, ACS Med. Chem. Lett., 2019, 10, pp. 1253−1259.