Enhanced immunogenicity of recombinant pneumococcal protein delivered using thermostable polymer particles

Abstract

Polymer particle-based delivery systems are safe and biocompatible approach to improve the properties of vaccine candidates. The existing pneumococcal vaccines require chemical conjugation step and cold chain storage which make them highly expensive and inaccessible to resource limited settings. Protein based vaccines are the next cohort for pneumococcal disease, however, they tend to be weakly immunogenic and need adjuvants as well as multiple doses to provide protective immune response. In this study, two conserved pneumococcal vaccine candidates namely, PsaA and PspA, were entrapped into polymer particles of different sizes prepared by double emulsion solvent evaporation method. In vitro studies indicated differences in release pattern and interaction with macrophage cells apart from size and surface charge. Nonetheless, both sized particles were able to enhance the antibody response without the use of adjuvant. Moreover, particle-based immunization sustained the antibody response and elicited secondary response after four months of single point immunization. Polymer particles possess better temperature stability and could be stored outside cold chain without any appreciable loss of immunogenicity. Thus, using pneumococcal protein-based polymer particles as vaccine candidate offer a safe and cost-effective approach which could reduce reliance on cold chain and increase their access to developing nations.