Ensilication of tetanus toxin C fragment for the development of thermostable vaccines

  • Aswin Doekhie

Student thesis: Doctoral ThesisPhD


The majority of vaccines consist of proteins derived from pathogens that, upon vaccination, provide humans with long-term immunity against infectious disease. Vaccine proteins are susceptible to environmental changes. Fluctuations in temperature are the foremost cause of protein degradation and will result in vaccines being ineffective. In short, many vaccines lack thermal stability. Vaccine manufacturer’s therefore store and transport vaccines under continuous refrigeration (2 – 8 °C), known as the “cold-chain”. This increases the longevity of vaccines but is also a very costly procedure. Studies have shown several operational problems within cold-chain and
this is reflected in the high prevalence of vaccine-preventable diseases, especially in developing countries.

This project investigated the application of a previously developed method, ensilication, to stabilise vaccine proteins with use of silica to prevent thermal denaturation. This could provide an alternative to freeze-drying (lyophilisation) as some vaccines use excipients to improve efficacy which makes them unsuitable for lyophilisation. The ‘sol-gel’ method on which ensilication is based uses an inorganic compound, tetra-ethyl ortho-silicate (TEOS), to produce a polymer particle which can link around and interact with biomolecules present in buffered aqueous solution. This protects against temporal fluctuations in dry powdered form. After storage, the ensilicated protein can be released using a chemical method that removes the silica shell. Recombinant tetanus toxin c fragment (TTCF) was the model protein (antigen) utilised here to establish the feasibility of vaccine ensilication.

Structural and physical analysis of ensilicated TTCF, pre- (native) and post-ensilication (released), showed the retention of protein structure and functional properties. Additionally, in vivo animal experiments confirmed retention of released TTCF immunogenicity in mice. This included ensilicated TTCF that was subjected to extreme heat, displaying the thermal resilience of ensilicated material. Finally, synchrotron small angle x-ray scattering (SAXS) experiments elucidated the mechanism of stabilisation. Overall, this study shows a promising application of ensilication for the development of thermostable vaccines.
Date of Award19 Jun 2019
Original languageEnglish
Awarding Institution
  • University of Bath
SponsorsAnnett Trust
SupervisorAsel Sartbaeva (Supervisor), Jean Van Den Elsen (Supervisor) & Francoise Koumanov (Supervisor)

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