Ensilicated tetanus antigen retains immunogenicity: in vivo study and time-resolved SAXS characterization (2020)

A. Doekhie a, R. Dattani b, Y-C. Chen a, Y. Yang c, A. Smith d, A. P. Silve a, F. Koumanov e, S.A. Wells g, K.J. Edler a, K.J. Marchbank *c, J.M.H. van den Elsen *f and A. Sartbaeva *a

a Department of Chemistry, b European Synchrotron Research Facility, c Institute of Cellular Medicine, d Diamond Light Source, e Department for Health, f Department of Biology and Biochemistry, g Department of Chemical Engineering. *share senior authorship.

a, e, f, g University of Bath, Claverton Down, Bath, BA2 7AY, United Kingdom.

b ESRF, 71 avenue des Martyrs, CS 40220, 38043 Grenoble Cedex 9, France.

c Newcastle University, Medical School, Newcastle upon Tyne, NE2 4HH, United Kingdom.

d Diamond Light Source Ltd, Harwell Campus, Didcot, OX11 0DE, United Kingdom.

Our recently developed ensilication approach can physically stabilize proteins in silica without use of a pre-formed particle matrix. Stabilisation is done by tailor fitting individual proteins with a silica coat using a modified sol-gel process. Biopharmaceuticals, e.g. liquid-formulated vaccines with adjuvants, frequently have poor thermal stability; heating and/or freezing impairs their potency. As a result, there is an increase in the prevalence of vaccine-preventable diseases in low-income countries even when there are means to combat them. One of the root causes lies in the problematic vaccine ‘cold-chain’ distribution. We believe that ensilication can improve vaccine availability by enabling transportation without refrigeration. Here, we show that ensilication stabilizes tetanus toxin C fragment (TTCF), a component of the tetanus toxoid present in the diphtheria, tetanus and pertussis (DTP) vaccine. Experimental in vivo immunization data show that the ensilicated material can be stored, transported at ambient temperatures, and even heat-treated without compromising the immunogenic properties of TTCF. To further our understanding of the ensilication process and its protective effect on proteins, we have also studied the formation of TTCF-silica nanoparticles via time-resolved Small Angle X-ray Scattering (SAXS). Our results reveal ensilication to be a staged diffusion-limited cluster aggregation (DLCA) type reaction. An early stage (tens of seconds) in which individual proteins are coated with silica is followed by a subsequent stage (several minutes) in which the protein-containing silica nanoparticles aggregate into larger clusters. Our results suggest that we could utilize this technology for vaccines, therapeutics or other biopharmaceuticals that are not compatible with lyophilization.

DOI: https://doi.org/10.1038/s41598-020-65876-3 – Scientific Reports