  Ensilication is a technology we developed that can physically stabilise
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, for example, liquid-formulated
vaccines with adjuvants, have poor thermal stability. Heating 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 stabilises tetanus toxoid C fragment (TTCF) and demonstrate
that this material can be stored and transported at ambient temperature without
compromising the immunogenic properties of TTCF in vivo. TTCF is a component of
the diphtheria, tetanus and pertussis (DTP) vaccine. To further our
understanding of the ensilication process, and its protective effect on
proteins we have 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, induced by the presence of TTCF protein at neutral pH. Analysis of
scattering data indicates tailor fitting of TTCF protein. The experimental in
vivo immunisation data confirms the retention of immunogenicity after release
from silica. Our results suggest that we could utilise this technology for
multicomponent vaccines, therapeutics or other biopharmaceuticals that are not
compatible with lyophilisation.
