Development of Silica-Immobilized Vaccines for Improving Thermo-Tolerance and Shelf-Life

Abstract

Introduction: It is estimated that 50% of vaccines produced annually are wasted because effectivity is dependent on protein structure and heat exposure disrupts the intermolecular interactions that maintain this structure. Since 90% of vaccines require a temperature-controlled supply chain, it is necessary to create a cold chain system to minimize vaccine waste. We have developed a more sustainable technology via the adsorption of Invasion Plasmid Antigen D (IpaD) onto mesoporous silica gels, improving the thermal stability of protein-based therapeutics.

Methods: The solution depletion method using UV-Vis was utilized to study the adsorption of IpaD onto silica gels. The silica-IpaD complex is heated above the denaturing temperature of the protein and then the IpaD is removed using N,N-Dimethyldodecylamine N-oxide (LDAO) and their secondary structure is tested using circular dichroism (CD).

Results: Pore diameter, pore volume and surface area were characterized for seven different silica gels. Silica gels designated as 6389, 6378, and 6375 had an adsorption percentage above 95% at pore volumes of 2.2, 2.8 and 3.8 cm³ mg-1, respectively. CD analyses confirmed that the adsorbed IpaD after the heat treatment displayed a similar "W" shape CD signal as the native IpaD, indicating the conservation of α-helices. In contrast, the unprotected IpaD after being exposed to high temperature shows a flat CD signal, demonstrating the loss of secondary structure.

Conclusion: We have successfully increased the thermo-tolerance for IpaD using mesoporous silica and continue to further optimize mesoporous silica's physiochemical properties to improve adsorption and desorption yields.

Keywords: IpaD protein; mesoporous silica; shigellosis; vaccines.

Figure 1

Hydrogen bonds between IpaD and mesoporous silica.

Figure 2

Average percent of IpaD adsorbed to mesoporous silica gel materials as a function of accessible pore volumes (cm³/g).

Figure 3

CD spectra for IpaD heated to 95°C for 150 minutes attached to silica gel 6339, native unheated IpaD, and IpaD denatured in PBS solution at 95°C for two hours. The blue curve is the average of 10 samples, and the green curve is the average of two samples.