Abstract
Conventional subunit vaccine regimes can be modified in order to stimulate strong immune responses resulting in memory cell formation. An adjuvant system that has gained increased attention in recent years is the use of particulate antigen delivery. Particulate systems have a number of advantages over conventional approaches since they are believed to be taken up preferentially by dendritic cells (DC) where they prolong the release of antigen resulting in enhanced T cell stimulation. Furthermore, they offer a versatile system that allows for targeted delivery of antigen and adjuvant to the same DC. A wide range of particle types have been used to enhance vaccine potency. Poly(lactic-co-glycolic) acid (PLGA), in particular, has been used successfully by many groups. However, there are a great variety of means to synthesise and characterise the desired particles. This study, firstly, set out to develop and optimise a protocol to generate nanoparticles with defined properties. A number of parameters were evaluated including, particle size, protein loading, protein coating and surface charge. In addition to conventional methods, such as electron microscopy and dynamic light scattering, particles were characterised by novel flow cytometric methods. While particles have been shown to adjuvant candidate vaccine proteins, this property should be enhanced when the particle is targeted to dendritic cells by increasing specific uptake. Specific targeting has previously been performed through either targeting with natural receptor ligands or monoclonal antibodies. However, there is currently conflicting data in other studies as to whether this can be achieved. It was thus the second objective of this study to devise methods to implement this technology and to determine whether targeting can be achieved through either approach. It was found that there was potential in targeting DC populations with monoclonal antibodies, while targeting with natural ligands yielded more mixed results. As a final component, the adjuvant properties of the particles rationally loaded with antigens and molecular adjuvant was tested in vivo in cattle using a viral challenge model. The experiment had a promising outcome with the vaccine particles inducing both T cell and antibody responses resulting in a degree of protection against virus challenge. Furthermore, it highlighted areas where the system, both the particles and the model, may be improved, which could form the basis of future work.