Immobilisation of GM-CSF onto particulate vaccine carrier systems.

Physical connection of vaccine carriers with immunostimulating cytokines may provide an interesting possibility to enhance the immune response of protective or therapeutic vaccines. As a first evaluation, various aluminium hydroxide adjuvants and poly(D,L-lactide-co-glycolide) (PLGA) microparticulates with modified positively and negatively charged surfaces were prepared to adsorb granulocyte-macrophage colony-stimulating factor (GM-CSF) under different pH conditions. Negatively charged surfaces were chosen to resemble physiological binding of GM-CSF to extracellular glycosaminoglycans, while modified positively charged surfaces may enhance GM-CSF adsorption due to electrostatic interaction. Release of GM-CSF was checked in vitro in a simulated interstitial environment. Anionic and cationic surfaces efficiently attracted GM-CSF to the carrier surface independently of the pH, while the composition of the carrier largely influenced the release of GM-CSF over time. Thus, the adsorption of GM-CSF to aluminium hydroxide adjuvants and PLGA microparticulates provides a simple and efficient possibility to physically connect the cytokine with these commonly used and potential vaccine carriers and may enable its localised delivery to the side of action.

Improved stimulation of human dendritic cells by receptor engagement with surface-modified microparticles.

Dendritic cells (DC) need to be stimulated before they can function to initiate immune responses. This study investigates whether microparticles loaded with antibodies specific for selected receptors expressed by DC can induce stimulation of these cells. Plain microparticles were compared with microparticles which were surface-loaded with specific antibodies for human CD40, Fc(gamma), alpha(v)beta3 and alpha(v)beta5 integrin receptors. The antibodies were either physically adsorbed or covalently linked to the microparticle surface. Anti-CD40 antibody and human IgG immobilised on the surface of microparticles induced enhanced DC maturation and activation as expressed by CD83 and CD86 upregulation. IL-12 secretion was induced at a detectable but relatively low level. Both anti-integrin antibodies (anti-alpha(v)beta3 and anti-alpha(v)beta5) induced comparable and considerable maturation of DC, but only anti-alpha(v)beta3 antibody induced significant activation of DC, whereas anti-alpha(v)beta5 did not. The stimulatory effects were most pronounced by employing microparticles with covalently linked antibodies, but were also observed to a minor extent when the antibodies were physically adsorbed to polystyrene and biodegradable poly(lactide-co-glycolide) microparticles. Engineering of microparticles by surface conjugation of specific ligands to stimulate DC may increase the effectiveness of microparticulate vaccine delivery systems.