RATIONAL DESIGN AND DEVELOPMENT OF CONTROLLED RELEASE SYSTEMS FOR NEW GENERATION VACCINES

Although vaccines are one of the most cost-effective prophylactic treatment1, some limitations reducing the worldwide coverage in both high- and low-income countries haven’t been overcome yet. Vaccines must be typically administered exploiting multiple-shot administration schedules to better activate the immune system. These administration schedules increase the distribution costs and logistical complexity of vaccines products. Moreover, having to administer multiple injections often decreases a patient's willingness to follow the treatment schedule, and generally, their adherence to the regimen. Single dose administration vaccines would help overcoming these limitations also increasing their cost-effectiveness and diffusion. Indeed, it was demonstrated that using sustained administration strategies induces a potent immune response in accordance with the prolonged antigen presentation to the germinal centres. The sustained exposure of the antigen to the immune cells better activates memory B cells and favour a stronger production of broadly neutralizing antibodies. This PhD project investigates the exploitation of Poly(lactic-co-glycolic acid) (PLGA) microparticles to develop an innovative single dose administration vaccine. PLGA polymer was selected in accordance with its biodegradability, biocompatibility and because the polymer is already approved for parenteral administration. Two different antigen models (i.e. ANT 1 and ANT 2) were selected to compare the effectiveness of the sustained administration strategy in both protein and glycoconjugate antigens. Initially, the two model antigens were exposed to physiological conditions (i.e. 37 °C at pH 7.4 for 14 days) to investigate their stability and suitability for prolonged administration (e.g. continuous administration through osmotic pumps (OPs) subcutaneously implanted). In vivo studies testing sustained administration schedules (i.e. fractionated administrations and osmotic pump systems) were performed in mice. Fractionated administrations of one dose the glycoconjugate model antigen (ANT1) induced a comparable immune response with respect to the classical prime + booster two-dose administration. However, when the recombinant protein antigen model (ANT2) was tested, the antibodies titres triggered by both fractionated injections and osmotic pumps were lower when compared with prime + booster administration schedule. Next, biodegradable PLGA-based microparticles were co-formulated with model antigens together with various other excipients to modulate the microparticles morphology, the antigen’s release speed and its stability. PLGA microparticles with different release kinetics were obtained; however, only the glycoconjugate model antigen (ANT1) resulted to be sufficiently stable when encapsuled in the PLGA system to be further investigated in in vivo studies. The microparticles were therefore tested in vivo in mice comparing the single microparticles administration with the classical prime + booster injection schedule. The single administration of the glycoconjugate model antigen (ANT1) loaded microparticles elicited an IgGs titre comparable to the one obtained with the double of dosage administered using the two shots administration schedule, supporting the initial hypothesis that antigen’s sustained release may enable the streamlining of the vaccine’s administration schedule and potentially may offer the opportunity of a single-dose administration. In conclusion, even if ANT 2 antigen results suggest that PLGA particles may be compatible only with some antigens models, the very positive results obtained testing ANT 1 microparticles in vivo demonstrated that this technology could be a successful strategy to obtain single administration vaccines with antigens sufficiently stable in the formulation conditions.