Encapsulation of antigen in poly(D,L-lactide-co-glycolide) microspheres protects from harmful effects of γ-irradiation as assessed in mice

During the last two decades, synthetic polymers such as poly(lactide-co-glycolide) (PLGA) have been investigated for the development of nano- or microparticles as adjuvants or antigen vehicles. To enable transfer of this technology to human settings, the issue of sterilisation is of central importance. Since most polymers are heat-sensitive, sterilisation of polymeric microspheres for parenteral administration is assured either by costly and laborious aseptical preparation or the more preferred gamma-irradiation. Many studies have investigated the effect of gamma-irradiation on various physiochemical properties of the microspheres, but investigations on immunological effects are rare. We prepared poly(lactide-co-glycolide) (PLGA) microspheres containing ovalbumin (OVA) and tested the effect of gamma-irradiation on the various immunological properties in mice. For reference, OVA was gamma-irradiated and tested equivalently. The ability of encapsulated or non-encapsulated OVA to trigger activation of dendritic cells (DCs) was not affected by irradiation. However, while gamma-irradiation of free OVA strongly influenced the antigen presentation, encapsulated OVA was not affected by irradiation. gamma-Irradiation of OVA also reduced the immunogenicity in mice with regard to OVA-specific IgG1 production. In contrast, the antibody and the T-cell responses in mice immunised with PLGA-encapsulated OVA were similar irrespective of the gamma-irradiation status. Hence, encapsulation of antigen into PLGA microspheres protects antigen from the potential detrimental effect of gamma-irradiation leading to inactivation or altered immunogenicity. Sterilisation by gamma-irradiation therefore enables a cost-effective production of PLGA-based antigen-delivery systems as compared to the more laborious and expensive aseptical production of such vaccines. (C) 2011 Elsevier B.V. All rights reserved.