J. Pharm. Pharmacol. 2000, 52: 1195±1201 # 2000 J. Pharm. Pharmacol. Received March 27, 2000 Accepted June 9, 2000 Biodegradable Microparticles with Different Release Pro®les: Effect on the Immune Response After a Single Administration via Intranasal and Intramuscular Routes IAN D. SPIERS, JIM E. EYLES, LES W. J. BAILLIE*, E. DIANE WILLIAMSON* AND H. O. ALPAR Pharmaceutical Sciences Institute, Aston University, Birmingham, B4 7ET and *DERA (Chemical and Biological Defence Sector), Porton Down, Salisbury, Wilts, SP4 0JQ, UK Abstract In the development of single-dose microparticulate vaccines, identi®cation of the type of protein release pro®le required to elicit high and sustainable immune responses is important. Microparticles exhibiting different protein release pro®les (continuous, pulsatile and plateau) were made by solvent evaporation or solvent extraction methods from biodegradable polymers encapsulating the model antigen, bovine serum albumin (BSA). The immune responses obtained after a single intranasal or intramuscular administration of microparticles were determined, and also after a subcutaneous boost after 11 months. Microparticles were manufactured with acceptable protein loading and average volume size ranging from 1 to 10 mm. The integrity of BSA extracted and released from micro- particles after 2 months incubation was retained. Microparticulate preparations adminis- tered by either intranasal or intramuscular routes, evoked rapid, high titre and long-lived (up to 11 months after priming) speci®c serum IgG responses which were signi®cantly greater than for free BSA. The type of protein release from microparticles had no signi®- cant effect on the systemic immune responses. Interestingly, a formulation exhibiting a plateau-release pro®le was the only microparticulate system capable of inducing sig- ni®cantly greater IgA responses than free BSA after intranasal immunization. This study shows the bene®t of microencapsulation in inducing high and long-lasting systemic immune responses after a single dose by both parenteral and mucosal delivery. We conclude that of the microparticles tested, the longevity and magnitude of humoral responses was not effected by the type of in-vitro protein release pro®le. Advances in biotechnology have led to a new generation of potential vaccines called subunit antigens. These highly puri®ed proteins are less toxigenic than current vaccines produced from deactivated pathogens and toxins. However, sub- unit antigens suffer from poor immunogenicity which necessitates the use of adjuvants and repeated dosing to induce the desired level of immunity. Ideal vaccine formulations should pro- vide high and long-lasting immune responses but also be pharmaceutically acceptable. A promising approach to achieving this is the use of biodegrad- able polymeric microparticles which have been shown to be effective adjuvants for many proteins including the model antigen bovine serum albumin (BSA) (Conway et al 1997), tetanus toxoid (Alpar & Almeida 1994) and the Yersinia pestis antigens (Eyles et al 1998a,b, 2000). Microparticles can also be used as single-dose vaccines which offer sig- ni®cant advantages over conventional immunization schedules (Cleland 1999; O'Hagan et al 1998). An important consideration in the use of microparticles as single-dose vaccines, is establishing the type of release pro®le required to induce sustainable immune responses after parenteral and mucosal delivery. The aim of this study was to compare the mucosal and systemic immune responses elicited after a single intranasal or intramuscular adminis- tration of protein-loaded polymeric microparticles with different protein release pro®les. Micro- particles were made from biodegradable polymers encapsulating the model protein BSA using either a Correspondence: H. O. Alpar, Pharmaceutical Sciences Institute, Aston University, Birmingham, B4 7ET, UK. E-Mail: H.O.Alpar@Aston.ac.uk