An Investigation of the Factors Controlling the Adsorption of Protein Antigens to Anionic PLG Microparticles JAMES CHESKO, JINA KAZZAZ, MILDRED UGOZZOLI, DEREK T. O’HAGAN, MANMOHAN SINGH Vaccine Delivery Group, Chiron Corporation, 4560 Horton St., Emeryville, California 94608 Received 18 March 2005; accepted 15 July 2005 Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jps.20472 ABSTRACT: This work examines physico-chemical properties influencing protein adsorption to anionic PLG microparticles and demonstrates the ability to bind and release vaccine antigens over a range of loads, pH values, and ionic strengths. Poly(lactide-co-glycolide) microparticles were synthesized by a w/o/w emulsification method in the presence of the anionic surfactant DSS (dioctyl sodium sulfosuccinate). Ovalbumin (OVA), carbonic anhydrase (CAN), lysozyme (LYZ), lactic acid dehydrogen- ase, bovine serum albumin (BSA), an HIV envelope glyocoprotein, and a Neisseria meningitidis B protein were adsorbed to the PLG microparticles, with binding efficiency, initial release and zeta potentials measured. Protein (antigen) binding to PLG microparticles was influenced by both electrostatic interaction and other mechanisms such as van der Waals forces. The protein binding capacity was directly proportional to the available surface area and may have a practical upper limit imposed by the formation of a complete protein monolayer as suggested by AFM images. The protein affinity for the PLG surface depended strongly on the isoelectric point (pI) and electrostatic forces, but also showed contributions from nonCoulombic interactions. Protein antigens were adsorbed on anionic PLG microparticles with varying degrees of efficiency under different conditions such as pH and ionic strength. Observable changes in zeta potentials and morphology suggest the formation of a surface monolayer. Antigen binding and release occur through a combination of electrostatic and van der Waals interactions occurring at the polymer-solution interface. ß 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2510–2519, 2005 Keywords: microparticles; antigen; vaccine delivery; polylactide-co-glycolide; protein adsorption; PLG; anionic particles; electrostatic; microscopy INTRODUCTION Next generation vaccines will be comprised mainly of recombinant protein antigens that are often poorly immunogenic. These vaccines will need optimal antigen delivery systems with or without an additional immunopotentiator to gen- erate potent immune responses. 1,2 Emulsions, micro/nanoparticles, aluminum salt adjuvants, and iscoms have all been used as delivery sys- tems to boost immune responses to vaccine antigens. Enhanced immune responses are induced through a variety of mechanisms, in- cluding increased persistence of antigen at the site of injection, improved targeting to antigen presenting cells, or enhanced protection of anti- gen linear, and conformational epitopes against degradation. 2–4 We have previously described studies which showed that anionic poly(lactide-co-glycolide) (PLG) microparticles were effective delivery sys- tems for adsorbed vaccine antigens, including recombinant proteins from Neisseria meningitidis type B (MB) 5 and human immunodeficiency virus 2510 JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 11, NOVEMBER 2005 Correspondence to: James Chesko (Telephone: 510-923- 3896; Fax: 510-923-2586; E-mail: james_chesko@chiron.com) Journal of Pharmaceutical Sciences, Vol. 94, 2510–2519 (2005) ß 2005 Wiley-Liss, Inc. and the American Pharmacists Association