Vaccine 29 (2011) 3390–3397 Contents lists available at ScienceDirect Vaccine journal homepage: www.elsevier.com/locate/vaccine Characterization and standardization of Sabin based inactivated polio vaccine: Proposal for a new antigen unit for inactivated polio vaccines Janny Westdijk a,∗ , Debbie Brugmans a , Javier Martin b , Aart van’t Oever a , Wilfried A.M. Bakker a , Lonneke Levels c , Gideon Kersten a a National Institute for Public Health, Unit Vaccinology, Antonie van Leeuwenhoeklaan 9, 3720 AL Bilthoven, The Netherlands b National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire, UK c Netherlands Vaccine Institute Antonie van Leeuwenhoeklaan 11, 3720 AL Bilthoven, The Netherlands article info Article history: Received 1 July 2010 Received in revised form 27 January 2011 Accepted 25 February 2011 Available online 11 March 2011 Keywords: Inactivated polio vaccine Sabin Antigenicity Immunogenicity abstract GMP-batches of Sabin-IPV were characterized for their antigenic and immunogenic properties. Antigenic fingerprints of Sabin-IPV reveal that the D-antigen unit is not a fixed amount of antigen but depends on antibody and assay type. Instead of the D-antigen unit we propose standardization of IPV based on a combination of protein amount for dose and D-antigenicity for quality of the vaccine. Although Sabin-IPV type 2 is less immunogenic than regular wild type IPV type 2, the immunogenicity (virus neutralizing titers) per microgram antigen for Sabin-IPV type 2 is in the same order as for wild type serotypes 1 and 3. The latter observations are in line with data from human trials. This suggests that a higher dose of Sabin-IPV type 2 to compensate for the lower rat immunogenicity may not be necessary. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Thanks to the Sabin oral poliovirus vaccine (OPV), the wild-type inactivated poliovirus vaccine (wt IPV) and the successful WHO campaign for Global Eradication of Polio [1,2] eradication of wild- type polio virus is at hand. One major disadvantage of attenuated OPV is that it can cause vaccine-associated paralytic poliomyeli- tis or outbreaks of vaccine-derived poliovirus [3]. If because of that OPV use is discontinued, the only vaccine available to induce and maintain immunity against polio will be IPV. To prepare for the post-eradication period and meet the demands for IPV, the production capacity of wt IPV would need to increase. However a major drawback of producing wt IPV is that the strains used require stringent containment measures, which restricts produc- tion to industrialized countries [4]. Therefore the development of Sabin IPV that can be produced economically on an large scale in developing countries may constitute an attractive option. WHO has requested NVI to develop a safe and effective candidate Sabin IPV. Different studies have reported the poor immunogenicity of Sabin type 2 and the lack of comparability between wt IPV and Sabin IPV with regard to antigenicity [5–8]. IPV antigenicity is expressed in D-antigen units. A complicating mat- ter in the comparison of antigenic and immunogenic properties is ∗ Corresponding author. Tel.: +31 302742474; fax: +31 302744426. E-mail address: janny.westdijk@rivm.nl (J. Westdijk). the fact that the D-antigen is not well defined. Manufacturers and Official Medicines Control Laboratories use their own antibodies and procedures. Collaborative studies have shown that this often causes problems when IPV-samples have to be quantified. This is the case for both antigenicity [9] as well as in immunoassays [10]. In this paper we have extended the study on antigenic and immunogenic properties of Sabin IPV with a panel of monoclonal antibodies (mabs) and two different methods to come to a pre- cise antigenic fingerprint of Sabin IPV. By quantification of protein and virus and measuring potency, we were able to compare anti- genic and immunogenic profiles of Sabin IPV and wt IPV. Based on the results of the characterization and standardization study we propose a better defined unit for inactivated poliovirus vaccines. 2. Materials and methods 2.1. Vaccine preparation wt IPV and International Reference (Pu91-01) [11] were pro- duced under cGMP conditions according to a routine production process [12,13]. Sabin IPV was produced under cGMP according to a slightly modified wt IPV production process. Vero cells were cultivated on micro carriers (Cytodex 1, GE Healthcare) suspended in fermentors, followed by infection with wild strains (Mahoney, MEF-1 or Saukett) or Sabin (LSc 2ab KP 2 ; P7 12 Ch2ab-KP 2 or Pfizer 457-III) strains. Virus was purified by filtration (clarifica- tion followed by ultra filtration, both Millipore), gel permeation 0264-410X/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.vaccine.2011.02.085