Replacement of in vivo human rabies vaccine potency testing by in vitro glycoprotein quantification using ELISA - Results of an international collaborative study.

Three different ELISAs quantifying rabies glycoprotein were evaluated as in vitro alternatives to the National Institutes of Health (NIH) in vivo potency test for batch release of human rabies vaccines. The evaluation was carried out as an international collaborative study supported by the European Partnership for Alternatives to Animal Testing (EPAA). This pre-validation study, the results of which are presented in this paper, compared three different ELISA designs, assessing their within- and between-laboratory precision. One of the ELISA designs was proposed to the European Directorate for the Quality of Medicines & HealthCare (EDQM) and accepted for an international collaborative study under the umbrella of the Biological Standardisation Programme.

A relevant in vitro ELISA test in alternative to the in vivo NIH test for human rabies vaccine batch release.

To assess the quality of vaccine batches before release, international regulation requires the control of potency of each lot of human rabies vaccines by the in vivo NIH challenge test. Meanwhile, the 3Rs strategy for animal testing encourages the replacement of the in vivo potency test by an in vitro assay. Consequently, since more than 10 years, an ELISA method has been implemented by ANSM in parallel to the NIH test for rabies vaccines lots. It consists in the evaluation of the glycoprotein content using a monoclonal antibody recognizing the trimeric native form of the glycoprotein. This ELISA method is able 1) to monitor the consistency of production with a similar profile than the NIH; 2) to detect a low quantity of glycoprotein in vaccines and 3) to agree with the manufacturer's NIH results by declaring a non compliant batch. This ELISA which characterizes the immunogenic form of the glycoprotein formulated in vaccines seems to be relevant to replace the NIH test and is a promising candidate to be standardized by a collaborative study.

Would an in vitro ELISA test be a suitable alternative potency method to the in vivo immunogenicity assay commonly used in the context of international Hepatitis A vaccines batch release?

Since many years Afssaps applies the 3R's strategy (replacement, reduction and refinement) for the use of laboratory animal testing in the framework of vaccine batch release. In this context, for Hepatitis A vaccines, a study was carried out to assess the feasibility of replacing the in vivo "Gold Standard" potency assay by the Afssaps' validated in-house antigen content in vitro assay on routine testing. The use of a panel of potent vaccine batches and reduced-potency samples by heating demonstrated a correlation between the two methods. This encourages Afssaps to progressively switch from in vivo to in vitro assay in the framework of Hepatitis A vaccines batch release.

Establishment of a national network of validated and qualified laboratories for neutralizing anti-vaccinia antibodies titration.

A Proficiency Testing Study (PTS) was organized in France by the French Health Products Safety Agency (Afssaps) aiming at assessing the performance of laboratories in performing a neutralizing anti-vaccinia antibodies titration method by plaque reduction neutralization test (PRNT). The ultimate goal was to establish a national network of qualified and validated laboratories. Five laboratories were included in the PTS and four submitted their data. Three samples of human sera containing various immunoglobulin concentrations (a "high" serum: s-576, a "medium" serum: Ref-19584 and a "low" serum: s-483) were tested by PRNT as described in a procedure supplied by Afssaps and developed in each laboratory during preliminary assays. Data were sent to Afssaps which performed the statistical analysis. The overall performance of the four participating laboratories was satisfactory. This allowed the four participating laboratories to be validated and then to be qualified by the Ministry of Health. Finally a national network for anti-vaccinia immunoglobulins titration was established.

Standardization of a neutralizing anti-vaccinia antibodies titration method: an essential step for titration of vaccinia immunoglobulins and smallpox vaccines evaluation.

The possibility of mass population vaccination with smallpox vaccine implies the development of anti-vaccinia immunoglobulins for the treatment of severe side effects following vaccination. We have chosen to develop and validate the "gold standard method" (plaque reduction neutralization assay) to titrate neutralizing anti-vaccinia antibodies in two different French laboratories belonging to the Department of Defense (CRSSA) and to the French Health Products Safety Agency (Afssaps). The results of precision, linearity and accuracy of the method led to consider the method as validated. In parallel, we have prepared and lyophilized a pool of anti-vaccinia plasma samples issued from a unique donor and qualified this preparation versus the first British standard to use it as an in-house standard with a titer of 25 international units (IU). This work will allow to titrate, in IU, sera from vaccinated persons in order (i) to titrate purified anti-vaccinia immunoglobulin preparations for vaccine severe side effect treatments; (ii) to investigate the level of neutralizing antibodies in the general population; and (iii) to investigate clinical trials of new generation smallpox vaccines. In the future, this will allow comparability of studies on either smallpox vaccines or on the serological status of the population.

New generation of cell culture assay for smallpox vaccine potency.

The potency of smallpox vaccines produced in the 1970s was tested by titration onto chorioallantoic membranes of fertilized hen eggs (CAM assay). The potency specification commonly approved for these vaccines was a titer above 10(8) pock-forming units per milliliter. We developed and validated a cell culture titration assay to have a more reliable potency test. The cell titration assay and the CAM assay were tested in parallel on 34 first-generation smallpox vaccine lots. These allowed us to demonstrate that a correlation does exist between the two titration techniques and to determine a new in-house specification for the cell titration method. This in vitro potency assay will allow us to test first-generation smallpox vaccines produced on the skin of living animals but will also give a hint of the potency specification that should be assigned for new generations of cell-derived smallpox vaccines.

Inactivated rabies vaccine control and release: use of an ELISA method.

Quality control of human rabies vaccines performed by National Control Laboratories (NCLs) prior to marketing vaccines batches requires in vivo and in vitro potency assays as requested by the relevant European Pharmacopoeia monographs, OMCLs guidelines and WHO technical recommendations. The aim of the present study was to check the suitability of an enzyme-linked immunosorbent assay (ELISA) using a virus neutralizing monoclonal antibody, directed to the rabies virus glycoprotein, to monitor the consistency of the lot to lot rabies vaccines production. Furthermore, this work was implemented to establish in house specifications for the glycoprotein content.

Collaborative study for the establishment of a European Phamacopoeia Biological reference preparation for Bordetella pertussis mouse antiserum for serological potency testing of acellular pertussis vaccines.

A collaborative study was organised by the European Directorate For the Quality of Medicines (EDQM) to assess the suitability of a candidate mouse antiserum as a European Pharmacopoeia Biological reference preparation (BRP) for acellular pertussis vaccine potency testing. The candidate antiserum was obtained by immunising mice with a five-component acellular pertussis vaccine: pertussis toxin (PT), filamentous haemagglutinin (FHA), pertactin (PRN) and Fimbrial 2/Fimbrial 3 (Fim 2&3). The study has been divided into two separate phases. Phase I was a pre-qualification study including three laboratories. This phase was aimed at pre-qualifying the candidate BRP (cBRP) and at documenting the impact of differences in the antibody detection methodology enzyme linked immunosorbent assay (ELISA) procedures on results of pertussis antisera calibration versus the currently used standard US standard pertussis antiserum (mouse) Lot 1 (SPAM-1) (United States Food and Drug Administration (USFDA) reference serum) and the cBRP. As no significant difference between the antibody titres determined by using the different ELISA methodologies was found, a large-scale study enrolling 13 laboratories (Phase II) was carried out, each participant performing its in-house methodology. Its aim was to calibrate the cBRP (in terms of the SPAM-1 reference) and to demonstrate its equivalence or superiority to internal references. The study showed that there was no difference in positive sera titres expressed relative to their corresponding internal reference (homologous situation) or the proposed standard (heterologous situation) reference. The cBRP can, therefore, reliably act as replacement for the in-house reference preparations. Further analysis of the outcome of this study enabled to assign to the cBRP a potency of 39, 138, 34 and 56 ELISA unit per millilitre, respectively, to its anti-PT, anti-FHA, anti-PRN and anti-Fim 2&3 antibody contents. The cBRP has been adopted by the European Pharmacopoeia Commission at its June 2000 session as Bordetella pertussis mouse anti-serum Ph Eur. BRP batch 1.

The assessment of OPV vaccines by the monkey neurovirulence test: why and how to qualify the experts in histology of central nervous system.

Prior to batch release of oral poliovirus vaccines (OPV) for marketing purpose, the World Health Organisation (WHO) and European pharmacopoeia require a monkey neurovirulence test to be performed both by the manufacturer and the relevant National Control Laboratory (NCL) to assess vaccine safety as regards neurovirulence. Due to the subjectivity of histological examination and of neural lesions scoring, the French NCL has set up a proficiency testing procedure to qualify a new expert.