The use of physicochemical and immunochemical assays to study antigen-adjuvant interactions for prediction of quality of diphtheria and tetanus toxoid vaccines
08 / 2007 - unknown
The final goal of the project is to replace large scale animal experiments for potency testing of diphtheria and tetanus toxoid vaccines. Several tests have been developed to evaluate the quality of the toxoids used in the vaccines. Toxoids are adsorbed to an adjuvant in the final product. The interaction between toxoids (antigen)and adjuvant has a pronounced effect on the immune response and as a result the quality of the final product. Fundamental research will be performed to study this interaction between toxoid (antigen) and adjuvant in more detail and correlate these data with immunogenicity. Based on this fundamental information physicochemical and immunochemical tests will be selected to monitor the quality of adsorbed diphtheria and tetanus toxoid vaccines. Vaccines play a crucial role in preventive health care. To guarantee safe and potent vaccines, many tests have to be performed. Some of these tests include animal experiments. Especially potency testing requires large numbers of animals while these animals experience severe distress due to the procedures applied. In the late 1980s NVI (then part of the RIVM) started a programme to gradually replace, refine and reduce the number of animals in statutory required quality control. The first approach was replacement of the lethal challenge procedure for potency testing of diphtheria and tetanus toxoid vaccines by serology. So far, development of serological models for diphtheria and tetanus toxoid vaccine has been successful (Vero cell test for D toxoid and ToBI test for D and T vaccines). Both Vero cell test and ToBI test have now been accepted by the European Pharmacopoeia (EP) and regulatory authorities have resulted in substantial reduction and refinement. As a final step, we envisage to replace these serological tests by non-animal methods. Changes in the concept of quality control make this possible. These changes mean that monitoring consistency in production is used to guarantee high product quality. First studies to apply this concept to diphtheria and tetanus vaccines have been performed successfully (in PAD 96-34 and PAD 98-21). The toxoid quality was studied by assessing comparability in structure using different (physico) chemical tests. However, these tests cannot easily be used for quality control of final products due to the presence of adjuvant, immune stimulating suspensions of aluminium salts. Antigen and adjuvant interact which makes application of most chemical tests difficult. Until recently, information on the interaction between antigens and adjuvant in vaccines and its effect on vaccine potency were limited. Recently, results from fundamental research into this issue have become available that might be relevant for routine vaccine quality control. In this proposal we aim to investigate antigen-adjuvant interactions in detail and study their effect on vaccine potency. Tetanus toxoid and diphtheria toxoid will be used as antigens. In addition, several model proteins are included to be able to get a more fundamental insight into the adsorption process and the effects on protein structure and function. Aluminium phosphate and aluminium hydroxide batches with different characteristics will be prepared. The study should result in a set of physicochemical and immunochemical tests that can monitor the quality of final lots of diphtheria and tetanus toxoid vaccines, i.e. toxoids adsorbed to aluminium salts. Procedures and criteria will be assessed to monitor antigen-adjuvant interactions during the toxoid vaccine preparation. This information can be utilised to confirm consistency in production and as a result in vaccine quality. The final goal is to replace potency testing of these toxoid vaccines in animals by a set of non-animal tests that confirm consistency in production. The tests developed and selected in the present proposal will be part of this set of tests.