The main objective is to build a safety profile of the vaccine candidate through a series of appropriate studies in animal and in-vitro systems. In addition to specific assays to measure toxicity, early pre-clinical studies aimed at evaluating immunogenicity and/ or efficacy can be used as an additional data source for the safety profile of the vaccine candidate. Dose-ranging studies could be included to provide early safety data on higher doses than are generally used for immunogenicity or efficacy. Specific safety studies applicable to live attenuated whole cell vaccines are required and these will include high dose challenge of immunocompromised mice in addition to the tests specified in the BCG vaccine monograph (European Pharmacopoeia - European Pharmacopoeia. Strasbourg, Cedex, France: Directorate for the Quality of Medicines of the Council of Europe (EDQM). BCG vaccine, freeze-dried. 01/2012:0163, 895-896 (2012).). Formal safety and toxicity studies will be required at Stage D and beyond and will be reviewed by the appropriate regulatory authority.
Safety testing at this Stage should first demonstrate that the vaccine material is suitable for use in animals. For example, protein components of protein/ adjuvant vaccines should be tested for and contain minimal levels of endotoxin, ensuring both that the candidate is safe for use in animals and that interpretation of immunogenicity and/ or efficacy data is not confounded by the presence of innate stimuli. Further evaluations of safety at this Stage are generally observational, and can be included in immunogenicity and efficacy studies. These should reveal an absence of safety signals such as excessive local inflammation at the site of injection or indications of anaphylaxis with repeated inoculations. Safety characteristics specific for live attenuated whole cell vaccines (strains of Mycobacterium tuberculosis (Mtb)or modified BCG) are described in Walker et al., 2010, and are aimed at demonstrating safety better than BCG, for example in the immunocompromised SCID mouse model.
As pre-clinical testing of immunogenicity or efficacy continues in stage B, safety characteristics should be documented to add to the safety profile of the candidate. Additional studies may be conducted to confirm and expand the safety data package for specific product targets or functions. Examples might include an evaluation of the tolerability to different doses of the vaccine or tests to investigate shedding of live viruses or bacteria. Safety should be confirmed if there are any changes to/ optimisation of the vaccine candidate (for example, removing the resistance marker from an attenuated strain of Mtb.)
Synopsis protocols should be prepared for any safety and toxicity studies required by the relevant National Regulatory Authorities (NRAs). At minimum, this generally includes a local tolerance and repeat-dose toxicity study conducted under Good Laboratory Practices (GLP). However, additional studies may be required depending on the vaccine candidate. For example, genotoxicity and carcinogenicity studies may be required for novel vaccine adjuvants. Early consultation with NRAs is recommended to ensure the proposed studies meet their expectations.
Relevant safety and toxicity studies should be performed only once the manufacturing process has been locked and GMP-quality material is available. At a minimum, Drug Product should be evaluated at the highest intended clinical dose, in an “N+1” regimen (i.e., including one more immunisation than will be performed clinically). Testing may be carried out using test/consistency lots or final process pre-release materials. Additional safety testing may be required for batch release of GMP material, and should be confirmed with the NRA.
Other studies such as bio-distribution, persistence, or stability of the insertion/ deletion in a genetically modified organism may be conducted as relevant for the vaccine. An example of such safety studies is given in Arbues et al. 2013 for the live attenuated Mtb vaccine – MTBVAC. Such studies are not an absolute requirement and therefore may not be described in regulatory documentation but can be informed by best practice and an understanding of the specific product characteristics.