Introduction
The main objective is to build a safety profile of the vaccine candidate through a series of appropriate studies in animal models and in-vitro systems. In addition to specific assays to measure toxicity, early pre-clinical studies aimed at evaluating immunogenicity and/ or efficacy should be used as an additional data source for compiling the safety profile of the vaccine candidate. 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. Strasbourg, Cedex, France: Directorate for the Quality of Medicines of the Council of Europe (EDQM). BCG vaccine, freeze-dried. 01/2012:0163, 895-896) or the WHO Recommendations to assure the quality, safety and efficacy of BCG.
In this TB vaccine development pathway, animal studies are referred to as Pre-clinical because of an emphasis on providing guidance for animal testing performed before entering the clinical stages i.e. up to Stage C. References are made to formal, published documents some of which use the terminology of non-clinical testing because they describe both pre- and post-clinical phase animal studies.
Formal non-clinical safety and toxicity studies will be required at Stage D and beyond and will be reviewed by the appropriate regulatory authority.
Vaccine technology specific considerations
Information and guidance on the safety considerations for specific vaccine platforms is available and should be followed because individual platforms may present particular safety concerns. Some platforms e.g. specific viral vectors and DNA plasmids already have a body of knowledge on safety and it is advisable to perform a literature search for relevant published information which can be helpful to design and justify a safety programme. The generic guidance document “WHO guidelines on non-clinical evaluation of vaccines. WHO Technical report series No927, 2005” contains information relating to specific vaccine types.
DNA/ RNA based vaccines: Guidance for non-clinical evaluation of DNA plasmid vaccines is given in FDA/CBER Guidance for Industry: Considerations for Plasmid DNA Vaccines for Infectious Disease Indications, 11/2007 and WHO Technical Report Series No 941, 2007. In addition to the usual considerations of administration route and specific formulation, any technique and device used to improve the uptake of the plasmid such as electroporation, needs to be evaluated. It is important that the technique / device evaluated in animal studies is as close as possible to that intended for clinical studies. Assays to assess the biodistribution, persistence and potential integration of the plasmid should be performed unless substantial information already exists with an almost identical or similar product.
Viral vector-based vaccines: The document, Guideline on quality, non-clinical and clinical aspects of live recombinant viral vectored vaccines EMA/CHMP/VWP/141697/2009 provides guidance to develop a strategy for safety testing of a viral vectored vaccine. This includes understanding of the nature of the virus from which the vector is derived and the potential effects of adding a heterologous antigen. Data should be gathered on the replication of the vectored vaccine, its virulence/ attenuation and its spread within the animal and shedding. The potential for neurovirulence should be evaluated in the brain, especially for the intranasal route of administration. Reproductive toxicity studies may be required dependent on the potential use of the vaccine during pregnancy or in women of child bearing age. Consideration should be given to available clinical and/or epidemiological data on similar viral vectors.
Sub-unit vaccines: If delivered with an adjuvant, the safety of the adjuvant alone must be assessed as well as the adjuvant and antigen combination, although the use of an adjuvant with a well-known safety profile might preclude the need for studies of the adjuvant alone. If species-specific proteins (e.g. cytokines) are used as novel adjuvants, the issue of species-specific response should be considered. The formulation proposed for clinical use should be evaluated.
- Identify in vitro and in vivo models to test for safety
- Test preclinical safety elements relevant to candidate
- Safety tests identified
- Safety evaluated; no evidence to suggest lack of safety
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 2nd Geneva consensus (Walker et al., 2010), and are aimed at demonstrating safety better than BCG, for example in the severe combined immunodeficient (SCID) mouse model.
- Expand testing to confirm the general safety attributes of the vaccine candidate(s)
- Evidence of safety properties in one or more in vitro and / or in vivo models, confirming and expanding on tests performed in Stage A
- Where relevant, safety in immunocompetent and immunocompromised animals demonstrated being as safe or safer than BCG
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.)
- Design pre-clinical safety and toxicology studies as required by regulatory guidelines
- Synopsis protocols for safety and toxicology studies prepared as relevant for the vaccine
Synopsis protocols should be prepared for any safety and toxicity studies required by the relevant National Regulatory Authorities (NRAs) (also refer to Function ‘Regulatory’). At a 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.
- Perform toxicology studies using DP from GMP run (or equivalent)
- Perform safety studies such as bio-distribution, persistence and for Genetically Modified Organism (GMO) requirements, as relevant for the vaccine
- Safety and toxicology profile of the DP acceptable
- Bio distribution, persistence and GMO requirements met, as relevant
Relevant safety and toxicity studies should be performed only once the manufacturing process has been locked and GMP-quality (or equivalent) 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.