As a product, the TB vaccine candidate progresses from a design on paper and prototypes in a laboratory into a commercial product in a vial. The aim of this function is to define how the vaccine should be characterised at each stage, and to define the criteria for quality. There is an increased level of control on the specifications of the vaccine candidate as it progresses through the stages, to become a safe and effective product against TB. This includes specifications for the drug substance (the biologically active ingredients), the excipients, and the contaminants that are included in the final drug product, together with the assays to accurately monitor these quality attributes.
Discovery is the stage where the technology and design of TB vaccine candidates are made, and when TB antigens, adjuvants, delivery system are screened based on expression (yield) and immune response in animals.
Key for the characterisation of the drug substance are assays to measure its identity, potency, purity, and stability. These assays require specific development and depend on the type of vaccine, for example a TB subunit vaccine will require a different assay for identity than a recombinant BCG. Identification and expression of the substance often includes gel electrophoresis, western-blot, or Enzyme Linked Immunosorbent Assay (ELISA) for a protein, and Polymerase Chain Reaction (PCR) for recombinant DNA. Potency could be bacterial viability (colony-forming unit) for a recombinant BCG, coupled to a marker assay for an immunological relevant effect representing protection. For a subunit vaccine it could be the concentration linked to a protective immunological effect, and for a viral vectored vaccine it would be titre linked to a similar output. For TB vaccines, T-cell epitopes and associated responses can be evaluated as markers for immunogenicity and potency. Examples include- antigenspecific stimulation of Interferon gamma production, measured by ELISpot, other cytokines, specific T-cell populations such as polyfunctional T-cells. Purity assays measure contaminants that originate from the expression system and culture medium used, such as host cell protein, host cell DNA, endotoxin or serum components, or from the process conditions used, e.g. detergents (Triton) or DNAse (benzonase).
The following guidelines on quality control of vaccine development provide further information: ICH Q8 Pharmaceutical Development, August 2009 (ICH Q8), ICH Q11 Development and Manufacture of Drug Substances (chemical entities and biotechnological/biological entities), May 2012 (ICH Q11) and ICH Q2, Validation of Analytical Procedures: Text and Methodology, nov 2005 (ICH Q2).
There is further characterisation of the vaccine substance / product for its identity, purity and potency. Evaluation of stability under the expected storage conditions must be performed at this stage, and this becomes a criterion for selection.
There is no correlate of protection for TB vaccines. This presents a challenge to determine the potency of vaccine candidate. Beside its concentration, several different marker assays are used as indicated above. The recently developed mycobacterial growth inhibition assay (MGIA) could be considered as a surrogate measure of a protective immune response.
The assays required for the testing of Critical Quality Attributes (CQA), the most relevant criteria for product quality with respect to safety and efficacy, are selected.
The assays selected for quality control and characterisation are developed, together with target specifications, for identity, potency, purity etc. These quality parameters of the substance and the product are referred as Bill of Testing (BoT), or Quality Target Product Profile (QTPP).
Note: the raw materials used for production of the substance and the product should be checked before being used in the lab. This quality control procedure is mandatory for current Good Manufacturing Practice (cGMP) operations. Certificates of Analysis of raw material must be collected and assays with target specifications selected for release.
In preparation for manufacturing of GMP material, the assays used for quality control and the Critical Process Parameters (CPP) must be qualified. The list of parameters that needs to be tested to release a product batch is confirmed and recorded in the BoT. Beyond this point the Product Specifications cannot be changed outside the original ranges without having major consequences (except for the excipients).
The material used for the toxicity study is produced according to cGMP or equivalent to GMP and must be characterised and released accordingly. The Phase I material is also produced and released.
During Phase 1, the assays for CQA continue their qualification, progressing to validation. The assays used for product characterisation could be slightly modified, to improve the sensitivity or accuracy of the test. This should not change the qualification or later validation status of the assays. Up to this point, the product reference would be from well described R&D production runs, and used to standardise assays. It could now be replaced by a GMP compliant reference.
The assays are used to release any new GMP material produced, or document changes in the drug product (within certain limits), and in the continuing stability studies.