Presentation Summary
Dr. Ralf Wagner, the section head of viral vaccines of the Paul-Ehrlich Institute in Germany started by explaining that the mRNA molecule emerges from a defined cascade of manufacturing steps, like (1) DNA template generation; (2) linearization; (3) in vivo transcription; (4) modification of the poly-A-tail and 5’ cap structures; (5) template degradation; (6) mRNA processing (purification, removal of free nucleotides, residual DNA and truncated RNA); (7) tailoring (complexing) for optimized in vivo delivery and performance; and, (8) pharmaceutical formulation (storage and stability).
All of these individual steps can affect mRNA vaccine quality and performance.
For example, for the first three steps, GMP compliance is a very important regulatory consideration, at least starting from the RNA transcription step. Also, defined, consistent and validated processes with relevant control tests need to be established to produce and control the intended mRNA molecule (sequence, length, … ).
Besides, elucidation of structure and impurities need to be defined, established and justified; and, all raw materials and enzymes used need to be pharmaceutical grade and consistent in quality.
There needs to be a consideration of the potential impact that those materials used during preparation/expression might have in the final product; as such, Dr. Wagner reminded us that qualified and reliable suppliers are essential.
Dr. Wagner emphasized that there are numerous potential strategies with significant impact for optimization, that need to be consistently defined and controlled for regulatory compliance (a good tip on these key aspects can be found in the publication Pardi et al, Nat Rev Discv, 2018).
In relation to step (5) template degradation and (6) mRNA processing, the key regulatory consideration and requirements demand established and validated purification processes, with defined acceptable purity level(s). Essential is also the definition and justification of impurities and upper limits, with the aim to reduce them to bellow an achievable minimum, that needs to be consistently achieved.
Overall, process validation/confirmation should be pursued by blind in-process controls, Key Performance Indicators (KPI), critical steps and intermediates.
There is a huge variety of potential approaches for delivery, optimization and stabilization of mRNA vaccines. For example, for efficient delivery into target cells, mRNAs are packaged into Lipid nanoparticles (LNPs), which use specific lipids with defined functions. The mRNA LNP formulation, can be highly specific for different kinds of vaccines, being considered a product specific property.
As such, the key regulatory considerations and requirements for adjuvating/complexing/delivery approaches emphasize the need to explain and demonstrate the rational for the selected specific approach, with an identification, definition and characterization of any formulation agents used.
Also, there needs to be a demonstration and assurance of process consistency and interactions between agent and mRNA, with definition and consistency of structurally important determinants and features, like 3D structures, or particle characteristics.
In relation to stabilization of the final encapsulated mRNA vaccine, the regulators acknowledge that there are too few data available in relation to novel vaccines for proper shelf-life assignment; as such, they advise to appropriately consider data from similar vaccine products of the same platform.
Even though, there are essential stability indicating parameters for the drug substance that need to be tested: appearance, pH, RNA content and integrity, activity cap percentage and poly-A-tail length, bacterial endotoxins, microbial limits, bioburden, and sterility.
In relation to the drug product: RNA plus lipid content, mRNA integrity, mRNA encapsulation efficiency, particle size, polydispersity, translational activity (“Potency”) are all good stability indicators that need to be evaluated.
The second part of Dr. Wagner’s talk, focused on novel adjuvants for protein and peptide vaccines, which is quite a challenging task due to the extremely diverse nature of substances, varied functions/modes of action and different safety profiles.
As such, the regulators aim at harnessing a basic framework of concepts, rather than specified instructions for individual substances.
In relation to the quality aspects of the adjuvant alone, the testing program needs to be designed and established based on the specific nature of the adjuvant, and the data needs to be presented in a self-standing section of the CTD dossier.
For the combination of Antigen and Adjuvant, the quality aspects are product-specific, and the final extent of testing requirements needs to be evaluated case-by-case, with detailed descriptions of the entire combination procedure, binding characteristics, stability of the association, and potential interfering effects, among other aspects.
