expression is increased. Moreover, even subtle changes in materials and process

conditions can drastically affect the safety and effectiveness of the vaccine. For

this reason, strict control and monitoring of the process is of utmost importance to

produce consistent, reproducible, and well-characterized products [86]. As a

general rule of thumb, the cell line has to be a GMP qualified cell line with a

manufacturing license, the cultivation has to be performed using GMP certified

media, and the virus material has to be produced in a GMP laboratory under GMP

conditions. An adequate quality management system (QMS) has to be adopted,

demonstrating that all documentations are according to GMP and the full history

of materials and equipment is outlined. More specifically, regulatory authorities

have to be assured that the vaccine is produced under controlled and stable

conditions, with suitable tests ensuring that the vaccine meets prospective criteria

(e.g., identity, purity, safety, potency, and stability) [87,88]. All equipment, as-

says and methods involved need to be validated. Standard operating procedures

(SOPs) for all process steps are required. Obviously, quality and purity of a

vaccine cannot be assured solely by downstream testing and assays, but depend

on strict control of the manufacturing process as well [86]. This includes, but is

not limited to, appropriate quality and purity of the starting materials (e.g., cells,

viruses, reagents, media, etc.), use of in-process controls (preferable process

analytical tools (PAT) tools), and adherence to validated process procedures [89].

This results in the regulatory definition of the drug substance and drug product

for vaccine production as follows: “The drug substance of a vaccine is defined as

the unformulated active (immunogenic) substance which may be subsequently

formulated with excipients to produce the drug product. The drug substance may be

whole bacterial cells, viruses, or parasites (live or killed); crude or purified antigens

isolated from killed or living cells; crude or purified antigens secreted from living

cells; recombinant or synthetic carbohydrate, protein or peptide antigens; poly-

nucleotides (as in mRNA and plasmid DNA vaccines); or conjugates” [89]. “The

drug product is the finished dosage form of the product. The drug product contains

the drug substance(s) formulated with other ingredients in the finished dosage form

ready for marketing. Other ingredients, active or inactive, may include adjuvants,

preservatives, stabilizers, and/or excipients. For vaccine formulation, the drug

substance(s) may be diluted, adsorbed, mixed with adjuvants or additives, and/or

lyophilized to become the drug product” [89].

Thus, keeping all regulatory issues in mind throughout the development many little

aspects need to be documented and carefully chosen right from the start. Detailed

guidance’s for industry are provided by the U.S. FDA and EU EMA and will slightly

vary depending on the vaccine type (e.g., inactivated, live, recombinant, etc.) [89,90].

In the following, a brief overview on basic aspects considered for a successful reg-

ulatory submission filing is given.

5.9.1

CELLULAR SOURCES

Cellular sources typically refer to cell lines of animal (insects, humans, and other

mammalians) origin. Cell bank systems consisting of a master cell bank (MCB)

and a working cell bank (WCB) are frequently adopted for the production of

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