efficiency. Different types of assays are applied to evaluate the biological activity of

virus production. Most of the assays are biochemical or cell-culture-based assays.

Molecular biology assays were extensively developed in the last twenty years to

identify more effectively viral variants and strains. Viral potency is the quantitative

measurement of the biological activity of a viral product. Thus, the potency of a viral

product refers to the comprehension of the relation between the product activity and

its biological quantity. As an example, a potency assay could be quantifying the

amount of protein needed to give a specific activity of a vaccine, such as protection of

a patient. The viral potency is thus dependent on the targeted molecule’s affinity and

its efficacy. For vaccines, the main target is to evaluate the product immunogenicity.

In such cases, the quantification techniques aim to describe the amount of antigen (or

antigen epitopes) which are necessary for the onset of an immune response in-vivo,

either on animals or in human patients. The protective effect of such induced immune

response is then further evaluated. The immune response quality will be evaluated

by the specific quantification of both B-cell humoral and specific antibodies release or

T-cell cytotoxic response to protect against the infectious disease.

In the case of a vaccine candidate, the major critical quality attribute (CQA) is

the antigen content and its bioactivity. An antigen can be of different forms de-

pending on the type of vaccine. Thus, when the vaccine candidate is an attenuated

vaccine, the amount of infectious and complete viral particles is of importance for

the product quality assessment. Whereas if the vaccine candidate is an inactivated

split vaccine, then only the antigen protein content is assessed. For other types of

viral products, like viral vectors aimed to be integrated within gene therapies or cell

therapies treatment strategies, the viral potency will here only target the product

capacity to infect naïve cells. Thus, the amount of infectious viral particles will be

the main read-out. These considerations will allow for the selection of the appro-

priate analytical tools and methodologies. In the case of a viral vector, the product

efficacy corresponds to the virus capacity to target specific cells, its entry in the

cells, and capacity to deliver a modified genome. Thus, here the main attribute of

the product is the infectivity and infectious dose of the product. Table 8.1 presents

the type of assay to target depending on the viral product application.

8.2.2

IMPLICATIONS OF PROCESS PHASE ON ANALYTICS CHOICES

The second element to consider for the selection of appropriate analytics is the

process sequence step. Analytics is not only implemented at the final step of the

manufacturing process for product qualification and lot-release. Many analytical

tools were developed to allow for the evaluation of process consistency or process

improvement across the different steps of the manufacturing process. Consequently,

analytical tools will be subject to different conditions with different challenges

depending on the production stage at which they are implemented.

After fill-and-finish process step, product quality and potency are assessed on highly

purified material. On the contrary, analytics implemented along the upstream and

downstream process need to cope with a wide range of purity. Thus, the matrix effect,

namely the impact of the solution in which the product is suspended, must be considered.

The composition of such a matrix might be ranging from spent media, purification saline

Analytics and virus production processes

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