the latter is in direct contact with the product within the production process. The

final goal of implementing such technologies is to achieve methodologies allowing

the assessment of the product quality across the different steps of the process thus

allowing for a real-time lot release. It is also intended to improve the assessment of

the process variability, to facilitate continuous improvement and automation of the

process while reducing duration and production costs.

8.4.1

OFF-LINE, AT-LINE, ON-LINE, AND IN-LINE DEFINITIONS

Most of the techniques that are applied for viral production and quantification are

off-line. This is the case of all quantification techniques that necessitate sampling

the production process and processing the analytical steps externally, the analytics

being located outside the production zone. Analyses are commonly long to perform

and necessitate a dedicated environment for example for the infectivity assays (see

section before). The limitations of off-line analyses is that they do not allow for

retro-control on the production process in real-time. Indeed, the durations to

complete such analyses are longer than the production steps (from 2 hours up to 1

week) and will generally be performed after sample storage.

On the contrary, at-line analyses are performed within the production zone close to

the production process. They still require process sampling but here, the assays are

much faster (30 min to 2 hours). This allows for a cell-based process to have in-

process monitoring, meaning informative quantification in reasonable time-frequency

to track the targeted biological event. As examples for targeted biological events,

common cell doubling times are of 20 to 30 hours and viral cycles are of 6 to 30 hours.

This allows the operators to exploit the at-line analytical results to correct process

deviations or to start new process phases based on such external quantifications.

To go further and reach automation of the production process, PAT targeted the

development of on-line and in-line tools. The distinction between those two types

of analytical tools is not always clearly set in the literature, therefore they are be re-

defined herein. Both are analytical tools giving access to information in real-time.

This means that the acquisition and analysis results are available in a time frame and

frequency much higher than for at-line tools. We refer here to measurements lasting

seconds or minutes. Such types of equipment are connected to the production

process and could be integrated into feedback control loops. Operators are no longer

involved either in sampling or changing the operating parameters on the process.

Probes or analytical equipment could be part of the regulation loops.

In-line defines for example a probe that is directly in contact with the analyte

inside the production process. Such analyses are non-destructive and commonly

provide results in a time frame of seconds. On-line, on the contrary, is not im-

plemented within the process but connected on a derivation thanks to a measure-

ment chamber. The analysis is also non-destructive.

8.4.2

PROCESS ANALYTICAL TECHNOLOGY FOR VIRAL PRODUCTION PROCESSES

All the PAT tools applied for cell-based culture processes associated with re-

combinant protein production could also be applied in the present case. Thus, all the

218

Bioprocessing of Viral Vaccines