Utilizing bacteriophage to define the minimum residence time within a plug flow reactor

Continuous Low pH Viral Inactivation: Operation and Scaling Strategy Informs Viral Clearance Study

A continuous viral inactivation (CVI) tubular reactor was designed for low pH viral inactivation within a continuous downstream system across multiple scales of operation. The reactors were designed to provide a minimum residence time of >60 minutes. The efficacy of this tubular reactor was tested with Xenotropic Murine Leukemia Virus (X-MuLV) through pulse injection experiments. It was determined that the minimum residence time of the small scale reactor design, when operated at the target process flow rate, occurred between 63-67 minutes. Inactivation kinetics were compared between continuous operation and standard batch practices using three monoclonal antibodies. The quantification of the virus log reduction values (LRV) were similar between the two modes of operation and most of the acid treated samples had virus concentrations below the limit of detection. However, residual infectivity was still present in the endpoint batch samples of two experiments while the continuous samples always remained below the limit of detection. This provides the foundation for leveraging a standard batch based model to quantify the LRV for a CVI unit operation. This article is protected by copyright. All rights reserved.

Model-based control for column-based continuous viral inactivation of biopharmaceuticals

Batch low-pH hold is a common processing step to inactivate enveloped viruses for biologics derived from mammalian sources. Increased interest in the transition of biopharmaceutical manufacturing from batch to continuous operation resulted in numerous attempts to adapt batch low-pH hold to continuous processing. However, control challenges with operating this system have not been directly addressed. This article describes a low-cost, column-based continuous viral inactivation system constructed with off-the-shelf components. Model-based, reaction-invariant pH controller is implemented to account for the nonlinearities with Bayesian estimation addressing variations in the operation. The residence time distribution is modeled as a plug flow reactor with axial dispersion in series with a continuously stirred tank reactor, and is periodically estimated during operation through inverse tracer experiments. The estimated residence time distribution quantifies the minimum residence time, which is used to adjust feed flow rates. Controller validation experiments demonstrate that pH and minimum residence time setpoint tracking and disturbance rejection are achieved with fast and accurate response and no instability. Viral inactivation testing demonstrates tight control of logarithmic reduction values over extended operation. This study provides tools for the design and operation of continuous viral inactivation systems in service of increasing productivity, improving product quality, and enhancing patient safety.