Low pH virus inactivation (VI) is a widely used step in the downstream purification process for monoclonal antibodies. It consists of using acidic titrants to lower the pH of the affinity eluate and subsequent hold to inactivate acid-labile viruses, followed by neutralization for further downstream processing. For proteins which are prone to low pH-induced aggregation, the scale-up of the low pH VI step poses significant challenges as it can result in undesirable product quality, mainly aggregate formation, due to insufficient mixing and the formation of hot spots.<br/><br/>In the work presented here, the 95% blend time is used to characterize mixing across different scales. To scale-up mixing conditions, power per unit volume has been extensively used in literature. However, this model is constrained by the geometry of the vessel and agitator, that cannot be met in small-scale experiments and sometime across different scales. Consequently, the 95% blend time is determined to establish a small-scale model and its dependence on various titrant addition and mixing parameters is investigated. The impact of using process buffers versus concentrated titrants for blend time studies is discussed. Blend time is determined up to large pilot-scale mixing vessels, and the results are compared across scales. The insights from these studies were then used to perform targeted experiments to assess the impact on product quality and de-risk process scale-up under well characterized conditions.

De-risking of the scale-up of low pH virus inactivation step for an aggregation-prone biopharmaceutical protein: Toward a better characterization of mixing conditions

ACS Spring 2022

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