Understanding TFF operations in cell and gene therapy bioprocessing

Background:
Tangential flow filtration (TFF) is often used in several steps within a bioprocess sequence to produce cell and gene therapies (CGT). These are typically for ultrafiltration (concentration), diafiltration or buffer-exchange, and sometimes for clarification and/or particulates removal. This unit operation is becoming an invaluable workhorse for the recovery of CGT products, including their materials (e.g., for component DNA or RNA purification, or lipid nanoparticle production). The current format commonly used in production are hollow fibres which come in different lengths, internal diameters, fibre thickness and membrane type. Another format used for TFF, but not often seen in CGT application, is the flat-sheet format. There is currently a lack of information as to the better format for certain CGT applications, nor are there systematic studies that compare the two formats and the different design parameters that affect their performance when applied to CGT. Scale-up of these two formats are also slightly different. For example, scale-up of flat sheet membranes have been made robust by maintaining the flow-path length while increasing the membrane width for increased surface area. The use of turbulence promoters is common but the effect of these on cells or viral vectors are unknown. Scale-up of hollow fibre membranes is different and may prove slightly challenging if different lengths are used in the different stages of process development. Given the increasing demand for CGT products, the need also grows for increased understanding of the unit operations involved to achieve a robust process design. This study aims to investigate the TFF operation for cell and gene therapy applications.

Project Description:
The project will build on our work on TFF scale-down characterisation for Mabs on flat-sheet membranes and extend this to TFF using hollow-fibre membranes. There is some work currently underway in the Rayat Group on lentiviral vector production focusing on TFF prior to ion exchange chromatography. However, TFF is applied at different points of the process and for different modalities (e.g., viral vectors, RNA) or process components (e.g., DNA, LNP) and so there is a need to investigate TFF at different places of the flowsheet. There is an opportunity to obtain a wide variety of data for various modalities, and at the same time, to use computation modelling to look at the aspect of TFF design which can affect performance in cell and gene therapy applications. The process knowledge and novel methods this project can generate will benefit the bioprocessing community.

Objectives:
The main aim of this study is to characterise and optimise TFF operations in cell and gene therapy bioprocessing. Specifically, the project aims to:
Evaluate the performance of the different formats of TFF in terms of productivity, product stability and recovery and impurity removal.
Apply novel modelling methodologies for the bioprocess development of TFF
Determine the key parameters which may affect the TFF performance for each format (e.g., hollow fibre length, membrane type, pore size, flat-sheet turbulence promoters etc)
Identify the key TFF conditions that enable the optimal recovery of different CGT products and components (e.g., RNA, DNA, LNPs, viral vectors)