2.1 Towards continuous closed-system processing
The monoclonal antibody (mAb) manufacturing industry, being more mature, serves as a strong precedent for the benefits of continuous processing—defined as an integrated, non-stop production method. Recent studies show that continuous processing can reduce costs by up to 35% at lower annual production scales.
The integration of machine learning and advanced analytics has enabled real-time monitoring and process control, enhancing consistency, efficiency and product quality. These advances not only reduce production costs but also improve access to mAb therapies. As continuous processing and analytics capabilities evolve, they offer a scalable pathway to meet rising global demand while maintaining economic viability.
For cell and gene therapies – characterised by higher variability and greater complexity – the potential benefits of continuous processing are even more significant. This approach could be well suited to gene therapies and allogeneic cell therapies, but application becomes more challenging for autologous cell therapies, which by their nature require small batch production. Realising this potential requires purpose-built, closed, sterile and automated systems, incorporating modular single-use technologies. Integrated online/in-line/at-line analytics fast enough to control manufacturing based on feedback, seamless data acquisition and Good Manufacturing Practice (GMP)-ready control systems are essential to support adaptive operation and drive the transition to continuous processing in CGT manufacturing.
Continuous mRNA LNP encapsulation
Repligen’s PAT solutions are designed to optimise performance across both Upstream and Downstream workflows. By using perfusion for example for lentivirus production as well as other envelope viruses enabling continuous upstream production and continuous clarified feed into the downstream process steps with integration of online metabolic analysis.
A compelling example of PAT-enabled continuous processing comes from a Repligen collaboration with a CDMO manufacturing mRNA encapsulated in lipid nanoparticles—a growing alternative to viral vectors due to its cost-efficiency. Repligen integrated the FlowVPX™ variable pathlength UV-Vis system directly into the production line to enable real-time quantification of mRNA concentration and in-process impurities. This online measurement supports continuous processing and reduces reliance on traditional offline testing. Crucially, FlowVPX™ also enables assessment of encapsulation efficiency at the end of the process. By embedding this analytic capability online, the CDMO can proactively manage and reduce the risk of batch failure at release.
Another compelling example is PAT-enabled continuous optimised upstream viral vector production comes with integration of Repligen’s MAVEN™ and MAVERICK™, bioprocessing analytics tools acquired from 908 Devices. MAVEN™ is a real-time glucose and lactate monitoring system, while MAVERICK™ is a Raman spectroscopy-based in-line bioprocess analyser and control instrument, therefore providing real-time insights into critical process parameters.
“If we want to reduce cost of this complex product without compromising safety there is no doubt that the field will move faster into continuous processing than monoclonal antibodies did.” – Rachel Legmann, Senior Director of Technology, Gene Therapy at Repligen
Advancing PAT integration
Progress toward continuous processing in CGT relies on seamless, non-destructive integration of Process Analytical Technologies. While existing sensors for pH, dissolved oxygen and metabolites are adapted from traditional bioprocessing, they often require large sample volumes, frequent calibration and complex modelling—making them poorly suited for small-scale, aseptic CGT workflows.
To address these barriers, modest redesigns and emerging innovations are improving integration.
- Sterile connectors, pre-sterilised single-use probes and non-invasive sensors are enabling closed-system compatibility. For example, PreSens® offers single-use, non-invasive optical sensors for oxygen and pH that weld directly into cell culture bags. Similarly, single-use flow-through cells can be added to perfusion lines for real-time monitoring.
- Repligen’s MAVEN™ focuses on real-time single use monitoring of glucose and lactate levels, crucial for cell culture processes. It integrates with bioreactors to provide data for process optimisation and control.
- Raman spectroscopy is gaining traction as a non-invasive, in-line tool for tracking nutrients and metabolites like glucose, lactate and ammonium via chemometric models. However, adoption is still limited by calibration needs and data complexity. Solutions like Merck’s ProCellics™ simplify Raman monitoring through integrated software and technical support. Repligen’s MAVERICK™ utilises Raman spectroscopy to measure multiple parameters in real-time, enabling continuous monitoring and control of bioprocesses across various bioreactors and cell lines.
2.2 The gap in real-time analytics – cell characterisation analytics
Many CGT-specific attributes of identity, potency and function still lack suitable sensing solutions, particularly for online or in-line cell characterisation, which could yield major cost and efficiency gains. There are currently no tools capable of providing real-time, non-invasive analytics for key metrics such as total and viable cell counts, CD4/CD8 ratios, cell identity, vector titre, full/empty capsid ratio and impurities. Cell characterisation currently relies on complex, offline assays, such as flow cytometry, PCR/ddPCR and enzyme-linked immunosorbent assays (ELISA), which require manual sampling, are slow and labour-intensive and disrupt the manufacturing process. These methods are difficult to miniaturise or automate for in-line or real-time use.
“It’s about streamlining the whole development life-cycle and manufacturing workflow through data. Once you do that, you can shave days off production, reduce costs, and accelerate time to market – that’s why analytics will be a game changer.” – Antoine Espinet, CEO of MFX
‘PATable’ surrogate parameters
A promising strategy for real-time monitoring of cell attributes involves the use of PATable surrogate markers – measurable indicators that correlate with cell identity, function or quality. A strategy proposed by the CGT Catapult is to combine high-throughput, high-content screening methods such as flow cytometry, gene expression profiling, liquid chromatography-mass spectrometry (LC-MS) and sequencing with PAT-compatible technologies like Raman spectroscopy to enable the development of robust correlations between complex, offline biomarkers and simpler, real-time measurements using in-line, online or at-line sensors. CGT Catapult are using these outputs to develop digital twins and enable advanced process control strategies.
Another example is the use of cytokine expression as a surrogate for infectious titer, a critical metric in viral production that is traditionally assessed via slow, manual assays. A recent study showed that cytokine expression within hours of infection correlates strongly with infectious titer. Platforms like Bio-Techne’s Ella system, a rapid, automated ELISA tool, enable fast, at-line cytokine measurement to support timely process control based on early infectious titer insights.
Leveraging enabling technologies (contactless, label-free)
To further overcome limitations in online, in-line or rapid at-line cell characterisation, the field is increasingly turning to enabling technologies inherently suited for real-time integration.
Typically label-free, non-invasive, non-contact and rapid sensing modalities – such as imaging (including holographic imaging), electrical impedance, Raman spectroscopy, UV-Vis spectroscopy and NIR spectroscopy and laser force cytology – offer potential for in-line, online or rapid at-line deployment. With approaches like microfluidic device integration, flow cells and dynamic sampling platforms, their potential is enhanced.