Amin Adibi is a biomedical engineer and a research assistant at the University of British Columbia. His areas of interest include cell manufacturing and bioprocess optimization, clinical translation of cellular therapies, health outcomes and cost-effectiveness modelling. Amin has an MSc degree from University of Calgary, where he focused on developing adjuvant MSC-based therapies for brain aneurysms. Follow him on twitter at @aminadibi
I ended the first part of the write-up on CCRM’s Cell and Gene Therapies Workshop (CGTW16) on a note by CCRM’s Dr. Nick Timmins on the importance of incorporating Quality by Design (QbD) in cell manufacturing. I also mentioned some back-of-the-envelope calculations that showed a ballpark estimate of 25,000 annual doses of CAR T cell therapies might be needed to address the demand in North America.
While the majority of the promising CAR T cell trials so far have used autologous cells, developing an allogeneic CAR T cell therapy is also being actively pursued by industry. From a manufacturing point of view, autologous and allogeneic cell therapies are drastically different. Autologous cell therapies should be scaled out: you need a very large number of relatively small bioreactors that work in parallel, as each dose is essentially a different product and requires its own quality control procedures. In contrast, producing more of an allogeneic cell therapy is a problem of scaling up: by using a larger bioreactor, more of the same batch of the product can be produced, which would significantly quality control cost and workload.
Unfortunately, scaling up has its own challenges as Dr. Gregory Russotti, VP Technical Operations at Celgene Cellular Therapeutics, pointed out. The reason, explains Dr. Russotti, is that in stirred tank bioreactors, as the scale goes up, agitation rates should be increased to maintain the required amount of dissolved oxygen (DO). However, with increasing agitation rate, small areas of intense turbulence – known as eddies – form in the media that dissipate hydrodynamic energy, which can potentially damage cells.
The size of eddies is the critical parameter. As the agitation rate goes up, eddies become smaller and, although it may feel counterintuitive at first, it is the smaller eddies that are problematic. If a particle – be it a single cell, cell aggregate or microcarrier – is completely surrounded by a relatively large eddy, it will move and rotate with it without putting much stress on the surface of the particle. Conversely, “if eddies are smaller than the particle, they will splash on it, causing damage to cells,” says Dr. Russotti. Therefore, the smaller your particle, the larger your bioreactor can be. He added: “the largest published scales for MSCs on microcarriers is 1000 L. In the CHO world you can go up to 20,000 L because your cell is about 15 µm – instead of 200 µm microcarriers – so your eddies can be smaller without damaging your cells.”
The next speaker was Dr. Aaron Dulgar-Tulloch, Director of BridGE@CCRM for GE Healthcare Cell Therapy Technologies, who talked about the vision of closed cell manufacturing systems. Dr. Dulgar-Tulloch noted that in academic settings, producing one batch of T cells under good manufacturing practice (GMP) conditions is a costly and highly labour intensive 14-day process. “You are sampling every day, there is a lot of feeding and media additions and you need highly classified cleanrooms,” he says. The problem is that most cell processing devices in academic labs do not connect to each other, requiring technicians to handle materials and cells from one device to another. A generic open CAR T cell production workflow, for instance, involves more than five non-integrative devices, more than 10 open reagent additions, and more than eight open transfers. Additionally, the entire process must be done in a highly classified cleanroom and lacks IT connectivity and quality management system (QMS) integration. This highly manual, disconnected and open process significantly increases the risk and the cost of failure.
In contrast, closed systems do not expose the product to the room environment, decrease variations and contamination risk, improve flexibility and efficient use of the facility, and allow for process automation, thereby significantly reducing staffing/space requirements, as well as the cost for energy, gowning and quality investigations. But if using completely closed systems is so desirable, why isn’t everybody doing it? The problem, Dr. Dulgar-Tulloch explained, is that by switching to completely closed systems, you are pushing process development costs and time requirements upfront. This may not be the ideal thing to do for companies that are racing to be the first to complete clinical trials and get to the market.
So, what is the middle ground here? Dr. Dulgar-Tulloch thinks the solution is to go for semi-closed automated perfusion systems. GE Healthcare’s Xuri Cell Expansion System, for instance, allows for continuous monitoring of DO and pH in single-use Cellbags. Perfusion rates can then be controlled automatically using DO as a surrogate marker for cell density. Advantages? This technology reduces process development costs down the road, can be scaled up or out and is not cost-prohibitive to implement early on. Disadvantages? Well, it is not completely closed, so you won’t have all the benefits. Dr. Dulgar-Tulloch also touched upon what remains to be done in future. “There is a need for improved process understanding,” he says, “as well as developing integrated single use sensors for metabolites and phenotype.” There is also a pressing need to standardize tubing sets and other connections between devices.
I always find scale up challenges interesting. Oftentimes, developing a promising therapy at the bench is just the first step toward many more that are required to make the therapy accessible to all patients. Still interested? Tune in next week for part 3 on clinical trials, health economic considerations and regulatory affairs.
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