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Celldom Aims to Ease Cell Therapy Potency Assay Challenges With New Instrument

Infusion bag close up

NEW YORK – Duke University spinout Celldom will use a recent National Cancer Institute grant to help autologous cell therapy manufacturers accomplish something the field has struggled with to date: defining and measuring their products' potency. 

Because autologous cell therapies are uniquely derived from a patient's own cells, the task of measuring the treatment's potency, or biological activity, has been a challenge, both for drug developers and regulators. 

"Cell-based medicines are not like small molecules," said Celldom CEO Benjamin Yellen. "These are living drugs that are heterogenous by nature and evolve over time. It's a different ballgame." 

Celldom is commercializing an instrument to more easily, directly, and quickly measure cell therapy potency. The instrument combines imaging-based phenotyping with molecular profiling. It first measures the functional properties of more than 100,000 CAR T-effector cells in co-culture within one experiment. Then, it uses these functional measurements to home in on which cells to retrieve for genomic characterization, which can help researchers identify and further study the cell subpopulations that dominate a patient's in vivo response. 

Yellen said the firm will use a recent $938,647 NCI Small Business Innovation Research (SBIR) grant to ensure its product meets all the requirements of a potency assay. "We would like to measure at least two or three cytokines and three surface markers so that we can do measurements, not only of potency but also [of] the identity of the cells and the purity of the population of cells that we introduce," he said. 

Cell therapy potency challenge 

With small molecule drugs, manufacturers can use a single potency assay to measure a large batch of the drug before release. This batch potency testing is possible with small molecule drugs manufactured with the same chemical compounds, but it is impossible with bespoke cell therapies, since each patient's harvested cells become the treatment they receive. Because the makeup of harvested cell populations differs from patient to patient, it becomes difficult to determine which cell clones are contributing to a bespoke therapy's efficacy. 

This puts cell therapy developers, and the agencies responsible for regulating these drugs, in a tricky position. Similar to how they require safety and purity testing plans from traditional drugmakers, reviewers at the US Food and Drug Administration want cell therapy developers to propose consistent, effective methods for measuring their products' potency. Without a solid potency testing plan in place, drugmakers are unlikely to net FDA approval. 

This was one of the chief reasons that the first autologous tumor-infiltrating lymphocyte (TIL) therapy, Iovance Biotherapeutics' Amtagvi (lifileucel), faced several years of regulatory delays. Ultimately, Iovance and the FDA agreed on a comprehensive matrix approach, involving myriad measurements that collectively comprised Amtagvi's potency measurement plan. The therapy entered the commercial market this February, decades after it was first developed. 

Around the same time as the Amtagvi approval, the FDA's Center for Biologics Evaluation and Research (CBER) began discussing the idea of using combined potency matrix approaches with industry. In January, regulators put out a new draft guidance in which they laid out a broader definition of product potency. 

The FDA's willingness to allow cell therapy makers to use a combination of approaches to measure their products' potency provides more regulatory clarity, but according to Yellen, integrating multiple measurements into the workflow can be cumbersome, time-consuming, and resource-intensive. 

"Right now, the way that [potency assay testing] is being done is all fragmented," he said. "You need multiple tools, and they're all subject to human error. It's very labor-intensive to do the whole potency assay measurement when it means measuring all attributes of the drug product. … It increases time and increases cost." 

While every cell therapy manufacturer — like every cell therapy itself — is different, Yellen said that as a baseline, developers usually perform a combination of flow cytometry and a live cell secretion assay, in which they measure some sort of cell secretion such as interferon gamma. From the flow cytometry measurements, he said they will often measure CD8 and CD4 T-cell populations and, in the case of CAR T-cell therapy, the chimeric antigen receptor, to make sure the cell has been edited as intended. 

"Then you have to do the follow-on sterility testing, which is mostly going to be micro plasma-based or PCR," he said. 

Finally, Yellen pointed out that all of these tests, when performed on a product in vitro, may not reflect the product's activity or composition in vivo. For instance, certain cells may appear to be enriched outside of the body, but that population of cells might not be the same one that is enriched when the therapy is infused in the patient. 

Celldom's product 

One advantage that Yellen believes Celldom's approach has over the current fragmented approach to establishing cell therapy potency is its ability to work on far fewer cells, which reduces the need for ex vivo cell expansion, he said. 

The instrument involves a standard 96-well plate, Yellen said, but at the bottom of each well there are 3,500 microwells, totaling around 300,000 or more microwells per plate. When Celldom creates the co-culture, it adds around 3,000 target cells and 3,000 T-effector cells into the same well, where they randomly sediment to the bottom due to gravity. 

"What happens as a result of that is that we get all of the different effector target ratios in every well," he said. "Instead of having to do it one well at a time, we use randomness to our advantage … so every well is a complete experiment, essentially. That, collectively, is the secret sauce that allows us to use very few numbers of cells." 

The firm also uses an imaging platform it developed to continuously monitor cell phenotype patterns over time, including cytotoxicity and growth rate. 

The firm will use the funds from the SBIR grant to further refine its product with the technical specifications needed for product potency measurement. But in the meantime, Yellen said Celldom is already starting to commercialize the instrument. 

"We're starting to deploy these instruments at different sites around the country and in Europe," he said, adding that Celldom is working with several early-stage and clinical-stage cell manufacturing companies, but declined to share which firms it is working with. The technology can measure the potency of a variety of autologous cell therapies, including CAR T-cell and T-cell receptor-T therapies, he said. 

Celldom's goal is to become a go-to partner for potency testing for academics, research centers, small biopharmaceutical companies, and others in the field. Beyond potency testing, the firm is also developing its technology to help researchers better characterize their products in the preclinical stage. 

"There's also a research component of this," Yellen said, explaining that Celldom will use the NCI grant to study which cell clones kill cancer cells and rapidly expand. The firm will conduct RNA sequencing of "the really super potent T cells," Yellen said, "to understand what makes them biologically more active or potent than other cells."