by Yelena Bronevetsky, PhD, Director of Product Management, Xcell Biosciences
Standard drug discovery and development pipelines have conditioned us to assume that only a small fraction of candidate therapies will eventually be deemed effective and safe enough to reach patients. In the world of cell therapy, a similar trend has taken place—but it may not be the same insurmountable problem.
Many cell therapy candidates appear quite promising during the early stages of small-scale research and process development, but eventually lead to disappointing outcomes when rolled out in clinical trials. While there are likely many contributing factors, there’s at least one explanation that has nothing to do with the usual vagaries of target selection, off-target toxicity, and other reasons that so many other types of therapeutic candidates fail in the drug development pipeline. Most cell therapies begin development using a single incubation and consumable technology platform for early-stage research but transition to a different platform for later-stage manufacturing and development. Many incubation platforms lack the precise environmental control and physiological relevance needed to support immune cells’ metabolic activity, ensuring they remain fit and potent in vivo.
Simply put, at least some of the failures in cell therapy today may be attributable not to complex biological factors but to the confounding variables introduced by having basic differences in technology platforms from one stage of development to the next. Shifting to an approach where the same platform is used consistently from the earliest to the latest stages of development, and across both small and large volume scale-up, may give cell therapy candidates a better chance at success. It would also streamline the entire workflow for cell therapy developers, allowing for the maintenance of metabolic fitness and avoiding the need to alter processes that get perfected in the early stages when they are translated to a different platform for late-stage use.
Snapshot: Late-Stage Failure
Anyone who works in cell therapy development probably has a familiar anecdote about a candidate that did very well in preclinical studies but fell apart later. While most of these failures happen behind the scenes, the community does occasionally get a glimpse into them through publications from researchers at academic medical institutions.
In one case, scientists at the Fred Hutchinson Cancer Research Center in Seattle reported on work they had done with chimeric antigen receptor (CAR) T cells designed to target a protein called ROR1.1 The target was chosen because it is highly expressed in tumor cell populations in triple-negative breast cancer and non-small cell lung cancer. In early-stage studies using tumor cell lines, these cells exhibited very potent cancer-killing function. But when the CAR T cells were administered in mouse and human studies, they showed poor tumor infiltration and cytotoxicity. Deeper analysis revealed that the cell products — which had been cultured and tested in vitro at the default environmental conditions, including oxygen concentrations used in traditional incubation platforms — had successfully reached the tumor site. The problem wasn’t targeting, but performance: when cells made it to their destination, they exhibited metabolic dysfunction and did not have the potency or persistence to function effectively against the tumors.
While the scientists in this project aimed to improve outcomes by adding other cancer treatments for a combination approach, such a model may not be practical for all cancers or for other diseases. Instead, two simple improvements may make a difference. First, using a more advanced incubation platform designed to metabolically prime cells for the tumor microenvironment — with its harsh, hypoxic conditions — could better condition cells to maintain their potency in vivo. Second, ensuring that this kind of cell expansion technology is used not just for in vitro research but also at larger scale for preclinical animal and GMP-grade clinical human studies would deliver a consistency and reproducibility that have been sorely lacking in current cell therapy development pipelines.
Metabolic Conditioning
The humble incubator gets little attention in most laboratory work, but for cell therapy development, it is actually the star of the show. The expansion process that takes place after cells are edited or enriched is fundamental to how cells will perform in patients: the environmental conditions used during cell expansion play a critical role in determining the biological conditions under which cells will be most effective in killing cancer.
The tumor microenvironment (TME) is an excellent example of this. Filled with suppressive forces, the TME typically features very low oxygen concentrations, high pressure levels, and a host of cells that inhibit the function of T cells. These conditions are radically different from those found in most cell expansion platforms, which are designed to grow as many cells as possible without concern for their metabolic fitness when challenged in vivo.
Generally, efforts to improve the function of a cell therapy center around the use of genetic engineering to confer higher potency and more durable persistence. But focusing instead on metabolic conditioning — training cells to endure the challenging environmental conditions they’ll face in vivo — may be even more effective. It’s the same kind of training we would associate with any high-performance task: deep-sea divers practice under the pressure of dozens or even hundreds of feet of water, not in the shallow end of a recreational pool.
For cell therapies, metabolic conditioning occurs when cell expansion conditions can more closely match the environmental conditions that cells will encounter in the body. For example, while low oxygen culture may yield slightly fewer cells than standard incubator conditions, it instead promotes metabolic rewiring that enables transferred cells to thrive in hostile tumor environments that might be deadly to cells that lack this training.
Mounting evidence from the scientific community underscores the association between incubation conditions and cells’ tumor-killing ability in vivo.2,3 For example, scientists have found that T cells cultured under low oxygen levels demonstrated higher cytotoxic function when infused into the body.4
Snapshot: High-Performing Cells
Metabolic conditioning for cell therapies has been enabled by a new generation of incubation technologies with more tunable parameters than the standard incubators that have been around for decades. Two features have a particularly noticeable impact for cell therapy development: the ability to carefully tune oxygen concentrations and hyperbaric pressure levels. Previously, these settings could not be precisely changed in incubators. But microenvironments within the body show a significant range of oxygen and pressure levels, making a one-size-fits-all approach inadequate for conditioning cells. While skin cells are accustomed to oxygen levels of 20% and pressure levels of just 1 PSI, cancer cells are more comfortable at 1% oxygen and 4 PSI. The ability to fine-tune environmental parameters in advanced incubation platforms is essential for conditioning therapeutic cells to the harsh environmental conditions under which they will be expected to perform.
One recent example shows the potential for sophisticated incubation in creating more potent cell therapies. Scientists at Labcorp Drug Development used an advanced cell expansion technology to prepare cells to face the harsh TME.5 In this project, they compared a conventional cell expansion approach with low-oxygen, high-pressure conditions to determine how this affected cancer-killing function in the cells.
The work was performed with CD19-CAR T cells that were expanded for 12 days, after which cytotoxic activity was measured with a targeted killing assay. The cells grown under optimized environmental conditions featured higher CAR expression than cells grown in standard settings, with double the yield of target cells. Researchers also evaluated CAR T cell cytotoxicity in a mouse model of B cell acute lymphoblastic leukemia. Mice that had been inoculated with NALM6 cells were treated with CD19-CAR T cells; after five weeks, the team assessed performance of the cell populations. The mice that received therapeutic cells grown under optimized environmental conditions experienced strong tumor control, with durable persistence of T cells in their blood. Overall, the team’s results indicated that CAR T cells cultured in hypoxic conditions at higher pressure had higher cytotoxicity than cells cultured in the usual conditions.
Bridging Technology
Clearly, metabolic conditioning for cell therapies is important — but fine-tuning environmental conditions and culture processes must also be consistent across all stages of therapeutic development. In too many cases, scientists use one type of cell expansion technology for early-stage research and an entirely different one for manufacturing. This is understandable, as the incubators and consumables used for process development may not make sense for high-capacity manufacturing work, and vice versa. The cell expansion platforms used in early-stage research also do not typically feature the levels of automation desirable in later-stage clinical trials and commercial manufacturing.
For better reproducibility and increased likelihood that promising early-stage cell therapy candidates turn into effective therapies, scientists should aim to use the same cell expansion platform throughout the development journey. Essentially, this can be thought of as a bridging technology for the entire drug discovery and development process: a foundation that works across all stages of research, whether in a small-scale, more flexible version for process development or a large-scale, automated version for clinical manufacturing. With consistent cell expansion technology, cell therapies should perform more predictably in later stages of development than they do right now. Such an approach would be amenable to being locked down for the 21 CFR compliance needed for clinical use.
Ideally, a bridging technology should also include advanced customization options to enable the kind of metabolic conditioning needed to generate more effective and more potent cell therapies. The ability to adjust environmental conditions like oxygen and pressure levels is an important factor in creating biologically representative microenvironments. Taken together, a consistent platform that better recreates in vivo conditions and can be used from early-stage research to late-stage development and manufacturing should improve the chances that a promising cell therapy candidate translates into a successful treatment when used in patients.