A new system may help solve the problem of shipping cells between laboratories and hospitals and clinics by developing an alternative to cryopreservation.
The U.S. Food and Drug Administration last year approved the first two cell therapy treatments, Kymriah (tisagenlecleucel), for acute lymphoblastic leukemia (ALL), and Yescarta (axicabtagene ciloleucel), a chimeric antigen receptor (CAR) T-cell treatment for large B-cell lymphoma.
More approvals are on the way. When they arrive, cell therapy providers will face a new problem: How to ship cells between laboratories that produce personalized medicines and the hospitals and clinics that store them until they are needed.
Today, this is often done by cryopreservation, which may not be ideal for a future where cell therapy is common.
A new alternative from UK startup Atelerix, Ltd., a spinoff of Newcastle University, could prove a more scalable system. It embeds cells in beads made of crosslinked alginate, an anionic polysaccharide found in the cell walls of brown algae that forms a viscous gum on contact with water.
The alginate slows the cells’ metabolism, so they remain viable for up to two weeks. The coatings are easy to remove, and clinicians can use the resulting cells immediately, says Che Connon, Atelerix’s chief scientific officer and a professor tissue engineering at Newcastle’s Institute of Genetic Medicine.
Cryopreservation is the most common way to preserve cells for shipping today. The process involves deep freezing cells with DMSO (dimethyl sulfoxide), which acts as an antifreeze. The DMSO prevents the formation of ice crystals, which can expand and damage cells. DMSO is also toxic to cells and must be thoroughly washed out of the cells to prevent contamination.
Once frozen, cryopreserved cells are stored using either liquid or vapor phase liquid nitrogen for aircraft travel or dry ice for shorter distances. Once thawed, those cells need time to acclimatize and grow. Cryopreservation requires technical specialists and complex infrastructure, which adds to the cost of cryopreservation. It has other issues as well.
“While the cells survive fine, some cells coming out of cryopreservation are not quite the same as those going in,” Connon says. “They may differ genetically and behaviorally.”
Finally, once the cells are thawed, they must be used within one to two hours. This requires surgeons, nurses, and patients to coordinate operating time.
“This can be a real headache,” Connon says. “It’s OK in clinical trials, where there are a small number of patients and the clinicians are excited and willing to change schedules to make it work. But it is going to be harder to coordinate when cell therapy procedures become common and more mundane.”
Shipping cells in liquid media, which miniaturizes the conditions within a bioreactor, seeks to overcome those limitations. Because there is no freezing or thawing, it reduces infrastructure costs. Unfortunately, the cells remain viable from only a few hours to two to three days and must usually be used quickly when they arrive. Cells are also susceptible to shear damage from liquid slopping around.
Alginate has a long history as a scaffold material in tissue engineering and to protect transplanted cells from the host’s immune system. Its use as a cell therapy transport system came about by accident.
Connon published his first paper on alginates ten years ago. It covered crosslinking the sugars for possible use as a biomaterial. Five years ago, he received a research grant to deliver stem cells to the surface of the eye. He decided to apply the cells to a structure that resembled a contact lens. Since he had not included enough money in the grant to develop an optimal biomaterial for the task, he encapsulated the stem cells in a material he already knew, alginate.
The system he used included an indicator that turned from pink to yellow as the cells respired. This warned him that he needed to change the media and nutrients.
“I noticed that the cells in the alginate gel were respiring more slowly than the other cells,” he says. “The cells were alive, but their metabolic demands were not very high. On a different day, I might have thought this was a nuisance and tried another material. Instead, I wondered how well those cells would survive outside the media under adverse conditions.”
At the time, cell therapy was a star just rising over the horizon. Yet Connon had a background in stem cell therapy and had done a post-doc in the field in Japan. He already had an inkling that logistics were going to be a problem for cell therapy.
He started investigating why alginate maintained cell viability. He found that lowering temperatures to just below room temperature (to 15-20 °C, well below 37 °C body temperature) kept the cells alive for up to two weeks. Varying the thickness and porosity of the coating made little difference.
Instead, Connon hypothesized that alginate mechanically stabilizes encapsulated cells by keeping them from moving.
“When we lower temperatures, the cell’s lipid membrane grows more rigid and prone to fracturing, and the cell could explode or die,” he says. “The alginate mechanically supports the membrane and prevents those fractures from occurring.”
He has developed a technique that can produce 3,500 alginate beads per minute. This involves sprinkling crosslinking solution (typically a salt) from a shower head into a stirred tank containing cells and liquid alginate. The beads form instantly when they meet.
Clinicians could keep the cells in the gel to increase the residency time of cell implants, like an artificial pancreas, or de-gel the beads with a multivalent salt to form a suspension for immediate injection. In addition to cell therapy, alginate-embedded cells could be used to culture cell assays for drug testing or biological research.
Today, many firms use cell assay kits. A standard kit has 96 wells. Most mammalian cells adhere to the walls of the cells, and adherent cells cannot be cryopreserved.
That means that vendors must ship the assay kit and cryopreserved cells separately. Researchers then thaw, grow, and plate the cells. For neuronal cells, it can take one month before anyone can run an assay.
Alginate cells could make it possible to ship plates that are ready to use as soon as the cells are de-gelled. Connon believes Atelerix could provide an important piece of the infrastructure for cell therapy in the future.
“Many of these cell therapy companies are going to become logistics company,” Connon says. “They are going to have to wrestle with how to get cells from patients to processing units and back into patients again.
“As these products start scaling up, they are more open to new ideas,” he says. “Now, they are thinking about logistics.”
Read more about Cell Therapy on AABME.org.