In the cell therapy field, encapsulated liver cell spheroids (ELS) – artificial liver organoids – help the liver regenerate during acute liver failure and can be useful during liver transplantation.
Before clinical trials, ELS production needs to be scaled up. However, in stem cell manufacturing for cell therapy, stem cells require a temperature-controlled, cold-chain transport system.
To better define the temperature requirements of ELS, Isobel Massie and colleagues designed an experiment comparing storage at different ultra-low temperatures1. They cryopreserved ELS and stored them at either -80°C or -170°C for up to a year. The former temperature is typical of an ultra-low freezer, while the latter represents the vapor phase of liquid nitrogen.
The ELS were removed from cold storage after 1, 2, 3, 6, 9, and 12 months – and recovery was assessed by evaluating cell viability and functional activity. The authors found that cell viability was significantly reduced to only 15% in ELS stored at -80°C, whereas 75% of those stored at -170°C remained viable.
Functional activity was determined by quantifying albumin secretion. ELS stored at -170°C exhibited consistently high albumin secretion. Strikingly, ELS stored at -80°C showed a 60% decrease in albumin secretion after only one month. By 12 months, albumin secretion was undetectable.
These results clearly indicate that cryopreservation in the vapor phase of liquid nitrogen is the ideal method of storing ELS if they are to remain viable for cell therapy.
Cells stored at -170°C can be transported for distribution at -80°C and still survive. To establish a new culture of cells, 100% viability is not necessarily required. If some cells survive the journey at -80°C, they can rapidly grow and expand the culture. Any cellular debris can be removed so as not to contaminate the cell culture.
The same is not true for ELS. Full recovery is required for ELS to be successful as an artificial liver. Furthermore, any cellular debris that accumulates upon thawing would be transferred into the patient and could initiate an immune response. Future work needs to be done to determine how long ELS can survive transportation at -80°C and remain effective in a cell therapy setting.
Reference
1. Massie I, et al. Storage temperatures for cold-chain delivery in cell therapy: a study of alginate-encapsulated liver cell spheroids stored at -80°c or -170°c for up to 1 year. Tissue Eng Part C Methods, March 2013.