Exploring the improvement of human cell cryopreservation

Regenerative medicine is an emerging technology and with hundreds of cell therapies currently in clinical trials there is a need to expand the limited knowledge related to their storage, shipment and preservation. The most widely used medium for human cell cryopreservation is 10%wt dimethyl sulfoxide (DMSO) in serum. However given its potential toxicity, DMSO usage is a key issue in cryopreservation. Methods specify the need to reduce cell exposure time to DMSO above 0°C as much as possible but the maximum amount of time cells can be exposed to DMSO to prevent a detrimental effect needs to be clarified. There are also regulatory issues and concerns with the xenotoxicity, ethics and supply of the other core component in the standard cryomedia formulation: Foetal Bovine Serum (FBS). Developing a viable alternative to FBS is crucial. In cryobiology literature thawing appears poorly understood. A stable process is as vital as freezing to prevent injury to cells. Protocols are currently too vague for cell therapy regulation and need improvement. The time dependent DMSO cytotoxicity was evaluated by overexposing cells to DMSO during and/or after cryopreservation. A broad investigation found that after 1 hour overexposure post thaw viability of human mesenchymal stem cells (hMSCs) was reduced from 96.3±0.6% to 74.1±4.0% and the co-expression of five key hMSC markers was changed from 97.9±1.3% to 68.3±2.6%. This significant change could cause indicate a change in product efficacy and affect patient health, to prevent this, DMSO exposure must be kept to below 1 hour. A range of alternative vehicle solutions were screened and human platelet lysate (hPL) investigated as an alternative. In depth experimentation with hPL as a cryopreservation vehicle solution and culture supplement (in place of FBS) found it to be a worthy, statistically similar alternative. With no xenological or ethical concerns, lower costs than other serum-free alternatives hPL could allow for a move away from xenological components. A heat transfer model was developed and determined that 720J is required to thaw a vial. Using the heat transfer model and additional factors such as pre-thaw stabilisation and on thaw dilution, a two-stage experiment found that the current standard process (warming in a 37°C waterbath) within the current paradigm of a 1.8mL cryovial is optimal but further work is required to define the process for scaled-up product.