Cryopreservation: The Cause of Stem Cell Therapy Trials Failure?
We recently stumbled upon a fantastic stem cell site called stemcellassays.com. One of the writers, Alexey Bersenev, dissects a publication from earlier this year about a stem cell trial that failed. In his words, this publication is “one of the best examples of how the analysis of cell therapy trial failure should be done!” 
The analysis was published in Cryotherapy in January this year by Dr Jacques Galipeau and his team and is based on discrepancy between mesenchymal stem cells (MSCs) preparation for US industry-sponsored trial versus European academic trials.  The publication reflects on four distinct MSC product variables that may apply to the apparent conundrum at hand: donor variance, epigenetic reprogramming, immunogenicity and cryopreservation. We highlight below a detailed excerpt from the cryopreservation section:
- Human clinical trials examining the use of MSCs almost universally use stored, cryopreserved products that are thawed and transfused within no more than a few hours. This logistical approach is convenient and logical and rests on the premise that similar handling of cryopreserved leukapheresis products used in autologous peripheral blood transplantation has good outcomes.
- However, all pre-clinical studies of MSCs in mouse models of human disease universally involve transfusion, transplantation or implantation of live, log phase of growth MSCs.
- Nearly no published pre-clinical report delivers cryopreserved MSCs immediately after thawing to experimental animals.
- “Is cryopreservation a truly innocuous transient state without bearing on MSC function at thaw?”
- This question has not been tested in a rigorous fashion in pre-clinical models. It is recognized that 20–30% of thawed MSCs are irreversibly compromised as ascertained by the trypan blue viability assay routinely used as a release parameter in most studies; this leaves roughly two thirds of a cell dose as “live” trypan-excluding cells at the time of transfusion.
- “However, viability is not a synonym for functionality”
In a previous publication the same research group demonstrated that cryopreserved MSCs, upon thawing displayed impaired immunosuppressive properties as a result of heat-shock response and impaired interferon-γ licensing. They also found that in vivo persistence of thawed human MSCs in transfused mice is markedly shortened compared with non-cryopreserved counterparts but that the deleterious effects of thawing are self-limited and reverse within 24 hours in vitro.
These results highlight a possible cause for the inefficacy of MSC-based immunotherapy clinical trials using cryopreserved MSC thawed immediately prior to infusion. It also raises the question whether it would be more beneficial for MSCs to undergo a post-thaw “rescue” prior to infusion to potentially improve performance and potency.
 The mesenchymal stromal cells dilemma—does a negative phase III trial of random donor mesenchymal stromal cells in steroid-resistant graft-versus-host disease represent a death knell or a bump in the road? Jacques Galipeau. Cytotherapy 2013; 15:2-8
 Cryopreserved mesenchymal stromal cells display impaired immunosuppressive properties as a result of heat-shock response and impaired interferon-gamma licensing. Francois M et al., Cytotherapy. 2012;14:147–152