As Jacques Galipeau reported in conferences and in the paper, cryopreservation could negatively affect therapeutic “immunomodulatory value” of mesenchymal stromal cells (MSC). There was no independent confirmation of Galipeau’s findings, and many MSC product developers remained skeptical. This week, Katarina Le Blanc published a report, which supports Galipeau’s conclusions and provides more insight into potential clinical value of this phenomenon. Let me just say – this paper could change the field!
Le Blanc concluded that freeze-thawed human MSC compared to fresh MSC possess:
- increased triggering of Instant Blood Mediated Inflammatory Reaction (IBMIR);
- strong activation of complement and coagulation cascades;
- increased sensitivity (lysis) to exposure of normal human serum;
- overall reduced immunomodulatory and blood regulatory properties;
- trend toward worse clinical response in GVHD clinical trials.
I’d like to summarize more clinical part of the study. 44 infusions of MSC were analyzed retrospectively. 9 of 44 were fresh MSC infusion, the rest freeze-thawed. Conclusions from clinical part:
- patients with fresh + early passage (1-2) MSC infusions showed 100% response rate
- patients with freeze-thawed + later passage (3-4) MSC infusions showed 50% response
- however this difference was not statistically significant (p=0.06)
- viability was the same between fresh/ cryopreserved MSC and between responders/ non-responders
- there was no difference in long-term engraftment of MSCs in tissues between fresh/ cryopreserved groups.
Significant limitation of clinical part of the study, mentioned by authors in discussion, is low number of comparable infusions (fresh n=9). This limitation affected statistical power of the study. The authors wrote:
A power analysis aiming at 80% power at the 0.05 significance level shows that we can only expect statistical significance for difference n clinical effect of more than 50%, meaning that we might ignore clinically relevant differences. We must therefore also consider trends, even though this could be considered speculative.
The authors performed a number of in vitro studies, testing immunomodulatory and blood regulatory properties of fresh versus frozen MSCs. Some interesting findings from this part:
- strong compliment lysis by normal human serum of cryopreserved MSCs was abrogated by addition of EDTA;
- despite the fact that level of IDO upon interferon-gamma licensing was much higher in fresh MSC, there was no difference in other immunomodulatory cytokine – IL-6;
- even though frozen MSCs were inferior to fresh in PHA-stimulated MLR, there was no difference in allo-stimulated MLR.
Overall, I think, this study is invaluable! Everyone, who is involved in MSC-based clinical trial must read it! Le Blank study confirms earlier finding by Galipeau’s group and could have a big impact on a field. As of now, we don’t have convincing positive results from Phases 2/3 of clinical trials, where MSCs are used as powerful immunomodulators (GVHD, Crohn’s disease). Contrary, we have a history of big failures of MSCs in “immunomodulatory trials”. For example, Osiris Phase 3 GVHD trial and very recent Athersys Phase 2 IBD trial. All clinical trials right now are utilizing frozen MSCs! Could a phenomenon, describing by Galipeau and Le Blanc, be a real deal breaker? Very much possible! I guess we will know for sure with more independent studies and with direct comparison of fresh versus frozen in clinical trials. Galipeu just started a trial for Crohn’s disease with freshly harvested MSCs. I hope they can include a small “frozen MSC” group.