The Father of Cord Blood Freezing (Cryopreservation)

Hal E. Broxmeyer, PhD,
Indiana University
School of Medicine
(1944 - 2021)

Cord blood transplantation is a clinically effective form of treatment for many patients with cancer and blood diseases who need a stem cell transplant (1-3). To date over 30,000 patients have been treated with cord blood transplants (3).

The precious ingredients in cord blood are the blood-forming (hematopoietic) stem cells and progenitor cells that can replicate and diversify to replace a patient's entire immune system. These cells are rare, comprising less than one percent of the cells in cord blood, but nonetheless a typical cord blood collection contains millions of blood-forming stem and progenitor cells.

Cord blood transplants can come from either public banks or from private/family banks in which the cord blood stem cells are stored in a cryopreserved frozen state. The key to cord blood banking is to properly cryopreserve the stem cells so that when they are thawed for therapy they are still alive and maintain the functional capacity of the cells to repopulate the blood cells in a patient's body.

A question that often comes up about stored cord blood, is how long can the stem and progenitor cells be maintained in frozen form and still be viable when they are thawed?

In theory, if the cord blood stem and progenitor cells were properly cryopreserved, it should be possible to keep them in a frozen state for many decades, if not longer, with subsequent retrieval of viable stem and progenitor cells.

Practically, this depends on the quality of the cryopreservation procedure. It depends on whether the storage facility assured that the cryogenic nitrogen tanks were maintained at a constant very low temperature. Finally it depends on the competence of the laboratory staff who thaw the cells to revive them.

There have been a number of studies on retrieval and viability testing of cord blood after many years of storage in liquid nitrogen-containing tanks. Our own studies, first reported in the late 1980's when we suggested that cord blood stem cells could serve as a substitute for bone marrow transplants, noted highly efficient cell recovery after a few months of storage in cryopreserved form (4).

This led us to establish the first proof-of-principle cord blood bank in my laboratory (1-3). We supplied the frozen cells for the first five cord blood transplants ever performed, which were all between HLA-identical siblings. We also banked cells for two of the next five cord blood transplants performed.

Over the decades since, we have demonstrated efficient cell recovery at 5 years (5), 10 years (6), 15 years (7), and most recently 23.5 years (8) after the cells were frozen in cryopreserved form. The accuracy of these tests rests on the fact that we have had continuous custody of these cells, and we have performed their post-thaw analysis with the same tests as their pre-freeze measurements.

Coming up in another 2-3 years we will perform a 30 year assessment of our oldest cord blood specimens. Until then, the longest time that cord blood has been frozen and subsequently thawed with efficient recovery of stem and progenitor cells is 23.5 years in a laboratory setting. The longest storage interval of frozen cells that were given to a patient as a cord blood transplant is at least 14 years (pers. comm., Dr. P. Rubinstein).

Based on the studies in our laboratory, it is likely that cord blood can be stored frozen for decades and still be a potent source of cells for transplantation.

It may take some time before clinical studies demonstrate the viability of stem cells from long-term storage that we have established in the laboratory. Clinical proof would require treating patients with cord blood units that had been in storage for decades. But public cord blood banks tend not to use older stored cord blood collections if they have newer ones. Hence clinical proof of long-term storage success may have to come from private/family cord blood banks, when their clients eventually use the cord blood as therapy for the baby it came from or for a related family member.

Dr. Broxmeyer is a Distinguished Professor, Mary Margaret Walther Professor Emeritus, and Professor of Microbiology and Immunology at the Indiana University School of Medicine (IUSM), Indianapolis, Indiana, and is Co-Leader of the National Cancer Institute Designated Indiana University Simon Cancer Center on Hematopoiesis, Malignant Hematology and Immunology. He was a co-founder of the CORD:USE hybrid public/family cord blood bank, which has since been acquired by Cryo-Cell.  He is a member of the National Marrow Donor Program (NMDP) Cord Blood Advisory Group.

References

1. Gluckman, E., Broxmeyer, H.E., Auerbach, A.D., Friedman, H., Douglas, G.W., Devergie, A., Esperou, H., Thierry, D., Socie, G., Lehn, P., Cooper, S., English, D., Kurtzberg, J., Bard, J. and Boyse, E.A. 1989. Hematopoietic reconstitution in a patient with Fanconi anemia by means of umbilical-cord blood from an HLA-identical sibling. New Engl. J. Medicine 321:1174-1178. PubMed: PMID2571931
2. Broxmeyer, H.E. and Smith, F.O. 2009. Cord Blood Hematopoietic Cell Transplantation. In: Thomas' Hematopoietic Cell Transplantation 4th Edition. Eds: Appelbaum, F.R., Forman, S.J., Negrin, R.S., and Blume, K.G. Wiley-Blackwell, West Sussex, United Kingdom, Section 4, Chapter 39, pp. 559-576.
3. Ballen, K.K., Gluckman, E., and Broxmeyer, H.E. 2013. Umbilical Cord Blood Transplantation - the first 25 years and beyond. Blood. 122:491-498. PubMed: PMC3952633
4. Broxmeyer, H.E., Douglas, G.W., Hangoc, G., Cooper, S., Bard, J., English, D., Arny, M., Thomas, L., and Boyse, E.A. 1989. Human umbilical cord blood as a potential source of transplantable hematopoietic stem/progenitor cells. Proc. Natl. Acad. Sci. USA. 86:3828-3832. PubMed: PMC287234
5. Broxmeyer, H.E., Hangoc, G., Cooper, S., Ribeiro, R.C., Graves, V., Yoder, M., Wagner, J., Vadhan-Raj, S., Benninger, L., Rubinstein, P. and Broun, E.R. 1992. Growth characteristics and expansion of human umbilical cord blood and estimation of its potential for transplantation of adults. Proc. Natl. Acad. Sci. USA 89:4109-4113. PubMed: PMC525642
6. Broxmeyer, H.E. and Cooper, S. 1997. High efficiency recovery of immature hematopoietic progenitor cells with extensive proliferative capacity from human cord blood cryopreserved for ten years. Clin. and Exp. Immunol. 107:45-53. PubMed: PMID9020936
7. Broxmeyer, H.E., Srour, E.F., Hangoc, G., Cooper, S., Anderson, J.A., and Bodine, D. 2003. High efficiency recovery of hematopoietic progenitor cells with extensive proliferative and ex-vivo expansion activity and of hematopoietic stem cells with NOD/SCID mouse repopulation ability from human cord blood stored frozen for 15 years. Proc Natl Acad Sci USA. 100:645-650. PubMed: PMC141050
8. Broxmeyer, H.E., Lee, M-R, Hangoc, G., Cooper, S., Prasain, N., Kim, Y-J, Mallett, C., Ye, Z., Witting, S., Cornetta, K., Cheng, L., and Yoder, M.C. 2011. Hematopoietic stem/progenitor cells, generation of induced pluripotent stem cells, and isolation of endothelial progenitors from 21- to 23.5-year cryopreserved cord blood. Blood. 117:4773-4777. PubMed: PMC3100689