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The Difference Between Stem Cell Viability and Potency: A Short Guide for Parents and Patients
When a patient receives a cord blood transplant, the patient's life depends on some of the stem cells in the cord blood finding their way into the bone marrow, where they start proliferating and dividing. This is called engraftment. Once engraftment starts, the patient's bone marrow begins to reconstitute the blood and immune system with new red blood cells, white blood cells and platelets that enter the blood stream. The stem cells that perform this spectacular feat represent about 0.1% of the total cord blood.
Parents can elect to donate their baby's cord blood to a public bank or store it privately in a family bank. You might assume that the status of the cord blood stem cells, that is their quality and potency, are monitored before and after freezing and certainly prior to use. Unfortunately, this is not necessarily the case.
When cord blood is collected, there are four tests that can be used to characterize the cells in the blood: 1. the number of total nucleated cells (TNC), 2. the viability (whether the cells are alive or dead), 3. the presence of a cell surface protein called CD34 that identifies blood-forming stem cells, and 4. the ability of the cells to grow and form colonies in a cell culture called the colony-forming unit (CFU) assay. Dr. Stephen Szilvassy explained both the CD34 and the CFU assays in the January 2013 issue of this Newsletter.
Now it might be expected that these tests represent the latest technology, but this is not so. They have remained essentially unchanged for more than 20 years. The CFU assay, for example, was first published in 1966 and with slight modifications, has remained unchanged. Even more troubling is that the properties that can predict stem cell engraftment and blood reconstitution, namely quality and potency (1,2), are not even tested. Indeed, the standard assays are so entrenched in the normal testing paradigm that it is almost heresy to suggest that they can be improved or replaced, despite scientific evidence to the contrary.
In 2002, HemoGenix completely "rebuilt" the CFU assay from the ground up. Instead of manually counting colonies or using a camera and software to count colonies under a microscope, we rely on the relationship between the cell's ability to produce chemical energy (in the form of ATP, adenosine triphosphate) and the ability of stem cells to proliferate. If a cell produces any ATP it is viable (i.e. alive). The ability to proliferate and engraft (i.e. stem cell health) are determined by the amount of ATP produced by the stem cells. This fundamental relationship between ATP and proliferation allows the potency of stem cells to be quantified in a standardized and validated manner according to FDA guidelines.
HemoGenix has developed proprietary tests that rely on measurements of ATP to assess the viability and potency of stem cells before and after cryopreservation.
STEMpredict is a HALO (Hematopoietic Assays via Luminescence Output) assay that was specifically designed to determine if cord blood stem cells demonstrate sufficient ATP to be stored for long periods of time. To do this, stem cells from a cord blood sample are grown in culture and the amount of ATP produced is compared to that of a control. The difference between the two predicts the proliferation ability or quality, which must meet or exceed a threshold to qualify for storage. STEMpredict only takes 3 days to perform, as opposed to 14 days for the CFU assay.
The second application is to ensure that when the cord blood stem cells are thawed, they will be potent enough to save a patient's life. HemoGenix is the only company that has developed a stem cell potency assay HALO-96 PQR that has the capability of predicting stem cell engraftment with over 90% accuracy. Research has shown that about 20% of all cord blood transplants fail to engraft due to insufficient stem cell potency (3).
Stem cell potency is a more complex measurement than stem cell quality. There is also a misconception that potency must correlate with clinical outcome. This is not necessarily the case and does not apply to cord blood stem cells. The National Marrow Donor Program (NMDP) requires (4) that potency testing be performed on a small thawed sample of the cord blood prior to transplantation, because potency predicts whether engraftment can occur, and allows the cord blood to be released for transplant. The HemoGenix HALO-96 PQR assay is compliant with both FDA potency regulations and the NMDP guidelines (4) for cord blood potency assays. No assay is perfect, but our 90% accuracy is a significant improvement compared with present day testing.
As illustrated by The Parent's Guide to Cord Blood Foundation, cord blood stem cell therapy has made monumental strides over the years to treat different diseases. Yet little attention has been paid to improving the tests that should characterize the stem cells that are responsible for the engraftment and reconstitution processes required for a successful transplantation. With the 5th edition FACT-NetCord Standards taking effect at the end of September 2013 that favor more rapid, reliable, robust, and above all, trustworthy tests, we hope to reduce the risk of graft failure and improve patient safety and clinical outcome.
More information can be found on the CFU and Equivalent Assays, Stem Cell Quality and Potency Testing, tests for Cell Therapy Products, STEMpredict and HALO-96 PQR to measure stem cell potency, on the HemoGenix website.
- Hall KM, Harper H, Rich IN (2012). Hematopoietic Stem Cell Potency for Cellular Therapeutic Transplantation, Advances in Hematopoietic Stem Cell Research, Dr. Rosana Pelayo (Ed.), ISBN: 978-953-307-930-1, InTech, DOI: 10.5772/31361
- Rich IN (2013) Potency, Proliferation and Engraftment of Stem Cell Therapeutics: The Relationship between Potency and Clinical Outcome for Hematopoietic Stem Cell Products. J. Cell Science & Therapy S13: 001. doi: 10.4172/2157-7013.S13-001
- Page KM, Zhang J, Mendizabal A, Wease S, Carter S, Shoulars K, Gentry T, Balber AE, Kurtzburg J. (2012). The Cord Blood Apgar: a novel scoring system to optimize selection of banked cord blood grafts for transplantation. Tranfusion 52:272-283. DOI: 10.1111/j.1537-2995.2011.03278.x
- Spellman S, Hurley CK, Brady C, Phillips-Johnson L, Chow R, Laughlin M, McMannis J, Reems J-A, Regan D, Rubinstein P, Kurtzburg J. (2011). Guidelines for the development and validation of new potency assays for the evaluation of umbilical cord blood. Cytotherapy. 13:848-855. DOI: 10.1111/j.1537-2995.2011.03278.x