The ability of a bone marrow, mobilized peripheral blood or umbilical cord blood units to produce short- and long-term engraftment and repopulation in a patient undergoing transplantation for a blood malignancy, is the most important function of a processing laboratory.
The "quality" of the stem cells transplanted must be ensured since the patients receiving the stem cell infusion have had their hematopoietic system partially or totally ablated by radiation and cytotoxic drugs and are at increased risk of dying if the transplanted cells do not engraft and repopulate their hematopoietic system. The first human autologous bone marrow transplantation (BMT) was performed by Kurnick et al in 1958. No assays to determine the "quality" of human transplanted cells with respect to their growth and engraftment potential were available until Pike and Robinson in 1971 applied the in vitro colony forming cell assay, first published in 1966, to human cells.
The cell processing laboratory is responsible for a quality product that is directly related to the success of the stem cell transplant. To this end, standards to maintain and enhance the quality and safety of the transplantation process through inspection and accreditation have been controlled by two groups in the United States, namely the American Association of Blood Banks (AABB) and Foundation for the Accreditation of Cellular Therapy (FACT) and in Europe by the Joint Accreditation Committee of ISCT-Europe and EBMT (JACIE). The U.S. Food and Drug Administration (FDA) has provided guidelines, especially since the implementation of gene therapy and ex vivo hematopoietic stem cell expansion protocols.
Methods to Determine Stem Cell "Quality"
There are 4 parameters that are normally used to assess the "quality"of a stem cell product prior to and after processing. These are nucleated cell count, viability and CD34+ cell number by flow cytometry and “progenitor cell assays” to monitor stem cell procedures and graft manipulations.
Prior to the introduction of flow cytometry, the colony-forming cell assay or “progenitor cell assay” as they have been called in the transplantation field were, and indeed still are, the only surrogate assays that have been used to detect growth potential of stem and progenitor cells during the cell processing procedure. Many transplant centers and umbilical cord blood storage facilities routinely perform the colony-forming cell assays for quality control purposes and clinical monitoring in a stem cell transplantation setting. However, their use has been called into question. In an article by Henon et al in 2001 the authors state, “Determination of the graft content in CFU-GM was the only one available until the end of the eighties. But, for technical reasons, and also because it does not actually evaluate the self-renewal potential of the cell products reinfused, it has now been commonly replaced by the determination of CD34+ cell amounts, which are known to contain the pluripotent hematopoietic stem cells.” Despite the availability of in vitro assays to detect stem cells with different degrees of “stemness” or primitiveness and therefore different degrees of self-renewal potential, the colony-forming assays suffer from many drawbacks. This has been discussed in the section on the Colony-Forming Cell Assays and The HALO® Platform versus the Colony Forming Assays.
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HALO® versus the Colony-Forming Assay