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How many stem cells are there in a stem cell product?

Traceable measurements of stem cell concentrations in stem cell products by means of flow cytometry

PTB-News 3.2016
Especially interesting for

transfusion and transplantation specialists



specialists in laboratory medicine

When transplanting stem cells, the dose is a decisive factor. To improve the determination of the dose by the measurement of the required concentration of viable stem cells, PTB has developed a reference procedure. It has been applied for the first time for comparison with results of the two methods that are currently used.

Fluorescence scatter diagram for the identification of the CD34-positive stem cells, of the white blood cells (leukocytes) and of the calibration particles that have been added to the sample.

Microscopic image of a blood smear of a patient with acute myeloid leukemia prior to stem cell transplantation. Apart from the biconcave red blood cells, three stained white blood cells are identified. The smaller white blood cell is a lymphocyte. The two larger cells are myeloid precursor cells of white blood cells, so-called "blasts", which are not found in the blood of healthy persons.

Some malignant tumors, such as, e.g., acute myeloid leukemia, can be treated by transferring stem cells from a donor. Flow cytometry is used to determine the required dose. For this purpose, the stem cells are identified and delimited from other cells by means of their cell surface antigens (CD) using fluorochrome-marked antibodies. In a flow cytometer, the fluorescence signals of the cells are recorded individually one after the other and plotted in a two-dimensional fluorescence scatter diagram. Presently applied routine protocols rely on the determination of the stem cell concentrations either relative to the known concentration of leukocytes or relative to the concentration of fluorescent calibration particles that had been added to the sample. The disadvantage of such relative measurements is the additional systematic and statistic contributions to the measurement uncertainty. The leukocyte concentration is determined with another instrument, an automated hematology analyzer. When using calibration particles, their number in the stem cell sample varies for production and/or pipetting reasons.

With the reference flow cytometric procedure developed at PTB, however, the sample volume is measured and the stem cell concentration directly determined from the number of stem cells. Compared with the two routine procedures used to date, the accuracy of the stem cell concentration measurement is increased by a factor of 6 (compared to the relative measurement with leukocytes) and by a factor of 2 (with respect to the relative measurement based on calibration particles).

Using such flow cytometers with integrated volume measurement for routine measurements of stem cell products would considerably simplify the analysis and, at the same time, improve its accuracy. To transfer this procedure to practical applications, systematic investigations on fresh and cryopreserved stem cell products are necessary.


Jörg Neukammer
Department 8.3
Biomedical Optics
Phone: +49 (0)30 3481-7241

Scientific publication

J. Neukammer, M. Kammel, J. Höckner, A. Kummrow, A. Ruf: Referenzverfahren zur Messung von Stammzellkonzentrationen. BIOspektrum 21, 294 (2015)