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This paper presents the main results of the study on chromosome and genome variability of mesenchymal stem cell cultures from bone marrow and adipose tissue carried out in the Laboratory of Mutagenesis, Research Centre for Medical Genetics, over the last three years. Genome stability was assessed from DNA damage using the DNA comet assay, karyotyping and registration of aneuploidy by the FISH method. We found that DNA damage rate in MSC cultures from bone marrow was 3.9% and 3.8% at the early (2-5) passages and the late (10-15) passages respectively. The cultures were characterized by high dispersion of individual values. Karyotyping showed mosaicism in both types of MSC cultures at the early and late stages of cultivation. The fraction of abnormal cells in some cultures amounted to 80-90%. Evaluation of aneuploidy in interphase cells revealed 1.34% of aneuploid cells (on the average) per one "conventional" chromosome; their overall frequency in the genome amounted to 20-40%. The frequency of aneuploid cells was similar at the early and late passages. Cultures with clones of trisomic and monosomic cells were revealed. The probability of occurrence of abnormal cells may increase by virtue of de novo mutations in the culture and as a result of positive selection of the cells existing in the organism that exhibit a higher reproduction rate in culture. Based on the experimental data on mutational process, selection of mutant cells and clone formation, it is concluded that cytogenetic control of stem cells is necessary to ensure the safety of cellular therapy.

It is demonstrated that the output optical signal of MTT test is directly proportional to the number of viable cells in the primary culture of mesenchymal cells (skin fibroblasts and mesenchymal stem cells from the bone marrow, placenta, and umbilical cord). The slope of the best curve in coordinates "cell number - optical signal" reflecting specific productivity of MTT-formazan characterizes mean dehydrogenase activity of cells and their physiological activity. It was found that in vitro dehydrogenase activity of primary cultures of mesenchymal cells increased during the first 3-5 passages and then tended to decrease. The variant of MTT method presented here can be used for standardization of cell materials.

The possibility of air-droplet cell transmission during cell transfer was experimentally confirmed, this appearing to be the most probable route of cross contamination of cell cultures. The consequences of such contamination are assessed and measures reducing the risk of intercellular contamination proposed.