Placental mesenchymal stem cells of fetal origin deposit epigenetic alterations during long-term culture under serum-free condition.

[severe combined immunodeficiency]

Objective : Fetal placental mesenchymal stem cells (fPMSCs ) have shown promising cell therapy potentials . However , their genetic and epigenetic stability during in vitro propagation has not been well studied . We thus interrogated the methylation alterations and tumorigenicity of fPMSCs after in vitro expansion using serum-free medium . Research design and methods : The properties of fPMSCs cultured in a serum-free medium at passage 3 and passage 8 were ascertained by determining their MSC markers , proliferative capacity , chromosomal stability , activity of global DNA methyltransferases and methylation profile . Their potential of malignant transformation was also evaluated in a severe combined immunodeficiency (SCID ) murine model . Results : The fPMSCs could maintain their MSC characteristics but quickly reached a senescent state of proliferation during in vitro expansion . 246 genes with differential DNA methylation of promoters were identified , along with a significantly downregulated global DNA methyltransferase activity . The genes associated with aging and tumorigenesis had a significantly demethylated tendency over in vitro propagation . However , the deposition of epigenetic alterations did not translate into malignant transformation in SCID mice . Conclusion : The fPMSCs cultured in serum-free medium have a tendency to deposit methylation modifications over in vitro expansion , therefore the detection of genetic and /or epigenetic alterations is necessary for fPMSCs before they are employed for clinical uses .