Effects of Long-Term In Vitro Expansion on Genetic Stability and Tumor Formation Capacity of Stem Cells.

Stem cell therapeutics are emerging as novel alternative treatments for various neurodegenerative diseases based on their regenerative potentials. However, stem cell transplantation might have side effects such as tumor formation that limit their clinical applications. Especially, in vitro expansion of stem cells might provoke genetic instability and tumorigenic potential. To address this issue, we analyzed genomic alterations of adult human multipotent neural cells (ahMNCs), a type of human adult neural stem cells, after a long-term in vitro culture process (passage 15) using sensitive analysis techniques including karyotyping, array comparative genomic hybridization (aCGH), and whole exome sequencing (WES). Although karyotyping did not find any major abnormalities in chromosomal number or structure, diverse copy number variations (CNVs) and genetic mutations were detected by aCGH and WES in all five independent ahMNCs. However, the number of CNVs and genetic mutations did not increase and many of them did not persist as in vitro culture progressed. Although most observed CNVs and genetic mutations were not shared by all five ahMNCs, nonsynonymous missense mutations at MUC4 were found in three out of five long-term cultured ahMNC lines. The genetic instability did not confer in vivo tumorigenic potential to ahMNCs. Collectively, these results indicate that, although genetic instability can be induced by long-term in vitro expansion of stem cells, it is not sufficient to fully exert tumor formation capacity of stem cells. Other functional effects of such genetic instability need to be further elucidated.