Concise Review: Molecular Cytogenetics and Quality Control: Clinical Guardians for Pluripotent Stem Cells.

Now that induced pluripotent stem cell (iPSC)-based transplants have been performed in humans and organizations have begun producing clinical-grade iPSCs, it is imperative that strict quality control standards are agreed upon. This is essential as both ESCs and iPSCs have been shown to accumulate genomic aberrations during long-term culturing. These aberrations can include copy number variations, trisomy, amplifications of chromosomal regions, deletions of chromosomal regions, loss of heterozygosity, and epigenetic abnormalities. Moreover, although the differences between iPSCs and ESCs appear largely negligible when a high enough n number is used for comparison, the reprogramming process can generate further aberrations in iPSCs, including copy number variations and deletions in tumor-suppressor genes. If mutations or epigenetic signatures are present in parental cells, these can also be carried over into iPSCs. To maximize patient safety, we recommend a set of standards to be utilized when preparing iPSCs for clinical use. Reprogramming methods that do not involve genomic integration should be used. Cultured cells should be grown using feeder-free and serum-free systems to avoid animal contamination. Karyotyping, whole-genome sequencing, gene expression analyses, and standard sterility tests should all become routine quality control tests. Analysis of mitochondrial DNA integrity, whole-epigenome analyses, as well as single-cell genome sequencing of large cell populations may also prove beneficial. Furthermore, clinical-grade stem cells need to be produced under accepted regulatory good manufacturing process standards. The creation of haplobanks that provide major histocompatibility complex matching is also recommended to improve allogeneic stem cell engraftment. Stem Cells Translational Medicine 2018;7:867-875.