[Present and Future of an iPS Cell Stock for Regenerative Medicine]

A haplobank of induced pluripotent stem cell (iPSC) lines derived from healthy donors with homozygous human leukocyte antigen(HLA), which is called "an iPSC stock", has been under construction in Japan. The iPSC stock is expected to enable HLA matching of a majority of recipients and reduce the risk of trans- plant rejection. Full-scale operations began in FY2013, with the aim of covering 30-50% of the Japanese population by FY2017 and most of the population by FY2022 with the iPSC stock. A novel feeder-free and xeno-free culture system for iPSCs was developed to comply with regulatory safety standards. In 2015, a clinical-grade iPSC line with homozygous HLA of the highest-frequency haplotype was released as a first in the world. Other clinical-grade lines are being generated successively. If all goes to plan, the first clinical research using the iPSC stock will start in 2017. However, many challenges remain to ensuring the future of iPSC stock. In accordance with the progress of the latest research, safety issues regarding iPSC-based cell therapy are being monitored with much interest, and one of the major concerns is tumorigenicity. We have to continue to discuss the extent of genomic abnormalities that would or would not be acceptable in not only iPSC-derived products but also iPSC stock, taking into account the risks and benefits of cell therapy. It is also necessary to demonstrate the clinical efficacy of HLA matching, which is indicated to promote graft survival and reduce immunosuppressive drug use.