Researchers have found that the process of extended culturing needed to generate therapeutically engineered human induced pluripotent stem cells (iPSCs) doesn’t necessarily increase the cells' likelihood of developing potentially deleterious or cancer-causing mutations. They claim their research, using iPSCs modified by homologous recombination to correct a retinal disease-causing gene, goes some way to allay fears that successive generations of modified iPSCs may undergo undesired mutations and instead suggests that such cells could in principal be used safely in cell-based therapies. The work is published today in the early online edition of PNAS, in a paper titled, "Genetic correction and analysis of induced pluripotent stem cells from a patient with gyrate atrophy."
Although human iPSCs can in theory be triggered to become any of the 220 mature cell types, there are worries about their suitability for human cell therapy, explains lead author Sara Howden, Ph.D., at the University of Wisconsin - Madison's Morgridge Institute for Research. Scientists are particularly concerned by the observation that iPSCs have a higher rate of mutation than embryonic stem cells and also a propensity to become cancerous. There are also concerns that iPSCs may retain some memory of their previous lineage.
To investigate the fate of engineered human iPSCs undergoing extended culturing, Dr. Howden’s team used episomal reprogramming to generate an induced pluripotent stem cell line derived from a patient with the degenerative eye disease gyrate atrophy. This was followed by homologous recombination to correct the disease-causing gene in the iPSCs.
Extensive characterization of the cells both before and after the process showed that the culture conditions required to correct the genetic defect didn’t substantially increase the number of mutations carried by the cells. “By showing that the process of correcting a genetic defect in patient-derived induced pluripotent cells is compatible with therapeutic use, we eliminated one barrier to gene therapy based on these cells,” Dr. Howden claims. “It also was the first to demonstrate that correction of a defective gene in patient-derived cells via homologous recombination is possible."
Co-author David Gamm, Ph.D., assistant professor at the department of ophthalmology and the Waisman Center Stem Cell Research Program, adds, “Although further development certainly is needed before such techniques may reach the clinical trial stage, our findings offer reason for continued hope. Dr. Howden and our collaborative group have overcome an important hurdle which, when considered in the context of other recent developments, may lead to personalized stem cell therapies that benefit people with genetic visual disorders.”