Introduction to iPSC Reprogramming and its Contribution to Stem Cell Technology

Posted by Janice on April 28th, 2021

iPSC technology has made great strides in the fields of stem cell biology and regenerative medicine since its emergence a decade ago. iPSCs are essentially derived from somatic stem cells and can be tailored to a patient's disease model. It is the primary source of cells for research into pathogenesis, drug screening, and experimental transplantation therapy. In particular, the iPSC technology combined with recent advances in gene editing and three-dimensional organoids makes iPSC-based platforms more powerful in a variety of applications, further promoting the development of precision medicine. Moreover, they not only have the same inherent high regenerative ability as ordinary stem cells but also their weak differentiation potential has been proved by medical research. In some cases, it can be used for cell therapy, especially for tumors, where it has low tumorigenicity.

iPSC reprogramming plays an important role in acquiring iPSCs, and its laboratory procedures should comply with rigorous standards. The generation of iPSCs is an extremely multi-step biological process, which includes the gradual loss of initial properties of somatic cells during reprogramming and the gradual acquisition of pluripotent stem cells at the end of reprogramming. The regulation of gene expression and epigenetic modification involved are the key factors that limit the efficiency of reprogramming.

To simplify iPSC induction, many different reprogramming technologies have emerged to generate iPSCs, each possessing its advantages and disadvantages. The vectors involved in reprogramming methods can be divided into three categories, including integrating viral vectors, non-integrating vectors, and non-DNA based delivery.

※  Using integrating viral vectors

Initially, iPSCs were created by introducing reprogramming factors using integrating viral vectors, such as retrovirus or lentivirus. However, iPSC technology is complicated by the potential risks posed by genome-integrating viruses. These iPSCs may cause insertion mutagenesis due to transgenic integration into the genome of host cells, which limits their clinical application.

※  Using non-integrating vectors

A series of non-integrating vectors, including viral vectors and non-viral vectors, have been successfully used to produce iPSCs. To date, these integration-free alternate methods have been developed and tested to overcome safety issues. The human pluripotent stem cells obtained by these non-integrated methods provide a more suitable cell resource for clinical applications.

Types of integration-free vectors including adenoviral vectors, Sendai virus (SeV) vector, episomal vectors, minicircle vector, expression plasmids, and liposomal magnetofection (LMF).

※  DNA-free delivery

Alternative approaches to avoiding the introduction of genetic modifications include delivering reprogrammed proteins or mRNA directly into cells, rather than expressing them from DNA. These methods have been demonstrated successfully, but can be more complicated to implement. In addition, the reprogramming of DNA-free technique avoids genetic manipulation and the integration of exogenous genetic material resulting from the use of viruses or other strategies, thereby reducing the risk of genetic changes and tumor occurrence.

Scientists are intrigued by the huge potential of iPSCs in transplantation therapy and regenerative medicine, but they warn that even if iPSCs do not develop oncogenic mutations during cell reprogramming, potentially harmful mutations may accumulate as iPSCs multiply in laboratory cultures.

Non-autologous or stem cells are difficult to match in humans, and iPSCs have not been widely used due to technical instability and immaturity. However, the success of iPSC generation opens a way to produce patient-specific pluripotent stem cells with fewer ethical issues than other stem cells. Once the technology matures, the vast majority of diseases in the future could be treated or even cured, if enough non-tumorigenic cells are available.