Ten Years of Induced Pluripotency

It has been a decade since researchers first discovered the recipe for reprogramming ordinary somatic cells into induced pluripotent stem cells, capable of generating all other cell types in the same way as embryonic stem cells. This was a transformative advance, as the ease of the method allowed near any research group to work with pluripotent cells. Making use of induced pluripotency in research and medicine is still very much a work in progress, however: great strides are being made in the production of cells and tissues for drug testing and other tissue engineering for research use, but the goals of generating patient-matched cells and tissues for cell therapies and transplantation are not proceeding as smoothly as was perhaps hoped by some. This popular science article surveys the field:

Human cortex grown in a petri dish. Eye diseases treated with retinal cells derived from a patient's own skin cells. New drugs tested on human cells instead of animal models. Research and emerging treatments with stem cells today can be traced to a startling discovery 10 years ago when researchers reported a way to reprogram adult mouse cells and coax them back to their embryonic state - pluripotent stem cells. A year later, they accomplished the feat with human cells. The breakthrough provides a limitless supply of induced pluripotent stem cells (iPSCs) that can then be directed down any developmental path to generate specific types of adult cells, from skin to heart to neuron, for use in basic research, drug discovery and treating disease. The dazzling iPSC breakthrough has spurred rapid progress in some areas and posed major challenges in others. It has already proved a boon to basic research, but applying the new technology to treat diseases remains daunting. Some types of cells have proved difficult to reprogram, and even the protocols for doing so are still in flux as this is still a very young field.

Six years after the iPSCs discovery, researchers in a very different field developed a new gene-editing technology of unprecedented speed and precision, known as CRISPR-Cas9. The potent new tool has revolutionized efforts to "cut and paste" genes and has been very quickly adopted by thousands of researchers in basic biology and drug development. CRISPR's speed and precision may some day allow stem cell researchers to reach their most ambitious goal: Genetically abnormal cells from patients with inherited diseases such as sickle cell anemia or Huntington's could be reprogrammed to the pluripotent stem cell state; their genetic defects could be "edited" in a petri dish before being differentiated into healthy adult cells. These cells could then be transplanted into patients to restore normal function. While that goal is still beyond reach, many early-stage clinical trials are underway using induced iPSCs to treat diseases, from diabetes and heart disease to Parkinson's. One trial has already treated its first patient. In 2014, scientists made iPSCs from skin cells of a woman with macular degeneration and then differentiated them into adult retinal cells. Surgeons transplanted the retinal cells into her eyes in order to treat the disease - the first patient treated using iPSCs. Preparations to treat a second patient using patient-derived cells were stopped because the researchers detected a mutation in one of the genes in the iPS cells. No reports had linked the gene to cancer, but they decided not to use the stem cells to eliminate any risk.

The success of treatments relies in part on stem cells' rapid rate of proliferation. Hundreds of billions of cells may sometimes be needed for a transplantation. But if just a few of the stem cells fail to differentiate into the target adult cells, they may reproduce rampantly when transplanted and form a tumor. "It's a two-edged sword. In the pre-transplant stage, you want stem cells that proliferate very rapidly. But after the transplant, if there are only five or 10 cells that didn't differentiate into adult cells, they can reproduce infinitely. They create a kind of residue of tumor." Research to ensure that all stem cells differentiate before transplantation is now one of the main issues in this field. To eliminate cancer risk, the researchers are now "deep sequencing" the genetic makeup of each of the stem cell lines they might use. They have also decided to use donor cell lines rather than the patient's own cells. This avoids the very expensive prospect of having to carry out quality checks like deep sequencing of each patient's own pluripotent cell lines.

The originators of the iPSC methodology are concerned about public perception that the rate of progress may be slower than expected. "I am fascinated by how rapidly science is advancing. It's amazing. But for the most part, developing new treatments - doing the science, testing the safety and effectiveness of new therapies­ - takes a great deal of money and many years. Developing new treatments may take 10 years, 20 years, 30 years. That is what we have been trying to say to our patients: 'We are making great progress, so do keep up your hope. But it takes time.'"

Link: https://www.ucsf.edu/news/2016/09/404271/induced-pluripotent-stem-cells-10-years-after-breakthrough


"Hundreds of billions of cells may sometimes be needed for a transplantation. But if just a few of the stem cells fail to differentiate into the target adult cells, they may reproduce rampantly when transplanted and form a tumor."

Surely you could take a form of SENS style WILT approach to this and maybe edit the telomerase gene so that it can only be active in the presence of an externally administered drug? Or is this much more difficult to achieve in practice?

Posted by: jim at September 29th, 2016 8:49 AM

It is safer to use Multipotent stem cells in my view these carry much lower risk and we are seeing new kinds of MPSCs being created using adult cells in Australia.

Posted by: Steve Hill at September 29th, 2016 11:35 AM

Posted by: jim at September 29th, 2016 8:49 AM: Surely you could take a form of SENS style WILT approach to this and maybe edit the telomerase gene so that it can only be active in the presence of an externally administered drug? Or is this much more difficult to achieve in practice?

I have a better and easier idea. Take the SENS style WILT approach, and be done with it ;) .

Posted by: Michael at September 29th, 2016 5:23 PM

Epigenetic marks such as DNA methylation change substantially when animals age. However, overexpression of a small number of factors can push the cell to transition to a new stable state that is associated with changes in the activity of thousands of genes. It became possible to obtain iPSC from adult and even elderly patients. The reprogramming leads to the restoration of embryonic telomere length and mitochondria recovery and so illustrate the reversibility potential of aging. Unfortunately, the reprogramming into iPSC in vivo leads to the formation of tumors. So, why not to try to reprogram in vivo cells of elderly patients only to the safe junior stage instead of the embryonic stage (with oncological danger). Even a non-specific action on DNA methylation (experiments with 5-azacytidine - inhibitor of DNA methyltransferase enzyme, Dnmt1, allows to reprogram the cells in vitro into safe tissue-regenerative multipotent stem cells (doi: 10.1073/pnas.1518244113). The DNA methyltransferase inhibitor, RG108 treatment of human bone marrow mesenchymal stromal cells resulted in increased activity of the anti-senescence genes TERT, bFGF, VEGF, and ANG while activity of the senescence-related genes ATM, p21, and p53 were decreased. The number of β-galactosidase-positive cells was significantly decreased (DOI: 10.1002/bab.1393)
Now we can selectively enforce silence or action to the elected genes by using reprogrammable CRISPR/dCas9-based systems armed with activators and repressors of transcription, and also with epigenetic modulators such as DNA methylation (Dnmt3) and demethylation (TET1) enzymes. It's time to use these tools, which do not introduce mutations in genomic DNA for search and for development of the methods of radical rejuvenation.

Posted by: Dmitry Dzhagarov at September 30th, 2016 2:32 PM

Quote: Mammalian DNA methylation is a critical epigenetic mechanism orchestrating gene expression networks in many biological processes. However, investigation of the functions of specific methylation events remains challenging. Here, we demonstrate that fusion of Tet1 or Dnmt3a with a catalytically inactive Cas9 (dCas9) enables targeted DNA methylation editing. Targeting of the dCas9-Tet1 or -Dnmt3a fusion protein to methylated or unmethylated promoter sequences caused activation or silencing, respectively, of an endogenous reporter. Targeted demethylation of the BDNF promoter IV or the MyoD distal enhancer by dCas9-Tet1 induced BDNF expression in post-mitotic neurons or activated MyoD facilitating reprogramming of fibroblasts into myoblasts, respectively. Targeted de novo methylation of a CTCF loop anchor site by dCas9-Dnmt3a blocked CTCF binding and interfered with DNA looping, causing altered gene expression in the neighboring loop. Finally, we show that these tools can edit DNA methylation in mice, demonstrating their wide utility for functional studies of epigenetic regulation.

Posted by: Dmitry Dzhagarov at September 30th, 2016 4:10 PM
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