It appears that scientists have finally succeeded in cloning adult human cells, a goal that has tantalized the field since the first successful cloning of an adult mammal, Dolly the sheep, in 1996. Two independent papers report the generation of embryonic stem cell lines from adult human donor cells via somatic cell nuclear transfer (SCNT). In the April 17 Cell Stem Cell, researchers led by Dong Ryul Lee at CHA University, Seoul, report that they reset DNA from a donor as old as 75. In the April 28 Nature, scientists led by Dieter Egli at the New York Stem Cell Foundation Research Institute and Mark Sauer at Columbia University, New York, describe a stem cell line generated from an adult with Type 1 diabetes. In theory, this technique could allow researchers to grow replacement cells or organs that are a perfect genetic match for a patient. In practice, it seems less of an advance because, post-Dolly, researchers developed alternative ways of making cells and tissues from donors.
The cloning field has experienced many setbacks along the way, including a fraudulent claim of human cloning in 2004 (see Jan 2006 news story). However, last year, scientists led by Shoukhrat Mitalipov at Oregon Health and Science University in Portland reported the first successful cloning of fetal human cells via nuclear transfer into eggs from which the nucleus had been removed. Mitalipov and colleagues credited their success to the use of gentler methods than previous protocols. Specifically, they fused donor nuclei to eggs using Sendai virus rather than injecting them, then gave the DNA 30 minutes to adjust before triggering cell division (see May 2013 news story).
To generate cells and tissues to treat adults, however, scientists need to be able to clone adult cells. To achieve this, Lee and colleagues modified Mitalipov’s method. Joint first authors Young Gie Chung and Jin Hee Eum introduced nuclei from fibroblasts of either a 35- or a 75-year-old man into enucleated donor eggs. They followed Mitalipov’s protocol, except that in about half the experiments they gave the DNA two hours to fuse with the eggs before activating meiosis with electroporation. Five of those eggs formed blastocysts, and two produced human embryonic stem cell lines. One line came from the older donor, demonstrating that even aged cells can be reprogrammed to an embryonic state. “The slightly prolonged incubation time … may provide extra time for reprogramming before the start of embryonic gene transcription,” the authors speculate.
Egli and colleagues further tweaked Mitalipov’s method to improve efficiency. They found that dilution of Sendai virus and calcium-free media delayed activation of the egg during fusion, and that histone deacetylase inhibitors and fetal bovine serum aided cell division and growth. With this, the authors report a success rate of about 10 percent in generating stem cell lines using SCNT, about a threefold improvement on Lee’s protocol. They derived three lines from a newborn donor and one line from a 32-year-old woman with Type 1 diabetes. Microarray analysis showed that the stem cell lines had a similar gene expression profile to those of normal embryonic stem cells. The authors differentiated the stem cells into several cell types, including neurons (see image below) and insulin-secreting cells, demonstrating potential usefulness for cell-replacement therapy.
Neurons from stem cells: ES cells differentiated into cells (nuclei stained blue) expressing the neuronal marker TUJ1 (red). [Image courtesy of Nature and Dieter Egli.]
While cloning human cells now seems possible, some scientists wonder if the technique is still necessary. Adult human cells can be relatively easily transformed into induced pluripotent stem (iPS) cells, and from there morphed into numerous cell types. This technique is now widely used to make research cell lines (see, e.g., Jan 2012 news story). On the other hand, iPS cells may be less desirable for transplants than embryonic stem cells, as the DNA may not completely reset (see May 2011 news story).
Human cloning produces true stem cells, but has its own ethical and technical drawbacks. In an accompanying Nature editorial, Insoo Hyun at Case Western Reserve University, Cleveland, Ohio, wrote, “Laboratory-produced human embryos have, at minimum, a symbolic value for most people and should not be used carelessly.” Their use should be regulated, and limited to research that greatly advances public health or scientific knowledge, Hyun wrote. Rudolf Jaenisch at the Massachusetts Institute of Technology in Cambridge suggested that nuclear transfer is unlikely to be useful for routine applications because it is quite difficult to obtain donor eggs. “In my opinion it’s more of a research tool,” he told Alzforum.—Madolyn Bowman Rogers.
- Chung YG, Eum JH, Lee JE, Shim SH, Sepilian V, Hong SW, Lee Y, Treff NR, Choi YH, Kimbrel EA, Dittman RE, Lanza R, Lee DR. Human somatic cell nuclear transfer using adult cells. Cell Stem Cell. 2014 Jun 5;14(6):777-80. Epub 2014 Apr 17 PubMed.
- Yamada M, Johannesson B, Sagi I, Burnett LC, Kort DH, Prosser RW, Paull D, Nestor MW, Freeby M, Greenberg E, Goland RS, Leibel RL, Solomon SL, Benvenisty N, Sauer MV, Egli D. Human oocytes reprogram adult somatic nuclei of a type 1 diabetic to diploid pluripotent stem cells. Nature. 2014 Jun 26;510(7506):533-6. Epub 2014 Apr 28 PubMed.
- Hyun I. Policy: Regulate embryos made for research. Nature. 2014 May 1;509(7498):27-8. PubMed.