Re: Is is technologically possible to clone a human?

Ethics aside, my younger sister passed away this weekend. If I want a daughter using her DNA, do we have the technology to create a clone of her?

Hi Devon,

I am very sorry to hear about the passing of your sister. I hope that you and your family will accept the condolences of all of us here at the MadSci Network.

I am afraid that the answer to your question is, "No. Using current technology it is not possible to clone a human via somatic cell nuclear transfer (SCNT)."

SCNT is a process whereby the nucleus of one organism is transferred into an ovum (egg cell) from which the original nucleus has been removed. In theory, this ovum containing the transplanted nucleus then grows into a new organism that is genetically identical (for the most part; see this answer) to the organism that provided the nucleus (aka the nucleus donor's clone).

It is important to distinguish between two applications of SCNT-mediated cloning. What I described above is known as reproductive cloning, where a new organism is created that is a reproduction of the original nuclear donor. The creation of embryos via SCNT also allows the collection of embryonic stem (ES) cells from those embryos, which can, in theory, then be grown into different cell types and tissues that are genetically identical to the nuclear donor, which means that they will not be rejected upon transplantation into the donor's body. This is what is known as therapeutic cloning.

While more than a dozen mammalian species have been reproductively cloned since Dolly the sheep was cloned in 1984, no primate species has been reproductively cloned using embryos created via SCNT. Some cloned rhesus macaques have been generated via embryo splitting, a process similar to the way that monozygotic twins are produced, but this does not involve nuclear transfer.

In 2007, Byrne et al., at the Oregon National Primate Research Center, announced that they had successfully created primate embryos via SCNT, and that they were able to obtain embryonic stem (ES) cells from these embryos that subsequently differentiated into different tissues. This was a report of successful therapeutic cloning of a primate species.

However, these researchers themselves report that, these SCNT-created embryos "failed to support a term pregnancy after embryo transfer despite considerable efforts." That is to say, they tried implanting these embryos into many female macaques, and none of them developed into a viable macaque.

This latter point raises the issue that the process of reproductive cloning is still highly resource-intensive; large numbers of embryos generated by SCNT have to be implanted in the uteruses of large numbers of females of the same species who will serve as potential surrogate mothers. For example, Dolly the sheep was the only one of 277 SCNT-created embryos to survive to term.

There has been quite a bit of research and debate regarding why primates have proven so difficult to clone via SCNT. For examples of this, you can take a look at the last four references below.

Even if the barriers to reproductive cloning of primates via SCNT can be overcome, the mathematical realities of current reproductive cloning technologies make it unlikely that those technologies will ever be applied effectively in humans.

References:
Byrne JA, Pedersen DA, Clepper LL, Nelson M, Sanger WG, Gokhale S, Wolf DP, Mitalipov SM.
Producing primate embryonic stem cells by somatic cell nuclear transfer.
Nature. 2007 Nov 22;450(7169):497-502. doi:10.1038/nature06357

Simerly C, Dominko T, Navara C, Payne C, Capuano S, Gosman G, Chong KY, Compton D, Hewitson L, Schatten G.
Molecular Correlates of Primate Nuclear Transfer Failures.
Science, 300:297, 2003.

Lanza R, Chung Y, West MD, Campbell KH.
Comment on "Molecular correlates of primate nuclear transfer failures".
Science. 2003 Sep 12;301(5639):1482; author reply 1482.

Baker M.
Monkey stem cells cloned.
Nature 2007: 447, 891.

Baker M.
Monkey embryonic stem cells cloned.
Nature Reports Stem Cells. Published online: 21 November 2007 | doi:10.1038/stemcells.2007.119