12 February 2004. Researchers in South Korea have apparently cloned the first human embryo. Perhaps equally significant, they have also extracted pluripotent stem cells from the embryo at the blastocyst stage.

As reported at the Sciencexpress website today, Woo Suk Hwang, Shin Yong Moon, and their colleagues of Seoul University created the human ES cell line by means of an autologous nuclear transfer. They removed the nuclei from oocytes, and then fused the oocytes with somatic cells—in this case, the cumulus cells that surround oocytes in the ovary—from the same donor. At the blastocyst stage, they harvested the inner cell mass that would give rise to the embryo itself.

These cells give every indication of being pluripotent stem cells. They express a number of embryonic stem cell markers, and, when broken into subsequent cell clumps, could be induced to form endodermic, mesodermic, and ectodermic cells of various types. In addition, in a culture medium designed for neural cell differentiation, the stem cells developed into nestin-positive cells, indicating that they had begun to follow the path toward a neuroectoderm fate.

When injected into the testes of mice, the stem cells formed germ-cell tumors called teratomas. Teratomas are unusual in that they contain cell types of many different kinds, including those from tissues other than where the tumor is located. These stem cell teratomas were found to contain cells resembling a variety of cell types including pigmented retinal epithelium, smooth muscle, bone, cartilage, connective tissue, and glandular epithelium.

The authors suggest that their success in creating the first human clones could be attributed to having a large number (242) of fresh human oocytes with which to work, as well as to their gentle method of removing the nuclei from the eggs (squeezing rather than sucking them out with a pipette). This research is likely to rekindle the ethics debate about reproductive and therapeutic cloning in the US.—Hakon Heimer.

Reference:
Hwang WS, Ryu YJ, Park JH, Park ES, Lee EG, Koo JM, Chun HY, Lee BC, Kang SK, Kim SJ, Ahn C, Hwang JH, Park KY, Cibelli JB, Moon SY. Evidence of a pluripotent human embryonic stem cell line derived from a cloned blastocyst. Science. 2004 Feb 12. Abstract