Discovery and types
In 1961 James Till and Ernest McCulloch in Toronto injected bone marrow cells into irradiated mice and saw lumps of blood cells grow in the spleen, proving that a single cell could produce many kinds of blood cells: the hematopoietic stem cell. Stem cells are classified by how much they can become. Embryonic stem cells from a blastocyst a few days after fertilization are pluripotent, able to form nearly any cell in the body, while adult stem cells in bone marrow, fat or skin are multipotent, limited to certain lineages. In 1998 James Thomson's team at the University of Wisconsin first grew human embryonic stem cells.
The ethics debate and iPS cells
Harvesting embryonic stem cells destroys an embryo, sparking intense bioethics debates, and in 2005 South Korean researcher Hwang Woo-suk was exposed for fabricating cloned embryonic stem cell results. The breakthrough came in 2006 when Shinya Yamanaka at Kyoto University added four genes (Oct4, Sox2, Klf4 and c-Myc) to skin cells and reprogrammed them into an embryonic-like state, creating induced pluripotent stem (iPS) cells. Because they come from a patient's own cells without embryos, the work earned the 2012 Nobel Prize in Physiology or Medicine. It showed that a cell's fate is set by how genes are regulated, not by changes to its DNA sequence.
Current treatments and cautions
Established therapies include blood stem cell transplants (bone marrow or cord blood) for leukemia and lymphoma, skin grafts for burns and limbal stem cell grafts for the cornea. iPS-derived cells were transplanted into a macular degeneration patient in Japan in 2014, and trials of dopamine neuron transplants for Parkinson's disease have run since 2018. Clinics marketing unapproved stem cell injections as cure-alls offer unproven benefits and real risks, so caution is warranted. Stem cell research is regulated alongside reproductive technology under bioethics laws.
FAQ
- Is banking my baby's cord blood worth it?
- Cord blood stem cells are used in transplants for some blood cancers and immune disorders, but the odds of a family ever using its own privately stored cord blood are low. Donating to a public bank is another option.
- Have iPS cells replaced embryonic stem cells?
- Not yet. iPS cells ease ethical concerns but carry risks such as genetic abnormalities and tumor formation, so both lines of research continue.
Sources reviewed: 2026-10-26
References
- Till, J. E., & McCulloch, E. A. (1961). A direct measurement of the radiation sensitivity of normal mouse bone marrow cells. Radiation Research, 14(2), 213–222.
- Thomson, J. A., et al. (1998). Embryonic stem cell lines derived from human blastocysts. Science, 282(5391), 1145–1147.
- Takahashi, K., & Yamanaka, S. (2006). Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. Cell, 126(4), 663–676.