Stem cell lines represent families of cells that divide on a constant basis resulting from a unique parent group of stem cells that replicate extensively. Most of the time, stem cell lines develop in artificial environments and serve for research purposes. In order to create embryonic stem cell lines, conditions similar to those in the womb are met, with all the nutrients necessary for the normal development. The stem cell lines that result from the division will continue the process of multiplication without specializing as long as no chemical signal interferes to initiate the differentiation. The number of stem cell lines available for distribution to researchers is not known at the moment.

According to the American National Institute of Health, the total number of stem cell lines is twenty-one. While those derived from embryonic biological material are the most widely appreciated, there are also adult stem cell lines that work well for research purposes. Good results have also been reported with research on stem cell lines derived from umbilical cord blood. The only problem with such lineage is that the cells have a specific genetic imprint included, and this specificity limits the experiments, as they are not functional for the treatment of genetic disorders for instance.

Another source of stem cells that provides the possibility to develop a lineage is in specialized somatic cells that are worked back into becoming stem cells again, through a reversal purpose. The main advantage for such stem cell lines is that the DNA of the donor is present in the stem cells so that the new biological material may be used efficiently as a therapy without painful procedures like bone marrow extraction. The main efforts of the medical research sector are directed towards developing media for the cultivation of stem cell lines without any use of animal ingredients.

Study models for stem cell lines development are quite numerous, and progress is being made into the creation of newer and more ethical ways of creating stem cell cures. For instance, scientists are trying to isolate stem cells from living tissues without causing any harm to the organism. This would be very much in the line followed and supported by pro-lifers who claim that any embryo that dies in the lab is a wasted life or a homicide. Although many other people only refer to embryos as human beings when they develop at superior stages, the debate remains open and opinions are definitely divided.