Stem cells are essentially primordial cells capable of becoming all or many of the 210 different kinds of tissues in the human body. They have been traditionally defined as not fully differentiated yet (i.e. not fully determined) to be any particular type of cell or tissue. They range from totipotent, i.e., almost totally undifferentiated and capable of becoming any tissue in the body (as in the early human embryo up to about the 4-day morula stage), to pluripotent, i.e., more differentiated and therefore only capable of becoming some cells or tissues in the body (as in the 5-7-day blastocyst stage of the early human embryo). This capacity to differentiate decreases as the fetus develops and is very limited in adult human beings. The cell is capable of indefinite reproduction and is independently capable of generating every tissue that ultimately constitutes an adult organism i.e. these cells show remarkable plasticity in their ability to trans-differentiate from one structure into a completely unrelated structure.
Cloning, in contrast, is a process of making a genetically identical organism through non-sexual means. It is of 3 types:
a) Recombinant DNA technology or DNA cloning (the transfer of a DNA fragment of interest from one organism to a self-replicating genetic element so that the DNA of interest can then be propagated in a foreign host cell
b) Reproductive cloning (technology used to generate an animal that has the same nuclear DNA as another currently or previously existing animal)
c) Therapeutic cloning (the production of human embryos for use in research in order to harvest stem cells that can be used to study human development and to treat disease).
The Department of Science and Technology, GoI, is actively encouraging work in this field. There are 13 or 14 centres in the country currently, where work is being done.
Theoretically, cloning may play a role in the following in future - Embryonic stem cells can be grown to produce organs or tissues to repair or replace damaged ones; reverse the aging process; infertile couples could have children, ability to manufacture bone, fat, connective tissue, or cartilage that matches the patients’ tissues exactly; treating heart attack victims by cloning their healthy heart cells and injecting them into the areas of the heart that have been damaged etc. But, these claims are years away from being realised yet.