Hemopoietic stem cell. Stem cells are the precursors to all cells in the body. In the embryo they are derived from blastocysts where they differentiate into the cells forming the main embryonic tissue layers, then further differentiate to create all specialized cells of the body. They can also be obtained from the umbilical cord blood, and from adult bone marrow and peripheral blood. As stem cells in the blood form white blood cells of the immune system, they can be cultured for the use in the treatment of cancer and other diseases of the immune system.