ABSTRACT
INTRODUCTION Stem cell biology is moving forward with rapid progress, and many exciting scientific and clinical developments have taken place recently in this field. Stem cells have been isolated from a variety of sources including preimplantation embryos, germ cells, fetuses, umbilical cords, and adult organs. They have been classified as hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), and embryonic stem cells (ESCs) based on characterization tests and plasticity. ESCs are generally pluripotent, while MSCs are multipotent and HSCs unipotent. The plasticity of all these types varies, decreasing as the human embryo develops into a fetus and then the adult. For example, human embryonic stem cells (hESCs) isolated from blastocysts are pluripotent and the most versatile, while the stem cells in adult organs are unipotent or multipotent. Since hESCs require the destruction of human embryos, hESC biology is charged with ethical controversies, emotion, hype, and frenzy and reinforced with political and commercial agendas and religious concerns. hESC research has also unjustly been associated with reproductive cloning. However, given the fact that hESCs can theoretically be differentiated into almost all 210 tissues of the human body, they hold the greatest potential to affect the lives of millions of people worldwide for the better by producing effective hESC-derived tissue therapy for several debilitating incurable diseases plaguing mankind.
