By Maria Somova, Year 12,
Stem Cells are the only type of cells that are able to self-renew, and recreate, or become any type of functional tissues. Unlike any other cells in human organism – blood, nerve or muscle cells, that are made to do one specific function, and do not normally replicate – some types of stem cells can become any tissue or create a fully new organism. They develop into different kinds of cells in the human body at early stages of life and development.
There are several categories of stem cells: totipotent, pluripotent, multipotent, oligopotent and unipotent. Totipotent cells are “the most powerful” ones, as the most essential characteristic of a totipotent stem cell is that it can become a fully functioning living organism. These cells can only be found and extracted from early embryonic tissues and can virtually become any type of tissue, apart from their primary function of creating a new organism. The most known example of a totipotent cell is the human zygote.
Pluripotent cells are the “next powerful” stem cells. Although they are not able to create new organisms, they still have the function of self-renewing and differentiating into any type of cell in the organism of humans. Using a more scientific vocabulary, pluripotent cells generate into any of the germ layers in the organism. Germ layers are groups of cells in an embryo that interact with each other as the embryo develops and contribute to the formation of all organs and tissues. All animals form two or three germ layers. In humans, there are three: ectoderm, endoderm and mesoderm. These three germ layers differentiate to form all cells, tissues and organs in an organism. The most prominent and natural pluripotent cells are embryonic cells that exist in early-stage embryos of humans. Other human pluripotent cells are iPS cells or induced pluripotent stem cells. These are types of cells that are tissue-specific – “self-renewing cells which possess endogenous functions for tissue renewal and repair at their respective resident tissues”, that are programmed to become functionally similar to embryonic stem cells. These cells are used in cellular therapy and regenerative medicine because of their non-controversial nature.
Then the next “level” of stem cells is multipotent stem cells. Multipotent cells can generate into a specific type of cells, like liver cells. A very good example of multipotent cells are the MSC or mesenchymal stem cells, that can differentiate into osteoblasts (a type of bone cell), myocytes (muscle cells), adipocytes (fat cells), and chondrocytes (cartilage cells).
Oligopotent cells are very similar to multipotent cells but are further limited in their function and the type of cells they can become. They can do so for cell types that are closely related. For example, the HSC or the hematopoietic stem cells that are derived from mesoderm can differentiate in blood cells, both myeloid and lymphoid. Myeloid cells include erythrocytes and platelets, while lymphoid cells are the two types of lymphocytes – B and T.
Last type of stem cells are unipotent cells, which are the most limited cells. Like muscle stem cells. Although they renew and differentiate, they can only do so in the same muscle cells.
Now, when it comes to the actual use of stem cells in medical research, there is an ongoing debate surrounding its ethical aspect. The two main arguments are for and against the use of stem cells. According to harvard.edu: “Proponents argue that embryonic stem cell research holds great promise for understanding and curing diabetes, Parkinson’s disease, spinal cord injury, and other debilitating conditions. Opponents argue that the research is unethical because deriving the stem cells destroys the blastocyst, an unimplanted human embryo, at the sixth to eighth day of development. As Bush declared when he vetoed the stem cell bill, the federal government should not support “the taking of innocent human life.” The debate comes down to whether the embryo can be considered a human at such early stages of development when it is only a clump of cells. However, some scientists argue that an embryo can be considered a human only after all major systems and organs are formed, and others say that after 14 days, the separation should be drawn, as the formation of twins and triplets is no longer possible.
Ultimately, the use of stem cells in modern medicine will help to defeat many diseases and improve the quality of life, however in the next few years those improvements are very unlikely due to the ongoing debate about the ethics of stem cell research.
