What are stem cells? Stem cells are cells in multicellular organisms that have not differentiated into specialized cells with specific functions.
In essence, they are the precursor building blocks of tissues and organs, and are used in research and therapies.
These are the three currently known types of stem cells:
- Embryonic stem cells are undifferentiated cells derived from embryos generated and cultured in vitro for assisted reproduction that have reached blastocyst stage (not ready for implantation) and legally donated for medical research. (The U.S. and the U.K. have informed consent rules that permit such donations.)
- Adult stem cells are undifferentiated cells found within differentiated systems or organs. The two best known adult stem cells are found in bone marrow: hematopoietic (or blood-forming) cells; and mesenchymal cells, which can generate bone, cartilage and fat. Hematopoietic cells can also come from peripheral blood or umbilical cord blood, and for therapies can be autologous (from the patient’s own body) or allogeneic (from others). Adult stem cells have also been found in the adult brain and may exist in other organs as well.
- Induced pluripotent stem cells (iPSCs) are adult stem cells derived from differentiated cells which have been reprogrammed to assume the basic characteristics of embryonic stem cells. This technology, just over a decade old, won the Nobel Prize for its discoverers in 2012. These cells are useful in drug development and disease modeling and have the highest potential for use in therapies where risk of rejection is high, as they can be made from the cells of the affected individual.
Stem cells demonstrate two principal characteristics: self-renewal / clonality, referring to the cell’s ability to reproduce itself over time without differentiation; and potency (sometimes called pluripotency), which is a stem cell’scapacity to differentiate.
Stem Cells In Treatment Of Diseases
The term “stem cell therapy” is used to indicate that stem cells are being used as part of a treatment modality. These cells can, for example, be transplanted, infused, or injected into the body. The rationale of using stem cells in treatment is that these cells have a unique ability to repair and replace specific damaged or abnormal cells arising from certain medical conditions, and could have the potential to cure certain conditions altogether.
Stem cells have already been used successfully since the 1970s to treat blood diseases such as lymphoblastic leukemia, myeloid leukemia, thalassemia, and multiple myeloma. This type of stem cell therapy, known as hematopoietic stem cell transplantation (HSCT), wherein the harvested stem cells are “transplanted” by intravenous infusion, was until recently the only proven clinical use of stem cells.
Stem cell transplantation takes place in three areas of treatment:
- To replace cells damaged either by cancer or by high-dose chemotherapy and radiotherapy treatments
- To provide a patient with a new immune system that would enable the identification and destruction of any remaining cancer cells persisting after chemotherapy or radiotherapy
- To provide limbal (corneal epithelial) cells to help burn patients needing ocular surface reconstruction, or for people with limbal stem cell deficiency
Stem cell transplantation in cancer cases is usually recommended only if certain criteria are met. The criteria may include type and stage of cancer, chance of relapse, sensitivity of the cancer to chemotherapy, and whether there is sufficient scientific evidence to support the treatment.
Several studies have been conducted on the applicability of stem cell therapy to conditions such as stroke and spinal cord injury, Parkinson’s disease, Alzheimer’s disease, as well as neuromuscular, heart, bone and joint diseases. Many successful trials have been conducted on animals, but only a few on humans. Of these, some have shown promise but only on a relatively small scale and so are not yet considered recommended clinical practices by the medical community.