19 Stem Cells

• Stem cells can differentiate into specialized cell types and undergo self-renewal to maintain the stem cell pool
• Different types of stem cells have varying cell potency levels, with potency decreasing as cell differentiation increases
• Stem cell research and medical applications raise ethical implications
• Differentiation is the process by which less specialized cells develop tissue-specific adaptations to become more specialized cell types
• Stem cells are undifferentiated and unspecialized cells that can undergo extensive proliferation and self-renewal through mitosis
• Stem cells can undergo symmetrical division to produce identical daughter stem cells or asymmetrical division to produce a progenitor daughter cell for specialized cell types
• Molecular signals switch genes on and off in stem cells to differentiate into specialized cell types
• As cell differentiation increases, more tissue-specific genes are switched on while genes allowing higher potency levels are switched off
• Stem cells are able to differentiate into specialised cells upon receiving specific gene expressions and the synthesis of tissue-specific structures that enable these specialised cells to perform certain functions
• In mammals, stem cells are commonly categorized according to their differentiation potential: totipotent, pluripotent, or multipotent
• Totipotent stem cells have the ability to differentiate into all cell types that make up an entire organism, including extra-embryonic tissue such as the placenta
• Multipotent stem cells can differentiate into several related specialized cell types but far fewer types than pluripotent stem cells
• Adult stem cells, like myeloid and lymphoid stem cells, are examples of multipotent stem cells found in different tissues of an organism after embryonic development
• The main purpose of multipotent adult stem cells is to produce specialized cells for growth and development, and for the replacement of cells lost due to cell death and injury
• Blood stem cells, like myeloid and lymphoid stem cells, found primarily in bone marrow, can differentiate into all types of blood cells, including red blood cells, white blood cells, and platelets, but not other cell types like kidney cells
• The life span of red blood cells and white blood cells is about 112 days and 3-4 days, respectively
• Neural stem cells can differentiate into nerve cells and neural support cells called glial cells
• Adult stem cells are not confined to adults who are 21 years of age; infants also have them
• Umbilical cord stem cells have multipotent differentiation potential
• Stem cell therapy involving adult stem cells has general advantages, such as the multipotent nature of adult stem cells ensuring differentiation into the respective specialized cell type, restoring function of damaged or diseased tissue
• Stem cell therapy involving adult stem cells also benefits from the self-renewing nature of stem cells, ensuring that transplanted stem cells constantly replicate in the patient to maintain a constant pool of stem cells
• There are two general approaches to stem cell therapies: stem cell transplant and genetically modified stem cell transplant
• Stem cell transplant involves obtaining adult stem cells directly from the donor organ or tissue in which they are found, providing therapies for illnesses like Parkinson's disease, leukaemia, multiple sclerosis, lupus, sickle-cell anaemia, and heart damage
• Leukaemia is characterized by an abnormal increase in the number of immature white blood cells called blast cells
• The treatment of choice for leukaemia is a bone marrow haematopoietic stem cell transplant
• In a bone marrow haematopoietic stem cell transplant, the patient is irradiated to remove existing haematopoietic cells and white blood cells, then healthy stem cells from a donor are multiplied and infused into the patient to restore blood function
• Stem cells are capable of self-renewal, ensuring a constant pool of cells that can differentiate into various blood cells when needed, without the need for repeated transplants
• Genetically modified stem cells can be used in gene therapy to treat genetic diseases by inserting a normal, functional allele into the patient's stem cells and reintroducing them back into the patient
• Ethics in bioethics involves principles like respect for persons, maximizing benefits/minimizing harms, and justice, to guide decisions in the face of conflicting choices
• Bioethics explores ethical questions related to the life sciences, helping individuals and organizations make decisions about behavior and policy regarding new biomedical knowledge and innovations
• Embryonic stem cells are pluripotent, capable of differentiating into any cell in the entire organism except extraembryonic tissue, while adult stem cells are typically multipotent, giving rise to cells of the tissue in which they are found
• Embryonic stem cells have advantages in research due to their ease of isolation, strong self-renewal ability, and pluripotency, potentially allowing treatment of a wider range of diseases
• Adult stem cells from the patient's body may not be effective in treating genetic disorders as they also carry the genetic mutations present in the patient
• Arguments against using embryonic stem cells include ethical concerns about violating the sanctity of life, treating embryos as spare parts, and the belief that adult stem cell research, with fewer ethical issues, could make greater advances if more resources were allocated to it
• Embryonic stem cells can potentially treat a wide range of diseases as they have the potential to grow indefinitely in a laboratory environment and can differentiate into almost all types of bodily tissue
• Treatments proposed include treatment for physical trauma, degenerative conditions (e.g. Parkinson’s disease), and genetic diseases (in combination with gene therapy)
• Embryos are not equivalent to human life:

  • Embryos are not conscious, cannot feel, and cannot survive outside the womb
  • An early embryo does not have the properties associated with being a person
  • Blastocysts are a cluster of human cells that have not differentiated into distinct organ tissue
  • Some believe life begins when the heartbeat develops or when the brain begins developing
  • Use of embryos does not go against the principle of non-maleficence
• Legislation on the period when ES cells can be extracted may help to minimise harm, e.g., UK legislation does not allow use of embryos more than 14 days old
• Surplus embryos created via in vitro fertility treatments can be used for creating new stem cell lines for research, helping to maximise benefits while minimising harm
• Induced pluripotent stem cells (iPSCs) are an alternative to ES cells:

  • Differentiated adult somatic cells can be reprogrammed to become pluripotent stem cells called iPSCs
  • iPSCs offer advantages like not generating or destroying human embryos, patient-specific cells, and personalized drug discovery efforts