7.1 Types and Sources of Stem Cells

Stem cells are the body's raw materials, capable of developing into various specialized cell types. They come in different forms, each with unique properties and potential applications in regenerative medicine and tissue engineering.

Exploring stem cells reveals their diverse sources, from embryos to adult tissues, and their varying abilities to self-renew and differentiate. Understanding these cells' properties and ethical considerations is crucial for harnessing their potential in treating diseases and injuries.

Types of Stem Cells

Types of stem cells

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• Embryonic stem cells (ESCs) derived from inner cell mass of blastocysts exhibit pluripotency differentiating into all three germ layers (ectoderm, mesoderm, endoderm) with high proliferation rate raising ethical concerns due to embryo destruction

• Adult stem cells (ASCs) found in various tissues of developed organisms display multipotency with limited differentiation potential specific to certain tissues (bone marrow, neural tissue) proliferate slower than ESCs with fewer ethical concerns

• Induced pluripotent stem cells (iPSCs) reprogrammed from adult somatic cells using specific transcription factors (Oct4, Sox2, Klf4, c-Myc) exhibit pluripotency similar to ESCs avoiding ethical issues and reducing immune rejection risk

Sources and applications of stem cells

• Embryonic sources from blastocysts of in vitro fertilization treat neurodegenerative diseases (Parkinson's, Alzheimer's) and spinal cord injuries

• Adult tissue sources:

  • Bone marrow contains hematopoietic and mesenchymal stem cells treating blood disorders (leukemia) and repairing bone and cartilage
  • Adipose tissue yields mesenchymal stem cells for soft tissue regeneration and wound healing
  • Dental pulp stem cells regenerate dental and craniofacial tissues
  • Skin epidermal stem cells create skin grafts and heal wounds

• Umbilical cord blood and tissue rich in hematopoietic and mesenchymal stem cells treat blood and immune system disorders (sickle cell anemia, lymphoma)

• Amniotic fluid and placenta contain multipotent stem cells used in fetal tissue engineering and regenerative medicine (heart valve reconstruction, neural tissue repair)

Ethics of stem cell use

• Embryonic stem cell research sparks controversies due to embryo destruction raising debates on moral status of embryos and religious objections

• Egg donation for research poses potential exploitation of women and health risks from ovarian stimulation

• Informed consent issues arise for proper embryo donation and future use of derived cell lines

• Chimera research creating human-animal hybrids raises ethical concerns about humanized animals

• Commercialization of stem cell therapies leads to unproven treatments and medical tourism requiring regulation of stem cell clinics

• Equitable access to stem cell therapies faces challenges due to high costs and socioeconomic disparities in healthcare

Properties of stem cells

• Self-renewal allows division and maintenance of undifferentiated state through symmetric (two identical stem cells) or asymmetric (one stem cell, one differentiated cell) division maintaining stem cell population

• Differentiation potential ranges from totipotency (zygote forming all cell types) to pluripotency (forming all three germ layers) to multipotency (forming multiple cell types within a lineage) to unipotency (forming only one cell type)

• Plasticity enables transdifferentiation into other cell types facilitating reprogramming and tissue regeneration

• Homing ability allows migration to sites of injury or inflammation enabling targeted cell therapy

• Paracrine effects through secretion of growth factors and cytokines promote tissue repair and regeneration

• Immunomodulatory properties regulate immune responses potentially treating autoimmune diseases (multiple sclerosis, rheumatoid arthritis)