Stem Cells and Types

Stem Cells

• Stem cells are unspecialized cells with the capacity for self-renewal, asymmetric division, and transformation into other mature cell types.
• They can be classified into embryonic stem cells, adult stem cells, and induced pluripotent stem cells.

Embryonic Stem Cells

• Derived from the inner cell mass of developing blastocysts.
• Pluripotent stem cells, capable of differentiating into all three germ layers: ectoderm, endoderm, and mesoderm.
• Self-renewal in-vivo and in-vitro.
• Pluripotency stem cell markers include OCT3/4, Nanog, Sox2, SSEA4, TRA1-81, and TRA1-60.
• Can form teratomas, which are tumors that contain cells from all three germ layers.

Adult Stem Cells

• Also referred to as somatic stem cells.
• Not entirely "adult," but rather "post-embryonic" stem cells.
• Mostly multipotent, rather than pluripotent.
• Limited differentiation potential.
• Capacity for self-renewal.
• Examples include hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs).

Mesenchymal Stem Cells

• Multipotent stem cells.
• Traditionally found in red bone marrow (stromal MSC).
• Can be isolated from other tissues, such as adipose tissue, peripheral blood, umbilical cord blood, and dental tissues.
• Differentiation potential includes adipocytes, chondrocytes, tenocytes, osteocytes, and myocytes.
• Surface antigens according to the International Society of Cellular Transplant (ISCT) include CD105, CD73, CD90, and CD45.
• Can be isolated using affinity for plastic adherence.
• Easy in-vitro expansion.
• High plasticity.
• Immune privileged.
• Immunomodulatory effects via cytokine secretion.

Hematopoietic Stem Cells

• Multipotent stem cells.
• Derived from mesoderm.
• Able to give rise to all blood cells (lymphoid, myeloid).
• Located in adult bone marrow, peripheral blood, and umbilical cord blood.
• Limited transdifferentiation potential (muscle, liver, bone).

Induced Pluripotent Stem Cells

• Genetically modified adult cells to resemble embryonic-like stem cells.
• May substitute for embryonic stem cells.
• Discovered in 2006 by Prof. Yamanaka and Takahashi, Nobel Prize.
• Potential for mutagenesis.
• Yamanaka factors include Oct4, Sox2, Klf4, and c-Myc.
• Highly expressed in embryonic stem cells.
• Developmental signaling network of embryonic stem cells.
• Determinant of embryonic stem cell pluripotency.

Umbilical Cord Blood

• Primary cell population includes lymphocytes and monocytes.
• Higher natural killer (NK) population.
• Lower T-lymphocyte population.
• Higher proportion of immature T-lymphocytes.
• Lower absolute numbers of cytokines.
• Presumption: higher ratio of anti- vs. pro-inflammatory cytokines.
• Low immunogenic cells.
• HSCs and MSCs migrate from the yolk sac and aorta-gonad-mesonephros to the placenta and then back to the fetal liver and bone marrow through the umbilical cord.

Other Stem Cells

• Dental mesenchymal stem cells: originate from ectomesenchyme and neural crest, with high neural regenerative potential and neurotrophic factor secretion.
• Amniotic fluid stem cells: likely released from fetal amniotic membrane, embryonic skin, digestive tract, and the respiratory and urogenital systems, with heterogeneous population, pluripotent markers, and MSC features.
• Cancer stem cells: tumorigenic, with similar characteristics to normal stem cells, including self-renewal and asymmetric division.