Stem Cells

Stem cells are the un-differentiated cells which have capacity of self renewal and differentiation. They are present in all multicellular organisms. Alexander Moximov was the Russian haematologist who postulated about stem cells.

Characteristics of stem cells

They have the capacity of

  • Self renewal: divide to form more stem cells

  • Differentiation: convert themselves to adult somatic cells

  • Trans differentiation: stem cell of one cell line differentiates into adult cell of other cell line

  • Extreme mitogenic potential: capacity to divide

  • Chemotaxis: migration in response to chemical stimuli

  • Niche & Homing: find their comfort zone and starts living there

  • Chemokine activity: cell to cell communication through protein molecules

Stem cells are classified on following basis

  • Potency: totipotent, pluripotent, multipotent, oligopotent, unipotent

  • Chronology: embryonic stem cells (ESCs), foetal stem cells (FSCs), cord blood cells (CSCs), adult stem cells (ASCs)

  • Characteristics: Haemopoeitic stem cells (HSCs), Mesenchymal stem cells (MSCs)

  • Tissue of homing: adipose tissue derived stem cells (ASCs), bone marrow stem cells(BMSCs), skin precursor cells (SPSCs), GUT

  • Others: very small embryonic cells ( VSEL)

The cells best suited for clinical transfers are

  • Multipotent

  • Adult stem cells

  • Mesenchymal stem cells

  • Adipose tissue stem cells

  • Autologus

  • There are only rare indications of allogenic transfers ex: blood dyscrasias & cancers. Stem cells from bone marrow are rich in growth factors.

There are following known accessible sources of autologous adult stem cells in humans

Bone marrow, which requires extraction by harvesting, that is, drilling into bone (typically the tibia, femur or iliac crest).

Adipose tissue (lipid cells), which requires extraction by liposuction.

Blood, which requires extraction through aphaeresis, wherein blood is drawn from the donor (similar to a blood donation) after pharmacological activation of bone marrow, and passed through a machine that extracts the stem cells and returns other portions of the blood to the donor.

Tooth, menstrual blood, hair follicles, skin

Division of stem cells

Illustration showing potency of stem cells at various stages of development