Blood consists of serum and three other main ingredients: erythrocytes (red blood
cells), thrombocytes (platelets) and leukocytes (white blood cells). Leukocytes
normally compose less than 1% of the blood volume but have important functions
in our defense against foreign and endogenous pathogens. Many different
leukocytes can be distinguished, the main types being lymphocytes (~75% T-cells,
~25% B-cells), monocytes and granulocytes. All these different blood cells arise
through distinct and tightly controlled developmental stages from hematopoietic
precursor cells, which reside in the bone marrow and thymus (Figure 1). However,
sequential mutations, chromosomal rearrangements and epigenetic changes can
cause a precursor cell to be blocked from further differentiation and to start
proliferate in a uncontrollable manner which results in cancer. Uncontrolled
proliferation of blood precursor cells is called leukemia. Different types of
leukemia are distinguished based on their lineage of origin; myeloid or
lymphoblastic leukemia. Lymphoblastic leukemia can be further divided into Bcell
precursor (BCP) or T-cell lymphoblastic leukemia. In acute lymphoblastic
leukemia malignant cells are arrested at a relative immature stage whereas in
chronic lymphocytic leukemia, cells have a more differentiated phenotype.
http://repub.eur.nl/res/pub/30596/111130_Homminga%2C%20Irene.pdf
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