Hematopoiesis is a complex process in which primitive and undifferentiated stem cells multiply (self-renewal) and differentiate into many different blood cell types. Hematopoiesis primarily takes place in the bone marrow that is composed of stromal cells and a microvascular network, which forms a suitable microenvironment for stem cell growth and development. Hematopoiesis starts with a common pluripotent stem cell, which can give rise to myeloid or lymphoid progenitor cells. These progenitor cells further differentiate into various cell lineages. The myeloid progenitor cells can differentiate into red cells (erythrocytes), platelets (thrombocytes) and various white blood cells (leucocytes) (Figure 1).1 Lymphoid progenitor cells develop into specific immunologic defence cells i.e. B-lymphocytes and T-lymphocytes. Leukemia is a malignant transformation of hematopoietic progenitor cells. The accumulation of malignant blood cells in the bone marrow and peripheral blood results in a disturbed hematopoiesis, with anemia, bleeding, bruising and a decreased resistance to infections. Additional symptoms include fever, malaise, fatigue, abdominal organomegaly, enlarged lymph nodes, headaches, bone aches and weight loss. Depending on the cell lineage involved, a further distinction can be made in myeloid and lymphoid leukemias. According to the rate of malignant cell growth, leukemias are divided into acute and chronic leukemias. Eighty to eighty-five percent of the children with leukemia present with an acute lymphoblastic leukemia (ALL) whereas the remainder 15% has an acute myeloid leukemia (AML). Children with ALL can be further divided into ALL originating from the B-lineage ALL (precursor B-ALL) in 85-90% of the children and ALL originating from the T-lineage (T-ALL) in 10-15% of the children.

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KOCR, Rotterdam, the Netherlands
R. Pieters (Rob)
Erasmus University Rotterdam
Erasmus MC: University Medical Center Rotterdam

van Grotel, M. (2008, September 24). Identification of prognostic genetic factors in pediatric T-cell acute lymphoblastic leukemia: prognostic genetic factors in pediatric T-ALL. Retrieved from http://hdl.handle.net/1765/13286