General View of Hematopoietic Stem Cell Transplantation
Over the past 60 years the field of hematopoietic stem cell transplantation has evolved from experimental animal models of marrow transplantation to curative therapy for tens of thousands of people yearly who are affected by a wide variety of marrow failure states, myeloid and lymphoid malignant diseases, immune deficiencies, and inborn errors of metabolism. Advances in transplantation immune biology combined with improvements in supportive care have made this evolution possible and have ushered in the modern era of hematopoietic stem cell transplantation.
Sources of Hematopoietic Stem Cell Transplantation
For human transplantation protocols, Hematopoietic Stem Cells can be collected from a variety of sources including the marrow, blood, and umbilical cord blood obtained at the time of delivery. Marrow is the traditional source of Hematopoietic Stem Cell Transplantation.
The marrow is typically aspirated by repeated placement of large bore needles into the posterior iliac crest, generally 50 to 100 aspirations simultaneously on both sides, while under regional or general anesthesia. The lowest cell dose to ensure stable long-term engraftment has not been defined with certainty, and a typical collection standard contains more than 2 x 108 nucleated marrow cells/kg recipient body weight. Current guidelines indicate that a volume of up to 20 mL/kg donor body weight is considered safe.
Hematopoietic stem cells are present in the blood at very low levels; however a number of different stimuli including chemotherapy, various hematopoietic growth factors and inhibitors of certain chemokine receptors, result in the mobilization of Hematopoietic Stem Cells from marrow to blood. Once in the blood, the Hematopoietic Stem Cells can be collected by apheresis, and this product has been termed peripheral blood progenitor cells (PBPCs) to differentiate from the term blood stem cells, which should be reserved for instances where the Hematopoietic Stem Cell population itself has been isolated.