Hematopoietic stem cells, from which blood originates, are the most studied and used in clinical practice, through a process that includes differentiation and transplant.
According to international transplant centre data, the pathologies that can most commonly be treated with cord stem cells are Acute Lymphoid Leukaemia, (ALL), Acute Myeloid Leukaemia (AML) and Chronic Myeloid Leukaemia (CML), Immunodeficiency and Thalassemia. One of the greatest advantages of cord blood is the extracted cells’ reduced ability to produce alloreactions (Graft Versus Host Disease, GVHD). Intravenous stem cell transplant protocols foresee a minimum equivalent dose of 3 x 107 (30 million) of mononucleate cells/kg of body weight, and with a histocompatibiltity of at least 4/6 loci.
New studies on transplants have shown that an intravenous transplant with at least two units of cord blood guarantees improved acceptance as the cellularity (i.e. concentration of transplanted cells) is a decisive fact for the transplant’s success, as is the immediate availability of the sample and its sterile state (i.e. non-contamination of transplanted cells by infectious agents). Recent studies on the use of stem cells by direct intramedullary injection have shown a faster recovery of the number of mononucleate cells (especially neutrophils) and platelets, with a smaller number of stem cells transplanted in situ. Storage of cord blood also offers the possibility of developing retroactive diagnostic investigations on hereditary and/or tumoral diseases.
Other protocols currently undergoing definition and validation concern the expansion of stem cells in vitro, transplants after reduced chemotherapy and the infusion of selected cells.
Autologous use
This is the personal use of stem cells, with total histocompatibiltity between the biological material and the transplant patient. For genetic pathologies, autologous transplants are not possible, unless gene therapy has been carried out to replace the faulty gene with a functioning one.
Heterologous or allogenic use
This is the use of stem cells for a recipient other than the donor. The possibility of two patients being histocompatible is rather low (1/40,000) but this is balanced by the number of samples available in international registers, now estimated at about 250,000 samples. In this way, 1/3 of patients requesting marrow stem cells, from peripheral or cord blood, can find a sample available in international registers.
Family use
This is the most common and most successful type of use in transplantology, given the immediate availability of the sample and the high probability that subjects belonging to the same family (1/4 being totally histocompatible). Thanks to this fact, 1/3 of transplants worldwide are carried out between blood relatives.
HLA standardisation
HLA stands for Human Leukocyte Antigens, also known as the histocompatibiltity system, comprising molecules that are found on the cell surface and that act as antigens: when they encounter another person’s immune system, they are recognised as being foreign and provoke an immune response. The HLA system is what causes transplant rejection:
if the tissue transplanted into a patient is not HLA-compatible (i.e. the cells making up the tissue do not have the same HLA antigens as the recipient), the transplant is recognised as foreign and is rejected. For this reason, it is necessary to check that donor and recipient are HLA-compatible before carrying out the transplant, using a procedure known as tissue standardisation. In addition to the field of organ and tissue transplants, the HLA system molecules also play an important role in immunological recognition mechanisms of all foreign substances that encounter the organism.
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