Hematopoietic progenitor cells (HPCs) or hematopoietic stem cells (HSCs) are cells present in blood and bone marrow. HPCs are capable of forming mature blood cells, such as red blood cells (the cells that carry oxygen), platelets (the cells that help stop bleeding) and white blood cells (the cells that fight infections). Click here to see differentiation pathways.
HPCs are used in the treatment of many malignant (e.g., leukemia, lymphoma) and non-malignant (e.g., sickle cell disease) diseases to replace or rebuild a patient's hematopoietic system. This type of treatment is called a bone marrow or stem cell transplant. HPCs also have been used in clinical trials with U.S. FDA oversight for the treatment of autoimmune diseases, genetic diseases and other indications. Here is a list of diseases for which stem cell transplant may be an option.
Bone marrow cells are collected during a surgical procedure that takes approximately an hour. The donors or patients often receive anesthesia. Next, doctors use hollow needles to remove the bone marrow from the hip bones. The bone marrow is liquid and looks like blood. Anticoagulants are added to prevent clumping. After the marrow is collected, the cell suspension is passed through a series of sterile filters of decreasing size to remove fat, bone particles and cellular debris. If there is a delay between collection and infusion, bone marrow may be stored at either room temperature or in a refrigerator for 24 to 48 hours. Bone marrow also may be cryopreserved, or frozen, if necessary — a procedure commonly used when it is collected for use in an autologous transplant. The frozen cells are usually stored in a liquid nitrogen freezer. Click here to learn more about this procedure.
Peripheral Blood Progenitor Cells (PBPCs) are another type of cell therapy product that contains HPCs. The cells are collected from the peripheral blood using an apheresis device, which acts like a centrifuge to remove whole blood from the donor and separate its components. A needle connected to tubing from the apheresis machine is typically placed in the donor's arm. Blood enters the machine and is processed so that the HPCs and other white blood cells are removed, while the remainder of the blood is returned to the donor through a second needle placed in the other arm. To increase the number of circulating progenitor cells collected, prior to apheresis the donor/patient is prepared or "mobilized" using recombinant hematopoietic growth factor administration. The growth factor is usually administered for several days before cell collection. Patients donating autologous PBPCs also may receive chemotherapy as part of mobilization. If there is a delay between collection and infusion, PBPCs may be stored at room temperature or in a refrigerator. PBPCs also can be cryopreserved, or frozen, if necessary— a procedure commonly used when they are collected for an autologous transplant. The frozen cells are usually stored in a liquid nitrogen freezer. Click here to learn more about this procedure.
Umbilical cord blood (UCB), once regarded as biological waste, is another source of HPCs. UCB can be collected in a safe manner by obstetricians or birthing staff following delivery of the baby. In either setting, UCB is collected into a bag. The unit then undergoes further processing (primarily to remove red blood cells) and cryopreservation (freezing) and is stored in a liquid nitrogen freezer for potential use at a later time. UCB can be stored in a private/family bank for potential use by a family member or in a public bank, to be used by anyone needing a transplant (i.e., an unrelated recipient).
UCB has several advantages as a source of HPCs. Because the HPCs in cord blood may be less mature, there can sometimes be greater differences in the tissue match (HLA match) between the donor product and the patient recipient. There also may be a decreased incidence of graft-versus-host disease (a complication of transplantation that can be life-threatening); and decreased search time, since units are banked and already HLA-typed. Patients with rare HLA types are often successful in finding a suitable cord graft when other sources are not available.
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