About Peripheral Blood Stem Cells



Peripheral Blood Stem Cells


Adult peripheral blood stem cell transplants are being used with increasing frequency for oncology patients. In conjunction with leading haematologists and oncologists in Gauteng, Netcells has provided flow cytometry testing, processing and storage services to many oncology patients.


What are Peripheral Blood Stem Cells?


Stem cells found in the blood stream can be harvested and used as bone marrow transplants. These cells are called peripheral blood stem cells (PBSC).


Bone marrow is the soft, sponge-like material found inside bones. It contains immature cells known as hematopoietic or blood forming stem cells. Hematopoietic stem cells divide to form more blood-forming stem cells, or they mature into one of 3 types of cells: White blood cells, which fight infection, red blood cells which carry oxygen and platelets which help with blood clotting. Most hematopoietic stem cells are found in the bone marrow, but some cells, called peripheral blood stem cells are found in the blood stream. Blood in the umbilical cord also contains hematopoietic stem cells. Cells from any of these sources can be collected and then transfused in patients to restore their stem cell reserve.


Peripheral Blood Stem Cell Transplants


Peripheral blood stem cell transplant (PBSCT) is a procedure that restores stem cells in the bone marrow that have been destroyed by high doses of chemotherapy and /or radiation therapy used to treat cancer.


Chemotherapy and radiation therapy generally affect cells that divide rapidly. They are used to treat cancer because cancer cells divide more often than most healthy cells. However, because bone marrow cells divide rapidly as well, high-dose treatments can severely damage or destroy the patient’s bone marrow. Without healthy bone marrow, the patient is no longer able to make the blood cells needed to carry oxygen, fight infection, and prevent bleeding. PBSCT replace stem cells destroyed by treatment. The healthy, transplanted stem cells can restore the bone marrow’s ability to produce the blood cells the patient needs.


PBSCT are most commonly used in the treatment of leukaemia and lymphoma. It is most effective when the leukaemia or lymphoma is in remission. PBSCT are also used to treat other cancers such as neuroblastoma (cancer arising in immature nerve cells, mostly in infants and children) and multiple myeloma.


There are three types of stem cell transplant:


  • Autologous transplants: when patients receive their own stem cells.
  • Allogeneic transplants: when patients receive stem cells from their brother, sister, or parent. An unrelated donor also may be used.
  • Syngeneic transplants: when patients receive stem cells from their identical twin.


Finding a match


To minimize potential side effects, doctors most often use transplanted cells that match the patient’s own stem cells as closely as possible. People have different sets of proteins, called human leukocyte-associated (HLA) antigens, on the surface of their cells. The set of proteins, called the HLA type, is identified by a special blood test.


In most cases, the success of allogeneic transplantation depends in part on how well the HLA antigens of the donor’s stem cells match those of the recipient’s stem cells. The higher the number of matching HLA antigens, the greater the chance that the patient’s body will accept the donor’s stem cells. In general, patients are less likely to develop a complication known as graft-versus-host disease (GVHD) if the stem cells of the donor and patient are closely matched.


Close relatives, especially brothers and sisters, are more likely than unrelated people to be HLA-matched. However, only 25 to 35 percent of patients have an HLA-matched sibling. The chances of obtaining HLA-matched stem cells from an unrelated donor are slightly better, approximately 50 percent. Among unrelated donors, HLA-matching is greatly improved when the donor and recipient have the same ethnic and racial background.


Because identical twins have the same genes, they have the same set of HLA antigens. As a result, the patient’s body will accept a transplant from an identical twin. However, identical twins represent a small number of all births, so syngeneic transplantation is rare.


Stem Cell collection from the donor


The stem cells used in PBSCT come from the bloodstream. A process called apheresis is used to obtain PBSCs for transplantation. For 4 or 5 days before apheresis, the donor may be given a medication to increase the number of stem cells released into the bloodstream. In apheresis, blood is removed through a large vein in the arm. The blood goes through a machine that removes the stem cells. The blood is then returned to the donor and the collected cells are stored. Apheresis typically takes 4 to 6 hours.


Apheresis usually causes minimal discomfort. During apheresis, the person may feel lightheadedness, chills, numbness around the lips, and cramping in the hands. Unlike bone marrow donation, PBSC donation does not require anesthesia. The medication that is given to stimulate the release of stem cells from the marrow into the bloodstream may cause bone and muscle aches, headaches, fatigue, nausea, vomiting, and/or difficulty sleeping. These side effects generally stop within 2 to 3 days of the last dose of the medication.


Stem Cell processing and storage


After the PBSC are collected, the cells are transported to the laboratory and the cells are counted and their viability is checked. The cells are then diluted between storage bags. Sometimes there are enough cells to store 10 bags and sometimes there are only 2 bags to store. This all depends on how successful the apheresis was and how many stem cells were released into the blood stream from the bone marrow. Once the cells have been diluted, a cryopreservative ,Dimethyl sulphoxide (DMSO), is added. This cryopreservative is added to the cells to prevent any crystallization of the fluid in the cell during the freezing process which may damage the cells. The bags containing the stem cells are then placed in a control rate freezer and the temperature of the bag is reduced to - 1800 Celsius. The storage bags are then placed in liquid nitrogen storage tanks, where the cells remain frozen at -1920 Celsius in the vapor phase of liquid nitrogen. After one week of storage, the viability of the stored stem cells is checked again.


The Transplant


After being treated with high-dose anticancer drugs and/or radiation, the patient receives the stem cells through an intravenous (IV) line just like a blood transfusion. This part of the transplant takes 1 to 5 hours.


After entering the bloodstream, the stem cells travel to the bone marrow, where they begin to produce new white blood cells, red blood cells, and platelets in a process known as “engraftment.” Engraftment usually occurs within about 2 to 4 weeks after transplantation. Doctors monitor it by checking blood counts on a frequent basis. Complete recovery of immune function takes much longer — up to several months for autologous transplant recipients and 1 to 2 years for patients receiving allogeneic or syngeneic transplants. Doctors evaluate the results of various blood tests to confirm that new blood cells are being produced and that the cancer has not returned.


Complications associated with Transplants


The major risk of PBSCT is an increased susceptibility to infection and bleeding as a result of the high-dose cancer treatment. Doctors may give the patient antibiotics to prevent or treat infection. They may also give the patient transfusions of platelets to prevent bleeding and red blood cells to treat anaemia. Patients who undergo PBSCT may experience short-term side effects such as nausea, vomiting, fatigue, loss of appetite, mouth sores, hair loss, and skin reactions.


With allogeneic transplants, a complication known as graft-versus-host disease (GVHD) sometimes develops. GVHD occurs when white blood cells from the donor (the graft) identify cells in the patient’s body (the host) as foreign and attack them. The most commonly damaged organs are the skin, liver, and intestines. This complication can develop within a few weeks of the transplant (acute GVHD) or much later (chronic GVHD). To prevent this complication, the patient may receive medications that suppress the immune system. Additionally, the donated stem cells can be treated to remove the white blood cells that cause GVHD in a process called “T-cell depletion”. If GVHD develops, it can be very serious and has to be treated with steroids and immunosuppressive agents.