Perth Haematology :: Dr Steven Ward
BMT = Bone Marrow Transplant
PBSCT = Peripheral Blood Stem Cell Transplant
Stem Cell = the cell in the bone marrow which is capable of regenerating all marrow and blood cells. It is a “self-renewing” cell. Without these cells the marrow would eventually “die-out” as the cells grew old and were removed.
In this brochure all information relates to autologous transplantation. This is transplantation from ones self, rather than from someone else (allogeneic transplantion).
Peripheral blood stem cells are used rather than bone marrow these days. It has been discovered that we can induce the marrow stem cells into the blood stream, and then collect these from a vein. This is easier than having to collect marrow. Marrow collection requires a general anaesthetic.
Stem cell collection is performed by an apheresis machine. This takes blood from a vein, processes it to remove the stem cells, then returns the other blood components (red blood cells, plasma and platelets) back to the patient by another vein. Either the veins in the arm are used (one on each side) or a special central line is used to allow adequate blood flow in and out. This is inserted under local anaesthetic in the upper chest, neck, or thigh.
Stem cell harvesting takes 6-8 hours and may need to be performed on 1-3 days to harvest enough cells. It is usually performed as a day-case.
The chart shows that stem cells must be collected in advance of the transplant. Usually stem cells are collected after initial chemotherapy to ensure the disease is responsive to the treatment and to start treating the disease.
At the appropriate time the stem cells are mobilised from the marrow where they usually reside into the blood stream. This is achieved by using chemotherapy plus G-CSF (a natural hormone that stimulates the marrow to produce stem cells). It take around 10 days for the marrow to produce sufficient stem cells in the blood to be able to collect enough for a transplant. The stem cell numbers are measured by a “CD34 count” blood test before collection begins. The CD34 counts are taken from around 9 days after starting therapy and are required each morning until the correct number is achieved. When the CD34 count is right apheresis (stem cell collection) starts.
Once the stem cells are collected they are carefully frozen and stored at –183ºC until needed. Further testing on the stem cell bag is done to count the number of stem cells in total. After enough stem cells are safely frozen, the transplant can begin (or further chemotherapy/radiotherapy given first). The frozen stem cells can be stored indefinitely.
The real treatment part of transplant is the high-dose therapy immediately prior to the stem cell infusion. The high-dose therapy does the job of killing as many tumour cells as possible. It is the higher dose than is usually tolerated that achieves this. One side effect is destruction of the normal marrow stem cells. Hence to survive after a transplant you have to have a stock of marrow stem cells—that’s when the frozen collected stem cells are used. These have not been exposed to high-dose therapy. The stem cells are given just like a blood transfusion. They make their way to the marrow and after about 12-15 days they’ve filled up the marrow and regenerated normal blood cells. At this time the patient starts to feel much better.