What are the Sources of Haematopoietic Stem Cells?
Initially, healthy bone marrow was the only source of getting haematopoietic stem cells (HSC). But with progress in medical science and many researches we have now 3 resources which has given more options to procure healthy stem cells and simultaneously increased the probability of treating many patients struggling with serious diseases.
Though resource of extracting haematopoietic stem cells (HSC) can be any one of these three types however clinical results are same. However utilization of these cells varies according to age of the donor and the recipient, the indication and the preference of the centres and the donors.
Normally bone marrow collection is ideal choice in children. However for adults, it can be bone marrow, peripheral blood stem cells or umbilical cord blood stem cells which depend on the availability of a suitable donor.
Different Sources of Stem Cells
1. Bone Marrow Haematopoietic Stem Cells (HSC): Bone Marrow Stem Cells are preferred in diseases like Thalassemia or Aplastic Anemia. With Bone Marrow as a graft source, recovery period is delayed as compared with peripheral blood stem cells but the risk of graft versus host disease is less.
Stem cells from bone marrow are collected by using aspiration needles from the iliac crest (hip bone). It is carried out under general anaesthesia, which is safe and painless process and the donor is being discharge the next day.
2. Peripheral Blood Stem Cells (PBSC) can also be collected from larger veins of body using apheresis technique on a cell separator machine after giving growth factor injections for 4-5 days. It is a very safe and reliable procedure taking only a few hours and does not require Anaesthesia. Stem cells can be collected even difficult to mobilize patients with plerixafor and G CSF support. This type of transplant is preferred for Leukaemia, Myeloma and Lymphomas.
3. Umbilical Cord Blood Stem Cells: Blood collected from placenta after birth, a rich source of Haematopoietic Stem Cells, can also be used for allogeneic stem cell transplants. Problem is low volume and cell dose resulting in delayed recovery / engraftment failure.
Bone marrow transplant is done over several sessions for a few days. Multiple sessions give the new stem cells the best chance to integrate themselves into your body. Average time taken prior to engraftment ranges from 3-4 weeks in the BMT unit. This process is known as engraftment.
Transplant Process includes following phases:
Stem Cell Collection: According to the transplant type, collection of stem cells can be done by the following two methods:
- Allogeneic transplant: Stem cells are collected from donors’ blood by cell separator machine or bone marrow aspiration.
- Autologous transplant: Stem Cells are collected by cell separator machine from patient’s own blood. Hence, it can be done only after disease has been brought under control by using standard treatment.
Stem Cell Conditioning: Conditioning is the name given to high dose chemotherapy or radiotherapy to destroy or suppress patient's existing bone marrow and provide immune-suppression so that donor stem cells can habitat in patient’s bone marrow and start functioning. Drugs used in conditioning differs by the underlying condition for which transplant is being done.
Stem Cell Infusion: After conditioning blood stem cells or bone marrow are given to the patient through veins, just like blood transfusion.
A needle called a central venous catheter or a port is installed on the upper right portion of the patient’s chest. This allows the fluid containing the new stem cells to flow directly into the heart. The stem cells then disperse throughout the body. Once healthy stem cells establish there and start producing blood cells.
The port is left in place because the bone marrow transplant is done over several sessions for a few days.
Engraftment: Time taken for blood production is called engraftment period. Before engraftment patient’s blood counts are markedly depressed for around 10-20 days, chances of infections are highs so patients are kept in strict isolation and hepa-filtered rooms. During this time patient require close monitoring of blood counts and regular blood/platelet transfusions.