F&Q ON STEM CELL TRANSPLANT

Recently there have been a number of articles on stem cell transplantation, which has generated lot of interest among the public. By definition a stem cell is one capable of self renewal and multiplication. Every living tissue has its origin from the stem cell.

Stem cell transplantation was first used in the treatment of blood disorders and it was a breakthrough. Conventionally known as bone marrow transplantation, the stem cells responsible for production of the blood cells reside in the bone marrow, which is a special tissue inside the cavity of the bones. The blood cells originate from the bone marrow from a parent cell or the "stem cell".

A more comprehensive terminology for bone marrow transplantation is haematopoietic stem cell transplantation or blood stem cell transplantation.

The word Haematopoiesis means blood cell production, which includes red cells, white cells and platelets.

What are the sources of haematopoietic stem cells?

The sources are bone marrow; from the blood circulation, also known as peripheral blood stem cells and Umbilical cord blood.

How is the stem cell obtained from the donor?

To collect stem cells from the bone marrow, the donor is given general anaesthesia and bone marrow is aspirated from multiple sites in the hip bone and collected in a bag. This takes about one to two hours depending on the quantity required, which again depends on the weight of the patient. There is usually no risk to the donor.

To collect stem cells from peripheral blood, the donor is given a special injection called growth factors to stimulate production of the stem cells in increased numbers. These will be circulating in the blood stream.

The donor is connected to a machine called the cell separator machine, which can separate the stem cells from the donor’s blood and return the rest of the blood to the donor.

How is the blood stem cell given to the patient?

It is given simply as an intravenous infusion like blood transfusion. The stem cells will automatically find their way home, which is the bone marrow. It will replace the patient’s diseased marrow to give healthy blood cells.

What are the prerequisites for transplants?

The main prerequisite is that the blood group should match. It is common knowledge that if a patient requires blood transfusion only the same group has to be used. Similarly for transplanting blood stem cells there is a system called Human Leucocyte antigen or HLA. These are proteins present on the surface of most of the cells. This system recognises self from non-self.

If a patient is exposed to stem cells with a different HLA antigen specificity, the patient’s immune system will recognise the stem cells as foreign and reject it.

Before a patient is scheduled for blood stem cell transplantation, it is mandatory to choose a donor with an identical HLA type. This can be checked by simple tests.

Who can be the donors for blood stem cell?

Siblings of the patient or a twin; Extended family members; Unrelated donors

What are the chances that a sibling will have identical HLA?

The HLA system for each individual is derived from both parents. Each individual inherits a set of antigens (proteins) from each parent. There is a one in four chance that the individual will have a HLA identical sibling. If there is no sibling donor, one has to explore options with extended family members or unrelated donors.

How are unrelated donors identified?

In the developed countries, there is a national bone marrow donor registry. It enrols voluntary donors who are willing to donate their bone marrow. The bone marrow registry maintains their data base with their HLA typing. Their fitness to donate marrow is also assessed.

The bone marrow registry is linked to other international registries. If a patient needs blood stem cell transplantation and if the patient has no suitable family donor, a search is made through the national registry on the electronic data base.

What is the consequence to the donor?

Bone marrow is a replenishable tissue. Donating bone marrow is more or less like donating blood. So there is no damage to the donor.



A donor is connected to a machine that separates stem cells from the blood.

What are the other sources?

Umbilical cord blood is a recent source, which shows great promise for patients who lack a family donor. Umbilical cord blood is rich in blood forming stem cells. Umbilical cord is the connecting link between the mother and the foetus.

Once the baby is born the umbilical cord is severed and disposed off. The discovery that the umbilical cord blood is a rich source of blood stem cells has led to the formation of cord blood banks around the world and the cord blood stem cells are stored for lifesaving purposes.

There are a number of private and public cord blood banks in many countries and it is networked.

What are the advantages of cord blood stem cells?

Cord blood stem cells are easily available. The degree of matching required between the patient and the donor can be less stringent compared to conventional bone marrow transplantation.

What are the diseases that can be treated by this method?

It can be classified into three main groups of diseases. Malignant diseases like Leukaemia or cancer of the blood cells; diseases where blood production itself is defective like Aplastic anaemia; and genetic diseases like Thalassemia and immune deficiency conditions.

How is the patient prepared?

For the donor blood stem cells to get into the patient’s bone marrow and start functioning, the patients have to be treated with high dose of chemotherapy to knock out his immune system and also to eradicate the diseased bone marrow.

What happens till the new bone marrow starts functioning?

This is a very critical period, as the patient will be left with no immunity till the new blood stem cells take over and he/she is highly susceptible to infections.

The patient has to be nursed in a very clean environment preferably in a room that can deliver filtered air so that all the micro organisms are filtered.

The patient will also require blood product support and antibiotic support. The need for a very aggressive supportive care makes blood stem cell transplantation expensive.

Can blood stem cell transplant be offered to patients in all age groups?

Till some years ago blood stem cell transplantation was offered to patients up to the fourth decade. With advances in techniques now we are able to offer blood stem cell transplantation even to elderly patients.

Can the patient’s own stem cells be used?

Yes in some situations patient’s own stem cells are collected, stored and transplanted after high dose chemotherapy treatment.