What Is Stem Cell Transplant- Definition, Types and Procedure

Stem cells are very important in today’s world to reach the next generation of medical science, this can be achieved by stem cell transplant

What Is Stem Cell Transplant

Stem cell transplant is a field of medical technology, where stem cells are implanted in the body of patients to induce growth of new and healthy cells and replace injured or non functional cells in the body, with the aid of chemotherapy.

Stem cells are unspecialized or undifferentiated cells with the ability to replicate the functionality of any specific cell type inside the body. This characteristic of stem cells, known as totipotency enables them to repair tissues, blood vessels and organs. Stem cells undergo self renewal by the process of mitotic cell division.

Since, organs in the body are limited while stem cells are not, stem cell transplantation is a revolutionary and promising technology in the domain of medical science. It can replace the surgical process of organ transplantation in the years to come.

This in turn minimizes risks associated with invasive methods involved in surgery. Stem cell transplantation provides stem cell donation features, beneficial for both the donor and recipient. Instead of sacrificing an organ, one can simply donate his stem cells to save someone’s life.

Stem cell transplants have already proved their potential by curing many child patients suffering from incurable diseases like leukemia. Umbilical cord transplant operations have effectively treated psychological disorders such as autism. Research studies and demonstration over the scope of stem cell transplantations are being conducted in prominent institutions. One such centre is the Harvard Stem Cell Research Institute.

Place to Find Stem Cells for Transplantation

Stem cells can be found anywhere in the body but are primarily concentrated in the bone marrow. Bone marrow is a delicate and spongy tissue found inside bones which consists of hematopoietic stem cells.

These cells upon transplantation into a recipient’s body can transform into other cell types having specialized functions, to compensate for a particular metabolic or genetic disorder. But, extraction of stem cells from bone marrow requires needle insertion into a large bone and the process is quite painful.

Research is underway to explore alternative sources of stem cells like umbilical cord, amniotic fluid etc.

Isolation of Stem Cells

Stem cells isolated from such samples have better chances of being accepted by the immune system of body. In addition to that, the process of extraction of such stem cell samples is non-invasive and hence not known to cause any painful sensation.

Stem cells, collected from the donor are cryogenically preserved until these are required for implantation in the body of the recipient.

What Can Stem Cell Transplant Cure

Stem cell transplants have been found to cure many malignant and non malignant disorders in the body.

Malignant	Non Malignant
Acute myeloid leukemia	Aplastic anemia
Neuroblastoma	Fanconi anemia

Limitations of Stem Cell Transplant

Stem cell transplantation has its own limitations as well. If the child is suffering from a genetic disorder, his stem cells will obviously consist of the same genetic defect. Hence transplantation will not cure the ailment related to genetic deformations.

Types of Stem Cell Transplant

Stem cell transplant techniques can be categorized on the basis of source of stem cells in the body, into following categories: –

Haematopoietic stem cell transplant (HSTC)

Hematopoietic stem cells refer to stem cells that have the ability to stimulate other cell types by a process known as hematopoiesis or blood formation.

The process of hematopoiesis or hemopoiesis is determined by the unique parameter known as stem cell factor, which is responsible for gene encoding. HSTC has known to be effective in the treatment of many malignant and incurable diseases in the body eg. Myeloma, Leukemia etc. These are further subdivided into two categories: Autogenic stem cell transplant and Allogenic stem cell transplant.

Type of Transplant	Process	Immunity
Autogenic stem cell transplant	Stem cells are extracted from patient himself/herself.	Body accepts injected stem cells more readily.
Allogenic stem cell transplant	Donor with matching HLA’s is selected	Immunity of body to foreign matter is countered using medications

For HSTC, the sources of stem cells are the following:

• Bone marrow
• Peripheral blood
• Umbilical cord blood

Bone Marrow Transplant

Bone marrow, a rich source of stem cells has largely been used for stem cell transplantation. In fact the terms stem cell transplant and bone marrow transplant are often used interchangeably.

In the bone marrow transplant method, stem cells are extracted from the mesoderm (middle layer) of marrow of patient or donor with the help of a flexible tube called catheter. This operation known as marrow harvest is carried under partial or whole anesthesia.

Chemotherapy or radiation therapy is done subsequently to destroy the infected or affected cells. Finally, stem cells are intravenously injected into the patient’s blood vessels.

Medications are given to suppress immunity system of body, which tends to reject any new or unfamiliar entrants. Stem cells take 24 hours to reach the bone marrow, where they grow, multiply and in due course develop the functionality of bone marrow cells.

Peripheral Blood Stem Cell Transplant

In this method, stem cells are extracted from the donor’s blood with the aid of a sterile needle and the arrangement to remove leukocytes.

The process of absorption of blood sample from body is referred to as Apharesis or Leukapharesis. Leukocytes contain the stem cells required for peripheral blood stem cell transplantation. Leukocytes or white blood cells are hence separated from erythrocytes.

Finally, the residual blood sample having erythrocytes or red blood cells is re-injected in the donor’s body. The entire process of blood intake, leukocyte withdrawal from blood sample and return of blood to the donor takes place with the aid of apheresis machine.

Medications like Granulocyte Colony stimulating factor (GSF) are given intravenously, so as to aid the inserted blood cells to reach the bone marrow.
Umbilical cord blood transplant: Cord blood refers to the residual blood of umbilical cord, after a baby has been delivered. It can be relatively obtained with ease from umbilical cord.

Umbilical cord has been found to have a higher percentage of stem cells as compared to blood vessels or bone marrow. But, the amount of blood in umbilical cord is very less, which makes its application limited to stem cell transplantation in children. It is more often used for paediatric transplantation.

Autologous Stem Cell Transplant

In this stem cell transplant procedure, stem cells are derived from the patient’s body. At first, stem cells are collected from blood and stored in cryogenic conditions, using liquid Nitrogen. This process is followed by exposure of patient to chemotherapy or irradiation, which enables the destruction of damaged cells.

Then, the stem cells are reinserted intravenously into blood vessels i.e. via a tube placed in vein.

Within a day, stem cells are able to reach the bone marrow. Upon reaching there, stem cells begin to grow and multiply. Gradually the bone marrow begins to grow, multiply ultimately restoring the healthy state of the body. This category of stem cell transplant is also known as high dose chemotherapy.

Allogenic Stem Cell Transplant

In allogenic stem transplant, a donor is selected such that their Human Leukocyte Antigens (HLA’s) are similar to those in the bone marrow of the recipient.

A human body consists of proteins on their white blood cells called HLA’s which like any other antigen trigger the production of antibodies to protect the body against foreign invading matter. These antigens are found in the mesenchymal stem cells of the marrow. The donor is generally a family member like parent or offspring.

In other cases, unrelated donors with matching antigens may be selected for stem cell transplantation. If antigens do not match, a metabolic disorder called Graft versus host disease (GVHD) will probably erupt, wherein the healthy transplanted cells attack the body cells.

On the basis of dosage of chemotherapy, Allogenic stem transplants may be categorized into the following: –

• Ablative therapy: In this transplant, patient is conditioned by providing high dosage of chemotherapy or radiotherapy. It is also known as myeloablative transplantation.
• Reduced intensity transplant: In this method, milder dosages of chemotherapy are applied during conditioning regimen. It is also referred to as non myeloablative allogeneic transplantation. The risks due to infections are much less as compared to ablative therapy.

On the basis of donor selected, Allogenic stem cell transplantation may be of the following types:

1. Syngeneic (Monozygotic) transplant: This refers to the stem cell transplant where monozygotes or identical twins act as donors. The precondition for transplant is that the genetic make up and tissue morphology of donor must be similar to that of the recipient.
2. Parent child transplant: A parent may act as recipient of the child’s stem cells or vice versa. Chances of HLA compatibility are quite high in parent offspring stem cell transplant due to blood relationship.
3. Stem cell transplant with the help of HLA compatible unrelated donor: Immunity of body to foreign matter is countered using medications A donor might be selected from databases of donors like Blood and Bone Marrow Program, after verification of the genetic constitution of the stem cells to be transplanted.
4. Stem cell transplant with banked blood: If found compatible with host’s genetic constitution, stem cells from public stem cell banks also can be used for transplant.

Stem cells transplant: From Extraction to Plantation

 Stem cell transplant consists of the following steps:

1. Stem cell extraction: Firstly a flexible tube called catheter is inserted in a large vein for collecting stem cell samples from blood or bone marrow of patient or donor. The process of extraction of stem cells from the body of donor is called apharesis. Extraction of stem cells from bone marrow is referred to as marrow harvest. The catheter provides chemotherapy as well. In case of cord blood transplantation, an inspection of stem cell compatibility is done with the help of pre-implantation genetic diagnosis (PGD). Medication given to the patient raises WBC count and suppresses immunity of body.
2. Processing: Leukocytes are the sources of stem cells in blood. From collected blood samples, red blood cells are eliminated by a process known as red blood cell depletion. Plasma is removed by the process of volume reduction.
3. Cryopreservation: The isolated stem cell samples are preserved at subzero temperatures in storage tanks of liquid Nitrogen known as cryogenic tanks or cryotanks.
4. Conditioning treatment: The patient is given high dosage of chemotherapy or radiation therapy for 5-10 days. Consequently, body’s immune response to transplanted stem cells is significantly suppressed.
5. Stem cell transfusion and recovery: Stem cells isolated previously are reinserted in the blood vessels of the patient’s body with the help of catheter, as in blood transfusion. The recipient is treated with antibiotic medications to significantly lower the resistance offered by the body to the newly injected stem cells. Gradually, stem cells can grow and multiply, form specialized cells to resume normal functioning of affected tissue or organ.