Bone Marrow Transplant: An Overview

The Bone Marrow:

Bone marrow is a gelatinous, soft tissue substance that fills the center of the bones in the human body. It is responsible for the production and storage of blood cells in the body. Every day, the bone marrow produces more than two hundred billion blood cells.

The bone marrow is of two types:
• Red Bone Marrow
• Yellow Bone Marrow

The red bone marrow contains immature cells, called hematopoietic stem cells (blood-forming cells), which multiply into three important and different types of blood cells:

• Red blood cells (erythrocytes) carry oxygen and essential nutrients to other tissues
• White blood cells (leukocytes) aid in fighting infections and diseases.
• Platelets (thrombocytes) aid in blood clot formation post injuries.

After maturity, these blood cells proceed from the bone marrow into the bloodstream. This is where these cells perform their respective functions which keep our body healthy and alive.

The yellow bone marrow contains stromal cells, called mesenchymal stem cells. These produce bone, fats, and cartilage. With time and age, the red bone marrow gets replaced by the yellow bone marrow.

The Bone Marrow Transplant:

Bone Marrow Transplant is a complex procedure that involves the transfusion of healthy bone marrow cells due to conditions that threaten the ability of bone marrow to function. Some of the common conditions are cancers, aplastic anemia, leukemia, or immune deficiency disorders.

On the basis of the donor, the different types of transplants are:

• Autologous transplant: The donor is patient himself. The stem cells taken from their own bodies replace the diseased blood cells.
• Syngeneic transplant: The donor is the patient's identical twin.
• Allogeneic transplant: The donor is the patient's parent, sibling or an unrelated donor.

There is also one more type of allogeneic transplant, Umbilical cord blood transplant, which involves the removal of stem cells from an infant's umbilical cord immediately after the delivery. As these cells are immature, they can reproduce, and can be frozen until there is a need for any transplant.

The Need for Bone Marrow Transplant:

A healthy bone marrow is vital in the functioning of many systems in the body.

Life-threatening conditions like aplastic anemia, sickle cell anemia, thalassemia, lymphoma, leukemia, multiple myeloma, congenital neutropenia, and even aggressive chemotherapy can affect the function of bone marrow. In such cases, the best treatment option or the potential cure is undergoing bone marrow or cord blood transplant.

Bone marrow transplant helps in:

• Replacement of non-functioning and diseased bone marrow with a healthy one to battle many life-threatening conditions
• Regeneration of a new immune system to fight against many diseases
• Replacement of bone marrow with normal functioning after chemotherapy
• Prevention from a genetic disease such as adrenoleukodystrophy

The Recipient, Donor & Matching:

One of the challenging processes of the bone marrow transplant is to find a matching donor.

Recipient: A complete physical examination and pre-transplant tests are performed to evaluate the functions of organs and the blood. This assures the surgeon whether the patient is capable of accepting the transplant.

Donor: The search begins with the patient himself and then diverts to parent, sibling, relative, unrelated person or umbilical cord blood. The donor will have to undergo several tests to determine the matching.

Matching: Approximately, 70% of patients do not have a related donor. In such cases, the human leukocyte antigen (HLA) tissue typing becomes the major factor in deciding a potential match.

The more similar the HLA marker, the more successful is the transplant. Non-related donors can be identified from donor registries.

The Transplantation Procedure:

Once the matching is successful, the transplant proceeds in the following way:

Stem Cell Harvesting: The bone marrow transplant is all about transferring stem cells from the donor to the recipient. The collection of stem cells is either from the peripheral system or the bone marrow. The peripheral blood stem cells (PBSCs) are collected via a machine needle (inserted into the donor’s vein) which separates the stem cells from the blood. The stem cells from the bone marrow are collected by placing a needle in the soft center of the bone (probably hip bone and the sternum), where stem cells are located.

Chemotherapy: The conditioning of the patient is done with high doses of chemotherapy/radiation in order to eradicate the malignancy or the diseased cells and make room for the growth of new bone marrow cells.

Stem Cell Transplant: After complete conditioning, the stem cells collected peripherally of from the bone marrow are infused into the bloodstream through the central venous catheter. These new cells then travel to the bone marrow where they will reproduce to become a healthy entity.

Supportive Care: To prevent any infections, supportive care is provided. This care includes frequent monitoring of any signs of complications, organ function, blood tests, etc.

Engraftment: The reproduction of the newly infused cells into new red blood cells, white blood cells, and platelets are known as engraftment. This process usually occurs between two to four weeks post-transplantation.

The Risks, Complications & Side-effects:

Considering the complexity of the procedure, it will be accompanied by various risks. Many recipients and donors are afraid of this aspect of the bone marrow transplant.

The Recipient:

• Pain due to gastrointestinal irritation or mouth sores is most common. This is usually caused due to the high doses of chemotherapy or radiation.
• Nausea, vomiting, and diarrhea also occur due to high doses of chemotherapy or radiation.
• Low red blood cells and low platelets resulting from non-functioning of the bone marrow can be life-threatening.
• Fluid overload results from a large amount of fluids given during the transplant which in some cases the kidneys cannot keep up. This overload can also lead to other complications such as high blood pressure, liver damage, and pneumonia.
• Respiratory distress can be compromised during the transplant. Pulmonary complications like inflammation of the airway, fluid overload, or even bleeding can arise.
• Graft failure can occur due to infections or insufficiency of the stem cell count to cause engraftment. In simple terms, when the recipient’s immune system rejects the donor’s stem cells.
• Graft-versus-host disease (GVHD) occurs due to tissue mismatch when the graft cells attack the host cells. Even with an identical donor antigen match, 40% of recipients can still develop GVHD.

The Donor:

There is minimal risk to the donors as the cells can be regenerated. However, during the surgical procedure, a reaction to anesthesia or a minor risk of infection can occur. Over 99 percent of donors make a full recovery after the procedure. So, technically one can donate several times in their lives.

The Survival Rate/The Success Rate:

According to the Worldwide Network for Blood and Marrow Transplantation report, every year more than 21,000 allogeneic transplants, 28,000 autologous transplants and 50,000 first hematopoietic stem cell transplants are performed worldwide.

Moreover, there is a continuous increase in this number by 10-20% annually. The rise in improved outcomes is may be due to reductions in infections, organ damage or GVHD.

The Recovery:

This is certainly a long process.

Regular blood tests should be undertaken for blood counts. These tests confirm whether new blood cells are being produced or any cancer or complication has returned. Additionally, doctors can also assess the new bone marrow functioning via bone marrow aspiration.

Complete recovery of autologous transplant recipients takes several months and for allogeneic transplant recipients, it takes 1 to 2 years.

Another major factor that contributes to your transplant recovery is good nutrition. Significant nutrients in your food help fight infections or repair any tissue damage. This will definitely help in keeping the bone marrow healthy!