About Acute Myeloid Leukemia (AML)
Acute myeloid leukemia (AML) is a cancer that starts inside the bone marrow, the soft, spongy tissue inside bones, where blood cells are made. The cancer grows from immature cells that would normally turn into white blood cells. Acute means the disease develops quickly. AML affects both children and adults. This type of cancer is less common among adults under their mid 40s. AML is more common in men than women.
There is no definitive answer as to the cause of AML.
A bone marrow transplant is a procedure to replace damaged or destroyed bone marrow with healthy bone marrow stem cells. Nowadays, a bone marrow transplant is more correctly referred to as "stem cell transplant". It is the stem cells, more specifically, the white stem cells that are transplanted in AML. These healthy stem cells replace damaged or destroyed bone marrow.
There are two types of bone marrow: red and yellow. Red marrow contains blood stem. Yellow marrow is made mostly of fat.
Normally, the red bone marrow makes blood stem cells (immature cells) that become mature blood cells over time. There are three kinds of blood cells that develop from these immature cells:
- Red blood cells that carry oxygen and other substances to all tissues of the body;
- White cells that fight infection and disease or
- Platelets that form blood clots to stop bleeding.
In AML, however, these immature cells called blasts do not develop into white cells, but instead multiply and crowd out the other mature blood cells.
When leukemia patients need a stem cell transplant, the patient’s siblings are the best source. There is a 25% chance of each sibling donor (with the same mother and father) being a match. Unfortunately, both of Darryl’s brothers, including his two nephews, were not a match.
Once siblings have been tested and a match not found, the recipient is placed in a bone marrow Registry. So far, there has not been a match for Darryl. Further testing of family members is not done because statistically the chances of finding a match among other family members is the same as finding one in the general population. Therefore, the need for seeking volunteer donors that will match Darryl’s HLA tissue typing.
About HLA Typing Test
Special blood tests called Human Leukocyte Antigen (HLA typing), also known as tissue matching, determines whether a patient has a suitable donor. These tests are not the same as matching blood types. In fact, you do not need to have the same blood type (A, B, O, AB) to be an HLA match.
Human leukocyte antigens are proteins located in the surface of white blood cells and other tissues in the body. HLA antigens play an important role in the immune system’s defense against invaders such as bacteria, viruses, and parasites. The HLA typing test will indicate whether the donor’s HLA antigens (proteins) are compatible with recipient’s. In other words, whether the donor’s tissue (stem cells) will be accepted by a recipient.
In transplants where the donor’s HLA is different from recipients the immune system of the recipient will recognize the donor’s HLA antigens as foreign. This causes rejection of the transplanted stem cells. In the best case scenario, the donor will have the exact HLA antigens as the recipient. The risk of transplant rejection is lessened for well-matched donor recipient pairs. Therefore, the more HLA antigens shared between a recipient and a donor, the better the potential outcome of the transplant. For bone marrow transplant a near perfect match is required.