Each year thousands of lives in the United States are prolonged by transplanted organs including the kidneys, heart, lung, liver, and pancreas. For a transplant to “take,” however, the body’s natural tendency to rid itself of foreign tissue must be overridden.
One way to avoid the rejection of transplanted tissue is tissue typing, which ensures that markers of self on the donor’s tissue are as similar as possible to those of the recipient. Every cell in the body has a double set of six major tissue antigens, and each of the antigens exists, in different individuals, in as many as 20 varieties. The chance of two people having identical transplant antigens is about one in 100,000.
A second way to avoid transplant rejection is to lull the recipient’s immune system into a less active state. This can be done with powerful immunosuppressive drugs such as cyclosporine A, or by using laboratory-manufactured antibodies that attack mature T cells.
When the immune response is severely depressed—in infants born with immune disorders or in people with cancer, for example—one possible remedy is a transfer of healthy bone marrow. Once introduced into the circulation, transplanted bone marrow cells can develop into functioning B and T cells.
In bone marrow transplants, a close match is extremely important. Not only is there a danger that the body will reject the transplanted bone marrow cells, but mature T cells from the bone marrow transplant may counterattack and destroy the recipient’s tissues. To prevent this situation, known as graft-versus-host disease, scientists use drugs or antibodies to “cleanse” the donor marrow of potentially dangerous mature T cells.
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Last Updated March 12, 2008