The Northwestern Memorial Hospital Transplant Program kidney desensitization process uses immunosuppressant drugs and a plasmapheresis to remove rejection-causing antibodies from the bloodstream. This process is done both before and after transplant, allowing many patients who would otherwise reject their transplanted kidney to successfully receive their transplant.
Desensitization is a process that removes harmful antibodies from the bloodstream. This can be done in patients who are incompatible with their potential donor because of blood type or tissue sensitivity. These antibodies, a natural part of our immune system, can cause organ rejection. People develop these antibodies through previous exposure to Human Lymphocyte Antigens (HLA) found in foreign tissues, such as a prior transplant, blood transfusion or pregnancy. The antibody removal process is a treatment called plasmapheresis, which is similar to hemodialysis.
Antibodies are proteins that are produced by white blood cells to help the body fight infection. Antibodies circulate in the blood and are the body's first line of defense in the immune response. These antibodies work hard to protect our bodies and keep us healthy. However, antibodies that are formed after exposure to human tissue, or anti-HLA antibodies, are bad for someone receiving a kidney transplant because they can attack and destroy foreign human tissues, such as a donated kidney. The anti-HLA antibodies react to markers on the foreign tissue called antigens. If a transplant is performed without desensitization on someone who has anti-HLA antibodies to the antigens on their donor kidney, then the kidney will be rejected immediately and will not work.
Understanding The Term “Sensitized”
About 30 percent of patients who are awaiting a kidney transplant are considered “sensitized.” A test called Panel Reactive Antibody (PRA) is used to estimate the amount of anti-HLA antibodies against foreign human tissue in each patient. The PRA tells us the likelihood of having an anti-HLA antibody against a particular donor. A patient is considered sensitized if their PRA is greater than 20 percent. This means they react or have anti-HLA antibodies to 20 percent of the most common HLA antigens. The level of sensitization increases as the PRA percentage increases. Having anti-HLA antibodies against foreign tissues (antigens) makes it harder to find a compatible living or deceased donor kidney. Sensitized patients may wait 3 to 4 times longer for a compatible deceased donor kidney than a non-sensitized patient would.
The Donor Cross-Match Test
In kidney donation, the most important test is the cross-match test. This test involves mixing blood (where the anti-HLA antibodies are located) from the recipient with blood cells (where the donor antigens are found) from the donor. If the test is negative, antibodies that would attack the donated organ are not present, and the transplant can safely proceed. A positive result shows that antibodies that would attack the donor are present, meaning the kidney would be rejected immediately and not work.
Options if You Have a Positive Cross-Match With Your Donor
At this stage, there are three options:
- Wait for another donor who has a negative cross-match
- Participate in a kidney paired donation (KPD)
- Undergo the desensitization process
ABO (Blood Type) Incompatibility
A simple test indicates a person's blood type. People are either type A, B, AB or O. The most common types are O and A. Only a small percentage of people have type B or AB. Most blood types form antibodies against the other blood types, meaning most patients cannot get blood transfusions or organ transplants from donors with blood types different from their own. This is called blood-type or "ABO" incompatibility.
There is a 35 percent chance that any two people will be blood-type incompatible. Approximately one-third of people who want to donate a kidney can't donate to their recipient because they have incompatible blood types.
Desensitization treatments can eliminate the antibodies in blood, and make kidney transplantation possible. These treatments use plasmapheresis and intravenous immune globulin, in a process very similar to that used to remove anti-HLA antibodies. Studies show that people with blood type O or B, who have an ABO-incompatible living donor, will benefit the most from these treatments.
The Kidney Paired Donation Program
If the patient is incompatible with their potential donor through either ABO blood type or cross-match testing, they can be evaluated to participate in the kidney paired donation program. This approach allows patients with willing, but incompatible donors to exchange kidneys. In a kidney paired donation, both patients get transplants and both donors give kidneys, but the kidneys go to a patient other than the patient for whom it was originally intended (see figure at right). It can be difficult to find a suitable exchange pair, but by using the kidney paired donation program, no pre-transplant desensitization treatments are required.
The Desensitization Process
The desensitization process begins with medications targeted to reduce the amount of anti-HLA antibodies in your blood. These medications are aimed at the blood cells that produce the antibodies. Next, the plasmapheresis treatments are started. These treatments involve a plasma exchange that removes harmful anti-HLA antibodies from the blood. After each treatment, the drug immune globulin (IVIg) is given to help prevent the harmful antibodies from coming back. The number of treatments a patient needs is determined by the level of anti-HLA antibodies present in their blood. These levels are checked frequently to determine if additional treatments are needed. Typically, 3 to 5 treatments are required before transplant. At the start of the plasmapheresis treatments, the patient receives anti-rejection medications to help prevent production of new anti-HLA antibodies. These anti-rejection medications are the same medications that the patient will continue to use after transplantation. Plasmapheresis treatments may be necessary following transplantation to reduce the risk of rejection. The number of treatments will depend on antibody levels. The majority of patients receive 3 to 6 treatments.
To learn more about desensitization, and to speak with program advisers, please call 312-695-0828.
Please Note: Patients considering the desensitization process before their kidney transplant should have a living donor before entering the program.