Donor organ rejection remains one of the main obstacles to successful organ transplantation. According to Science Magazine, approximately 40 percent of all transplant patients experience at least one episode of acute rejection. Immune suppression and lifetime monitoring act to minimize organ rejection after transplantation, and screening before transplantation acts to minimize the risk of rejection at all.
Organ transplants are screened for compatibility between the donor and recipient. This involves both blood and tissue typing. If blood types are not appropriately matched, the body immediately rejects the organ, called hyperacute rejection.
The key to tissue typing is to ensure that the recipient will not produce antibodies against antigens on the donor tissue, called acute rejection. After successful tissue typing, crossmatching confirms that the donor tissue will not bring antibodies into the recipient that will attack his or her organs. A donor that has had a pregnancy, received blood transfusions or received a previous transplant may have such antibodies. A positive cross-match (i.e., negative result) is expected to result in organ rejection and is considered a “no go” for transplantation.
New treatments are addressing incompatible cross-matches. By treating recipients with immunoglobulin, some rejection risks can be minimized. The United Network for Organ Sharing provides a list of who handles the steps for transplant screening.
Rejection is graded and treated based on a scale applicable to a specific organ or tissue based on signs and symptoms. See an example for heart transplantation. Monitoring transplanted organs after they are in the recipient is important for heading off rejection early. The traditional standard is biopsy, but in 2009 a Stanford researcher developed a new test to monitor the level of donor DNA in the recipient’s blood to indicate rejection of the donated tissue.
Transplant recipients undergo lifetime treatment with anti-rejection drugs as standard care. Drugs used to minimize the risk of rejection include anti-metabolites and immune suppressants that limit the growth of T cells, inhibit the actions of T and B cells or inhibit proteins involved in immune cell activation. A full list of such drugs is available from Roche.
Transplants of the future
Some researchers are pursuing chimerism and other methods of growing organs for transplantation that allows recipients to receive tissues made from their own cells, bypassing donor tissues that are “foreign.” The work has moved from understanding the concept in animals to microchimerism in humans, though the work is ongoing. If successful, this work will eliminate the need to wait for a positive match via screening and take drugs for immune suppression after transplantation.