CHAPTER 171
Transplantation
Transplantation is the removal of living, functioning cells, tissues, or organs from the body and then their transfer back into the same body or into a different body.
The most common type of transplantation is a blood transfusion (see page 1026). Blood transfusions are used to treat millions of people each year. More typically, transplantation refers to the transfer of organs (solid organ transplants) or tissues.
Organ transplantation, unlike blood transfusion, involves major surgery, the use of drugs to suppress the immune system (immunosuppressants), and the possibility of transplant rejection and serious complications, including death. However, for people whose vital organs have failed, organ transplantation may offer the only chance of survival.
Donors
A tissue or organ donor can be a living person or a person who has recently died (deceased donor).
Tissues and organs from living donors are preferable because they are usually healthier. Stem cells (from bone marrow or blood) and kidneys are the tissues most often donated by living donors. Usually, a kidney can be safely donated because the body has two kidneys and can function well with only one. Living donors can also donate a part of the liver or a lung. Organs from living donors are usually transplanted within minutes of being removed. In the United States, being paid to donate an organ is illegal, but reimbursement for cells and tissues is allowed.
Some organs, such as the heart, obviously cannot be taken from living donors. Organs from deceased donors usually come from people who previously agreed to donate organs. In many states, people can indicate their willingness to donate organs on their driver’s license, although family members are also consulted even when donor status is indicated on the license. Permission for donation also may be obtained from the deceased’s closest family member when the deceased’s wishes are unknown. Deceased donors can be otherwise healthy people who have been in a major accident, as well as those who died of a medical disorder. Doctors do not take the potential for organ donation into account when deciding whether to recommend withdrawal of life support from people who are terminally ill or who are brain dead (see box on page 708).
One donor can provide several people with transplants. For example, one donor could provide two corneas, a pancreas, two kidneys, two liver segments, two lungs, and a heart. When people die, organs deteriorate quickly. Some organs last only a few hours outside the body. Other organs, if kept cold, can last a few days.
In the United States, a national organization (United Network for Organ Sharing) matches donors and recipients for transplantation through the use of a computer database. The database includes all people who are on a waiting list for a transplant, along with their tissue type. When organs become available, that information is entered and a match is made, allowing transplantation to occur with minimal delay.
Did You Know…
Some people with medical disorders can still become organ donors. Doctors evaluate the condition of the organs after a person dies and then decide whether they can be used.
Pretransplantation Screening
Because transplantation is somewhat risky and donor organs are scarce, potential recipients are screened for factors that may affect the likelihood of success.
Tissue Matching: The immune system normally attacks foreign tissue (see page 1096), including transplants. This reaction is called rejection. Rejection is triggered when the immune system recognizes certain molecules on the surface of a cell as foreign. These cell-surface molecules are called antigens.
For blood transfusions, rejection is relatively easily avoided because red blood cells have only three main antigens on their surface. These antigens determine the blood type and are called A, B, and Rh. Doctors test to make sure that antigens in the donor blood and the recipient blood are a complete match.
For organ transplantation, however, many antigens are involved. These antigens are called human leukocyte antigens (HLA) and occur on the surface of every cell in the body. Each person has unique HLA, which determines the tissue type. Ideally, the donor’s tissue type exactly matches the recipient’s tissue type. However, a perfect HLA match is extremely rare, and some people are too ill to wait for a highly compatible donor. In these cases, doctors sometimes use donor tissue that is not an exact match but that is a close match. A close HLA match between the donor and recipient reduces the frequency and severity of rejection and improves the long-term outcome. With the use of immunosuppressants, the success of transplantation is less affected by the degree of matching.
Before transplantation, the recipient’s blood is screened for antibodies against the tissues of the donor. The body may have produced such antibodies in response to a blood transfusion, a previous transplant, or a pregnancy. If these antibodies are present, transplantation is not possible because immediate, severe rejection will occur. Although some procedures and drugs are available to remove the antibodies, there is less experience with these techniques and they are not widely used.
Medical Screening: Some disorders, in particular cancers and infections, can be transmitted during transplantation. Doctors screen donors for cancer by thoroughly reviewing their medical history and carefully inspecting the organ in the operating room at the time of organ recovery. Organs containing cancers are obviously not used for transplant. The decision to use organs from donors who previously had cancer in another organ is made based on the likelihood that tumor cells persist or may have spread to the organ being transplanted.
Most bacterial infections are evident to doctors based on the donor’s overall health and have often been diagnosed and treated even before the decision to donate. If treatment has been adequate, organ transplantation is safe, although the recipient may receive additional antibiotic treatment. To prevent transmission of viral infections, which are often not so obvious, doctors usually test the donor’s blood. Viral infections for which blood tests are done include cytomegalovirus (CMV), Epstein-Barr virus (EBV), hepatitis B and C viruses, human immunodeficiency virus (HIV), and human T-cell lymphotropic virus (HTLV). Some viral infections in the donor, such as HIV and HTLV, mean that transplantation cannot be done. Other viral infections, such as CMV and EBV, do not prevent transplantation, but the recipient must take antiviral drugs afterwards.
Because organ transplant recipients are given immunosuppressants in high doses at the time of transplant, recipients who have active infections or cancers cannot undergo transplant until these conditions are controlled or cured. Many immunosuppressants are also unsafe for fetuses, so pregnant women cannot undergo transplant. However, some women who have received a transplant may be able to get pregnant and have healthy babies once the function of their transplanted organ is stable and their immunosuppressants can be specially adjusted.
People with poor overall health, other medical problems in addition to single organ failure, and certain viral infections are less likely to do well with a transplant. The decision to transplant is individualized to the person’s specific circumstances.
Psychosocial Screening: The lifelong regimen of drugs, treatments, and follow-up visits required to keep a transplanted organ functioning is quite demanding, and not all people are willing or able to comply. In addition to nurses and doctors, psychiatrists and social workers are involved to help people and their families understand the long-term commitment and difficulties involved in accepting a transplant. Everybody’s input is important in determining whether organ transplantation is right for a person.
Suppression of the Immune System
Even if tissue types are closely matched, transplanted organs, unlike transfused blood, are usually rejected unless measures are taken to prevent rejection. Rejection results in destruction of the transplanted organ and can cause fever, chills, nausea, fatigue, and sudden changes in blood pressure. Rejection, if it occurs, usually begins soon after transplantation but can occur after weeks, months, or even years. Rejection can be mild and easily controlled or severe, worsening despite treatment.
Rejection can usually be controlled with drugs that suppress the immune system and the body’s ability to recognize and destroy foreign substances. With the use of these immunosuppressants, the transplanted organ is more likely to survive. Immunosuppressants must be taken indefinitely. High doses are usually necessary only during the first few weeks after transplantation or during an episode of rejection. After that, smaller doses can usually prevent rejection (maintenance immunosuppression). A further reduction of immunosuppression may be required if recipients suffer from serious infections or side effects, but reducing the dose of the immunosuppressant increases the risk of rejection. At the first sign of rejection, doctors increase the dose of the immunosuppressant, change the type of immunosuppressant, or add an additional immunosuppressant.
DRUGS USED TO PREVENT TRANSPLANT REJECTION
| DRUG | POSSIBLE SIDE EFFECTS | COMMENTS |
| Corticosteroids (potent anti-inflammatory drugs that suppress the immune system as a whole) | ||
| Dexamethasone Prednisolone Prednisone |
Excess hair on the face Facial puffiness Fragile skin High blood sugar levels (as occur in diabetes mellitus) Muscle weakness Osteoporosis Stomach ulcers Water retention |
Given by vein in high doses at the time of transplantation Gradual reduction of the dose to a maintenance dose given by mouth, usually indefinitely |
| Polyclonal immunoglobulins (antibodies directed toward specialized cells of the immune system) | ||
| Antilymphocyte globulin Antithymocyte globulin |
Severe allergic (anaphylactic) reactions with fever and chills, usually occurring only after the first or second dose Reaction to the foreign proteins in the drug with fever, rash, and joint pain (serum sickness) |
Given by vein Used at the time of transplantation or for rejection episodes |
| Monoclonal antibodies (antibodies that target lymphocytes) | ||
| Basiliximab Daclizumab Infliximab |
Drug tolerance (the drug becomes less effective for subsequent rejection episodes) Fever |
Given by vein Used at the time of transplantation or for rejection episodes |
| Muromonab (OTK3) | Irritation of the digestive tract Joint pain Muscle pain Seizures Severe allergic (anaphylactic) reactions Shaking (rigors) |
Severe side effects usually only after the first few doses |
| Calcineurin inhibitors (drugs that prevent activation and expansion of the immune system) | ||
| Cyclosporine | Excessive hairiness (hirsutism) Gum enlargement High blood pressure Increased risk of cancer Kidney damage Liver damage Tremor |
Given by mouth Used as maintenance immunosuppression in people who have received a solid organ transplant |
| Tacrolimus | Diarrhea Headache Heart enlargement High blood pressure Increased risk of lymphoma Insomnia Kidney damage Liver damage Nausea Tremor |
Given by mouth Used as maintenance immunosuppression in people who have received a solid organ transplant |
| Rapamycins (drugs that prevent proliferation of lymphocytes) | ||
| Everolimus | Anemia | Given by mouth |
| Sirolimus | Diarrhea High blood pressure Increased cholesterol levels Increased risk of lymphoma Joint pain Low potassium levels Rash |
Used with corticosteroids or calcineurin inhibitors in people who have received a kidney or liver transplant Everolimus usually given to people who have received a heart transplant |
| Mitotic inhibitors (drugs that suppress cell division and thus the production of white blood cells) | ||
| Azathioprine | Hepatitis (rare) Increased risk of infection Low white blood cell count Nausea Tendency to bleed Tiredness Vomiting |
Given by mouth Used as maintenance immunosuppression in people who have received a solid organ transplant |
| Mycophenolate mofetil | Blood infection (sepsis) Diarrhea Increased risk of lymphoma Nausea Vomiting |
Given by mouth Used as maintenance immunosuppression in people who have received a solid organ transplant |
Complications: Although immunosuppressants suppress the immune system’s reaction to the transplanted organ, they also reduce the ability of the immune system to fight infections and to destroy cancer cells. Thus, transplant recipients are at increased risk of developing infections and certain cancers.
Recipients may get the same infections that any person recovering from surgery would. Such infections include those of the surgical site or the transplanted organ, pneumonia, or urinary infections. People also are at risk for unusual (opportunistic) infections that affect mainly people with weakened immune systems. Such infections may be caused by bacteria (for example, Listeria or Nocardia), viruses (for example, CMV or EBV), fungi (for example, Pneumocystis or Aspergillus), or parasites (for example, Toxoplasma).
Cancers due to immunosuppression include certain skin cancers, lymphoma, cervical cancer, and Kaposi’s sarcoma.
Kidney Transplantation
For people of all ages who have irreversible kidney failure, kidney transplantation is a lifesaving alternative to dialysis. In the United States, more than 17,000 kidneys are transplanted each year. Over 95% of kidneys from living donors are functioning 1 year after transplantation. Three percent to 5% of these kidneys stop functioning each year after the first. About 82 to 91% of kidneys from deceased donors are functioning 1 year after transplantation. Five percent to 8% of these kidneys stop functioning each year after the first. Transplanted kidneys sometimes function for more than 30 years. People with successful kidney transplants can usually lead normal, active lives.
About two thirds of transplanted kidneys come from deceased donors. The kidneys are removed, cooled, and transported quickly to a medical center for transplantation to a person who has a compatible blood and tissue type and who does not make antibodies to the tissues of the donor.
Kidney transplantation is a major operation. The donated kidney is placed in the pelvis through an incision and is attached to the recipient’s blood vessels and bladder. Usually, the nonfunctioning kidneys are left in place. Occasionally, they are removed because they are causing uncontrollable high blood pressure or are infected.
Despite the use of immunosuppressants, one or more episodes of rejection may occur after transplantation. Acute rejection can be accompanied by fever, decreased urine production with weight gain, pain and swelling of the kidney, and elevated blood pressure. Blood tests show deteriorating kidney function. Because these symptoms can also occur with infections or drug toxicity, the diagnosis of rejection can be confirmed with a needle biopsy of the kidney.
Acute rejection occurs within 3 to 4 months of transplantation. It can usually be controlled with high doses of immunosuppressants or antibody therapy given for a short time. Sometimes, using a different drug for maintenance immunosuppression helps control rejection.
Chronic rejection that develops over many months to years is relatively common and causes kidney function to gradually deteriorate. If rejection cannot be controlled, the kidney will fail and dialysis must be started again. The rejected kidney may be left in place unless fever, tenderness, blood in the urine, or high blood pressure persists. The chance of success with second transplants is almost as good as that with first transplants.
Compared with the general population, kidney transplant recipients are 10 to 15 times more likely to develop cancer, probably because the immune system helps defend the body against cancer as well as infections. Cancer of the lymphatic system (lymphoma) is 30 times more common among kidney transplant recipients than the general population, but lymphoma is still uncommon. Skin cancer is common.
Liver Transplantation
Liver transplantation is the only option for people whose liver no longer functions. A whole liver can be obtained only from a person who has died, but a living donor can provide a part of the liver. A donated liver can be stored for 8 to 15 hours. Many people die while waiting for a suitable liver, but 85 to 90% of liver transplant recipients survive for at least 1 year. Most recipients are people whose liver has been destroyed by primary biliary cirrhosis, hepatitis, or drug toxicity (such as high doses of acetaminophen). People whose liver has been destroyed by alcoholism can receive a transplant if they stop drinking. Liver transplantation is also done for some people who have liver cancer that is not too far advanced. About 86% of patients who receive a transplant to treat cancer are still alive after 1 year. Although viral hepatitis and autoimmune disorders tend to recur in the transplanted liver, survival is still good.
The damaged liver is removed through an incision in the abdomen, and the new liver is connected to the recipient’s blood vessels and bile ducts. Usually, blood transfusions are required. Typically, the operation lasts 4 1/2 hours or more, and the hospital stay is 7 to 12 days.
Liver transplants are rejected somewhat less vigorously than transplants of other organs, such as the kidney and heart. Nonetheless, immunosuppressants must be taken after transplantation. If the recipient develops an enlarged liver, nausea, pain, fever, jaundice, or abnormal liver function (detected by blood tests), doctors may do a biopsy using a needle. Biopsy results help doctors determine whether the liver is being rejected and whether immunosuppressant therapy should be adjusted.
Heart Transplantation
Heart transplantation is reserved for people who have severe heart failure and who cannot be treated effectively with drugs or other forms of surgery. In some medical centers, heart machines can keep people alive for weeks or months until a compatible heart can be found. Also, newly developed, implant-able artificial hearts are being used to tide people over until a heart is available or, in some experimental situations, to be used as a long-term replacement. Nonetheless, many people die while waiting.
About 95% of people who have had a heart transplant are substantially better able to exercise and carry out daily activities than they were before the transplantation. About 85% of heart transplant recipients survive for at least 1 year.
Through an incision in the chest, most of the damaged heart is removed, but the back walls of the upper heart chambers (atria) are left. The donated heart is then attached to what remains of the recipient’s heart. The procedure takes about 3 to 5 hours. The hospital stay after this operation is usually 7 to 14 days.
Immunosuppressants must be taken to prevent rejection of a transplanted heart. Rejection, if it occurs, usually causes fever, weakness, and a rapid or other abnormal heart rhythm. With rejection, the transplanted heart may not function well, causing low blood pressure and fluid accumulation in the legs and sometimes the abdomen, resulting in swelling—a condition called edema. Fluid may also accumulate in the lungs. If rejection is mild, no symptoms may occur, but electrocardiography (ECG) may detect changes in the heart’s electrical activity.
If doctors suspect rejection, they usually do a biopsy. A catheter is inserted through an incision in the neck into a vein and is threaded to the heart. A device at the end of the catheter is used to remove a small piece of heart tissue, which is examined under a microscope. Doctors also routinely do biopsies once a year to look for rejection that has not yet caused symptoms.
Nearly half of all deaths that occur after heart transplantation are due to infections. About one fourth of people who have a heart transplant develop atherosclerosis in the coronary arteries.
Lung and Heart-Lung Transplantation
Lung transplants are done for people whose lungs no longer function. Most recipients are people who have severe chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis, cystic fibrosis, α1-antitrypsin deficiency, and primary pulmonary hypertension. Usually, one lung is transplanted, but two lungs can be transplanted. When a lung disorder has also damaged the heart, one or both lungs and a heart may be transplanted at the same time. Because preserving a lung for transplantation is difficult, lung transplantation must be done as soon as possible after a lung has been obtained.
Lung transplants can come from a living donor or from someone who has recently died. A living donor cannot donate more than one entire lung and usually donates only one lobe. A person who has died can provide both lungs or the heart and lungs.
Through an incision in the chest, the recipient’s lung or lungs are removed and replaced with those of the donor. The blood vessels to and from the lung (pulmonary artery and pulmonary vein) and the main airway (bronchus) are connected to the transplanted lung or lungs. The operation takes 4 to 8 hours for one lung and 6 to 12 hours for two lungs. A heart and lung may be transplanted at the same time. The hospital stay after these operations is usually 7 to 14 days.
About 70% of people who receive a lung transplant survive for at least 1 year. The risk of infection is high because the lungs are continually exposed to air, which contains bacteria and other microorganisms that can cause disease. The site at which the airway is attached sometimes heals poorly. Scar tissue may form, narrowing the airway, reducing air flow, and causing shortness of breath. Treatment of this complication consists of widening (dilating) the airway—for example, by placing a stent (a wire-mesh tube) in the airway to hold it open.
Rejection of a lung transplant can be difficult to detect, evaluate, and treat. More than 80% of people who receive a lung transplant develop some symptoms of rejection within a month of transplantation. Symptoms include fever, shortness of breath, and weakness. Weakness develops because the transplanted lung cannot provide enough oxygen to supply the body. Later, scar tissue may form in the small airways and gradually block them, possibly indicating gradual rejection.
Pancreas Transplantation
Pancreas transplantation is done for people with diabetes whose pancreas cannot make any insulin. It is a major operation, requiring a long incision in the abdomen and a general anesthetic. The recipient’s pancreas is not removed. Typically, the operation takes about 3 hours and the hospital stay is 1 to 3 weeks.
More than 80% of people with diabetes who receive a pancreas transplant have normal blood sugar levels afterward and no longer need insulin, but they trade this for the need to take immunosuppressants, with the risk of infections and other side effects. Because injectable insulin is a safe and reasonably effective treatment for diabetes, pancreas transplantation is usually done only in certain diabetic people. People who are most likely to benefit include those who repeatedly have life-threatening low blood sugar levels from use of insulin, and those who also need a kidney transplant. People who need a kidney transplant need to have their abdomen opened and to take immunosuppressants anyway, so they incur few additional risks if they receive a pancreas transplant at the same time.
PANCREATIC ISLET CELL TRANSPLANTATION
The cells in the pancreas that produce insulin are called islet cells. Islet cells may be separated from the pancreas of a deceased donor. The islet cells are then transplanted by injecting them into a vein that goes to the liver. The islet cells lodge in the small blood vessels of the liver, where they can live and produce insulin. Sometimes two or three infusions are done, requiring two or three deceased donors.
Some people must have their pancreas removed because of disorders such as chronic pancreatitis (see page 161). Such people will then become diabetic even if they were not diabetic previously. After the pancreas is removed, doctors can sometimes harvest the islet cells from the person’s own pancreas. These islet cells can then be transplanted back into the person’s body (autologous transplantation). Because the cells are the person’s own, immunosuppressants are not needed.
Transplanting islet cells is simpler and safer than a pancreas transplant, and about 75% of people who receive an islet cell transplant no longer need insulin. However, the long-term success of islet cell transplantation is not yet proved.
Stem Cell Transplantation
Stem cells are unspecialized cells from which other more specialized cells can be derived. Stem cells obtained from embryos and fetuses are thought to be best because they are more likely to survive transplantation than those obtained from children or adults. However, adults also have some kinds of stem cells. Stem cells for different kinds of blood cells can be obtained from the bone marrow (bone marrow transplantation) or, in small numbers, from the blood.
Stem cell transplantation can be used as part of the treatment for blood disorders such as leukemia, certain types of lymphoma (including Hodgkin lymphoma), aplastic anemia, thalassemia, sickle cell anemia, and some congenital metabolic or immunodeficiency disorders (such as chronic granulomatous disease). Certain types of stem cells can also be used as transplants for people whose bone marrow has been destroyed by high doses of chemotherapy or radiation therapy used to treat some cancers. Stem cell transplantation may some day become useful for treating other disorders, such as Parkinson’s disease and Alzheimer’s disease, in which the transplanted stem cells can become brain cells.
Stem cells may be the person’s own cells (autologous transplantation) or those of a donor (allogeneic transplantation). When the person’s own stem cells are used, they are collected before chemotherapy or radiation therapy because these treatments can damage stem cells. They are injected back into the body after the treatment.
For bone marrow transplantation, the donor is usually given a general anesthetic. Doctors then remove marrow from the donor’s hip bone with a syringe. Removal of bone marrow takes about 1 hour.
Sometimes stem cells from adults are obtained from blood during an outpatient procedure. First, the donor is given a drug that causes the bone marrow to release more stem cells into the bloodstream. Then blood is removed through a catheter inserted in one arm and is circulated through a machine that removes stem cells. The rest of the blood is returned to the person through a catheter inserted in the other arm. Usually, about six 2- to 4-hour sessions during a period of 1 to 2 weeks are required to obtain enough stem cells. Stem cells can be preserved for later use by freezing them.
Stem cells are injected into the recipient’s vein. The injected stem cells migrate to and begin to multiply in the recipient’s bones and produce blood cells.
Stem cell transplantation is risky because the recipient’s white blood cells have been destroyed or reduced in number by chemotherapy or radiation therapy. As a result, the risk of infection is very high for about 2 to 3 weeks—until the donated stem cells can produce enough white blood cells to protect against infections.
Another problem is that the new bone marrow obtained from another person may produce cells that attack the recipient’s cells, causing graft-versus-host disease (see page 1031). Furthermore, the original disorder may recur.
The risk of infection can be reduced by keeping the recipient in isolation for a period of time (until the transplanted cells begin to produce white blood cells). During this time, everyone entering the room must wear masks and gowns and wash their hands thoroughly. Antibodies isolated from the donor’s blood may be given intravenously to the recipient to help protect against infection. Growth factors, which stimulate the production of blood cells, can help reduce the risk of infection and graft-versus-host disease.
What Are Stem Cells?
Stem cells are undifferentiated cells that have the potential to become one of 200 types of cells in the body, including blood, nerve, muscle, heart, glandular, and skin cells. Some stem cells can be triggered to become any kind of cell in the body. Others are already partially differentiated and can only become, for example, any kind of nerve cell. Stem cells divide, producing more stem cells, until they are triggered to specialize. Then as they continue to divide, they become more and more specialized until they lose the ability to be anything but one kind of cell.
Researchers hope to use stem cells to repair or replace cells or tissues damaged or destroyed by such disorders as Alzheimer’s disease, Parkinson’s disease, diabetes, and spinal injuries by triggering the genes that cause the stem cells to specialize. Researchers are so far able to obtain stem cells from four sources:
Embryos: During in vitro fertilization, sperm from the man and several eggs from the woman are placed in a culture dish. The sperm fertilizes the egg and the resulting cell divides, forming an embryo. Several of the healthiest-looking embryos are placed in the woman’s uterus. The rest are discarded or frozen to be used later if needed. Stem cells can be obtained from the embryos that are not used. Because the embryos then lose the ability to grow into a complete human being, the use of stem cells from embryos is controversial, but researchers think that these stem cells have the most potential for producing different kinds of cells and for surviving after transplantation.
Fetuses: After 8 weeks of development, an embryo is called a fetus. Stem cells can be obtained from fetuses that have been miscarried or aborted.
Umbilical Cord: Stem cells can be obtained from the blood in the umbilical cord or placenta after a baby is born. These stem cells can produce only blood cells and have been used for transplantation only in recent years.
Children and Adults: The bone marrow and blood of children and adults contain stem cells. These stem cells can produce only blood cells. These stem cells are most often used for transplantation.
Recipients of a stem cell transplant usually remain in the hospital for 1 to 2 months. After discharge from the hospital, follow-up visits are necessary at regular intervals. Most people need at least 1 year to recover.
Corneal Transplants and Why They Usually Work
Corneal transplantation is a common and highly successful type of transplantation. A scarred or cloudy cornea can be replaced with a clear, healthy one. Doctors using a surgical microscope carry out the procedure in about 1 hour. Donated corneas come from people who have recently died. A general or local anesthetic is used. The donated cornea is cut to the right size, the damaged cornea is removed, and the donated cornea is sewn in place. The recipient usually stays in the hospital 1 or 2 nights but may go home the same day.
A cornea is rarely rejected because it does not have its own blood supply. It receives oxygen and other nutrients from nearby tissues and fluid. The components of the immune system that initiate rejection in response to a foreign substance—certain white blood cells and antibodies—are carried in the bloodstream. Thus, these cells and antibodies do not reach the transplanted cornea, do not encounter the foreign tissue there, and do not initiate rejection. Tissues with a rich blood supply are much more likely to be rejected.
Transplantation of Other Organs
Skin grafts can be used in people who have lost large areas of skin—for example, because of extensive burns. Skin grafting is most successful when healthy skin is removed from one part of the body and grafted to another part. When such grafting is not possible, skin from a donor or even from animals (such as pigs) can be used as a temporary measure. Such grafts last only a short time, but they can provide temporary protection until normal skin grows to replace them. The amount of skin available for grafting may be increased by growing small pieces of the person’s skin in a tissue culture or by making many tiny cuts in the grafted skin, so that it can be stretched to cover a much larger area.
Cartilage may be transplanted successfully without the use of immunosuppressants. The body’s immune system attacks transplanted cartilage much less vigorously than other tissues. In children, cartilage is usually used to repair defects in the ears or nose. In adults, it can be used to repair joints damaged by injury and occasionally by arthritis.
Corneas, the transparent domes on the surface of the eyes, can usually be transplanted successfully without the use of immunosuppressants.
Bone from one part of the body can be used to replace bone in another part. Bone transplanted from one person to another survives only a short time. However, it stimulates growth of new bone, stabilizes the area until new bone can form, and provides a framework for new bone to fill in.
Transplantation of the small intestine may be used when the intestine does not absorb nutrients because of a disorder or has had to be removed because of a disorder or injury, and other forms of nutrition have failed. Intestinal transplants are particularly prone to both infection and rejection, and less than 80% last for more than 1 year. Because the small intestine contains a large amount of lymphatic tissue, the new intestinal tissue may produce cells that attack the recipient’s cells, causing graft-versus-host disease.
Parkinson’s disease can be treated by transplanting tissue from a person’s adrenal glands to that person’s brain. Alternatively, brain tissue from aborted fetuses can be used. Both procedures can relieve symptoms. However, the ethics of using tissue from aborted fetuses is controversial.
Thymus glands from aborted or miscarried fetuses can be transplanted into children who are born without a thymus gland (a disorder called DiGeorge syndrome). When the thymus gland is missing, the immune system is impaired, because white blood cells, which are a vital part of the immune system’s defense against foreign substances, mature in the thymus gland. Transplantation of a thymus gland restores the impaired immune system in these children. However, the new thymus may produce cells that attack the recipient’s cells, causing graft-versus-host disease.
Rarely, transplantation of limbs and faces from one person to another has been attempted, but this technique is experimental.
Reattaching a Body Part
If fingers, hands, and arms are relatively undamaged after being severed from the body, they can sometimes be reattached successfully. Reattachment of legs is less successful. The severed part is kept clean and is put in a plastic bag and placed on ice until it can be used. Prompt reattachment is crucial so that the blood supply to the severed part can be restored.