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Transplantation - The replacement of a worn-out organ by a new one
Transplantation

Sometimes a part of our body can be so ravaged by disease that it can't be saved no matter what we do, and transplantation of a new organ may be the best option to help. Approximately, sixty years ago, scientists were on the cusp of a revolutionary scientific breakthrough. Since the first successful human to human transplant of a cornea in 1905 has done, transplantation as a form of treatment has been investigated and researched. Early attempts usually ended in failure until effective drugs to control rejection were discovered and transplantation became more commonly available. Success finally came in the early 1950s, when several kidney transplants within a few years gave new life to ailing patients. In the following decades, doctors learned how to transplant other organs successfully, and they dramatically improved recovery rates. Today, most organ transplants are relatively safe, routine procedures, and transplantation is considered to be the best treatment option for thousands of patients every year.

Now, organ replacement field is now solidly entrenched in modern medical therapy. Numerous patients have received new kidneys, livers, and hearts. Other organs (lung, pancreas, and intestine) are also routinely transplanted, although in less numbers. Organ replacement therapy has resulted in more active, productive, and meaningful lives of recipients of all organs. In the preceding decades, researchers had had some success transplanting organs in animals, and there had even been a few failed attempts at human organ transplants. Numerous studies showed that human organ transplantation was feasible, and that it would be enormously beneficial to thousands of patients, but nobody had been able to make it work.

Each year, tens of thousands of people receive a gift of life in the form of kidney, heart, lungs, liver, or pancreas. Nevertheless, as medicine advances, transplants of the heart, liver and lungs are also regularly carried out nowadays. However, this process still suffers from such as shortage of the available organs. Let’s read on to know the facts regarding transplantation and the science behind it.

Whatever caused the organ to fail in the first place, transplantation offers a second chance at a normal life.
What is transplantation?

Have you ever moved from one place to another? Say, one city to another or even to one country to another? We call people who have moved from one place to another as transplants. Transplant means moving something from one place to another and often involves a little bit of hassle. In scientific terms, transplantation refers to the movement of an organ, tissue or general body part from one place to another.

Transplants are one of the most miraculous achievements of modern medicine. They involve the donation of organs from one person to another and enable about thousands of people to take on a new lease of life all over the world every year. The term covers transplantation of solid organs (such as kidney or heart), tissues (such as skin) or clusters of specialized cells (such as brain cells or the pancreatic cells that produce insulin). Generally, we may need an organ transplant if one of our organs has failed. This can happen because of illness or injury. When we have an organ transplant, doctors remove an organ from another person and place it in our body. The organ may come from a living donor or a donor who has died.

An isograft uses tissue from a genetically identical donor, like a twin
How many types of transplants?

There are many types of transplant for instance Autograft, Allograft, Isograft and Xenograft (xenotransplantation).

  • An autograft is tissue that is transplanted from one part of the body to another part of the same body. It is the transplantation of organs, tissues, or even particular proteins from one part of the body to another in the same person. For example; in bypass surgeries, doctors graft veins or arteries from other parts of the body to replace blocked sections of important arteries, such as the coronary artery. The donor vessels often come from the leg or the wall of the inner chest.
  • Isoograft is the transplantation of organ or tissue from a donor to a genetically identical recipient like the twins. Some examples of procedures that can involve an isograft may include bone marrow transplant and kidney transplant from living donors, along with donations of cadaver tissue. Monozygotic twins can donate tissue and organs to each other for use in isografts
  • Allograft/homograft, which is a transplant of an organ or tissue between two genetically non-identical members of the same species. Most human tissue and organ transplants are Allografts. Allotransplantation is the movement of an organ, tissue or other body part from one person to another. Just like an in-state or in-country move, the organ or tissue being transferred stays within the same species. And you don't always have to be dead before your organs or tissues can be transplanted. For example, in kidney transplants, a living person can donate one of his or her kidneys to another person because most of us can survive with just one of these organs.
  • Xenograft is a transplant of organs or tissues from one species to another. The xeno in xenotransplantation is derived from the Greek for foreign or strange. Blood transfusions from animals to man were performed in England and France from the early seventeenth century. These were the first clinical attempts at xenotransplantation. Solid organ transplants, attempted in the 20th century, had one or two successes, again mainly in concordant transplants. For example, what happens if a patient needs a new heart? In case of kidneys, donors managed with one kidney in the emergency. How about a non-human donor? Believe it or not, this has been done before. During the 1980's, doctors transplanted the heart of a baboon into a human infant in an attempt to save her life. ‘Baby Fae’ survived for just 20 days after the controversial operation. The cause of death was organ rejection.
A cornea transplant replaces diseased or scarred corneal tissue with healthy tissue from an organ donor.
What kind of organs can be transplanted?

Replacing a damaged or diseased body part with a healthy one is the process involved in transplantation. Many parts of the body, including cells, tissues and whole organs, can be transplanted. The most common type of cell transplant which we see in daily basis is the blood transfusion. Bone marrow stem cells are also routinely transplanted to treat people with leukemia and other cancers. In this case, the patients have lost their own bone marrow cells due to damage by chemotherapy or radiation therapy. The most common tissue transplants include corneas and bone. A transplanted cornea (the transparent layer in front of the eye) can clear a person’s vision by removing scarring after infection or injury. Less commonly transplanted is skin. Transplanted skin benefits burn victims by promoting healing and providing a temporary protection from infection. With a genetic defect — for example, people with cystic fibrosis may need a lung transplant. Other people may also be unlucky enough to develop a disease that leads to organ failure — for example, in some people a cold or flu can cause cardiomyopathy, a disease that weakens heart muscle. People may wait up to three years for an organ transplant. However, once the operation takes place, the result is often a life-saving miracle. Some patients have lived an extra 40 years after receiving a new kidney.

  • Cell transplants – replacing damaged or dead cells in diseases such as diabetes, Alzheimer’s or Parkinson’s disease
  • Tissue transplants – replacing skin, corneas, blood, blood vessels or bone.
  • Organ transplants – replacing diseased organs, such as hearts, lungs, livers, pancreas or kidneys.
Your body is constantly patrolled by white blood cells that behave like suspicious police officers. White blood cells scan the barcode of every cell they come across – if the barcode is incorrect, they attack.
How transplantation works?

An organ transplant is the transplantation of a whole or partial organ from one body to another (or from a donor site on the patient's own body), for the purpose of replacing the recipient's damaged or failing organ with a working one from the donor site. It is not that easy to transplant an organ from one body to another. Every cell in our body is tagged with a protein pattern, like a barcode, stamped onto its surface. The barcode identifies your cells as belonging to you and nobody else. Your body is constantly patrolled by white blood cells that behave like suspicious police officers. White blood cells scan the barcode of every cell they come across – if the barcode is incorrect, they attack. Organ transplantation involves the insertion of foreign cells and the recipient’s white blood cells can quickly notice the incorrect barcode. This is called ‘organ rejection’. Early organ transplant surgeons used a clever trick to get around this issue. They realized that identical twins have the same protein barcode stamped on their cells. This means that transplantation between identical twins does not result in rejection.

We see, then, that the success of the transplant depends on the similarity between the host and transplanted tissues. Thus, it is the host and transplanted tissues which matters the most. Thus, it is clear that the most successful transplants would involve tissue taken from one part of a person’s body and transplanted to another part. In cases of severe burns, for example, healthy skin can replace badly, burned areas of skin. Because identical twins are genetically identical, their cells have the same self markers, and organs can be transplanted from one twin to another with little fear of tissue rejection.

The next best source for tissue for a transplant, and the most common source, is a person whose cell surface markers closely match those of the host. Usually the transplanted tissue comes from a person who has recently died. The donor is usually brain-dead, but his or her heart is kept beating by life-support equipment. Some organs – primarily kidneys – can be harvested from someone who has died and whose heart has stopped beating. This discovery could increase the supply of organs available for transplant. In some cases, living people can donate organs; one of two healthy kidneys can be donated to a needy recipient, as can sections of liver.

What is the fate of immune system in organ transplantation?

Transplant rejection is a phenomenon in which a transplant recipient's immune system attacks the transplanted organ or tissue. Generally, antigens are recognized as foreign by our immune system and starts attacking them. When a person receives an organ from someone else during transplant surgery, that person's immune system may recognize that it is foreign. This is because the person's immune system detects that the antigens on the cells of the organ are different or not "matched." Mismatched organs, or organs that are not matched closely enough, can trigger a blood transfusion reaction or transplant rejection.

To help prevent this reaction, doctors type, or match both the organ donor and the person who is receiving the organ. The more similar the antigens are between the donor and recipient, the less likely that the organ will be rejected. Tissue typing ensures that the organ or tissue is as similar as possible to the tissues of the recipient. The match is usually not perfect. No two people, except identical twins, have identical tissue antigens. So to solve this, doctors use medicines to suppress the recipient's immune system, by giving immunosuppressants. The goal is to prevent the immune system from attacking the newly transplanted organ when the organ is not closely matched. If these medicines are not used, the body will almost always launch an immune response and destroy the foreign tissue. There are some exceptions, though. Cornea transplants are rarely rejected because the cornea has no blood supply. Also, transplants from one identical twin to another are almost never rejected.

There are three types of rejection:

  • Hyperacute rejection occurs a few minutes after the transplant when the antigens are completely unmatched. The tissue must be removed right away so the recipient does not die. This type of rejection is seen when a recipient is given the wrong type of blood. For example, when a person is given type A blood when he or she is type B.
  • Acute rejection may occur any time from the first week after the transplant to 3 months afterward. All recipients have some amount of acute rejection. A single episode of acute rejection can be recognized and promptly treated, usually preventing organ failure, but recurrent episodes lead to chronic rejection. It is believed that the process of acute rejection is mediated by the cell mediated pathway, specifically by mononuclear macrophages and T-lymphocytes.
  • Chronic rejection can take place over many years. The body's constant immune response against the new organ slowly damages the transplanted tissues or organ. Fortunately, much work is currently being done on chronic rejection, both in the lab and clinically. Some new agents not yet in use clinically look to be particularly effective at combating chronic rejection. As these new drugs appear long term graft survival will hopefully increase. In many situations, the current standard treatment for chronic rejection is retransplantation. This approach is not satisfactory, however, because it makes the existing organ shortage worse, and retransplantation is more difficult from a surgical perspective.
Blood group and tissue typing – these have to be compatible, or the recipient's body will "reject" the transplanted organ
Who can donate?

Almost anyone can be considered as a donor, even children and elderly people. Few basic things should be taken into consideration for organ donation. Age and general medical condition need to be taken into account when deciding which organs can be donated, actually very few people are considered not suitable at all. A patient with severe asthma, for example, will not be able to donate their lungs, but could well be able to donate other organs such as heart, kidney or liver. To become a donor, you need to tell your family. Before a decision is made about who will receive the donated organs, several things have to be taken into account by the transplant unit:

  • Blood group and tissue typing – these have to be compatible, or the recipient's body will "reject" the transplanted organ
  • Height and weight compatibility
  • Time spent on the waiting list
  • Degree of "medical urgency" around the recipients state of health
  • Other health conditions that may make transplantation too risky.
Xenotransplantation is a medical breakthrough that can potentially shorten the number of names on the transplant list Xenotransplantation is the transplantation of organs from a different species, such as pigs to humans.
New life for pig-to-human transplants - Gene-editing technologies have breathed life into the languishing field of xenotransplantation. Pig insulin is well tolerated by humans, and was widely used for many years.
How organ transplantation changing the world?

Since the early days of transplantation, medical and surgical techniques have advanced hugely, making successful recovery and long-term survival for the recipient a far more likely outcome. Survival rates for heart transplant patients are now around 80 per cent at the five year point, and liver transplants are even more successful with around 90 per cent after five years. However, many more people than this remain on the waiting list, hoping for a donor. Without the possibility of a transplant, many of these patients would have died – and sadly lots still do, as they sit on the waiting list, hoping for a donor to become available. If there is no suitable recipient on the waiting list, organs will not be retrieved from a potential donor.

The human toll of suffering in patients who need transplants is great, and their quality of life is poor. However, due to the shortage of human organs, xenotransplantation has emerged as an alternative therapy. Xenotransplantation is the transfer of living cells, tissues, and/or organs from one species to another. Unless the number of organ donors increases, many see xenotransplantation as the possibility to save the lives of those needing organ transplants. Extensive research in xenotransplantation has been propelled by the critical shortage of allotransplants. With the advent of genetic engineering and cloning technologies, pigs are currently available with a number of different manipulations that protect their tissues from the human immune response, resulting in increasing pig graft survival in nonhuman primate models. Genetically modified pigs offer hope of a limitless supply of organs and cells for those in need of a transplant.

References

  • Biology of humans ---- Goodenough, McGuire, Wallace
  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4517320/
  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3246856/
  • https://med.nyu.edu/highschoolbioethics/briefs/xenotransplantation
  • http://www.stuff.co.nz/life-style/well-good/teach-me/67810689/Organ-donation-the-gift-of-a-lifetime
  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1129087/
  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3246856/