Inquiry into Life 15th Edition by Sylvia Mader ,Michael Windelspecht

Exercise 1

Matching Organs for Transplantation
As we have seen in this chapter, the kidneys are essential for life. Because humans normally have two kidneys, but can function quite normally with only one, the kidney was an obvious choice as the first complex organ to be successfully transplanted (Fig. 16A). This occurred in 1954 at Peter Bent Brigham Hospital in Boston, where one of 23-year-old Ronald Herrick's kidneys was transplanted into his twin, Richard, who was dying of kidney disease. The operation was successful enough to allow Richard to live another eight years, while his brother lived with one kidney for over 50 years.
It was no accident, however, that the first successful transplant was performed between twins. Most cells and tissues of the body have molecules on their surface that can vary between individuals; that is, they are polymorphic. The major blood groups are a familiar example. Some individuals have only type A antigen on their red blood cells, some have only type B, some have both (blood type AB), and some have neither (blood type O). Because an individual naturally has antibodies against the A or B antigens their own cells lack, it is essential to make sure that donor blood is compatible before giving someone a blood transfusion. Moreover, because other cells besides red blood cells also have these antigens, the first requirement when attempting to match a potential organ donor with a recipient is to make sure the blood types match.
Another step in matching organs for transplantation involves determining whether the donor and the recipient share the same proteins, called human leukocyte antigens (HLAs) or major histocompatibility complex (MHC) proteins. As the latter name implies, these are the major molecules (antigens) that are recognized by the recipient's immune system when transplanted tissue is rejected. Various types of tests can be done to determine what types of MHC molecules the donor cells and recipient cells have, but the ideal situation would be a perfect MHC match between the donor organ and the recipient. This occurs 25% of the time between siblings who have the same mother and father, and also may occur by chance between unrelated individuals.
A final test that is usually performed prior to kidney transplantation is a crossmatching procedure in which the potential donor's cells are mixed with the blood (serum) of the recipient. This is to detect whether the recipient has any antibodies that could damage the cells of the donor kidney. Such antibodies could be present in patients who have been exposed to mismatched MHC molecules through a previous transplantation, blood transfusion, or even pregnancy. Even if the donor and recipient seem closely matched, if the recipient has preformed antibodies that could react with the donor organ, the organ would probably go to another recipient.
Because a perfect match (such as between two identical twins) is rare, transplantations would not have become as commonplace as they are today without the development of immunosuppressive drugs that help prevent transplant rejection. Generally, the drugs used for this purpose cause an overall suppression of the immune system, leaving transplant patients more susceptible to infections. Because transplant patients usually need to take these drugs for the rest of their lives, there is a need for new drugs that specifically target the cells responsible for the transplant rejection reaction, but leave the rest of the immune system intact.
In order to increase the odds of finding matching kidney donors, the National Kidney Registry has begun using a computerized matching system to find matches. Often, a patient who needs a transplant has one or more potential donors who are willing, but incompatible. The "donor chain" concept allows one of that patient's donors to provide a kidney to a compatible stranger, who in turn has potential donors who could donate to other patients. In an example from 2010, a father in New Jersey donated a kidney to a man in Los Angeles who was a part of a chain of five transplants that resulted in a successful kidney transplant for the New Jersey man's 22-month-old child.
Figure 16A : Preparing for transplantation.
A donor kidney, kept moist and sterile inside a plastic bag, arrives in an operating room.
How might the ability to produce organs in a lab from a patient's own stem cells change the process described in this article? What new challenges would it present?