Small-Bowel Transplantation 1987 – A New Immunosuppressant Opens the Way

The small intestine is a long, snake-shaped tube extending from the stomach to the large intestine. About 6 meters long, it is where most digestion and nutrient absorption occur. Cells lining its inner wall secrete various enzymes, but most digestive enzymes are secreted by the pancreas and enter the small intestine through the pancreatic duct. Cells in the intestinal villi (fingerlike projections on the inner wall) carry nutrients from inside the small intestine into capillaries, after which blood vessels circulate the nutrients to the body's organs.

Although small-bowel transplantation had been attempted since the 1960s, the results were often disappointing because the recipient rejected the foreign tissue. This remained the situation until a report about a new immunosuppressant discovered in 1984 in soil containing the bacterium Streptomyces tsukubaensis was published by Japanese researchers in 1987. The drug was tacrolimus (also called FK-506). Its introduction led to an increase in successful transplants. Later, additional advances in drug treatments to reduce transplant rejection further improved patient survival rates.

The small intestine is one of the most difficult organs to transplant because it is densely colonized by microorganisms, strongly expresses antigens and contains many white blood cells. Before attempting a transplant for intestinal failure, physicians first try total parenteral nutrition (TPN), in which liquid nutrition is delivered through a catheter placed directly into a vein. Unfortunately, long-term TPN can lead to complications such as liver failure, bone disorders, infections and vascular damage related to catheter placement.

Causes of small-bowel transplant failure include:

• Crohn's disease (inflammation of the small intestine)
• Necrotizing enterocolitis (tissue death in infants)
• Hirschsprung's disease (intestinal paralysis) 

Donor intestines usually come from people who have died. However, intestines from living donors can also be used by transplanting sections taken from relatives. Small-bowel transplantation can also sometimes be performed together with transplantation of other organs, such as the liver.

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