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Why do immunosuppressant drugs increase the risk of infection?

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Kidney transplant — transplant British surgeon Andrew Ready flushing a donated kidney during a transplant at Queen Elizabeth Hospital, Birmingham, England, 2006.

Immunosuppressant drugs increase the risk of infection because they are specifically designed to inhibit the immune system, which is the body’s primary defense against germs such as bacteria, viruses, and fungi.123

In the context of transplant surgery, these drugs are necessary to prevent the recipient's body from rejecting the foreign donor organ. They achieve this by interfering with the development, activation, or proliferation of T cells and other white blood cells that would otherwise identify and attack the graft as a foreign invader.145

Because these medications suppress the very cells responsible for scouting out and destroying pathogens, the patient’s ability to defend against microbial infections is significantly reduced. Consequently, transplant recipients must be monitored closely for signs of infection, and medical teams often take strict precautions—such as air filtration and protective gear—to minimize the patient's exposure to potential pathogens during the period of intensive immunosuppression.2356