• Mayo Clinic Minute: How the immune system can make getting an organ transplant trickier

If waiting for an organ transplant weren't difficult enough, some patients are forced to wait longer than others because of something called "sensitization." Dr. Andrew Bentall, a Mayo Clinic transplant nephrologist, explains how the body's immune system can affect whether a transplant will be successful and why living organ donation is one of the keys to avoiding sensitization problems.

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It's one of the biggest hurdles for people needing an organ transplant, and it's caused by their own immune system.

"People can get sensitized from transplantation from previous transplants, from blood transfusions and also from pregnancy," Dr. Bentall says.

He says it happens when a person has antibodies that cause their immune system to reject a transplanted organ.

"The immune system doesn't recognize the organ as an organ," Dr. Bentall explains. "It just says: 'This is foreign. I'm not used to having this in my body, and I'm developed to be able to reject foreign things."

Sensitization can cause a person to wait much longer for an organ transplant.

But researchers have developed drugs that can help protect a transplanted organ in someone whose body is sensitized.

"It stops the antibodies from killing ... the cells there," Dr. Bentall says. "It's a drug that's very effective for that, to be able to let people who either have an unexpected antibody-mediated rejection episode, or one that we may be expecting, to get through that difficult period."

Dr. Bentall says patients with sensitization also do better when they're able to find a living donor. That's because even if they are sensitized to a specific donor's organ, transplant programs often are able to match them to a different living donor and trade one living donor organ for another.

It's a win-win that's only possible when more people decide to be living donors.