Good news for the Tin Man: Pig heart transplants work in baboons for 2+ years

If I only had a heart…

My favorite character in the Wizard of Oz was the Tin Man because of the scene where he cries and starts to rust, causing Dorothy to rush to his aid with an oil can. He is such a tender heap of metal that just needs a heart to be whole. How could you not feel for this sensitive character?

Tin Man, Wizard of Oz

Tin Man, Wizard of Oz

In the end, the Tin Man does get a heart, but it’s actually a heart-shaped clock. Being the nerd that I am, I always wish that he got an actual living heart. And this is where I tie in this tangent to today’s blog. A study came out this week that was able to keep transplanted pig hearts alive in baboons for more than two years – news that would make the Tin Man cry with joy.

The beat goes on from pig to baboon

While this news might sound bizarre, it’s actually a really impressive and important study that could lay down the ground work for transplanting animal organs into humans who desperately need them. Currently over 120,000 people in the US are on on the organ transplant list, and more than 20 people die each day waiting for an organ. For these patients, pig organs, which are similar in size to human organs, might be their temporary life-line while they wait to be matched with a human donor. The study was a collaboration between two teams in the US and Germany and was published in the journal Nature Communications.

As with any organ transplant, the main concern is rejection. Our immune systems are hard-wired to recognize and eliminate foreign agents. That’s why if a patient needs a heart transplant, they can’t receive a heart from just anyone, let alone an animal. They need to find a compatible donor that shares enough genetic similarity so that their immune system doesn’t reject the transplant. But even when patients receive organs from compatible donors, they are forced to take immunosuppressive drugs for the rest of their lives to prevent transplant rejection.

Photo credit (Nick Saltmarsh)

Photo credit (Nick Saltmarsh)

Here’s where this study has made a breakthrough. The teams discovered that they could transplant pig hearts into baboons using a combination of gene therapy and immune-suppressing antibodies. On the gene therapy side, the pigs were genetically altered to lack molecular markers that caused blood clotting in primates. They paired this with antibody treatments that blocked the baboon’s immune system from attacking the pig heart. This combination therapy kept the grafted pig hearts safe and happily functioning for more than 900 days.

Two hearts one baboon

How they transplanted the pig hearts is the really interesting part of this story. The pig heart was hooked up to the baboon’s circulatory system through the abdomen, but they left the baboon’s actual heart so the baboon could function normally while allowing scientists to study the function of the pig heart at the same time. Both hearts and the baboons survived for more than two years, which is longer than their previous benchmarks of 180 (median) and 500 (longest) days.

First author on the study Muhammad Mohiuddin commented on the significance of their study:

Muhammad Mohiuddin

Muhammad Mohiuddin

“It is very significant because it brings us one step closer to using these organs in humans. Xenotransplants—organ transplants between different species—could potentially save thousands of lives each year that are lost due to a shortage of human organs for transplantation.”

 

The next chapter in this story is for the authors to transplant pig hearts into baboons that have their own hearts removed and determine whether their combination therapy is successful in achieving the same results.

Even though much work remains to be done, Mohiuddin shared that he could see pig hearts in humans “in the foreseeable future.”

“In our opinion, this regimen appears potentially safe for human application for patients suffering from end-stage organ failure who might be candidates for initial trials of xenotransplantation.”


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