Explained: How a human got a pig's heart and why world's watching the case with bated breath

Reports say the surgeons went ahead with the transplant that constituted a last-ditch attempt at keeping him alive on January 7 after receiving the go-ahead under compassionate grounds from US health authorities. Such authorisation, the hospital said, is required where an experimental medical product is the only option available for a patient faced with a serious or life-threatening medical condition.

A human transplant had been ruled out for Bennett with reports saying that such a decision is usually based on pock underlying health condition of the patient. "It was either die or do this transplant. I want to live. I know it's a shot in the dark, but it's my last choice. He is reported to have said a day before the surgery.

"This organ transplant demonstrated for the first time that a genetically-modified animal heart can function like a human heart without immediate rejection by the body, the University of Maryland School of Medicine (UMSOM), whose faculty conducted the surgery, said in a press statement on January 10.

How is the patient recovering?

Three days after the surgery, the hospital said Bennett was responding well to the transplant although it was still too early to rule on the success of the operation. Doctors said he is being closely observed to ascertain how the new organ is performing.

Prior to the operation, Bennett had spent several months on a heart-lung bypass machine. But doctors said he is now able to breathe on his own although he is still connected to the device so as to not put pressure on his the transplanted heart. Doctors said that the next few weeks will be critical for his recovery.

Dr Bartley P Griffith, who conducted the surgery to put the pig heart into Bennett said they are "proceeding cautiously" but are "optimistic that this first-in-the-world surgery will provide an important new option for patients in the future. Dr Muhammad M Mohiuddin, professor of surgery at UMSOM, added that the "successful procedure provided valuable information to help the medical community improve this potentially life-saving method in future patients".

How can such transplantation help?

Transplanting or grafting of animal organs, a process known as xenotransplantation, has been pursued by modern medical science for decades, but experts have found it difficult to surmount the challenge presented by the immune system's rejection of an alien organ, ending in deadly outcomes for patients.

UMSOM said xenotransplants were largely abandoned after the 1984 case involving Stephanie Fae Beauclair, better known as Baby Fae, in California. Born with a fatal heart condition, the infant had received a baboon heart transplant but died within a month of the procedure due to the immune system's rejection of the foreign heart.

Reports point out that superficial wounds have been treated since at least the 1800s with skin grafts from various animals but success with transplant of complex organs has proved more problematic even though pig heart valves have been used for replacing valves in humans "for many years. One of the best known cases of organ transplant concerns a group of 13 people who received kidneys from chimpanzees in the 1960s. While all the recipients died within weeks, one patient went on to live for an additional nine months.

Mohiuddin, who is the UMSOM xenotransplantation programme's scientific director and is regarded as being one of the "world's foremost experts on transplanting animal organs", said that the surgery on Bennett was "the culmination of years of highly complicated research to hone this technique in animals with survival times that have reached beyond nine months".

More than 6,000 patients die each year in the US alone waiting for an organ transplant, UMSOM pointed out, with Griffith noting that this "breakthrough surgery... brings us one step closer to solving the organ shortage crisis" as there are "simply not enough donor human hearts available to meet the long list of potential recipients".

What did it take to carry out the surgery?

The transplanted heart was harvested from a pig that had undergone genetic editing that saw scientists remove three genes "that would have led to rejection of pig organs by humans along with one that would have led to excessive growth of pig heart tissue.

Further, six human genes that would have facilitated the organ's acceptance by the human body were inserted into the pig genome, meaning that a total of 10 unique gene edits were carried out in the pig by the US biotech firm Revivicor.

Reports said that on the day of the surgery, the team at UMM removed the pig's heart and placed it in a perfusion device designed to keep it in readiness for the surgery. Apart from the genetic changes effected in the donor pig, Bennett himself received an experimental anti-rejection drug made by another US-based firm, Kiniksa Pharmaceuticals.

While the procedure has received sensational coverage in the media, experts have pointed out that there are still a lot of questions that still need to be answered about its viability and safety. Art Caplan, a professor of bioethics at New York University, was cited by CNN as saying that it is too early to call the heart transplant a success and it remains to be seen if Bennett has a good quality of life for months.

Source: News18