Xenotransplantation: What is this ‘landmark’ surgery all about and what progress has been made so far

The University of Maryland Medical Center in Baltimore early this year successfully executed a landmark surgery that was a step towards organ transplantation and the struggle of finding organ donors forever. 57-year-old David Bennett’s ailing heart was replaced with the genetically altered heart of a pig. He was suffering from arrhythmia, a disorder that affects the rhythm of heartbeats.

Unfortunately, he died on March 8, but it was not immediately clear if his death occurred due to the xenotransplant heart.

The US Food and Drug Administration granted emergency authorization to this experimental procedure on December 31, 2021.

Cross-species transplant

The procedure called xenotransplantation involves “any procedure that involves the transplantation, implantation or infusion into a human recipient of either (a) live cells, tissues, or organs from a nonhuman animal source, or (b) human body fluids, cells, tissues or organs that have had ex vivo contact with live nonhuman animal cells, tissues or organs”.

It is seen as an alternative to clinical transplantation of human organs whose global demand exceeds supply by a large gap. The first Xenotransplantation was tried in the 1980s when the human heart of a newborn with a congenital heart defect was replaced by that of a baboon’s heart. The surgery was successful but the patient died after a few months when the immune system rejected the baboon’s heart.

Xenotransplantation can provide an alternative supply of organs to patients with life-threatening organ defects. The recent transplant showed no signs of rejection for several weeks. He was doing his regular activity with physical therapy.

Why the heart of a pig was used?

Pigs’ anatomical and physiological parameters are similar to that of humans, which is why their heart valves is used for replacing damaged valves of humans for 50 years now. Also, breeding pigs along with different varieties that match the specific needs of a human recipient in a large farm is cost-effective.

Genetically engineered pig

To preempt the chances of molecular incompatibility between pigs and humans leading to immune complications, genetic engineering tweaks the genome of the pig to that the human immune system does not recognize that it is that of a pig, increasing chances of the surgery being successful.

In the latest case, the donor pig’s hearts went through 10 genetic modifications, and four pig gens were replaced by six human genes. Revivicor, a regenerative medicine company provided for the pig. Before the surgery, the pig’s heart was removed from the pig’s body and placed in a special machine to preserve it until Bennett’s surgery.