Despite the allusion to the supernatural in its name, the Ghost Heart is a fascinating discovery in regenerative medicine that has the potential to meet the need for heart transplants globally and therefore keep many patients alive for longer.
In the summer of 2023, Doris Taylor and her research team at The Texas Heart Institute created The Ghost Heart by stripping the living cells from a pig's heart. This is done using a soapy solution which leaves “ghostly” white protein shells that retain the form of the organ. The heart can then serve as a scaffold which can be injected with the recipient's blood or bone marrow stem cells.
This is not the first time there have been attempts to use animal organs in the human body. Xenotransplantation is when non-human cells, tissues, or organs are used to treat medical conditions in humans. An example of this was a case in 2022 when Doctors at the University of Maryland Medical Centre in the US performed the world’s first genetically modified pig heart transplant. The patient was David Bennet, 57, who was living with terminal heart disease and had been deemed ineligible for a human heart transplant. The patient received a pig heart that had been genetically modified: human genes were added, and some pig genes were removed, but the heart still essentially comprised pig cells within a pig scaffold. As a result, Bennet had to take anti-rejection drugs that suppressed his immune system. Unfortunately, unbeknownst to the doctors, the heart was carrying a pig virus that ultimately killed the patient two months following the transplant. Taylor believes that these sorts of problems are avoided with the ghost heart as her team removes the pig cellular material from the scaffold, leaving only the protein structure and blood vessel channels behind. The proteins are so similar to human scaffold proteins that they don’t appear to cause rejection.
Pig hearts are similar to human hearts in size and structure; both have four chambers - two atria and two ventricles - responsible for pumping blood. Structures from pig hearts such as valves have been safely used in humans. This could mean an end to organ shortages and anti-rejection drugs, as well as a revolution in cardiovascular surgery. Furthermore, the discovery of the Ghost Heart could advance organ donation moving towards the future.
Many barriers complicate the organ donation process, including religious beliefs, being from an underrepresented minority group, difficulties in obtaining consent, lack of understanding, general ethical concerns, and organ shortage in general. In the NHS, patients who are initially placed on the Routine list wait 18-24 months on average to receive a transplant. This includes those patients who deteriorated and were transferred to the Urgent list. Some patients still wait much longer than average, and some shorter. Patients on the Super-Urgent list have the shortest wait but this is because they are critically ill. The use of the Ghost Heart, would hypothetically overcome these challenges.
There are two main hurdles facing Doris Taylor’s team of scientists at the Texas Heart Institute. The first is the time and cost it takes to grow the cells. Heart cells are unable to divide (which is why the heart cannot repair itself), however, stem cells which are used to build the ghost heart, do divide. They can also form into specialised cells - in this case, heart cells. Nobel Prize laureate Dr. Shinya Yamanaka discovered a method to make stem cells out of blood or skin cells from an adult, and Taylor and her team employed this method to obtain stem cells and then grow those cells into billions of copies. After that, the team used chemicals to differentiate them into heart cells, which allowed them to produce billions and billions of heart cells. The second hurdle is enabling the heart to mature once the cells are delivered into it - all while maintaining sterility in the absence of any antibiotics. The immature heart cells must be trained to pump together, all whilst keeping them sterile without an immune system. Creating a Ghost Heart is therefore difficult.
Doris Taylor’s discovery of the Ghost Heart has created the capacity for other treatments following the same blueprint - using animal organ structures to replace different organs and improve survival rates. This could potentially change the way organ transplants are carried out in the future.