First human head transplant could happen in two years
A radical plan for transplanting a head onto someone else’s body is set to be announced. But is such ethically sensitive surgery even feasible?
IT'S heady stuff. The world's first attempt to transplant a human head will be launched this year at a surgical conference in the US. The move is a call to arms to get interested parties together to work towards the surgery.
The idea was first proposed in 2013 by Sergio Canavero of the Turin Advanced Neuromodulation Group in Italy. He wants to use the surgery to extend the lives of people whose muscles and nerves have degenerated or whose organs are riddled with cancer. Now he claims the major hurdles, such as fusing the spinal cord and preventing the body's immune system from rejecting the head, are surmountable, and the surgery could be ready as early as 2017.
Canavero plans to announce the project at the annual conference of the American Academy of Neurological and Orthopaedic Surgeons (AANOS) in Annapolis, Maryland, in June. Is society ready for such momentous surgery? And does the science even stand up?
The first attempt at a head transplant was carried out on a dog by Soviet surgeon Vladimir Demikhov in 1954. A puppy's head and forelegs were transplanted onto the back of a larger dog. Demikhov conducted several further attempts but the dogs only survived between two and six days.
The first successful head transplant, in which one head was replaced by another, was carried out in 1970. A team led by Robert White at Case Western Reserve University School of Medicine in Cleveland, Ohio, transplanted the head of one monkey onto the body of another. They didn't attempt to join the spinal cords, though, so the monkey couldn't move its body, but it was able to breathe with artificial assistance. The monkey lived for nine days until its immune system rejected the head. Although few head transplants have been carried out since, many of the surgical procedures involved have progressed. "I think we are now at a point when the technical aspects are all feasible," says Canavero.
This month, he published a summary of the technique he believes will allow doctors to transplant a head onto a new body (Surgical Neurology International,
doi.org/2c7). It involves cooling the recipient's head and the donor body to extend the time their cells can survive without oxygen. The tissue around the neck is dissected and the major blood vessels are linked using tiny tubes, before the spinal cords of each person are cut. Cleanly severing the cords is key, says Canavero.
The recipient's head is then moved onto the donor body and the two ends of the spinal cord – which resemble two densely packed bundles of spaghetti – are fused together. To achieve this, Canavero intends to flush the area with a chemical called polyethylene glycol, and follow up with several hours of injections of the same stuff. Just like hot water makes dry spaghetti stick together, polyethylene glycol encourages the fat in cell membranes to mesh.
Next, the muscles and blood supply would be sutured and the recipient kept in a coma for three or four weeks to prevent movement. Implanted electrodes would provide regular electrical stimulation to the spinal cord, because
research suggests this can strengthen new nerve connections.
When the recipient wakes up, Canavero predicts they would be able to move and feel their face and would speak with the same voice. He says that physiotherapy would enable the person to walk within a year. Several people have already volunteered to get a new body, he says.
The trickiest part will be getting the spinal cords to fuse. Polyethylene glycol has been shown to prompt the growth of spinal cord nerves in animals, and Canavero intends to use brain-dead organ donors to test the technique. However, others are sceptical that this would be enough. "There is no evidence that the connectivity of cord and brain would lead to useful sentient or motor function following head transplantation," says Richard Borgens, director of the Center for Paralysis Research at Purdue University in West Lafayette, Indiana.
If polyethylene glycol doesn't work, there are other options Canavero could try. Injecting stem cells or olfactory ensheathing cells – self-regenerating cells that connect the lining of the nose to the brain – into the spinal cord, or creating a bridge over the spinal gap using stomach membranes have shown promise in helping people walk again after spinal injury. Although unproven, Canavero says the chemical approach is the simplest and least invasive.
But what about the prospect of the immune system rejecting the alien tissue? Robert White's monkey died because its head was rejected by its new body. William Mathews, chairman of the AANOS, says he doesn't think this would be a major problem today. He says that because we can use drugs to manage the acceptance of large amounts of tissue, such as a leg or a combined heart and lung transplant, the immune response to a head transplant should be manageable. "The system we have for preventing immune rejection and the principles behind it are well established."
Canavero isn't alone in his quest to investigate head transplants. Xiao-Ping Ren of Harbin Medical University in China recently showed that it is possible to perform a basic head transplant in a mouse (CNS Neuroscience & Therapeutics, doi.org/2d5). Ren will attempt to replicate Canavero's protocol in the next few months in mice, and monkeys.
2 comments: