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neuromorphogenesis:
First human head transplant could happen in two years
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 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.”
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