Will the first human head transplant happen soon? According to Sergio Canavero, it will - and he'll be the man to do it.
In 2015, Canavero announced his intention to carry out the pioneering operation, with the head being that of a Russian man, Valery Spiridonov, who has a muscle degenerative disease. The source of the donor body was never specified. More recently, Canavero has said that a Chinese patient will be the first to have their head transplanted. So who is Sergio Canavero, and what's his background? The Turin-based Italian neurosurgeon has had a productive research career: his name appears on 112 papers on PubMed, dating back to 1990. His main interest is pain, specifically central pain syndromes, in which damage to the brain or spinal cord leads to chronic, often difficult-to-treat pain. Canavero's first paper on head transplantation was published in 2013 (in a journal that regular readers may befamiliar with.) However, his interest in radical transplant surgery dates back 25 years: in 1992, Canavero published a speculative paper on "Total eye transplantation for the blind: a challenge for the future." What if, Canavero asked, it were possible to implant an donor eye into a recipient's socket, before connecting it up to the brain by encouraging the optic nerve to grow into place? He never revisited this idea. The 2013 paper introduced two acronyms which Canavero has gone on to use regularly. HEAVEN, or "HEad Anastomosis VENture", refers to the overall project to carry out the first human head transplant. GEMINI, the etymology of which is unclear, is the key procedure that will make the head transplant possible: the fusion, or connection, of two severed spinal cords into one. Spinal cord fusion or reconnection is, to put it mildly, a technical challenge. It's the holy grail of spinal cord injury - the power to reconnect a severed spinal cord could allow countless people to move, and feel, again. But it isn't easy. Canavero claims to have cracked the problem. In September 2016, Canavero announced that"GEMINI has landed - spinal cord fusion achieved." The secret, he says, is a combination of a very sharp cut - to minimize damage to the nerve cells - and PEG, polyethylene glycol. PEG, Canavero says, has "the uncanny capacity to literally re-fuse neuronal cell membranes submitted to mechanical disruption." In the same issue of the journal, Canavero's South Korean collaborator C-Yoon Kim reported that PEG produced "partial restoration of motor function" in mice whose spinal cords were severed. The Kim et al. paper is to date the only evidence that Canavero's GEMINI works, and the results are not very impressive. Compared to a control group, the PEG-treated mice recovered slightly better from the lesion, but the difference wasn't statistically significant. All of the control group and 3/8 of the PEG group died within 2 weeks
As well as mice, Kim et al. also studied the effects of PEG in re-fusing the spinal cords of rats, but the results of this experiment were inconclusive because most of the animals died due to "a storm that filled the underground lab." Beyond fusing the spinal cord, a head transplant would also require connecting up blood vessels, such that the head could receive blood from its new body. This is a technical challenge, although not perhaps as tricky as spinal cord fusion. As early as 1908, Charles Guthrie connected the head of a dog onto the body of another dog, and there have been several refinements of this eerie procedure since. Canavero and a team of Chinese researchers recently reported the creation of a Cronenbergesque two-headed rat, although there was no attempt at spinal cord fusion here - just blood vessel redirection which allowed the second head to live attached to the other rat's body (for 6 hours).
What about the ethics of all this? Are these animal experiments justified? And if Canavero ever gets his hands on a human patient, what then? Even on an optimistic view, someone undergoing this surgery runs a high risk of death, paralysis, or pain - the very central pain syndrome that Canavero spent his previous career studying and treating. Even with the patient's informed consent, it's not clear that decapitation is compatible with the Hippocratic Oath. Perhaps Canavero will be able to find a hospital ethics committee somewhere willing to approve the study, but would that make it ethical? Here's the words of a 2001 paper in the Lancet on the topic of ethics:
When decisions are left largely to the principles of individual doctors or local ethics standards, unethical actions may ensue... public statements by physicians that they acted without abuse, according to the local standard of care, and after approval by local ethics committees has not made [research that violates generally accepted standards, such as the Declaration of Helsinki] more ethical.
Canavero would do well to remember these words; after all, he wrote them.
Overall, my impression is that Canavero is nowhere near ready to carry out a head transplant and I doubt that he will ever attempt the procedure. He seems sincere in his motivations, and the animal experiments, while inconclusive, are not completely worthless. But the fact is that Canavero and his collaborators have yet to show that their techniques can reconnect the two halves of the spinal cord of the same animal with a good functional outcome in the long term - let alone of two animals.
As P. Z. Myers said, "show me a dog walking across the stage with a transplanted body", and only then it might make sense to start thinking about a human trial.
Is it fair to compare Canavero to the disgraced 'pioneer' of stem-cell therapy, Paolo Macchiarini? There are certainly similarities between the two surgeons - such as their flair for publicity, and claims to have found the 'holy grail' of their fields of medicine. I hope however that Canavero won't end up like Macchiarini has: his reputation in ruins, his science discredited, and his patients dead.