The rise of the ‘new human’ – how stem cells are revolutionising medicine.

Siddhartha Mukherjee's brilliant The Song of The Cell explains how these building blocks will upend our understanding of life itself.
very cell in your body, from toenail to brain, comes from a single original cell: the fertilized egg that was you at conception. So every different organ and tissue in the human body can in principle be produced by an embryonic cell, or stem cell. That being the case, why don’t we grow new limbs after injury, like salamanders and starfish do? Alas, our cells don’t always do what we’d wish. At least, not yet.

The prospect of the kind of “cellular engineering” that might make such therapies possible is one among many themes of The Song of The Cell, whose author, the oncologist Siddhartha Mukherjee, previously wrote the bestselling The Emperor of All Maladies: A Biography of Cancer (2010). Cancer itself is a recurring thread here too, being another way in which our cells can rebel against our hopes and desires. (There are some particularly moving scenes at the bedside of a friend and patient of the author’s.) What can make the disease so intractable, he explains, is that a single tumour can contain cells that have mutated in different ways, so that it is “an assemblage of nonidentical diseases”. So even novel therapies that sequence a tumour’s genome are not guaranteed to succeed.

No one knows how the planet’s first biological cell – the shared ancestor of all living things, from magic mushrooms to Liz Truss – constructed itself, billions of years ago. But somehow a bunch of proto-genetic material surrounded itself with a protective bubble and life got going. Later, single cells decided it might be worth getting together – perhaps huddling for defence, though again no one really knows – and so multicellular organisms such as shrubs and lizards were eventually made possible. As Mukherjee explains, cells have evolved into exquisite nanobots, packed with all sorts of machinery for energy production, replication, and – in the case of immune cells – hunting and killing.

Immunotherapy – the re-education of a patient’s own immune cells, the better to target cancer or other disease – is one of the cutting-edge medical interventions that really interest Mukherjee, and he relates some fascinating case studies of how it can work or fail. The problem is often that the supercharged immune cells go after other innocent organs (say, the liver) as well as the enemy. In a short but excellent chapter on the covid-19 pandemic, meanwhile, Mukherjee explains the especially vicious cellular effects of the Sars-Cov-2 virus’s hijacking and subverting of the immune system itself. Still it isn’t known how exactly this is done. “The monotony of answers is humbling, maddening,” the author writes. “We don’t know. We don’t know. We don’t know.”

What we do know, however, is already impressive. The fact that living tissues are made from cells was first discovered only in the late 17th century, by microscope-building investigators such as Robert Hooke and the Dutch cloth merchant Antonie Van Leeuwenhoek. (Hooke called them “cells” because their structure reminded him of monks’ rooms.) Two hundred years later, it was still common for surgeons who dropped a scalpel on a blood-and-pus-soaked floor simply to wipe it off on their gowns for reuse. (Pus was thought to have splendid healing powers.) And now, a mere 150 years later, we can rewrite the DNA inside cells to cure some kinds of vision or hearing loss.
By engaging in such medical magic, Mukherjee argues that we are in a sense creating “new humans”, which might be thought a slight overstatement, but one cannot begrudge him his delight in his chosen science. Indeed, the subject of the cell is so vast in his hands – covering not only the anatomy of single cells, but also everything from IVF and heart attacks to battlefield medicine, deep-brain stimulation for depression, the Thalidomide disaster, the discovery of insulin, and gene-edited babies – that he has effectively attempted to write a book about the entirety of human biology and modern medicine. The guiding metaphor of “new humans”, as we allegedly shall be once immunological and genetic engineering becomes routine, is therefore structurally useful if not altogether convincing.

It is fortunate, then, that Mukherjee he is such an engaging writer, alert to both nanoscopic beauty and the potential deceptions of metaphor. After a particularly gruelling hospital episode, he comments: “Ever since that evening, I never use the word ‘bloodbath’ casually.” The most immediate parts of the book, indeed, are the periodic case studies from the author’s clinical practice, written with compassionate warmth and humour, and the personal glimpses into an ordinary scientific life and the dedication that goes with it. At one lovely point, he relates how he spends Monday mornings alone in a darkened room at his hospital, looking at blood samples under a microscope. It’s his favourite time of day. “I love looking at cells, in the way a gardener loves looking at plants.”

He also has an amusing habit of describing British places (Oxford, Oldham) as interminably rainy or foggy purgatories in which scientists must nonetheless doggedly pursue the truth, with wry asides at “the English habit of deadly euphemism” he encountered as a student. One scientific mentor, he relates, had a habit of reacting to an idea he thought ludicrous by calling it “subtle”. Mukherjee remembers: “At lab meetings, I must confess, I was often rather subtle.” In a more flattering sense of that term, he still is.