Editing Humanity: The CRISPR Revolution and the New Era of Genome Editing

CHAPTER 9 DELIVERANCE OR DISASTER

The conceptual seeds of genetic engineering date back deep into the 20th century, two decades before the double helix and more than a decade before the demonstration that DNA, not protein, was the genetic material.

In 1932, some five hundred scientists traveled to Ithaca, New York, for the Sixth International Congress of Genetics. The registration fee was $10, a room in a hall of residence $1.75. Delegates could go for a day trip to Niagara Falls, attend a group picnic, or listen to an organ recital in Sage Chapel on the Cornell campus. The scientific program was dominated by the rock stars of the era: Thomas Hunt Morgan and his colleagues—Hermann Muller, A. H. Sturtevant, and Curt Stern—from the famous “fly room” at Columbia University. In a lab that smelled of rotten bananas, Morgan’s group anointed the fruit fly as the ideal model organism to establish the “chromosome theory of heredity.” Morgan’s momentous discoveries were accepted as universal truths: His group built the first genetic maps of chromosomes and demonstrated that X-rays cause gene mutations. Morgan won the Nobel Prize the following year. But the answer to the existential question: “What is the gene?” would only emerge twenty-one years later, courtesy of Crick, Watson, and Rosalind Franklin.

Relegated to a Saturday breakout session, Hubert Goodale, the chief geneticist at the Mount Hope Farm in the northwestern corner of Massachusetts, didn’t have the horsepower of a Morgan; instead of a fly room, he had a “mouse house” and a good story about applying genetic principles to animal breeding. Mount Hope was a leading genetics center in the United States: Goodale kept meticulous breeding records of poultry, cattle, pigs, and other animals, producing marked improvements in egg size, milk, and pork production. The farm’s prize bull was named Satisfaction, but not for the reason you might think: an average Mount Hope cow sired by Satisfaction produced three times as much milk as a typical dairy cow.¹ Goodale’s talk, entitled “Genetical Engineering,” was perhaps the first public conceptualization of genetic engineering.²

The year 1932 was also when Aldous Huxley published Brave New World.³ Almost two decades later, genetic engineering made its science fiction debut. In his 1951 novel Dragon’s Island, Jack Williamson wrote:

Man may now become his own maker. He can remove the flaws in his own imperfect species, before the stream of life flows on to leave him stranded on the banks of time with the dinosaurs and trilobites—if he will only accept the new science of genetic engineering.

Written two years before the double helix, Williamson understandably took some pleasure in his foresight—only to learn that the Oxford English Dictionary had unearthed a previous use of the phrase in 1949. “Everybody is famous, if only for fifteen minutes,” he said.⁴

On March 19, 1953, Francis Crick wrote a long letter to his twelve-year-old son, Michael, at boarding school. As sneak peeks go, it was pretty special. “My dear Michael,” Crick wrote, “Jim Watson and I have made the most remarkable discovery. We have solved the structure of deoxyribosenucleic acid (D.N.A.)…” On the next page, Crick sketched the double helix, showing the pairing of the four bases—C with G, A with T. After several more pages of near textbook detail, Crick invited his son to view the model during his half-term break. He signed off, “Lots of love, daddy.”⁵ Showing maturity beyond his years, Michael held onto his father’s letter. It was a wise decision: sixty years later, Crick’s letter fetched a world-record price at auction—$6.3 million. Half the proceeds went to the Salk Institute in San Diego, where Crick spent his final years.^I

One week earlier, Watson had written a similar letter to one of his scientific idols, Caltech virologist Max Delbrück. Watson shared that he and Crick had fashioned a model of DNA with intertwining strands glued by interlocking base pairs running through its core, and would shortly submit a report to Nature. In a rare moment of humility, Watson conceded that (as had happened before) their model might be wrong. Then again, “If by chance, it is right, then I suspect we may be making a slight dent into the manner in which DNA can reproduce itself.”⁶

Crick and Watson’s historic success was made possible by data collected by Rosalind Franklin at King’s College London. Franklin, working with her student Raymond Gosling, was a brilliant experimentalist, but uninterested in using her X-ray photographs of DNA crystals in trivial pursuit of building models. Crick was the mathematical brains in the Cambridge partnership, but as the late Brenda Maddox, Franklin’s biographer, observed, he was unlikely “to have reached the goal without the pushing and prodding of the gauche young man from Chicago.”⁷

In early 1953, Maurice Wilkins showed Watson a pristine, unpublished X-ray image of DNA—photograph 51—taken by Gosling six months earlier. To a trained eye, the trademark “X” pattern visible on “Photograph 51” could only mean that DNA was a helix. Watson pieced the final parts of the puzzle together. Working with cut-out representations of the four constituent bases of DNA, Watson’s pairings—adenine (A) with thymine (T), cytosine (C) with guanine (G)—completed the structure of the molecule of life, two months shy of his twenty-fifth birthday.

A few weeks later, on April 25, 1953, the world—or at least Nature subscribers—got their first glimpse of the double helix. It was a family affair: the eight-hundred-word report was typed up by Watson’s sister Elizabeth, while the double helix was elegantly sketched by Crick’s wife, Odile. The report began with an immortal English understatement:

We wish to suggest a structure for the salt of deoxyribonucleic acid (DNA). This structure has novel features which are of considerable biological interest.⁸

Word traveled slowly in those days. It took the New York Times six weeks before it saw fit to print a front-page story on the double helix. Watson and Crick published a follow-up paper in which they proposed that “the precise sequence of the bases is the code which carries the genetical information.” For the next decade, the smartest minds in life sciences set about deciphering the code and figuring out how it was broken in genetic diseases. Only then could they contemplate how to fix it.

Watson has been justifiably criticized for his sexist portrayal of Franklin (“terrible Rosie”) in The Double Helix, which was published over Crick’s objections in 1968. In subsequent editions and other venues, he has acknowledged the importance of her scientific contributions. But Maddox, Franklin’s biographer, defended Watson. “If it weren’t for Watson, no one would have heard of Rosalind Franklin. He is deservedly in the top rank of writers of the 20th century.”⁹ Franklin died of ovarian cancer in 1958, denying her a thoroughly deserved share of the Nobel Prize. Today her contributions are widely recognized. In the 2015 West End production of the play Photograph 51, Nicole Kidman starred as Franklin.

Six months after Crick and Watson picked up their Nobel Prizes, Salvador Luria declared: “If knowledge is power, the science of genetics has placed in the hands of man an impressive amount of power in the last few decades.”¹⁰ But a new question loomed large: “Does the new knowledge of the genetic material and of its function open the door for a more direct attack on human heredity?”¹¹ Drawing an analogy with the physicists who split the atom and developed the atomic bomb, Luria was certain that geneticists would soon gain the power to contemplate “a direct attack on the human germ plasm.”

A big name in bacterial circles, Rollin Hotchkiss was one of the first scientists to articulate concerns about the dangers of human genetic engineering. After excelling in high school in the 1920s and completing his PhD at Yale in organic chemistry in just three years, Hotchkiss turned to microbiology, discovering antibiotics and the first chemical modification to DNA.¹² Hotchkiss thought it was natural to feel “instinctive revulsion” at the thought of meddling with human nature but it would surely be done. “The pathway will, like that leading to all of man’s enterprise and mischief, be built from a combination of altruism, private profit, and ignorance,” he said.¹³ Humans have long sought to improve on nature—seeking shelter, foraging for food, and defeating disease, whether modifying the diet of a baby diagnosed with phenylketonuria or administering chemotherapy to interfere with DNA replication in a cancer patient. Human genetic manipulation was on the horizon, Hotchkiss warned, and “we are going to yield when the opportunity presents itself.” It was not too soon “to diminish the dangers to which this course will expose us.”

Robert Sinsheimer, who passed away in 2018, is known as one of the architects of the Human Genome Project. In May 1985, while chancellor of the University of California Santa Cruz, he hosted a workshop to discuss a “big science” initiative to sequence the human genome (and put Santa Cruz on the map).^II Sinsheimer’s role in catalyzing the inception of the genome project crowned more than four decades in molecular biology. In 1953, he embarked on a six-month visit to Delbrück’s lab to learn about phages. (Ironically, the greatest minds of the era were studying phages and bacteria, but oblivious to CRISPR.)

Sinsheimer studied a phage named ΦX174, the smallest phage known. His work helped lay the foundation for the sequencing of the very first complete genome, by Fred Sanger in Cambridge in 1977. Along the way, Sinsheimer demonstrated that the viral genome was merely a single strand of DNA, a stunning result that overturned six years of double helix dogma, like “finding a unicorn in the ruminant section of the zoo,” Sinsheimer said. He followed that with another heretical result: the ΦX174 DNA wasn’t even a linear molecule, but a ring. The enzyme that closed the loop—DNA ligase—proved to be the missing link in the ability to replicate the virus in a test tube. In 1967, Sinsheimer collaborated with Nobel laureate Arthur Kornberg to successfully replicate ΦX174 that could infect bacteria. The result was even picked up by President Lyndon Johnson, who said on television, “Some geniuses at Stanford University have created life in the test tube!”

By this time, Sinsheimer was thinking hard about far-reaching implications of genetic advancement. The year before, he delivered a talk on the future of molecular biology at an event to celebrate the 75th anniversary of Caltech. He spent months preparing his lecture, mulling over the ramifications of humanity acquiring the keys to its own inheritance. On October 26, 1966, sporting a bow tie, Sinsheimer walked to the podium to warm applause, and addressed his “fellow prophets” in the audience. The title of his lecture was “The End of the Beginning.”

He began by recalling his travels through the breathtaking canyons and landscapes of Arizona and Utah, where the sands of time formed layers of rock visible in cross section along the river gorges, revealing a billion years of geologic history. “On that immense scale,” Sinsheimer said, “a foot represents the passage of perhaps 100,000 years. All of man’s recorded history took place as an inch was deposited. All of organized science a millimeter. All we know of genetics, a few tens of microns. If we remember that timescale, then what vision can seem too long?”¹⁴ Then he said this:

The dramatic advances of the past few decades have led to the discovery of DNA and to the decipherment of the universal hereditary code, the age-old language of the living cell. And with this understanding will come control of processes that have known only the mindless discipline of natural selection for two billion years. And now the impact of science will strike straight home, for the biological world includes us. We will surely come to the time when man will have the power to alter—specifically and consciously—his very genes. This will be a new event in the universe. The prospect is to me awesome in its potential for deliverance or equally, for disaster.

Sinsheimer’s mesmerizing words envisioning a future of human genetic modification predated the recombinant DNA revolution and genetic engineering, let alone the invention of DNA sequencing and the Human Genome Project. How might we change our genes, he asked rhetorically? Might we “alter the uneasy balance of our emotions. Could we be less warlike, more self-confident, more serene?” After two billion years, he said, “this is, in a sense, the end of the beginning.”

Sinsheimer followed his speech with a powerful essay in American Scientist on “The Prospect of Designed Genetic Change.”¹⁵ “There is much talk about the possibility of human genetic modification—of designed genetic change,” he wrote. “A new eugenics” was potentially “one of the most important concepts to arise in the history of mankind. I can think of none with greater long-range implications for the future of our species.” Star Trek had just debuted on television in 1966, but no fancy hyperdrives or teleports were needed to conjure up visions of mankind boldly going where no one had gone before.

One hopeful idea was to treat diabetes by reanimating the insulin gene that, except for a few specialized cells in the pancreas, lies dormant in the human body. Viruses could be used to deliver the insulin gene to the necessary cells once scientists had sequenced and resynthesized it. Sinsheimer wasn’t advocating for a utopian super race but for equality of opportunity. He wasn’t pushing for Galtonian state-sponsored coercion but rather a voluntary improvement of the cognitively disadvantaged, such as 50 million Americans with an IQ of 90 or less. Should we “continue to accept the innumerable, individual tragedies inherent in the outcome of this mindless, age-old throw of dice,” or instead “shoulder the responsibility for intelligent genetic intervention”? The stakes, Sinsheimer argued, were little short of astronomical:

Copernicus and Darwin demoted man from his bright glory at the focal point of the universe to be merely the current head of the animal line on an insignificant planet. In the mirror of our newer knowledge, we can begin to see that in truth we are far more than another ephemeral form in the chain of evolution. Rather we are an historic innovation. We can be the agent of transition to a wholly new path of evolution. This is a cosmic event.

Sinsheimer’s vision of “genetic change, specifically of mankind,” was fueled by the successful elucidation of the universal genetic code. The beauty of the double helix had immediately suggested how DNA could replicate itself, each strand unzipped becoming the template for a new daughter strand. Kornberg won the Nobel Prize for identifying the key enzyme, DNA polymerase. But with the genetic material now reduced to atomic detail, the big question in biology became: what is the code that governs how the instructions inscribed in DNA are communicated and translated into proteins?

During the course of the 1950s, the work of Crick, Watson, Sydney Brenner, and others established the central dogma. A messenger RNA facsimile ferries instructions from the cell’s data center (the nucleus) to the protein-manufacturing sites in the heartland (the cytoplasm). But what about the code itself? Proteins are made up of twenty different amino acids, whereas the DNA alphabet only has four letters. A two-base code would only yield a maximum of sixteen building blocks (4x4), whereas a triplet code (4x4x4) could in principle give rise to as many as sixty-four building blocks.

In 1959, Marshall Nirenberg, a biochemist at the NIH, developed a cell-free system to synthesize proteins in a test tube by mixing the raw ingredients—DNA, RNA, enzymes, and radioactively labeled amino acids. His colleague Bruce Ames felt the project was “suicidal.” With Nirenberg traveling in California, his German student, Heinrich Matthaei, found himself alone in the lab after midnight on a Saturday morning (May 27, 1961). Thirty-six hours earlier, President John Kennedy, inspired by Alan Shepard’s achievement in becoming the first American in space, asked Congress to commit to “landing a man on the moon and returning him safely to the earth.”

Here in the late-night tranquility of an empty lab, Matthaei was poised to crack the first clue in the genetic code that governs life on earth, propelling the field of genetic engineering into orbit. He pipetted a synthetic strand of RNA made up entirely of just one base (uracil, U) into his cell-free solution. The resulting peptide was composed entirely of one amino acid—phenylalanine. Clearly some combination of U’s provided the necessary code for phenylalanine. The first square in the 64-square genetic code bingo card—UUU—had been filled. Soon they had a second letter: CCC corresponded to proline.

That summer, Nirenberg delivered a lecture at a major conference in Moscow. His initial talk was attended by only a smattering of scientists, but Crick arranged for Nirenberg to give an encore performance in a plenary session. Nirenberg was heartily congratulated by Crick and other scientific legends afterwards and felt a bit like a rock star. An American literature student, who had spent the day touring art museums, was electrified hearing about Nirenberg’s results from his roommate. That student, one Harold Varmus, would later win the Nobel Prize for cancer research and become the director of the NIH.

The following year, Crick and Watson received their Nobel Prizes. By this time, Crick had proven that the genetic code was indeed made up of 64 triplets. “We are coming to the end of an era in molecular biology,” Crick said in his Nobel address. “If the DNA structure was the end of the beginning, the discovery of Nirenberg and Matthaei is the beginning of the end.”

In August 1967, Nirenberg wrote a guest editorial for Science magazine, entitled “Will society be prepared?” The implications of the revolution in biochemical genetics, as he called it, and the prospect of “genetic surgery” were weighing heavily on him. Nirenberg believed that scientists were going to be able to reprogram cells—initially microbes, but eventually humans. And that made him nervous. He wrote:

[M]an may be able to program his own cells with synthetic information long before he will be able to assess adequately the long-term consequences of such alterations… and long before he can resolve the ethical and moral problems which will be raised. When man becomes capable of instructing his own cells, he must refrain from doing so until he has sufficient wisdom to use this knowledge for the benefit of mankind. I state this problem well in advance of the need to resolve it, because decisions concerning the application of this knowledge must ultimately be made by society, and only an informed society can make such decisions wisely.¹⁶

The following year, it was Nirenberg’s turn to win an all-expenses paid trip to Sweden. His students, one of whom was an ambitious physician named William French Anderson, hung a banner in his lab that read “UUU are great Marshall.” Back home in Germany, however, Matthaei could only reflect on the Stockholm snub. Unlike Rosalind Franklin, he was still alive and eligible when the call came. But Nirenberg shared the stage with two others, and in Nobel math, four into three doesn’t go.

By this time, some scientists were seeing a different side of genetic engineering—the concept of gene therapy. One of the first to do so was yet another Nobel laureate, Joshua Lederberg. The son of a rabbi, Lederberg graduated from Stuyvesant High School in New York at the age of fifteen. He was barely twice that age when, in 1958, he won the Nobel Prize, for discovering the transmission of genetic material between bacteria, including the process of transduction, involving phages. Sharing the prize that year were Lederberg’s former supervisor, Edward Tatum, and George Beadle. (There was no mention of Lederberg’s wife, Esther, who performed many of the crucial experiments and coauthored papers with her husband.) Lederberg went on to become the president of the Rockefeller University and a NASA consultant who coined the term “exobiology.” Some believe he was the model for the hero in Michael Crichton’s debut novel, The Andromeda Strain.

At a symposium on “The Future of Man” in London in 1962, Lederberg expressed sympathy with the “noble aims” of eugenics while noting it had been “perverted to justify unthinkable inhumanity.” Advances in biology ultimately “could diagnose, then specify, the actual DNA composition of ideal man.” But Lederberg proposed a new term, “euphenics,” meaning the developmental engineering of organs as opposed to genetic engineering of the germline.¹⁷

In 1966, Tatum predicted that viruses could be used in “genetic therapy” via the introduction of new genes into defective cells of particular organs. He went on to describe what we now call ex vivo gene therapy. “The first successful genetic engineering will be done with the patient’s own cells,” he declared. The desired new gene would be taken from a healthy donor and transferred into the patient’s cells. “The rare cell with the desired change will then be selected, grown into a mass culture, and re-implanted in the patient’s liver.”¹⁸

In a commentary for the Washington Post in January 1968, Lederberg launched a trial balloon for his idea of gene therapy—using viruses for vaccination. Drawing inspiration from Kornberg’s demonstration of DNA replication in a test tube, Lederberg suggested that by screening enough natural viruses, it might be possible to isolate a virus that had naturally captured a medically important human gene, such as insulin or the gene encoding the missing enzyme in phenylketonuria.¹⁹ He even considered “extracting DNA molecules that code, say, for insulin and chemically grafting these to the DNA of an existing tempered virus,” forming the basis for virogenic therapy in man. Lederberg thought his idea of somatic gene therapy was more practical and palatable than genetic engineering, or “direct tackling of the germ line.”²⁰

In 1968, Nirenberg’s medical student French Anderson, decided to add his name to the chorus of those advocating for gene therapy. “In order to insert a correct gene into cells containing a mutation, it will first be necessary to isolate the desired gene from a normal chromosome. Then this gene will probably have to be duplicated to provide many copies. And, finally, it will be necessary to incorporate the correct copy into the genome of the defective cell.”²¹ Anderson’s ideas were too fanciful for the New England Journal of Medicine, which rejected the manuscript after some lively internal debate. One editorial member judged Anderson’s proposal to be “a worthwhile adventure in pure speculation.”

I. Perhaps inspired by Crick’s auction windfall, Watson auctioned off his Nobel medal. It was bought by Russian oligarch (and part-owner of Arsenal) Alisher Usmanov. After meeting Watson in Moscow and learning that he wanted to use the proceeds for charity, Usmanov agreed to loan the medal back to Watson. It was returned to Cold Spring Harbor in an armored truck.

II. Sinsheimer wanted to leave his mark on UCSC but he was also hoping to save a $36 million pledge from the Hoffman Foundation for a space telescope that had been fully funded by the Keck Foundation. Sinsheimer didn’t get his genome institute but UCSC would go on to play a major role in the completion of the first draft of the human genome.