This animation depicts the CRISPR-Cas9 method for genome editing – a powerful new technology with many applications in biomedical research, including the potential to treat human genetic disease or provide cosmetic enhancements. (Feng Zhang/McGovern Institute for Brain Research/MIT)

[This story has been revised and updated.]

Genetic engineering isn't new, but CRISPR is, and it's a stunningly fast, flexible, cheap way to manipulate the code of life. It's so revolutionary — and unnerving — that hundreds of scientists, policymakers and the president's science adviser gathered Tuesday in Washington for the start of a three-day summit on the implications of this astonishing technology.

Developed only in the past four years, the CRISPR technique exploits a natural process used by ordinary bacteria to defend against invasive viruses. It enables rank-and-file scientists — just about anyone with a modern laboratory and the right skills — to alter specific genes within plants and animals and make those changes heritable. This kind of gene editing could potentially be used in gene therapies targeting a variety of devastating, heritable diseases.

But many researchers argue that it is too soon, and potentially too dangerous, to tinker with the human genome in a way that is passed down to future generations. One objection is simply pragmatic: Biological systems are extremely complex, and changing human genes could have unintended and undesirable consequences. And many bioethicists are not comfortable with the prospect that gene editing could be used for purely cosmetic enhancements, or in an attempt to give certain people physical and intellectual advantages.

“The overriding question is when, if ever, we will want to use gene editing to change human inheritance," summit chair David Baltimore of Caltech said in his introductory remarks.

The summit kicked off Tuesday morning at the headquarters of the National Academy of Sciences, which is one of the sponsors, along with the National Academy of Medicine, the Royal Society (United Kingdom), and the Chinese Academy of Sciences. The Chinese scientists have been aggressive in using CRISPR, and one team made news this year when it reported results from experiments on nonviable human embryos.

The first set of speakers put the summit in historical context. An Egyptian historian, Ismail Serageldin of the Library of Alexandria, offered a broad view of human engagement with the natural world: “We have been playing god ever since we domesticated plants and animals."

Daniel Kevles, an emeritus historian at Yale, offered a tutorial on the eugenics movement in the early 20th century, noting that although it reached its genocidal zenith in Nazi Germany, it also had intellectual support in the United States on both ends of the political spectrum. He said that today, the driving force for human genetic modification will be consumer demand, with the biotech industry serving as "a new player in this game."

Alta Charo, a professor of law and bioethics at the University of Wisconsin at Madison, reviewed the different approaches that countries have taken in trying to regulate gene therapy. She favored a precautionary approach that she said would not suppress innovation, arguing that responsible oversight would allow researchers to take more chances. "We have the chance to back up at the end, and change course," she said.

The reason CRISPR is so controversial is that it works well on mammalian"germline" cells, such as sperm, eggs and embryonic cells, and the genetic editing can therefore result in heritable traits. Baltimore said he hopes the final session Thursday will produce recommendations for a path forward.

The gathering has an obvious analog to the famous Asilomar conference of 1975. That gathering on the Monterey Peninsula was called after scientists realized they could splice DNA from one organism into another. Their primary purpose was to ensure that such work was safe, both for the researchers and the natural world, recalled Baltimore, who was among the participants. The Asilomar conference produced a set of safety protocols that allowed the research to continue.

Now comes CRISPR. The technique borrows a move from bacteria. In a bacterium's DNA are segments of genetic information that bear the likeness of viral pathogens, kind of like the FBI's Most Wanted bulletins at the post office. The bacterium has an enzyme, called Cas9, that can read that likeness, scout the environment for anything looking the same, and then, when finding a likely suspect, snip lengthwise the entwined double-helix DNA strands of the invader.

The CRISPR technique uses the Cas9 enzyme as a gene-snipper. If properly targeted, it can precisely edit genes. Getting to a high level of precision has been tricky to date, but researchers have made great strides in just the few years since the idea of using the enzyme for gene editing emerged from laboratories in Massachusetts and California. (Who, exactly, discovered the CRISPR technique and deserves the patents for it is a matter of intense legal wrangling.)

Tuesday morning, even as the scientists gathered at the National Academy, news broke from the journal Science that researchers at the Broad Institute, Harvard University and M.I.T. have come up with a new way to use CRISPR that reduces the potential for off-target gene-snipping. This promises to enhance the efficiency of the gene-editing tool. Among the authors of the new paper is one of the pioneers of the CRISPR technique, Feng Zhang — who is here for the summit.

“It’s the tip of the iceberg," Zhang said during a panel discussion on the latest scientific breakthroughs. "These are all systems that came from nature. They were discovered by basic biology."

He pointed out that living things have been evolving for billions of years, and that they use a great number of enzymes that potentially can be harnessed by human scientists to edit genes.

"If we look into natural diversity, there are many more systems that will likely prove to be even more powerful," Zhang said.  "We may be able to take the human editing technology to an even higher level.”

In a meeting with a strikingly large media contingent, Baltimore said he thinks the simplicity of CRISPR has been somewhat over-hyped.

"It's not something you can do in a garage," he said.

And Jennifer Doudna, a professor of molecular and cell biology at the University of California at Berkeley and one of the pioneers of the CRISPR technology, told reporters that it will be many years before this technique results in treatments for human diseases. As for human enhancement, that's also a long way off, she said.

"We don't understand enough yet about the human genome, and how genes interact, and which genes give rise to certain traits to edit for human enhancement today," she said.

George Church, a Harvard Medical School geneticist who published one of the early papers on the use of CRISPR on mammalian cells, pointed out that people in his field have been doing genetic modification for decades, and said there are already 2,000 gene therapy trials underway, none of which use CRISPR. What's really different with this new technique, he said, is the cost.

“It's about 1,000 times cheaper for an ordinary academic to do," Church said. "It could be a game-changer.”

When a reporter asked how long it would be before humans have wings, Church answered without missing a beat:

“We already have 747s. Way better than wings.”

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