During the Second International Summit of Human Gene Editing an unexpected announcement was made. He Jiankui, a Chinese researcher, stated that two girls, Lulu and Nana, had been born after being genetically modified. He used CRISPR cas9, a relatively new technique to destroy the CCR5 receptor, the gateway of HIV. Somehow their resistance to HIV was genetically encoded.

Yuval Harari, historian and visionary, describes that Homo sapiens as we know it, will cease to exist. Artificial intelligence and biotechnology will take the human species to another level. The author speaks of a Homo deus that has become capable of modifying its own nature. We have spent years with the announcement of different experiments that make use of genetic engineering to modify the human being. We have thousands of clinical trials and six approved drugs that use genetic engineering to cure different diseases (cancer, blindness, immunodeficiency, etc.). However, there have been some attempts that go beyond the strictly therapeutic. Elizabeth Parrish, CEO of Bioviva, a company that markets anti-ageing treatments, decided to give herself extra copies of the gene telomerase. This treatment has been proved to extend the life of mice by 13-24%. Josiah Zayner, CEO of The Odin, injected a treatment to activate muscle growth. Although the nature of the treatments is based on sound scientific principles, in neither of these last two cases are many details known of whether the treatments worked.

What was different about Lulu and Nana? Why has this case led to so much debate? These changes have occurred in the germ line. Not only have Lulu and Nana been genetically modified, but their offspring too. The germ line of human beings had never been modified.

Various aspects of this experiment have been criticized. First, the girls had to be born healthy. There is much consensus among the scientific community that experimental therapies should be applied first for very serious illnesses, situations where the potential benefits are far greater than the risks of a new therapy. In fact, the first uses of CRISPR cas9 are for sickle cell anaemia and cases of cancers that are refractory to treatment. These girls have been exposed to a totally unnecessary risk for a potential preventive benefit. We are still characterizing the risks associated with CRISPR cas9 therapies. Secondly, the effect of the genetic changes is not known. Nana only has one of the two homologous chromosomes modified. Therefore, she would not have achieved resistance to HIV. In addition, both in Nana and in Lulu, the specific edition introduced is not exactly the one found in nature and provides resistance to HIV. Thirdly, the situation has also exposed an error in the self-regulation of the scientific community. During the First International Summit on Human Gene Editing a moratorium was established on implanting modified embryos, which He Jiankui has skipped.

In spite of the premeditation and the risk exposed, the girls are very likely to be healthy. This is not such a dramatic case of errors in gene therapy as the one two decades ago in which several people died. However, it is a time of significant reflection.

Will we have people modified by CRISPR in the germ line? Most likely we will. But at the right time. There is a need for sufficient scientific information (we do not yet have this) and transparency. There is a need for a global vision to which the scientific community adheres. There is a need for informed debate that includes the scientific community, the regulatory bodies and society to decide where we want to go as a society.

Where might it end up? Geneticist George Church, of Harvard University, has compiled a list of genetic traits that have an important impact on the organism. The list includes resistance to various infectious diseases, reduced ageing, a lower likelihood of cancer, etc. In fact, this list includes the gene editing of Lulu and Nana. However, it is unlikely that many humans will be modified with these modifications in the coming years. This Homo deus will take a few years to become established. We will far more likely see the application of CRISPR to cure serious diseases in somatic cells (non- germ line).

Opinion article by Marc Güell, head of the Translational Synthetic Biology Research Group at the Department of Experimental and Health Sciences of UPF.