One more step towards genetically modified humans

In 2018, humanity took perhaps the most radical step forward in all of history. It is not an exaggeration: it was the year that the first genetically modified humans were born, thanks to He Jiankui's experiments. What evolution takes millennia to sculpt, the selection of favorable characteristics for survival, we can now achieve in a few months of work in a laboratory. Few discoveries have had such profound implications for our future.

The headline of this breakthrough is spectacular, but when we read the fine print we realize that, in reality, there are still many nuances to take into account. The technique that He Jiankui used to cut and paste the DNA of three embryos, called CRISPR-Cas9, has represented a revolution in the field of genetic editing because of how it facilitates and accelerates the process, but the limitations it has make it infeasible to apply it to people today. For example, it is known that CRISPR can cut the genome in unexpected places and introduce random changes that can have serious consequences. In experiments on human embryos, it has been seen that this sometimes causes catastrophic alterations of the chromosomes. Furthermore, even when the editing is done in the right place, the changes are not always exactly what had been planned. For this reason, the consensus is that wanting to edit human embryos is, right now, irresponsible, and, as a consequence, experts have proposed a moratorium and most countries have laws that prevent it.

A new technique

Meanwhile, science is advancing. This summer, two articles have been published that validate what could be the successor to CRISPR, a technique called base editing (base editing, in English). Its principles date back to the 90s, and it allows changing the bases that make up DNA one by one, instead of cutting and repairing, as CRISPR does. It has already been used in gene therapy experiments to correct errors in sick people, although the death of a six-year-old girl in 2025 in Shanghai, likely due to complications from the procedure, has for now halted these applications. However, its use in embryo manipulation is becoming popular, as the following two articles demonstrate.

In the first, a study led by Kathy K. Niakan, from the University of Cambridge, published in the journal Nature, researchers have used base editing to delete a gene called NANOG in human embryos and follow them for a week. The first observation they make is that the editing is very precise, without cuts outside the target gene. The main conclusion of the research is that NANOG is necessary for the correct development of the embryo, something that until now could not be carried out with the methods available or in studies with mouse embryos.

In the second work, directed by Dieter Egli, from Columbia University, currently only pre-published in a repository, it is demonstrated that human embryos can be edited with this system without producing any of the feared chromosomal alterations that are usually seen with CRISPR, and the embryos develop completely normally, at least during the time they have been followed in the laboratory.

Both studies have used base editing for purely experimental purposes, to advance knowledge of the human development process and without any intention of taking steps towards the manipulation of embryos to be implanted in uteri so that they result in a living being. But it escapes no one that one of the consequences of these works is to contribute significantly to demonstrating that base editing is a reliable improvement on the tools we had until now. They are not yet ready to be used in humans, but every day it gets closer. Where is all this leading us? For the moment, it is revitalizing a debate that, after the uproar of 2018, had been somewhat sidelined.

A public debate is needed

Somewhere in China there are three girls who have a genome altered by the hand of science. We know nothing about them, not what their names are, nor if they are okay, nor if they are aware of being the first of what could end up becoming a new species of humans, because it seems very likely that they will not be the last. Base editing allows us to think that one of the barriers that prevented us from continuing along this path, the uncertainty of the possible side effects of CRISPR, is collapsing.

In the coming years, the technique will be perfected, to the point that, with total certainty, it will offer enough guarantees to be applied in humans. There will still be other obstacles, but, sooner or later, the limitations will be mainly ethical. Then, it will be necessary for us, as humanity, to ask ourselves some uncomfortable questions: will we want to open the door to genetic manipulation of offspring for everyone who can afford it? Will we be able to prevent it from being done once it is proven to be feasible? These are dilemmas that until now seemed typical of science fiction but are becoming issues that must be considered seriously.