That's the hope of researchers led by Yuet Kan of the University of California, San Francisco – and they have proved the basic principle, altering the genome of induced pluripotent stem cells (iPSCs) to give them a rare natural mutation that allows some people to resist HIV.

Kan's work relies on "genome editing" – snipping out a particular DNA sequence and replacing it with another. It's much more precise than traditional forms of genetic engineering, in which sequences are added to the genome at random locations.

To alter the stem cells, Kan's team turned to the CRISPR-Cas9 system, a super-efficient method of genome editing based on an ancient bacterial "immune system". In bacteria, the system takes fragments of DNA from invading viruses and splices them into the cell's own DNA, where they act like "wanted" posters, allowing the viruses to be recognised and attacked in future.