He Jiankui, the researcher, took sperm and eggs from the couples, performed in vitro fertilisation with the eggs and sperm, and then edited the genomes of the embryos using CRISPR/Cas9. The editing targeted a gene, CCR5, that codes for a protein that HIV uses to enter cells. He was trying to reproduce the phenotype of a specific mutation in the gene, CCR5-Δ32, that few people naturally have and that possibly confers innate resistance to HIV, as seen in the case of the Berlin Patient.  However, rather than introducing the known CCR5-Δ32 mutation, he introduced a frameshift mutation intended to make the CCR5 protein entirely nonfunctional. According to He, Lulu and Nana carried both functional and mutant copies of CCR5 given mosaicism inherent in the present state of the art in germ-line editing. There are forms of HIV that use a different receptor instead of CCR5; therefore, the work of He did not theoretically protect Lulu and Nana from those forms of HIV. He used a preimplantation genetic diagnosis process on the embryos that were edited, where three to five single cells were removed, and fully sequenced them to identify chimerism and off-target errors. He says that during the pregnancy, cell-free fetal DNA was fully sequenced to check for off-target errors, and an amniocentesis was offered to check for problems with the pregnancy, but the mother declined. Lulu and Nana were born in secrecy in October 2018. They were reported by He to be normal and healthy.