Scientists in China have reported genetically modifying human embryos in what is only the second published experiment of its kind. Last year, a different team of Chinese researchers edited human embryos in an attempt to remove genes responsible for a dangerous blood disorder. In this new research, scientists from Guangzhou Medical University tried to add a mutation to embryos instead, attempting to make them HIV-resistant. In both cases, the experiments were only partially successful, and were carried out using non-viable human embryos that were incapable of growing into adults.