“Limit on Lab-Grown Human Embryos Dropped by Stem-Cell Body: The International Society for Stem Cell Research Relaxed the Famous 14-Day Rule on Culturing Human Embryos in Its Latest Research Guidelines”, 2021-05-26 (; similar):
The international body representing stem-cell scientists has torn up a decades-old limit on the length of time that scientists should grow human embryos in the lab, giving more leeway to researchers who are studying human development and disease.
Previously, the International Society for Stem Cell Research (ISSCR) recommended that scientists culture human embryos for no more than 2 weeks after fertilization. But on 26 May, the society said it was relaxing this famous limit, known as the 14-day rule. Rather than replace or extend the limit, the ISSCR now suggests that studies proposing to grow human embryos beyond the 2-week mark be considered on a case-by-case basis, and be subjected to several phases of review to determine at what point the experiments must be stopped.
The ISSCR made this change and others to its guidelines for biomedical research in response to rapid advances in the field, including the ability to create embryo-like structures from human stem cells. In addition to relaxing the ‘14-day rule’, for instance, the group advises against editing genes in human embryos until the safety of genome editing is better established. “It’s been a major revision”, says Robin Lovell-Badge, a stem-cell biologist at the Francis Crick Institute in London and chair of the ISSCR steering committee that wrote the new guidelines.
…For example, the guidelines now describe terms under which mitochondrial-replacement therapy could be used in medical research. Some metabolic diseases are caused by genetic mutations in the mitochondria, the power generators in cells, which children receive from their mothers. In cases where a mother’s mitochondria carry these mutations, doctors can now swap the nucleus from the mother’s egg cell into a donor cell with healthy mitochondria, whose nucleus has been removed, before in vitro fertilization (IVF). A baby born as a result of this technique would have mitochondrial genes from the donor, but their nuclear DNA would come from the mother and from the father whose sperm is used in IVF.
…The ISSCR guide also weighs in on whether it’s okay to edit the genes of human embryos or egg or sperm cells intended for implantation, and concludes that this science is still too risky…The ISSCR allows that the concept might be valuable in the future, for scientifically defensible reasons, once the science has advanced, and after extensive review. “As a matter of absolute principle, we do not say that heritable editing is absolutely wrong in every possible circumstance”, says Charo.