In May, the International Society for Stem Cell Research (ISSCR) released new guidelines that relaxed the 14-day rule, taking away the hard barrier. Although only a few labs around the world have perfected the techniques needed to culture human embryos up to day 14, the science is advancing rapidly. The relaxed rule allows lab groups, in countries where it is legal, to apply to the regulators for permission to continue research past 14 days.
As a way of skirting the boundary, researchers have in the past five years developed an array of human embryo models, most of which are formed from mixtures of stem cells. These models mimic multiple, but brief, phases of early development and can be made without using the scarce and ethically fraught human embryos donated by people undergoing in vitro fertilization (IVF) treatment. So far, the 14-day rule doesn’t apply to these embryo models. But, as they get more sophisticated, with the potential to form recognizable structures, or even organs, they enter their own ethical grey area.
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