From an ethical perspective [nature.com], there is little reason to consider human stem cell–derived tissue constructs as more problematic than human tissue explants—brain slices, for instance—maintained in vitro. But the situation is somewhat different for provocative new studies exploring the ability of pluripotent stem cells to organize into structures that have features of the early embryo, however poor the resemblance at present.
Two papers published in the past year—one focused on the mouse and the other on humans—report that embryonic stem cells differentiated under certain conditions can give rise to structures in which the three embryonic germ layers are reproducibly patterned (van den Brink et al., 2014; Warmflash et al., 2014). Furthermore, in the study on the human system, the biological pathways involved are proposed to be similar to those functioning in vivo. Though more characterization is needed, patterned human cell colonies with embryo-like germ layers may therefore be potential models for research on early human development; such work is otherwise difficult or entirely unfeasible to carry out and could be hugely informative about human developmental disorders. Research both to understand patterned embryo-like structures and to improve them as models for human biology should therefore continue.
But should we be concerned from an ethical or regulatory perspective about growing embryo-like structures from pluripotent stem cells in a dish? Could such structures be seen, now or in the future, as violating current regulations on human embryo culture? Conversely, should such regulations be revisited when considering structures that are derived not from the union of gametes but rather from cells in a dish?