For starters, how could researchers turn stem cells into mature cell types? (discovermagazine.com)
Otherwise «you can't grow them very large and you will be hampered in trying to get the organoid to develop more mature cell types and structures.» (scientificamerican.com)
Others have suggested that the apparent transdifferentiation might result from immature cells fusing with mature cell types from other tissues. (sciencemag.org)