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If we know how to cause embryonic stem cells to differentiate into different tissue types, and we know how embryonic development turns those tissues into organs, why can’t we yet grow entire human organs from stem cells?

What I’m asking here is specifically what gap in our knowledge currently accounts for this technology not yet being in use.

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Whilst the Science Museum of London points out that we seem to be close to developing complete human organs, there appears to be a few more years before we are able to grow the first complete usable organ.

For example, Lytal (2018) points out that so far, scientists haven’t been able to create complete adult human kidneys because they’re too complex, but Andy McMahon’s lab at USC Stem Cell (part of the Keck School of Medicine of USC) is coaxing stem cells to organize themselves into simplified, mini versions.

Lytal has quoted McMahon saying

Regenerative medicine is still a relatively young field, and it’s still early days. When it comes to that final phase of translating stem cell discoveries into clinical therapies for patients, it won’t be individual universities working in isolation. It will be multi-institutional collaborations with our neighbors that will transform medicine over the course of the 21st century.

Lytal also points out that while organ (re)generation research is underway, researchers in Megan McCain’s lab at the USC Viterbi School of Engineering are building human heart tissue and researchers in Henry Sucov's Lab, at USC Stem Cell, are trying to harness the heart’s innate ability to heal. They’re studying a regenerative type of heart muscle cell called a mononuclear diploid cardiomyocyte (MNDCM) — see Patterson et al. (2018).

Newborns have large numbers of these cells, but adults have relatively few, so the adult body has trouble regenerating heart tissue after injury.

When they looked for these cells in mice, they found that some mice had more of these cells than other mice did. They traced that variation to a gene called Tnni3k. Their research suggests that blocking the gene might boost numbers of regenerative cells.

The work in Megan McCain's lab...

poses problems that call for the mindset of an engineer. It turns out that heart muscle cells don’t fully mature in the typical laboratory environment for growing cells—a petri dish filled with warm, nutritious liquid. To develop properly, heart muscle cells need to get some exercise by contracting in the rhythm of a beating heart. To do this, they need structure and resistance, which the lab’s researchers provide in the form of a tiny scaffold called a chip. (Lytal, 2018)

So while we have been able to create certain tissues using stem cells, creating a complete and transplantable human organ is a lot more complex and requires further research, which is well underway with the work in labs of the University of Southern California.

References

Lytal, C. (2018). Growing hope: New organs? Not yet, but stem cell research is getting closer Retrieved from : https://stemcell.keck.usc.edu/new-organs-not-yet-but-stem-cell-research-is-getting-closer/

Patterson, M., Barske, L., Van Handel, B., Rau, C. D., Gan, P., Sharma, A., ... & Shen, H. (2017). Frequency of mononuclear diploid cardiomyocytes underlies natural variation in heart regeneration. Nature genetics, 49(9), 1346–1353 doi: 10.1038/ng.3929 Pubmed Central: PMC5736145

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