MIT engineers turn skin cells directly into neurons for cell therapy

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"Converting one type of cell to another — for example, a skin cell to a neuron — can be done through a process that requires the skin cell to be induced into a “pluripotent” stem cell, then differentiated into a neuron. Researchers at MIT have now devised a simplified process that bypasses the stem cell stage, converting a skin cell directly into a neuron.

Working with mouse cells, the researchers developed a conversion method that is highly efficient and can produce more than 10 neurons from a single skin cell. If replicated in human cells, this approach could enable the generation of large quantities of motor neurons, which could potentially be used to treat patients with spinal cord injuries or diseases that impair mobility. ..."

From the highlights and abstract (1):

"Highlights

• Proliferation history offers a principal axis to distinguish TF effect on fate

• Levels of individual TFs differentially influence the rate of conversion

• Proliferation history shapes the cell’s response to levels of pioneer TF, Ngn2

• Driving early hyperproliferation increases direct conversion of adult human fibroblasts

Summary

The sparse and stochastic nature of conversion has obscured our understanding of how transcription factors (TFs) drive cells to new identities. To overcome this limit, we develop a tailored, high-efficiency conversion system that increases the direct conversion of fibroblasts to motor neurons 100-fold. By tailoring the cocktail to a minimal set of transcripts, we reduce extrinsic variation, allowing us to examine how proliferation and TFs synergistically drive conversion.

We show that cell state—as set by proliferation history—defines how cells interpret the levels of TFs. Controlling for proliferation history and titrating each TF, we find that conversion correlates with levels of the pioneer TF Ngn2. By isolating cells by both their proliferation history and Ngn2 levels, we demonstrate that levels of Ngn2 expression alone are insufficient to predict conversion rates. Rather, proliferation history and TF levels combine to drive direct conversion. Finally, increasing the proliferation rate of adult human fibroblasts generates morphologically mature induced human motor neurons at high rates."

From the highlights and abstract (2):

"Highlights

• Compact, conversion cassettes are compatible with diverse delivery vectors

• Cocktail and conversion culture conditions influence the cell states of iMNs

• Optimized conversion cocktail supports neurotrophin-free conversion to iMN-like cells

• iMNs display electrical activity and graft in vivo within the central nervous system

Summary

Direct conversion generates patient-specific, disease-relevant cell types, such as neurons, that are rare, limited, or difficult to isolate from common and easily accessible cells, such as skin cells. However, low rates of direct conversion and complex protocols limit scalability and, thus, the potential of cell-fate conversion for biomedical applications.

Here, we optimize the conversion protocol by examining process parameters, including transcript design; delivery via adeno-associated virus (AAV), retrovirus, and lentivirus; cell seeding density; and the impact of media conditions.

Thus, we report a compact, portable conversion process that boosts proliferation and increases direct conversion of mouse fibroblasts to induced motor neurons (iMNs) to achieve high conversion rates of above 1,000%, corresponding to more than ten motor neurons yielded per cell seeded, which we achieve through expansion.

Our optimized, direct conversion process generates functional motor neurons at scales relevant for cell therapies (>107 cells) that graft with the mouse central nervous system. High-efficiency, compact, direct conversion systems will support scaling to patient-specific, neural cell therapies."

MIT engineers turn skin cells directly into neurons for cell therapy | MIT News | Massachusetts Institute of Technology "A new, highly efficient process for performing this conversion could make it easier to develop therapies for spinal cord injuries or diseases like ALS"

1) Proliferation history and transcription factor levels drive direct conversion to motor neurons (no public access)

2) Compact transcription factor cassettes generate functional, engraftable motor neurons by direct conversion (no public access)

Researchers at MIT have devised a simplified process to convert a skin cell directly into a neuron. This image shows converted neurons (green) that have integrated with neurons in the brain’s striatum after implantation.

Graphical abstract (1)

Graphical abstract (2)