In the mid-2000s, Mark Kotter, MD, PhD, was running a lab studying oligodendrocytes when he started his training in neurosurgery. As a neurosurgeon, he had access to rare brain samples and was able to harvest human neuronal tissue which is typically challenging to obtain. When he compared human oligodendrocytes to rat oligodendrocytes back in the lab, the cells looked the same. But he noticed that they behaved very differently.
When he realized this, Kotter told GEN, the floor dropped beneath him. He thought, “What am I doing here?” He didn’t know if the work he was doing (in animal models) would be relevant to humans. “I didn’t want to end up as a rat doctor,” he said.
At that time, he jumped into pluripotent stem cell research, but oligodendroctytes were incredibly hard to differentiate; it took 170 days to reprogram them. He was desperately looking for alternatives. Then, in 2010, work by Thomas C. Südhof, MD, professor in the department of molecular & cellular physiology at Stanford Medicine, and professor investigator, Howard Hughes Medical Institute along with Marius Wernig, MD, PhD, professor of pathology and a co-director of the Institute for Stem Cell Biology and Regenerative Medicine at Stanford University not only changed the course of his research forever, it also challenged the definition of cell identity.
New tools needed
Ninety percent of drugs fail because, asserted Kotter, we don’t understand complex diseases. And they are not understood because there is an inability to tease apart disease processes, many of which happen at the interplay of different cell types. “We don’t understand the pathology,” he noted, “and we work mostly in the wrong species.”
“There is not a single mouse on this planet that has Alzheimer’s,” he said.
The ideal starting point for research on human diseases, he added, is a human cell or a tissue that has the target condition. But working with human neurons is incredibly difficult.
Then Südhof and Wernig further defined the molecular determinants of neural cell fate decisions. They worked to generalize this principle and they turned one cell into another cell with no intermediate steps using transcription factors. “It looks like you can jump from any cell to any other cell type,” asserted Kotter. “It just goes direct. You don’t have any of the intermediate steps. So, it’s 10 times faster.”
But this idea shifts a paradigm of what cell identity is. Developmental biology, explained Kotter, defines cell identity as the product of differentiation leaning heavily on the history—specifically the epigenetic history—of cells. But the new paradigm suggests that cell identity is not a history; it is a transcriptomic state that can be de-convoluted to a core set of transcription factors. “What we have found is that we can take these transcriptomic states and recreate them by finding new transcription factors for different cell types.”
Building with Legos
At bit.bio they do this by embedding constructs into genomic safe harbor sites which both protects the cell and also protects the program being inserted from silencing. This is the company’s opti-ox (optimized inducible overexpression) cellular reprogramming technology. A clonal population can be expanded, and when the genetic cassette switched on, the entire culture turns into neurons.
The company previously developed this system for numerous cells, and multiple neurons. With 18 launches to date in 2024, bit.bio’s ioCells portfolio comprises 37 products, including ioWild Type Cells, ioDisease Model Cells, and ioCRISPR-Ready Cells. And now, with the release of commercially available astrocytes (ioAstrocytes), the neuronal tool set is complete. Astrocytes are important support cells in the brain; they are homeostatic, important for synaptic transmission, and modulate the immune response of the brain. They are one of the major homeostatic cells in the brain.
Scientists can assemble all major cell types of the brain (excitatory, inhibitory, motor and sensory neurons, astrocytes, oligodendrocytes, and microglia). Like Lego pieces, they can mix healthy cell types with disease model cells and tease out complex disease processes.
Mixing different cells together can elucidate how they interact. Researchers can now construct their own reductionist model of the brain. Healthy neurons and cells with disease mutations enable experiments that tease out the importance of each of the cells in the pathological process. Relationships between the different cells can be deconvoluted in any disease context and modeled in a human system.
And bit.bio added that there are many different areas where the cells may be useful in the future. “By providing highly consistent cells with essential functional properties of human astrocytes, we’re unlocking novel ways for advancing neuroinflammation research, conducting in-depth neural network studies, and performing screening and toxicity assessments for potential therapeutics,” noted Farah Patell-Socha, PhD, vice president of research products at bit.bio.
