The research team has optimized the process of transforming stem cells into insulin-producing beta cells in the laboratory using biological and physical separation methods. The results can be used for more efficient transplantation of beta cells in patients with type 1 diabetes.
Researchers at Harvard University used single-cell sequencing to identify a protein produced exclusively by beta cells created in the laboratory from stem cells. This made it possible to increase the amount of obtained beta-cells from 30 to 80%. The results of the work were published in the journal Nature.
In 2014, the Douglas Melton’s laboratory showed for the first time that stem cells can be turned into functional beta cells, creating a potential source of insulin for diabetics. Then, at the initial stage of the study, beta cells made up 30% of the final cell mixture.
“To improve from 30 percent, we needed to really understand the other 70 percent of the resulting cells”, – said Adrian Veres, a graduate student in the Melton lab and lead author of the current study. “Until recently, we couldn’t take a sample of our cells and ask what cell types were in there. Now, with the revolution in single-cell sequencing, we can go from nothing to the full list.”
Two-step increase in beta cells.
“We applied single-cell sequencing and molecular biology to describe the kinds of cells that we were able to make from stem cells. The beginning of manipulation is to always know what you’re working with”, – said Melton, co-director of the Harvard Stem Cell Institute.
All cells contain the same set of genes, but cell types differ depending on which genes are active (expressed). The researchers used single-cell sequencing to identify a complete map of genes that are expressed in tens of thousands of individual cells. They then grouped the cells based on their expression patterns.
As expected, in some cells, gene-expression models were similar to hormone-producing cells in the human pancreas: alpha cells producing glucagon and beta cells producing insulin. In addition, unexpectedly, researchers have discovered a new type of cell that produces the neurotransmitter serotonin.
The team also found a protein that is expressed only in beta cells. This meant that scientists could use it as a biological “hook” to extract beta cells from the mixture.
In collaboration with scientists from Semma Therapeutics, the Harvard team developed a second method of enriching the cell population with beta cells: physically separating all the cells in the mixture, and then allowing them to group themselves again.
This clustering technique has increased the number of beta cells. It was based on the hypothesis that cells that produce hormones are more attracted to each other than to cells that do not produce hormones.
The simultaneous use of both approaches increased the differentiation of stem cells into beta cells in the population from 30 to 80 percent.
“As we work toward putting stem cell-derived beta cells into patients, a purer mixture means that we can use a smaller, less invasive device to deliver the same amount of functional cells”, – said Felicia Pagliuca, Vice President of Cell Biology Research and Development at Semma Therapeutics.
The ability to control the percentage of beta cells in a mixture is the key discovery of this study. Now scientists can focus on what will be the optimal mixture of different types of cells.
“The big question for us right now is whether 80 percent beta cells is what we want”, – said Veres. “Maybe you need more of the other cell types to help regulate the beta cells, so that they function correctly. We’re going to find out how the cell types interact with each other.”