Scientists generate millions of naive human pluripotent stem cells

Buffalo, NY—For decades, the huge disease-curing potential of human stem cells has been hampered by the inability to generate sufficient quantities of mature human cells in vivo.

Now a team of scientists from the University of Buffalo has developed a method that dramatically increases the production of mature human cells in mouse embryos. The production of human cells in vivo is important because cells made in petri dishes often do not behave as they do in the body.

This study was published in Science Advances on May 13.

“This is the basic research that allows us to use mouse embryos to better understand human development,” said the author and professor of UB’s Jacobs Institute for Medical Sciences in Physiology and Biophysics. Said Dr. Jian Feng.

“By further developing our technology, more effective mice for studying diseases that produce larger amounts of certain types of mature human cells and have a significant impact on humans, such as malaria and COVID-19. You will be able to create a model, “says Feng.

Also, because this method produces a large number of mature human cells, it is a material for treating chronic diseases such as diabetes and renal failure by replacing damaged cells in the patient with healthy human cells or tissues. May generate.

Infectious disease application

Feng explained that to study COVID-19, it might be possible to create a much better mouse model of components of the human immune system and human respiratory system.

It may also be possible to generate mice with more mature human red blood cells using the new method. Such mice are very effective in studying malaria, a disease that affects only humans by destroying red blood cells.

“We have to answer a lot of questions before this technology can help, but this is the first time we have generated so many mature human cells in mouse embryos,” Feng said.

Millions of mature human cells in 17 days

Previous efforts to generate human cells in mouse embryos have produced small amounts of immature cells that are difficult to quantify. In contrast, the UB method yielded millions of mature human cells in mouse embryos in 17 days.

In this study, the researchers injected 10-12 naive human stem cells when mouse blastocysts were 3.5 days old. Later, mouse embryos developed millions of mature human cells, including red blood cells, eye cells, and hepatocytes.

“We know that up to 4% of the total cell numbers in mouse embryos are human cells,” Feng said. “This is a low estimate because we cannot quantify the large amount of human red blood cells produced in mouse embryos.”

He said these mature human erythrocytes have no nuclei and therefore cannot be counted by the method scientists use to quantify the total number of cells.

Team skills included overcoming key challenges. Converts human pluripotent stem cells, which can differentiate into all types of cells in the body, into a form compatible with the inner cell mass in mouse blastocysts – 3-day-old mouse embryos. Human stem cells are “priming”, whereas the inner cell mass in mouse blastocysts is naive.

“When primed human cells are placed in mouse blastocysts, they do not develop,” Von said, probably due to a mismatch between the different stages of development of the cells.

“We wanted to see if human-primed cells, like pluripotent stem cells in mouse blastocysts, can return to a naive state,” Feng said. “This is what we did.”

“Our method is to temporarily block mTOR kinase for 3 hours to shock naive human priming cells,” Feng said. “Blocking mTOR kinase triggers a series of events that rewires gene expression and cellular metabolism, rendering primed cells naive.”

When late-stage human-primed stem cells were returned to their initial state, the poorly developed naive state allowed human stem cells to co-generate with the inner cell mass of mouse blastocysts.

“Injected human stem cells develop at a much faster pace in mouse embryos and support the generation of millions of mature human cells in 17 days,” Feng said.

In addition to Feng, UB’s co-authors are Zhixing Hu, Hanqin Li, Houbo Jiang, Yong Ren, and Boyang Zhang in the Department of Physiology and Biophysics, and Xinyang Yu and Michael J. Buck in the Department of Biochemistry. Jacobs School. Other co-authors are Jingxin Qiu and Aimee B. Stablewski from Roswell Park Comprehensive Cancer Center.

Funding for this research was provided by NYSTEM and the Buffalo Blue Sky Initiative.