New technique to study how myeloids become white blood cells

Their findings appear in the journal Blood.

Myeloids are blood stem cells from bone marrow or the spinal cord that are turned into common types of white blood cells like neutrophils and macrophages through the process of myeloid differentiation. Deficiencies in this differentiation process cause leukemia, or cancer of the white blood cells. Researchers in the field had previously studied myeloid differentiation using two types of cell systems. In one method of study, scientists performed experiments using primary cells, or those cells taken directly from animals. Scientists have also utilized leukemia tumor cells in this research by returning them to their previous myeloid stem cell-like states. However, primary cells are hard to grow and manipulate genetically, and tumor cells still contain the genetic mutations that caused these cells to divide uncontrollably in the first place.

The drawbacks of these systems prompted Associate Professor of Cell and Developmental Biology and corresponding author Fei Wang to develop a different system to better understand the mechanisms of myeloid differentiation. Wang and his team began by turning mouse embryonic stem cells into myeloid progenitor cells. They then added a protein called Hoxb8 to these cells that had been shown previously to immortalize myeloid progenitor cells so that they do not die and grow indefinitely.

"This really simplified the whole system, so, number one, we didn't have to deal with animals or human bodies, and, number two, we immortalized these cells so that they can be easily handled in culture and maintain normal myeloid progenitor cell genetic information," Wang said.

The researchers wanted to prove that their model is effective in determining the molecular mechanisms important to myeloid differentiation. Enzymes called protein kinases are known to mediate processes like cell development, immune response, and cell differentiation. They screened a variety of protein kinase inhibitors to find potential key regulators of myeloid differentiation. A protein kinase inhibitor of a molecule called mTor, a master regulator of cell behavior, was found to interfere with myeloid differentiation, signifying that mTor is a key regulator of this process. A variety of experiments were performed both inside and outside the mouse body with mTor to further prove that this molecule is necessary for myeloid differentiation.

"The function of this molecule had not been defined prior to this study in the context of myeloid differentiation," Wang said, "This is the first evidence showing that this molecule plays a significant role in myeloid differentiation." This finding serves as a proof of principle that the new system provides a powerful tool for future studies of normal and abnormal myeloid differentiation. "Using this system, we can introduce genetic manipulations that tell us something very important about how normal myeloid differentiation works, and what kind of molecular events in this process can go wrong, leading to diseases like leukemia," Wang said.

"People can use this as a platform for large-scale screening analysis for drugs that potentially can promote myeloid differentiation and can slow down or stop myeloid disease processes."