PHILADELPHIA (July 24, 2023) — Researchers at Fox Chase Cancer Center have made a new discovery about the transcription factor ThPOK that may be useful in the treatment of sepsis, other types of pathogen invasion, and ultimately, cancer.
Discovered in 1997 by Dietmar J. Kappes, PhD, director of the Transgenic Mouse Facility and a professor in the Nuclear Dynamics and Cancer research program at Fox Chase, the ThPOK gene plays a key role in the generation of CD4 T-cells, white blood cells that play a critical role in immune function. The groundbreaking discovery laid the foundation for a generation of research into this master-regulator of CD4 T cell development and function.
In a study published in the prestigious journal Nature Immunology, Kappes and a team of researchers report the new finding that ThPOK also limits the production of neutrophils — a type of white blood cell that act as the immune system’s first line of defense — and promotes a pro-inflammatory effect of neutrophils.
This discovery is the result of intensive collaboration between Kappes and Jayati Basu, PhD, of the Lerner Research Institute at the Cleveland Clinic, and Nathan Salomonis, PhD, and H. Leighton “Lee” Grimes, PhD, both of Cincinnati Children’s Hospital Medical Center. Basu and Grimes are former postdoctoral fellows in the Kappes lab at Fox Chase. This discovery was made as a result of several key experiments. First, Kappes and Basu inserted a fluorescent reporter gene into the ThPOK locus so that its expression could be detected using a technique called flow cytometry. This allowed the researchers to identify individual cells that expressed ThPOK and the organs where it was highly expressed, as well as to track the way these ThPOK-expressing cells moved through an organism.
“By using a ThPOK reporter mouse model we were able to show that ThPOK was expressed in different types of leukocytes in the bone marrow where we hadn’t suspected ThPOK was expressed at all,” Kappes said. “In particular ThPOK was detected in all neutrophils, as well as their precursor stages.”
This discovery suggested that ThPOK was necessary for neutrophil development and served as a “brake” to maintain neutrophil equilibrium and that this brake is installed via regulation of cellular process called mRNA splicing.
Next, they used a mouse model called a knockout model where ThPOK was not expressed.
“We found a lot more neutrophils arising in these knockout mice, and the function of the neutrophils was enhanced,” Kappes said. “The consequence was that there was a greater level of neutrophil-mediated response to pathogens.”
Kappes said the immune system has several types of cells that have specialized tools that they deploy in response to whatever infection they are fighting.
“It is a big deal to have the ability to increase the proportion of a particular kind of immune cell,” Kappes said. “Because neutrophils are the first line of defense, they don’t care much for the specifics of what they are attacking and will respond to any kind of infection.”
To further test the role of ThPOK in neutrophil development, Kappes and his co-authors used a mouse model of sepsis and found that the mice in the ThPOK knockout model had a greater ability to control sepsis than normal mice that expressed ThPOK.
“Eliminating ThPOK created more neutrophils with enhanced function to fight sepsis, which is still a major human health issue,” Kappes said.
The immune system is increasingly understood to be a weapon that can be used in conjunction with other treatment regimens that exist for treating cancer. “This particular finding, even though it was found to be useful in fighting sepsis, and by inference, other pathogen invasion, also has relevance for cancer, specifically in leukemia” Kappes said.
Prior and ongoing studies from the Kappes lab indicate that ThPOK can act as both a negative and positive regulator of cancer development, depending on the cellular context. Figuring all this out will occupy the Kappes lab and collaborators for many years to come.
The paper, “ThPOK is a Critical Multifaceted Regulator of Myeloid Lineage Development,” was published in Nature Immunology.