Gene Variants Linked to Leukemia Drive Autoimmunity

An Australian biomedical research group reports new insights into why leukemia patients are also more likely to develop autoimmune diseases such as rheumatoid arthritis or aplastic anemia, raising hopes for treatments that target these cells.

Cancers can grow when tumor cells are not identified or destroyed by the immune system. Autoimmune diseases occur when the immune system attacks the body’s own cells, mistaking them for harmful or foreign cells. Previous work had shown found that killer T cells, which are responsible for destroying harmful cells and pathogens, play a role in the link. The new work out of Garvan Institute of Medical Research narrowed the source down to gene variations associated with leukemia that also affect a protein that controls the growth of killer T cells, turning them rogue and leading to autoimmune diseases. 

“We showed that these rogue killer T cells are driving the autoimmunity. They’re probably one of the cell types most directly contributing to autoimmune disease,” says Dr. Etienne Masle-Farquhar, a postdoctoral researcher in the Immunogenomics and Genomic Medicine Labs at Garvan. “Our research also narrows down a few pathways that might be helpful in targeting these cells for future treatments.”

Masle-Farquhar notes that it was known that people with various autoimmune diseases acquire these rogue killer T cells over time, but also that inflammation can cause immune cells to proliferate and develop mutations. “We set out to discover whether the rogue T cells were causing these autoimmune conditions, or simply associated with them,” he adds.

The Garvan researchers used new high-resolution screening methods to look at blood from children with rare inherited autoimmune diseases. They then applied CRISPR/Cas9 gene editing in mouse models to find out what happens when STAT3—a protein found throughout the body that is critical for various cell functions, including controlling the immune system’s B cells and T cells—is genetically altered.

They found that if these proteins are altered, they can cause rogue killer T cells to grow unchecked, resulting in enlarged cells that bypass immune checkpoints to attack the body’s own cells. In addition, even just 1­–2% of a person’s T cells going rogue could cause autoimmune disease.

“It’s never been clear what the connection between leukemia and autoimmune disease is—whether the altered STAT3 protein is driving disease, or whether leukemic cells are dividing and acquiring this mutation just as a by-product. It’s a real chicken-and-egg question, which Dr. Masle-Farquhar's work has been able to solve,” says Professor Chris Goodnow, Head of the Immunogenomics Lab and Chair of The Bill and Patricia Ritchie Foundation at Garvan. “This gives some really good cracks in the coalface of where we might do better in terms of stopping these diseases, which are sometimes life threatening,” he says.

Future applications could include better targeting of medication, like already TGA-approved JAK inhibitors, based on the presence of these mutations. “We can now go and look for T cells with STAT3 variations. That’s a big step forward in defining who’s the bad guy,” Goodnow adds.

The study also identified two specific receptor systems that are linked to stress. “Part of what’s driving these rogue cells to expand as killer T cells is the stress-sensing pathways. There is a lot of correlation between stress, damage and ageing. Now we have tangible evidence of how that’s connected to autoimmunity,” Goodnow says.

The team’s research may help develop screening technologies that clinicians could use to sequence the complete genome of every cell in a blood sample, to identify which cells might turn rogue and cause disease. Further study is needed to determine whether rogue killer T cells are involved in all autoimmune diseases, and what proportion of people with rheumatoid arthritis and other autoimmune conditions have rogue cells and STAT3 variations.

The findings were published in the journal Immunity.