Researchers at Washington University School of Medicine have found a promising extra application of an experimental drug currently undergoing trials for rheumatoid arthritis, finding that they were able to prevent a common, life-threatening side-effect of stem cell transplants.

Studying mice, the researchers found the drug prevented what's known as graft-versus-host disease, a debilitating, sometimes lethal condition that develops when transplanted stem cells attack the body's own organs or tissues.

About half of patients receiving donor stem cells develop graft-versus-host disease, which can linger for months or years after their transplants. In some cases, patients die not from their cancer but from the complication itself. Current treatments are not effective.

In past work, this research team defined the role of molecules called JAK1/2 kinases and their signaling pathways in immune cell activation and graft-vs-host disease.

In the new study, these same researchers evaluated ruxolitinib and baricitinib, particular Janus Kinase (JAK) inhibitor, and found baricitinib to be the superior of the two drugs in reducing and preventing graft-versus-host-disease in mice. 

"Transplanted donor stem cells — and more specifically, the T cells in the donor stem cell product — are particularly good at fighting off leukemia, but these cells can go haywire, unfortunately, and attack the patient's healthy tissues, causing graft-versus-host disease," the study authors explained.

"The typical ways we can reduce the effects of the disease also tend to weaken the T cells' ability to attack the cancer. We're looking for a treatment strategy that stops the disease without shutting down T cells' assault on the cancer."

Surprisingly, baricitinib did more than shut down graft-versus-host disease. It actually boosted the ability of the donor T cells to fight the cancer.

The drug appears to stop graft-versus-host disease by simply keeping the donor T cells circulating in the bloodstream, away from vital organs.

Simultaneously, the drug makes the leukemia cells more vulnerable to immune attack from the donor T cells, which are now mostly confined to the bloodstream, where the cancer is.

The drug also appeared to boost levels of specific immune cells that put the brakes on a runaway immune response that can make graft-versus-host disease worse.

These apparently independent effects are specific to baricitinib and may explain why other JAK inhibitors did not work as well, according to senior author John F. DiPersio, deputy director of Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine.

The researchers emphasized the finding that the drug not only prevented graft-versus-host disease from developing in the mice but reversed established disease, suggesting possible options for patients already affected by it.

"We were surprised to achieve 100% survival of mice with the most severe model of graft-versus-host disease," said first author Jaebok Choi, an assistant professor of medicine. "We are now studying the multi-pronged ways this drug behaves in an effort to develop an even better version for eventual use in clinical trials."