Myocarditis in Cancer Patients Is Driven by Specific Immune Cells

In a new study, researchers from UC San Francisco and Vanderbilt University Medical Center have identified specific immune cells that cause a potentially lethal heart inflammation -called myocarditis- in a small fraction of patients treated with powerful cancer immunotherapy drugs.

Myocarditis is inflammation of the heart muscle. It can cause chest pain, shortness of breath, and rapid or irregular heart rhythms. Myocarditis can weaken the heart and its electrical system. As a result, the heart’s ability to pump blood declines. In severe cases, myocarditis causes clots and may lead to stroke, heart attack, heart failure and even death.

The form of myocarditis the researchers studied is a rare but deadly side effect of cancer immunotherapy drugs called immune checkpoint inhibitors (ICIs). 

ICI is a type of therapy method that can improve the anti-tumor immune response by regulating the activity of T cells. ICI treatment has proven lifesaving for many cancer patients and fewer than one percent of patients who receive ICI develop myocarditis.

However, according to Javid Moslehi, MD, chief of Cardio-Oncology and Immunology for the UCSF Heart and Vascular Center, nearly half of patients who do experience ICI-caused myocarditis die as a result. 

Using genetically altered mice to mimic human ICI-caused myocarditis in the new study, the researchers found an excess of immune system cells called CD8 T lymphocytes in the inflamed heart tissue of mice with myocarditis. 

“We earlier observed many T cells in patients who had died, but in the mice we performed several key experiments to show that the T lymphocytes really are drivers of the disease process, and not merely innocent bystanders,” Moslehi said. “There are therapeutic implications to this study.” 

The results of the study led the researchers to conclude that activation of CD8 T cells is necessary to trigger myocarditis in ICI-treated cancer patients and therefore immunosuppressive therapies that affect CD8 T cells might play a beneficial role.

Their new findings already have led them to begin investigating better ways to prevent and treat myocarditis. The research team already has reported a case study in which they used Abatacept, a rheumatoid arthritis drug that suppresses the activation of CD8 T cells, to successfully treat myocarditis in a cancer patient. 

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