According to a study published in the journal Nature, researchers from UC San Francisco and Vanderbilt University Medical Center identified particular immune cells that cause lethal cardiac damage in a small subsection of cancer immunotherapy patients.

In the study, the researchers studied immune checkpoint inhibitors (ICIs), a form of myocarditis established as an infrequent but deadly side effect of cancer immunotherapy drugs. ICIs target proteins that serve as gatekeepers for immune system responses, holding unwanted inflammation in check. But blocking these checkpoint proteins with ICIs releases the brakes on immune responses, therefore helping the immune system to attack established tumors effectively.

The findings of the study showed that immune system cells called CD8 T lymphocytes were predominately present in the inflamed heart tissue of the study model afflicted with myocarditis. They also discovered that the CD8 T cells were selectively activated. These cells proliferated in a clone-like fashion in myocarditis and targeted a key protein involved in muscle contraction in the heart, called alpha-myosin heavy chain (alpha-MHC). 

(Source: https://theprint.in/health/specific-immune-cells-cause-myocarditis-in-cancer-patients-study/1223143/ )