TIGIT upholds peripheral tolerance in ICI-myocarditis

Immune checkpoint inhibitors (ICIs) have transformed cancer immunotherapy. ICIs optimize T cell activation and recognition to kill tumor cells. However, ICI treatments may also activate self- reactive immune cells. Cancer patients may then experience immune-related adverse events (irAEs), which can target the heart. Cardiac irAEs, like ICI-myocarditis, have low incidence but the highest mortality rate of all irAEs. Considering that ICI-treatments are suitable for 40% of cancer patients, ICI-myocarditis presents a significant public health risk. In our preliminary studies, we found that 1) PD-1 blockade caused myocarditis in 20% of mice, 2) PD-1 KO mice with myocarditis show high expression of T-cell immunoreceptor with Ig & ITIM domains (TIGIT) on T cells, 3) Other types of myocarditis like experimental autoimmune myocarditis (EAM) and Coxsackievirus B3 (CVB3) induced myocarditis also had high TIGIT+ T cells, 4) Regulatory T cells (Tregs) are the main expressors of TIGIT in myocarditis, and 5) Stimulation of TIGIT shielded the heart from myocarditis. In this project, we propose the PD-1/PD-L1 pathway together with TIGIT are essential for peripheral tolerance in protecting the heart from myocarditis. In Aim 1, we will study the role of TIGIT in ICI-myocarditis. We theorize that the loss of TIGIT signaling combined with PD-1 blockade will break the peripheral tolerance that protects the heart and worsen ICI- myocarditis severity. We will administrate a co-blockade of a blocking αTIGIT mAb with a blocking αPD-1 mAb (Subaim 1.1). We will examine TIGIT-expressing Tregs as the main protectors against ICI-myocarditis by treating TIGITfl/fl FoxP3cre mice with an αPD-1 blockade mAb (Subaim 1.2). In Aim 2, we will inspect the therapeutic potential of TIGIT for ICI-myocarditis. We hypothesize that upregulating TIGIT signaling will prevent and treat ICI-myocarditis. First, we will use an agonistic αTIGIT mAb and see its effect in treating and improving ICI-myocarditis disease (Subaim 2.1). Then we will test the overexpression of TIGIT in Tregs in preventing ICI-myocarditis by using viral vector delivery of TIGITfl-stop-fl plamid into FoxP3cre mice (Subaim 2.2). Our results may help elucidate a novel therapeutic target for ICI-induced myocarditis by using the TIGIT pathway. This would greatly help cancer patients who suffer from this devastating adverse effect because of their cancer treatment. Since TIGIT is expressed in other kinds of myocarditis, we can also explore this therapy in other inflammatory cardiovascular conditions.