Unraveling the Molecular Mechanisms of Immunotherapy-Associated Myocarditis

Immune checkpoint inhibitors (ICIs) have revolutionized cancer treatment by enhancing immune-based anti- tumor responses. Despite their efficacy, especially when used in combination, ICI treatment can lead to immune- related toxicities, which can affect any organ. ICI-myocarditis refers to inflammation of the heart, is a particularly severe toxicity,with high mortality (up to 50%). To better understand mechanisms of ICI-myocarditis, our groups have generated mouse models that replicate the disease both clinically and pathophysiologically. In tumor- bearing, ICI-treated mice, myocardial immune infiltration resulted in cardiomyopathy and arrhythmias; mice genetically deficient in immune checkpoints die prematurely from fulminant myocarditis. While immune dysregulation plays a critical role in ICI-myocarditis, our findings highlighted the surprising, yet essential roles of cardiac-protective factors in mitigating ICI-myocarditis. We specifically showed that Mesencephalic Astrocyte- Derived Neurotrophic Factor (MANF), secreted by the heart, plays a protective role in ICI-myocarditis with ICI downregulating MANF in the heart. This proposal aims to uncover the molecular mechanisms underlying cardiac immune privilege. Our preliminary data suggested that MANF induces expression of FGL1 (Fibrinogen-like 1), a negative immune checkpoint ligand for LAG3 (Lymphocyte-activating 3) expressed on T lymphocytes. These findings raise the intriguing possibility that direct cardiac-T cell interaction regulates immune privilege in the heart. We further provide evidence that genetic deletion of Lag3 or Fgl1 (in combination with Pdcd1) results in myocarditis, highlighting the critical role of the MANF/FGL1/LAG3 axis in the myocarditis. We hypothesize that MANF upregulates cardiac FGL1 to modulate the cardiac immune microenvironment (CIME), mitigating ICI-myocarditis while preserving anti-tumor immunity. Without this investigation, addressing the critical risk of mortality in ICI- treated patients will remain a significant challenge, hindering efforts to improve patient outcomes and minimize cardiotoxicity. Aim examines the functional importance of MANF/FGL1/LAG3 axis in ICI-myocarditis using both genetic and tumor-bearing, ICI treated mouse models. Aim 2 investigates the mechanisms underlying the MANF-induced cardiac FGL1 expression using iPSC-derived cardiomyocytes. Aim 3 dissects the crosstalk between cardiomyocytes and effector T cells derived from the same ICI-myocarditis patient. We will also define the MANF/FGL1/LAG3 expression and CIME in human ICI-myocarditis hearts; as well as mouse CIME and tumor immune microenvironment using mouse myocarditis models. The findings from this research are expected to fill critical gaps in understanding ICI-myocarditis and provide strategies to mitigate cardiac toxicity while preserving anti-tumor immunity. This study could reshape cancer immunotherapy, optimizing patient safety and improving treatment outcomes by balancing immune regulation in both the heart and the tumor microenvironment. Project Number: 1R01CA305864-01A1 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Chunru Lin (+2 co-PIs) | Institution: UNIVERSITY OF TX MD ANDERSON CAN CTR, HOUSTON, TX | Award Amount: $706,739 | Activity Code: R01 | Study Section: Integrative Myocardial Physiology/Pathophysiology A Study Section [MPPA] View on NIH RePORTER: https://reporter.nih.gov/project-details/11364611