Immunotherapies represent a major advance in oncology and an increasing number of patients will benefit from them. However, activation of the immune system can lead to severe myocarditis with a fatality rate up to 50%. The pathophysiological mechanisms of myocarditis induced by anti-PD-1 and anti-CTLA-4, the most commonly used immune checkpoint inhibitor (ICIs), are poorly understood and require models to study this cardiotoxicity. PD-1 and CTLA-4 KO mouse models do show cardiomyopathy but still do not reflect the immuno-induced myocarditis observed in patients.

Our objective is to develop a preclinical mouse model to characterize in vivo the pathophysiological mechanisms of ICIs-induced myocarditis.

We used a syngeneic model with adult BALB/c mice grafted with murine melanoma cells. Ten days after graft, mice were treated every 2days with peritoneal injection of a combination of anti-PD-1 (6.5mg/kg) and anti-CTLA-4 (20mg/kg) monoclonal antibodies. A group of ICIs-treated mice with melanoma also received diphtheria toxin to amplify the cardiotoxic response, by depletion of regulatory T cells. To follow-up the cardiac function, an ECG was recorded before each ICIs injection and 1week after the 3rd injection before euthanasia. A submaxillary blood sample was taken before and after ICIs injection. To investigate inflammation, hearts were dissected for transcriptomic analysis and immunostaining.

All transplanted mice developed a palpable melanocytic tumor. They maintained a stable clinical condition (no weight loss or signs of pain). ECG analysis showed some arrhythmias and numerous extrasystoles. Analyses are currently underway to determine the characteristics of the different intervals in each of the groups tested and to verify the significance of the results. qPCR analyzes are in progress to verify the inflammatory state of the myocardium. We are looking for changes in the expression of genes of the JAK/STAT pathway and of the NLRP3 inflammasome, including the GBP5, GBP6, and CCDC175, CXCL9, CXCL11 genes which have been described in cardiac biopsies from patients.

This model of in vivo cardiotoxicity is very important to unravel the mechanisms that lead to immuno-induced myocarditis. The results obtained will be integrated with data from patients followed at the Cardio-Oncology center in Marseille and those from the in vitro hiPSC model in order to better understand the pathology and identify prognosis markers.