Previous cardiovascular injury is a prerequisite for immune checkpoint inhibitor‐associated lethal myocarditis in mice.

Aims: Immune checkpoint inhibitors (ICIs) are antineoplastic drugs designed to activate the immune system's response against cancer cells. Evidence suggests that they may lead to immune‐related adverse events, particularly when combined (e.g., anti‐CTLA‐4 plus anti‐PD‐1), sometimes resulting in severe conditions such as myocarditis. We aimed to investigate whether a previously sustained cardiac injury, such as pathological remodelling due to hypertension, is a prerequisite for ICI therapy‐induced myocarditis. Methods: We evaluated the cardiotoxicity of ICIs in a hypertension (HTN) mouse model (C57BL/6). Weekly doses were administered up to day 21 after the first administration. Our analysis encompassed the following parameters: (i) survival and cardiac pathological remodelling, (ii) cardiac function assessed using pressure‐volume (PV)‐loops, with brain natriuretic peptide (BNP) serving as a marker of haemodynamic dysfunction and (iii) cardiac inflammation (cytokine levels, infiltration, and cardiac antigen autoantibodies). Results: After the first administration of ICI combined therapy, the treated HTN group showed a 30% increased mortality (P = 0.0002) and earlier signs of hypertrophy and pathological remodelling compared with the untreated HTN group. BNP (P = 0.01) and TNF‐α (<0.0001) increased 2.5‐ and 1.7‐fold, respectively, in the treated group, while IL‐6 (P = 0.8336) remained unchanged. Myocarditis only developed in the HTN group treated with ICIs on day 21 (score >3), characterised by T cell infiltration and increased cardiac antigen antibodies (86% showed a titre of 1:160). The control group treated with ICI was unaffected in any evaluated feature. Conclusions: Our findings indicate that pre‐existing sustained cardiac damage is a necessary condition for ICI‐induced myocarditis. [ABSTRACT FROM AUTHOR]