Preliminary exploration of the role of CD8 ⁺ T cells in anti‑PD‑1 antibody‑induced myocarditis in C57BL/6 mice with Lewis lung carcinoma

Globally, ~33% of patients with non-small cell lung cancer receiving anti-PD-1 antibody therapy may experience significant immune-related adverse events (irAEs). Among these, myocarditis is a rare but lethal irAE. The aim of the present study was to preliminarily explore the role of CD8⁺ T cells in anti-PD-1 antibody-induced myocarditis in C57BL/6 mice with Lewis lung carcinoma (LLC). Orthotopic transplantation models were established using wild-type or CD8 knockout (CD8^-/-) C57BL/6 mice. Wild-type and CD8^-/- C57BL/6 mice were separately divided into three groups: Control, LLC and LLC + anti-PD-1. LLC cell suspensions (1x10⁵ cells) with 50 µl Matrigel Matrix were orthotopically injected into the left lung lobe of wild-type or CD8^-/- C57BL/6 mice. Following needle removal, the incision was sutured. At 10 days post-surgery, mice in the anti-PD-1 groups received an intraperitoneal injection of anti-PD-1 antibody (200 µg). After 3 weeks, all mice were humanely euthanized via intraperitoneal injection of sodium pentobarbital (200 mg/kg). The histopathological examination of tumor, lung and heart tissue was performed by Masson's trichrome and hematoxylin and eosin staining. Reverse transcription-quantitative PCR was carried out to determine the mRNA expression of monocyte chemotactic protein-1, interleukin-6, interferon-γ and tumor necrosis factor-α in myocardial tissue. Flow cytometry was used to analyze the ratio of CD8⁺ and CD4⁺ T cells and macrophages in myocardial tissues. Anti-PD-1 therapy effectively inhibited tumor growth and mitigated lung tissue damage. In wild-type C57BL/6 mouse, treatment with anti-PD-1 was associated with myocardial injury, inflammatory responses and a notable increase in the ratios of CD8⁺ and CD4⁺ T cells and macrophages. However, in CD8^-/- C57BL/6 mice, no significant differences were observed in myocardial histopathology, inflammatory cytokine levels and the ratios of CD4⁺ T cells and macrophages between the control, LLC and LLC + anti-PD-1 groups. Anti-PD-1 therapy did not cause significant damage to myocardial tissue. The presence of CD8⁺ T cells facilitated the development of anti-PD-1-induced myocarditis by activating CD4⁺ T cells, macrophages and inflammatory responses.