Abstract Body (Do not enter title and authors here):
Background: Doxorubicin (DR), the most commonly used chemotherapy, results in dose-dependent cardiotoxicity in part by causing oxidative stress, cardiomyocyte death, and cardiac fibrosis. Whether these elicit a cardiac immune response that contributes to DR cardiomyopathy and could be targeted for cardio-protection is unknown. We hypothesized that an aberrant T-cell immune response secondary to cardiac damage contributes to DR cardiomyopathy.
Methods: We treated wild type (WT) mice and CD8⁺ T-cell antigen restricted OTI mice with 5.0 mg/kg of DR or PBS weekly for 4 or 8 weeks and performed targeted antibody depletion of CD8⁺ and CD4⁺ T-cells. Primary mouse T-cells and cardiac fibroblasts (CFB) were used for mechanistic studies. Whole blood was analyzed by flow cytometry and proteomics in human and canine lymphoma patients before and after DR initiation.
Results: DR treated mice exhibited cardiac CD8⁺ T-cell infiltration alongside hallmarks of DR cardiomyopathy, including declined ejection fraction (EF) measured by echocardiography, cardiac cell death, and fibrosis determined by TUNEL and picrosirius red stain. Cardiac CD8⁺ T-cells co-localized with αSMA⁺ CFB and had enhanced expression of the degranulation marker CD107a and IFNγ in DR compared to PBS treated mice. DR hearts also showed increased gene and protein expression of the IFNγ inducible chemokines Cxcl9 and Cxcl10. DR resulted in increased circulating CD8⁺ T-cells and the frequency of activated CD8⁺ cells in the cardiac draining lymph nodes. Targeted antibody depletion of CD8⁺ but not CD4⁺ T-cells in the onset of DR treatment improved EF and decreased cardiac fibrosis. OTI mice were protected from DR induced EF decline, cardiac T-cell infiltration, and cardiac fibrosis, indicating an antigen-specific CD8⁺ T-cell response. Mechanistically, DR induced ICAM-1 expression on CFB and ICAM-1 dependent adhesion of activated CD8⁺ T-cells, which in turn increased CFB αSMA expression. Contact between CD8⁺ T-cells and DR-treated CFB caused CD8⁺ T-cell degranulation and Granzyme B release that contributed to CFB activation. Human and canine cancer patients followed longitudinally had increased circulating CD8⁺ T-cells after anthracycline treatment, and human plasma levels of CXCL9/CXCL10 correlated with decreased EF post DR.
Conclusion: Our data demonstrate a novel role for cytotoxic T-cells in DR cardiomyopathy across 3 species, through CXCL9/10-dependent cardiotropism and CD8⁺ T-cell dependent fibrosis.