Abstract Body: Introduction:
Immune checkpoint inhibitors (ICIs, such as anti-CTLA-4 or anti-PD-1) have especially been effective in cancer therapies. However, ICIs treatment can result in myocarditis, the most serious complication of ICIs, which has a case fatality rate as high as 40%. Here, we investigate CXCR3 blockade for targeted treatment of myocardial inflammation in ICI myocarditis while considering concurrent tumor treatment. We hypothesize that CXCR3 blockade will have a direct effect on reducing CD8+ T-cell mediated cardiomyocyte cardiotoxicity without affecting tumor treatment.
Methods:
To study the impact of CXCR3 blockade on myocardial inflammation, we established an in vitro cardiomyocyte apoptosis model by co-culturing cardiomyocytes and MRL-WT mice CD8+ T-cells with/without ICI stimulation or MRL-Pdcd1-/- mice CD8+ T-cells. We then blocked CXCR3 to assess the effect on CD8+ T cell-mediated cytotoxicity against cardiomyocytes. To assess CXCR3 blockade in an in vivo model of ICI myocarditis accounting for tumor, we treated MRL mice inoculated with B16F1 melanoma cells with six doses of 400 µg each of anti-PD1 and anti-CTLA4 and investigated the effects of CXCR3-CXCL9/10 blockade on hearts and tumors.
Results:
In vitro CD8+ T-cell and cardiomyocyte co-culture demonstrated mitigation of cardiomyocytes apoptosis with CXCR3 blockade (Fig. 1 A-C), suggesting decreased CD8+ T-cell cytotoxicity with CXCR3 blockade. In vivo treatment with dual immunotherapy (anti-PD1/anti-CTLA4 monoclonal antibodies) in the tumor MRL mouse model demonstrated significant tumor volume reduction, which was not impacted by concurrent treatment with anti-CXCR3 or anti-CXCL9/10 (Fig. 1 D-F). Concurrently, myocarditis occurred in the group treated with immunotherapy alone, not in anti-CXCL9/10 or anti-CXCR3 (Fig. 1 G-H).
Conclusions:
CXCR3 blockade reduces CD8+ T-cell cytotoxicity against cardiomyocytes and mitigates myocarditis in an in vivo tumor ICI myocarditis mouse model without affecting anti-tumor ICI efficacy, positioning CXCR3 as a promising target for therapeutic intervention.