Abstract Body: Background: Immunotherapy, particularly PD-1/PD-L1 blockers, is effective in cancer treatment but can cause rare, but potentially fatal heart issues. Despite the significant impact of these adverse events, there is limited research into the underlying mechanisms of immune checkpoint inhibitor (ICI)-mediated cardiotoxicity. PD-L1, which is abundantly expressed in cardiac tissue, particularly exhibits high expression levels over myeloid cells. However, the precise role of myeloid-specific PD-L1 signaling in mediating autoimmune cardiac disease pathology remains unclear.
Methods and Results: To study the role of myeloid cell-specific PD-L1 (myeloid-PD-L1) in cardiac pathophysiology, we generated myeloid-specific PD-L1 KO mice, using Lyz2tm1(Cre) Ifo systems. As expected, PD-L1 expression was significantly down-regulated in Mφs from myeloid-PD-L1 KOs. The cardiac function was followed by echocardiography. Controls and myeloid-PD-L1-KO hearts had comparable ventricular function at 1 month of age. Interestingly, as early as 2 months of age, myeloid-PD-L1-KOs displayed marked cardiac dysfunction as reflected by reduced LVEF, LVFS, and HF markers. Immune profiling was conducted whether chronic inflammation contributes to cardiac dysfunction and remodeling at a later age as observed at 2 and 3 months of age. Interestingly, excessive systemic inflammation and substantial immune infiltration (innate and adoptive), activation, and a pro-inflammatory cytokine storm were detected in the KO hearts. Furthermore, myeloid-PD-L1 KO hearts showed increased recruitment of pro-inflammatory CCR2+ monocytes and macrophages.
Conclusion: Our data with myeloid-PD-L1 KOs suggest that deleting PD-L1 in myeloid lineage promotes myocardial and systemic inflammation through innate and adaptive immune cell activation and recruitment of CCR2+ MΦs. Subsequently, this leads to impaired cardiac pathophysiology. Thus, these translational studies will directly evaluate the potential of targeting myeloid-PD-L1 signaling to alleviate cardiac damage.