Paradoxical Role of Myeloid Cell PD-L1 Expression in AKI

Background: Blocking of immune checkpoint molecules Programmed Death-1 (PD-1) and its ligands PD-L1 and PD-L2 have revolutionized cancer therapy via activation of anti-tumor immunity. However, this checkpoint inhibitor therapy also led to increase in immune check-point inhibitor (ICPI)-associated inflammatory diseases including acute kidney injury (AKI) suggesting a protective role of PD-1 and its ligands in AKI. While PD-1 is mainly expressed on T-cells, PD-L1 and PD-L2 are expressed on tumor, stromal, and immune cells including myeloid cells. Treatment of mice with antibodies to PD-1, PD-L1 and PD-L2 worsens ischemia reperfusion injury (IRI). Expression of PD-1 on the T-regulatory cells (Tregs) is important for protection from IRI (ASN Kidney week 2020, PO-0152). However, the role of PD-L1 expression on myeloid cells, as related to AKI remains a knowledge gap. Methods: To investigate the role of PD-L1 expression on myeloid cells, we generated mice with deletion of PD-L1 in myeloid cells using lysozyme-driven Cre (LysM-Cre) to generate PD-L1fl/fl.LysM-Cre mice. Mice were subjected to unilateral IRI and euthanized on day 14 after nephrectomy of contralateral kidney on day 13 or subjected to Cisplatin-induced renal injury. Blood, spleen and kidneys were analyzed for immunophenotype, and kidneys were analyzed for inflammation and injury by flow cytometry, histopathology and quantitative PCR. Results: Deletion of PD-L1 in myeloid cells resulted in an overall inflammatory phenotype in mice as represented by lymphadenopathy and splenomegaly with greater accumulation of activated and memory T-cells that produced more proinflammatory cytokines. However, despite the inflammatory conditions, PD-L1fl/fl.LysM-Cre mice displayed lower levels of injury and kidney dysfunction as compared to PD-L1 sufficient mice with IRI or cisplatin. While the infiltration of neutrophils in the PD-L1 deficient mice was lower, the infiltration of monocytes was significantly higher. Interestingly, the dendritic cells in the spleen and kidneys of PD-L1 deficient mice expressed lower levels of co-stimulatory molecules suggesting of lower activation status. Conclusion: The data reveals a paradoxical role of PD-L1 expression in myeloid cells in promoting ischemic and cisplatin AKI, such that myeloid-cell specific deletion of PD-L1 was protective in AKI via promoting a tolerogenic milieu. Funding: NIDDK Support, Private Foundation Support