Abstract B032: Tumor PD-L1 suppresses NK cell function through crosstalk with dendritic cells and IL-12 release
Authors: Yang Jiuling , Goekbuget Deniz , Wang Li , Driks Hannah , Fong Lawrence , Blelloch Robert 
Published: February 2025

Abstract
Immune checkpoint inhibitors targeting the PD-1/PD-L1 pathway are thought to primarily function through the enhancement of CD8+ T cell-mediated killing of tumor cells, which requires the recognition of MHC-I-tumor antigen peptide complexes on the tumor cells by the T-cell receptor. Therefore, a proposed mechanism of resistance to PD-1/PD-L1 inhibitors is the downregulation of MHC-I on the tumor cell surface. However, previous studies using MHC-I-deficient mouse tumor models have shown evidence of continued inhibition of tumor growth by these inhibitors. The mechanisms underlying this regulation in the absence of MHC-I are unclear. Here, we use genetic mouse models to investigate these mechanisms. We generated MHC-I-deficient tumor models by knocking out β-2 microglobulin (B2M), a critical component of the MHC-I complex, and compared B2m single versus B2m; Pdl1 double knockout (KO) models of murine colorectal cancer, MC38. To identify the target cell population for PD-L1 in the MHC-I-deficient context, we utilized various cell type-specific Cre recombinases with a conditional KO allele for the PD-L1 receptor, PD-1 in mice. These Cre recombinases included ones specific for NK cells (NKp46-Cre), dendritic cells (DCs) (CD11c-Cre), conventional type 1 DCs (cDC1s) (XCR1-Cre), and macrophages (LysM-Cre), respectively. Our data show that PD-L1 significantly promotes tumor growth in the absence of MHC-I. Depletion of NK cells using antibodies completely abolished this effect, indicating an NK cell-dependent mechanism. However, this impact is not directly mediated by PD-1 on NK cells. Instead, it is dependent on PD-1 expressed on dendritic cells, particularly cDC1s, as deletion of the Pd1 gene in CD11c+ or XCR1+ cells in mice abolished the impact of PD-L1 on tumor growth. This suggests an indirect regulation of NK cells by tumor cell PD-L1 through cDC1s. To identify the cell signaling pathways impacted by the loss of PD-L1, we performed single-cell RNA sequencing (scRNA-seq) of the tumor-infiltrated lymphocytes from B2m single versus B2m; Pdl1 double KO MC38 tumors in wild-type mice. Our scRNA-seq analysis revealed increased IL-12 production by a CCR7+CD205+ migratory subset of cDC1s with the loss of PD-L1 on tumor cells. Neutralization of IL-12 signaling by antibody blockade abolished any role for PD-L1 in the growth of MHC-I deficient tumors, showing that cDC1s regulate NK cell function through IL-12. In conclusion, our findings uncover a novel role for PD-L1 in regulating NK cell function through IL-12 release by cDC1s. These insights provide a rationale for continuing PD-1/PD-L1 blockade even following the downregulation of MHC-I by tumor cells. These results should also motivate the development of therapeutic strategies aimed at targeting dendritic cells and their IL-12 release to enhance NK cell killing, especially for the treatment of MHC-I deficient tumors.
Citation Format: Jiuling Yang, Deniz Goekbuget, Li Wang, Hannah Driks, Lawrence Fong, Robert Blelloch. Tumor PD-L1 suppresses NK cell function through crosstalk with dendritic cells and IL-12 release [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr B032.