Abstract
The endoplasmic reticulum aminopeptidase ERAP1 regulates innate and adaptive immune responses by trimming peptides for presentation by major histocompatibility complex (MHC) class I molecules. Previously, we have shown that genetic or pharmacological inhibition of ERAP1 on murine and human tumor cell lines perturbs the engagement of NK cell inhibitory receptors Ly49C/I and Killer-cell Immunoglobulin-like receptors (KIRs), respectively, by their specific ligands (MHC class I molecules), thus leading to NK cell killing. However, the effect of ERAP1 inhibition in tumor cells was highly variable, suggesting that its efficacy may depend on several factors, including MHC class I typing. To identify MHC class I alleles and KIRs that are more sensitive to ERAP1 depletion, we stably silenced ERAP1 expression in human HLA class I-negative B lymphoblastoid cell line 721.221 (referred to as 221) transfected with a panel of KIR ligands (i.e. HLA-B*51:01, -Cw3, -Cw4 and -Cw7), or HLA-A2 which does not bind any KIR, and tested their ability to induce NK cell degranulation and cytotoxicity. No change in HLA class I surface expression was detected in all 221 transfectant cells after ERAP1 depletion. In contrast, CD107a expression levels were significantly increased on NK cells stimulated with 221-B*51:01 cells lacking ERAP1, particularly in the KIR3DL1-positive NK cell subset. Consistently, genetic or pharmacological inhibition of ERAP1 impaired the recognition of HLA-B*51:01 by the YTS NK cell overexpressing KIR3DL1*001, suggesting that ERAP1 inhibition renders HLA-B*51:01 molecules less eligible for binding to KIR3DL1. Overall, these results identify HLA-B*51:01/KIR3DL1 as one of the most susceptible combinations for ERAP1 inhibition, suggesting that individuals carrying HLA-B*51:01-like antigens may be candidates for immunotherapy based on pharmacological inhibition of ERAP1.
Highlights
Natural killer (NK) cells provide the first important line of defence against infections and malignancies through direct recognition and killing of altered cells [1, 2]
To identify killer cell immunoglobulin-like receptors (KIRs)-HLA class I interactions more sensitive to ERAP1 inhibition, we stably reduced ERAP1 expression in HLA class I-negative 221 cells transfected with a panel of KIR ligands (i.e. HLA-B*51:01, -Cw3, -Cw4 and -Cw7), or HLA-A2 which does not bind any KIR, and tested their ability to induce NK cell degranulation and cytotoxicity
To identify KIR/HLA class I combinations susceptible to ERAP1 inhibition, we took advantage of 221 cell line, which does not express the endogenous HLA class I alleles (HLA-A, -B and -C), and 221 transfectant cells overexpressing ligands of inhibitory KIRs: HLA-B*51:01 for KIR3DL1, HLA-Cw4 for KIR2DL1, and HLA-Cw3 and HLA-Cw7 for KIR2DL2 and KIR2DL3
Summary
Natural killer (NK) cells provide the first important line of defence against infections and malignancies through direct recognition and killing of altered cells [1, 2]. The engagement of inhibitory receptors by MHC class I molecules on healthy cells normally suppresses the activation of autologous NK cells [4]. Inhibitory receptors typically recognise a group of classical and non-classical MHC class I molecules with specific amino acid sequences at positions 77-83 of the alpha-1 domain [6]. Based on these sequences, some HLA-B and HLA-A molecules are classified as Bw4 allotypes [6]. In the absence of the “permissive” HLA class I alleles, HLA-E molecules are not functionally expressed on the cell surface. Transfection of 221 cells with signal peptides derived from “permissive” HLA class I molecules has been shown to induce surface expression of HLA-E [11]
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