KIR2DL4 ligand(s)

BSF 2007282 – Porgador/Campbell Executive Report KIR2DL4 (2DL4) is an activating receptor expressed on human NK cells. It was reported that 2DL4 binds HLA-G, which is normally expressed in pregnant women, but a role for 2DL4 in pregnancy is unclear. Therefore, we postulated existence of additional ligands for 2DL4.

A soluble 2DL4 extracellular domain fused to IgG1 Fc (2DL4-Ig) was found to bind to several HLA-G-deficient tumor lines. To identify the novel 2DL4 ligand, we performed a genome-wide siRNA screen. The top 25 “hits” were validation tested and four were chosen for follow-up studies.

Two of the top four validated hits encode enzymes that perform the final steps in synthesis of a glycosaminoglycan, and the other two encode surface proteins. We confirmed that the glycosaminoglycan binds to 2DL4, and the major binding site was identified on 2DL4 by mutation analysis. We are currently testing the impacts of mutating the ligand binding site on 2DL4 function.

During these studies, we also identified ligands for another NK cell activating receptor, NKp44. We first showed that NKp44 can directly interact with flavivirus envelope proteins to induce NK cell degranulation and IFN( secretion. We also demonstrated an interaction between NKp44 and proliferating cell nuclear antigen (PCNA) on tumor cells, which surprisingly inhibited NK cell function.

The characterization of these novel ligands significantly improves our understanding of how 2DL4 and NKp44 influence human health. Furthermore, our results provide the groundwork to develop therapeutic agonists or antagonists for these receptors that can be used to specifically manipulate NK cell functions in patients.