Inhibitory Killer Cell Immunoglobulin-like Receptors and NKG2A (KIR/NKG2A)

Inhibitory Killer cell Immunoglobulin-like Receptors (KIRs) and the NKG2A/CD94 complex are key immune checkpoint receptors found on Natural Killer (NK) cells and certain T cell subsets [Vivier et al., 2012, Nature]. These receptors maintain self-tolerance by binding to Human Leukocyte Antigen (HLA) class I molecules on host cells, which triggers inhibitory signaling via immunoreceptor tyrosine-based inhibitory motifs (ITIMs) [Purdy & Campbell, 2009, Front Immunol]. Specifically, inhibitory KIRs (such as KIR2DL1/2/3) recognize classical HLA-A, -B, or -C molecules, while the NKG2A/CD94 heterodimer recognizes the non-classical HLA-E molecule [André et al., 2018, Nature]. In many cancers, tumors exploit this mechanism by overexpressing HLA molecules to suppress NK cell-mediated surveillance and escape immune destruction [Borst et al., 2020, Nat Rev Immunol]. Therapeutic antibodies like monalizumab (anti-NKG2A) and lirilumab (anti-KIR) are designed to block these interactions, effectively releasing the brakes on the innate immune system to promote anti-tumor activity [Creelan & Antonia, 2017, Cancer Control]. These agents are frequently investigated in combination with PD-1/PD-L1 inhibitors to provide a dual blockade of both innate and adaptive immune checkpoints [Van Hall et al., 2019, OncoImmunology].

Other names

Inhibitory KIRsNKG2ACD159aKiller cell immunoglobulin-like receptorsHLA class I receptorsNK cell checkpointsCD94/NKG2A complexKLRC1KIR2DLKIR3DL

Antagonistic monoclonal antibodies bind to inhibitory KIRs or NKG2A, preventing their interaction with HLA class I ligands (HLA-A, B, C, or E) on target cells. This blockade removes inhibitory signaling in NK cells and CD8+ T cells, lowering the threshold for activation and enhancing cytolytic activity against tumor cells [André et al., 2018, Nature; Vey et al., 2012, Blood].