NKG2A Immune Checkpoint Natural killer group protein 2A (NKG2A) is a cell surface receptor and member of the NKG2 family that can form a heterodimer with CD94 on the cell surface, also known as KLRD1, another NK cell-expressed C-type lectin. The non-classical MHC class I molecule HLA-E is the major ligand of NKG2A-CD94. These inhibitory receptors interact with MHC I ligands on target cells, leading to complete inhibition of NK cell granule polarization and cytotoxic granule release prevention.