Mouse and Human Antibodies that Bind HLA-E-Leader Peptide Complexes and Enhance NK Cell Cytotoxicity

HLA-E is a non-classical class Ib molecule that has limited polymorphism and binds HLA class Ia leader peptides (VL9). HLA-E-VL9 complexes interact with the natural killer (NK) cell receptors NKG2A-C/CD94 and regulate NK cell-mediated cytotoxicity. Here we isolated a murine IgM antibody 3H4, that specifically recognized HLA-E-VL9 bound complexes and enhanced killing of HLA-E-VL9-expressing cells by an NKG2A+ NK cell line. Structural analysis revealed how 3H4 prevents CD94/NKG2A docking on HLA-E-VL9 by binding with an overlapping footprint. Upon in vitro maturation, an affinity-optimized 3H4 IgG showed enhanced NK killing of HLA-E-VL9-expressing cells. Remarkably, HLA-E-VL9-specific IgM autoantibodies with similar specificity and functions to 3H4 were subsequently isolated from naive B cells of cytomegalovirus (CMV)-negative, healthy male human donors. Thus, a repertoire of germline low affinity HLA-E-VL9-reactive antibodies are present in both naive human and murine B cell repertoires. These antibodies can enhance NK cell cytotoxicity and therefore have potential for therapeutic modulation of NK cell function.