A high affinity monoclonal antibody against HLA-E-VL9 enhances natural killer cell anti-tumor killing.

Natural killer (NK) cells kill target cells following triggering via germline-encoded receptors interacting with target cell-expressed ligands (direct killing), or via antibody-dependent cellular cytotoxicity (ADCC) mediated by FcγRIIIa. NK cytotoxicity is modulated by signaling through activating or inhibitory receptors. A major checkpoint is mediated by the NK inhibitory receptor NKG2A/CD94 and its target cell ligand, HLA-E, which is complexed with HLA signal sequence-derived peptides termed VL9 (HLA-E-VL9). We have previously reported the isolation of a murine HLA-E-VL9-specific IgM antibody 3H4 and the generation of a higher affinity IgG version (3H4v3). Here we have used phage display library selection to generate a high affinity version of 3H4v3, called 3H4v31, with an ∼700 fold increase in binding affinity. We show using an HLA-E-VL9+ K562 tumor model that, in vitro, the addition of 3H4v31 to target cells increased direct killing of targets by CD16-negative NK cell line NK-92 and also mediated ADCC by NK-92 cells transfected with CD16. Moreover, ADCC by primary NK cells was also enhanced in vitro by 3H4v31. 3H4v31 was also able to bind and enhance target cell lysis of endogenously expressed HLA-E-VL9 on human cervical cancer and human pancreatic cancer cell lines. In vivo, 3H4v31 slowed the growth rate of HLA-E-VL9+ K562 tumors implanted into NOD/SCID/IL2rγ null mice compared to isotype control when injected with NK-92 cells intratumorally. Together, these data demonstrate that mAb 3H4v31 can enhance NK cell killing of HLA-E-VL9-expressing tumor cells in vitro by both direct killing activity and by ADCC. Moreover, mAb 3H4v31 can enhance NK cell control of tumor growth in vivo. We thus identify HLA-E-VL9 monoclonal antibodies as a promising novel anti-tumor immunotherapy. One Sentence Summary: A high affinity monoclonal antibody against HLA-E-VL9 enhances natural killer cell anti-tumor killing by checkpoint inhibition and antibody dependent cellular cytotoxicity.

Opportunities and challenges for T cell-based influenza vaccines.

Vaccination remains our main defence against influenza, which causes substantial annual mortality and poses a serious pandemic threat. Influenza virus evades immunity by rapidly changing its surface antigens but, even when the vaccine is well matched to the current circulating virus strains, influenza vaccines are not as effective as many other vaccines. Influenza vaccine development has traditionally focused on the induction of protective antibodies, but there is mounting evidence that T cell responses are also protective against influenza. Thus, future vaccines designed to promote both broad T cell effector functions and antibodies may provide enhanced protection. As we discuss, such vaccines present several challenges that require new strategic and economic considerations. Vaccine-induced T cells relevant to protection may reside in the lungs or lymphoid tissues, requiring more invasive assays to assess the immunogenicity of vaccine candidates. T cell functions may contain and resolve infection rather than completely prevent infection and early illness, requiring vaccine effectiveness to be assessed based on the prevention of severe disease and death rather than symptomatic infection. It can be complex and costly to measure T cell responses and infrequent clinical outcomes, and thus innovations in clinical trial design are needed for economic reasons. Nevertheless, the goal of more effective influenza vaccines justifies renewed and intensive efforts.

The antibodies 3D12 and 4D12 recognise distinct epitopes and conformations of HLA-E.

The commonly used antibodies 3D12 and 4D12 recognise the human leukocyte antigen E (HLA-E) protein. These antibodies bind distinct epitopes on HLA-E and differ in their ability to bind alleles of the major histocompatibility complex E (MHC-E) proteins of rhesus and cynomolgus macaques. We confirmed that neither antibody cross-reacts with classical HLA alleles, and used hybrids of different MHC-E alleles to map the regions that are critical for their binding. 3D12 recognises a region on the alpha 3 domain, with its specificity for HLA-E resulting from the amino acids present at three key positions (219, 223 and 224) that are unique to HLA-E, while 4D12 binds to the start of the alpha 2 domain, adjacent to the C terminus of the presented peptide. 3D12 staining is increased by incubation of cells at 27°C, and by addition of the canonical signal sequence peptide presented by HLA-E peptide (VL9, VMAPRTLVL). This suggests that 3D12 may bind peptide-free forms of HLA-E, which would be expected to accumulate at the cell surface when cells are incubated at lower temperatures, as well as HLA-E with peptide. Therefore, additional studies are required to determine exactly what forms of HLA-E can be recognised by 3D12. In contrast, while staining with 4D12 was also increased when cells were incubated at 27°C, it was decreased when the VL9 peptide was added. We conclude that 4D12 preferentially binds to peptide-free HLA-E, and, although not suitable for measuring the total cell surface levels of MHC-E, may putatively identify peptide-receptive forms.