Inhibition of the NKp44-PCNA Immune Checkpoint Using a mAb to PCNA

Cancer Immunol Res. 2019 Jul;7(7):1120-1134. doi: 10.1158/2326-6066.CIR-19-0023. Epub 2019 Jun 4.


mAb-based blocking of the immune checkpoints involving the CTLA4-B7 and PD1-PDL1 inhibitory axes enhance T-cell-based adaptive immune responses in patients with cancer. We show here that antitumor responses by natural killer (NK) cells can be enhanced by a checkpoint-blocking mAb, 14-25-9, which we developed against proliferating cell nuclear antigen (PCNA). PCNA is expressed on the surface of cancer cells and acts as an inhibitory ligand for the NK-cell receptor, NKp44-isoform1. We tested for cytoplasmic- and membrane-associated PCNA by FACS- and ImageStream-based staining of cell lines and IHC of human cancer formalin fixed, paraffin embedded tissues. The mAb, 14-25-9, inhibited binding of chimeric NKp44 receptor to PCNA and mostly stained the cytoplasm and membrane of tumor cells, whereas commercial antibody (clone PC10) stained nuclear PCNA. NK functions were measured using ELISA-based IFNγ secretion assays and FACS-based killing assays. The NK92-NKp44-1 cell line and primary human NK cells showed increased IFNγ release upon coincubation with mAb 14-25-9 and various solid tumor cell lines and leukemias. Treatment with 14-25-9 also increased NK cytotoxic activity. In vivo efficacy was evaluated on patient-derived xenografts (PDX)-bearing NSG mice. In PDX-bearing mice, intravenous administration of mAb 14-25-9 increased degranulation (CD107a expression) of intratumorally injected patient autologous or allogeneic NK cells, as well as inhibited tumor growth when treated long term. Our study describes a mAb against the NKp44-PCNA innate immune checkpoint that can enhance NK-cell antitumor activity both in vitro and in vivo.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal / pharmacology*
  • Apoptosis
  • Cell Proliferation
  • Cytotoxicity, Immunologic / drug effects
  • Cytotoxicity, Immunologic / immunology*
  • Head and Neck Neoplasms / drug therapy*
  • Head and Neck Neoplasms / immunology
  • Head and Neck Neoplasms / metabolism
  • Head and Neck Neoplasms / pathology
  • Humans
  • Killer Cells, Natural / drug effects*
  • Killer Cells, Natural / immunology
  • Killer Cells, Natural / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Inbred NOD
  • Mice, SCID
  • Natural Cytotoxicity Triggering Receptor 2 / antagonists & inhibitors*
  • Natural Cytotoxicity Triggering Receptor 2 / immunology
  • Proliferating Cell Nuclear Antigen / chemistry*
  • Proliferating Cell Nuclear Antigen / immunology
  • Squamous Cell Carcinoma of Head and Neck / drug therapy*
  • Squamous Cell Carcinoma of Head and Neck / immunology
  • Squamous Cell Carcinoma of Head and Neck / metabolism
  • Squamous Cell Carcinoma of Head and Neck / pathology
  • Tumor Cells, Cultured
  • Xenograft Model Antitumor Assays


  • Antibodies, Monoclonal
  • NCR2 protein, human
  • Natural Cytotoxicity Triggering Receptor 2
  • PCNA protein, human
  • Proliferating Cell Nuclear Antigen