PD-L1 Antibodies to Its Cytoplasmic Domain Most Clearly Delineate Cell Membranes in Immunohistochemical Staining of Tumor Cells

Cancer Immunol Res. 2015 Dec;3(12):1308-15. doi: 10.1158/2326-6066.CIR-15-0116. Epub 2015 Nov 6.


Blocking the programmed death-1 (PD-1) pathway has clinical benefit in metastatic cancer and has led to the approval of the mAbs pembrolizumab and nivolumab to treat melanoma and nivolumab for non-small cell lung cancer. Expression of PD-L1 on the cell surface of either tumor cells or infiltrating immune cells is associated with a higher likelihood of response to PD-1 blockade in multiple studies. Most mAbs to PD-L1 in use are directed to its extracellular domain and immunohistochemically stain tumor tissue with a mixture of cytoplasmic and membrane staining. Cytoplasmic staining obscures the interpretation of a positive reaction on the tumor cell membrane, and thus affects the accuracy of PD-L1 scoring systems. We developed a mAb to the cytoplasmic domain of PD-L1, 405.9A11 (9A11), which is both more selective for membranous PD-L1 and more sensitive in IHC and Western blotting, compared with previous mAbs specific for the PD-L1 extracellular domain. Here, we compare immunohistochemical staining patterns of PD-L1 expression in five types of tumors, using five PD-L1 mAbs: 9A11, 7G11, and three commercially available mAbs. We demonstrate that 9A11, as well as two other cytoplasmic domain-specific mAbs, E1L3N and SP142, can clearly delineate the membrane of PD-L1-positive cells in formalin-fixed paraffin-embedded tissue and facilitate interpretation of staining results.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Monoclonal / immunology*
  • Antibodies, Monoclonal / pharmacology*
  • Antibodies, Monoclonal, Humanized / immunology
  • Antibodies, Monoclonal, Humanized / pharmacology
  • B7-H1 Antigen / immunology*
  • Cell Line, Tumor
  • Cell Membrane / immunology*
  • Humans
  • Neoplasms / immunology*
  • Neoplasms / pathology
  • Nivolumab
  • Programmed Cell Death 1 Receptor / immunology*
  • Protein Structure, Tertiary
  • Staining and Labeling
  • Tissue Embedding


  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Humanized
  • B7-H1 Antigen
  • CD274 protein, human
  • PDCD1 protein, human
  • Programmed Cell Death 1 Receptor
  • Nivolumab
  • pembrolizumab