Glycosylation-independent binding of monoclonal antibody toripalimab to FG loop of PD-1 for tumor immune checkpoint therapy

MAbs. 2019 May/Jun;11(4):681-690. doi: 10.1080/19420862.2019.1596513. Epub 2019 Apr 19.


Monoclonal antibody (mAb)-based blockade of programmed cell death 1 (PD-1) or its ligand to enable antitumor T-cell immunity has been successful in treating multiple tumors. However, the structural basis of the binding mechanisms of the mAbs and PD-1 and the effects of glycosylation of PD-1 on mAb interaction are not well understood. Here, we report the complex structure of PD-1 with toripalimab, a mAb that is approved by China National Medical Products Administration as a second-line treatment for melanoma and is under multiple Phase 1-Phase 3 clinical trials in both China and the US. Our analysis reveals that toripalimab mainly binds to the FG loop of PD-1 with an unconventionally long complementarity-determining region 3 loop of the heavy chain, which is distinct from the known binding epitopes of anti-PD-1 mAbs with structural evidences. The glycan modifications of PD-1 could be observed in three potential N-linked glycosylation sites, while no substantial influences were detected to the binding of toripalimab. These findings benefit our understanding of the binding mechanisms of toripalimab to PD-1 and shed light for future development of biologics targeting PD-1. Atomic coordinates have been deposited in the Protein Data Bank under accession code 6JBT.

Keywords: PD-1; Toripalimab; complex structure; glycosylation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal / genetics
  • Antibodies, Monoclonal / metabolism*
  • Antibodies, Monoclonal / therapeutic use
  • Antibodies, Monoclonal, Humanized / genetics
  • Antibodies, Monoclonal, Humanized / metabolism*
  • Antibodies, Monoclonal, Humanized / therapeutic use
  • B7-H1 Antigen / metabolism
  • Cell Line, Tumor
  • Complementarity Determining Regions / genetics
  • Epitopes / genetics
  • Epitopes / metabolism*
  • Glycosylation
  • Humans
  • Immunotherapy / methods*
  • Melanoma / immunology
  • Melanoma / therapy*
  • Mice
  • Mice, Inbred C57BL
  • Neoplasms, Experimental / immunology
  • Neoplasms, Experimental / therapy*
  • Programmed Cell Death 1 Receptor / immunology
  • Programmed Cell Death 1 Receptor / metabolism*
  • Protein Binding


  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Humanized
  • B7-H1 Antigen
  • Complementarity Determining Regions
  • Epitopes
  • PDCD1 protein, human
  • Programmed Cell Death 1 Receptor
  • toripalimab

Grants and funding

This study was supported by National Science & Technology Major Project [2015ZX09102017, 2017ZX09302009], Strategic Priority Research Program of Chinese Academy of Sciences (CAS) [XDA12020358, XDB29040201].