PD-L1:CD80 Cis-Heterodimer Triggers the Co-stimulatory Receptor CD28 While Repressing the Inhibitory PD-1 and CTLA-4 Pathways

Immunity. 2019 Dec 17;51(6):1059-1073.e9. doi: 10.1016/j.immuni.2019.11.003. Epub 2019 Nov 19.


Combined immunotherapy targeting the immune checkpoint receptors cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death 1 (PD-1), or CTLA-4 and the PD-1 ligand (PD-L1) exhibits superior anti-tumor responses compared with single-agent therapy. Here, we examined the molecular basis for this synergy. Using reconstitution assays with fluorescence readouts, we found that PD-L1 and the CTLA-4 ligand CD80 heterodimerize in cis but not trans. Quantitative biochemistry and cell biology assays revealed that PD-L1:CD80 cis-heterodimerization inhibited both PD-L1:PD-1 and CD80:CTLA-4 interactions through distinct mechanisms but preserved the ability of CD80 to activate the T cell co-stimulatory receptor CD28. Furthermore, PD-L1 expression on antigen-presenting cells (APCs) prevented CTLA-4-mediated trans-endocytosis of CD80. Atezolizumab (anti-PD-L1), but not anti-PD-1, reduced cell surface expression of CD80 on APCs, and this effect was negated by co-blockade of CTLA-4 with ipilimumab (anti-CTLA-4). Thus, PD-L1 exerts an immunostimulatory effect by repressing the CTLA-4 axis; this has implications to the synergy of anti-PD-L1 and anti-CTLA-4 combination therapy.

Keywords: CD28; CD80; CTLA-4; Cis-interaction; PD-1; PD-L1; Trans-endocytosis; heterodimer; homodimer; immunotherapy.

Publication types

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

MeSH terms

  • Animals
  • Antibodies, Monoclonal, Humanized / pharmacology
  • Antineoplastic Agents / pharmacology
  • B7-1 Antigen / metabolism*
  • B7-H1 Antigen / metabolism*
  • CD28 Antigens / metabolism*
  • CTLA-4 Antigen / antagonists & inhibitors*
  • Cell Line, Tumor
  • Female
  • HEK293 Cells
  • Humans
  • Immunotherapy / methods
  • Ipilimumab / pharmacology
  • Jurkat Cells
  • Lymphocyte Activation
  • Mice
  • Mice, Inbred BALB C
  • Neoplasms / immunology
  • Neoplasms / therapy
  • Programmed Cell Death 1 Receptor / antagonists & inhibitors*
  • Signal Transduction / drug effects
  • Signal Transduction / immunology


  • Antibodies, Monoclonal, Humanized
  • Antineoplastic Agents
  • B7-1 Antigen
  • B7-H1 Antigen
  • CD274 protein, human
  • CD28 Antigens
  • CD80 protein, human
  • CTLA-4 Antigen
  • CTLA4 protein, human
  • Ipilimumab
  • PDCD1 protein, human
  • Programmed Cell Death 1 Receptor
  • atezolizumab