Related Experiment Video
Updated: Aug 12, 2025
Co-immunoprecipitation Assay for Studying Functional Interactions Between Receptors and Enzymes
Published on: September 28, 2018
The CTLA-4 immune checkpoint protein regulates PD-L1:PD-1 interaction via transendocytosis of its ligand CD80
Alan Kennedy1, Maximillian A Robinson1, Claudia Hinze1
1UCL Institute of Immunity and Transplantation, London, UK.
Abstract:
CTLA-4 and PD-1 are key immune checkpoint receptors that are targeted in the treatment of cancer. A recently identified physical interaction between the respective ligands, CD80 and PD-L1, has been shown to block PD-L1/PD-1 binding and to prevent PD-L1 inhibitory functions. Since CTLA-4 is known to capture and degrade its ligands via transendocytosis, we investigated the interplay between CD80 transendocytosis and CD80/PD-L1 interaction. We find that transendocytosis of CD80 results in a time-dependent recovery of PD-L1 availability that correlates with CD80 removal. Moreover, CD80 transendocytosis is highly specific in that only CD80 is internalised, while its heterodimeric PD-L1 partner remains on the plasma membrane of the antigen-presenting cell (APC). CTLA-4 interactions with CD80 do not appear to be inhibited by PD-L1, but efficient removal of CD80 requires an intact CTLA-4 cytoplasmic domain, distinguishing this process from more general trogocytosis and simple CTLA-4 binding to CD80/PD-L1 complexes. These data are consistent with CTLA-4 acting as modulator of PD-L1:PD-1 interactions via control of CD80.
Insights
Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) removes CD80 from antigen-presenting cells, which restores the availability of PD-L1. This mechanism modulates PD-L1:PD-1 interactions, impacting cancer immunotherapy.
Area of Science:
- Immunology
- Cancer Biology
- Molecular Medicine
Background:
- Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and Programmed cell death protein 1 (PD-1) are critical immune checkpoints in cancer therapy.
- A known interaction between CD80 and PD-L1 inhibits PD-L1/PD-1 binding and PD-L1's suppressive functions.
- CTLA-4 captures and degrades its ligands through transendocytosis.
Purpose of the Study:
- To investigate the interplay between CD80 transendocytosis and the CD80/PD-L1 interaction.
- To understand how CTLA-4 influences PD-L1 availability and function.
Main Methods:
- Studied the effect of CD80 transendocytosis on PD-L1 availability.
- Investigated the specificity of CD80 internalization by CTLA-4.
- Assessed the role of the CTLA-4 cytoplasmic domain in CD80 removal.
Main Results:
- CD80 transendocytosis by CTLA-4 leads to time-dependent recovery of PD-L1 availability, correlated with CD80 removal.
- CD80 transendocytosis is specific, internalizing only CD80 while PD-L1 remains on the antigen-presenting cell (APC) surface.
- PD-L1 does not inhibit CTLA-4 binding to CD80, but efficient CD80 removal requires an intact CTLA-4 cytoplasmic domain.
Conclusions:
- CTLA-4 modulates PD-L1:PD-1 interactions by controlling CD80 availability through a specific transendocytosis mechanism.
- This process is distinct from general trogocytosis and highlights a novel regulatory pathway in immune checkpoint function.
