PD-L1 Binds to B7-1 Only In Cis on the Same Cell Surface

Area of Science:

• Immunology
• Molecular Biology
• Cancer Research

Background:

• Programmed death ligand 1 (PD-L1) mediated immunosuppression is crucial for peripheral tolerance and tumor immune evasion.
• PD-L1 interacts with PD-1, but also with B7-1 (CD80), influencing T-cell function.
• The precise binding interaction and functional role of PD-L1 with B7-1 require further elucidation for optimizing cancer immunotherapy.

Purpose of the Study:

• To investigate the molecular orientation and binding characteristics of PD-L1 to B7-1.
• To understand the functional implications of PD-L1 and B7-1 interaction in the context of cancer immunotherapy.

Main Methods:

• Cell-to-cell binding assays, ELISA, and flow cytometry were employed to examine PD-L1 and B7-1 interactions.
• Purified proteins were used to confirm binding affinities under different conditions.
• NanoBiT proximity assays were utilized to demonstrate binding in cis on the same cell surface.

Main Results:

• PD-L1-transfected cells did not bind to B7-1-transfected cells in trans assays.
• A strong binding interaction between PD-L1 and B7-1 was observed with purified proteins when PD-L1 was flexible, and this binding was competed by soluble PD-1 and B7-1.
• NanoBiT assays confirmed that PD-L1 and B7-1 bind in cis on the same cell surface, suggesting PD-L1 bends via its flexible stalk to interact with B7-1.

Conclusions:

• The PD-L1-B7-1 interaction occurs in cis, not in trans, suggesting a model where PD-L1 binding to B7-1 on the same cell can competitively block PD-L1/PD-1 or B7-1/CD28 interactions.
• This in cis binding orientation highlights the functional significance of co-expressing PD-L1 and B7-1 on the same cell.
• Coexpression of PD-L1 and B7-1 was observed on tumor-infiltrating myeloid cells, indicating potential therapeutic targets for cancer immunotherapy.