PT  - JOURNAL ARTICLE
AU  - Chaudhri, Apoorvi
AU  - Xiao, Yanping
AU  - Klee, Alyssa N
AU  - Wang, Xiaoxu
AU  - Zhu, Baogong
AU  - Freeman, Gordon J.
TI  - PD-L1 binds to B7-1 only in cis on the same cell surface
AID  - 10.1158/2326-6066.CIR-17-0316
DP  - 2018 Jan 01
TA  - Cancer Immunology Research
PG  - canimm.0316.2017
4099  - http://cancerimmunolres.aacrjournals.org/content/early/2018/06/05/2326-6066.CIR-17-0316.short
4100  - http://cancerimmunolres.aacrjournals.org/content/early/2018/06/05/2326-6066.CIR-17-0316.full
AB  - Programmed death ligand 1 (PD-L1)-mediated immune suppression regulates peripheral tolerance and is often co-opted by tumors to evade immune attack. PD-L1 binds to PD-1 but also binds to B7-1 (CD80) to regulate T-cell function. Binding interactions of PD-L1 with B7-1 and its functional role need further investigation to understand differences between PD-1 and PD-L1 tumor immunotherapy. We examined the molecular orientation of PD-L1 binding to B7-1 using cell-to-cell binding assays, ELISA, and flow cytometry. As expected, PD-L1 transfected cells bound to PD-1 transfected cells and B7-1 cells bound to CD28 or CTLA-4 transfected cells; however, PD-L1 cells did not bind to B7-1 cells. By ELISA and flow cytometry with purified proteins, we found PD-L1 and B7-1 had a strong binding interaction only when PD-L1 was flexible. Soluble PD-1 and B7-1 competed for binding to PD-L1. Binding of native PD-L1 and B7-1 in cis on the same cell surface was demonstrated with Nanobit proximity assays. Thus, PD-L1-B7-1 interaction can occur in cis on the same cell but not in trans between two cells, which suggests a model in which PD-L1 can bend via its 11-amino acid, flexible stalk to bind to B7-1 in cis, in a manner that can competitively block the binding of PD-L1 to PD-1 or of B7-1 to CD28. This binding orientation emphasizes the functional importance of coexpression of PD-L1 and B7-1 on the same cell. We found such coexpression on tumor-infiltrating myeloid cells. Our findings may help better utilize these pathways in cancer immunotherapy.