A defucosylated anti-PD-L1 monoclonal antibody 13-mG(2a)-f exerts antitumor effects in mouse xenograft models of oral squamous cell carcinoma

Programmed cell death ligand-1 (PD-L1) is a type I transmembrane glycoprotein expressed on antigen-presenting cells and several tumor cells, including melanoma and lung cancer cells. A strong correlation has been reported between PD-L1 expression in tumor cells and negative prognosis in cancer patients. Previously, we established an anti-PD-L1 monoclonal antibody (mAb), L(1)Mab-13 (IgG(1), kappa), by immunizing mice with PD-L1-overexpressing CHO-K1 cells. L(1)Mab-13 specifically reacts with endogenous PD-L1 in lung cancer cell lines in flow cytometry and Western blot applications, and stains a plasma membrane-like pattern in lung cancer tissues via immunohistochemical analysis. In this study, we investigated whether L(1)Mab-13 reacts with oral cancer cell lines and exerts antitumor activities. Because L(1)Mab-13 lacks antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), we first converted the subclass of L(1)Mab-13 from IgG(1) into IgG(2a) (13-mG(2a)), and further produced a defucosylated version (13-mG(2a)-f) using FUT8-deficient ExpiCHO-S (BINDS-09) cells. Defucosylation of 13-mG(2a)-f was confirmed using fucose-binding lectins, such as Aleuria aurantia and Pholiota squarrosa lectins. The dissociation constants (K(D)) for 13-mG(2a)-f in SAS and HSC-2 oral cancer cells were determined via flow cytometry to be 2.8 × 10(−9) M and 4.8 × 10(−9) M, respectively, indicating that 13-mG(2a)-f possesses extremely high binding affinity. In vitro analysis demonstrated that 13-mG(2a)-f showed moderate ADCC and CDC activities against SAS and HSC-2 oral cancer cells. In vivo analysis revealed that 13-mG(2a)-f significantly reduced tumor development in SAS and HSC-2 xenografts in comparison to control mouse IgG, even after injection seven days post-tumor inoculation. Taken together, these data demonstrate that treatment with 13-mG(2a)-f may represent a useful therapy for patients with PD-L1-expressing oral cancers.