Clinical efficacy of anti-programmed death ligand 1 antibody HFC-L1/c4G12 in dogs with malignant tumors: an exploratory study.

Cancer in dogs remains a major challenge in modern veterinary medicine. Immunotherapy using immune checkpoint inhibitors (ICIs) is available for various human tumor types, and recent veterinary clinical studies have shown that ICIs are a promising approach for treating canine cancers. A canine chimeric anti-PD-L1 antibody, c4G12 (HFC-L1), has been investigated for canine cancer immunotherapy; however, its clinical benefits have not been well characterized in tumors other than pulmonary metastatic (stage IV) oral malignant melanoma (OMM). To explore the efficacy and safety of HFC-L1, we conducted a clinical study in dogs with stage I-III OMM or other tumor types (n=12). HFC-L1 treatment at a dose of 5 mg/kg every 2 weeks was well tolerated, and no grade 3 or higher treatment-related adverse events were reported. Among the dogs eligible for response evaluation (n=10), a partial response was observed in one dog with squamous cell carcinoma, resulting in an objective response rate of 10%. In addition, in a dog with ceruminous cell carcinoma, clinical evidence of a tumor response was observed in metastatic lung lesions. Together, these results suggest that the HFC-L1 therapy is applicable for the treatment of various tumor types, although its clinical benefits should be further evaluated in clinical studies involving a larger number of dogs with each tumor type.