Serum Concentration of CD137 and Tumor Infiltration by M1 Macrophages Predict the Response to Sintilimab plus Bevacizumab Biosimilar in Advanced Hepatocellular Carcinoma Patients

Abstract

Purpose: This study aimed to investigate the biomarkers of sintilimab (anti-PD-1) plus IBI305 (a bevacizumab biosimilar) in advanced hepatocellular carcinoma (HCC), as well as their safety and efficacy. Patients and Methods: A total of 50 patients with advanced HCC received sintilimab (200 mg) plus IBI305 (7.5 or 15 mg/kg), treated every 3 weeks in a phase Ib clinical study. We performed baseline serum cytokine analysis using bead-basedmultiplex immunoassay and multiplex immunofluorescence on tissue specimens to discover novel biomarkers of response to VEGF/PD-1 combination therapy in HCC. Results: The overall response rate was 34.0% (17/50). The median progression-free survival (PFS) and the median overall survival were 10.5 and 20.2 months, respectively. The incidence of grade 3 to 5 adverse events was lower in the 7.5 mg/kg (13.8%) than in the 15 mg/kg (28.6%) dose groups. Biomarker analysis showed that the serum CD137 concentration was significantly higher in patients with clinical benefit (CB) than in those without CB (median, 32.8 pg/mL vs. 19.8 pg/mL, P=0.034). A markedly longer PFS was observed in patients with high CD137 concentrations compared with those with low concentrations (median, 14.2 months vs. 4.1 months, P = 0.001). The higher density of M1 macrophages (CD68+CD163-) in the stroma was also associated with higher efficacy (P = 0.033) and a longer PFS (P = 0.024). Conclusions: Sintilimab plus IBI305 was well tolerated and was effective therapy for advanced HCC. Both serum concentrations of CD137 and tumor infiltration of M1 macrophages may serve as potential predictive biomarkers.