In the recent study, the researchers used a combination blockade of PD-1 and CXCR4. They analyzed the efficacy of specifically blocking CXCR4 on standard anti–PD-1 immunotherapy in hepatocellular carcinoma models. Most previous studies and clinical trials tested AMD3100, a small-molecule antagonist of CXCR4, which has a short half-life and a complex mechanism of action.