BMP9‐induced vascular normalisation improves the efficacy of immunotherapy against hepatitis B virus‐associated hepatocellular carcinoma

BACKGROUND: In the past decade, the field of tumour immunotherapy has made a great progress. However, the efficacy of immune checkpoint blocking (ICB) in the treatment of hepatocellular carcinoma (HCC) remains limited. Cytotoxic lymphocyte trafficking into tumours is critical for the success of ICB. Therefore, additional strategies that increase cytotoxic lymphocyte trafficking into tumours are urgently needed to improve patient immune responses. METHODS: Paired adjacent tissue and cancerous lesions with HBV‐associated HCC were subjected to RNA‐seq analysis. Bone morphogenetic protein (BMP9), which reflects vessel normalisation, was identified through Cytoscape software, clinical specimens and Gene Expression Omnibus (GEO) datasets for HCC. The functional effects and mechanism of BMP9 on the tumour vasculature were evaluated in cells and animals. An ultrasound‐targeted microbubble destruction (UTMD)‐mediated BMP9 delivery strategy was used to normalise the vasculature and evaluate therapeutic efficacy mediated by cytotoxic lymphocytes (NK cells) in combination with a PD‐L1 antibody in human cancer xenografts of immune‐deficient mice. RESULTS: We discovered that hepatitis B virus (HBV) infection‐induced downregulation of BMP9 expression correlated with a poor prognosis and pathological vascular abnormalities in patients with HCC. BMP9 overexpression in HBV‐infected HCC cells promoted intra‐tumoural cytotoxic lymphocyte infiltration via vascular normalisation by inhibiting the Rho‐ROCK‐myosin light chain (MLC) signalling cascade, resulting in enhanced efficacy of immunotherapy. Furthermore, UTMD‐mediated BMP9 delivery restored the anti‐tumour function of cytotoxic lymphocytes (NK cells) and showed therapeutic efficacy in combination with a PD‐L1 antibody in human cancer xenografts of immune‐deficient mice. CONCLUSIONS: HBV‐induced BMP9 downregulation causes vascular abnormalities that inhibit intra‐tumoural cytotoxic lymphocyte infiltration, providing a rationale for developing and combining immunotherapy with BMP9‐based therapy to treat HBV‐associated HCC.