Blocking of PD-1/PD-L1 Promotes Hepatic Regeneration in Small-for-Size Liver Following Partial Resection Through Macrophage Polarization

Background: Small-for-size syndrome following liver surgery is characterized with compromised liver regeneration. Liver macrophage is important to initiate liver regeneration, and modulation of immune microenvironment through macrophage may accelerate liver regeneration. However, the role of macrophage in liver regeneration is still debated. Methods: Serum PD-L1 was detected after major hepatectomy and minor hepatectomy in humans and rats. Liver regeneration in rats was marked with liver-to-body weight ratio and kinetic growth rate, Ki67 and PCNA, and macrophage polarization was accessed by iNOS, CD163 expression by IHC and iNOS/CD163 ratio. Rat hepatocyte BRL or human hepatocyte LO2, were co-cultured with rat bone marrow derived macrophages or human macrophages THP-1. BMS-1 and Nivolumab were applied to block PD-1/PD-L1 in vitro and in vivo. Findings: Serum PD-L1 levels showed significantly higher after major hepatectomy than these of minor resection in both humans and rats; compromised liver regeneration after extended hepatectomy in rats was associated with intrahepatic and serum PD-L1 upregulation and M2 macrophage polarization. M1 macrophages increased proliferation of hepatocytes through IL-6, and M2 macrophages decreased hepatocyte proliferation; blocking PD-1/PD-L1 reversed the effect of M2 macrophages on in vitro hepatocytes survival, and promoted liver growth in rats through M1 macrophage polarization. Interpretation: Comprised hepatic regeneration following extended hepatectomy is characterized with M2 macrophage polarization and upregulated PD-L1 expression; blocking PD-1/PD-L1 induces M1 macrophage polarization and boosts liver regeneration. Funding Statement: The National Natural Science Foundation of China (No.81971881 and U1604282) and The Medical Science and Technology Program of Henan Province, China (No. SBGJ2018023). Declaration of Interests: The authors declare that there is no conflict of interest regarding the authorship and publication of this paper. All the authors have no interest with any business company. Ethics Approval Statement: The human study protocol was approved by the Research Committee of the Affiliated Hospital of Zhengzhou University (registration number: 2019-KY-21) and conformed to the ethical guidelines of the 1975 Declaration of Helsinki. All the patients were enrolled into the Affiliated Hospital of Zhengzhou University - Liver Surgery and Transplant Protocol and were given informed consent to use the tissue samples for experimental purposes. Experimental protocol was approved by the local ethics committee for animal experiments of Zhengzhou University (registration number: 2019-KY-183), and was carried out in accordance with the ARRIVE guideline.