A first-in-human study to evaluate a personalized neoantigen-based mRNA-loaded dendritic cell vaccine, in combination with ablation, in patients with hepatocellular carcinoma.

e14513 Background: Local recurrence of Hepatocellular Carcinoma (HCC) following potentially curative resection or ablation is an inevitable risk. T cells recognizing neoantigens are present in most cancers including HCC and offer a specific and highly immunogenic target for the personalized vaccination as an adjuvant therapy. The purpose of this study is to evaluate the safety and T cell immune response of a personalized neoantigen-based mRNA loaded dendritic cell (DC) vaccine (LK101) combined with regular ablation in patients with HCC (NCT03674073). Methods: Each patient’s fresh tumor biopsy and matched peripheral blood sample were subjected to whole-exome sequencing and RNA-sequencing. Following determination of somatic mutations and gene expression, up to 30 in silico–predicted potential neoantigens were selected with bioinformatic tool. DCs were generated from the monocytes enriched by leukapheresis, followed by transfection with neoantigen-encoding mRNA through electroporation. In total, 7 doses of LK101 were administered at 1.5×10 7 cells/injection intradermally with 4-dose priming weekly and 3 boosters in 4-week intervals. The primary endpoint of the clinical study was safety, and key secondary endpoints were immunogenicity, overall survival and recurrence. 24 HCC patients at HKLC stage IIa were enrolled 1:1 to ablation control arm and ablation combined with DC (LK101) arm. Results: The study was completed, patients were followed up for a median of 48.4 months and 38.8 months in vaccination arm and control arm. All of adverse events were Grade 1-2. Most frequent treatment-related adverse events are injection site reactions, inclusive of local pain (63.6%), itch (27.3%) and others (27.3%), such as redness and edema. 3 patients in ablation control arm died, whereas all vaccinated patients survived. The 1-year and 2-year recurrence rates in vaccination arm compared with control arm are 18.2% vs. 33.3% and 36.4% vs. 51.4%, respectively. LK101 induced neoantigen-specific T cell responses were investigated by ELISpot analysis. Overall, all patients elicited at least one measurable response. Immune responses to 60-90% of neoantigen peptides were seen post vaccination across patients. Both preexisting immune response and De Novo immune response that targeted neoantigens were observed in vaccinated patients. Moreover, both CD4 and CD8 positive effector memory T cells showed the trend of increase, and PD-1 positive T cells reduced in peripheral blood of patients after vaccination. Conclusions: Combination of LK101 with ablation therapy has a manageable safety profile, showing the evidence of immune activation and potential of prolonged survival. In combination with regular ablation, neoantigen based mRNA loaded DC vaccine is a promising immunotherapy for the treatment of HCC. Clinical trial information: NCT03674073 .