Background: CYT001 (CYTLIMIC Inc.) is a novel cancer vaccine involving artificial intelligence (AI)-designed shared-antigen peptides and optimal combined adjuvants that boost the cancer-immunity cycle. The two multi-HLA reactive peptides heat shock protein 70 (HSP70) and glypican 3 (GPC3) were screened by an AI-based prediction system according to the proteome, mRNA, and histopathology data fromhuman samples. These immunogenic peptides were confirmed to show cross-reactivity to HLA-A 24:02, 02:01, and 02:06. Poly-ICLC (Oncovir Inc.) binds to Toll-like receptor 3 (TLR3) and melanoma differentiation antigen 5 (MDA5) on antigen-presenting cells (APCs)and activates APCs. LAG-3Ig (Immutep Inc.) binds to the major histocompatibility complex (MHC) class II molecules of APCs and activates APCs. Both poly-ICLC and LAG-3Ig synergistically activate antigen-specific CTL reactions as effective combination adjuvants. The present study aims to evaluate the safety and tolerability of CYT001 (mixture of HSP70 peptide [2.0 mg], GPC3 peptide [2.0 mg], poly-ICLC [1.0 mg], and LAG-3Ig [1.4 mg]) in patients with advanced hepatocellular carcinoma (HCC). Methods: This is a single-center, phase 1, open-label, single-arm, investigator-initiated clinical trial of CYT001 for advanced HCC patients with no eligible standard systemic therapy, Child–Pugh A liver disease, and HLA-A 24:02, 02:01, or 02:06. Enrolled patients will receive CYT001 as a subcutaneous injection on days 1, 8, 15, and 21 in the 1st and 2nd cycles, days 1 and 15 in the 3rd and 4th cycles, and day 1 in the 5th cycle or later of 28-day cycles. The primary endpoint is dose-limiting toxicity, and the secondary endpoints are safety and the response rate. The transition of the CTL reactions of both the HSP70 and GPC3 peptides will be evaluated using blood samples of the subjects. Exploratory analyses include investigation of candidate biomarkers for treatment efficacy using liver tumor biopsy samples (baseline and after the 1st cycle) and blood samples (baseline and every days of administration). Clinical trial information: jRCT2031190072.