Profiling of hepatocellular carcinoma neoantigens reveals immune microenvironment and clonal evolution related patterns.

ABSTRACT

OBJECTIVE: Neoantigens derived from tumor-specific genomic alterations have demonstrated great potential for immunotherapeutic interventions in cancers. However, the comprehensive profile of hepatocellular carcinoma (HCC) neoantigens and their complex interplay with immune microenvironment and tumor evolution have not been fully addressed. METHODS: Here we integrated whole exome sequencing data, transcriptome sequencing data and clinical information of 72 primary HCC patients to characterize the HCC neoantigen profile, and systematically explored its interactions with tumor clonal evolution, driver mutations and immune microenvironments. RESULTS: We observed that higher somatic mutation/neoantigen load was associated with better clinical outcomes and HCC patients could be further divided into two subgroups with distinct prognosis based on their neoantigen expression patterns. HCC subgroup with neoantigen expression probability high (NEP-H) showed more aggressive pathologic features including increased incidence of tumor thrombus (P=0.038), higher recurrence rate (P=0.029), more inclined to lack tumor capsule (P=0.026) and with more microsatellite instability sites (P=0.006). In addition, NEP-H subgroup was also characterized by higher chance to be involved in tumor clonal evolution [odds ratio (OR)=46.7, P<0.001]. Gene set enrichment analysis revealed that upregulation of MYC and its targets could suppress immune responses, leading to elevated neoantigen expression proportion in tumor cells. Furthermore, we discovered an immune escape mechanism that tumors could become more inconspicuous by evolving subclones with less immunogenicity. We observed that smaller clonal mutation clusters with higher immunogenicity in tumor were more likely to involve in clonal evolution. Based on identified neoantigen profiles, we also discovered series of neoantigenic hotspot genes, which could serve as potential actionable targets in future. CONCLUSIONS: Our results revealed the landscape of HCC neoantigens and discovered two clinically relevant subgroups with distinct neoantigen expression patterns, suggesting the neoantigen expression should be fully considered in future immunotherapeutic interventions.