Screening of candidate antigens in HBV related-HCC. The aberrantly expressed genes were first explored, where 5391 overexpressed genes that likely encode tumor-associated antigens were screened to identify potent HBV related-HCC antigens (Fig. 1A). Subsequently, we identified 5663 genes that mutated in HBV related-HCC and the top 20 mutated genes were showed in Fig. 1B. Of note, TP53, CTNNB1, and TTN were the most frequently mutated genes (Fig. 1B). Combining the expression and mutation data of HBV related-HCC, 720 genes that were highly expressed and mutated in HBV related-HCC were identified as potential candidate antigens (Fig. 1C).
To explore the best candidates for mRNA vaccine targets from the aforementioned overexpressed and mutated genes, we further found 96 genes were significantly associated with overall survival (OS), of which 23 genes significantly correlated with the relapse free survival (RFS) (Fig. 1D and 1E). In view of the critical role of antigen-presenting cells (APCs) in the function of mRNA vaccines, we analyzed the correlation between these 23 genes with APCs using TIMER algorithm. We found that the expression levels of EPS8L3, TCOF1, EZH2 and NOP56 were positively associated with macrophages, dendritic cells (DCs), and B cells (Fig. 1F and 1G), and could act as potential tumor antigens that can be processed and presented by the APCs. More importantly, the survival analysis demonstrated that 4 gene candidates were also associated with poor prognosis (Fig. 1H), suggesting the critical role for HBV related-HCC development and progression. Taken together, EPS8L3, TCOF1, EZH2 and NOP56 were identified as potential candidates for HBV related-HCC with potential immune provocative effects and can be processed and presented by APCs to induce anti-tumor immune response.
Identifying specific immune subtypes. Immune related genes might mirror the distinct tumor immune microenvironments (TIME), and thus helpful to identify suitable patients for mRNA vaccination. A total of 1286 immune related gene profiles of HBV related-HCC were extracted from ICGC and 121 prognosis genes were identified to construct consensus clustering. Two immune phenotypes (IS1 and IS2) were obtained according the maximum variance across the groups and minimum variance within the group (Fig. 2A). The principal component analysis (PCA) further validated that these two subtypes could be well distinguished (Fig. 2B). IS2 had the poor prognosis while IS1 was associated with better prognosis (Fig. 2E). Similarly, in the TCGA cohort, IS2 had a worse survival probability than IS1 (Fig. 2C, 2D, and 2F), indicating the stability and reproducibility of the results. Taken together, the immunotyping associated with the clinical outcomes of HBV induced-HCC, and patients with IS2 tumors could have worse prognoses.
Association between immune phenotypes and mutational status. As tumor mutational burden (TMB) is closely associated with immunotherapeutic efficacy, including mRNA vaccine 15, we assessed the TMB and mutation number in TCGA between distinct immune phenotypes. As shown in Fig. 2G, IS2 showed significantly higher TMB compared to IS1. Consistently, IS2 also had a significantly higher mutation number than IS1 (Fig. 2H). The waterfall diagrams of these two immune phenotypes were showed in Fig. 2I and 2J. Comparing with IS1 (88.46%), IS2 had higher mutation rates (96.08%). These results demonstrated that immune phenotypes can predict mutational status in HBV related-HCC, with IS2 having higher TMB and mutated genes than IS1, and that patients with IS2 may be more suitable for the mRNA vaccine.
Cellular and molecular characteristics of different immune phenotypes. Since the effectiveness of mRNA vaccine was influenced by tumor immune status, previously reported 28 immune infiltrating cells were determined by ssGSEA across TCGA and ICGC cohorts. The results showed that the immune cell composition displayed significantly different in the two subtypes. As shown in Fig. 3A and 3B, 26 immune cells including central memory CD8 T cells, central memory CD4 T cells, effector memory CD8 T cells, effector memory CD4 T cells, monocytes, neutrophil, CD56bright natural killer, regulatory T cell, and myeloid-derived suppressor cells (MDSC) were significantly higher in IS1 compared to IS2 in TCGA cohort. Therefore, IS1 is immune “hot” and immunosuppressive phenotypes, while IS2 is an immune “cold” phenotype. Meanwhile, ICGC cohort show similar trends (Fig. 3C and 3D). Immune infiltration in patients with IS2 (immune “cold” phenotype) might be induced by mRNA vaccine. In order to demonstrate the reliability of this immunotyping, we further determined the relationship between these two immune subtypes investigated in our study and previously reported six immune categories (C1: Wound healing; C2: IFN-γ; dominant; C3: Inflammatory; C4: Lymphocyte depleted; C5: Immunologically quiet; C6: TGF-β dominant) 16. As exhibited in Fig. 3E, the C3 subtype is less frequent in IS2. Conversely, we recorded a wider representation of the C4 subtype in the IS2 group. Interestingly, C3 and C4 were associated with better and inferior prognoses respectively. These findings confirm the prognostic value of our immune subtypes. Additionally, C4 was mainly clustered into IS2, confirming that IS2 is immunologically cold. These findings further confirm the efficacy and prognostic value of our immune subtypes.
Moreover, we compared the 56 previously defined molecular signatures between the immune subtypes and identified 20 molecular signatures were significantly different (Fig. 3F). As shown in Fig. 3F, IS1 had the higher scores for lymphocyte infiltration, leukocyte fraction, macrophage regulation, dendritic cells, Th17 cells, TCR richness, TCR shannon, stromal fraction, and TGF-β response. Additionally, in both TCGA and ICGC cohorts, immunosuppressive checkpoint BTLA, CD200, and PDCD1LG2 were significantly higher in IS1 than IS2 (Supplementary Fig. 1). IS1 is an immune-hot phenotype and immunosuppressive microenvironment, while IS2 is an immune-cold phenotype, consistent with the cellular signature results. Therefore, mRNA vaccine used in IS2 might turn “cold” tumor to “hot” by stimulate the immune response.
Immune landscape of HBV related-HCC. By using the immune gene expression profiles of individual patients, immune landscape of HBV related-HCC was constructed to visualize the immune distribution. The two immune subtypes are inversely distributed in the immune landscape (Fig. 4A and 4B). As shown in Fig. 4C, principal component 2 (PC2, vertical axis) was most negative correlated with central memory CD4 T cells, effector memory CD4 T cells, gamma delta T, immature dendritic cell, and type 2 T helper cell, and most positively correlated with activated CD8 T cell. On the contrary, principal component 1 (PC1, vertical axis) was most negatively correlated with activated CD4 T cell and most positively correlated with eosinophil and natural killer cell (Fig. 4C). Additionally, the same subtype also displayed opposing distribution, suggesting significant intra-cluster heterogeneity within the subtypes (Fig. 4D). IS2 were then divided into three subsets based on the location of immune landscape. The enrichment scores of several immune cells were significantly low in IS2A and IS2B than IS2C (Fig. 4F). Thus, the mRNA vaccine might be relatively more effective in IS2A and IS2B. Survival analysis revealed that the OS was significantly different among the five immune subtypes, with IS1A and IS1B showing better prognosis and IS2A and IS2B showing worse prognosis (Fig. 4E). Taken together, immunophenotype-based immune landscape can accurately identify the immune components and predict the prognosis of each HBV related HCC patient, which is conducive to the selection of personalized mRNA vaccine treatment regimen.
Construction and evaluation of predictors for suitable patients. Firstly, differential gene expressions were analyzed between IS1 and IS2 (Supplementary Fig. 2). Then, by using machine learning methods, the most representative genes of IS2 were chosen to identify immune “cold” phenotypes. Through binomial deviance and Boruta analyses, 24 genes and 66 genes were identified respectively (Fig. 5A-C). Thirteen genes shared by the two methods were identified as specific features of IS1 and IS2 tumors (Fig. 5D). The 13 genes predictor genes had an AUC of 1 in the ICGC cohort and 0.828 in the TCGA cohort, respectively. Taken together, the gene-set of 13 predictors (XAF1, TRIM22, LYRM4, SERPING1, SKA3, CDK4, SLC35B2, RPSA, CHKA, DTYMK, FOXM1, NLE1, and POLR1D) has an excellent performance in distinguish of HBV related-HCC suitable for mRNA vaccine.