Screening of differential immune-related genes with prognostic value
Among 80 patients with EGFR-mutated LUAD, the immune score could be calculated by immunocyte-related genes. Significant difference in immune score was observed between the high immune score group (n=26) and low immune score group (n=54) (Figure 1A, p<0.001). Above the 80 patients with EGFR-mutated LUAD, 79 patients had complete clinical information (Table 1). Based on the mRNA expression profiles of 79 patients, the differentially expressed genes (1769) were screened between the high and low immune score group, of which 1050 genes were up-regulated and 719 genes were down-regulated (Figure 1B). Using univariate Cox regression, 396 genes with significant prognostic value were eventually obtained.
Table 1. The information of LUAD with EGFR positive status.
Clinical factors
|
The number of patients (n=79)
|
Sex
|
|
Male
|
33
|
Female
|
46
|
AJCC stage
|
|
Stage I
|
32
|
Stage II
|
22
|
Stage III
|
18
|
Stage IV
|
6
|
Survival status
|
|
Alive
|
54
|
Dead
|
25
|
Age (median,year)
|
40-86 (70)
|
Overall Survival (median,month)
|
0.59-101.64 (18.17)
|
Comparison of TMB between the high and low immune score group
According to the TMB data of 80 patients, we assesed the TMB score of each patient, and compared the tumor mutation profile between the high and low immune score group. The result showed that TMB score of the low immune score group was higher than that of the high immune score group, in spite of the difference is not statistically significant (p=0.07). In Figure 1C, differences could be found in these mutant genes between the high and low immune score group, such as BOCRL1 (24% vs 6%), leucine rich repeat containing 7 (LRRC7) (19% vs 6%), family with sequence similarity 47 member C (FAM47C) (15% vs 2%), olfactory receptor family 5 subfamily F member 1 (OR5F1) (15% vs 6%), CUB and Sushi multiple domains 3 (CSMD3) (12% vs 24%), etc.
Enrichment analysis of differential immune-related genes with prognostic value
To explore the potential functions of 396 genes with prognostic value, we performed GO function and KEGG pathway enrichment analysis. The GO terminology for biological processes, molecular functions and cellular component terms were listed (Figure 2A, 2B and 2C). Top GO terms were significantly enriched in biological functions related to T cell differentiation, immune response, cell cycle and cell proliferation. In addition, pathway enrichment analysis of KEGG were mainly Cell cycle, Cell adhesion molecules and Cytokine-cytokine receptor interaction which were also related to the immune response(Figure 2D).
Identification gene signature and construction risk model
Among the 396 differential prognostic genes, the LASSO Cox regression model was applied to screen the most prognostic genes. We used a random sampling method of 10-cross validation to identify a three-gene signature (BTLA, BUB1B and CENPE), which was closely related to immunosuppressive TME. Importantly, we found that the signature constructed by three genes was the most suitable prognostic model by confirmation and verification. Then, 80 patients were divided into the high risk group and low risk group according to the median risk score (Materials and Methods).
Evaluating the prognostic value of the gene signature
To further evaluate the prognostic value of the gene signature, Kaplan–Meier survival curves showed that patients in the high risk group had shorter overall survival (OS) than the low risk group (Figure 3A, p=0.0053). The risk score distribution, number of patients, distribution of patient survival time, and cumulative distribution of survival samples were also shown (Figure 3B-3E). Heat map of three gene expressions showed there were differences in the expression of three genes between high risk group and low risk group (Figure 3F).
Validating the validity and reliability of the gene signature
Four external datasets (GSE31210, GSE26939, GSE72094, and GSE11969), including 212 EGFR-mutated LUAD with clinical information, were used as a validating set. According to the median risk score of the three genes (BTLA, BUB1B and CENPE), 212 patients were divided into the high and low risk group (Materials and Methods). Figure 4A was a heat map of three gene expressions. The ROC curve was used to assess the prognostic value of the gene signature. As shown in Figure 4B, it can be found that the AUC of the gene signature at 12 months and 36 months was 0.8 and 0.7, respectively. Kaplan–Meier survival curves showed that patients of high risk group had shorter OS than these in the low risk group (Figure 4C, p =0.035). The above results indicated that our gene signature was feasible.
Estimating the abundance of immune cells infiltration
CIBERSORT was used to estimate the abundance of immune cells infiltration. The abundance of 24 types immune cells infiltration were normalized relative proportions in the high and low risk group (Figure 5A and 5B). The results showed that the immune activity of B cells and macrophages were higher in the low-risk group, in contrast the immune activity of NK cells and T cells were higher in the high-risk group.