The characteristics of patients
We downloaded RNA-sequencing profiles and clinicopathological results of 395 BLCA patients from the TCGA-BLCA dataset. BLCA patients were randomly divided into the experimental group (131 cases) and the training group (264 cases). For most clinicopathological parameters in the Table 1, we can see that there is no significant difference between the testing set and the training set.
Table1
Differentially expressed genes analysis
We are based on filter conditions p<0.05 and logFCfilter=3, 4669 differentially expressed genes were screened. The results showed that among 4669 differentially expressed genes, 2726 genes were up-regulated and 1943 genes were down-regulated. We selected 350 differentially expressed IRGs according to the list of differentially expressed genes.
Immune signature can predict the prognosis of BLCA patients
We performed a univariate Cox regression analysis to determine the prognostic value of IRGs. To avoid overfitting, we performed LASSO analysis, which revealed six genes in Figure 1a-b as predictors of patient prognosis. Then, we perform univariate Cox proportional risk regression analysis based on the training set and build a predictive model: risk score=(LRP1*1.388) + (OAS1*0.767) + (CGA*1.303) + (PPY*1.719) + (SCG2*1.299) + (ADCYAP1R1*1.644) in Figure 1c. OAS1 was protective factors while five genes were risk factors.
Figure 1. LASSO analysis and forest plot.
- Cross validation.
- Lasso coefficient spectrum.
- Variable Cox model results.
Establish prediction model based on multivariate Cox regression analysis: risk score=(LRP1*0.215)+(OAS1*-0.192)+(CGA*0.193)+(PPY*0.491)+(SCG2*0.144). We used multivariate Cox regression analysis to obtain a risk score for each patient in the training set. We divided patients into high-risk and low-risk groups using a median risk score as a cut-off. In addition, we ranked the risk scores for all patients and outlined their distribution. The patient's risk score and survival time were represented by a dot plot. We used the heatmap to show the expression patterns of the five IRGs in patients with different risk scores.
In order to verify the accuracy of the training group, we verified the data obtained by the training group through the test set. We divided the test set into high-risk and low-risk groups based on patient risk scores. The results showed that, according to the survival analysis, patients with high-risk scores had a low survival rate and those with low-risk scores had a high survival rate. The prognosis was better than that of the high-risk group (p=0.006), as shown in Figure 2a. The AUC in Figure 2b is 0.639. Survival status, risk score, and survival time distribution of patients were represented by scatter plots, as shown in Figure 2c-d. The expression of the five resulting genes was shown by heat map, as shown in Figure 2e.
Figure 2. The six immune-related gene signatures in the test set were validated. A Survival analysis. B ROC curve analysis. C risk score. D survival status. E heat map
We also evaluated the robustness of 6-IRGs signature. In Figure 3a, risk score is a factor in poor prognosis in BLCA patients (p<0.001). The AUC is 0.689, as shown in Figure 3b. The life status, risk score distribution and expression of 17 IRGs of patients are shown in Figure 3c-e.
Figure 3. The markers of 6 immune-related genes were verified in all sets. A Survival analysis. B ROC curve analysis. C risk score. D survival status. E heat map
The 6‑genes immune signature is an independent prognostic factor for BLCA patients
We used univariate Cox regression analysis to evaluate the impact of patients' clinicopathological factors and immune characteristic risk scores on the overall survival time of patients, as shown in Table 2. It is concluded that age, grade, stage and risk score are the risk factors affecting survival time. Multivariate Cox regression analysis showed that 6-IRGs risk score was an independent prognostic factor (HR= 1.14, 95% CI 1.09-1.18;p<0.001).
Table2
The 6‑genes immune signature and relationship between clinical case parameters
This study analyzed the relationship between 6-IRGs features in Figure 4a-f and clinicopathological parameters of patients, including grade, TNM stage, age, lymph node status, tumor size, and distant metastasis. The results showed that 6-IRGs risk scores were significantly higher in patients with TNM stage, age ≥65 years, lymph node metastasis, large tumor size, and distant metastasis.
Figure 4. Relationship between clinicopathological parameters and immune characteristics of patients.
The 6‑IRGs signature and tumor immune microenvironment
According to the CIBERSORT algorithm, we obtained the proportion of 22 immune cells in each BLCA sample. We then compared 22 types of immune cells in the high-risk and low-risk groups. The proportions of T cell follicular helper and dendritic cells activated were significantly higher in the high-risk group in Figure 5a. In 22 types of immune cells, B cells naive, Mast cells resting, Neutrophils, T cells CD4 memory activated were related to better survival time in Figure 5b-e (on the verge of statistical significance, p=0.039, 0.021,0.031, 0.021, respectively).
Figure 5. Risk score, overall survival and tumor-infiltrating immune cells.
The immune signature and TMB
We analyzed the mutational spectrum of each BCLA patient. The results showed that from the mutant spectrum of the training group and the experimental group, the top 20 genes with the most significant mutations were TP53, TTN, KMT2D, etc(Figure 6AB).Subsequently, we observed that Survival probability of TMB high-risk group is higher than low-risk group (p=0.006) in Figure 6C. As shown in Figure 6D, we also calculated the TMB of each sample and found that the TMB was lower in the high risk score group (p=0.033).
Figure 6. AB. BLCA patients with high-risk and low-risk population mutant spectrum.
C. Relationship between survival time and tumor mutation load.
D. Differences in tumor mutation burden between high-risk and low-risk populations.
The immune signature and patients response to ICI treatment
IPS predicts BLCA patients' response to ICIs on a computer through a machine learning-based evaluation scheme. Since we did not find information on ICI treatment in the TCGA BLCA dataset, we used two subtype IPS values (IPS-CTLA-4_pos and IPS_PD-1_pos) as proxies for BCLA patients' response to anti-CTLA-4 and PD-1 treatment. In Figure 7 AB, we can see that the relative probability of response to anti-CTLA-4 and PD-1 therapy in low-risk ratings was higher (p=0.0055). Studies have shown that patients with high immune signature scores are not suitable for ICI treatment, while low scores patients may be more suitable for ICI treatment. In addition, we compared the expression levels of immune checkpoints and their ligands in high-risk and low-risk groups, as shown in Figure 7C. It can be seen that PD-L1 was slightly increased in high-risk score patients, and PD-L1 was significantly increased (p=0.01).
Figure 7. PD-1/PD-L1 and CTLA4 immunotherapy analysis