Previous studies have revealed that TNBC is critically related to the expression of PD-L1 in the tumor microenvironment (TME). Furthermore, accumulating data have shown that PD-1/PD-L1 inhibitors are able to induce durable clinical responses in some TNBC patients29. The KEYNOTE-355 trial suggested that pembrolizumab (an anti-PD-1 antibody)-chemotherapy showed a significant and clinically meaningful improvement in progression-free survival (PFS) versus placebo-chemotherapy among patients with mTNBC30. The IMpassion130 trial revealed that atezolizumab (an anti-PD-L1 antibody) plus nab-paclitaxel significantly improved progression-free survival (PFS) and median OS in patients with mTNBC, especially for PD-L1-positive patients31. However, the IMpassion 131 trial revealed that the combination of atezolizumab and paclitaxel did not improve PFS or OS compared with paclitaxel alone, suggesting that the specific mechanisms of anti-PD-1/PD-L1 immunotherapies for mTNBC still need to be further explored31, 32.
In the present study, we used the cyclic single pairing method33 and 0 or 1 matrix to verify the signatures of lncRNA pairs to predict the prognosis of TNBC. Therefore, only pairs with high or low expression need to be detected without examining the specific expression value of each lncRNA. Ten pairs with prognostic values were identified by univariate Cox regression analysis. Some lncRNAs of the 10 pairs have been reported to be critically involved in tumorigenesis, such as USP30-AS134–36, HLA-DQB1-AS137, 38, and MIR155HG39–41. Based on the LASSO regression analysis, we constructed a risk assessment model composed of 3 DEirlncRNA pairs (USP30-AS1|SERPINB9P1, AL731567.1|AC004585.1, AC110995.1|AC007991.2). We further plotted ROC curves for 2, 3 and 5 years, and the model exhibited remarkable prognostic validity. The patients were divided into a high-risk and a low-risk group according to the identified cut-off point. The results of the survival analysis showed that the survival probability of the high-risk group was lower than that of the low-risk group. The results of univariate and multivariate Cox proportional hazard regression analyses showed that clinical stage and risk score were independent predictive factors for TNBC. In addition, age and T stage were significantly related to the risk score. The risk score increased as age and T stage increased. The highest increase in the risk score was found in patients with the T4 stage, which was much higher compared to patients with the T1-T3 stage. The results of the T1, T2 and T3 stages exhibited no significant difference, which may result from the limited samples of patients with low stages.
Immune checkpoint molecules have been identified as key modulators of the immune response, and their expression is closely related to the level of tumor-infiltrating immune cells, response to immunotherapy, and survival of patients42. We evaluated the immune infiltration status among the samples using XCELL, TIMER, QUANTISEQ, MCPCOUNTER, EPIC, CIBERSORT-ABS, and CIBERSORT. We further investigated the relationship between the risk score and ICI-related biomarkers in the TCGA database. The results revealed that low risk scores were positively related to high expression of PD-1, PD-L1, PD-L2, CTLA4, TIM3, and IDO1 (p < 0.05). Despite progress in understanding the underlying tumor biology, clinical outcomes for TNBC unfortunately remain poor, and chemotherapy is still the mainstay of treatment for TNBC43–46. Thus, we evaluated the association of risk values with the IC50 of some commonly used chemotherapy agents. We further found that this risk model may be beneficial in helping physicians choose more effective chemotherapy agents.
We identified the lncRNA USP30-AS1 based on the StarBase and MEM databases. USP30-AS1 is an antisense lncRNA that plays a critical role in regulating gene expression at the replication, transcription, and translation levels47. The function of antisense lncRNAs is not related to the position of encoding genes but to the coexpressed protein-encoding genes. We further predicted potential target genes of USP30-AS1 and discovered that genes encoding PD-1 (PDCD1) and PD-L1 (CD274) were also included, and the expression levels of PD-1 and PD-L1 were positively correlated with USP30-AS1 expression. The results indicated that USP30-AS1 may be involved in the regulation of PD-1 expression. Furthermore, the predicted target genes were used to perform GO analysis and KEGG pathway analysis. A KEGG pathway, cytokine‒cytokine receptor interaction, was significantly enriched by the predicted target genes. In addition, most genes in this pathway were positively regulated by USP30-AS1, suggesting that USP30-AS1 was closely associated with the tumor immune response. Therefore, we speculate that USP30-AS1 may serve as a potential target molecule to affect the efficacy of immunotherapy, and the potential mechanism is that it activates the transcription and upregulates the expression of PD-L1 to promote the immune escape of patients with TNBC.
However, our study has some limitations. First, our immune-related prognostic features of lncRNA pairs were developed through retrospective studies. Thus, prospective cohort studies are needed to further validate our results. Second, although functional annotation has revealed that lncRNA USP30-AS1 can regulate the expression of PD-L1, in vivo and in vitro experiments are further needed to explore the specific mechanisms.