BC is one of the most common and aggressive malignant diseases. Due to the unique urinary-storage function of the bladder, intravesical instillation was used to treat NMIBC in a BC patient in 1976, thus establishing bacillus Calmette-Guérin (BCG) instillation as the gold standard adjunctive therapy for NMIBC, and opening a new chapter in the immunotherapy of BC. BCG instillation and anti-programmed cell death protein 1 (PD-1)/PD-L1 immune-checkpoint blocking have been used successfully to treat early and late BC via different immunotherapeutic approaches , thus providing a good model for studying the mechanism of tumor immune response and improving the efficiency of immunotherapy.
The development of high-throughput sequencing and biomolecular technology has facilitated breakthroughs in immunotherapy, making it a promising therapeutic approach for cancers. However, only 25% of advanced/metastatic BCs respond to anti-PD-1/PD-L1 ICIs , indicating the need to develop new immunotherapy approaches and predict new biomarkers to fully explore the curative potential of immunotherapy in patients with BC.
IFN-γ stimulates the immune editing of tumor cells and modulates the tumor immune-resistance mechanism, thus promoting tumor progression. Immune activation of IFN-γ in tumor cells can promote lymphocyte migration and inhibit angiogenesis, mainly due to the influence of tumor cells, monocytes, endothelial cells, and fibroblasts, to induce the expression of MHC and secrete CXCL9, CXCL10, and CXCL11 [19–21]. In order to design better therapeutic targets, differentiate immunotherapy populations, and balance the antitumor and immune-escape abilities of BC, we therefore established an IFN-γ signature containing five genes (RIPK2, RBCK1, PTPN6, ITGB7, LATS2) to assess the prognosis of BC patients.
We explored the efficacy of this signature by combining the five genes and examining the survival and ROC curves, which showed that the IFN-γ signature had good prognostic performance (AUC = 0.702). We then established a nomogram using four independent factors (age, grade, stage, risk) that were most significantly related to the prognosis of BC, which confirmed the good predictive effect of the IFN-γ signature.
The IFN-γ signature-related genes play an important role in immunobiological pathways. For example, T cells are the key cells in cellular immunity , with important roles in immune tolerance and immune homeostasis. High infiltration by Treg cells has been associated with poor survival in various types of cancer . M2 macrophages are closely related to the growth and survival of various tumor cells [24, 25], and exhausted T cells in the TME are major targets of immunotherapies in BC . The current results showed that M0 and M2 macrophages and resting mast cells were positively associated with the risk score, suggesting that M0 and M2 macrophages were significantly up-regulated in the high-risk group, while CD8 T cells, CD4 memory resting T cells, CD4 memory activated T cells, follicular helper T cells, and resting NK cells were negatively correlated with risk scores. In addition, GO enrichment analysis showed that, in the BP category, T cell activation, regulation of T cell activation, regulation of T cell activation and presentation of exogenous peptide antigen via MHC class II, antigen processing and presentation of peptide antigen via MHC class II, and antigen processing and presentation of peptide or polysaccharide antigen via MHC class II were related to the IFN-γ-related signature, while the signature was highly enriched in MHC class II protein complex in the CC category. These results were consistent with the analysis of the IFN signature, and further confirmed the effectiveness of the signature and its risk profile for predicting tumor-infiltrating immune cells and guiding the selection of clinical immunotherapies.
Integrin β7 (ITGB7) is associated with immune cell infiltration. It is expressed on the surface of leukocytes and plays an important role in the homing of immune cells to intestinal-related lymphoid tissues and facilitating the retention of lymphocytes in the gut epithelium. The role of ITGB7 expression in promoting tumor progression has also been reported in different types of tumors, such as colorectal cancer, fibrosarcoma, multiple myeloma, pancreatic cancer, and cervical cancer [26–30]. A study of patients with colorectal cancer found a significant reduction in the number of β7 + cells in the tumor tissue compared with the adjacent normal tissue. β7 expression was decreased in tumor-derived CD8 + T cells compared with normal tissue-derived CD8 + T cells. In addition, analysis of bulk RNA expression data from a public platform showed that high ITGB7 expression was associated with longer patient survival, higher cytotoxic immune cell infiltration, lower somatic copy number alterations, decreased mutation frequencies of APC and TP53, and a better immunotherapy response. ITGB7 deficiency reduced the infiltration of activated CD8 + T cells, effector memory CD8 + T cells, IFNγ + CD8 + T cells, IFNγ + NK cells, and CD103 + dendritic cells, and thus accelerated the development and progression of colorectal cancer in Apcmin/+ spontaneous and MC38 orthotopic models. ITGB7 downregulation also inhibited focal adhesion kinase and Src phosphorylation in a cell co-culture model of multiple myeloma . In pancreatic cancer, ITGB7 transcription was shown to be regulated in a reactive oxygen species-related nuclear factor erythroid 2-related factor 2-dependent manner, and ITGB7 was inhibited by N-acetyl-L-cysteine in pancreatic cancer cells, thus accelerating the progression of pancreatic cancer. All the above evidence suggests that ITGB7 may inhibit cancer pathogenesis via maintaining antitumor immunity.
Protein tyrosine phosphatase nonreceptor type 6 (PTPN6) is a nonreceptor protein tyrosine phosphatase, which mainly acts as a tumor suppressor through phosphorylation of carcinogenic kinases. PTPN6 was shown to be associated with the prognosis and progression of gastric cancer and hepatocellular carcinoma[33, 34], and can be used as a prognostic factor in peripheral T cell lymphomas. Recent studies suggested that PTPN6 was overexpressed in BC tissues and was significantly correlated with grade, T stage, N stage, and low PTPN6 expression was significantly associated with poorer OS in BC patients. Based on analysis of TCGA database, PTPN6 may be a new prognostic biomarker of BC . LATS2 encodes a serine/threonine protein kinase and has been reported to be a member of the LATS tumor-suppressor gene family involved in the hippocampus signaling pathway. The above results confirmed that the genes included in our signature were significantly correlated with tumor development and prognosis. In addition, the current drug sensitivity results confirmed the correlation between these genes and antineoplastic drug sensitivity.
In this study, we determined the prognostic value of an IFN-γ signature in BC based on TCGA database. We also discussed the relationship between this IFN-γ signature and immune cell infiltration in the BC microenvironment. However, the study had several limitations. First, the sample size of TCGA database was limited. Second, this was a retrospective study and lacked experimental verification of the findings. Further clinical trials are therefore needed to confirm our observations, and to clarify the mechanism responsible for the prognostic value of the IFN-γ-related signature in BC.