In the current study, we demonstrated that a prognostic model constructed with 27 immune-related gene pairs from 43 independent immune-related genes predicted OS and DFS in breast cancer. Many of the identified immune-related genes have been previously investigated in breast cancer research. The application of gene expression profiles to construct prognostic models has been studied; however, owing to the heterogeneity of organisms and differences in technology platforms, the accuracy of the analysis method requires verification23. Relative sequencing and pairing of genes to preprocess an immune-related gene pairs prognostic model has provided reliable results for many tumors24,25.
Breast cancer stem-like cells were rendered as sensitive to γδTc cytotoxicity as non-stem-like cells by preventing increased MICA shedding via ADAM inhibitor GW280264X26. This approach, using MICA shedding to enhance γδTc targeting of cancer types, was considered an immune evasion mechanism26. Genetic knockdown and pharmacological blockade of Rac1/Rac2 upregulated claudin-1 and prohibited the strong metastatic potential of TNBC characterized by a mesenchymal-like phenotype27. RNF144A is known to be downregulated in a subset of primary breast tumors and suppresses breast cancer growth and metastasis through, at least in part, targeting HSPA2 for ubiquitination and degradation in a ubiquitin ligase activity-dependent manner28. HSPA2 has been shown to be upregulated in various types of human cancers and promotes cancer cell growth, angiogenesis, migration, invasion, and metastasis through distinct mechanisms28. PPRP4 via NEDD4 downregulates ROBO1, which is implicated as a tumor suppressor in various cancers, resulting in activation of SRC and FAK, thus promoting breast cancer metastasis29. PLXNB3 is reportedly overexpressed in breast cancer tissues30, and CD74 is associated with poor breast cancer prognosis31. MIF can activate NF-kB through CD74 to control the dynamics and stability of mitochondria, thus promoting carcinogenesis by preventing apoptosis32. CD74 expression in the membrane and cytoplasm of breast cancer cells was found to be higher than that in normal breast tissue. Downregulation of CD74 was shown to decrease the invasion and migration of MDA-MB-231 breast cancer cells33. Finally, in ER + breast cancer cells, interaction between CRABP2 and LATS1 promotes LATS1 ubiquitination and inactivates the Hippo signaling pathway, thus promoting invasion and metastasis of ER + breast cancer34.
Other identified immune-related genes in the current study have been investigated in relation to immunotherapy for other cancers. As an agonist of Toll-like receptors TLR7 and TLR8, R848 is the driving factor of the M1 anti-tumor macrophage phenotype in vitro. R848-loaded nanoparticles effectively delivered drugs to tumor-associated macrophages in vivo35. A CCR1 antagonist has been shown to reduce T cell transportation to the omentum and liver in obesity-related cancer36. CXCL14 inhibits human papillomavirus-associated head and neck cancer by restoring expression of MHC-I in tumor cells and promoting antigen-specific CD8 + T cell response37. IL18 can inhibit CD4 + CD25 + Foxp3 + T cells through accumulation of pre-mNK cells and memory-type CD8 + T cells and enhanced the therapeutic effects of ICIs on the peritoneal dissemination of malignant tumors or melanoma metastasis via tail vein injection38. The CXCL14 / ACKR2 pathway of autocrine fibroblasts is a clinically relevant stimulator for epithelial-mesenchymal transition (EMT), tumor cell invasion, and metastasis. ACKR2 is a newly identified mediator of CXCL14 function, which is a potential pathway related to drug targets39. Taken together, these studies support that immune-related genes identified in the current study play important roles in the occurrence and development of tumors through immune cells. Immune-related genes have thus gradually become targets of immunotherapy or the means to enhance the effects of immunotherapy. However, some of the identified immune-related genes, such as APOBEC3G, PLXNB1, and C3AR1, have not been previously studied in breast cancer and warrant further exploration.
Additionally, the study findings revealed that M2 and M0 macrophages were highly expressed in high-risk breast cancer patients, while CD8 T cells and naïve B cells were highly expressed in low-risk breast cancer patients. M2 and M0 macrophages are associated with poor prognosis in colon cancer22. Some studies have demonstrated that M2 macrophages might impart outgrowth and M1 macrophages may contribute to dormancy behaviors in metastatic breast cancer cells. Research has also demonstrated that EMT and secondary metastatic sites are regulated by selected macrophage phenotypes in the liver metastatic microenvironment. These results indicate that macrophages could be a potential therapeutic target for limiting death due to malignant metastases in patients with breast cancer40. The presence of CD8 + T cells in breast cancer is associated with a significant reduction in the relative risk of death from disease in both ER- and ER + subtypes of HER2 + breast cancer. Thus, inclusion of TILs may improve risk stratification in patients with breast cancer classified into these subtypes41. Intratumor infiltration of B cells is significantly impaired during hepatocellular carcinoma progression. High densities of tumor-infiltrating B cells imply a better clinical outcome. Therapies designed to target B cells may be a novel strategy for hepatocellular carcinoma42. Therefore, different immune cells have different effects on breast cancer prognosis. Macrophages may promote the metastasis of breast cancer, while CD8 + T cells and B cells may inhibit the growth of breast cancer. Their individual effects and related molecular mechanisms need to be further investigated.
In this study, the identified immune-related genes were associated with multiple pathways related to immune cell infiltration and migration and immune checkpoint enhancement. Among them, regulation of the leukocyte-mediated cytotoxicity pathway is associated with tumor progression and decreased CD8 + infiltration in pancreatic cancer43. The T cell migration pathway can enhance tumor immunity and increase the efficacy of ICI in preclinical breast cancer models44. This pathway can enhance T cells into tumors and intratumoral T-cell diversity45. A previous study identified the chemokine signal regulator FROUNT as a target to control tumor-associated macrophages by the chemokine receptor binding pathway46. Anti-PD-L1 combined with Liposomal-AMD3100, a CXCR4 antagonist, exerted an increased antitumor effect and prolonged survival in a murine TNBC model compared with monotherapies, measured by chemokine response47. CD3 bispecific antibody promoted tumor cell killing by cross-linking the CD3 component of the T cell receptor complex pathway with a tumor-associated antigen on the surface of the target cell48. These results indicate that immune-related pathways may play an important role in the treatment of breast cancer in the future. Consistent with these conclusions, our study determined that upregulation of these pathways was closely associated with low-risk patients. CCR chemokine receptor binding, immunoglobulin complex circulation, and regulation of cell killing pathways have not been studied in tumors but warrant further in vivo and in vitro studies.
It is necessary to gather information regarding the expression of multiple immune-related genes in the application of our prognostic model. The reliability of our model requires further verification in a large clinical patient population. Our two datasets originated from retrospective studies; thus, our prognostic model needs to be more widely validated in prospective cohort studies. In addition, the immune-related genes and related pathways associated with our prognostic model, and their molecular mechanisms, require further verification in vitro and in vivo.