Rationale: Immune checkpoint inhibitors (ICIs) against the PD-1/PD-L1 pathway showed limited success in non-small cell lung cancer (NSCLC) patients, especially in those with activating epidermal growth factor receptor (EGFR) mutations. Elucidation of the mechanisms underlying EGFR-mediated tumor immune escape and the development of effective immune therapeutics are urgently needed. Immunoglobulin-like transcript (ILT) 4, a crucial immunosuppressive molecule initially identified in myeloid cells, is enriched in solid tumor cells and promotes the malignant behavior of NSCLC. However, the upstream regulation of ILT4 overexpression and its function in tumor immunity of NSCLC with EGFR activation remains unclear.

Tumor-infiltrating immune cells (TICs) are highly relevant to tumor development and are promising prognostic biomarkers. However, the precise assessment of TICs is limited by the deficiencies of traditional measurements, such as the lack of phenotypic markers. Here, we analyzed the composition of TICs in cervical cancer based on RNA expression data with a metagene approach called CIBERSORT and evaluated the prognostic value of TICs. The immune infiltration profiles functioned as intrinsic features to distinguish cervical cancer from normal tissue. According to the Cox regression analysis, higher levels of activated memory CD4+ T cells were independently associated with favorable overall survival (OS) (hazard ratio [HR] = 0.71, 95% confidence interval [CI]: 0.57-0.89; p = 0.003), whereas a higher fraction of activated mast cells was independently associated with adverse outcomes (HR = 1.53, 95% CI: 1.23-1.91; p < 0.001). Furthermore, a novel prognostic model named aTMNs (activated memory CD4+ T cells, activated mast cells and activated natural killer [NK] cells) was constructed to predict OS in cervical cancer with high accuracy (area under the curve [AUC] = 0.723, concordance index [C-index] = 0.738): risk score = -0.34508 × (proportion of activated memory CD4+ T cells) + 0.426841 × (proportion of activated mast cells) + 0.272202 × (proportion of activated NK cells). The aTMNs model outperformed the immunomodulator model (AUC = 0.673, C-index = 0.693). Overall, TICs are important prognostic determinants in cervical cancer and may be a useful resource for the development of effective immunotherapy.

Background: Current immunotherapies including checkpoint blockade therapy have limited success rates in certain types of cancers. Identification of alternative checkpoint molecules for the development of effective strategies for tumor immunotherapy is urgently needed. Immunoglobulin-like transcript 4 (ILT4) is an immunosuppressive molecule expressed in both myeloid innate cells and malignant tumor cells. However, the role of tumor-derived ILT4 in regulating cancer biology and tumor immunity remains unclear. Methods: ILT4 expression in tumor cells and patient samples was determined by real-time PCR, flow cytometry, and immunohistochemistry. T cell senescence induced by tumor was evaluated using multiple markers and assays. Moreover, metabolic enzyme and signaling molecule expression and lipid droplets in tumor cells were determined using real-time PCR, western blot and oil red O staining, respectively. Loss-of-function and gain-of-function strategies were used to identify the causative role of ILT4 in tumor-induced T cell senescence. In addition, breast cancer and melanoma mouse tumor models were performed to demonstrate the role of ILT4 as a checkpoint molecule for tumor immunotherapy. Results: We reported that ILT4 is highly expressed in human tumor cells and tissues, which is negatively associated with clinical outcomes. Furthermore, tumor-derived ILT4/PIR-B (ILT4 ortholog in mouse) is directly involved in induction of cell senescence in naïve/effector T cells mediated by tumor cells in vitro and in vivo. Mechanistically, ILT4/PIR-B increases fatty acid synthesis and lipid accumulation in tumor cells via activation of MAPK ERK1/2 signaling, resulting in promotion of tumor growth and progression, and induction of effector T cell senescence. In addition, blocking tumor-derived PIR-B can reprogram tumor metabolism, prevent senescence development in tumor-specific T cells, and enhance antitumor immunity in both breast cancer and melanoma mouse models. Conclusions: These studies identify a novel mechanism responsible for ILT4-mediated immune suppression in the tumor microenvironment, and prove a novel concept of ILT4 as a critical checkpoint molecule for tumor immunotherapy.