Background: A better understanding of the molecular mechanisms that manifest in the immunosuppressive tumor microenvironment (TME) is crucial for developing more efficacious immunotherapies for hepatocellular carcinoma (HCC), which has a poor response to current immunotherapies. Regulatory T (Treg) cells are key mediators of HCC-associated immunosuppression. We investigated the selective mechanism exploited by HCC that lead to Treg cells expansion and to find more efficacious immunotherapies. Methods: We used matched tumor tissues and blood samples from 150 patients with HCC to identify key factors of Treg cells expansion. We used mass cytometry (CyTOF) and orthotopic cancer mouse models to analyze overall immunological changes after growth differentiation factor 15 (GDF15) gene ablation in HCC. We used flow cytometry, coimmunoprecipitation, RNA sequencing, mass spectrum, chromatin immunoprecipitation and Gdf15 ^–/–, OT-I and GFP transgenic mice to demonstrate the effects of GDF15 on Treg cells and related molecular mechanism. We used hybridoma technology to generate monoclonal antibody to block GDF15 and evaluate its effects on HCC-associated immunosuppression. Results: GDF15 is positively associated with the elevation of Treg cell frequencies in patients wih HCC. Gene ablation of GDF15 in HCC can convert an immunosuppressive TME to an inflammatory state. GDF15 promotes the generation of peripherally derived inducible Treg (iTreg) cells and enhances the suppressive function of natural Treg (nTreg) cells by interacting with a previously unrecognized receptor CD48 on T cells and thus downregulates STUB1, an E3 ligase that mediates forkhead box P3 (FOXP3) protein degradation. GDF15 neutralizing antibody effectively eradicates HCC and augments the antitumor immunity in mouse. Conclusions: Our results reveal the generation and function enhancement of Treg cells induced by GDF15 is a new mechanism for HCC-related immunosuppression. CD48 is the first discovered receptor of GDF15 in the immune system which provide the possibility to solve the molecular mechanism of the immunomodulatory function of GDF15. The therapeutic GDF15 blockade achieves HCC clearance without obvious adverse events.

Tamoxifen remains the most effective treatment for estrogen receptor α (ERα)‐positive breast cancer. However, many patients still develop resistance to tamoxifen in association with metastatic recurrence, which presents a tremendous clinical challenge. To better understand tamoxifen resistance from the perspective of the tumor microenvironment, the whole microenvironment landscape is charted by single‐cell RNA sequencing and a new cancer‐associated fibroblast (CAF) subset, CD63⁺ CAFs, is identified that promotes tamoxifen resistance in breast cancer. Furthermore, it is discovered that CD63⁺ CAFs secrete exosomes rich in miR‐22, which can bind its targets, ERα and PTEN, to confer tamoxifen resistance on breast cancer cells. Additionally, it is found that the packaging of miR‐22 into CD63⁺ CAF‐derived exosomes is mediated by SFRS1. Furthermore, CD63 induces STAT3 activation to maintain the phenotype and function of CD63⁺ CAFs. Most importantly, the pharmacological blockade of CD63⁺ CAFs with a CD63‐neutralizing antibody or cRGD‐miR‐22‐sponge nanoparticles enhances the therapeutic effect of tamoxifen in breast cancer. In summary, the study reveals a novel subset of CD63⁺ CAFs that induces tamoxifen resistance in breast cancer via exosomal miR‐22, suggesting that CD63⁺ CAFs may be a novel therapeutic target to enhance tamoxifen sensitivity.

Oestrogen receptor alpha (ERα) is a well-known target of endocrine therapy for ERα-positive breast cancer. ERα-negative cells, which are enriched during endocrine therapy, are associated with metastatic relapse. Here we determine that loss of ERα in the invasive front and in lymph node metastasis in human breast cancer is significantly correlated with lymphatic metastasis. Using in vivo and in vitro experiments, we demonstrate that ERα inhibits breast cancer metastasis. Furthermore, we find that ERα is a novel regulator of vinculin expression in breast cancer. Notably, ERα suppresses the amoeboid-like movement of breast cancer cells by upregulating vinculin in 3D matrix, which in turn promotes cell–cell and cell–matrix adhesion and inhibits the formation of amoeboid-like protrusions. A positive association between ERα and vinculin expression is found in human breast cancer tissues. The results show that ERα inhibits breast cancer metastasis and suggest that ERα suppresses cell amoeboid-like movement by upregulating vinculin.

Forkhead box P3 (FOXP3), an X-linked tumor suppressor gene, plays an important role in breast cancer. However, the biological functions of FOXP3 in breast cancer angiogenesis remain unclear. Here we found that the clinical expression of nuclear FOXP3 was inversely correlated with breast cancer angiogenesis. Moreover, the animal study demonstrated that FOXP3 significantly reduced the microvascular density of MDA-MB-231 tumors transplanted in mice. The cytological experiments showed that the supernatant from FOXP3-overexpressing cells exhibited a diminished ability to stimulate tube formation and sprouting in HUVECs in vitro. In addition, expression of vascular endothelial growth factor (VEGF) was downregulated by FOXP3 in breast cancer cell lines. Luciferase reporter assays and chromatin immunoprecipitation assays demonstrated that FOXP3 can directly interact with the VEGF promoter via specific forkhead-binding motifs to suppress its transcription. Importantly, the inhibitory effects of FOXP3 in the supernatant on tube formation and sprouting in HUVECs could be reversed by adding VEGF in vitro. Nuclear FOXP3 expression was inversely correlated with VEGF expression in clinical breast cancer tissues, and FOXP3 downregulation and VEGF upregulation were both correlated with reduced survival in breast cancer data sets in the Kaplan–Meier plotter. Taken together, our data demonstrate that FOXP3 suppresses breast cancer angiogenesis by downregulating VEGF expression.

Sorafenib is one of the few effective first-line drugs approved for the treatment of advanced hepatocellular carcinoma (HCC). However, the development of drug resistance is common among individuals with HCC. Recent evidence indicated that the anticancer activity of sorafenib mainly relies on the induction of ferroptosis. Furthermore, in our study, genes that suppress ferroptosis, especially GPX4 and DHODH, were enriched in sorafenib-resistant cells and primary tissues and were associated with poor prognosis of HCC patients who received sorafenib treatment. Therefore, a new ferroptosis inducer comprising a multiplex small interfering RNA (multi-siRNA) capable of simultaneously silencing GPX4 and DHODH was created. Then, exosomes with high multi-siRNA loading and HCC-specific targeting were established by fusing the SP94 peptide and the N-terminal RNA recognition motif (RRM) of U1-A with the exosomal membrane protein Lamp2b. The results from the in vitro and in vivo experiments indicate that this tumor-targeting nano-delivery system (Exo^{SP94-lamp2b-RRM}-multi-siRNA) could enhance sorafenib-induced ferroptosis and overcome sorafenib resistance. Taken together, HCC-targeted exosomes (Exo^{SP94-Lamp2b-RRM}) could specifically deliver multi-siRNA to HCC tissues, enhance sorafenib-induced ferroptosis by silencing GPX4 and DHODH expression and consequently increase HCC sensitivity to sorafenib, which opens a new avenue for clinically overcoming sorafenib resistance from the perspective of ferroptosis.