**2.2 Tumor-immune cells crosstalk**

Alongside the tumor–tumor communication, MVs were proven to facilitate the crosstalk between the tumor and its surrounding stroma and immune cells which ultimately leads to cancer immune evasion. In breast cancer cells, the secretion of both tumor MV and TDE induced the expression of Wnt5a in tumor-associated macrophages. Macrophage Wnt5a promoted ß-catenin-independent Wnt signaling in breast cancer cells when delivered by macrophage-derived MVs and Exo, resulting in enhanced tumor invasion. This shows how EV-based cell-cell communication can drive tumor-associated immune cells to stimulate tumor growth [11]. MVs-enriched preparations induced the differentiation of monocytes producing anti-inflammatory cytokines such as IL-10. In line with this, early stimulation with tumor MV triggered macrophage polarization towards an anti-inflammatory phenotype with decreased anti-tumor cytotoxic potential. Additionally, as T cells represent the first line of the immune defense, tumor cells appear to suppress T cell activity and diminish antitumoral immune response via MVs-mediated cell-cell communication. For instance, leukemia-derived MVs deliver miRNAs to T cells, which alters T cell phenotype [13] (**Figure 1**). Moreover, MVs released by irradiated breast cancer cells were shown

#### **Figure 1.**

*Exosome PD-L1 (similar to tumor PD-L1) can bind to PD-1 on T cells, induce T cell apoptosis, and inhibit T cell activation and proliferation [14].*

to carry abundant immune-suppressive proteins, such as programmed cell death ligand 1 (PD-L1) which inhibited cytotoxic T cell activity and enabled tumor growth (**Figure 1**)[15].

### **2.3 TDE-mediated epithethelial mesenchymal transition**

TDEs, through their miRNAs proteins, DNAs, mRNAs lncRNAs, initiate the transformation of epithelial cells to mesenchymal cells. This transformation was due to the loss of epithelial E-cadherin expression, cell-cell adhesion and cell polarity, and gaining of vimentin expression [16].
