Regulatory T cells (Treg) and tumor-exosomes are thought to play a role in preventing the rejection of malignant cells in patients bearing nasopharyngeal carcinoma (NPC).

Treg recruitment by exosomes derived from NPC cell lines (C15/C17-Exo), exosomes isolated from NPC patients’ plasma (Patient-Exo), and CCL20 were tested in vitro using Boyden chamber assays and in vivo using a xenograft SCID mouse model (n = 5), both in the presence and absence of anti-CCL20 monoclonal antibodies (mAb). Impact of these NPC exosomes (NPC-Exo) on Treg phenotype and function was determined using adapted assays (FACS, Q-PCR, ELISA, and MLR). Experiments were performed in comparison with exosomes derived from plasma of healthy donors (HD-Exo). The Student’s t test was used for group comparisons. All statistical tests were two-sided.

CCL20 allowed the intratumoral recruitment of human Treg. NPC-Exo also facilitated Treg recruitment (3.30±0.34 fold increase, P < .001), which was statistically significantly inhibited (P < .001) by an anti-CCL20 blocking mAb. NPC-Exo also recruited conventional CD4⁺CD25^- T cells and mediated their conversion into inhibitory CD4⁺CD25^high cells. Moreover, NPC-Exo enhanced (P = .0048) the expansion of human Treg, inducing the generation of Tim3^Low Treg with increased expression of CD25 and FOXP3. Finally, NPC-Exo induced an overexpression of cell markers associated with Treg phenotype, properties and recruitment capacity. For example, GZMB mean fold change was 21.45±1.75 (P < .001). These results were consistent with a stronger suppression of responder cells’ proliferation and the secretion of immunosuppressive cytokines (IL10, TGFB1).

Interactions between NPC-Exo and Treg represent a newly defined mechanism that may be involved in regulating peripheral tolerance by tumors and in supporting immune evasion in human NPC.