Tumour Cells Incorporate Exosomes Derived from Dendritic Cells through a Mechanism Involving the Tetraspanin CD9

Exosomes (Exos) are secreted nanovesicles that contain membrane proteins and genetic material, which can be transferred between cells and contribute to their communication in the body. We show that Exos, obtained from mature human dendritic cells (DCs), are incorporated by tumour cells, which after Exos treatment, acquire the expression of HLA-class I, HLA-class II, CD86, CD11c, CD54 and CD18. This incorporation reaches its peak eight hours after treatment, can be observed in different cell tumour lines (SK-BR-3, U87 and K562) and could be a means to transform non-immunogenic into immunogenic tumour cells. Interestingly, tetraspanins, which are expressed by the tumour cells, have their surface level decreased after Exo treatment. Furthermore, the intensity of Exo incorporation by the different tumour cell lines was proportional to their CD9 expression levels and pre-treatment of Exos with anti-CD9 decreased their incorporation (by SK-BR-3 cells). This modification of tumour cells by DC-derived Exos may allow their use in new immunotherapeutic approaches to cancer. Furthermore, by showing the involvement of CD9 in this incorporation, we provide a possible selection criterion for tumours to be addressed by this strategy.