Qualitative differences in T‐cell activation by dendritic cell‐derived extracellular vesicle subtypes

Exosomes, nano‐sized secreted extracellular vesicles (EVs), are actively studied for their diagnostic and therapeutic potential. In particular, exosomes secreted by dendritic cells (DCs) have been shown to carry MHC‐peptide complexes allowing efficient activation of T lymphocytes, thus displaying potential as promoters of adaptive immune responses. DCs also secrete other types of EVs of different size, subcellular origin and protein composition, whose immune capacities have not been yet compared to those of exosomes. Here, we show that large EVs (lEVs) released by human DCs are as efficient as small EVs (sEVs), including exosomes, to induce CD4 + T‐cell activation in vitro . When released by immature DCs, however, lEVs and sEVs differ in their capacity to orient T helper (Th) cell responses, the former favouring secretion of Th2 cytokines, whereas the latter promote Th1 cytokine secretion (IFN‐γ). Upon DC maturation, however, these functional differences are abolished, and all EVs become able to induce IFN‐γ. Our results highlight the need to comprehensively compare the functionalities of EV subtypes in all patho/physiological systems where exosomes are claimed to perform critical roles. Synopsis Dendritic cell (DC)‐derived extracellular vesicle (EV) subtypes show functional heterogeneity depending on the DC maturation stage, thus highlighting the importance of characterizing all EV subtypes for their function. Human primary dendritic cell (DC)‐derived EVs of different sizes, including large EVs and mixed exosomes and non‐exosomal small EVs, induce equally well activation and proliferation of allogeneic T lymphocytes. When produced by immature DCs, large EVs induce prominent secretion of Th2‐associated cytokines, whereas medium and small EVs induce secretion of Th1‐associated cytokines. The different qualitative activities of large and small/medium EVs are due to different ratios of EV surface‐exposed T cell‐binding proteins CD40, DC‐SIGN (abundant only on small/medium EVs) and CD80 (present on all EVs). When produced by IFN‐γ‐matured DCs, all EVs induce prominent secretion of Th1‐associated cytokines, thus displaying similar functional activities. Graphical Abstract Dendritic cell (DC)‐derived extracellular vesicle (EV) subtypes show functional heterogeneity depending on the DC maturation stage, thus highlighting the importance of characterizing all EV subtypes for their function.