In vivo impact of ASML-exosomes on leukocyte activation. Rats received 3-times 2x106 DC, subcutaneously and/or 7-times 500 μg ASML-exosomes, i.v. as described in MM. Rats were sacrificed 3d after the 3rd DC application to analyze the draining LNC, SC and PBL. (A) Number of draining LNC (mean ± SD, 3 rats), (B) leukocyte activation markers, IL2, IL12 and IFNγ expression (flow cytometry, mean ± SD, 3 rats and representative examples), (C) MDSC (flow cytometry, mean ± SD, 3 rats), (D) 3H-thymidine incorporation after 3d in vitro culture and (E) cytotoxic activity against ASML and AS (NK susceptible) targets after 10d in vitro culture in the presence of ASML lysate (mean ± SD, triplicates). (A-E) Significant differences to lymphocytes from untreated rats: *, differences between lymphocytes from rats receiving DC or DC plus ASML-exosomes are indicated as ns (not significant) or s (significant, p <0.01). In vivo, ASML-exosomes support recruitment and/or proliferation of draining LNC and CD11b, CD86, IL12 and IFNγ expression. Despite an increase in MDSC in the peripheral blood, ASML-exosomes support DC vaccination-induced T cell expansion and cytotoxic activity.