Body fluids contain many populations of extracellular vesicles (EV) that differ in size, cellular origin, molecular composition, and biological activities. EV in seminal plasma are in majority originating from prostate epithelial cells, and hence are also referred to as prostasomes. Nevertheless, EV are also contributed by other accessory sex glands, as well as by the testis and epididymis. In a previous study, we isolated EV from seminal plasma of vasectomized men, thereby excluding contributions from the testis and epididymis, and identified two distinct EV populations with diameters of 50 and 100 nm, respectively. In the current study, we comprehensively analyzed the protein composition of these two EV populations using quantitative Liquid Chromatography-Mass Spectrometry (LC-MS/MS). In total 1558 proteins were identified. Of these, ≈45% was found only in the isolated 100 nm EV, 1% only in the isolated 50 nm EV, and 54% in both 100 nm and 50 nm EV. Gene ontology (GO) enrichment analysis suggest that both originate from the prostate, but with distinct biogenesis pathways. Finally, nine proteins, including KLK3, KLK2, MSMB, NEFH, PSCA, PABPC1, TGM4, ALOX15B, and ANO7, with known prostate specific expression and alternate expression levels in prostate cancer tissue were identified. These data have potential for the discovery of EV associated prostate cancer biomarkers in blood.

Small extracellular vesicles (sEVs) are nanosized vesicles. Death receptor 5 (DR5) mediates extrinsic apoptosis. We engineer DR5 agonistic single-chain variable fragment (scFv) expression on the surface of sEVs derived from natural killer cells. PDGFR transmembrane domain delivers DR5-scFvs to the surface of sEVs. DR5-scFv sEVs rapidly induce apoptosis of different types of DR5 ⁺ cancer cells, myeloid-derived suppressor cells (MDSCs), and cancer-associated fibroblasts (CAFs). DR5-scFv sEVs migrate specifically to DR5 ⁺ tumors in vitro and in vivo. Systemic delivery of DR5-scFv sEVs significantly inhibits the growth of DR5 ⁺ melanoma, liver cancer, and breast cancer and prolongs mouse life span without significant toxicity. DR5-scFv sEVs are significantly more efficacious than DR5 antibodies in vivo. In organotypic patient-derived melanoma slice cultures, DR5-scFv sEVs effectively inhibit melanoma cells and MDSCs and activate CD8 ⁺ T cells. Our studies demonstrate that DR5-scFv sEVs can inhibit tumor growth by targeting tumor cells and immunosuppressive stromal cells in the TME.

Seminal plasma induces immune tolerance towards paternal allogenic antigens within the female reproductive tract and during foetal development. Recent evidence suggests a role for extracellular vesicles in seminal plasma (spEVs). We isolated spEVs from seminal plasma that was donated by vasectomized men, thereby excluding any contributions from the testis or epididymis. Previous analysis demonstrated that such isolated spEVs originate mainly from the prostate. Here we observed that when isolated fluorescently labelled spEVs were mixed with peripheral blood mononuclear cells, they were endocytosed predominantly by monocytes, and to a lesser extent also by T‐cells. In a mixed lymphocyte reaction, T‐cell proliferation was inhibited by spEVs. A direct effect of spEVs on T‐cells was demonstrated when isolated T cells were activated by anti‐CD3/CD28 coated beads. Again, spEVs interfered with T cell proliferation, as well as with the expression of CD25 and the release of IFN‐γ, TNF, and IL‐2. Moreover, spEVs stimulated the expression of Foxp3 and IL‐10 by CD4+CD25+CD127‐ T cells, indicating differentiation into regulatory T‐cells (Tregs). Prior treatment of spEVs with proteinase K revoked their effects on T‐cells, indicating a requirement for surface‐exposed spEV proteins. The adenosine A2A receptor‐specific antagonist CPI‐444 also reduced effects of spEVs on T‐cells, consistent with the notion that the development of Tregs and their immune suppressive functions are under the influence of adenosine‐A2A receptor signalling. We found that adenosine is highly enriched in spEVs and propose that spEVs are targeted to and endocytosed by T‐cells, after which they may release their adenosine content into the lumen of endosomes, thus allowing endosome‐localized A2A receptor signalling in spEVs targeted T‐cells. Collectively, these data support the idea that spEVs can prime T cells directly for differentiation into Tregs.