The biological relevance of extracellular vesicles (EV) in intercellular communication has been well established. Thus far, proteins and RNA were described as main cargo. Here, we show that EV released from human bone marrow derived mesenchymal stromal cells (BM-hMSC) also carry high-molecular DNA in addition. Extensive EV characterization revealed this DNA mainly associated with the outer EV membrane and to a smaller degree also inside the EV. Our EV purification protocol secured that DNA is not derived from apoptotic or necrotic cells. To analyze the relevance of EV-associated DNA we lentivirally transduced Arabidopsis thaliana-DNA (A.t.-DNA) as indicator into BM-hMSC and generated EV. Using quantitative polymerase chain reaction (qPCR) techniques we detected high copy numbers of A.t.-DNA in EV. In recipient hMSC incubated with tagged EV for two weeks we identified A.t.-DNA transferred to recipient cells. Investigation of recipient cell DNA using quantitative PCR and verification of PCR-products by sequencing suggested stable integration of A.t.-DNA. In conclusion, for the first time our proof-of-principle experiments point to horizontal DNA transfer into recipient cells via EV. Based on our results we assume that eukaryotic cells are able to exchange genetic information in form of DNA extending the known cargo of EV by genomic DNA. This mechanism might be of relevance in cancer but also during cell evolution and development.

BackgroundSuccessful treatment of acute radiation syndromes relies on immediate supportive care. In patients with limited hematopoietic recovery potential, hematopoietic stem cell (HSC) transplantation is the only curative treatment option. Because of time consuming donor search and uncertain outcome we propose MSC treatment as an alternative treatment for severely radiation-affected individuals.Methods and FindingsMouse mesenchymal stromal cells (mMSCs) were expanded from bone marrow, retrovirally labeled with eGFP (bulk cultures) and cloned. Bulk and five selected clonal mMSCs populations were characterized in vitro for their multilineage differentiation potential and phenotype showing no contamination with hematopoietic cells. Lethally irradiated recipients were i.v. transplanted with bulk or clonal mMSCs. We found a long-term survival of recipients with fast hematopoietic recovery after the transplantation of MSCs exclusively without support by HSCs. Quantitative PCR based chimerism analysis detected eGFP-positive donor cells in peripheral blood immediately after injection and in lungs within 24 hours. However, no donor cells in any investigated tissue remained long-term. Despite the rapidly disappearing donor cells, microarray and quantitative RT-PCR gene expression analysis in the bone marrow of MSC-transplanted animals displayed enhanced regenerative features characterized by (i) decreased proinflammatory, ECM formation and adhesion properties and (ii) boosted anti-inflammation, detoxification, cell cycle and anti-oxidative stress control as compared to HSC-transplanted animals.ConclusionsOur data revealed that systemically administered MSCs provoke a protective mechanism counteracting the inflammatory events and also supporting detoxification and stress management after radiation exposure. Further our results suggest that MSCs, their release of trophic factors and their HSC-niche modulating activity rescue endogenous hematopoiesis thereby serving as fast and effective first-line treatment to combat radiation-induced hematopoietic failure.

The therapeutic effect of mesenchymal stromal cells (MSC) in tissue regeneration is based mainly on the secretion of bioactive molecules. Here, we report that the radioprotective effect of mouse bone marrow derived mesenchymal stromal cells (mMSC) can be attributed to extracellular vesicles (EV) released from mMSC. The transplantation of mMSC-derived EV into lethally irradiated mice resulted in long-term survival but no improvement in short-term reconstitution of the recipients. Importantly, the radiation rescue was efficient without additional hematopoietic support. In vitro we show a protection by EV of irradiated hematopoietic stem cells but not progenitor cells using stroma-cell cultures and colony-forming assays. After systemic infusion into lethally irradiated recipients, labeled EV traveled freely through the body reaching the bone marrow within 2 hours. We further show that long-term repopulating Sca-1 positive and c-kit low-positive stem cells were directly targeted by EV leading to long-term survival. Collectively, our data suggest EV as an effective first-line treatment to combat radiation-induced hematopoietic failure which might also be helpful in alleviating myelosuppression due to chemotherapy and toxic drug reaction. We suggest the infusion of MSC-derived EV as efficient and immediate treatment option after irradiation injuries. STEM CELLS 2017;35:2379-2389 SIGNIFICANCE STATEMENTRadiation as used in conditioning of patients prior to hematopoietic stem cell transplantation is associated with severe side effects. Previous research has shown survival-promoting properties of mouse mesenchymal stromal cells in a model of lethal irradiation without support of hematopoietic stem cells. This phenomenon formerly was attributed to "paracrine" effects. In recent years, extracellular vesicles (EVs) have gained increasing interest as mediators of intercellular communication based on their capability to transfer new information to sites of action without loss at physiological barriers. This novel data demonstrate that EV derived from mouse bone marrow-derived mesenchymal stromal cells are the active component of these cells providing a radiation-protective effect. Results show that hematopoietic, long-term repopulating stem cells are targeted rapidly by the EV and thereby rescued from radiation damage. These results open a new line of treatment options for patients suffering from radiotherapy induced myelosuppression without the potential side effects of cell therapies.