Extracellular Vesicles (EVs) are small membranous particles secreted by the cells. They play an important role in intercellular communication and can transport a variety of biomolecules, including proteins, lipids, and nucleic acids, to target cells. The scientific community recently considered EVs attractive candidates for developing targeted drug delivery systems (DDSs), given their biocompatibility, low immunogenicity, stability in biofluids, and capability to cross biological barriers. Most studies have shown the feasibility of incorporating desired moieties at the EV surface through the genetic modification of EV-producing cells, exploiting the fusion with proteins enriched at the EV membrane. Tetraspanins are transmembrane proteins enriched in EVs, already exploited for EV isolation or tracking upon fusion with fluorescent reporters. CD81 is a well-characterized tetraspanin with ubiquitous protein expression, overexpression tolerance and a limited number of encoded protein isoforms with respect to other EV-associated tetraspanins. Here, I have explored a CD81-based approach for EV targeting. CD81, in full-length or truncated form, was used to guide the expression into EVs of an anti-HER2 moiety, namely the light chains of trastuzumab, within three different constructs, including turbo-GFP (tGFP) as a reporter: CD81-tGFP as master control, CD81-antiHER2-tGFP and CD81delta-antiHER2-tGFP. The first part of the project was dedicated to the characterization of chimeric proteins at cellular and vesicular levels. CD81-based constructs were successfully expressed in HEK239T cells with a preferential enrichment in organelle fractions, underlying the expected involvement in the intracellular vesicular trafficking. Next, chimeric proteins were also found in the derived EVs, with a similar expression trend, corroborated by imaging flow cytometry. Nanoparticle tracking analysis and cryogenic electron microscopy acquisitions confirmed that CD81-fusion proteins boosted EV release without altering the size distribution. Subsequently, I tested the binding capacity of the chimeric proteins to HER2 receptor through orthogonal techniques, such as AlphaLISA and immunoprecipitation. Confocal imaging, also on live cells, confirmed EV internalization into breast cancer cells, depending on the recipient cell type and the presence of HER2 receptor. Moreover, chimeric EVs loaded with doxorubicin were able to mediate a concentration-dependent cytotoxic effect on recipient breast cancer cells. Of note, messenger RNA provided a valuable readout of the in vivo delivery capability of the CD81-engineered EVs, since detected by digital droplet PCR in breast cancer tumour xenografts from mice treated with chimeric EVs. The results presented in this thesis highlighted the feasibility of using CD81 fusion proteins for cell targeting and cargo delivery, ultimately opening new perspectives for the development of EV-based therapeutics.

Background: The focus of this study was to investigate how producing human bone marrow (hBM) derived mesenchymal stromal cell (MSC) extracellular vehicles (EVs) in a high purity isolation system would affect their established characterization criteria and address the validity of these methods of EV production. Additionally, we set out to functionally characterize the hBM-MSC-EVs for their identified immunomodulatory ability while also assessing the presence of novel MSC-EV marker NRP1 identified by our group to further affirm its validity as a functional MSC-EV identity marker. Methods: Each hBM-MSC-EV donor was cultured in a hollow-fiber bioreactor system in non-stimulating serum/xeno-free conditions for 25 days to produce EVs persistently under quiescent conditions to characterize the hBM-MSC-EVs in their native form. EVs were isolated by traditional PEG-based precipitation for preliminary characterization to monitor bioreactor production wherein they were characterized using multimodal tangential flow filtration coupled with fast protein liquid chromatograph (FPLC) size exclusion/high-affinity purifications to obtain the final highly purified EV sample. Additionally, functional analysis of their immunomodulatory ability, EVs and MSCs were incubated with activated peripheral blood mononuclear cells (PBMCs) as an in-vitro model to evaluate their potency. Results: The hBM-MSC-EVs produced from the bioreactor system showed consistent characterization in accordance with the MISEV2018 establish criteria. We were also able to demonstrate their functional ability by observing statistically significantly immunomodulatory ability of activated PBMCs equivalent to native MSC ability. We were also able to validate the present of NRP1 on all hBM-MSC-EV samples produced confirming its validity as a MSC-EV marker. Conclusion: The significance of the results obtained from this study confirms the production of MSC-EV using a bioreactor and high purity isolation for obtaining consistent MSC-EVs for downstream investigation. Additionally, we were able to demonstrate the significance of MSC-EVs on MSC signaling for immunomodulation by showing equivalent functional potency when tested in-vitro. These results contribute to further understanding the biological attributes of MSC-EVs and contribute to the validation of currently established characterization guidelines.

Les exosomes apoptotiques (ApoExo) sont des vésicules extracellulaires (EVs) dérivées de lésions vasculaires et libérées par des cellules endothéliales (ECs) apoptotiques dont la taille, les protéines, le profil en ARN et l'activité enzymatique sont différents de ceux des corps apoptotiques classiques. Notre groupe a montré que les ApoExos accéléreraient le rejet vasculaire en association avec les anti-LG3 circulants, des auto-anticorps (auto-Ac) dirigés contre le LG3, le fragment 5' du perlécan. Nous avons également démontré le rôle de biomarqueur et le rôle effecteur des anti-LG3 dans les lésions vasculaires rénales, à la fois dans les reins natifs et transplantés. La néphrite lupique (NL) est une manifestation fréquente et grave du lupus érythémateux disséminé (LED). Il n'existe pas de biomarqueurs du dysfonctionnement rénal progressif dans la NL. Nous émettons l'hypothèse que les ApoExos stimulent des cellules B spécifiques qui existent dans le répertoire immunitaire normal et que les conditions pro-inflammatoires prévalant chez les patients atteints de LED, telles que l'activation accrue des récepteurs Toll-like (TLRs), amplifient cette réponse, conduisant à la production d'anti-LG3, un auto-Ac important dans l'établissement de la NL. Des cellules B productrices d’anti-LG3 ont été trouvées dans la cavité péritonéale de souris saines et ont produit des anti-LG3 suite à une stimulation in vitro avec des agonistes des TLR1/2, TLR4, TLR7 et TLR9. Il est intéressant de noter que ces cellules sont absentes de la cavité péritonéale de souris saines ayant reçu une injection d'ApoExos. En explorant l'importance fonctionnelle des TLRs dans le déclenchement d'une réponse auto-immune dans un modèle murin lupique, nous montrons que les agonistes de TLRs connus pour contribuer à la pathogenèse du LED (TLR2, 4, 7 et 9) déclenchent une production significativement plus élevée d'IgM anti-LG3, alors que la stimulation des TLRs qui ne sont pas associés à la pathogenèse du LED (TLR3 et 5) ne le fait pas. L’injection d'ApoExo a également déclenché l'axe auto-immun IL-23/IL-17 (mesuré par ELISA et essai cytokinique), augmenté les cellules B de centres germinatifs spléniques (mesuré par cytométrie de flux), augmenté les taux circulants d’IgG totaux, d’anti-LG3 et d’auto-Ac classiques du LED (mesuré par micropuce et ELISA) par rapport à l’injection de véhicule. Des niveaux élevés d'IgG anti-LG3 circulants sont observés chez les souris prédisposées au LED par rapport aux souris saines (mesurés par ELISA), ainsi qu'une proportion accrue de cellules B1 spléniques et de cavité péritonéale (mesurés par cytométrie de flux) augmentant avec l’établissement de la maladie. Ces observations suggèrent un rôle spécifique des ApoExos dans la modulation de la production d'auto-Ac qui, à son tour, déclenche l'involution microvasculaire importante dans les maladies auto-immunes et le rejet de greffe. Ces observations suggèrent également que les cellules B spécifiques de LG3 peuvent être modulées dans des conditions pro-inflammatoires telles que celles qui prévalent chez les patients atteints de LED, conduisant à la production d'auto-Ac. Une meilleure compréhension de l'impact de ces mécanismes permettra d'améliorer l'identification, la prédiction et la prise en charge de la NL. / Apoptotic exosomes (ApoExo) are vascular injury derived extracellular vesicles (EVs) released by apoptotic endothelial cells (ECs) with distinct size, protein, RNA profile and enzymatic activity from classical apoptotic bodies. Our group showed that ApoExo accelerated vascular rejection in association with circulating anti-LG3, autoantibodies (autoAb) against LG3, the 5’ fragment of the perlecan. We have also unravelled biomarkers and effector roles of anti-LG3 in kidney vascular damage in both native and transplanted kidneys. Lupus Nephritis (LN) is a common and serious manifestation of systemic lupus erythematosus (SLE). Biomarkers of progressive renal dysfunction in LN, are lacking. We hypothesize that ApoExo stimulate specific B cells that exist in the normal immune repertoire and that the pro-inflammatory conditions prevalent in SLE patients, such as increased Toll-like Receptors (TLRs) activation, amplify this response, leading to anti-LG3 production, autoAb of importance in LN development. B cells producing anti-LG3 were found in the peritoneal cavity of healthy mice and produced anti-LG3 AutoAb when stimulated in vitro with TLR 1/2, 4, 7 and 9 agonists. Interestingly, these cells disappeared from the peritoneal cavity of healthy mice infused with ApoExo. ApoExo infusion also triggered circulating IL-23/IL-17 autoimmune axis (measured by cytokines assay), increased splenic germinal centre B cells (measured by flow cytometry), increased total circulating IgG, anti-LG3 and classical autoAb (measured by microarray and ELISA) compared to vehicle infusion. Elevated circulating anti-LG3 IgG levels are found in SLE prone mice compared to healthy ones (measured by ELISA) as well as an increased proportion of splenic and peritoneal cavity B1 cells (measured by flow cytometry). Exploring the functional importance of TLRs in triggering such a response, we show that while TLR agonists known to contribute to SLE pathogenesis (TLR2, 4, 7 and 9) triggered significantly higher IgM anti-LG3 production, stimulation of TLR that are not associated with SLE pathogenesis (TLR3 and 5) did not. These observations suggest a specific role for ApoExo in modulating the production of autoAb which, in turn, trigger microvascular involution of importance in autoimmune diseases and transplant rejection. These observations also suggest that LG3-specific B cells may be modulated under pro-inflammatory conditions such as those prevalent in lupus patients, leading to production of autoAb. A better understanding of the impact of these mechanisms will lead to improved identification, prediction, and management of LN.