Potency of exosomes from Adult-derived human liver stem cells (ADHLSCs) to treat Crigler Najjar syndrome

Background and aims Extracellular vesicles, EVs (MP, microparticles; and EXO, exosomes) are nano-size vesicles released by many cell types. They mediate intracellular communication by delivering proteins, lipids and/or genetic information (coding and non-coding RNAs) to recipient cells. Adult-derived human liver stem cells (ADHLSCs) are currently in clinical development for the treatment of liver diseases. Clinical and preclinical data seem to indicate a higher clinical effect than what could be expected from the number of cells that have engrafted, suggesting that other mechanisms may be at play. Therefore, we aim to know whether the EVs have therapeutic effects and whether they can contribute to ADHLSC-mediated correction of Crigler Najjar syndrome. Methods ADHLSCs were cultured for 2 days in DMEM supplemented with 10% EXO free FBS and 1% P/S. The conditioned medium was collected, and MP and EXO fractions were harvested by serial centrifugation. FACS and western blotting were used to evaluate the presence of MP and EXO using specific markers. RT-qPCR was performed on RNA extracted from the MP and EXO to investigate the presence of mRNAs of interest in each sample. Results We demonstrated that CD40L, a specific marker of MP, is expressed in ADHLSC-derived MP, while ALIX and CD9, which are specific EXO markers, are expressed in ADHLSC-derived EXO. ALIX was also highly expressed in the EXO fraction derived from a metabolic donor suffering from Crigler-Najjar syndrome, showing that this “EXO marker” can be found in EXO from both healthy and metabolic sources. In order to analyze the EXO fraction by flow cytometry, EXO were incubated with EXO-specific beads and stained for CD9. Using this method, we were able to confirm the expression of CD9 at the surface of the EXO. Characterization of the mRNA by qPCR showed a high expression of UGT1A1 in EXO. This finding supports the hypothesis that EXO may play a role in ADHLSC-mediated correction of Crigler-Najjar syndrome. Conclusions In summary, our study shows that we are able to isolate and characterize MP and EXO released by ADHLSCs. High expression of UGT1A1 mRNA in EXO may support a potential role for ADHLSC-derived EXO in the treatment of Crigler-Najjar syndrome. Further work will be needed to confirm this hypothesis. Keywords ADHLSCs, Extracellular vesicles, Exosomes, Crigler-Najjar, UGT1A1