Introduction: Previously, we established a simple method for deriving mesenchymal stem cells (MSCs) from human induced pluripotent stem cells (iPSC-MSCs). These iPSC-MSCs were capable of forming osteogenic structures in scaffolds and nanofibers. The objective of this study is to systematically characterize the mesenchymal characteristics of the iPSC-MSCs by comparing them to bone marrow-derived MSCs (BM-MSCs). Methods: Two iPSC-MSC lines (named as mRNA-iPSC-MSC-YL001 and lenti-iPSC-MSC-A001) and one BM-MSC line were used for the study. Cell proliferation, presence of mesenchymal surface markers, tri-lineage differentiation capability (osteogenesis, chondrogenesis, adipogenesis), and expression of “stemness” genes were analyzed in these MSC lines. Results: The iPSC-MSCs were similar to BM-MSCs in terms of cell morphology (fibroblast-like) and surface antigen profile: CD29+, CD44+, CD73+, CD90+, CD105+, CD11b–, CD14–, CD31–, CD34–, CD45– and HLA-DR–. A faster proliferative capability was seen in both iPSC-MSCs lines compared to the BM-MSCs. The iPSC-MSCs showed adequate capacity of osteogenesis and chondrogenesis compared to the BM-MSCs, while less adipogenic potential was found in the iPSC-MSCs. The iPSC-MSCs and the tri-lineage differentiated cells (osteoblasts, chondrocytes, adipocytes) all lack expression of “stemness” genes: OCT4, SOX2, GDF3, CRIPTO, UTF1, DPPA4, DNMT3B, LIN28a, and SAL4. Conclusions: The MSCs derived from human iPSCs with our method have advanced proliferation capability and adequate osteogenic and chondrogenic properties compared to BM-MSCs. However, the iPSC-MSCs were less efficient in their adipogenicity, suggesting that further modifications should be applied to our method to derive iPSC-MSCs more closely resembling the naïve BM-MSCs if necessary.

The year 2023 marks the 25th anniversary of the discovery of RNAi. RNAi-based therapeutics enable sequence-specific gene knockdown by eliminating target RNA molecules through complementary base-pairing. A systematic review of published and ongoing clinical trials was performed. Web of Science, PubMed, and Embase were searched from January 1, 1998, to December 30, 2022 for clinical trials using RNAi. Following inclusion, data from the articles were extracted according to a predefined protocol. A total of 90 trials published in 81 articles were included. In addition, ongoing clinical trials were retrieved from ClinicalTrials.gov, resulting in the inclusion of 48 trials. We investigated how maturation of RNAi-based therapeutics and developments in delivery platforms, administration routes, and potential targets shape the current landscape of clinically applied RNAi. Notably, most contemporary clinical trials used either N-acetylgalactosamine delivery and subcutaneous administration or lipid nanoparticle delivery and intravenous administration. In conclusion, RNAi therapeutics have gained great momentum during the past decade, resulting in five approved therapeutics targeting the liver for treatment of severe diseases, and the trajectory depicted by the ongoing trials emphasizes that even more RNAi-based medicines also targeting extra-hepatic tissues are likely to be available in the years to come.

Delivery of genes to mouse liver is routinely accomplished by tail-vein injections of viral vectors or naked plasmid DNA. While viral vectors are typically injected in a low-pressure and -volume fashion, uptake of naked plasmid DNA to hepatocytes is facilitated by high pressure and volumes, also known as hydrodynamic delivery. In this study, we compare the efficacy and specificity of delivery of vesicular stomatitis virus G glycoprotein (VSV-G) pseudotyped lentiviral vectors to mouse liver by a number of injection schemes. Exploiting in vivo bioluminescence imaging as a readout after lentiviral gene transfer, we compare delivery by (1) "conventional" tail-vein injections, (2) "primed" injections, (3) "hydrodynamic" injections, or (4) direct "intrahepatic" injections into exposed livers. Reporter gene activity demonstrate potent and targeted delivery to liver by hydrodynamic injections. Enhanced efficacy is confirmed by analysis of liver sections from mice treated with GFP-encoding vectors, demonstrating 10-fold higher transduction rates and gene delivery to ∼80% of hepatocytes after hydrodynamic vector delivery. In summary, lentiviral vector transfer to mouse liver can be strongly augmented by hydrodynamic tail-vein injections, resulting in both reduced off-target delivery and transduction of the majority of hepatocytes. Our findings pave the way for more effective use of lentiviral gene delivery in the mouse.

The expression of short hairpin RNAs (shRNAs) may result in unwanted activity from the co-processed passenger strand. Recent studies have shown that shortening the stem of conventional shRNAs abolishes passenger strand release. These Dicer-independent shRNAs, expressed from RNA polymerase III (Pol III) promoters, rely on Ago2 processing in resemblance to miR-451. Using strand-specific reporters, we tested two designs, and our results support the loss of passenger strand activity. We demonstrate that artificial primary microRNA (pri-miRNA) transcripts, expressed from Pol II promoters, can potently silence a gene of choice. Among six different scaffolds tested, miR-324 and miR-451 were readily re-targeted to direct efficient knockdown from either a CMV or a U1 snRNA promoter. Importantly, the miR-shRNAs have no passenger strand activity and remain active in Dicer-knockout cells. Our vectors are straightforward to design, as we replace the pre-miR-324 or -451 sequences with a Dicer-independent shRNA mimicking miR-451 with unpaired A-C nucleotides at the base. The use of Pol II promoters allows for controlled expression, while the inclusion of pri-miRNA sequences likely requires Drosha processing and, as such, mimics microRNA biogenesis. Since this improved and tunable system bypasses the requirement for Dicer activity and abolishes passenger strand activity completely, it will likely prove favorable in both research and therapeutic applications in terms of versatility and enhanced safety.

Retinal gene therapy using RNA interference (RNAi) to silence targeted genes requires both efficacy and safety. Short hairpin RNAs (shRNAs) are useful for RNAi, but high expression levels and activity from the co-delivered passenger strand may cause undesirable cellular responses. Ago2-dependent shRNAs (agshRNAs) produce no passenger strand activity. To enhance efficacy and to investigate improvements in safety, we have generated VEGFA-targeting agshRNAs and microRNA (miRNA)-embedded agshRNAs (miR-agshRNAs) and inserted these RNAi effectors in Pol II/III-driven expression cassettes and lentiviral vectors (LVs). Compared with corresponding shRNAs, agshRNAs and miR-agshRNAs increased specificity and safety, while retaining a high knockdown efficacy and abolishing passenger strand activity. The agshRNAs also caused significantly smaller reductions in cell viability and reduced competition with the processing of endogenous miR21 compared with their shRNA counterparts. RNA sequencing (RNA-seq) analysis of LV-transduced ARPE19 cells revealed that expression of shRNAs in general leads to more changes in gene expression levels compared with their agshRNA counterparts and activation of immune-related pathways. In mice, subretinal delivery of LVs encoding tissue-specific miR-agshRNAs resulted in retinal pigment epithelium (RPE)-restricted expression and significant knockdown of Vegfa in transduced RPE cells. Collectively, our data suggest that agshRNAs and miR-agshRNA possess important advantages over shRNAs, thereby posing a clinically relevant approach with respect to efficacy, specificity, and safety.