The Cas9/guide RNA (Cas9/gRNA) system is commonly used for genome editing. mRNA expressing Cas9 can induce innate immune responses, reducing Cas9 expression. First-generation Cas9 mRNAs were modified with pseudouridine and 5-methylcytosine to reduce innate immune responses. We combined four approaches to produce more active, less immunogenic second-generation Cas9 mRNAs. First, we developed a novel co-transcriptional capping method yielding natural Cap 1. Second, we screened modified nucleotides in Cas9 mRNA to identify novel modifications that increase Cas9 activity. Third, we depleted the mRNA of uridines to improve mRNA activity. Lastly, we tested high-performance liquid chromatography (HPLC) purification to remove double-stranded RNAs. The activity of these mRNAs was tested in cell lines and primary human CD34+ cells. Cytokines were measured in whole blood and mice. These approaches yielded more active and less immunogenic mRNA. Uridine depletion (UD) most impacted insertion or deletion (indel) activity. Specifically, 5-methoxyuridine UD induced indel frequencies as high as 88% (average ± SD = 79% ± 11%) and elicited minimal immune responses without needing HPLC purification. Our work suggests that uridine-depleted Cas9 mRNA modified with 5-methoxyuridine (without HPLC purification) or pseudouridine may be optimal for the broad use of Cas9 both in vitro and in vivo.

The lung has a very unique architecture to enable efficient transfer of oxygen and carbon dioxide required for oxidative metabolism. Inhaled gases travel through the airway tubes via trachea bronchi and bronchioles to the alveoli enriched with blood vessels, the primary site of gas exchange. Inflation and deflation of the lung is a prerequisite for gas exchange at the alveoli. This process requires multiple components like the extracellular matrix, smooth muscle cells, and cartilage for support and flexible collagen and the elastin fiber network for flexibility during inflation and deflation. Precisely regulated surface fluids, electrolytes, and mechanical activity of secretory

Gene therapy has always been a promising therapeutic approach for Cystic Fibrosis (CF). However, numerous trials using DNA or viral vectors encoding the correct protein resulted in a general low efficacy. In the last years, chemically modified messenger RNA (cmRNA) has been proven to be a highly potent, pulmonary drug. Consequently, we first explored the expression, function and immunogenicity of human (h)CFTR encoded by cmRNAhCFTR in vitro and ex vivo, quantified the expression by flow cytometry, determined its function using a YFP based assay and checked the immune response in human whole blood. Similarly, we examined the function of cmRNAhCFTR in vivo after intratracheal (i.t.) or intravenous (i.v.) injection of the assembled cmRNAhCFTR together with Chitosan-coated PLGA (poly-D, L-lactide-co-glycolide 75:25 (Resomer RG 752 H)) nanoparticles (NPs) by FlexiVent. The amount of expression of human hCFTR encoded by cmRNAhCFTR was quantified by hCFTR ELISA, and cmRNAhCFTR values were assessed by RT-qPCR. Thereby, we observed a significant improvement of lung function, especially in regards to FEV0.1, suggesting NP-cmRNAhCFTR as promising therapeutic option for CF patients independent of their CFTR genotype.

Backgroundβ-Thalassemia is an inherited hematological disorder caused by mutations in the human hemoglobin beta (HBB) gene that reduce or abrogate β-globin expression. Although lentiviral-mediated expression of β-globin and autologous transplantation is a promising therapeutic approach, the risk of insertional mutagenesis or low transgene expression is apparent. However, targeted gene correction of HBB mutations with programmable nucleases such as CRISPR/Cas9, TALENs, and ZFNs with non-viral repair templates ensures a higher safety profile and endogenous expression control.MethodsWe have compared three different gene-editing tools (CRISPR/Cas9, TALENs, and ZFNs) for their targeting efficiency of the HBB gene locus. As a proof of concept, we studied the personalized gene-correction therapy for a common β-thalassemia splicing variant HBBIVS1–110 using Cas9 mRNA and several optimally designed single-stranded oligonucleotide (ssODN) donors in K562 and CD34+ hematopoietic stem cells (HSCs).ResultsOur results exhibited that indel frequency of CRISPR/Cas9 was superior to TALENs and ZFNs (P < 0.0001). Our designed sgRNA targeting the site of HBBIVS1–110 mutation showed indels in both K562 cells (up to 77%) and CD34+ hematopoietic stem cells—HSCs (up to 87%). The absolute quantification by next-generation sequencing showed that up to 8% site-specific insertion of the NheI tag was achieved using Cas9 mRNA and a chemically modified ssODN in CD34+ HSCs.ConclusionOur approach provides guidance on non-viral gene correction in CD34+ HSCs using Cas9 mRNA and chemically modified ssODN. However, further optimization is needed to increase the homology directed repair (HDR) to attain a real clinical benefit for β-thalassemia.Electronic supplementary materialThe online version of this article (10.1186/s40348-018-0086-1) contains supplementary material, which is available to authorized users.

In vitro transcribed (IVT) mRNA therapies is a promising approach for the effective and safe treatment of various diseases. However, IVT‐mRNA triggers immune responses due to recognition by human RNA sensors, but incorporation of chemically modified nucleosides have been shown to reduce such responses. Nonetheless, an assay reflecting the complexity of the human immune system is still needed. Here, we present a simple and fast ex vivo method called “RNA Immunogenic Assay” for measuring the immunogenicity of IVT‐mRNA in human whole blood. Chemically modified and unmodified mRNA were complexed with a transfection reagent (TransIT), and co‐incubated in human whole blood and specific cytokines were quantified (TNF‐α, INF‐α, IL‐6, and IL‐12p70) using ELISAs. The qPCR analysis was conducted to unveil the activation of specific immune pathway. Our findings demonstrated that the complete replacement of uridine with pseudouridine reduced TNF‐α, IL‐6, and IL‐12p70 levels and did not elevate the expression of genes involved in immune response against RNA including IRF7/3, EIF2A, & RNASEL. In addition, we observed that the transcript length was not found to be a confounding factor in RNA immunogenicity generation and our assay provide the feasibility to dissect donor specific immune response against mRNA therapeutics.

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