Type I interferon response against viral and non-viral gene transfer in human tumor and primary cell lines

Potential health risks of mRNA-based vaccine therapy: A hypothesis

Therapeutic applications of synthetic mRNA were proposed more than 30 years ago, and are currently the basis of one of the vaccine platforms used at a massive scale as part of the public health strategy to get COVID-19 under control. To date, there are no published studies on the biodistribution, cellular uptake, endosomal escape, translation rates, functional half-life and inactivation kinetics of synthetic mRNA, rates and duration of vaccine-induced antigen expression in different cell types. Furthermore, despite the assumption that there is no possibility of genomic integration of therapeutic synthetic mRNA, only one recent study has examined interactions between vaccine mRNA and the genome of transfected cells, and reported that an endogenous retrotransposon, LINE-1 is unsilenced following mRNA entry to the cell, leading to reverse transcription of full length vaccine mRNA sequences, and nuclear entry. This finding should be a major safety concern, given the possibility of synthetic mRNA-driven epigenetic and genomic modifications arising. We propose that in susceptible individuals, cytosolic clearance of nucleotide modified synthetic (nms-mRNAs) is impeded. Sustained presence of nms-mRNA in the cytoplasm deregulates and activates endogenous transposable elements (TEs), causing some of the mRNA copies to be reverse transcribed. The cytosolic accumulation of the nms-mRNA and the reverse transcribed cDNA molecules activates RNA and DNA sensory pathways. Their concurrent activation initiates a synchronized innate response against non-self nucleic acids, prompting type-I interferon and pro-inflammatory cytokine production which, if unregulated, leads to autoinflammatory and autoimmune conditions, while activated TEs increase the risk of insertional mutagenesis of the reverse transcribed molecules, which can disrupt coding regions, enhance the risk of mutations in tumour suppressor genes, and lead to sustained DNA damage. Susceptible individuals would then expectedly have an increased risk of DNA damage, chronic autoinflammation, autoimmunity and cancer. In light of the current mass administration of nms-mRNA vaccines, it is essential and urgent to fully understand the intracellular cascades initiated by cellular uptake of synthetic mRNA and the consequences of these molecular events.

Exosomes for mRNA delivery: a novel biotherapeutic strategy with hurdles and hope

Over the past decade, therapeutic messenger RNAs (mRNAs) have emerged as a highly promising new class of drugs for protein replacement therapies. Due to the recent developments, the incorporation of modified nucleotides in synthetic mRNAs can lead to maximizing protein expression and reducing adverse immunogenicity. Despite these stunning improvements, mRNA therapy is limited by the need for the development of safe and efficient carriers to protect the mRNA integrity for in vivo applications. Recently, leading candidates for in vivo drug delivery vehicles are cell-derived exosomes, which have fewer immunogenic responses. In the current study, the key hurdles facing mRNA-based therapeutics, with an emphasis on recent strategies to overcoming its immunogenicity and instability, were highlighted. Then the immunogenicity and toxicity of exosomes derived from various cell sources were mentioned in detail. Finally, an overview of the recent strategies in using exosomes for mRNA delivery in the treatment of multiple diseases was stated.

Efficient reduction of synthetic mRNA induced immune activation by simultaneous delivery of B18R encoding mRNA

The application of synthetic modified messenger RNA (mRNA) is a promising approach for the treatment of a variety of diseases and vaccination. In the past few years, different modifications of synthetic mRNA were applied to render the mRNA more stable and less immunogenic. However, the repeated application of synthetic mRNA still requires the suppression of immune activation to avoid cell death and to allow a sufficient production of exogenous proteins. Thus, the addition of type I interferon (IFN) inhibiting recombinant protein B18R is often required to avoid IFN response. In this study, the ability of B18R encoding mRNA to prevent the immune response of cells to the delivered synthetic mRNA was analyzed. The co-transfection of enhanced green fluorescent protein (eGFP) mRNA transfected fibroblasts with B18R encoding mRNA over 7-days resulted in comparable cell viability and eGFP protein expression as in the cells transfected with eGFP mRNA and incubated with B18R protein. Using qRT-PCR, significantly reduced expression of interferon-stimulated gene Mx1 was detected in the cells transfected with B18R mRNA and stimulated with IFNβ compared to the cells without B18R mRNA transfection. Thereby, it was demonstrated that the co-transfection of synthetic mRNA transfected cells with B18R encoding mRNA can reduce the IFN response-related cell death and thus, improve the protein expression.

In Vitro Evaluation of a Novel mRNA-Based Therapeutic Strategy for the Treatment of Patients Suffering from Alpha-1-Antitrypsin Deficiency

In single-gene disorders, like alpha-1-antitrypsin deficiency (AATD), a gene mutation causes missing or dysfunctional protein synthesis. This, in turn, can lead to serious complications for the patient affected. Furthermore, single-gene disorders are associated with severe early-onset conditions and necessitate expensive lifelong care. Until nowadays, therapeutic treatment options are still limited, cost-intensive, or lack effectiveness. For these reasons, we aim to develop a novel mRNA-based therapeutic strategy for the treatment of single-gene disorders, such as AATD, which is based on the induction of de novo synthesis of the functional proteins. Therefore, an alpha-1-antitrypsin (AAT) encoding mRNA was generated by in vitro transcription. After in vitro delivery of the mRNA to different cells, protein expression and functionality, as well as adverse effects and mRNA serum stability, were analyzed. Our results show that the AAT mRNA-transfected cells express the AAT protein in high amounts within the first 24 h. Moreover, the expressed AAT protein is highly functional, since the activity of elastase is significantly inhibited. Our data also show that mRNA concentrations up to 1 μg per 150,000 cells have no adverse effects on cell viability and immune activation. Furthermore, the encapsulated AAT encoding mRNA is stable and functional in human serum for up to 30 min. Overall, the proposed project provides an innovative, highly promising, and safe therapeutic approach and, thus, promises a novel progress in the treatment of single-gene disorders, whereby affected patients could greatly benefit.

A plasmid-based reverse genetics system for mammalian orthoreoviruses driven by a plasmid-encoded T7 RNA polymerase

Mammalian orthoreoviruses (reoviruses) have served as highly useful models for studies of virus replication and pathogenesis. The development of a plasmid-based reverse genetics system represented a major breakthrough in reovirus research. The current reverse genetics systems for reoviruses rely on the expression of T7 RNA polymerase within cells transfected with reovirus gene-segment cDNA plasmids. In these systems, the T7 RNA polymerase is provided by using a recombinant vaccinia virus expressing T7 RNA polymerase or a cell line constitutively expressing T7 RNA polymerase. Here, we describe an alternative plasmid-based rescue system driven by a plasmid-encoded T7 RNA polymerase, which could increase the flexibility of such reverse genetics systems. Although this approach requires transfection of an additional plasmid, virus recovery was achieved when A549, BHK-21, or L929 cells were co-transfected with a reovirus 10-plasmid set together with a plasmid encoding T7 RNA polymerase. Theoretically, this system offers the possibility to generate reoviruses in any cell line, including those amenable to propagation of viral vectors for clinical use. Thus, this approach will increase the flexibility of reverse genetics for basic studies of reovirus biology and foster development of reoviruses for clinical applications.

Nucleofection of expression vectors induces a robust interferon response and inhibition of cell proliferation

The interferon (IFN) response, induced as a side effect after transfection of nucleic acids into mammalian cells, is known but inadequately described. We followed the IFN response, the fate of cells, and the possible mechanisms leading to this response in NIH3T3 mouse fibroblasts after DNA nucleofection. The gateway destination vector, phGf, and its derivatives encoding toxic and non-toxic variants of the minor structural proteins of polyomaviruses, VP2 and VP3, were used. DNA vector sequences induced in cells the production of high levels of IFN and the upregulation of the IFN-inducible genes, Mx-1, STAT1, IRF1, and IRF7. The IFN response was not restricted to phGf-derived plasmids. In nucleofected cells, upregulation of the modified γ-histone 2A.X indicating DNA damage and inhibition of cell proliferation were also observed. Although 3T3 cells expressed the Toll-like receptor-9 (TLR9) and vectors used for nucleofection contained unmethylated CpGs, signaling leading to IFN induction was found to be TLR9 independent. However, the early activation of nuclear factor-kappa B suggested the participation of this transcription factor in IFN induction. Surprisingly, in contrast to nucleofection, transfection using a cationic polymer induced only a poor IFN response. Together, the results point to a strong side effect of nucleofection.

Recombination of replicon and helper RNAs and the emergence of propagation-competent vectors upon Sindbis virus vector production

Sindbis vectors have shown remarkable antitumor efficacy and tumor-targeting capacity in animal models and hold promise for cancer therapy. Different packaging systems are used to produce propagation-incompetent Sindbis vectors. However, the vectors produced using either DH-BB single helper RNA or split helper RNA can spread in permissive cell cultures. We investigated the mechanisms of vector spreading and show, here, that recombination occurs between the replicon and DH-BB helper RNA, leading to formation of the full-length virus genome. Split helper RNA may not completely prevent wild-type reversion, although the frequency is greatly reduced. Contrary to propagation of Sindbis DH-BB vectors, Sindbis split helper vectors were frequently able to spread without cytopathic effect (CPE), a feature that was linked to wild-type reversion. Our results support the hypothesis that the non-cytopathic local spreading constantly observed with Sindbis split helper vector results from unspecific packaging of helper RNAs into vector particles and co-infection with particles containing replicon and helper RNAs. Several malignant cell lines with defective interferon responses were found to be permissive for non-cytopathic spreading of the Sindbis split helper vector. Interferon-α suppressed the spreading providing a possible option to control the vector.

Bioreducible polymer-delivered siRNA targeting human telomerase reverse transcriptase for human cancer gene therapy

The success of siRNA therapeutics for cancer therapy largely depends on the delivery carrier that can safely and efficiently escort siRNA from the extracellular environment into the targeted human cancer cells. Over the past few years, disulfide-containing (bioreducible) cationic polymers have been designed, prepared and successfully applied as nonviral carriers for powerful gene/siRNA transfer, meanwhile displaying lower cytotoxicity as compared with their counterparts lacking the disulfide linkage, in part due to the intracellular degradation of the disulfide linkage. We have recently developed bioreducible disulfide-based polyethylenimine (SSPEI) for potent in vitro and in vivo delivery of siRNA targeting human telomerase reverse transcriptase (hTERT). It was found that SSPEI-delivered hTERT siRNA induced significant growth inhibition of different human cancer cells in vitro and also tumor growth suppression in vivo. Importantly, the SSPEI, at an appropriate dose, revealed a negligible adverse effect on cellular metabolic activity in vitro and liver and kidney function in vivo.

Specific inhibition of SRC kinase impairs malignant glioma growth in vitro and in vivo

Malignant glioma is a severe cancer with a poor prognosis. Local occurrence and rare metastases of malignant glioma make it a suitable target for gene therapy. Several studies have demonstrated the importance of Src kinase in different cancers. However, these studies have focused mainly on Src-deficient mice or pharmacological inhibitors of Src. In this study we have used Src small hairpin RNAs (shRNAs) in a lentiviral backbone to mimic a long-term stable treatment and determined the role of Src in tumor tissues. Efficacy of Src shRNAs was confirmed in vitro demonstrating up to 90% target gene inhibition. In a mouse malignant glioma model, Src shRNA tumors were almost 50-fold smaller in comparison to control tumors and had significantly reduced vascularity. In a syngenic rat intracranial glioma model, Src shRNA-transduced tumors were smaller and these rats had a survival benefit over the control rats. In vivo treatment was enhanced by chemotherapy and histone deacetylase inhibition. Our results emphasise the importance of Src in tumorigenesis and demonstrate that it can be efficiently inhibited in vitro and in vivo in two independent malignant glioma models. In conclusion, Src is a potential target for RNA interference-mediated treatment of malignant glioma.

Oncolytic Semliki forest virus vector as a novel candidate against unresectable osteosarcoma

Oncolytic viruses are a promising tool for treatment of cancer. We studied an oncolytic Semliki Forest virus (SFV) vector, VA7, carrying the enhanced green fluorescent protein gene (EGFP), as a novel virotherapy candidate against unresectable osteosarcoma. The efficiency and characteristics of the VA7-EGFP treatment were compared with a widely studied oncolytic adenovirus, Ad5Delta24, both in vitro and in vivo. VA7-EGFP resulted in more rapid oncolysis and was more efficient at low multiplicities of infection (MOI) when compared with Ad5Delta24 in vitro. Yet, in MG-63 cells, a subpopulation resistant to the VA7-EGFP vector emerged. In subcutaneous human osteosarcoma xenografts in nude mice treatment with either vector reduced tumor size, whereas tumors in control mice expanded quickly. The VA7-EGFP-treated tumors were either completely abolished or regressed to pinpoint size. The efficacy of VA7-EGFP vector was studied also in an orthotopic osteosarcoma nude mouse model characterized by highly aggressive tumor growth. Treatment with oncolytic SFV extended survival of the animals significantly (P < 0.01), yet none of the animals were finally cured. Sera from SFV-treated mice contained neutralizing antibodies, and as nude mice are not able to establish IgG response, the result points out the role of IgM class antibodies in clearance of virus from peripheral tumors. Furthermore, biodistribution analysis at the survival end point verified the presence of virus in some of the brain samples, which is in line with previous studies demonstrating that IgG is required for clearance of SFV from central nervous system.

Replication competent Semliki Forest virus prolongs survival in experimental lung cancer

We evaluated the therapeutic potential of the replication competent vector VA7-EGFP, which is based on the avirulent Semliki Forest virus (SFV) strain A7 (74) carrying the EGFP marker gene in an orthotopic lung cancer tumor model in nude mice. We have previously shown that this oncolytic vector destroys tumor cells efficiently in vitro and in vivo (in subcutaneous tumor model). Tumor growth in animals with orthotopically implanted adenocarcinoma cells (A549) were monitored during the study with small animal CT. We show that locally administered virotherapy with VA7-EGFP increased survival rate in experimental lung cancer significantly (p < 0.001) comparable to results obtained with the second generation conditionally replicating adenoviral vector Ad5-Delta24TK-GFP, used for comparison. The limited efficacy in systemically administered oncolytic viruses is the essential problem in oncolytic virotherapy and also in this study we were not able to elicit significant response with systemic administration route. Despite the fact that tumor microenvironment in orthotopic lung cancer is more optimal, viruses failed to home to the tumors and were unable to initiate efficient intratumoral replication. Clearly, the efficacy of virotherapy is influenced by many factors such as the route of virus administration, immunological and physiological barriers and cancer cell-specific features (IFN-responsiveness).

Evaluation of cancer virotherapy with attenuated replicative Semliki forest virus in different rodent tumor models

Semliki Forest virus (SFV) is one of the latest candidates for a virotherapeutic agent against cancer, and recent studies have demonstrated its efficacy in tumor models. In the present study, we examined the antitumor efficacy of an avirulent SFV strain A7(74) and its derivative, a replication-competent SFV vector VA7-EGFP, in a partially immunodeficient mouse tumor model (subcutaneous A549 human lung adenocarcinoma in NMRI nu/nu mouse) and in an immunocompetent rat tumor model (intracranial BT4C glioma in BDIX rat). When subcutaneous mouse tumors were injected 3 times with VA7-EGFP, intratumorally treated animals showed almost complete inhibition of tumor growth, while systemically treated mice displayed only delayed tumor growth (intravenous injection) or no response at all (intraperitoneal injection). This was at least partially due to a strong type I interferon (IFN) response in the tumors. The animals did not display any signs of abnormal behavior or encephalitis, even though SFV-positive foci were detected in the brain after the initial blood viremia. Intracranial rat tumors were injected directly with SFV A7(74) virus and monitored with magnetic resonance imaging. Tumor growth was significantly reduced (p < 0.05) with one virus injection, but the tumor size continued to increase after a lag period and none of the treated animals survived. Three virus injections or T-cell suppression with dexamethasone did not significantly improve treatment efficacy. It appeared that the local virotherapy induced extensive production of neutralizing anti-SFV antibodies that most likely contributed to the insufficient treatment efficacy. In conclusion, we show here that SFV A7(74) is a potential oncolytic agent for cancer virotherapy, but major immunological hurdles may need to be overcome before the virus can be clinically tested.