A vaccinia virus recombinant transcribing an alphavirus replicon and expressing alphavirus structural proteins leads to packaging of alphavirus infectious single cycle particles

Engineering Rapalog-Inducible Genetic Switches Based on Split-T7 Polymerase to Regulate Oncolytic Virus-Driven Production of Tumour-Localized IL-12 for Anti-Cancer Immunotherapy

The approval of different cytokines as anti-neoplastic agents has been challenged by dose-limiting toxicities. Although reducing dose levels affords improved tolerability, efficacy is precluded at these suboptimal doses. Strategies combining cytokines with oncolytic viruses have proven to elicit potent survival benefits in vivo, despite promoting rapid clearance of the oncolytic virus itself. Herein, we developed an inducible expression system based on a Split-T7 RNA polymerase for oncolytic poxviruses to regulate the spatial and temporal expression of a beneficial transgene. This expression system utilizes approved anti-neoplastic rapamycin analogues for transgene induction. This treatment regimen thus offers a triple anti-tumour effect through the oncolytic virus, the induced transgene, and the pharmacologic inducer itself. More specifically, we designed our therapeutic transgene by fusing a tumour-targeting chlorotoxin (CLTX) peptide to interleukin-12 (IL-12), and demonstrated that the constructs were functional and cancer-selective. We next encoded this construct into the oncolytic vaccinia virus strain Copenhagen (VV-iIL-12mCLTX), and were able to demonstrate significantly improved survival in multiple syngeneic murine tumour models through both localized and systemic virus administration, in combination with rapalogs. In summary, our findings demonstrate that rapalog-inducible genetic switches based on Split-T7 polymerase allow for regulation of the oncolytic virus-driven production of tumour-localized IL-12 for improved anti-cancer immunotherapy.

Development of a Novel Chikungunya Virus-Like Replicon Particle for Rapid Quantification and Screening of Neutralizing Antibodies and Antivirals

Chikungunya fever is a mosquito-transmitted infectious disease that induces rash, myalgia, and persistent incapacitating arthralgia. At present, no vaccines or antiviral therapies specific to Chikungunya virus (CHIKV) infection have been approved, and research is currently restricted to biosafety level 3 containment. CHIKV-like replicon particles (VRPs) are single-cycle infectious particles containing viral structure proteins, as well as a defective genome to provide a safe surrogate for living CHIKV to facilitate the testing of vaccines and antivirals. However, inefficient RNA transfection and the potential emergence of the competent virus through recombination in mammalian cells limit VRP usability. This study describes a transfection-free system for the safe packaging of CHIK VRP with all necessary components via transduction of mosquito cell lines using a single baculovirus vector. We observed the release of substantial quantities of mosquito cell-derived CHIK VRP (mos-CHIK VRP) from baculovirus-transduced mosquito cell lines. The VRPs were shown to recapitulate viral replication and subgenomic dual reporter expression (enhanced green fluorescent protein [eGFP] and luciferase) in infected host cells. Interestingly, the rapid expression kinetics of the VRP-expressing luciferase reporter (6 h) makes it possible to use mos-CHIK VRPs for the rapid quantification of VRP infection. Treatment with antivirals (suramin or 6-azauridine) or neutralizing antibodies (monoclonal antibodies [MAbs] or patient sera) was shown to inhibit mos-CHIK VRP infection in a dose-dependent manner. Ease of manufacture, safety, scalability, and high throughput make mos-CHIK VRPs a highly valuable vehicle for the study of CHIKV biology, the detection of neutralizing (NT) antibody activity, and the screening of antivirals against CHIKV. IMPORTANCE This study proposes a transfection-free system that enables the safe packaging of CHIK VRPs with all necessary components via baculovirus transduction. Those mosquito cell-derived CHIK VRP (mos-CHIK VRPs) were shown to recapitulate viral replication and subgenomic dual reporter (enhanced green fluorescent protein [eGFP] and luciferase) expression in infected host cells. Rapid expression kinetics of the VRP-expressing luciferase reporter (within hours) opens the door to using mos-CHIK VRPs for the rapid quantification of neutralizing antibody and antiviral activity against CHIKV. To the best of our knowledge, this is the first study to report a mosquito cell-derived alphavirus VRP system. Note that this system could also be applied to other arboviruses to model the earliest event in arboviral infection in vertebrates.

Facile method for delivering chikungunya viral replicons into mosquitoes and mammalian cells

Reverse genetics is an important tool in the elucidation of viral replication and the development of countermeasures; however, these methods are impeded by laborious and inefficient replicon delivery methods. This paper demonstrates the use of a baculovirus to facilitate the efficient delivery of autonomous CHIKV replicons into mosquito and mammalian cells in vitro as well as adult mosquitoes in vivo. The efficacy of this approach was verified via co-localization among an eGFP reporter, nsP1, and dsRNA as well as through the inhibition of an RNA-dependent RNA polymerase (RdRp) null mutation (DDAA) in nsP4, or the treatment of a known antiviral compound (6-azauridine). We also investigated the correlation between CHIKV replicon-launched eGFP expression and the effectiveness of CHIKV replicon variants in inducing IFN-β expression in human cell lines. This delivery method based on a single vector is applicable to mosquito and mammalian cells in seeking to decipher the mechanisms underlying CHIKV replication, elucidate virus-host interactions, and develop antivirals. This study presents an effective alternative to overcome many of the technological issues related to the study and utilization of autonomous arbovirus replicons.

Self-replicating alphavirus RNA vaccines

Recombinant nucleic acids are considered as promising next-generation vaccines. These vaccines express the native antigen upon delivery into tissue, thus mimicking live attenuated vaccines without having the risk of reversion to pathogenicity. They also stimulate the innate immune system, thus potentiating responses. Nucleic acid vaccines are easy to produce at reasonable cost and are stable. During the past years, focus has been on the use of plasmid DNA for vaccination. Now mRNA and replicon vaccines have come into focus as promising technology platforms for vaccine development. This review discusses self-replicating RNA vaccines developed from alphavirus expression vectors. These replicon vaccines can be delivered as RNA, DNA or as recombinant virus particles. All three platforms have been pre-clinically evaluated as vaccines against a number of infectious diseases and cancer. Results have been very encouraging and propelled the first human clinical trials, the results of which have been promising.

Tumor Restrictions to Oncolytic Virus

Oncolytic virotherapy has advanced since the days of its conception but therapeutic efficacy in the clinics does not seem to reach the same level as in animal models. One reason is premature oncolytic virus clearance in humans, which is a reasonable assumption considering the immune-stimulating nature of the oncolytic agents. However, several studies are beginning to reveal layers of restriction to oncolytic virotherapy that are present before an adaptive neutralizing immune response. Some of these barriers are present constitutively halting infection before it even begins, whereas others are raised by minute cues triggered by virus infection. Indeed, we and others have noticed that delivering viruses to tumors may not be the biggest obstacle to successful therapy, but instead the physical make-up of the tumor and its capacity to mount antiviral defenses seem to be the most important efficacy determinants. In this review, we summarize the constitutive and innate barriers to oncolytic virotherapy and discuss strategies to overcome them.