Kunjin Virus Replicon Vaccine Vectors Induce Protective CD8⁺T-Cell Immunity

Abstract

Replicon-based vectors of positive-strand RNA viruses are becoming more and more popular for development of antiviral and anticancer vaccines (reviewed in reference 24). Several features make these vectors a desirable choice for development of highly efficient and safe vaccines. These include (i) a high level of expression of encoded heterologous genes (HGs) due to the ability of replicon RNA to amplify itself; (ii) exclusively cytoplasmic replication, which eliminates any possible complications associated with nuclear splicing and/or chromosomal integration; (iii) inability of the replicon RNA to escape from the transfected (or infected) cell, thus limiting the spread of the vaccine vector in the immunized subject, which makes these vectors biologically safe; and (iv) relatively small genome size (7 to 9 kb), allowing easy manipulations with the cDNA and generation of recombinants. An additional beneficial feature of replicon vectors is a variety of modalities that can be used to deliver replicon RNA into cells (Fig. 1A) (24). It can be either delivered directly as naked RNA transcribed in vitro (RNA based), packaged first into virus-like particles (VLPs) and then delivered via infection with these VLPs, or delivered in the form of plasmid DNA, which encodes replicon cDNA placed under the control of a mammalian expression promoter (DNA based), allowing the production of functional replicon RNA in vivo by the cellular RNA polymerase II (Fig. 1A). Replicon-based expression vectors have been developed for representatives of most positive-strand RNA virus families, including alphaviruses, picornaviruses, and flaviviruses (reviewed in reference 24). However, the great majority of the data on immunogenic properties of replicon vectors in laboratory animals have been accumulated using replicons of alphaviruses such as Sindbis virus (SIN), Semliki Forest virus (SFV), and Venezuelan equine encephalitis virus (VEE) (see reference 47 for a review and references 8, 10, 11, and 39 for more recent studies). In general, these studies showed that alphavirus replicon vectors induced strong antibody and CD8 ϩ T-cell responses to encoded immunogens and in most cases protected immunized animals from appropriate virus or tumor challenges. All three delivery modalities were effective; however, VLP delivery was shown to be the most efficient. In comparative studies of conventional (nonreplicating) plasmid DNA vectors and alphavirus DNA-based replicon vectors, the latter generally induced stronger immune responses and at significantly lower DNA concentrations than did conventional vectors (4, 17). However, in some studies the efficiency of immune responses induced by DNA-based alphavirus replicons appeared to depend on the nature of the encoded immunogen, and the immunity to some immunogens was shown to be similar to or lower than that induced by the same amount of conventional plasmid DNA vector (10,22).We have been developing replicon vectors derived from the flavivirus Kunjin (KUN) (25,27,52,53). The KUN replicon expression system,...

Mimicking live flavivirus immunization with a noninfectious RNA vaccine

“…Application of naked, self-replicating RNA derived from a positive-stranded RNA virus and expressing a heterologous gene has successfully been used to elicit a specific humoral and cellular immune response (36)(37)(38). However, the same principle can also be applied in the form of a DNA vaccine in which the viral sequence is placed under the control of a eukaryotic promoter to drive the transcription of the noninfectious, replicating RNA in vivo (36,37).…”

“…However, the same principle can also be applied in the form of a DNA vaccine in which the viral sequence is placed under the control of a eukaryotic promoter to drive the transcription of the noninfectious, replicating RNA in vivo (36,37). Similarly, application of DNA from which infectious RNA corresponding to an attenuated flavivirus is transcribed in vivo has recently been introduced as an experimental vaccine against West Nile virus (10).…”

Selectively replicating viral vectors

“…212 a -Virus replicon vectors appear to induce strong antibody and CD8 + T-cell responses to encoded immunogenes and have been shown to protect immunized animals from tumor challenge. 213 One self -replicating RNA ( replicon ) vaccine vector derived from an Australian flavivirus Kunjin was recently shown to induce a protective CD8 + T-cell response after a single immunization in a murine B16 melanoma model. 213 The degree of the CD8 + T-cell responses appears to be comparable to other viruses.…”

“…213 One self -replicating RNA ( replicon ) vaccine vector derived from an Australian flavivirus Kunjin was recently shown to induce a protective CD8 + T-cell response after a single immunization in a murine B16 melanoma model. 213 The degree of the CD8 + T-cell responses appears to be comparable to other viruses. 214 -216 Kunjin replicons do not cause overt apoptosis or cytopathic effect of the host cell while replicating within the cytoplasm.…”

Viral vectors for use in the development of biodefense vaccines

“…The KUN vaccine vector is non-cytopathic and directed prolonged expression of heterologous genes in cultured cells [103]. Vaccinating mice with the KUN vector expressing murine polyepitope stimulated protective CTL responses in the mice against a recombinant VV or against a B16-OVA tumor challenge [104]. Similar to KUN, YF virus engineered to express OVA was able to elicit protective CTL responses in vaccinated mice against a lethal challenge with malignant melanoma cells expressing OVA [105].…”