Vaccines to die for

Immune modulating effect by a phosphoprotein-deleted rabies virus vaccine vector expressing two copies of the rabies virus glycoprotein gene

The type of immune response induced by a vaccine is a critical factor that determines its effectiveness in preventing infection or disease. Inactivated and live rabies virus (RV) vaccine strains elicit an IgG1-biased and IgG1/IgG2a-balanced antibody response, respectively. However, IgG2a antibodies are potent inducers of anti-viral effector functions, and therefore, a viral vaccine vector that can elicit an IgG2a-biased antibody response may be more effective against RV infection. Here we describe the humoral immune response of a live replication-deficient phosphoprotein (P)-deleted RV vector (SPBN-DeltaP), or a recombinant P-deleted virus that expresses two copies of the RV glycoprotein (G) gene (SPBN-DeltaP-RVG), and compare it to a UV-inactivated RV. Mice inoculated with UV-inactivated RV induced predominantly an IgG1-specific antibody response, while live recombinant SPBN-DeltaP exhibited a mixed IgG1/IgG2a antibody response, which is consistent with the isotype profiles from the replication-competent parental viruses. Survivorship in mice after pathogenic RV challenge indicates a 10-fold higher efficiency of live SPBN-DeltaP compared to UV-inactivated SPBN-DeltaP. In addition, SPBN-DeltaP-RVG induced a more rapid and robust IgG2a response that protected mice more effectively than SPBN-DeltaP. Of note, 10(3)ffu of SPBN-DeltaP-RVG-induced anti-RV antibodies that were 100% protective in mice against pathogenic RV challenge. The increased immune response was directed not only against RV G but also against the ribonucleoprotein (RNP), indicating that the expression of two RV G genes from SPBN-DeltaP-RVG enhances the immune response to other RV antigens as well. In addition, Rag2 mice inoculated intramuscularly with 10(5)ffu/mouse of SPBN-DeltaP showed no clinical signs of rabies, and no viral RNA was detected in the spinal cord or brain of inoculated mice. Therefore, the safety of the P-deleted vectors along with the onset and magnitude of the IgG2a-induced immune response by SPBN-DeltaP-RVG indicate that this vector holds great promise as either a therapeutic or preventative vaccine against RV or other infectious diseases.

Gene therapy of mesothelioma

Despite improved diagnostic skills and new chemotherapeutic regimens, malignant mesothelioma (MM) remains a pathological disease with survival expectations after diagnosis remaining < 1 year. As the incidence of this disease has yet to peak, there is a pressing need for new therapeutic approaches. One such approach is gene therapy, which inserts 'therapeutic' genes into (generally) tumour cells seeking to induce tumour regression via a number of different theoretical mechanisms. This approach may be particularly relevent for mesothelioma as it is localised to body cavities and is readily accessible for biopsy sampling or for gene delivery. Furthermore, as MM patients rarely die from distant metastases, treating the primary tumour site may result in significant symptomatic and survival benefit. Herein, the paper discusses past, present and future views on gene therapy in the treatment of MM.

The role of particle-mediated DNA vaccines in biodefense preparedness

Particle-mediated epidermal delivery (PMED) of DNA vaccines is based on the acceleration of DNA-coated gold directly into the cytoplasm and nuclei of living cells of the epidermis, facilitating DNA delivery and gene expression. Professional antigen-presenting cells and keratinocytes in the skin are both targeted, resulting in antigen presentation via direct transfection and cross-priming mechanisms. Only a small number of cells need to be transfected to elicit humoral, cellular and memory responses, requiring only a low DNA dose. In recent years, data have accumulated on the utility of PMED for delivery of DNA vaccines against a number of viral pathogens, including filoviruses, flaviviruses, poxviruses, togaviruses and bunyaviruses. PMED DNA immunization of rodents and nonhuman primates results in the generation of neutralizing antibody, cellular immunity, and protective efficacy against a broad range of viruses of public health concern.

Particle-mediated DNA vaccine delivery to the skin

Particle-mediated DNA vaccines employ a physical, intracellular delivery device to achieve the deposition of plasmid DNA-based expression vectors directly into the interior of cells of the skin. The resultant bolus of transient antigen expression in keratinocytes and trafficking dendritic cells results in the induction of humoral and cellular immune responses in various animal models and humans, mimicking characteristics of live or live-vectored vaccines. Ultimately, DNA vaccine success in the clinic will depend on both the successful intracellular delivery of a plasmid vector and an immunostimulator or adjuvant to maximise humoral and cellular immune responses to the encoded antigen(s). To this end, recent DNA vaccine clinical trials are confirming the importance of an intracellular delivery system, while preclinical studies in animal models are demonstrating the feasibility of augmenting responses through the use of DNA-encoded immunostimulators. Particle-mediated DNA vaccines represent a promising tool for developing candidate vaccines against some of the more difficult infectious, parasitic and oncologic disease targets.

Apoptosis is essential for the increased efficacy of alphaviral replicase-based DNA vaccines

Alphaviral replicons can increase the efficacy and immunogenicity of naked nucleic acid vaccines. To study the impact of apoptosis on this increased effectiveness, we co-delivered an anti-apoptotic gene (Bcl-X(L)) with the melanocyte/melanoma differentiation antigen TRP-1. Although cells co-transfected with Bcl-X(L) lived longer, produced more antigen and elicited increased antibody production in vivo, co-delivery of pro-survival Bcl-X(L) with antigen significantly reduced the ability of the replicase-based vaccine to protect against an aggressive tumor challenge. These data show for the first time that the induction of apoptotic cell death of transfected cells in vivo is required for the increased effectiveness of replicase-based vaccines. Our findings also provide an explanation for the paradoxical observation that replicase-based DNA vaccines are much more immunogenic than conventional constructs despite reduced antigen production.

Danger, death and DNA vaccines

DNA vaccines, although successful in many animal models of various diseases, remain insufficiently immunogenic in humans. Among the countless approaches to improve them is the stimulation of the innate immune system by promoting the apoptotic death of the transfected host cells, which is the focus of this review.

DNA vaccines and apoptosis: to kill or not to kill?

The apoptotic machinery has become the latest target of vaccinologists attempting to improve the efficacy of DNA vaccines. While workers have previously sought to induce apoptotic death in transfected DCs as a means to activate immunity, a new approach (see related article on pages 109–117) instead seeks to delay apoptosis in host DCs after DNA vaccination.

Alphavirus-based DNA vaccine breaks immunological tolerance by activating innate antiviral pathways

Cancer vaccines targeting 'self' antigens that are expressed at consistently high levels by tumor cells are potentially useful in immunotherapy, but immunological tolerance may block their function. Here, we describe a novel, naked DNA vaccine encoding an alphavirus replicon (self-replicating mRNA) and the self/tumor antigen tyrosinase-related protein-1. Unlike conventional DNA vaccines, this vaccine can break tolerance and provide immunity to melanoma. The vaccine mediates production of double-stranded RNA, as evidenced by the autophosphorylation of dsRNA-dependent protein kinase R (PKR). Double-stranded RNA is critical to vaccine function because both the immunogenicity and the anti-tumor activity of the vaccine are blocked in mice deficient for the RNase L enzyme, a key component of the 2',5'-linked oligoadenylate synthetase antiviral pathway involved in double-stranded RNA recognition. This study shows for the first time that alphaviral replicon-encoding DNA vaccines activate innate immune pathways known to drive antiviral immune responses, and points the way to strategies for improving the efficacy of immunization with naked DNA.

Immunomodulation by apoptosis-inducing caspases for an influenza DNA vaccine delivered by gene gun

Apoptosis-inducing caspases have been tested for immunomodulatory effect on a gene gun-delivered DNA vaccine which expresses influenza hemagglutinin. Attenuated murine caspase 2 and a chimera of murine caspase 2 prodomain and human caspase 3 strongly enhanced humoral and cell-mediated immune response to hemagglutinin when they were co-administered with an immunogen DNA. In contrast, wild-type caspases did not enhance the DNA-raised immune response. Caspase dose-dependent antibody response curve revealed that the antibody level was in inverse relation to the amount of administered caspase. These findings indicate that bland apoptosis of antigen-harboring cells can elicit enhanced immune responses. Extensive apoptosis interferes with the generation of immune response. Gene gun delivery involving caspases elicited type-2 immune responses that characterized with dominant IL-4 and IgG1 production. ELISPOT assays showed that CD4 T cells were preferentially activated, while CD8 T cell response remained at marginal level. Using attenuated caspases for gene gun DNA vaccination is a useful approach to amplify type-2 immune responses.