Th1-biased immune responses induced by DNA-based immunizations are mediated via action on professional antigen-presenting cells to up-regulate IL-12 production

Production and Immunogenicity of FeLV Gag-Based VLPs Exposing a Stabilized FeLV Envelope Glycoprotein

The envelope glycoprotein (Env) of retroviruses, such as the Feline leukemia virus (FeLV), is the main target of neutralizing humoral response, and therefore, a promising vaccine candidate, despite its reported poor immunogenicity. The incorporation of mutations that stabilize analogous proteins from other viruses in their prefusion conformation (e.g., HIV Env, SARS-CoV-2 S, or RSV F glycoproteins) has improved their capability to induce neutralizing protective immune responses. Therefore, we have stabilized the FeLV Env protein following a strategy based on the incorporation of a disulfide bond and an Ile/Pro mutation (SOSIP) previously used to generate soluble HIV Env trimers. We have characterized this SOSIP-FeLV Env in its soluble form and as a transmembrane protein present at high density on the surface of FeLV Gag-based VLPs. Furthermore, we have tested its immunogenicity in DNA-immunization assays in C57BL/6 mice. Low anti-FeLV Env responses were detected in SOSIP-FeLV soluble protein-immunized animals; however, unexpectedly no responses were detected in the animals immunized with SOSIP-FeLV Gag-based VLPs. In contrast, high humoral response against FeLV Gag was observed in the animals immunized with control Gag VLPs lacking SOSIP-FeLV Env, while this response was significantly impaired when the VLPs incorporated SOSIP-FeLV Env. Our data suggest that FeLV Env can be stabilized as a soluble protein and can be expressed in high-density VLPs. However, when formulated as a DNA vaccine, SOSIP-FeLV Env remains poorly immunogenic, a limitation that must be overcome to develop an effective FeLV vaccine.

A retrospective analysis of the Alzheimer's disease vaccine progress - The critical need for new development strategies

The promising results obtained with aducanumab and solanezumab against Alzheimer's disease (AD) strengthen the vaccine approach to prevent AD, despite of the many clinical setbacks. It has been problematic to use conjugated peptides with Th1/Th2 adjuvants to induce immune responses against conformational epitopes formed by Aβ oligomers, which is critical to induce protective antibodies. Hence, vaccination should mimic natural immunity by using whole or if possible conjugated antigens, but biasing the response to Th2 with anti-inflammatory adjuvants. Also, selection of the carrier and cross-linking agents is important to prevent suppression of the immune response against the antigen. That certain compounds having phosphorylcholine or fucose induce a sole Th2 immunity would allow antigens with T-cell epitopes without inflammatory autoimmune reactions to be used. Another immunization method is DNA vaccines combined with antigenic ones, which favors the clonal selection and expansion of high affinity antibodies needed for immune protection, but this also requires Th2 immunity. Since AD transgenic mouse models have limited value for immunogen selection as shown by the clinical studies, screening may require the use of validated antibodies and biophysical methods to identify the antigens that would be most likely recognized by the human immune system and thus capable to stimulate a protective antibody response. To induce an anti-Alzheimer's disease protective immunity and prevent possible damage triggered by antigens having B-cell epitopes-only, whole antigens might be used; while inducing Th2 immunity with sole anti-inflammatory fucose-based adjuvants. This approach would avert a damaging systemic inflammatory immunity and the suppression of immunoresponse against the antigen because of carrier and cross-linkers; immune requirements that extend to DNA vaccines.

DNA/MVA Vaccines for HIV/AIDS

Since the initial proof-of-concept studies examining the ability of antigen-encoded plasmid DNA to serve as an immunogen, DNA vaccines have evolved as a clinically safe and effective platform for priming HIV-specific cellular and humoral responses in heterologous "prime-boost" vaccination regimens. Direct injection of plasmid DNA into the muscle induces T- and B-cell responses against foreign antigens. However, the insufficient magnitude of this response has led to the development of approaches for enhancing the immunogenicity of DNA vaccines. The last two decades have seen significant progress in the DNA-based vaccine platform with optimized plasmid constructs, improved delivery methods, such as electroporation, the use of molecular adjuvants and novel strategies combining DNA with viral vectors and subunit proteins. These innovations are paving the way for the clinical application of DNA-based HIV vaccines. Here, we review preclinical studies on the DNA-prime/modified vaccinia Ankara (MVA)-boost vaccine modality for HIV. There is a great deal of interest in enhancing the immunogenicity of DNA by engineering DNA vaccines to co-express immune modulatory adjuvants. Some of these adjuvants have demonstrated encouraging results in preclinical and clinical studies, and these data will be examined, as well.

PD1-based DNA vaccine amplifies HIV-1 GAG-specific CD8+ T cells in mice

Viral vector-based vaccines that induce protective CD8+ T cell immunity can prevent or control pathogenic SIV infections, but issues of preexisting immunity and safety have impeded their implementation in HIV-1. Here, we report the development of what we believe to be a novel antigen-targeting DNA vaccine strategy that exploits the binding of programmed death-1 (PD1) to its ligands expressed on dendritic cells (DCs) by fusing soluble PD1 with HIV-1 GAG p24 antigen. As compared with non-DC-targeting vaccines, intramuscular immunization via electroporation (EP) of the fusion DNA in mice elicited consistently high frequencies of GAG-specific, broadly reactive, polyfunctional, long-lived, and cytotoxic CD8+ T cells and robust anti-GAG antibody titers. Vaccination conferred remarkable protection against mucosal challenge with vaccinia GAG viruses. Soluble PD1-based vaccination potentiated CD8+ T cell responses by enhancing antigen binding and uptake in DCs and activation in the draining lymph node. It also increased IL-12-producing DCs and engaged antigen cross-presentation when compared with anti-DEC205 antibody-mediated DC targeting. The high frequency of durable and protective GAG-specific CD8+ T cell immunity induced by soluble PD1-based vaccination suggests that PD1-based DNA vaccines could potentially be used against HIV-1 and other pathogens.

The role of gamma interferon in DNA vaccine-induced tumor immunity targeting simian virus 40 large tumor antigen

The central role of CD4+ T lymphocytes in mediating DNA vaccine-induced tumor immunity against the viral oncoprotein simian virus 40 (SV40) large tumor antigen (Tag) has previously been described by our laboratory. In the present study, we extend our previous findings by examining the roles of IFN-γ and Th1-associated effector cells within the context of DNA immunization in a murine model of pulmonary metastasis. Immunization of BALB/c mice with plasmid DNA encoding SV40 Tag (pCMV-Tag) generated IFN-γ-secreting T lymphocytes that produced this cytokine upon in vitro stimulation with mKSA tumor cells. The role of IFN-γ as a mediator of protection against mKSA tumor development was assessed via in vivo IFN-γ neutralization, and these experiments demonstrated a requirement for this cytokine in the induction immune phase. Neutralization of IFN-γ was associated with a reduction in Th1 cytokine-producing CD4+ and CD8+ splenocytes, as assessed by flow cytometry analysis, and provided further evidence for the role of CD4+ T lymphocytes as drivers of the cellular immune response. Depletion of NK cells and CD8+ T lymphocytes demonstrated the expendability of these cell types individually, but showed a requirement for a resident cytotoxic cell population within the immune effector phase. Our findings demonstrate the importance of IFN-γ in the induction of protective immunity stimulated by pCMV-Tag DNA-based vaccine and help to clarify the general mechanisms by which DNA vaccines trigger immunity to tumor cells.

Serine/threonine kinase PKR: a sentinel kinase that discriminates a signaling pathway mediated by TLR4 from those mediated by TLR3 and TLR9

Cells of the innate immune system discriminate between "noninfectious self" and "infectious nonself" via pattern recognition receptors known as Toll-like receptors (TLRs). Though TLRs and the related interleukin 1 receptors share considerable homology in their cytoplasmic domains and adaptor molecules, signaling cascades may substantially differ from one another depending on the adaptor proteins recruited. Here we show that ectopic overexpression of catalytically inactive dominant-negative PKR expression system suppressed NF- kappa B activation mediated by TLR3, TLR9, TNF receptor 1 and 2 (TNF-R 1/2), but not by TLR4. Physiological relevance of the observations described here are discussed.

Soluble cytokines can act as effective adjuvants in plasmid DNA vaccines targeting self tumor antigens

There are few vaccination strategies available for the reproducible generation of a cytotoxic T cell (CTL) response, particularly in the setting of immunizing against a tumor antigen. Plasmid-based DNA vaccination offers several advantages as compared to MHC class I peptide-based vaccines or DNA immunization using viral vectors. Plasmid-based DNA vaccines are easily produced, can potentially elicit both an MHC class I and class II response, and have little infectious potential. Plasmid-based vaccines, however, have been poorly immunogenic. The systemic immune response generated after plasmid vaccination relies on in vivo transfection of local antigen presenting cells (APC) and both direct presentation and "cross priming" of antigen by professional and non-professional APC. Therefore, methods to enhance the function of APC, such as simultaneous inoculation with plasmids encoding cytokine genes, has resulted in an enhancement of detectable immunity after vaccination. We questioned whether local application of soluble cytokines would be effective in enhancing the systemic immune response elicited after DNA vaccination. Using a self-tumor antigen model, we vaccinated rats with a plasmid-based rat neu intracellular domain (ICD) DNA construct and either no adjuvant, soluble GM-CSF, or IL-12. We demonstrate that the addition of soluble GM-CSF or IL-12 to rat neu ICD DNA vaccination elicits detectable neu specific T cell immunity; specifically the generation of CTL. Antibodies directed against rat neu were not elicited with this approach, indicating that the neu specific T cell immune response elicited with plasmid DNA was skewed towards cell-mediated rather than humoral immunity.

Type I IFN modulates the immune response induced by DNA vaccination to pseudorabies virus glycoprotein C

DNA vaccines have the capacity to induce strong Th1-biased immune responses that are of major importance to providing protection against intracellular pathogens. In the present study we have focused on the role played by type I IFN in immune responses induced after DNA vaccination. Mice lacking the IFNAR1 chain of the type I IFN receptor (IFNAR K/O mice) were immunized with a plasmid encoding glycoprotein C of pseudorabies virus (PRV-gC). After DNA vaccination, wild-type (WT) mice showed features characteristic of Th1 immune responses, such as high IgG2a:IgG1 anti-PRV Ab ratio and antigen-specific IFN-gamma production by spleen cells. In contrast, IFNAR K/O mice showed a significantly lower IgG2a:IgG1 Ab ratio and IFN-gamma production. In addition, the percentage of CD8(+) and B lymph-node cells expressing CD69 after PRV-gC DNA vaccination was lower in IFNAR K/O than in WT mice. These results support a major role played by type I IFN in shaping Th1 immune responses after DNA vaccination. Codelivery of plasmids encoding IL-12 and IL-18 along with the plasmid encoding PRV-gC restored Th1 responses in IFNAR K/O mice.

Immunisation with DNA encoding Leishmania infantum protein papLe22 decreases the frequency of parasitemic episodes in infected hamsters

We tested in outbred golden hamsters the protective potential of highly immunogenic Leishmania infantum protein papLe22 which we recently identified. Immunisation was performed using papLe22 cDNA, administered as a single intramuscular injection. The level of antibodies directed against total leishmanial antigens was significantly decreased in the vaccinated hamsters as compared with the controls, indicating that the administration of papLe22 cDNA downregulated the Th2 type response and suggesting that the immune response was reoriented toward the cell-mediated type. The presence of the parasite kDNA in the peripheral blood was systematically detected as early as 3 weeks post infection in all mock-vaccinated hamsters. By contrast, in the vaccinated animals the occurrence of the episodes of Leishmania circulation was reduced by 50%. The immunisation presenting efficacy in this highly susceptible species which develop VL similar in gravity to human and canine disease should prove also efficient in naturally infected hosts. The marked decrease of the frequency of parasite circulation induced by papLe22 cDNA immunisation appears therefore important and potentially able to reduce transmission and thus to control the spread of the disease.

Type 1/Type 2 immunity in infectious diseases

T helper type 1 (Th1) lymphocytes secrete secrete interleukin (IL)-2, interferon-gamma, and lymphotoxin-alpha and stimulate type 1 immunity, which is characterized by intense phagocytic activity. Conversely, Th2 cells secrete IL-4, IL-5, IL-9, IL-10, and IL-13 and stimulate type 2 immunity, which is characterized by high antibody titers. Type 1 and type 2 immunity are not strictly synonymous with cell-mediated and humoral immunity, because Th1 cells also stimulate moderate levels of antibody production, whereas Th2 cells actively suppress phagocytosis. For most infections, save those caused by large eukaryotic pathogens, type 1 immunity is protective, whereas type 2 responses assist with the resolution of cell-mediated inflammation. Severe systemic stress, immunosuppression, or overwhelming microbial inoculation causes the immune system to mount a type 2 response to an infection normally controlled by type 1 immunity. In such cases, administration of antimicrobial chemotherapy and exogenous cytokines restores systemic balance, which allows successful immune responses to clear the infection.