The efficacy of DNA vaccination is enhanced in mice by targeting the encoded protein to dendritic cells

Specific Cell Targeting by Toxoplasma gondii Displaying Functional Single-Chain Variable Fragment as a Novel Strategy; A Proof of Principle

Toxoplasma gondii holds significant therapeutic potential; however, its nonspecific invasiveness results in off-target effects. The purpose of this study is to evaluate whether T. gondii specificity can be improved by surface display of scFv directed against dendritic cells' endocytic receptor, DEC205, and immune checkpoint PD-L1. Anti-DEC205 scFv was anchored to the T. gondii surface either directly via glycosylphosphatidylinositol (GPI) or by fusion with the SAG1 protein. Both constructs were successfully expressed, but the binding results suggested that the anti-DEC-SAG1 scFv had more reliable functionality towards recombinant DEC protein and DEC205-expressing MutuDC cells. Two anti-PD-L1 scFv constructs were developed that differed in the localization of the HA tag. Both constructs were adequately expressed, but the localization of the HA tag determined the functionality by binding to PD-L1 protein. Co-incubation of T. gondii displaying anti-PD-L1 scFv with tumor cells expressing/displaying different levels of PD-L1 showed strong binding depending on the level of available biomarker. Neutralization assays confirmed that binding was due to the specific interaction between anti-PD-L1 scFv and its ligand. A mixed-cell assay showed that T. gondii expressing anti-PD-L1 scFv predominately targets the PD-L1-positive cells, with negligible off-target binding. The recombinant RH-PD-L1-C strain showed increased killing ability on PD-L1+ tumor cell lines compared to the parental strain. Moreover, a co-culture assay of target tumor cells and effector CD8+ T cells showed that our model could inhibit PD1/PD-L1 interaction and potentiate T-cell immune response. These findings highlight surface display of antibody fragments as a promising strategy of targeting replicative T. gondii strains while minimizing nonspecific binding.

Recombinant antigen delivery to dendritic cells as a way to improve vaccine design

Dendritic cells are central to the development of immunity, as they are specialized in initiating antigen-specific immune responses. In this review, we briefly present the existing knowledge on dendritic cell biology and how their division in different dendritic cell subsets may impact the development of immune responses. In addition, we explore the use of chimeric monoclonal antibodies that bind to dendritic cell surface receptors, with an emphasis on the C-type lectin family of endocytic receptors, to deliver antigens directly to these cells. Promising preclinical studies have shown that it is possible to modulate the development of immune responses to different pathogens when monoclonal antibodies fused to pathogen-derived antigens are used to deliver the antigen to different subsets of dendritic cells. This approach can be used to improve the efficacy of vaccines against different pathogens.

Targeting dendritic cells to advance cross-presentation and vaccination outcomes

Dendritic cells (DCs) are a complex network of specialised antigen-presenting cells that are critical initiators of adaptive immunity. Targeting antigen directly to DCs in situ is a vaccination strategy that selectively delivers antigen to receptors expressed by DC subtypes. This approach exploits specific DC subset functions of antigen uptake and presentation. Here, we review DC-targeted vaccination strategies that are designed to elicit effective cross-presentation for CD8+ T cell immunity. In particular, we focus on approaches that exploit receptors highly expressed by mouse and human cDCs equipped with superior cross-presentation capacity. These receptors include DEC205, Clec9A and XCR1. Targeting DC receptors Clec12A, Clec4A4 and mannose receptor is also reviewed. Outcomes of DC-targeted vaccination in mouse models through to human clinical trials is discussed. This is a promising new vaccination approach capable of directly targeting the cross-presentation pathway for prevention and treatment of tumours and infectious diseases.

Heterologous DNA Prime- Subunit Protein Boost with Chikungunya Virus E2 Induces Neutralizing Antibodies and Cellular-Mediated Immunity

Chikungunya virus (CHIKV) has become a significant public health concern due to the increasing number of outbreaks worldwide and the associated comorbidities. Despite substantial efforts, there is no specific treatment or licensed vaccine against CHIKV to date. The E2 glycoprotein of CHIKV is a promising vaccine candidate as it is a major target of neutralizing antibodies during infection. In this study, we evaluated the immunogenicity of two DNA vaccines (a non-targeted and a dendritic cell-targeted vaccine) encoding a consensus sequence of E2_CHIKV and a recombinant protein (E2*_CHIKV). Mice were immunized with different homologous and heterologous DNAprime-E2* protein boost strategies, and the specific humoral and cellular immune responses were accessed. We found that mice immunized with heterologous non-targeted DNA prime- E2*_CHIKV protein boost developed high levels of neutralizing antibodies, as well as specific IFN-γ producing cells and polyfunctional CD4⁺ and CD8⁺ T cells. We also identified 14 potential epitopes along the E2_CHIKV protein. Furthermore, immunization with recombinant E2*_CHIKV combined with the adjuvant AS03 presented the highest humoral response with neutralizing capacity. Finally, we show that the heterologous prime-boost strategy with the non-targeted pVAX-E2 DNA vaccine as the prime followed by E2* protein + AS03 boost is a promising combination to elicit a broad humoral and cellular immune response. Together, our data highlights the importance of E2_CHIKV for the development of a CHIKV vaccine.

Recent advances in antigen targeting to antigen-presenting cells in veterinary medicine

Advances in antigen targeting in veterinary medicine have gained traction over the years as an alternative approach for diseases that remain a challenge for traditional vaccines. In addition to the nature of the immunogen, antigen-targeting success relies heavily on the chosen receptor for its direct influence on the elicited response that will ensue after antigen uptake. Different approaches using antibodies, natural or synthetic ligands, fused proteins, and DNA vaccines have been explored in various veterinary species, with pigs, cattle, sheep, and poultry as the most frequent models. Antigen-presenting cells can be targeted using a generic approach, such as broadly expressed receptors such as MHC-II, CD80/86, CD40, CD83, etc., or focused on specific cell populations such as dendritic cells or macrophages (Langerin, DC-SIGN, XCR1, DC peptides, sialoadhesin, mannose receptors, etc.) with contrasting results. Interestingly, DC peptides show high specificity to DCs, boosting activation, stimulating cellular and humoral responses, and a higher rate of clinical protection. Likewise, MHC-II targeting shows consistent results in enhancing both immune responses; an example of this strategy of targeting is the approved vaccine against the bovine viral diarrhea virus in South America. This significant milestone opens the door to continuing efforts toward antigen-targeting vaccines to benefit animal health. This review discusses the recent advances in antigen targeting to antigen-presenting cells in veterinary medicine, with a special interest in pigs, sheep, cattle, poultry, and dogs.

Dendritic Cell-Targeted Therapies to Treat Neurological Disorders

Dendritic cells (DCs) are the immune system's highly specialized antigen-presenting cells. When DCs are sluggish and mature, self-antigen presentation results in tolerance; however, when pathogen-associated molecular patterns stimulate mature DCs, antigen presentation results in the development of antigen-specific immunity. DCs have been identified in various vital organs of mammals (e.g., the skin, heart, lungs, intestines, and spleen), but the brain has long been thought to be devoid of DCs in the absence of neuroinflammation. However, neuroinflammation is becoming more recognized as a factor in a variety of brain illnesses. DCs are present in the brain parenchyma in trace amounts under healthy circumstances, but their numbers rise during neuroinflammation. New therapeutics are being developed that can reduce dendritic cell immunogenicity by inhibiting pro-inflammatory cytokine production and T cell co-stimulatory pathways. Additionally, innovative ways of regulating dendritic cell growth and differentiation and harnessing their tolerogenic capability are being explored. Herein, we described the function of dendritic cells in neurological disorders and discussed the potential for future therapeutic techniques that target dendritic cells and dendritic cell-related targets in the treatment of neurological disorders.

Sustained viremia suppression by SHIVSF162P3CN-recalled effector-memory CD8+ T cells after PD1-based vaccination

HIV-1 functional cure requires sustained viral suppression without antiretroviral therapy. While effector-memory CD8⁺ T lymphocytes are essential for viremia control, few vaccines elicit such cellular immunity that could be potently recalled upon viral infection. Here, we investigated a program death-1 (PD1)-based vaccine by fusion of simian immunodeficiency virus capsid antigen to soluble PD1. Homologous vaccinations suppressed setpoint viremia to undetectable levels in vaccinated macaques following a high-dose intravenous challenge by the pathogenic SHIV_SF162P3CN. Poly-functional effector-memory CD8⁺ T cells were not only induced after vaccination, but were also recalled upon viral challenge for viremia control as determined by CD8 depletion. Vaccine-induced effector memory CD8⁺ subsets displayed high cytotoxicity-related genes by single-cell analysis. Vaccinees with sustained viremia suppression for over two years responded to boost vaccination without viral rebound. These results demonstrated that PD1-based vaccine-induced effector-memory CD8⁺ T cells were recalled by AIDS virus infection, providing a potential immunotherapy for functional cure.

HIV-1/AIDS remains a major global pandemic although treatment regimen has improved. Identifying efficacious vaccines and therapeutics to achieve long-term viral control with very low/undetectable plasma viral loads in the absence of antiretroviral therapy, a status known as functional cure, would be highly beneficial. We previously demonstrated that antigens fused to a soluble program death-1 (PD1) domain could effectively bind and be cross-presented by dendritic cells that constitutively expressed PD1 ligands. When applied in the form of DNA vaccination, this antigen-targeting strategy was highly immunogenic in mice. Here, we investigated the efficacy of the PD1-based DNA vaccine approach against pathogenic simian-human immunodeficiency virus challenge in rhesus monkeys. Our results showed that homologous PD1-based DNA vaccinations induced highly functional effector-memory CD8⁺ T cells carrying a unique cytotoxicity gene expression profile. These T cells actively supressed viremia in monkeys and were re-activated via boost vaccination at 2 years after viral challenge without viral rebound. In summary, our study demonstrates the potential application of PD1-based DNA vaccination to control AIDS virus infection.

Conventional type 1 dendritic cells induce TH 1, TH 1-like follicular helper T cells and regulatory T cells after antigen boost via DEC205 receptor

Conventional dendritic cells (cDCs) are specialized in antigen presentation. In the mouse spleen, cDCs are classified in cDC1s and cDC2s, and express DEC205 and DCIR2 endocytic receptors, respectively. Monoclonal antibodies (mAbs) αDEC205 (αDEC) and αDCIR2 have been fused to different antigens to deliver them to cDC1s or cDC2s. We immunized mice with αDEC and αDCIR2 fused to an antigen using Poly(I:C) as adjuvant. The initial immune response was analyzed from days 3 to 6 after the immunization. We also studied the influence of a booster dose. Our results showed that antigen targeting to cDC1s promoted a pro-inflammatory T_H 1 cell response. Antigen targeting to cDC2s induced T_FH cells, GCs, and plasma cell differentiation. After boost, antigen targeting to cDC1s improved the T_H 1 cell response and induced T_H 1-like T_FH cells that led to an increase in specific antibody titers and IgG class switch. Additionally, a population of regulatory T cells was also observed. Antigen targeting to cDC2s did not improve the specific antibody response after boost. Our results add new information on the immune response induced after the administration of a booster dose with αDEC and αDCIR2 fusion mAbs. These results may be useful for vaccine design using recombinant mAbs.

Targeting Antigens to Different Receptors on Conventional Type 1 Dendritic Cells Impacts the Immune Response

Targeting Ag to surface receptors on conventional type 1 dendritic cells can enhance induction of Ab and T cell responses. However, it is unclear to what extent the targeted receptor influences the resulting responses. In this study, we target Ag to Xcr1, Clec9A, or DEC-205, surface receptors that are expressed on conventional type 1 dendritic cells, and compare immune responses in BALB/c and C57BL/6 mice in vitro and in vivo after intradermal DNA vaccination. Targeting hemagglutinin from influenza A to Clec9A induced Ab responses with higher avidity that more efficiently neutralized influenza virus compared with Xcr1 and DEC-205 targeting. In contrast, targeting Xcr1 resulted in higher IFN-γ⁺CD8⁺ T cell responses in spleen and lung and stronger cytotoxicity. Both Clec9A and Xcr1 targeting induced Th1-polarized Ab responses, although the Th1 polarization of CD4⁺ T cells was more pronounced after Xcr1 targeting. Targeting DEC-205 resulted in poor Ab responses in BALB/c mice and a more mixed Th response. In an influenza challenge model, targeting either Xcr1 or Clec9A induced full and long-term protection against influenza infection, whereas only partial short-term protection was obtained when targeting DEC-205. In summary, the choice of targeting receptor, even on the same dendritic cell subpopulation, may strongly influence the resulting immune response, suggesting that different targeting strategies should be considered depending on the pathogen.

A DNA Vaccine That Encodes an Antigen-Presenting Cell-Specific Heterodimeric Protein Protects against Cancer and Influenza

Immunogenicity of DNA vaccines can be increased by constructing the DNA in such a way that it encodes secreted homodimeric fusion proteins that target antigen-presenting cells (APCs). In this study, we have developed novel APC-targeting vaccine molecules with an increased flexibility due to introduction of a heterodimerization motif. The heterodimeric proteins permit four different fusions within a single molecule, thus allowing expression of two different APC-targeting moieties and two different antigens. Two types of heterodimeric fusion proteins were developed that employed either the ACID/BASE or the Barnase/Barstar motifs, respectively. The ACID/BASE heterodimeric vaccines conferred protection against challenges with either influenza virus or tumor cells in separate preclinical models. The ACID/BASE motif was flexible since a large number of different targeting moieties and antigens could be introduced with maintenance of specificity, antigenicity, and secretion. APC-targeting ACID/BASE vaccines expressing two different antigens induced antibody and T cell responses against either of the two antigens. Heterodimeric ACID/BASE DNA vaccines were of approximately the same potency as previously reported homodimeric DNA vaccines. The flexibility and potency of the ACID/BASE format suggest that it could be a useful platform for DNA vaccines that encode APC-targeting fusion proteins.

Dendritic Cells in HIV/SIV Prophylactic and Therapeutic Vaccination

Dendritic cells (DCs) are involved in human and simian immunodeficiency virus (HIV and SIV) pathogenesis but also play a critical role in orchestrating innate and adaptive vaccine-specific immune responses. Effective HIV/SIV vaccines require strong antigen-specific CD4 T cell responses, cytotoxic activity of CD8 T cells, and neutralizing/non-neutralizing antibody production at mucosal and systemic sites. To develop a protective HIV/SIV vaccine, vaccine regimens including DCs themselves, protein, DNA, mRNA, virus vectors, and various combinations have been evaluated in different animal and human models. Recent studies have shown that DCs enhanced prophylactic HIV/SIV vaccine efficacy by producing pro-inflammatory cytokines, improving T cell responses, and recruiting effector cells to target tissues. DCs are also targets for therapeutic HIV/SIV vaccines due to their ability to reverse latency, present antigen, and augment T and B cell immunity. Here, we review the complex interactions of DCs over the course of HIV/SIV prophylactic and therapeutic immunizations, providing new insights into development of advanced DC-targeted HIV/SIV vaccines.

Recent advances on HIV DNA vaccines development: Stepwise improvements to clinical trials

According to WHO (World Health Organization) reports, more than 770,000 people died from HIV and almost 1.7 million people becoming newly infected in the worldwide in 2018. Therefore, many attempts should be done to produce a forceful vaccine to control the AIDS. DNA-based vaccines have been investigated for HIV vaccination by researches during the recent 20 years. The DNA vaccines are novel approach for induction of both type of immune responses (cellular and humoral) in the host cells and have many advantages including high stability, fast and easy of fabrication and absence of severe side effects when compared with other vaccination methods. Recent studies have been focused on vaccine design, immune responses and on the use of adjuvants as a promising strategy for increased level of responses, delivery approaches by viral and non-viral methods and vector design for different antigens of HIV virus. In this review, we outlined the aforementioned advances on HIV DNA vaccines. Then we described the future trends in clinical trials as a strong strategy even in healthy volunteers and the potential developments in control and prevention of HIV.

Dendritic Cells/Macrophages-Targeting Feature of Ebola Glycoprotein and its Potential as Immunological Facilitator for Antiviral Vaccine Approach

In the prevention of epidemic and pandemic viral infection, the use of the antiviral vaccine has been the most successful biotechnological and biomedical approach. In recent times, vaccine development studies have focused on recruiting and targeting immunogens to dendritic cells (DCs) and macrophages to induce innate and adaptive immune responses. Interestingly, Ebola virus (EBOV) glycoprotein (GP) has a strong binding affinity with DCs and macrophages. Shreds of evidence have also shown that the interaction between EBOV GP with DCs and macrophages leads to massive recruitment of DCs and macrophages capable of regulating innate and adaptive immune responses. Therefore, studies for the development of vaccine can utilize the affinity between EBOV GP and DCs/macrophages as a novel immunological approach to induce both innate and acquired immune responses. In this review, we will discuss the unique features of EBOV GP to target the DC, and its potential to elicit strong immune responses while targeting DCs/macrophages. This review hopes to suggest and stimulate thoughts of developing a stronger and effective DC-targeting vaccine for diverse virus infection using EBOV GP.

A DNA-Modified Live Vaccine Prime-Boost Strategy Broadens the T-Cell Response and Enhances the Antibody Response against the Porcine Reproductive and Respiratory Syndrome Virus

The Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) induces reproductive disorders in sows and respiratory illnesses in growing pigs and is considered as one of the main pathogenic agents responsible for economic losses in the porcine industry worldwide. Modified live PRRSV vaccines (MLVs) are very effective vaccine types against homologous strains but they present only partial protection against heterologous viral variants. With the goal to induce broad and cross-protective immunity, we generated DNA vaccines encoding B and T antigens derived from a European subtype 1 strain that include T-cell epitope sequences known to be conserved across strains. These antigens were expressed either in a native form or in the form of vaccibodies targeted to the endocytic receptor XCR1 and CD11c expressed by different types of antigen-presenting cells (APCs). When delivered in skin with cationic nanoparticles and surface electroporation, multiple DNA vaccinations as a stand-alone regimen induced substantial antibody and T-cell responses, which were not promoted by targeting antigens to APCs. Interestingly, a DNA-MLV prime-boost strategy strongly enhanced the antibody response and broadened the T-cell responses over the one induced by MLV or DNA-only. The anti-nucleoprotein antibody response induced by the DNA-MLV prime-boost was clearly promoted by targeting the antigen to CD11c and XCR1, indicating a benefit of APC-targeting on the B-cell response. In conclusion, a DNA-MLV prime-boost strategy, by enhancing the potency and breadth of MLV vaccines, stands as a promising vaccine strategy to improve the control of PRRSV in infected herds.

In vivo targeting of DNA vaccines to dendritic cells using functionalized gold nanoparticles

The clinical success of dendritic cell (DC)-based genetic immunization remains critically dependent on the availability of effective and safe nano-carriers for targeting antigen-encoded DNA vaccines to DCs, the most potent antigen-presenting cells in the human body in vivo. Recent studies revealed the efficacies of mannose receptor-mediated in vivo DC-targeted genetic immunization by liposomal DNA vaccine carriers containing both mannose-mimicking shikimoyl and transfection enhancing guanidinyl functionalities. However, to date, the efficacies of this approach have not been examined for metal-based nanoparticle DNA vaccine carriers. Herein, we report for the first time, the design, synthesis, physico-chemical characterization and bioactivities of gold nanoparticles covalently functionalized with a thiol ligand containing both shikimoyl and guanidinyl functionalities (Au-SGSH). We show that Au-SGSH nanoparticles can deliver DNA vaccines to mouse DCs under in vivo conditions. Subcutaneous administration of near infrared (NIR) dye-labeled Au-SGSH showed significant accumulation of the NIR dye in the DCs of the nearby lymph nodes compared to that for the non-targeting NIR-labeled Au-GSH nanoconjugate containing only a covalently tethered guanidinyl group, not the shikimoyl-functionality. Under prophylactic settings, in vivo immunization (s.c.) with the Au-SGSH-pCMV-MART1 nanoplex induced a long-lasting (180 days) immune response against murine melanoma. Notably, mannose receptor-mediated in vivo DC-targeted immunization (s.c.) with the Au-SGSH-MART1 nanoplex significantly inhibited established melanoma growth and increased the overall survivability of melanoma-bearing mice under therapeutic settings. The Au-SGSH nanoparticles reported herein have potential use for in vivo DC-targeted genetic immunization against cancer and infectious diseases.

A DNA Vaccine Encoding the Gn Ectodomain of Rift Valley Fever Virus Protects Mice via a Humoral Response Decreased by DEC205 Targeting

The Rift Valley fever virus (RVFV) is responsible for a serious mosquito-borne viral disease in humans and ruminants. The development of a new and safer vaccine is urgently needed due to the risk of introduction of this arbovirus into RVFV-free continents. We recently showed that a DNA vaccine encoding eGn, the ectodomain of the RVFV Gn glycoprotein, conferred a substantial protection in the sheep natural host and that the anti-eGn IgG levels correlated to protection. Addressing eGn to DEC205 reduced the protective efficacy while decreasing the antibody and increasing the IFNγ T cell responses in sheep. In order to get further insight into the involved mechanisms, we evaluated our eGn-encoding DNA vaccine strategy in the reference mouse species. A DNA vaccine encoding eGn induced full clinical protection in mice and the passive transfer of immune serum was protective. This further supports that antibodies, although non-neutralizing in vitro, are instrumental in the protection against RVFV. Addressing eGn to DEC205 was also detrimental to protection in mice, and in this species, both the antibody and the IFNγ T cell responses were strongly decreased. Conversely when using a plasmid encoding a different antigen, i.e., mCherry, DEC205 targeting promoted the antibody response. Altogether our results show that the outcome of targeting antigens to DEC205 depends on the species and on the fused antigen and is not favorable in the case of eGn. In addition, we bring evidences that eGn in itself is a pertinent antigen to be included in a DNA vaccine and that next developments should aim at promoting the anti-eGn antibody response.

Dendritic cell targeted Ccl3- and Xcl1-fusion DNA vaccines differ in induced immune responses and optimal delivery site

Fusing antigens to chemokines to target antigen presenting cells (APC) is a promising method for enhancing immunogenicity of DNA vaccines. However, it is unclear how different chemokines compare in terms of immune potentiating effects. Here we compare Ccl3- and Xcl1-fusion vaccines containing hemagglutinin (HA) from influenza A delivered by intramuscular (i.m.) or intradermal (i.d.) DNA vaccination. Xcl1 fusion vaccines target cDC1s, and enhance proliferation of CD4⁺ and CD8⁺ T cells in vitro. In contrast, Ccl3 target both cDC1 and cDC2, but only enhance CD4⁺ T cell proliferation in combination with cDC2. When Ccl3- or Xcl1-HA fusion vaccines were administered by i.m. DNA immunization, both vaccines induced Th1-polarized immune responses with antibodies of the IgG2a/IgG2b subclass and IFNγ-secreting T cells. After i.d. DNA vaccination, however, only Xcl1-HA maintained a Th1 polarized response and induced even higher numbers of IFNγ-secreting T cells. Consequently, Xcl1-HA induced superior protection against influenza infection compared to Ccl3-HA after i.d. immunization. Interestingly, i.m. immunization with Ccl3-HA induced the strongest overall in vivo cytotoxicity, despite not inducing OT-I proliferation in vitro. In summary, our results highlight important differences between Ccl3- and Xcl1- targeted DNA vaccines suggesting that chemokine fusion vaccines can be tailor-made for different diseases.

Dendritic Cell Targeting Using a DNA Vaccine Induces Specific Antibodies and CD4+ T Cells to the Dengue Virus Envelope Protein Domain III

Dengue fever has become a global threat, causing millions of infections every year. An effective vaccine against all four serotypes of dengue virus (DENV) has not been developed yet. Among the different vaccination strategies available today, DNA vaccines are safe and practical, but currently induce relatively weak immune responses in humans. In order to improve immunogenicity, antigens may be targeted to dendritic cells (DCs), the main antigen presenting cells and orchestrators of the adaptive immune response, inducing T and B cell activation. It was previously shown that a DNA vaccine encoding a fusion protein comprised of an antigen and a single-chain Fv antibody (scFv) specific for the DC endocytic receptor DEC205 induced strong immune responses to the targeted antigen. In this work, we evaluate this strategy to improve the immunogenicity of dengue virus (DENV) proteins. Plasmids encoding the scFv αDEC205, or an isotype control (scFv ISO), fused to the DENV2 envelope protein domain III (EDIII) were generated, and EDIII specific immune responses were evaluated in immunized mice. BALB/c mice were intramuscularly (i.m.) immunized three times with plasmid DNAs encoding either scDEC-EDIII or scISO-EDIII followed by electroporation. Analyses of the antibody responses indicated that EDIII fusion with scFv targeting the DEC205 receptor significantly enhanced serum anti-EDIII IgG titers that inhibited DENV2 infection. Similarly, mice immunized with the scDEC-EDIII plasmid developed a robust CD4⁺ T cell response to the targeted antigen, allowing the identification of two linear epitopes recognized by the BALB/c haplotype. Taken together, these results indicate that targeting DENV2 EDIII protein to DCs using a DNA vaccine encoding the scFv αDEC205 improves both antibody and CD4⁺ T cell responses. This strategy opens perspectives for the use of DNA vaccines that encode antigens targeted to DCs as a strategy to increase immunogenicity.

DNA and mRNA vaccination against allergies

Allergen-specific immunotherapy, which is performed by subcutaneous injection or sublingual application of allergen extracts, represents an effective treatment against type I allergic diseases. However, due to the long duration and adverse reactions, only a minority of patients decides to undergo this treatment. Alternatively, early prophylactic intervention in young children has been proposed to stop the increase in patient numbers. Plasmid DNA and mRNA vaccines encoding allergens have been shown to induce T helper 1 as well as T regulatory responses, which modulate or counteract allergic T helper 2-biased reactions. With regard to prophylactic immunization, additional safety measurements are required. In contrast to crude extracts, genetic vaccines provide the allergen at high purity. Moreover, by targeting the encoded allergen to subcellular compartments for degradation, release of native allergen can be avoided. Due to inherent safety features, mRNA vaccines could be the candidates of choice for preventive allergy immunizations. The subtle priming of T helper 1 immunity induced by this vaccine type closely resembles responses of non-allergic individuals and-by boosting via natural allergen exposure-could suffice for long-term protection from type I allergy.

Sortase A: A Model for Transpeptidation and Its Biological Applications

Molecular biologists and chemists alike have long sought to modify proteins with substituents that cannot be installed by standard or even advanced genetic approaches. We here describe the use of transpeptidases to achieve these goals. Living systems encode a variety of transpeptidases and peptide ligases that allow for the enzyme-catalyzed formation of peptide bonds, and protein engineers have used directed evolution to enhance these enzymes for biological applications. We focus primarily on the transpeptidase sortase A, which has become popular over the past few years for its ability to perform a remarkably wide variety of protein modifications, both in vitro and in living cells.

Analysis of the effect of promoter type and skin pretreatment on antigen expression and antibody response after gene gun-based immunization

Monoclonal antibodies (mAbs) have enabled numerous basic research discoveries and therapeutic approaches for many protein classes. However, there still exist a number of target classes, such as multi-pass membrane proteins, for which antibody discovery is difficult, due in part to lack of high quality, recombinant protein. Here we describe the impact of several parameters on antigen expression and the development of mAbs against human claudin 4 (CLDN4), a potential multi-indication cancer target. Using gene gun-based DNA delivery and bioluminescence imaging, we optimize promoter type by comparing expression profiles of four robust in vivo promoters. In addition, we observe that most vectors rapidly lose expression, ultimately reaching almost background levels by three days post-delivery. Recognizing this limitation, we next explored skin pretreatment strategies as an orthogonal method to further boost the efficiency of mAb generation. We show that SDS pretreatment can boost antigen expression, but fails to significantly increase mAb discovery efficiency. In contrast, we find that sandpaper pretreatment yields 5-fold more FACS⁺ anti-CLDN4 hybridomas, without impacting antigen expression. Our findings coupled with other strategies to improve DNA immunizations should improve the success of mAb discovery against other challenging targets and enable the generation of critical research tools and therapeutic candidates.

Codon optimization and improved delivery/immunization regimen enhance the immune response against wild-type and drug-resistant HIV-1 reverse transcriptase, preserving its Th2-polarity

DNA vaccines require a considerable enhancement of immunogenicity. Here, we optimized a prototype DNA vaccine against drug-resistant HIV-1 based on a weak Th2-immunogen, HIV-1 reverse transcriptase (RT). We designed expression-optimized genes encoding inactivated wild-type and drug-resistant RTs (RT-DNAs) and introduced them into mice by intradermal injections followed by electroporation. RT-DNAs were administered as single or double primes with or without cyclic-di-GMP, or as a prime followed by boost with RT-DNA mixed with a luciferase-encoding plasmid (“surrogate challenge”). Repeated primes improved cellular responses and broadened epitope specificity. Addition of cyclic-di-GMP induced a transient increase in IFN-γ production. The strongest anti-RT immune response was achieved in a prime-boost protocol with electroporation by short 100V pulses done using penetrating electrodes. The RT-specific response, dominated by CD4+ T-cells, targeted epitopes at aa 199–220 and aa 528–543. Drug-resistance mutations disrupted the epitope at aa 205–220, while the CTL epitope at aa 202–210 was not affected. Overall, multiparametric optimization of RT strengthened its Th2- performance. A rapid loss of RT/luciferase-expressing cells in the surrogate challenge experiment revealed a lytic potential of anti-RT response. Such lytic CD4+ response would be beneficial for an HIV vaccine due to its comparative insensitivity to immune escape.

A Rift Valley fever virus Gn ectodomain-based DNA vaccine induces a partial protection not improved by APC targeting

Rift Valley fever virus, a phlebovirus endemic in Africa, causes serious diseases in ruminants and humans. Due to the high probability of new outbreaks and spread to other continents where competent vectors are present, vaccine development is an urgent priority as no licensed vaccines are available outside areas of endemicity. In this study, we evaluated in sheep the protective immunity induced by DNA vaccines encoding the extracellular portion of the Gn antigen which was either or not targeted to antigen-presenting cells. The DNA encoding untargeted antigen was the most potent at inducing IgG responses, although not neutralizing, and conferred a significant clinical and virological protection upon infectious challenge, superior to DNA vaccines encoding the targeted antigen. A statistical analysis of the challenge parameters supported that the anti-eGn IgG, rather than the T-cell response, was instrumental in protection. Altogether, this work shows that a DNA vaccine encoding the extracellular portion of the Gn antigen confers substantial—although incomplete—protective immunity in sheep, a natural host with high preclinical relevance, and provides some insights into key immune correlates useful for further vaccine improvements against the Rift Valley fever virus.

A vaccine made from the genome of Rift Valley fever virus (RVFV) offers partial protection, but pieces of the puzzle are missing, say scientists. French and Spanish researchers, led by the French National Institute for Agricultural Research’s Isabelle Schwartz-Cornil, tested in sheep three slightly-differing vaccine candidates using RVFV genes. Such DNA vaccines are designed to generate proteins which a host’s immune system can use to arm itself against a genuine viral infection. Two of the candidates, designed to target cells that would present the viral proteins to the host’s immune system, provided some benefit to the vaccinated sheep. However, the third untargeted candidate, was the most efficient at protecting sheep, although not completely, and at boosting antibody levels despite not neutralizing the virus. These results provide hope for DNA vaccines against RVFV, and offer direction for future research effort.

DEC205-DC targeted DNA vaccine against CX3CR1 protects against atherogenesis in mice

Studies disrupting the chemokine pathway CX3CL1 (fractalkine)/ CX3CR1 have shown decreased atherosclerosis in animal models but the techniques used to interrupt the pathway have not been easily translatable into human trials. DNA vaccination potentially overcomes the translational difficulties. We evaluated the effect of a DNA vaccine, targeted to CX3CR1, on atherosclerosis in a murine model and examined possible mechanisms of action. DNA vaccination against CX3CR1, enhanced by dendritic cell targeting using DEC-205 single chain variable region fragment (scFv), was performed in 8 week old ApoE-/- mice, fed a normal chow diet. High levels of anti-CX3CR1 antibodies were induced in vaccinated mice. There were no apparent adverse reactions to the vaccine. Arterial vessels of 34 week old mice were examined histologically for atherosclerotic plaque size, macrophage infiltration, smooth muscle cell infiltration and lipid deposition. Vaccinated mice had significantly reduced atherosclerotic plaque in the brachiocephalic artery. There was less macrophage infiltration but no significant change to the macrophage phenotype in the plaques. There was less lipid deposition in the lesions, but there was no effect on smooth muscle cell migration. Targeted DNA vaccination to CX3CR1 was well tolerated, induced a strong immune response and resulted in attenuated atherosclerotic lesions with reduced macrophage infiltration. DNA vaccination against chemokine pathways potentially offers a potential therapeutic option for the treatment of atherosclerosis.

Exploiting Nanobodies' Singular Traits

The unique class of heavy chain-only antibodies, present in Camelidae, can be shrunk to just the variable region of the heavy chain to yield VHHs, also called nanobodies. About one-tenth the size of their full-size counterparts, nanobodies can serve in applications similar to those for conventional antibodies, but they come with a number of signature advantages that find increasing application in biology. They not only function as crystallization chaperones but also can be expressed inside cells as such, or fused to other proteins to perturb the function of their targets, for example, by enforcing their localization or degradation. Their small size also affords advantages when applied in vivo, for example, in imaging applications. Here we review such applications, with particular emphasis on those areas where conventional antibodies would face a more challenging environment.

B lymphocytes as direct antigen-presenting cells for anti-tumor DNA vaccines

In spite of remarkable preclinical efficacy, DNA vaccination has demonstrated low immunogenicity in humans. While efforts have focused on increasing cross-presentation of DNA-encoded antigens, efforts to increase DNA vaccine immunogenicity by targeting direct presentation have remained mostly unexplored. In these studies, we compared the ability of different APCs to present antigen to T cells after simple co-culture with plasmid DNA. We found that human primary peripheral B lymphocytes, and not monocytes or in vitro derived dendritic cells (DCs), were able to efficiently encode antigen mRNA and expand cognate tumor antigen-specific CD8 T cells ex vivo. Similarly, murine B lymphocytes co-cultured with plasmid DNA, and not DCs, were able to prime antigen-specific T cells in vivo. Moreover, B lymphocyte-mediated presentation of plasmid antigen led to greater Th1-biased immunity and was sufficient to elicit an anti-tumor effect in vivo. Surprisingly, increasing plasmid presentation by B cells, and not cross presentation of peptides by DCs, further augmented traditional plasmid vaccination. Together, these data suggest that targeting plasmid DNA to B lymphocytes, for example through transfer of ex vivo plasmidloaded B cells, may be novel means to achieve greater T cell immunity from DNA vaccines.

Enhanced contraception of canine zona pellucida 3 DNA vaccine via targeting DEC-205 in mice

Zona pellucida 3 (ZP3) is a potential antigen for the development of contraceptive vaccines to control animal population. In this study, we designed a canine ZP3 (CZP3) DNA vaccine through targeting DEC-205 (named as pcD-scFv-CZP3c) and investigated its contraceptive effect in mice. Female BALB/c mice were intramuscularly immunized 3 times at 2 weeks intervals. After immunization, humoral and cellular immune responses were detected by ELISA and flow cytometry. The results showed that pcD-CZP3 and pcD-scFv-CZP3c induced CZP3-specific antibody (Ab) responses both in serum and vaginal secretions compared to pcDNA3.1. Additionally, compared to pcD-CZP3, pcD-scFv-CZP3c increased the levels of CZP3-specific Abs after a third immunization. Abs induced by these two DNA vaccines could bind with mice and dogs oocytes. Moreover, pcD-scFv-CZP3c enhanced the activation of CD4⁺ T cells characterized by the increased frequencies of CD4⁺CD44⁺ T cells. Finally, the contraceptive effect was evaluated in the immunized mice. These two DNA vaccines significantly decreased a mean litter size of mice compared to pcDNA3.1, but pcD-scFv-CZP3c group showed the smallest mean litter size. The mean litter size of pcD-scFv-CZP3 were 3.2 ± 0.742 and 4.6 ± 1.118 in two mating tests, which were significantly lower than pcDNA3.1(P < 0.001 and P < 0.05). Our results suggest that the CZP3 DNA vaccine targeted with DEC-205 may be a potential strategy for developing a contraceptive DNA vaccine.

Dendritic cell targeted HIV-1 gag protein vaccine provides help to a recombinant Newcastle disease virus vectored vaccine including mobilization of protective CD8+ T cells

Introduction

Recombinant Newcastle Disease virus (rNDV) vectored vaccines are safe mucosal applicable vaccines with intrinsic immune‐modulatory properties for the induction of efficient immunity. Like all viral vectored vaccines repeated inoculation via mucosal routes invariably results to immunity against viral vaccine vectors. To obviate immunity against viral vaccine vectors and improve the ability of rNDV vectored vaccines in inducing T cell immunity in murine air way we have directed dendritic cell targeted HIV‐1 gag protein (DEC‐Gag) vaccine; for the induction of helper CD4⁺ T cells to a Recombinant Newcastle disease virus expressing codon optimized HIV‐1 Gag P55 (rNDV‐L‐Gag) vaccine.

Methods

We do so through successive administration of anti‐DEC205‐gagP24 protein plus polyICLC (DEC‐Gag) vaccine and rNDV‐L‐Gag. First strong gag specific helper CD4⁺ T cells are induced in mice by selected targeting of anti‐DEC205‐gagP24 protein vaccine to dendritic cells (DC) in situ together with polyICLC as adjuvant. This targeting helped T cell immunity develop to a subsequent rNDV‐L‐Gag vaccine and improved both systemic and mucosal gag specific immunity.

Results

This sequential DEC‐Gag vaccine prime followed by an rNDV‐L‐gag boost results to improved viral vectored immunization in murine airway, including mobilization of protective CD8⁺ T cells to a pathogenic virus infection site.

Conclusion

Thus, complementary prime boost vaccination, in which prime and boost favor distinct types of T cell immunity, improves viral vectored immunization, including mobilization of protective CD8⁺T cells to a pathogenic virus infection site such as the murine airway.

Enhanced effects of DNA vaccine against botulinum neurotoxin serotype A by targeting antigen to dendritic cells

As dendritic cells (DCs) play a critical role in priming antigen-specific immune responses, the efficacy of DNA vaccines may be enhanced by targeting the encoded antigen proteins to DCs. In this study, we constructed a DC-targeted DNA vaccine encoding the Hc domain of botulinum neurotoxin serotype A (AHc) fused with scDEC, a single-chain Fv antibody (scFv) specific for the DC-restricted antigen-uptake receptor DEC205. Intramuscular injections of mice with the DC-targeted DNA vaccine (pVAX1-scDEC-AHc) stimulated more DCs to mature than the non-targeted DNA vaccine (pVAX1-SAHc) in the splenocytes. The DC-targeted DNA vaccine could induce more DCs maturation at the site of inoculation. The DC-targeted DNA vaccine induced stronger AHc-specific humoral immune responses, lymphocyte proliferative responses and protective potency against BoNT/A in mice than did pVAX1-SAHc. Moreover, the DC-targeting DNA vaccine provided effective protection after only two inoculations. In summary, these results showed that the DC-targeted fusion DNA vaccine could generate strong immunity, indicating that maturation of DCs induced by pVAX1-scDEC-AHc may be helpful for priming and boosting immune responses. Thus, we propose that the strategy of targeting antigen to DCs in vivo via DEC205 can enhance effectively the potency of DNA vaccines against BoNTs or other pathogens in an animal model.

In vivo targeting of protein antigens to dendritic cells using anti-DEC-205 single chain antibody improves HIV Gag specific CD4+ T cell responses protecting from airway challenge with recombinant vaccinia-gag virus

Introduction

Targeting antigens to dendritic cells (DCs) in vivo via a DC‐restricted endocytic receptor, DEC205, has been validated to enhance immunity in several vaccine platforms. Particularly atttractive is selected delivery of proteins to DCs in vivo because it enables proteins to be more immunogenic and provides a cheaper and effective way for repeated immunizations.

Methods

In this study, we tested the efficacy of a single chain antibody to DEC205 (scDEC) to deliver protein antigens selectively to DCs in vivo and to induce protective immunity.

Results

In comparison to soluble Ovalbumin (OVA) antigen, when recombinant scDEC:OVA protein was injected subcutaneously (s.c.) into mice, the OVA protein was selectively presented by DCs to both TCR transgenic CD8⁺ and CD4⁺ T cells approximately 500 and 100 times more efficient than soluble OVA, respectively, and could persist for seven days following s.c. injection of the scDEC205:OVA. Similarly selective targeting of HIV Gag P24 to DCs in vivo using scDEC‐Gag protein plus polyICLC vaccine resulted in strong, long lasting, polyfuntional CD4⁺ T cells in mice which were protective against airway challenge by a recombinant vaccinia‐gag virus.

Conclusion

Thus targeting protein antigens to DCs using scDEC can be used either alone or in combination with other strategies for effective immunization.

Enhanced humoral and CD8+ T cell immunity in mice vaccinated by DNA vaccine against human respiratory syncytial virus through targeting the encoded F protein to dendritic cells

Human respiratory syncytial virus (RSV) is the most important cause of serious lower respiratory tract infection in infants, the elderly, and the immunocompromised population. There is no licensed vaccine against RSV until now. It has been reported that targeting antigen to DEC205, a phagocytosis receptor on dendritic cells (DCs), could induce enhanced CD4+ and CD8+ T cell responses in mice. To develop RSV DNA vaccine and target the encoded antigen protein to DCs, the ectodomain of fusion glycoprotein (sF, amino acids: 23-524) of RSV was fused with anti-DEC205 single-chain Fv fragment (scDEC) and designated scDECF. Following successful expression from the recombinant plasmid of pVAX1/scDECF, the recombinant protein of scDECF was found capable of specifically binding to DEC205 receptor on CHOmDEC205 cells, and facilitating uptake of RSV F by DC2.4 cells in vitro. Furthermore, the higher levels of RSV-specific IgG antibody responses and neutralization antibody titers, as well as RSV F-specific CD8+ T cell responses were induced in mice immunized intramuscularly by pVAX1/scDECF than by the control plasmid of pVAX1/scISOF encoding sF protein fused with isotype matched control single-chain Fv fragment (scISO). Compared with pVAX1/scISOF, both the ratio of IgG2a/IgG1, >1, and the enhanced IFN-γ cytokine were induced in mice following pVAX1/scDECF immunization, which exhibited a Th1 dominant response in pVAX1/scDECF vaccinated mice. Notably, the elevated efficiency of RSV F protein bound by DCs in vivo could also be observed in mice inoculated by pVAX1/scDECF. Collectively, these results demonstrate the enhanced IgG and CD8⁺ T cell immune responses have been induced successfully by DNA vaccine against RSV by targeting F antigen to DCs via the DEC205 receptor, and this DC-targeting vaccine strategy merits further investigation.

A novel dendritic cell targeting HPV16 E7 synthetic vaccine in combination with PD-L1 blockade elicits therapeutic antitumor immunity in mice

Human papilliomavirus (HPV) oncogene E7, essential for the transformation and maintenance of the malignancy of cervical cancer cells, represents an ideal tumor-specific antigen for vaccine development. However, due to the poor immunogenicity of E7 protein, an effective therapeutic E7 vaccine is still lacking. Dendritic cells (DCs) are probably the most potent antigen presenting cells for the induction of cytotoxic T lymphocyte (CTL) response, which is crucial for tumor control. In this study, we tested whether targeting the E7 antigen to DCs in vivo would elicit therapeutic antitumor CTL response. We generated the DEC205-specific single-chain variable fragment (scFv) and E7 long peptide fusion protein [scFv(DEC205)-E7] based on the novel method of protein assembly we recently developed. This fusion protein vaccine demonstrated highly efficient DC-targeting in vivo and elicited much stronger protective CTL response than non-DC-targeting control vaccine in naive mice. Furthermore, the scFv(DEC205)-E7 vaccine showed significant therapeutic antitumor response in TC-1 tumor bearing mice. Importantly, PD-L1 blockade further improved the therapeutic effect of the scFv(DEC205)-E7 vaccine. Thus, the current study suggests an efficient strategy for cervical cancer immunotherapy by combining the DC(DEC205)-targeting E7 vaccine and PD-L1 blockade.

Mycobacterium tuberculosis infection and vaccine development

Following HIV/AIDS, tuberculosis (TB) continues to be the second most deadly infectious disease in humans. The global TB prevalence has become worse in recent years due to the emergence of multi-drug resistant (MDR) and extensively-drug resistant (XDR) strains, as well as co-infection with HIV. Although Bacillus Calmette-Guérin (BCG) vaccine has nearly been used for a century in many countries, it does not protect adult pulmonary tuberculosis and even causes disseminated BCG disease in HIV-positive population. It is impossible to use BCG to eliminate the Mycobacterium tuberculosis (M. tb) infection or to prevent TB onset and reactivation. Consequently, novel vaccines are urgently needed for TB prevention and immunotherapy. In this review, we discuss the TB prevalence, interaction between M. tb and host immune system, as well as recent progress of TB vaccine research and development.

Genetic Immunization With In Vivo Dendritic Cell-targeting Liposomal DNA Vaccine Carrier Induces Long-lasting Antitumor Immune Response

A major limiting factor retarding the clinical success of dendritic cell (DC)-based genetic immunizations (DNA vaccination) is the scarcity of biologically safe and effective carrier systems for targeting the antigen-encoded DNA vaccines to DCs under in vivo settings. Herein, we report on a potent, mannose receptor selective in vivo DC-targeting liposomes of a novel cationic amphiphile with mannose-mimicking shikimoyl head-group. Flow cytometric experiments with cells isolated from draining lymph nodes of mice s.c. immunized with lipoplexes of pGFP plasmid (model DNA vaccine) using anti-CD11c antibody-labeled magnetic beads revealed in vivo DC-targeting properties of the presently described liposomal DNA vaccine carrier. Importantly, s.c. immunizations of mice with electrostatic complex of the in vivo DC-targeting liposome and melanoma antigen-encoded DNA vaccine (p-CMV-MART1) induced long-lasting antimelanoma immune response (100 days post melanoma tumor challenge) with remarkable memory response (more than 6 months after the second tumor challenge). The presently described direct in vivo DC-targeting liposomal DNA vaccine carrier is expected to find future exploitations toward designing effective vaccines for various infectious diseases and cancers.

Priming with two DNA vaccines expressing hepatitis C virus NS3 protein targeting dendritic cells elicits superior heterologous protective potential in mice

Development an effective vaccine may offer an alternative preventive and therapeutic strategy against HCV infection. DNA vaccination has been shown to induce robust humoral and cellular immunity and overcome many problems associated with conventional vaccines. In this study, mice were primed with either conventional pVRC-based or suicidal pSC-based DNA vaccines carrying DEC-205-targeted NS3 antigen (DEC-NS3) and boosted with type 5 adenoviral vectors encoding the partial NS3 and core antigens (C44P). The prime boost regimen induced a marked increase in antigen-specific humoral and T-cell responses in comparison with either rAd5-based vaccines or DEC-205-targeted DNA immunization in isolation. The protective effect against heterogeneous challenge was correlated with high levels of anti-NS3 IgG and T-cell-mediated immunity against NS3 peptides. Moreover, priming with a suicidal DNA vaccine (pSC-DEC-NS3), which elicited increased TNF-α-producing CD4+ and CD8+ T-cells against NS3-2 peptides (aa 1245-1461), after boosting, showed increased heterogeneous protective potential compared with priming with a conventional DNA vaccine (pVRC-DEC-NS3). In conclusion, a suicidal DNA vector (pSC-DEC-NS3) expressing DEC-205-targeted NS3 combined with boosting using an rAd5-based HCV vaccine (rAd5-C44P) is a good candidate for a safe and effective vaccine against HCV infection.

Surface display of an anti-DEC-205 single chain Fv fragment in Lactobacillus plantarum increases internalization and plasmid transfer to dendritic cells in vitro and in vivo

BACKGROUND

Lactic acid bacteria (LAB) are promising vehicles for delivery of a variety of medicinal compounds, including antigens and cytokines. It has also been established that LAB are able to deliver cDNA to host cells. To increase the efficiency of LAB-driven DNA delivery we have constructed Lactobacillus plantarum strains targeting DEC-205, which is a receptor located at the surface of dendritic cells (DCs). The purpose was to increase uptake of bacterial cells, which could lead to improved cDNA delivery to immune cells.

RESULTS

Anti-DEC-205 antibody (aDec) was displayed at the surface of L. plantarum using three different anchoring strategies: (1) covalent anchoring of aDec to the cell membrane (Lipobox domain, Lip); (2) covalent anchoring to the cell wall (LPXTG domain, CWA); (3) non-covalent anchoring to the cell wall (LysM domain, LysM). aDec was successfully expressed in all three strains, but surface location of the antibody could only be demonstrated for the two strains with cell wall anchors (CWA and LysM). Co-incubation of the engineered strains and DCs showed increased uptake when anchoring aDec using the CWA or LysM anchors. In a competition assay, free anti-DEC abolished the increased uptake, showing that the internalization is due to specific interactions between the DEC-205 receptor and aDec. To test plasmid transfer, a plasmid for expression of GFP under control of an eukaryotic promoter was transformed into the aDec expressing strains and GFP expression in DCs was indeed increased when using the strains producing cell-wall anchored aDec. Plasmid transfer to DCs in the gastro intestinal tract was also detected using a mouse model. Surprisingly, in mice the highest expression of GFP was observed for the strain in which aDec was coupled to the cell membrane.

CONCLUSION

The results show that surface expression of aDec leads to increased internalization of L. plantarum and plasmid transfer in DCs and that efficiency depends on the type of anchor used. Interestingly, in vitro data indicates that cell wall anchoring is more effective, whereas in vivo data seem to indicate that anchoring to the cell membrane is preferable. It is likely that the more embedded localization of aDec in the latter case is favorable when cells are exposed to the harsh conditions of the gastro-intestinal tract.

Investigating Evolutionary Conservation of Dendritic Cell Subset Identity and Functions

Dendritic cells (DCs) were initially defined as mononuclear phagocytes with a dendritic morphology and an exquisite efficiency for naïve T-cell activation. DC encompass several subsets initially identified by their expression of specific cell surface molecules and later shown to excel in distinct functions and to develop under the instruction of different transcription factors or cytokines. Very few cell surface molecules are expressed in a specific manner on any immune cell type. Hence, to identify cell types, the sole use of a small number of cell surface markers in classical flow cytometry can be deceiving. Moreover, the markers currently used to define mononuclear phagocyte subsets vary depending on the tissue and animal species studied and even between laboratories. This has led to confusion in the definition of DC subset identity and in their attribution of specific functions. There is a strong need to identify a rigorous and consensus way to define mononuclear phagocyte subsets, with precise guidelines potentially applicable throughout tissues and species. We will discuss the advantages, drawbacks, and complementarities of different methodologies: cell surface phenotyping, ontogeny, functional characterization, and molecular profiling. We will advocate that gene expression profiling is a very rigorous, largely unbiased and accessible method to define the identity of mononuclear phagocyte subsets, which strengthens and refines surface phenotyping. It is uniquely powerful to yield new, experimentally testable, hypotheses on the ontogeny or functions of mononuclear phagocyte subsets, their molecular regulation, and their evolutionary conservation. We propose defining cell populations based on a combination of cell surface phenotyping, expression analysis of hallmark genes, and robust functional assays, in order to reach a consensus and integrate faster the huge but scattered knowledge accumulated by different laboratories on different cell types, organs, and species.

DNA vaccines encoding DEC205-targeted antigens: immunity or tolerance?

Targeting of antigens to the endocytic uptake receptor DEC205 resulted in enhanced antigen presentation by dendritic cells (DCs). In combination with adjuvants for DC maturation, proteins coupled to an antibody against DEC205 induced strong pathogen-specific immune responses, whereas without additional adjuvant tolerance could be induced. As less is known about DNA vaccines encoding DEC205-targeted antigens, we explored the immunogenicity and efficacy of a dendritic cell-targeted DNA vaccine against influenza A virus (IAV) delivered by electroporation. Although coupling of haemagglutinin to a single-chain antibody against DEC205 enhanced antigen presentation on MHC class II and activation of T-cell receptor-transgenic CD4 T cells, the T-cell responses induced by the targeted DNA vaccine in wild-type BALB/c mice were significantly reduced compared with DNA encoding non-targeted antigens. Consistently, these mice were less protected against an IAV infection. Adoptive transfer experiments were performed to assess the fate of the antigen-specific T cells in animals vaccinated with DNA encoding DEC205-targeted antigens. By this, we could exclude the general deletion of antigen-specific T cells as cause for the reduced efficacy, but observed a local expansion of antigen-specific regulatory T cells, which could suppress the activation of effector cells. In conclusion, DNA vaccines encoding DEC205-targeted antigens induce peripheral tolerance rather than immunity in our study. Finally, we evaluated our DNA vaccines as prophylactic or therapeutic treatment in an allergen-induced asthma mouse model.

ESAT-6 Targeting to DEC205+ Antigen Presenting Cells Induces Specific-T Cell Responses against ESAT-6 and Reduces Pulmonary Infection with Virulent Mycobacterium tuberculosis

Airways infection with Mycobacterium tuberculosis (Mtb) is contained mostly by T cell responses, however, Mtb has developed evasion mechanisms which affect antigen presenting cell (APC) maturation/recruitment delaying the onset of Ag-specific T cell responses. Hypothetically, bypassing the natural infection routes by delivering antigens directly to APCs may overcome the pathogen's naturally evolved evasion mechanisms, thus facilitating the induction of protective immune responses. We generated a murine monoclonal fusion antibody (α-DEC-ESAT) to deliver Early Secretory Antigen Target (ESAT)-6 directly to DEC205+ APCs and to assess its in vivo effects on protection associated responses (IFN-γ production, in vivo CTL killing, and pulmonary mycobacterial load). Treatment with α-DEC-ESAT alone induced ESAT-6-specific IFN-γ producing CD4+ T cells and prime-boost immunization prior to Mtb infection resulted in early influx (d14 post-infection) and increased IFN-γ+ production by specific T cells in the lungs, compared to scarce IFN-γ production in control mice. In vivo CTL killing was quantified in relevant tissues upon transferring target cells loaded with mycobacterial antigens. During infection, α-DEC-ESAT-treated mice showed increased target cell killing in the lungs, where histology revealed cellular infiltrate and considerably reduced bacterial burden. Targeting the mycobacterial antigen ESAT-6 to DEC205+ APCs before infection expands specific T cell clones responsible for early T cell responses (IFN-γ production and CTL activity) and substantially reduces lung bacterial burden. Delivering mycobacterial antigens directly to APCs provides a unique approach to study in vivo the role of APCs and specific T cell responses to assess their potential anti-mycobacterial functions.

Efficient vaccine against pandemic influenza: combining DNA vaccination and targeted delivery to MHC class II molecules

There are two major limitations to vaccine preparedness in the event of devastating influenza pandemics: the time needed to generate a vaccine and rapid generation of sufficient amounts. DNA vaccination could represent a solution to these problems, but efficacy needs to be enhanced. In a separate line of research, it has been established that targeting of vaccine molecules to antigen-presenting cells enhances immune responses. We have combined the two principles by constructing DNA vaccines that encode bivalent fusion proteins; these target hemagglutinin to MHC class II molecules on antigen-presenting cells. Such DNA vaccines rapidly induce hemagglutinin-specific antibodies and T cell responses in immunized mice. Responses are long-lasting and protect mice against challenge with influenza virus. In a pandemic situation, targeted DNA vaccines could be produced and tested within a month. The novel DNA vaccines could represent a solution to pandemic preparedness in the advent of novel influenza pandemics.

A novel method for synthetic vaccine construction based on protein assembly

In the history of vaccine development, the synthetic vaccine is a milestone that is in stark contrast with traditional vaccines based on live-attenuated or inactivated microorganisms. Synthetic vaccines not only are safer than attenuated or inactivated microorganisms but also provide the opportunity for vaccine design for specific purposes. The first generation of synthetic vaccines has been largely based on DNA recombination technology and genetic manipulation. This de novo generation is occasionally time consuming and costly, especially in the era of genomics and when facing pandemic outbreaks of infectious diseases. To accelerate and simplify the R&D process for vaccines, we developed an improved method of synthetic vaccine construction based on protein assembly. We optimized and employed the recently developed SpyTag/SpyCatcher technique to establish a protein assembly system for vaccine generation from pre-prepared subunit proteins. As proof of principle, we chose a dendritic cell (DC)-targeting molecule and specific model antigens to generate desired vaccines. The results demonstrated that a new vaccine generated in this way does not hamper the individual function of different vaccine components and is efficient in inducing both T and B cell responses. This protein assembly strategy may be especially useful for high-throughput antigen screening or rapid vaccine generation.

Targeting DNA vaccines to myeloid cells using a small peptide

Targeting DNA vaccines to dendritic cells (DCs) greatly enhances immunity. Although several approaches have been used to target protein Ags to DCs, currently there is no method that targets DNA vaccines directly to DCs. Here, we show that a small peptide derived from the rabies virus glycoprotein fused to protamine residues (RVG-P) can target DNA to myeloid cells, including DCs, which results in enhanced humoral and T-cell responses. DCs targeted with a DNA vaccine encoding the immunodominant vaccinia B8R gene via RVG-P were able to restimulate vaccinia-specific memory T cells in vitro. Importantly, a single i.v. injection of B8R gene bound to RVG-P was able to prime a vaccinia-specific T-cell response that was able to rapidly clear a subsequent vaccinia challenge in mice. Moreover, delivery of DNA in DCs was enough to induce DC maturation and efficient Ag presentation without the need for adjuvants. Finally, immunization of mice with a DNA-vaccine encoding West Nile virus (WNV) prM and E proteins via RVG-P elicited high titers of WNV-neutralizing Abs that protected mice from lethal WNV challenge. Thus, RVG-P provides a reagent to target DNA vaccines to myeloid cells and elicit robust T-cell and humoral immune responses.

In situ modulation of dendritic cells by injectable thermosensitive hydrogels for cancer vaccines in mice

Attempts to develop cell-based cancer vaccines have shown limited efficacy, partly because transplanted dendritic cells (DCs) do not survive long enough to reach the lymph nodes. The development of biomaterials capable of modulating DCs in situ to enhance antigen uptake and presentation has emerged as a novel method toward developing more efficient cancer vaccines. Here, we propose a two-step hybrid strategy to produce a more robust cell-based cancer vaccine in situ. First, a significant number of DCs are recruited to an injectable thermosensitive mPEG-PLGA hydrogel through sustained release of chemoattractants, in particular, granulocyte-macrophage colony-stimulating factor (GM-CSF). Then, these resident DCs can be loaded with cancer antigens through the use of viral or nonviral vectors. We demonstrate that GM-CSF-releasing mPEG-PLGA hydrogels successfully recruit and house DCs and macrophages, allowing the subsequent introduction of antigens by vectors to activate the resident cells, thus, initiating antigen presentation and triggering immune response. Moreover, this two-step hybrid strategy generates a high level of tumor-specific immunity, as demonstrated in both prophylactic and therapeutic models of murine melanoma. This injectable thermosensitive hydrogel shows great promise as an adjuvant for cancer vaccines, potentially providing a new approach for cell therapies through in situ modulation of cells.

Enhanced immunogenicity of HIV-1 envelope gp140 proteins fused to APRIL

Current HIV-1 vaccines based on the HIV-1 envelope glycoprotein spike (Env), the only relevant target for broadly neutralizing antibodies, are unable to induce protective immunity. Env immunogenicity can be enhanced by fusion to costimulatory molecules involved in B cell activation, such as APRIL and CD40L. Here, we found that Env-APRIL signaled through the two receptors, BCMA and TACI. In rabbits, Env-APRIL induced significantly higher antibody responses against Env compared to unconjugated Env, while the antibody responses against the APRIL component were negligible. To extend this finding, we tested Env-APRIL in mice and found minimal antibody responses against APRIL. Furthermore, Env-CD40L did not induce significant anti-CD40L responses. Thus, in contrast to the 4-helix cytokines IL-21 and GM-CSF, the TNF-superfamily members CD40L and APRIL induced negligible autoantibodies. This study confirms and extends previous work and shows that fusion of Env-based immunogens to APRIL can improve Env immunogenicity and might help in designing HIV vaccines that induce protective humoral immunity.

Increased generation of HIV-1 gp120-reactive CD8+ T cells by a DNA vaccine construct encoding the chemokine CCL3

DNA vaccines based on subunits from pathogens have several advantages over other vaccine strategies. DNA vaccines can easily be modified, they show good safety profiles, are stable and inexpensive to produce, and the immune response can be focused to the antigen of interest. However, the immunogenicity of DNA vaccines which is generally quite low needs to be improved. Electroporation and co-delivery of genetically encoded immune adjuvants are two strategies aiming at increasing the efficacy of DNA vaccines. Here, we have examined whether targeting to antigen-presenting cells (APC) could increase the immune response to surface envelope glycoprotein (Env) gp120 from Human Immunodeficiency Virus type 1 (HIV-1). To target APC, we utilized a homodimeric vaccine format denoted vaccibody, which enables covalent fusion of gp120 to molecules that can target APC. Two molecules were tested for their efficiency as targeting units: the antibody-derived single chain Fragment variable (scFv) specific for the major histocompatilibility complex (MHC) class II I-E molecules, and the CC chemokine ligand 3 (CCL3). The vaccines were delivered as DNA into muscle of mice with or without electroporation. Targeting of gp120 to MHC class II molecules induced antibodies that neutralized HIV-1 and that persisted for more than a year after one single immunization with electroporation. Targeting by CCL3 significantly increased the number of HIV-1 gp120-reactive CD8⁺ T cells compared to non-targeted vaccines and gp120 delivered alone in the absence of electroporation. The data suggest that chemokines are promising molecular adjuvants because small amounts can attract immune cells and promote immune responses without advanced equipment such as electroporation.

Targeted DNA vaccines eliciting crossreactive anti-idiotypic antibody responses against human B cell malignancies in mice

BACKGROUND

Therapeutic idiotypic (Id) vaccination is an experimental treatment for selected B cell malignancies. A broader use of Id-based vaccination, however, is hampered by the complexity and costs due to the individualized production of protein vaccines. These limitations may be overcome by targeted DNA vaccines encoding stereotyped immunoglobulin V regions of B cell malignancies. We have here investigated whether such vaccines might elicit cross-reactive immune responses thus offering the possibility to immunize subsets of patients with the same vaccine.

METHODS

Fusion vaccines targeting patient Id to mouse Major Histocompatibility Complex (MHC) class II molecules (chimeric mouse/human) or chemokine receptors (fully human) on antigen-presenting cells (APC) were genetically constructed for two Chronic Lymphocytic Leukemia (CLL) patients and one prototypic stereotyped B-cell receptor (BCR) commonly expressed by Hepatitis C Virus (HCV)-associated Non Hodgkin Lymphoma (NHL). The A20 murine B lymphoma cells were engineered to express prototypic HCV-associated B cell lymphoma BCR. Anti-Id antibody responses were studied against stereotyped and non-stereotyped BCRs on CLL patients' cells as well as transfected A20 cells.

RESULTS

DNA vaccination of mice with Id vaccines that target APC elicited increased amounts of antibodies specific for the patient's Id as compared with non targeted control vaccines. Anti-Id antibodies cross-reacted between CLL cells with closely related BCR. A20 cells engineered to express patients' V regions were not tumorigenic in mice, preventing tumor challenge experiments.

CONCLUSIONS

These findings provide experimental support for use of APC-targeted fusion Id DNA vaccines for the treatment of B cell lymphoma and CLL that express stereotyped BCRs.