Immunogenicity testing of a novel engineered HIV-1 envelope gp140 DNA vaccine construct

Enhanced effect of modified Zika virus E antigen on the immunogenicity of DNA vaccine

It has been reported worldwide that the Zika virus (ZIKV) could be transmitted through placentas and sexual contact. ZIKV can also cause Guillain-Barre syndrome, microcephaly and neurological abnormalities. However, there are no approved vaccines available. We constructed six DNA vaccine candidates and tested the immunogenicity. Tandem repeated envelope domain Ⅲ (ED Ⅲ × 3) induced highly total IgG and neutralization antibody, as well as CD8⁺ T cell responses. Also, stem region-removed envelope (E ΔSTEM) elicited a robust production of IFN-γ in mice. To examine in vivo protection, we used mice treated with an IFNAR1 blocking antibody before and after the challenge. Vaccination with the two candidates led to a decline in the level of viral RNAs in organs. Moreover, the sera from the vaccinated mice did not enhance the infection of Dengue virus in K562 cells. These findings suggest the potential for the development of a novel ZIKV DNA vaccine.

Designed DNA-Encoded IL-36 Gamma Acts as a Potent Molecular Adjuvant Enhancing Zika Synthetic DNA Vaccine-Induced Immunity and Protection in a Lethal Challenge Model

Identification of novel molecular adjuvants which can boost and enhance vaccine-mediated immunity and provide dose-sparing potential against complex infectious diseases and for immunotherapy in cancer is likely to play a critical role in the next generation of vaccines. Given the number of challenging targets for which no or only partial vaccine options exist, adjuvants that can address some of these concerns are in high demand. Here, we report that a designed truncated Interleukin-36 gamma (IL-36 gamma) encoded plasmid can act as a potent adjuvant for several DNA-encoded vaccine targets including human immunodeficiency virus (HIV), influenza, and Zika in immunization models. We further show that the truncated IL-36 gamma (opt-36γt) plasmid provides improved dose sparing as it boosts immunity to a suboptimal dose of a Zika DNA vaccine, resulting in potent protection against a lethal Zika challenge.

Immunogenicity of a novel enhanced consensus DNA vaccine encoding the leptospiral protein LipL45

Leptospirosis is a bacterial zoonotic disease caused by an infection with a spirochete belonging to the genus Leptospira. In animals, leptospirosis displays a wide range of pathologies, including fever, abortion, icterus, and uveitis. Conversely, infection in humans is associated with multi-organ injury, resulting in an increased rate of fatalities. Pathogenic leptospires are able to translocate through cell monolayers at a rate significantly greater than that of non-pathogenic leptospires. Thus, vaccine approaches have been focused on targeting bacterial motility, lipopolysaccharides (LPSs), lipoproteins, outer-membrane proteins (OMPs) and other potential virulence factors. Previous studies have indicated that leptospiral proteins elicit long-lasting immunological memory in infected humans. In the study reported here, the efficacy of a synthetic consensus DNA vaccine developed against the Leptospira membrane lipoprotein LipL45 was tested. After in vivo electroporation (EP) mediated intramuscular immunization with a synthetic LipL45 DNA vaccine (pLipL45) immunized mice developed a significant cellular response along with the development of anti-LipL45-specific antibodies. Specifically, the pLipL45 vaccine induced a significant Th1 type immune response, indicated by the higher production of IL-12 and IFN-γ cytokines. The results presented here are the first demonstration that a LipL45 based DNA immunogen has potential as a anti-Leptospira vaccine.

An Enhanced Synthetic Multiclade DNA Prime Induces Improved Cross-Clade-Reactive Functional Antibodies when Combined with an Adjuvanted Protein Boost in Nonhuman Primates

The search for an efficacious human immunodeficiency virus type 1 (HIV-1) vaccine remains a pressing need. The moderate success of the RV144 Thai clinical vaccine trial suggested that vaccine-induced HIV-1-specific antibodies can reduce the risk of HIV-1 infection. We have made several improvements to the DNA platform and have previously shown that improved DNA vaccines alone are capable of inducing both binding and neutralizing antibodies in small-animal models. In this study, we explored how an improved DNA prime and recombinant protein boost would impact HIV-specific vaccine immunogenicity in rhesus macaques (RhM). After DNA immunization with either a single HIV Env consensus sequence or multiple constructs expressing HIV subtype-specific Env consensus sequences, we detected both CD4(+) and CD8(+) T-cell responses to all vaccine immunogens. These T-cell responses were further increased after protein boosting to levels exceeding those of DNA-only or protein-only immunization. In addition, we observed antibodies that exhibited robust cross-clade binding and neutralizing and antibody-dependent cellular cytotoxicity (ADCC) activity after immunization with the DNA prime-protein boost regimen, with the multiple-Env formulation inducing a more robust and broader response than the single-Env formulation. The magnitude and functionality of these responses emphasize the strong priming effect improved DNA immunogens can induce, which are further expanded upon protein boost. These results support further study of an improved synthetic DNA prime together with a protein boost for enhancing anti-HIV immune responses.

IMPORTANCE

Even with effective antiretroviral drugs, HIV remains an enormous global health burden. Vaccine development has been problematic in part due to the high degree of diversity and poor immunogenicity of the HIV Env protein. Studies suggest that a relevant HIV vaccine will likely need to induce broad cellular and humoral responses from a simple vaccine regimen due to the resource-limited setting in which the HIV pandemic is most rampant. DNA vaccination lends itself well to increasing the amount of diversity included in a vaccine due to the ease of manufacturing multiple plasmids and formulating them as a single immunization. By increasing the number of Envs within a formulation, we were able to show an increased breadth of responses as well as improved functionality induced in a nonhuman primate model. This increased breadth could be built upon, leading to better coverage against circulating strains with broader vaccine-induced protection.

HIV DNA Vaccine: Stepwise Improvements Make a Difference

Inefficient DNA delivery methods and low expression of plasmid DNA have been major obstacles for the use of plasmid DNA as vaccine for HIV/AIDS. This review describes successful efforts to improve DNA vaccine methodology over the past ~30 years. DNA vaccination, either alone or in combination with other methods, has the potential to be a rapid, safe, and effective vaccine platform against AIDS. Recent clinical trials suggest the feasibility of its translation to the clinic.

HIV-1 Env DNA vaccine plus protein boost delivered by EP expands B- and T-cell responses and neutralizing phenotype in vivo

An effective HIV vaccine will most likely require the induction of strong T-cell responses, broadly neutralizing antibodies (bNAbs), and the elicitation of antibody-dependent cellular cytotoxicity (ADCC). Previously, we demonstrated the induction of strong HIV/SIV cellular immune responses in macaques and humans using synthetic consensus DNA immunogens delivered via adaptive electroporation (EP). However, the ability of this improved DNA approach to prime for relevant antibody responses has not been previously studied. Here, we investigate the immunogenicity of consensus DNA constructs encoding gp140 sequences from HIV-1 subtypes A, B, C and D in a DNA prime-protein boost vaccine regimen. Mice and guinea pigs were primed with single- and multi-clade DNA via EP and boosted with recombinant gp120 protein. Sera were analyzed for gp120 binding and induction of neutralizing antibody activity. Immunization with recombinant Env protein alone induced low-titer binding antibodies with limited neutralization breath. In contrast, the synthetic DNA prime-protein boost protocol induced significantly higher antibody binding titers. Furthermore, sera from DNA prime-protein boost groups were able to neutralize a broader range of viruses in a panel of tier 1 clade B viruses as well as multiple tier 1 clade A and clade C viruses. Further investigation of synthetic DNA prime plus adaptive EP plus protein boost appears warranted.

Immunology of infants through adolescents: responses to emulate for HIV vaccines

PURPOSE OF REVIEW

The major target groups for an HIV vaccine include breastfeeding infants and adolescents. Differential immune maturity in these age groups may significantly impact vaccine efficacy, and should be taken into account when developing vaccines. Here we review these differences, with an emphasis on the immune response to vaccines for HIV and other pathogens. Recommendations for potential adaptation of current HIV vaccines are also made.

RECENT FINDINGS

An effective neonatal vaccine needs to be immunogenic in the presence of maternal antibody, and must induce cytotoxic T-lymphocyte responses, neutralizing antibody responses, both systemic and mucosal. There is renewed hope in the possibility of stimulating neutralizing antibodies with HIV vaccination. DNA vaccines are promising for neonates, but will need appropriate boosting. Certain adjuvants and vector delivery systems are more suitable for neonates. Adolescents may have stronger immune responses to HIV vaccines than adults, and will also require induction of mucosal neutralizing humoral and cellular immunity.

SUMMARY

Some current HIV vaccine strategies may need adaptation for neonates and suitable product development should be accelerated. Vaccines could induce better responses in adolescents and therefore should not be discarded prematurely. Development of vaccines that have potential for these age groups is an urgent global priority.

Strategies for improving the efficacy of a H6 subtype avian influenza DNA vaccine in chickens

A low-pathogenicity avian influenza H6N2 virus was used to investigate approaches to improve DNA vaccine efficacy. The viral hemagglutinin (HA) gene or its chicken biased HA gene, incorporating a Kozak sequence, was cloned into a pCAGGS vector to produce the pCAG-HAk and pCAG-optiHAk constructs. Following two intramuscular injections, the seroconversion rate in vaccinated chickens with 10, 100 or 300 μg pCAG-HAk were 87.5%, 75% and 75%, respectively. The profile of H6 hemagglutination inhibition (HI) antibodies induced by different doses of pCAG-HAk during the 8-week study period was similar. The HI titer rose significantly in the three different dose groups following the booster and reached a plateau 2-3 weeks post-booster. In a single dose vaccination group with 100 μg pCAG-HAk, a maximum seroconversion rate reached 53.3% at 5 weeks post-vaccination. The earliest time of seroconversion appeared two weeks after DNA immunization. Following two electroporation (EP) vaccinations with 100 μg pCAG-HAk, all birds seroconverted and the HI antibody titers were significantly higher than those using intramuscular immunization, suggesting that EP was more efficient than intramuscular delivery of the DNA vaccines. In comparison, chickens immunized with 10 or 100 μg pCAG-optiHAk showed 37.5% and 87.5% seroconversion rates, respectively, at 3 weeks following the booster. The pCAG-HAk was not significantly different from the pCAG-optiHAk in either the seroconversion rate or H6 HI titer, suggesting that the codon-optimized HA DNA vaccine did not achieve significantly better immunogenicity than the pCAG-HAk vaccine.

Improving the expression of recombinant soluble HIV Envelope glycoproteins using pseudo-stable transient transfection

The Envelope glycoprotein (Env) of the human immunodeficiency virus (HIV) is the target of neutralizing antibodies (NAbs). So far, HIV Env-derived immunogens have not been able to elicit broad neutralizing antibody responses against primary isolates. Identifying conditions that will permit the efficient production of different soluble HIV Env proteins will facilitate a high throughput comparative analysis of the immunogenicity of diverse Env constructs, potentially identifying Env forms that are more conducive to the elicitation of anti-HIV NAbs. Here we compared different cell types, transfection reagents, transfection conditions and different DNA expression vectors on soluble HIV Envelope expression levels. We identified optimal expression conditions and developed a protocol to streamline and maximize production of diverse HIV Env constructs. Using this optimized platform, milligram quantities of purified soluble HIV Env trimer can be routinely achieved in a rapid and cost-effective manner.

A DNA vaccine targeting the receptor-binding domain of Clostridium difficile toxin A

Clostridium difficile is a pathogen with increasing severity for which host antibody responses provide protection from disease. DNA vaccination has several advantages compared to traditional vaccine methods, however no study has examined this platform against C. difficile toxins. A synthetic gene was created encoding the receptor-binding domain (RBD) of C. difficile toxin A, optimized for expression in human cells. Gene expression was examined in vitro. Mice were inoculated and then challenged with parenteral toxin A. Vaccination provided high titer antibodies and protected mice from death. This represents the first report of DNA vaccine inducing neutralizing antibodies to C. difficile toxin A.

Effect of peptide pools on effector functions of antigen-specific CD8+ T cells

Peptide pools are routinely used to study antigen specific T cell responses, both in epitope discovery as well as immune monitoring. However, optimal assay conditions such as concentration of peptides or the best possible number of peptides per pool have not been defined. Thus, we examined whether different peptide concentrations or varying number of peptides per pool influence effector functions of antigen-specific human T-cells. PBMC isolated from HLA-A2-positive individuals with known responses to frequently recognised dominant CD8+ T cell epitopes derived from four different viruses (influenza virus, CMV, EBV, or HCV) were studied. PBMC were cultured with one of these HLA-A2 restricted peptides and varying concentrations of overlapping peptide pools derived from unrelated viruses specific for the hepatitis D and E viruses, the subjects have not been exposed to. Importantly, unrelated peptide pools inhibited the proliferation of IV-M1(58), CMVpp65(495-503), EBV-BMLF(1259-267) and HCV NS3(1073)-specific CD8 T-cells in a dose dependent manner. Similarly, an increase in the number of peptides per pool also impaired antigen specific CD8+ T cell proliferation. In contrast, secretion of cytokines such as IL-2, IL-10, IFN-gamma, TNF-alpha or IP-10 as well as cytotoxicity was not affected by these unrelated peptide pools. The inhibition of proliferation could be restored by blocking PD-1/PDL-1 interaction and was not dependent on DMSO when DMSO concentration was <or=0.5%. Thus, peptide-specific CD8 T-cell proliferation but not cytokine production may be largely underestimated when using a peptide pool which warrants caution in immunomonitoring during clinical trials and in epitope discovery studies.

DNA vaccines: ready for prime time?

Since the discovery, over a decade and a half ago, that genetically engineered DNA can be delivered in vaccine form and elicit an immune response, there has been much progress in understanding the basic biology of this platform. A large amount of data has been generated in preclinical model systems, and more sustained cellular responses and more consistent antibody responses are being observed in the clinic. Four DNA vaccine products have recently been approved, all in the area of veterinary medicine. These results suggest a productive future for this technology as more optimized constructs, better trial designs and improved platforms are being brought into the clinic.

Expression of the gp150 maedi visna virus envelope precursor protein by mammalian expression vectors

There are very few previous reports of expression of native full-length maedi visna virus (MVV) Env gp150 protein in the literature. Therefore the use of different plasmid and viral expression vectors to obtain full-length gp150 was investigated. A mammalian expression plasmid, pN3-Env, was constructed containing the MVV env gene encoding the precursor protein gp150 Env. The functionality of the recombinant plasmid was tested for expression in HEK293 cells. A recombinant modified vaccinia Ankara virus, MVA-Env, with expression detected in avian cells was also made. The expression of the MVV gp150 Env precursor protein was shown for the first time upon transfection of the eukaryotic HEK293 cells by the pN3-Env plasmid DNA as demonstrated by Western blot analysis. These plasmid or viral expression vectors are of potential use in MVV vaccines.

Using pCIN-mIL-4 DNA vector to express mRNA and protein and to improve herpes simplex virus-induced Behcet's disease symptoms in mice

Behcet's disease (BD) is a chronic, recurrent, inflammatory, multisystemic disorder characterized primarily by vasculitis. The etiopathogenesis of BD involves immunogenetics, infectious organisms (streptococcus, herpes simplex virus), immunoregulation and vascular dysfunctions. We previously found that immunoregulation associated with viral infection was important to the development of BD-like symptoms. Recently, we demonstrated that Th2 cytokines up-regulated by Th2 adjuvant were efficient in attenuating or improving these BD-like symptoms. In order to directly augment IL-4 expression, a DNA vector (pCIN-mIL-4) was administered to BD-like mice using the Helios gene gun system. Two injections of the pCIN-mIL-4 vector, spread over 2 weeks, attenuated or improved the mucocutaneous symptoms of 10 out of 12 BD-like mice in our study. The improved mucocutaneous symptoms were crust in face, ulcer in mouth, scruff, back, genital and erythema. This improvement also correlated with induction of IL-4 mRNA in lymph nodes, protein in serum and intracellular IL-4 staining in splenocytes. Normal control mice (n = 10) injected with the pCIN-mIL-4 vector expressed IL-4 mRNA and showed more splenocytes stained with anti-IL-4 antibody (5.77 +/- 0.92%) than did mice injected with the pCIN control vector (3.34 +/- 0.25%; p = 0.02). These findings indicate that an IL-4 DNA vector could be used to express mRNA and protein in vivo and further suggest that such an IL-4 DNA vector could be used as a therapeutic treatment in recurrent inflammation shifted to T helper type 1 cytokine production.

Enhanced cellular immune responses elicited by an engineered HIV-1 subtype B consensus-based envelope DNA vaccine

An important goal for human immunodeficiency virus (HIV) vaccines is to develop immunogens that induce broader and more potent cellular immune responses. In this study of DNA vaccine potency, we constructed a novel subtype B env gene (EY2E1-B) with the goal of increasing vaccine antigen immune potency. The vaccine cassette was designed based on subtype B-specific consensus sequence with several modifications, including codon optimization, RNA optimization, the addition of a Kozak sequence, and a substituted immunoglobulin E leader sequence. The V1 and V2 loops were shortened and the cytoplasmic tail was truncated to prevent envelope recycling. Three different strains of mice (BALB/c, C57BL/6, and HLA-A2 transgenic mice) were immunized three times with pEY2E1-B or the primary DNA immunogen pEK2P-B alone. The analysis of specific antibody responses suggested that EY2E1-B could induce a moderate subtype B-specific antibody response. Moreover, this construct was up to four times more potent at driving cellular immune responses. Epitope mapping results indicated that there is an increase in the breadth and magnitude of cross-reactive cellular responses induced by the EY2E1-B immunogen. These properties suggest that such a synthetic immunogen deserves further examination for its potential to serve as a component antigen in an HIV vaccine cocktail.

Immunogenicity of novel consensus-based DNA vaccines against avian influenza

The frequency of H5N1 avian influenza outbreaks in China and Eastern Europe has raised concern in the world health community regarding the potential for an influenza pandemic. Efforts to monitor the disease will only provide minimal warning in a global society, and steps must be taken to prevent the morbidity and mortality associated with past pandemics. The current stockpiling of antibody-inducing "bird flu" vaccines assumes the strain that emerges will be the same as strains currently circulating. We propose a novel consensus-based approach to vaccine development, employing a DNA vaccine strategy that can provide more highly cross-reactive cellular immunity against lethal influenza infection. We show such constructs can induce strong cellular immunity against H5 influenza antigens.