Chemokine-adjuvanted electroporated DNA vaccine induces substantial protection from simian immunodeficiency virus vaginal challenge

Functional role of TrIL-1β in Takifugu rubripes defense against Cryptocaryon irritans infection

The Japanese puffer, Takifugu rubripes, is a commercially important fish species in China that is under serious threat from white spot disease (cyptocaryoniasis), which leads to heavy economic losses. We previously found that interleukin-1β (IL-1β), an important cytokine with a potential role in resistance against pathogens, was one of the most significantly differentially up-regulated proteins in the gills and spleen of T. rubripes infected by the protozoan parasite Cryptocaryon irritans. In this study, we assessed the potential function of T. rubripes IL-1β (TrIL-1β) in fish infected with C. irritans. Phylogenetic analysis indicated that the TrIL-1β protein sequence was most closely related to that of Atlantic salmon (Salmo salar) (67.2 %). The incubation experiments revealed that TrIL-1β may reduce trophont activity by destroying membranes. Immunofluorescence experiments showed that recombinant TrIL-1β promoted the expression of endogenous IL-1β, which penetrated and disrupted the cell membranes of trophonts. Transmission electron microscopy showed that the IL-1β group had less tissue damage compared with control groups of fish. IL-1β-small interfering RNA and IL-1β overexpression experiments were performed in head kidney primary cells, and challenge experiments were performed in vitro. Quantitative RT-PCR results showed that TrIL-1β regulated and activated MyD88/NF-κB and MyD88/MAPK/p38 signaling pathways during C. irritans infection. TrIL-1β also promoted the differential expression of IgM, showing that it was involved in humoral immunity of T. rubripes. The cumulative mortality experiment show that TrIL-1β could protect fish against C. irritans infection. These results enrich current knowledge about the molecular structure of TrIL-1β. They also suggested that recombinant TrIL-1β could be used as an adjuvant in a subunit vaccine against C. irritans infection, which is of profound importance for the prevention and control of parasitic diseases in T. rubripes.

DNA Vaccines: History, Molecular Mechanisms and Future Perspectives

The history of DNA vaccine began as early as the 1960s with the discovery that naked DNA can transfect mammalian cells in vivo. In 1992, the evidence that such transfection could lead to the generation of antigen-specific antibody responses was obtained and supported the development of this technology as a novel vaccine platform. The technology then attracted immense interest and high hopes in vaccinology, as evidence of high immunogenicity and protection against virulent challenges accumulated from several animal models for several diseases. In particular, the capacity to induce T-cell responses was unprecedented in non-live vaccines. However, the technology suffered its major knock when the success in animals failed to translate to humans, where DNA vaccine candidates were shown to be safe but remained poorly immunogenic, or not associated with clinical benefit. Thanks to a thorough exploration of the molecular mechanisms of action of these vaccines, an impressive range of approaches have been and are currently being explored to overcome this major challenge. Despite limited success so far in humans as compared with later genetic vaccine technologies such as viral vectors and mRNA, DNA vaccines are not yet optimised for human use and may still realise their potential.

Mucosal chemokine adjuvant enhances synDNA vaccine-mediated responses to SARS-CoV-2 and provides heterologous protection in vivo

The global coronavirus disease 2019 (COVID-19) pandemic has claimed more than 5 million lives. Emerging variants of concern (VOCs) continually challenge viral control. Directing vaccine-induced humoral and cell-mediated responses to mucosal surfaces may enhance vaccine efficacy. Here we investigate the immunogenicity and protective efficacy of optimized synthetic DNA plasmids encoding wild-type severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein (pS) co-formulated with the plasmid-encoded mucosal chemokine cutaneous T cell-attracting chemokine (pCTACK; CCL27). pCTACK-co-immunized animals exhibit increased spike-specific antibodies at the mucosal surface and increased frequencies of interferon gamma (IFNγ)+ CD8+ T cells in the respiratory mucosa. pCTACK co-immunization confers 100% protection from heterologous Delta VOC challenge. This study shows that mucosal chemokine adjuvants can direct vaccine-induced responses to specific immunological sites and have significant effects on heterologous challenge. Further study of this unique chemokine-adjuvanted vaccine approach in the context of SARS-CoV-2 vaccines is likely important.

Harnessing Recent Advances in Synthetic DNA and Electroporation Technologies for Rapid Vaccine Development Against COVID-19 and Other Emerging Infectious Diseases

DNA vaccines are considered as a third-generation vaccination approach in which antigenic materials are encoded as DNA plasmids for direct in vivo production to elicit adaptive immunity. As compared to other platforms, DNA vaccination is considered to have a strong safety profile, as DNA plasmids neither replicate nor elicit vector-directed immune responses in hosts. While earlier work found the immune responses induced by DNA vaccines to be sub-optimal in larger mammals and humans, recent developments in key synthetic DNA and electroporation delivery technologies have now allowed DNA vaccines to elicit significantly more potent and consistent responses in several clinical studies. This paper will review findings from the recent clinical and preclinical studies on DNA vaccines targeting emerging infectious diseases (EID) including COVID-19 caused by the SARS-CoV-2 virus, and the technological advancements pivotal to the improved responses-including the use of the advanced delivery technology, DNA-encoded cytokine/mucosal adjuvants, and innovative concepts in immunogen design. With continuous advancement over the past three decades, the DNA approach is now poised to develop vaccines against COVID-19, as well as other EIDs.

Parenterally Administered Porcine Epidemic Diarrhea Virus-Like Particle-Based Vaccine Formulated with CCL25/28 Chemokines Induces Systemic and Mucosal Immune Protectivity in Pigs

Generation of a safe, economical, and effective vaccine capable of inducing mucosal immunity is critical for the development of vaccines against enteric viral diseases. In the current study, virus-like particles (VLPs) containing the spike (S), membrane (M), and envelope (E) structural proteins of porcine epidemic diarrhea virus (PEDV) expressed by the novel polycistronic baculovirus expression vector were generated. The immunogenicity and protective efficacy of the PEDV VLPs formulated with or without mucosal adjuvants of CCL25 and CCL28 (CCL25/28) were evaluated in post-weaning pigs. While pigs intramuscularly immunized with VLPs alone were capable of eliciting systemic anti-PEDV S-specific IgG and cellular immunity, co-administration of PEDV VLPs with CCL25/28 could further modulate the immune responses by enhancing systemic anti-PEDV S-specific IgG, mucosal IgA, and cellular immunity. Upon challenge with PEDV, both VLP-immunized groups showed milder clinical signs with reduced fecal viral shedding as compared to the control group. Furthermore, pigs immunized with VLPs adjuvanted with CCL25/28 showed superior immune protection against PEDV. Our results suggest that VLPs formulated with CCL25/28 may serve as a potential PEDV vaccine candidate and the same strategy may serve as a platform for the development of other enteric viral vaccines.

CCR10 expression is required for the adjuvant activity of the mucosal chemokine CCL28 when delivered in the context of an HIV-1 Env DNA vaccine

An effective prophylactic vaccine targeting HIV must induce a robust humoral response and must direct the bulk of this response to the mucosa-the primary site of HIV transmission. The chemokine, CCL28, is secreted by epithelial cells at mucosal surfaces and recruits' cells expressing its receptor CCR10. CCR10 is predominantly expressed by IgA + ASCs. We hypothesized that co-immunization with plasmid DNA encoding consensus envelope antigens with plasmid-encoded CCL28 would enhance anti-HIV IgA responses at mucosal surfaces. Indeed, animals receiving pCCL28 and pEnvA/C had significantly increased HIV-specific IgA in fecal extract. Surprisingly, CCL28 co-immunization induced a significant increase in anti-HIV IgG in the serum in mice compared to those receiving pEnvA/C alone. These robust antibody responses were not associated with changes in the frequency of germinal center B cells but depended upon the expression of CCR10, as these responses we abolished in CCR10-deficient animals. Finally, immunization with CCL28 led to increased frequencies in HIV-specific CCR10 + and CCR10 + IgA + B cells in the small intestine and Peyer's patches of vaccinated animals as compared to those receiving pEnvA/C alone. These data indicate that CCL28 administration can enhance antigen-specific humoral responses systemically and at mucosal surfaces.

Adjuvant Screen Identifies Synthetic DNA-Encoding Flt3L and CD80 Immunotherapeutics as Candidates for Enhancing Anti-tumor T Cell Responses

Overcoming tolerance to tumor-associated antigens remains a hurdle for cancer vaccine-based immunotherapy. A strategy to enhance the anti-tumor immune response is the inclusion of adjuvants to cancer vaccine protocols. In this report, we generated and systematically screened over twenty gene-based molecular adjuvants composed of cytokines, chemokines, and T cell co-stimulators for the ability to increase anti-tumor antigen T cell immunity. We identified several robust adjuvants whose addition to vaccine formulations resulted in enhanced T cell responses targeting the cancer antigens STEAP1 and TERT. We further characterized direct T cell stimulation through CD80-Fc and indirect T cell targeting via the dendritic cell activator Flt3L-Fc. Mechanistically, intramuscular delivery of Flt3L-Fc into mice was associated with a significant increase in infiltration of dendritic cells at the site of administration and trafficking of activated dendritic cells to the draining lymph node. Gene expression analysis of the muscle tissue confirmed a significant up-regulation in genes associated with dendritic cell signaling. Addition of CD80-Fc to STEAP1 vaccine formulation mimicked the engagement provided by DCs and increased T cell responses to STEAP1 by 8-fold, significantly increasing the frequency of antigen-specific cells expressing IFNγ, TNFα, and CD107a for both CD8⁺ and CD4⁺ T cells. CD80-Fc enhanced T cell responses to multiple tumor-associated antigens including Survivin and HPV, indicating its potential as a universal adjuvant for cancer vaccines. Together, the results of our study highlight the adjuvanting effect of T cell engagement either directly, CD80-Fc, or indirectly, Flt3L-Fc, for cancer vaccines.

Intramuscular Immunization with Chemokine-Adjuvanted Inactive Porcine Epidemic Diarrhea Virus Induces Substantial Protection in Pigs

Intramuscular (IM) immunization is generally considered incapable of generating a protective mucosal immune response. In the swine industry, attempts to develop a safe and protective vaccine for controlling porcine epidemic diarrhea (PED) via an IM route of administration have been unsuccessful. In the present study, porcine chemokine ligand proteins CCL25, 27, and 28 were constructed and stably expressed in the mammalian expression system. IM co-administration of inactivated PEDV (iPEDV) particles with different CC chemokines and Freund’s adjuvants resulted in recruiting CCR9+ and/or CCR10+ inflammatory cells to the injection site, thereby inducing superior systemic PEDV specific IgG, fecal IgA, and viral neutralizing antibodies in pigs. Moreover, pigs immunized with iPEDV in combination with CCL25 and CCL28 elicited substantial protection against a virulent PEDV challenge. We show that the porcine CC chemokines could be novel adjuvants for developing IM vaccines for modulating mucosal immune responses against mucosal transmissible pathogens in pigs.

Chemokine-Adjuvanted Plasmid DNA Induces Homing of Antigen-Specific and Non-Antigen-Specific B and T Cells to the Intestinal and Genital Mucosae

Plasmid DNA is a promising vaccine platform that together with electroporation can elicit significant systemic Ab responses; however, immunity at mucosal sites remains low. In this study, we sought to program T and B cells to home to the gastrointestinal and vaginal mucosae using genetic chemokine adjuvants and assessed their impact on immune homeostasis in various distinct immune compartments. BALB/c mice were immunized i.m. with plasmid DNA encoding a model Ag HIV-1 Env gp140 and selected chemokines/cytokine and boosted intravaginally with gp140 recombinant protein. Isolated splenocytes, intestinal lymphocytes, and genital lymphocytes as well as serum and intestinal luminal contents were assessed for Ag-specific reactivity. In addition, flow cytometric analysis was performed to determine the impact on immune homeostasis at these sites. Different molecular chemokine/cytokine adjuvants effected significant alterations to the recruitment of B and T cells to the spleen, vaginal and intestinal mucosae, for example CCL25 enhanced splenic and vaginal Ag-specific T cell responses whereas CCL28 increased the levels of specific T cells only in the vaginal mucosa. The levels of Ab could be modulated in the systemic circulation, as well as the vaginal vault and intestinal lumen, with CCL20 playing a central role. Our data demonstrate that the CCL20, CCL25, and CCL28 genetic chemokine adjuvants enhance the vaccine Ag-specific humoral and cellular responses and induce homing to the intestinal and female genital mucosae.

Mucosal Vaccine Approaches for Prevention of HIV and SIV Transmission

Optimal protective immunity to HIV will likely require that plasma cells, memory B cells and memory T cells be stationed in mucosal tissues at portals of viral entry. Mucosal vaccine administration is more effective than parenteral vaccine delivery for this purpose. The challenge has been to achieve efficient vaccine uptake at mucosal surfaces, and to identify safe and effective adjuvants, especially for mucosally administered HIV envelope protein immunogens. Here, we discuss strategies used to deliver potential HIV vaccine candidates in the intestine, respiratory tract, and male and female genital tract of humans and nonhuman primates. We also review mucosal adjuvants, including Toll-like receptor agonists, which may adjuvant both mucosal humoral and cellular immune responses to HIV protein immunogens.

Lessons for general vaccinology research from attempts to develop an HIV vaccine

In the past when large investments have been made in tackling narrow scientific challenges, the enormous expansion in our knowledge in one small area has had a spill-over effect on research and treatment of other diseases. The large investment in HIV vaccine development in recent years has the potential for such an effect on vaccine development for other diseases. HIV vaccine developers have experienced repeated failure using the standard approaches to vaccine development. This has forced them to consider immune responses in greater depth and detail. It has led to a recognition of the importance of epitopic specificity in both antibody and T cell responses. Also, it has led to an understanding of the importance of affinity maturation in antibody responses and the quality of T cell responses in T cell-mediated immunity. It has advanced the development of many novel vaccine vectors and vehicles that are now available for use in other vaccines. Further, it has focused attention on the impact of research funding mechanisms and community engagement on vaccine development. These developments and considerations have implications for vaccinology more generally. Some suggestions are made for investigators working on other "hard-to-develop" vaccines.

Molecular characterization, phylogenetic analysis and adjuvant effect of channel catfish interleukin-1βs against Streptococcus iniae

Channel catfish is one of the most extensively cultured species worldwide, which is widely used as a classical model for comparative immunology. Interleukin-1β (IL1β) is an immunoregulatory cytokine with the potential to enhance the immune response induced by vaccines in many animals. To characterize the molecular characterization and identify the immunoadjuvant role of channel catfish IL1β, molecular cloning, phylogenetic analysis, and expression of two IL1β genes were performed, the bioactivity of their recombinant proteins (rIL1β1 and rIL1β2) were detected in vitro and their adjuvant effects on a subunit vaccine encoding C5a peptidase (pSCPI) of Streptococcus iniae were evaluated. The results indicated that two IL1βs remained highly conserved possessing five conserved motifs compared with other fish IL1βs, although there were 28 nucleotide differences and 16 amino acid differences between channel catfish IL1β1 and IL1β2. Analysis of the ratios of nonsynonymous (dN) and synonymous (dS) substitutions revealed that fish IL1β genes were subjected to negative/purifying selection with global dN/dS ratios value 0.425. The results of adjuvant effect showed that compared with injection of pSCPI alone, co-injecting pSCPI with both rIL1β1 and rIL1β2 significantly enhanced antibody levels, serum bactericidal activity, lysozyme activity, alternative complement hemolytic activity, and the expression of endogenous IL1β and TNF-α in head kidney and spleen. Although vaccination with rIL1β1 or rIL1β2 failed to offer immunoprotection against S. iniae infection, the RPS (relative percent survival) of pSCPI+rIL1β1 and pSCPI+rIL1β2 groups were both higher than pSCPI alone (RPS, 50%), with 64.26% and 60.71%, respectively. Moreover, pSCPI+rIL1β1+rIL1β2 offered significantly higher (P < 0.05) immunoprotection (RPS, 75%) against S. iniae infection than pSCPI alone. Our present results not only enrich the molecular structure study of fish IL1βs but also signify that two recombinant channel catfish IL1βs can be used as potential adjuvants in a subunit vaccine model against bacterial infection, which are of profound importance to prevent and control bacterial disease in channel catfish.

Defensive Driving: Directing HIV-1 Vaccine-Induced Humoral Immunity to the Mucosa with Chemokine Adjuvants

A myriad of pathogens gain access to the host via the mucosal route; thus, vaccinations that protect against mucosal pathogens are critical. Pathogens such as HIV, HSV, and influenza enter the host at mucosal sites such as the intestinal, urogenital, and respiratory tracts. All currently licensed vaccines mediate protection by inducing the production of antibodies which can limit pathogen replication at the site of infection. Unfortunately, parenteral vaccination rarely induces the production of an antigen-specific antibody at mucosal surfaces and thus relies on transudation of systemically generated antibody to mucosal surfaces to mediate protection. Mucosa-associated lymphoid tissues (MALTs) consist of a complex network of immune organs and tissues that orchestrate the interaction between the host, commensal microbes, and pathogens at these surfaces. This complexity necessitates strict control of the entry and exit of lymphocytes in the MALT. This control is mediated by chemoattractant chemokines or cytokines which recruit immune cells expressing the cognate receptors and adhesion molecules. Exploiting mucosal chemokine trafficking pathways to mobilize specific subsets of lymphocytes to mucosal tissues in the context of vaccination has improved immunogenicity and efficacy in preclinical models. This review describes the novel use of MALT chemokines as vaccine adjuvants. Specific attention will be placed upon the use of such adjuvants to enhance HIV-specific mucosal humoral immunity in the context of prophylactic vaccination.

Killed Whole-Cell Oral Cholera Vaccine Induces CCL20 Secretion by Human Intestinal Epithelial Cells in the Presence of the Short-Chain Fatty Acid, Butyrate

Short-chain fatty acids (SCFAs), such as acetate, butyrate, and propionate, modulate immune responses in the gut. However, the effect of SCFAs on mucosal vaccine-induced immune cell migration is poorly understood. Here, we investigated whether SCFAs modulate chemokine expression induced by the killed whole-cell oral cholera vaccine, Shanchol™, in human intestinal epithelial cells. Shanchol™ induced expression of CCL2, CCL5, CCL20, and CXCL10 at the mRNA level, but not at the protein level. Interestingly, CCL20 secretion was substantially increased by co-stimulation with Shanchol™ and butyrate, while neither acetate nor propionate showed such effect. Enhanced CCL20 secretion was associated with GPR109A activation, and histone deacetylase (HDAC) inhibition. In addition, co-treatment with Shanchol™ and butyrate synergistically increased the secretion of adenosine triphosphate (ATP). Moreover, CCL20 secretion was decreased by inhibiting the extracellular ATP receptor P2X7. However, neither inflammasomes nor caspases were involved in CCL20 production. The culture supernatant of cells treated with Shanchol™ and butyrate augmented human immature dendritic cell migration. Collectively, these results suggest that butyrate enhances Shanchol™-induced CCL20 production in human intestinal epithelial cells via HDAC inhibition and ATP-P2X7 signaling by activating GPR109A. These effects potentially enhance the mucosal immune responses in the gut induced by this oral cholera vaccine.

Monkey Models and HIV Vaccine Research

Since the discovery of acquired immunodeficiency syndrome (AIDS) in 1981, it has been extremely difficult to develop an effective vaccine or a therapeutic cure despite over 36 years of global efforts. One of the major reasons is due to the lack of an immune-competent animal model that supports live human immunodeficiency virus (HIV) infection and disease progression such that vaccine-induced correlates of protection and efficacy can be determined clearly before human trials. Nevertheless, rhesus macaques infected with simian immunodeficiency virus (SIV) and chimeric simian human immunodeficiency virus (SHIV) have served as invaluable models not only for understanding AIDS pathogenesis but also for studying HIV vaccine and cure. In this chapter, therefore, we summarize major scientific evidence generated in these models since the beginning of the AIDS pandemic. Hopefully, the accumulated knowledge and lessons contributed by thousands of scientists will be useful in promoting the search of an ultimate solution to end HIV/AIDS.

Applications of chemokines as adjuvants for vaccine immunotherapy

Vaccinations are expected to aid in building immunity against pathogens. This objective often requires the addition of an adjuvant with certain vaccine formulations containing weakly immunogenic antigens. Adjuvants can improve antigen processing, presentation, and recognition, thereby improving the immunogenicity of a vaccine by simulating and eliciting an immune response. Chemokines are a group of small chemoattractant proteins that are essential regulators of the immune system. They are involved in almost every aspect of tumorigenesis, antitumor immunity, and antimicrobial activity and also play a critical role in regulating innate and adaptive immune responses. More recently, chemokines have been used as vaccine adjuvants due to their ability to modulate lymphocyte development, priming and effector functions, and enhance protective immunity. Chemokines that are produced naturally by the body's own immune system could serve as potentially safer and more reliable adjuvant options versus synthetic adjuvants. This review will primarily focus on chemokines and their immunomodulatory activities against various infectious diseases and cancers.

Workshop report: Nucleic acid delivery devices for HIV vaccines: Workshop proceedings, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland, USA, May 21, 2015

On May 21st, 2015, the U.S. National Institute of Allergy and Infectious Diseases (NIAID) convened a workshop on delivery devices for nucleic acid (NA) as vaccines in order to review the landscape of past and future technologies for administering NA (e.g., DNA, RNA, etc.) as antigen into target tissues of animal models and humans. Its focus was on current and future applications for preventing and treating human immunodeficiency virus (HIV) infection and acquired immune deficiency syndrome (AIDS) disease, among other infectious-disease priorities. Meeting participants presented the results and experience of representative clinical trials of NA vaccines using a variety of alternative delivery devices, as well as a broader group of methods studied in animal models and at bench top, to improve upon the performance and/or avoid the drawbacks of conventional needle-syringe (N-S) delivery. The subjects described and discussed included (1) delivery targeted into oral, cutaneous/intradermal, nasal, upper and lower respiratory, and intramuscular tissues; (2) devices and techniques for jet injection, solid, hollow, and dissolving microneedles, patches for topical passive diffusion or iontophoresis, electroporation, thermal microporation, nasal sprayers, aerosol upper-respiratory and pulmonary inhalation, stratum-corneum ablation by ultrasound, chemicals, and mechanical abrasion, and kinetic/ballistic delivery; (3) antigens, adjuvants, and carriers such as DNA, messenger RNA, synthesized plasmids, chemokines, wet and dry aerosols, and pollen-grain and microparticle vectors; and (4) the clinical experience and humoral, cellular, and cytokine immune responses observed for many of these target tissues, technologies, constructs, and carriers. This report summarizes the presentations and discussions from the workshop (https://web.archive.org/web/20160228112310/https://www.blsmeetings.net/NucleicAcidDeliveryDevices/), which was webcast live in its entirety and archived online (http://videocast.nih.gov/summary.asp?live=16059).

Immunogenicity and efficacy of DNA/MVA HIV vaccines in rhesus macaque models

INTRODUCTION

Despite 30 years of research on HIV, a vaccine to prevent infection and limit disease progression remains elusive. The RV144 trial showed moderate, but significant protection in humans and highlighted the contribution of antibody responses directed against HIV envelope as an important immune correlate for protection. Efforts to further build upon the progress include the use of a heterologous prime-boost regimen using DNA as the priming agent and the attenuated vaccinia virus, Modified Vaccinia Ankara (MVA), as a boosting vector for generating protective HIV-specific immunity. Areas covered: In this review, we summarize the immunogenicity of DNA/MVA vaccines in non-human primate models and describe the efficacy seen in SIV infection models. We discuss immunological correlates of protection determined by these studies and potential approaches for improving the protective immunity. Additionally, we describe the current progress of DNA/MVA vaccines in human trials. Expert commentary: Efforts over the past decade have provided the opportunity to better understand the dynamics of vaccine-induced immune responses and immune correlates of protection against HIV. Based on what we have learned, we outline multiple areas where the field will likely focus on in the next five years.

CCL28 chemokine: An anchoring point bridging innate and adaptive immunity

Chemokines are an extensive family of small proteins which, in conjunction with their receptors, guide the chemotactic activity of various immune cells throughout the body. CCL28, β- or CC chemokine, is involved in the host immunity at various epithelial and mucosal linings. The unique roles of CCL28 in several facets of immune responses have attracted considerable attention and may represent a promising approach to combat various infections. CCL28 displays a broad spectrum of antimicrobial activity against gram-negative and gram-positive bacteria, as well as fungi. Here, we will summarize various research findings regarding the antimicrobial activity of CCL28 and the relevant mechanisms behind it. We will explore how the structure of CCL28 is involved with this activity and how this function may have evolved. CCL28 displays strong homing capabilities for B and T cells at several mucosal and epithelial sites, and orchestrates the trafficking and functioning of lymphocytes. The chemotactic and immunomodulatory features of CCL28 through the interactions with its chemokine receptors, CCR10 and CCR3, will also be discussed in detail. Thus, in this review, we emphasize the dual properties of CCL28 and suggest its role as an anchoring point bridging the innate and adaptive immunity.

•

Chemokines play a vital role in cell migration in response to a chemical gradient by a process known as chemotaxis.

•

CCL28 is a β- or CC chemokine that is involved in host immunity through the interactions with its chemokine receptors, CCR10 and CCR3.

•

CCL28 is constitutively expressed in a wide variety of tissues including exocrine glands and is inducible through inflammation and infections.

•

CCL28 has been shown to exhibit broad spectrum antimicrobial activity against gram-positive bacteria, gram-negative bacteria, and some fungi.

•

CCL28 displays strong homing capabilities for B and T cells and orchestrates the trafficking and functioning of lymphocytes.

•

In this review, we emphasize the antimicrobial and immunomodulatory feature of CCL28 and its role as bridge between innate and adaptive immunity.

Pilot study of safety and feasibility of DNA microseeding for treatment of spontaneous canine melanoma

Spontaneous canine malignant melanoma provides an excellent pre-clinical model to study DNA vaccines for melanoma immunotherapy. A USDA-approved xenogeneic human tyrosinase (huTYR) plasmid DNA vaccine delivered intramuscularly induces detectable immune responses and has clinical activity in some dogs with melanoma. The objective of this pilot study was to evaluate the feasibility, safety and immunogenicity of huTYR plasmid DNA administered to the skin via microseeding in dogs with spontaneous melanoma. DNA microseeding utilizes a modified tattooing device as an alternate and potentially more potent delivery method for DNA immunization. DNA was delivered to shaved inner thigh skin of six companion dogs with melanoma approximately every 14 days for a planned total of four vaccination time points. An anti-huTYR ELISA was used to test pre- and post-treatment sera. Biopsies of treated skin were obtained for detection of huTYR transgene expression. DNA microseeding was well tolerated with no significant toxicity detected beyond local site irritation, and there were no signs of autoimmunity. huTYR-expressing cells were observed in biopsies of huTYR DNA microseeding sites. Increased humoral anti-huTYR antibodies were seen in two of five evaluable dogs following microseeding compared to baseline. DNA microseeding is well tolerated in companion dogs with melanoma. Further investigation is needed to determine if combining DNA microseeding with other immunotherapy regimens potentiates this delivery platform for cancer immunotherapy.

Adjuvants: tailoring humoral immune responses

PURPOSE OF REVIEW

The development and availability of new-generation adjuvants beyond aluminum and emulsion formulations, together with a deeper understanding of the mechanistic role of adjuvant formulations in stimulating innate immunity and offer opportunities to improve candidate vaccine designs intended to protect against HIV-1 acquisition.

RECENT FINDINGS

Currently, major efforts in vaccine development focus on improving prime-boost vaccine regimens to enhance efficacy beyond 31% observed in the RV144 phase 3 study and to develop a pathway to induce broadly reactive HIV neutralizing antibodies. Advances in HIV-1 envelope (Env) immunogen design and improved adjuvant formulations are moving at a parallel pace. This review highlights steps underway to rationally pair vaccine concepts with improved adjuvant formulations in preclinical and early phase 1 clinical evaluation.

SUMMARY

New adjuvants with immune-potentiating properties are currently being tested in combination with recent HIV Env-containing immunogens in prime-boost and subunit protein-only regimens. Greater emphasis is being applied to formulation science, delivery, and targeted safety and immune evaluation with these adjuvants in clinical trials. The need to develop an HIV vaccine that induces more potent and long-lived protective immunity will necessitate continued efforts to optimize adjuvanted vaccine formulations.

HIVIS-DNA or HIVISopt-DNA priming followed by CMDR vaccinia-based boosts induce both humoral and cellular murine immune responses to HIV

Background

In order to develop a more effective prophylactic HIV-1 vaccine it is important optimize the components, improve Envelope glycoprotein immunogenicity as well as to explore prime-boost immunization schedules. It is also valuable to include several HIV-1 subtype antigens representing the world-wide epidemic.

Methods

HIVIS-DNA plasmids which include Env genes of subtypes A, B and C together with Gag subtypes A and B and RTmut/Rev of subtype B were modified as follows: the Envelope sequences were shortened, codon optimized, provided with an FT4 sequence and an immunodominant region mutated. The reverse transcriptase (RT) gene was shortened to contain the most immunogenic N-terminal fragment and fused with an inactivated viral protease vPR gene. HIVISopt-DNA thus contains fewer plasmids but additional PR epitopes compared to the native HIVIS-DNA. DNA components were delivered intradermally to young Balb/c mice once, using a needle-free Biojector® immediately followed by dermal electroporation. Vaccinia-based MVA-CMDR boosts including Env gene E and Gag-RT genes A were delivered intramuscularly by needle, once or twice.

Results

Both HIVIS-DNA and HIVISopt-DNA primed humoral and cell mediated responses well. When boosted with heterologous MVA-CMDR (subtypes A and E) virus inhibitory neutralizing antibodies were obtained to HIV-1 subtypes A, B, C and AE. Both plasmid compositions boosted with MVA-CMDR generated HIV-1 specific cellular responses directed against HIV-1 Env, Gag and Pol, as measured by IFNγ ELISpot. It was shown that DNA priming augmented the vector MVA immunological boosting effects, the HIVISopt-DNA with a trend to improved (Env) neutralization, the HIVIS-DNA with a trend to better (Gag) cell mediated immune reponses.

Conclusions

HIVIS-DNA was modified to obtain HIVISopt-DNA that had fewer plasmids, and additional epitopes. Even with one DNA prime followed by two MVA-CMDR boosts, humoral and cell-mediated immune responses were readily induced by priming with either DNA construct composition. Priming by HIV-DNA augmented neutralizing antibody responses revealed by boosting with the vaccinia-based heterologous sequences. Cellular and antibody responses covered selected strains representing HIV-1 subtypes A, B, C and CRF01_AE. We assume this is related to the inclusion of heterologous full genes in the vaccine schedule.

MyD88/CD40 Genetic Adjuvant Function in Cutaneous Atypical Antigen-Presenting Cells Contributes to DNA Vaccine Immunogenicity

Therapeutic DNA-based vaccines aim to prime an adaptive host immune response against tumor-associated antigens, eliminating cancer cells primarily through CD8+ cytotoxic T cell-mediated destruction. To be optimally effective, immunological adjuvants are required for the activation of tumor-specific CD8+ T cells responses by DNA vaccination. Here, we describe enhanced anti-tumor efficacy of an in vivo electroporation-delivered DNA vaccine by inclusion of a genetically encoded chimeric MyD88/CD40 (MC) adjuvant, which integrates both innate and adaptive immune signaling pathways. When incorporated into a DNA vaccine, signaling by the MC adjuvant increased antigen-specific CD8+ T cells and promoted elimination of pre-established tumors. Interestingly, MC-enhanced vaccine efficacy did not require direct-expression of either antigen or adjuvant by local antigen-presenting cells, but rather our data supports a key role for MC function in "atypical" antigen-presenting cells of skin. In particular, MC adjuvant-modified keratinocytes increased inflammatory cytokine secretion, upregulated surface MHC class I, and were able to increase in vitro and in vivo priming of antigen-specific CD8+ T cells. Furthermore, in the absence of critical CD8α+/CD103+ cross-priming dendritic cells, MC was still able to promote immune priming in vivo, albeit at a reduced level. Altogether, our data support a mechanism by which MC signaling activates an inflammatory phenotype in atypical antigen-presenting cells within the cutaneous vaccination site, leading to an enhanced CD8+ T cell response against DNA vaccine-encoded antigens, through both CD8α+/CD103+ dendritic cell-dependent and independent pathways.

Molecular cloning, expression and the adjuvant effects of interleukin-8 of channel catfish (Ictalurus Punctatus) against Streptococcus iniae

Interleukin-8 (IL-8) as an important cytokine involving in inflammatory and immune response, has been studied as effective adjuvants for vaccines in mammals. However, there are fewer reports about the characterization and adjuvant effects of IL-8 in fish. In this study, cloning and sequence analysis of IL-8 coding region of channel catfish (Ictalurus punctatus) were conducted, mature IL-8(rtIL-8) was expressed and evaluated for its adjuvant effects on the immunoprotection of subunit vaccine encoding α-enolase (rENO) of Streptococcus iniae from several aspects in channel catfish. The results showed co-vaccination of rENO with rtIL-8 enhanced immune responses including humoral and cellular immunity, with higher relative percent survival(RPS,71.4%) compared with the moderate RPS of rENO alone(50%) against S. iniae infection at 4 week post vaccination. While rtIL-8 failed to maintain long-lasting immune protection, only with RPS of 26.67% in rENO + rtIL-8-vaccinated fish compared with that of rENO alone(20%) at 8 week, signifying that IL-8 hold promise for use as potential immunopotentiator in vaccines against bacterial infections in fish, whereas it is insufficient to extend the immunoprotection for long time, and further studies are required to understand the mechanisms of IL-8 used as an adjuvant and seek for more effective way to strengthen the adjuvanticity of IL-8.

New developments in an old strategy: heterologous vector primes and envelope protein boosts in HIV vaccine design

Prime/boost vaccination strategies for HIV/SIV vaccine development have been used since the early 1990s and have become an established method for eliciting cell and antibody mediated immunity. Here we focus on induction of protective antibodies, both broadly neutralizing and non-neutralizing, with the viral envelope being the key target antigen. Prime/boost approaches are complicated by the diversity of autologous and heterologous priming vectors, and by various forms of envelope booster immunogens, many still in development as structural studies aim to design stable constructs with exposure of critical epitopes for protective antibody elicitation. This review discusses individual vaccine components, reviews recent prime/boost strategies and their outcomes, and highlights complicating factors arising as greater knowledge concerning induction of adaptive, protective immunity is acquired.

Lactobacillus plantarum displaying CCL3 chemokine in fusion with HIV-1 Gag derived antigen causes increased recruitment of T cells

Background

Chemokines are attractive candidates for vaccine adjuvants due to their ability to recruit the immune cells. Lactic acid bacteria (LAB)-based delivery vehicles have potential to be used as a cheap and safe option for vaccination. Chemokine produced on the surface of LAB may potentially enhance the immune response to an antigen and this approach can be considered in development of future mucosal vaccines.

Results

We have constructed strains of Lactobacillusplantarum displaying a chemokine on their surface. L. plantarum was genetically engineered to express and anchor to the surface a protein called CCL3Gag. CCL3Gag is a fusion protein comprising of truncated HIV-1 Gag antigen and the murine chemokine CCL3, also known as MIP-1α. Various surface anchoring strategies were explored: (1) a lipobox-based covalent membrane anchor, (2) sortase-mediated covalent cell wall anchoring, (3) LysM-based non-covalent cell wall anchoring, and (4) an N-terminal signal peptide-based transmembrane anchor. Protein production and correct localization were confirmed using Western blotting, flow cytometry and immunofluorescence microscopy. Using a chemotaxis assay, we demonstrated that CCL3Gag-producing L. plantarum strains are able to recruit immune cells in vitro.

Conclusions

The results show the ability of engineered L. plantarum to produce a functional chemotactic protein immobilized on the bacterial surface. We observed that the activity of surface-displayed CCL3Gag differed depending on the type of anchor used. The chemokine which is a part of the bacteria-based vaccine may increase the recruitment of immune cells and, thereby, enhance the reaction of the immune system to the vaccine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-015-0360-z) contains supplementary material, which is available to authorized users.

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.