Enhancement of a biotechnological platform for the purification and delivery of a human papillomavirus supercoiled plasmid DNA vaccine

New biotechnological strategies are being explored, aimed at rapid and economic manufacture of large quantities of DNA vaccines with the required purity for therapeutic applications, as well as their correct delivery as biopharmaceuticals to target cells. This report describes the purification of supercoiled (sc) HPV-16 E6/E7 plasmid DNA (pDNA) vaccine from a bacterial lysate, using an arginine-based monolith, presenting a spacer arm in its configuration. To enhance the performance of the purification process, monolith modification with the spacer arm can improve accessibility of the arginine ligand. By using a low NaCl concentration at pH 7.0, a condition to eliminate the RNA impurity directly in the flow through was established. The pH increase to 7.5 allowed the elimination of non-functional pDNA isoforms, the sc pDNA being recovered by increasing the ionic strength. As well as a binding capacity of 2.53 mg/mL obtained with a pre-purified sc pDNA sample, the column also purified sc pDNA from high lysate loading, with capacities above 1 mg/mL. Due to the sample displacement phenomena, non-functional pDNA isoforms were eliminated throughout column loading, favoring the degree of purity of final sc pDNA of 93.3%-98.5%. Thereafter, purified sc pDNA was successfully encapsulated into CaCO₃-gelatin nano-complexes. Delivery of the pDNA-carriers to THP-1 cells was assessed through pDNA cellular uptake evaluation and correct E6 expression was verified by mRNA and protein detection. A biotechnological platform was established for sc pDNA purification and delivery to dendritic cells, stimulating further in vivo studies.

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Recent advances in chromatographic purification of plasmid DNA for gene therapy and DNA vaccines: A review

The wide spread of infectious diseases have provoked the scientists to develop new types of vaccines. Among the different types of vaccines, the recently discovered plasmid DNA vaccines, have gained tremendous attentions in the last few decades as a modern approach of vaccination. The scientific interest in plasmid DNA vaccines is attributed to their prominent efficacy as they trigger not only the cellular immune response but also the humoral immune responses. Moreover, pDNA vaccines are easily to be stored, shipped and produced. However, the purification of the pDNA vaccines is a crucial step in their production and administration, which is usually conducted by different chromatographic techniques. This review summarizes the most recent chromatographic purification methods provided in the literature during the last five years following our last review in 2013, including affinity chromatography, hydrophobic interaction chromatography, ion exchange chromatography, multimodal chromatography, sample displacement chromatography and miscellaneous chromatographic methods.

Vaccination strategies against Zika virus

The epidemic emergence of Zika virus (ZIKV) in 2015-2016 has been associated with congenital malformations and neurological sequela. Current efforts to develop a ZIKV vaccine build on technologies that successfully reduced infection or disease burden against closely related flaviviruses or other RNA viruses. Subunit-based (DNA plasmid and modified mRNA), viral vectored (adeno- and measles viruses) and inactivated viral vaccines are already advancing to clinical trials in humans after successful mouse and non-human primate studies. Among the greatest challenges for the rapid implementation of immunogenic and protective ZIKV vaccines will be addressing the potential for exacerbating Dengue virus infection or causing Guillain-Barré syndrome through production of cross-reactive immunity targeting related viral or host proteins. Here, we review vaccine strategies under development for ZIKV and the issues surrounding their usage.

Combination recombinant simian or chimpanzee adenoviral vectors for vaccine development

Recombinant adenoviral vector (rAd)-based vaccines are currently being developed for several infectious diseases and cancer therapy, but pre-existing seroprevalence to such vectors may prevent their use in broad human populations. In this study, we investigated the potential of low seroprevalence non-human primate rAd vectors to stimulate cellular and humoral responses using HIV/SIV Env glycoprotein (gp) as the representative antigen. Mice were immunized with novel simian or chimpanzee rAd (rSAV or rChAd) vectors encoding HIV gp or SIV gp by single immunization or in heterologous prime/boost combinations (DNA/rAd; rAd/rAd; rAd/NYVAC or rAd/rLCM), and adaptive immunity was assessed. Among the rSAV and rChAd tested, rSAV16 or rChAd3 vector alone generated the most potent immune responses. The DNA/rSAV regimen also generated immune responses similar to the DNA/rAd5 regimen. rChAd63/rChAd3 and rChAd3 /NYVAC induced similar or even higher levels of CD4+ and CD8+ T-cell and IgG responses as compared to rAd28/rAd5, one of the most potent combinations of human rAds. The optimized vaccine regimen stimulated improved cellular immune responses and neutralizing antibodies against HIV compared to the DNA/rAd5 regimen. Based on these results, this type of novel rAd vector and its prime/boost combination regimens represent promising candidates for vaccine development.

Development of a human live attenuated West Nile infectious DNA vaccine: conceptual design of the vaccine candidate

West Nile virus has become an important epidemiological problem attracting significant attention of health authorities, mass media, and the public. Although there are promising advancements toward addressing the vaccine need, the perspectives of the commercial availability of the vaccine remain uncertain. To a large extent this is due to lack of a sustained interest for further commercial development of the vaccines already undergoing the preclinical and clinical development, and a predicted insignificant cost effectiveness of mass vaccination. There is a need for a safe, efficacious and cost effective vaccine, which can improve the feasibility of a targeted vaccination program. In the present report, we summarize the background, the rationale, and the choice of the development pathway that we selected for the design of a live attenuated human West Nile vaccine in a novel infectious DNA format.

Antiparasitic DNA vaccines in 21st century

Demands for effective vaccines to control parasitic diseases of humans and livestock have been recently exacerbated by the development of resistance of most pathogenic parasites to anti-parasitic drugs. Novel genomic and proteomic technologies have provided opportunities for the discovery and improvement of DNA vaccines which are relatively easy as well as cheap to fabricate and stable at room temperatures. However, their main limitation is rather poor immunogenicity, which makes it necessary to couple the antigens with adjuvant molecules. This paper review recent advances in the development of DNA vaccines to some pathogenic protozoa and helminths. Numerous studies were conducted over the past 14 years of 21st century, employing various administration techniques, adjuvants and new immunogenic antigens to increase efficacy of DNA vaccines. Unfortunately, the results have not been rewarding. Further research is necessary using more extensive combinations of antigens; alternate delivery systems and more efficient adjuvants based on knowledge of the immunomodulatory capacities of parasitic protozoa and helminths.

Pharmaceutical grade large-scale plasmid DNA manufacturing process

For pharmaceutical applications of plasmid DNA, either direct or indirect, certain quality standards are required. Whereas for direct gene transfer into human "Good Manufacturing Practice" (GMP) grade is mandatory, for GMP production of, e.g., viral vectors (AAV, etc.) the plasmid DNA used needs not necessarily be produced under GMP. Besides such regulatory aspects up-scaling of the plasmid DNA production process from research laboratory scale (up to a few milligrams) to industrial scales (milligram to gram scales) is an issue that is addressed here.

Plasmid fermentation process for DNA immunization applications

Plasmid DNA for immunization applications must be of the highest purity and quality. The ability of downstream purification to efficiently produce a pure final product is directly influenced by the performance of the upstream fermentation process. While several clinical manufacturing facilities already have validated fermentation processes in place to manufacture plasmid DNA for use in humans, a simple and inexpensive laboratory-scale fermentation process can be valuable for in-house production of plasmid DNA for use in animal efficacy studies. This chapter describes a simple fed-batch fermentation process for producing bacterial cell paste enriched with high-quality plasmid DNA. A constant feeding strategy results in a medium cell density culture with continuously increasing plasmid amplification towards the end of the process. Cell banking and seed culture preparation protocols, which can dramatically influence final product yield and quality, are also described. These protocols are suitable for production of research-grade plasmid DNA at the 100 mg-to-1.5 g scale from a typical 10 L laboratory benchtop fermentor.

Dielectrophoresis based continuous-flow nano sorter: fast quality control of gene vaccines

We present a prototype nanofluidic device, developed for the continuous-flow dielectrophoretic (DEP) fractionation, purification, and quality control of sample suspensions for gene vaccine production. The device consists of a cross injector, two operation regions, and separate outlets where the analytes are collected. In each DEP operation region, an inhomogeneous electric field is generated at a channel spanning insulating ridge. The samples are driven by ac and dc voltages that generate a dielectrophoretic potential at the ridge as well as (linear) electrokinetics. Since the DEP potential differs at the two ridges, probes of three and more species can be iteratively fully fractionated. We demonstrate the fast and efficient separation of parental plasmid, miniplasmid, and minicircle DNA, where the latter is applicable as a gene vaccine. Since the present technique is virtually label-free, it offers a fast purification and in-process quality control with low consumption, in parallel, for the production of gene vaccines.

Quantifying transcription of clinically relevant immobilized DNA within a continuous flow microfluidic reactor

Flow-through reactors are commonly used to control and optimize reagent delivery and product removal. Although recent research suggests that transcription reactions using picogram quantities of cDNA produce RNA efficiently in a flow-through microreactor, there has not been a detailed study on the mass transport and reagent dependence of microfluidic transcription reactions. We present a novel microreactor that contains H5 influenza cDNA immobilized directly onto the reactor walls to study the kinetics and reagent dependence of in vitro transcription reactions on a microfluidic platform. Enzyme and the rNTP substrate continuously flow over the cDNA and create RNA, which flows to a downstream collection well. Using nanogram quantities of cDNA, we found that enzyme limiting conditions caused by the concentration of cDNA in a small-volume microreactor channel may be partially overcome as the enzyme binds and concentrates near the channel wall. Kinetics confirm this phenomenon and show that the timescale for enzyme binding can be approximated by t(f) = cDNA/Q[E]. Surprisingly, on-chip transcription reactions have a strong dependence on the rNTP concentration from 5 to 9 mM despite a low consumption rate of rNTP molecules that is largely independent of the flow rate. Faster flow rates decrease the time it takes to fill DNA promoter sites with enzyme while additionally refreshing rNTP and MgCl(2) to allow for a greater consumption of rNTP. These two effects cause reactions with higher concentrations of cDNA in the reactor channel to have a greater dependence on the flow rate. At high flow rates (>0.37 nL/s), the reaction rate begins to drop, likely because of the release and escape of enzyme molecules from the cDNA layer. This critical flow rate can be predicted by a new modified Peclet number, Pe(m) = L(c)V/D, where L(c) is the full length of the tightly packed cDNA molecules, V is the velocity at the DNA/fluid interface, and D is the diffusivity of the enzyme molecule. Together, these insights can inspire reactor designs for a variety of applications.

Generic plasmid DNA production platform incorporating low metabolic burden seed-stock and fed-batch fermentation processes

DNA vaccines have tremendous potential for rapid deployment in pandemic applications, wherein a new antigen is "plugged" into a validated vector, and rapidly produced in a validated, fermentation-purification process. For this application, it is essential that the vector and fermentation process function with a variety of different antigen genes. However, many antigen genes are unpredictably "toxic" or otherwise low yielding in standard fermentation processes. We report cell bank and fermentation process unit operation innovations that reduce plasmid-mediated metabolic burden, enabling successful production of previously known toxic influenza hemagglutinin antigen genes. These processes, combined with vector backbone modifications, doubled fermentation productivity compared to existing high copy vectors, such as pVAX1 and gWiz, resulting in high plasmid yields (up to 2,220 mg/L, 5% of total dry cell weight) even with previously identified toxic or poor producing inserts.

Methods for constructing and evaluating antitumor DNA vaccines

An antitumor DNA vaccine is a bacterial DNA plasmid that encodes the complementary DNA (cDNA) of a tumor antigen. When injected into recipients, antitumor DNA vaccines have been shown to elicit both humoral and cellular immunity against the encoded tumor antigen. These vaccines represent a relatively new immunotherapeutic technique being investigated as a means to deliver a target antigen and elicit or augment antitumor antigen-specific immune responses. One of the primary advantages of DNA vaccines as opposed to some other methods of antigen delivery is that they can be easily constructed, purified, and delivered to recipients. In this review we describe this process, detailing the procedures used to construct, purify, deliver, and evaluate the efficacy of DNA vaccines. We begin by describing the process of molecularly constructing the vaccine, from selecting a bacterial plasmid to form the backbone of the vaccine, cloning the antigen cDNA into this plasmid, and confirming the sequence and orientation of the completed vaccine. This is then followed by a series of experiments that can be used to ensure that the antigen encoded by the vaccine is transcribed and translated after being taken up by eukaryotic cells. We then describe large-scale purification procedures that can be used to obtain sufficient quantities of plasmid DNA to conduct in vivo immunization experiments. Finally, we provide an immunization protocol that can be used to evaluate the immunological efficacy of the constructed DNA vaccine. By following these protocols, it is possible to construct, purify, deliver, and evaluate the efficacy of antitumor DNA vaccines.

Isolation and purification of recombinant outer surface protein C (rOspC) of Borrelia burgdorferi sensu lato

The aim of this work was isolation and purification of the major immunodominant protein, Outer surface protein C (OspC) of three members of the species group Borrelia burgdorferi, the causative agent of Lyme disease. Our aim was to obtain this protein in a quantity and purity sufficient for immunization of experimental animals. For optimalization of protein purification's yield we used immobilized metal ion affinity chromatography (IMAC) under different conditions. The greatest efficiency was achieved by using of HiTrap Chelating Column under native conditions.

Elicitation of strong immune responses by a DNA vaccine expressing a secreted form of hepatitis C virus envelope protein E2 in murine and porcine animal models

AIM: To characterize the immunogenicity of a hepatitis C virus (HCV) E2 DNA vaccine alone or with a protein vaccine boost in murine and porcine animal models.

METHODS: A DNA vaccine expressing a secreted form of HCV E2 protein was constructed and used to vaccinate mice and piglets with or without boosting with a recombinant E2 protein vaccine formulated with CpG ODN and 10% Emulsigen. The immunogenicity of HCV E2 vaccines was analyzed by ELISA for antibody responses, MTT assay for lymphocyte proliferation, ELISPOT for the number of interferon-γ secreting cells, and cytotoxic T lymphocyte assays.

RESULTS: Intradermal injection of E2 DNA vaccine induced strong Th1-like immune responses in mice. In piglets, E2 DNA vaccine elicited moderate and more balanced immune responses. A DNA vaccine prime and protein boost vaccination strategy induced significantly higher E2-specific antibody levels and shifted the immune response towards Th2-like ones in piglets.

CONCLUSION: A DNA vaccine expressing a secreted form of HCV E2 protein elicited E2-specific immune responses in mice and piglets. Recombinant E2 protein vaccination following DNA immunization significantly increased the antibody response in piglets. These HCV E2 vaccines may represent promising hepatitis C vaccine candidates for further investigations.

Lessons from the cat: development of vaccines against lentiviruses

Feline immunodeficiency virus (FIV) is a natural infection of domestic cats, which produces a disease with many similarities to human immunodeficiency virus (HIV) infection in man. The virus is an important cause of morbidity and mortality in pet cats worldwide. As such an effective vaccine is desirable both for its use in veterinary medicine and also as a model for the development of an HIV vaccine. A large number of candidate vaccines have been tested against feline immunodeficiency virus. These include inactivated virus and infected cell vaccines, DNA and viral vectored vaccines, subunit and peptide vaccines and vaccines using bacterial vectors. Ultimately, the development of inactivated virus and infected cell vaccines led to the release of the first licensed vaccine against FIV, in 2002. This review highlights some of the difficulties associated with the development of lentiviral vaccines and some of the lessons that have been learned in the FIV model that are of particular relevance to the development of HIV vaccines.

A reversed phase HPLC assay for the simultaneous quantitation of non-ionic and ionic surfactants in bioprocess intermediates

This report describes a rapid and accurate reversed phase HPLC method for the simultaneous quantitation of multiple surfactants in various bioprocess solution matrices including cell lysates. Separation and quantitation of a mixture of the cationic detergent domiphen bromide from the non-ionic detergent Triton X-100 in crude cell mixtures can be achieved within 15 min using a TSK-gel C18-NPR reversed phase column and an aqueous mobile phase gradient of acetonitrile:water with the reagent PIC-B8 as ion-pairing modifier. The linear dynamic range for quantitation of domiphen bromide (DB) and Triton in this assay extends from 20 to 2000 microM. Linear regression analyses from the standard curve determinations showed an R2 of > or = 0.990. The assay does not show any interferences from proteins or other cellular contaminants such as nucleic acids. The assay has been used to evaluate clearance of these compounds throughout the purification process of an adenovirus-based vaccine candidate, as well as to determine the effects of process changes on detergent clearance.

Bioprocess engineering issues that would be faced in producing a DNA vaccine at up to 100 m3 fermentation scale for an influenza pandemic

The risk of a pandemic with a virulent form of influenza is acknowledged by the World Health Organization (WHO) and other agencies. Current vaccine production facilities would be unable to meet the global requirement for vaccine. As a possible supplement a DNA vaccine may be appropriate, and bioprocess engineering factors bearing on the use of existing biopharmaceutical and antibiotics plants to produce it are described. This approach addresses the uncertainty of timing of a pandemic that precludes purpose-built facilities. The strengths and weaknesses of alternative downstream processing routes are analyzed, and several gaps in public domain information are addressed. The conclusion is that such processing would be challenging but feasible.

A simple method for the production of plasmid DNA in bioreactors

The need for large quantities of purified plasmid DNA has increased as the applications of DNA vaccines continue to expand. This chapter describes a simple, scaleable procedure based on the fed-batch cultivation of various Escherichia coli clones, which can be easily implemented and scaled-up to large bioreactors. Although some clones may require minor modifications to the feeding strategy, in general, this procedure, implemented as described, is likely to support the production of milligram to gram quantities of plasmid DNA.

DNA vaccination using bacillus Calmette-Guerin-DNA as an adjuvant to enhance immune response to three kinds of swine diseases

In order to enhance the immune efficacy of DNA vaccination, experiments were conducted to investigate the regulating effects of Bacillus Calmette-Guerin (BCG)-DNA as an adjuvant on immune responses of mice against foot-and-mouth disease (FMD), Aujeszky's disease (AjD) and classical swine fever (CSF). BCG-DNA was purified from BCG by ion-exchange chromatography. Three DNA vaccines (pVSG, pVgD and pVE2) against the respective infection were constructed, and BCG-DNA was coimmunized to mice by muscle injection. The results showed that titres of specific immunoglobulin (Ig)G to the vaccines mounted remarkably in the sera of the adjuvant covaccinated mice (P < 0.01). Antibody isotype IgG2a and IgG1 also increased, respectively, in mice coimmunized with BCG-DNA compared with those of the control groups (P < 0.01). Cellular immune cytokine interferon-gamma and cytotoxic T lymphocytes were detected in coimmunized BCG-DNA groups (P < 0.05). Whereas interleukin-4, humoral immune cytokine, was not significant (P > 0.05). These results suggest that codelivery of BCG-DNA with DNA vaccines against FMD, AjD and CSF can enhance the induction of antigen-specific, especially, cell-mediated immunity.

Preparation and purification of recombinant outer surface protein A (rOspA) of Borrelia burgdorferi sensu stricto and Borrelia afzelii

The recombinant Outer surface protein A (rOspA) from Borrelia burgdorferi is a possible immunogen for protection of infected humans and animals against development of Lyme borreliosis (Lyme disease), a chronic tick-borne disease characterised by diverse dermatologic, neurologic, rheumatic, and cardiac manifestations. For several years, research and development have been directed towards a vaccine for the prevention of this debilitating disease. Numerous animal studies demonstrate that pre-existing antibodies against the outer surface proteins of B. burgdorferi can prevent infection and disease caused by this organism. In this communication, using recombinant DNA technology, genes from B. burgdorferi sensu stricto and B. afzelii were inserted into E. coli-expression vectors and the rOspA were produced. Our aim was to obtain rOspA protein in a purity and quantity desirable for immunization of experimental animals. rOspA is currently the most developed, molecularly-defined vaccine candidate for the prevention of Lyme borreliosis.

Current progress in tuberculosis vaccine development

The tuberculosis vaccine field has blossomed in the past 10 years, with over a hundred new candidates going through animal model testing, and several now entering or approaching clinical trial evaluation. In this brief review the current animal screening models are discussed, as are the various types of new vaccines that have been developed. New approaches, especially in the area of BCG boosting in various prime/boost protocols, are starting to show considerable promise. More sophisticated readouts, including imaging approaches such as magnetic resonance imaging, and better definition of the immunopathology of the lung disease process, should help accelerate vaccine development even further in the next decade.

DermaVir, a novel HIV immunisation technology

DermaVir is a novel topical immunisation designed to target Langerhans cells (LC), the epidermal precursors of dendritic cells. LC serve as a vehicle to process and transfer antigens from the skin to T cell areas in the lymphoid organs. The HIV DNA delivered by DermaVir to LC expresses most viral regulatory and structural genes and induces T cell-mediated immune responses with broad specificity. In chronically infected macaques, DermaVir administered with antiretroviral drugs, suppressed viral load rebound after treatment interruption and improved survival. DermaVir is a promising antiretroviral treatment approach with a unique mechanism of action for combination with currently used drugs.

Purification of plasmids for gene therapy and DNA vaccination

This chapter covers the different aspects of the production and purification of plasmids for gene therapy and DNA vaccination. Process issues are extensively covered and complemented with information related to plasmid DNA structure, vector construction, product specifications and quality assurance and control.

Plasmid DNA for pharmaceutical applications

With the advent and progress of recombinant DNA technology into a variety of fields such as medical therapy, preventive or curative vaccination or the induction of regeneration, the demand for large quantities of highly purified DNA is increasing. Traditional methods of purifying plasmids usually require sophisticated methodology if the DNA is to be separated from RNA and other contaminating organic components. In particular, methods for obtaining supercoiled covalently closed circular (CCC) plasmid DNA in pure form, cope with the requirement that other plasmid topologies also produced have to be separated from the final product. The innovative technology of capillary gel electrophoresis (CGE) contributes a sensitive tool to the short list of applicable quality control assays for clinical grade plasmid DNA.

Strategies for designing and optimizing new generation vaccines

Although the field of immunology developed in part from the early vaccine studies of Edward Jenner, Louis Pasteur and others, vaccine development had largely become the province of virologists and other microbiologists, because the model for classic vaccines was to isolate the pathogen and prepare a killed or attenuated pathogen vaccine. Only recently has vaccinology returned to the realm of immunology, because a new understanding of immune mechanisms has allowed translation of basic discoveries into vaccine strategies.

Production, purification and analysis of an experimental DNA vaccine against rabies

BACKGROUND

The basic and applied research efforts devoted to the development of DNA vaccines must be accompanied by manufacturing processes capable of being scaled up and delivering a clinical-grade product. This work describes a rapid process of this kind, based on hydrophobic interaction chromatography (HIC) for the production of milligram quantities of an experimental DNA rabies vaccine. Its properties and protective activity are tested in comparison with the same plasmid DNA purified with a commercial kit.

METHODS

The experimental DNA vaccine encoding the rabies virus glycoprotein was amplified in vivo in Escherichia coli. The plasmid was isolated by alkaline lysis, pre-purified and concentrated by isopropanol and (NH4)2SO4 precipitation, and purified by HIC and dialysis. Product quality was controlled by using high-performance liquid chromatography (HPLC), Southern slot blotting, agarose gel electrophoresis, the kinetic-QCL Limulus amoebocyte lysate assay, and protein assays. The expression of the rabies virus glycoprotein was tested in vitro in neuroblastoma cells. The production of rabies-virus-neutralising antibodies and the protection against an intracerebral virus challenge were tested in mice.

RESULTS

One hundred and forty-two milligrams of the plasmid, with an HPLC purity greater than 99% were obtained from 4.5 l medium. Control analysis showed that the vaccine conforms to specifications in terms of impurities (endotoxins, genomic DNA, RNA, proteins). Furthermore, the final experimental vaccine induces rabies-virus-neutralising antibodies and protects mice against a rabies virus challenge.

CONCLUSIONS

This study demonstrates that the method developed for the purification of milligram amounts of plasmid delivers an endotoxin-free, experimental rabies DNA vaccine, with protective activity similar to that obtained with the vaccine purified using a commercial kit.

Toward a defined anti-Leishmania vaccine targeting vector antigens: characterization of a protective salivary protein

Leishmania parasites are transmitted to their vertebrate hosts by infected phlebotomine sand fly bites. Sand fly saliva is known to enhance Leishmania infection, while immunity to the saliva protects against infection as determined by coinoculation of parasites with vector salivary gland homogenates (SGHs) or by infected sand fly bites (Kamhawi, S., Y. Belkaid, G. Modi, E. Rowton, and D. Sacks. 2000. Science. 290:1351-1354). We have now characterized nine salivary proteins of Phlebotomus papatasi, the vector of Leishmania major. One of these salivary proteins, extracted from SDS gels and having an apparent mol wt of 15 kD, was able to protect vaccinated mice challenged with parasites plus SGH. A DNA vaccine containing the cDNA for the predominant 15-kD protein (named SP15) provided this same protection. Protection lasted at least 3 mo after immunization. The vaccine produced both intense humoral and delayed-type hypersensitivity (DTH) reactions. B cell-deficient mice immunized with the SP15 plasmid vaccine successfully controlled Leishmania infection when injected with Leishmania plus SGH. These results indicate that DTH response against saliva provides most or all of the protective effects of this vaccine and that salivary gland proteins or their cDNAs are viable vaccine targets against leishmaniasis.

Technologies for the design, discovery, formulation and administration of vaccines

This paper summarizes major technologies, with emphasis on applications to preventive vaccines for infectious diseases. A limited number of examples of each technology are provided.

Genomic tools for gene and protein discovery in malaria: toward new vaccines

Advances in malaria vaccine and drug development have been hindered in part by the complex multistage life cycle of the parasite, much of which is inaccessible to study, and by a large genome encoding over 5000 genes. Two human models of immunity to malaria, however, suggest that the development of an effective vaccine is within reach. We have outlined a strategy to identify the expression of hundreds to thousands of potential vaccine targets employing recently developed technologies for gene and protein expression. Combined with the exciting developments of malaria DNA vaccine technologies, these approaches form the basis for malaria subunit vaccines that may mimic the protective efficacy of our human model systems and provide the foundation for novel approaches to vaccine development for a range of pathogens.

Vaccination of mice with DNA encoding a large fragment of botulinum neurotoxin serotype A

The potential utility of using DNA vaccination to protect mice from the microbial neurotoxin, botulinum toxin type A, was evaluated. A synthetically derived gene encoding a carboxyl-terminal 50 kDa fragment of the toxin was placed in two sites in the DNA inoculation vehicle pCMVint-BL (Vical), one predicted to lead to MHC I processing (pJT-1 construct) and the other to direct MHC II processing (pJT-2 construct). Mice were then inoculated at 3 week intervals with these two constructs and with the vehicle alone and evaluated for protection from botulinum toxin by i.p. challenges with various toxin doses. Protection was observed at about week 10-11 from toxin doses of 25-100 LD(50). Only animals inoculated with pJT-2 exhibited protection. In dose-response experiments, 50 micrograms of DNA was the minimal dose required to elicit a protective response against serotype A, while protection against serotypes B or E was not obtained. With standard ELISA testing, a relationship was observed between the level of protection and the level of ELISA reactive antibody. Our results support the concept that DNA vaccination is a viable methodology to use in cases where protection from toxins is the goal.

Towards an HIV-1 vaccine: lessons from studies in macaque models

The development of a safe and effective vaccine for the prevention of AIDS has thus far proven to be extremely difficult, at least in part due to complexities associated with HIV-1 and its pathogenesis. The recent description of individuals transiently infected with HIV-1, as well as persons who survived HIV-1 infection for more than 15 years, indicates the ability of the immune response of certain individuals to control HIV-1 infection. Moreover, vaccination-challenge experiments in macaques infected with simian immunodeficiency virus have shown that protection against infection or development of disease may be achieved in the absence of sterilizing immunity, suggesting that the goals for AIDS vaccine development may have to be redefined. In addition, evaluation of new lentivirus vaccine strategies may largely benefit from the use of the newly developed chimeric simian-human immunodeficiency viruses, allowing the testing of HIV-1 antigen based vaccines in macaques.

Inhibitory effect of lipopolysaccharide on immune response after DNA immunization is route dependent

The DNA prepared from E. coli contained high levels of lipopolysaccharide (LPS). When antigen-encoding DNA was injected into mice, toxicity and increased IgM responses were observed. A method for purifying high yields of DNA (up to 12 mg/L of broth culture) with very low levels of LPS (0.05 ng/mg) was developed. When this purified DNA was used for immunization studies, the toxicity and increased IgM responses were abrogated. Thus, LPS was added to DNA in order to examine its influence on the IgG and cytotoxic T lymphocyte (CTL) response after intramuscular (i.m.) or intradermal (i.d.) DNA immunization. The IgG response to DNA-encoded antigen was inhibited in a dose-dependent manner by the i.d., but not the i.m., route of immunization. Surprisingly, no effect on the CTL response was observed. Therefore, the ability to produce high yields of plasmid DNA with very low levels of endotoxin contamination is advantageous for DNA immunization studies, not only for toxicologic but also for immunologic considerations. Furthermore, these results provide further evidence that immune induction occurs via different mechanisms after i.m. and i.d. DNA immunization.

Designer vaccines for parasitic diseases

Conventional ways of developing vaccines against infections, either on pragmatic grounds or by identifying protective antigens and attempting to mimic natural immune responses, have largely been unsuccessful for parasitic-infections, mainly because of the complexity of the immunological processes involved. It is clear that a new approach is required and it is now known that the "immunological environment" in which the immune response is initiated is as, or more, important than the actual antigens used. CD4+ and CD8+ T1 cells, through the agency of IL-2 and IFN-gamma, direct the response towards cell-mediated immunity involving cytotoxicity and macrophage activation, whereas T2 cells, through the agency of IL-4 and IL-10, direct the response towards antibody production. The two poles are counter-regulatory in that IFN-gamma inhibits antibody formation and IL-4 and IL-10 inhibit macrophage activation. However, immune responses are not immutable and can be artificially driven towards one or other pole, for example IFN-gamma, IL-2 and IL-12 favour T1 responses, whereas IL-4 and IL-10 favour the T2 type. With this knowledge, it is possible to design recombinant or nucleic acid vaccines that include gene products or genes for desirable cytokines as well as the appropriate antigen. For example, in experimental leishmaniasis, protective immune responses can be induced by the incorporation of genes for IL-2 and IFN-gamma into recombinant Salmonella typhimurium vectors and nucleic acid vaccines. A similar approach might be appropriate in experimental schistosomiasis, in which exogenous IL-12 drives the immune response towards the T1 pole and ameliorates T2-mediated pathology. These approaches require novel delivery systems and these have already begun to produce encouraging results. However, simply modifying the nature and route of administration of the vaccine is not enough and attention has now turned to the effector molecules involved, for example nitric oxide, and the signaling systems that are modified by the presence of particular cytokines.