Comparisons of DNA-mediated immunization procedures directed against surface glycoproteins of human immunodeficiency virus type-1 and hepatitis B virus

Generation of an immune microenvironment as a novel mechanism for myotoxins to potentiate genetic vaccines

We recently reported that administration of low doses of myotoxins at vaccination sites potentiated antigen-specific T-cell immunity induced by genetic cancer vaccines in mice, an effect which was superior to TLR agonists. In the current study, we found unexpectedly that the mechanism of this potent adjuvant effect was immune-mediated. Myotoxins induced sterile inflammation at vaccination sites, associated with a predominant infiltration of dendritic cells (DC). Inhibition of DC recruitment abrogated the immune stimulation effect of myotoxins, suggesting the requirement for DC. Genetic profiling of myotoxin-treated tissues revealed characteristics of an immune microenvironment with up-regulation of chemokines, proinflammatory cytokines, Toll-like receptors (TLR) and their endogenous ligands, and activation of innate immunity. Mechanistic experiments in vivo also elucidated the requirement for genes triggering DC maturation including TLR signaling and CD40. These studies suggest that myotoxins-induced sterile inflammation generates a favorable microenvironment that promotes multiple stages in the development of adaptive immunity. This novel mechanism of immune potentiation may be exploited for development of adjuvants for genetic vaccines against infectious pathogens and cancer.

Oral Plasmid DNA Delivery Systems for Genetic Immunisation

The use and optimisation of plasmid DNA delivery systems for the purposes of eliciting transgene specific immune responses to orally administered DNA encoded antigen represents a significant challenge. Here, we have outlined a multicomponent polymer modified liposomal delivery system that offers potential for oral administration of plasmid DNA. It is shown that the polymer/liposome formulated DNA is able to elicit markedly enhanced transgene specific cytokine production following in vitro restimulation of splenocytes with recombinant antigen. This is discussed with reference to recent publications and the potential of plasmid DNA delivery systems for the purposes of genetic immunisation, as reported in selected literature, is assessed.

DNA-vaccination via tattooing induces stronger humoral and cellular immune responses than intramuscular delivery supported by molecular adjuvants

Tattooing is one of a number of DNA delivery methods which results in an efficient expression of an introduced gene in the epidermal and dermal layers of the skin. The tattoo procedure causes many minor mechanical injuries followed by hemorrhage, necrosis, inflammation and regeneration of the skin and thus non-specifically stimulates the immune system. DNA vaccines delivered by tattooing have been shown to induce higher specific humoral and cellular immune responses than intramuscularly injected DNA. In this study, we focused on the comparison of DNA immunization protocols using different routes of administrations of DNA (intradermal tattoo versus intramuscular injection) and molecular adjuvants (cardiotoxin pre-treatment or GM-CSF DNA co-delivery). For this comparison we used the major capsid protein L1 of human papillomavirus type 16 as a model antigen. L1-specific immune responses were detected after three and four immunizations with 50 μg plasmid DNA. Cardiotoxin pretreatment or GM-CSF DNA co-delivery substantially enhanced the efficacy of DNA vaccine delivered intramuscularly by needle injection but had virtually no effect on the intradermal tattoo vaccination. The promoting effect of both adjuvants was more pronounced after three rather than four immunizations. However, three DNA tattoo immunizations without any adjuvant induced significantly higher L1-specific humoral immune responses than three or even four intramuscular DNA injections supported by molecular adjuvants. Tattooing also elicited significantly higher L1-specific cellular immune responses than intramuscularly delivered DNA in combination with adjuvants. In addition, the lymphocytes of mice treated with the tattoo device proliferated more strongly after mitogen stimulation suggesting the presence of inflammatory responses after tattooing. The tattoo delivery of DNA is a cost-effective method that may be used in laboratory conditions when more rapid and more robust immune responses are required.

Prevention of viral hepatitis in HIV co-infection

Co-infection of HIV-positive patients with hepatitis viruses worsens the long-term prognosis and this is summative for each new infection in any individual. Vaccination against hepatitis A or B may be effective but response rates are reduced in HIV infected patients. Improvement in response can be induced through extra doses, higher doses and HAART-induced increase in the CD4 count. Hepatitis B and C may also be prevented through counselling about safer sex, particularly condom use. In intravenous drug users, harm reduction, counselling and the use of needle/syringe exchange schemes may be helpful.

Marked enhancement of the antigen-specific immune response by combining plasmid DNA-based immunization with a Schiff base-forming drug

Although plasmid DNA (pDNA)-based immunization has proven efficacy, the level of immune responses that is achieved by this route of vaccination is often lower than that induced by traditional vaccines, especially for primates and humans. We report here a simple and potent method to enhance pDNA-based vaccination by using two different plasmids encoding viral or bacterial antigens. This method is based on coadministration of low concentrations of a recently described immunopotentiating, Schiff base-forming drug called tucaresol which has led to significant augmentation of antigen-specific humoral and cellular immune responses. Our data suggest that enhancement of the immune response with tucaresol might provide a powerful tool for the further development of pDNA-based immunization for humans.

Gene gun DNA vaccination with Rev-independent synthetic HIV-1 gp160 envelope gene using mammalian codons

DNA immunization with HIV envelope plasmids induce only moderate levels of specific antibodies which may in part be due to limitations in expression influenced by a species-specific and biased HIV codon usage. We compared antibody levels, Th1/Th2 type and CTL responses induced by synthetic genes encoding membrane bound gp160 versus secreted gp120 using optimized codons and the efficient gene gun immunization method. The in vitro expression of syn.gp160 as gp120 + gp41 was Rev independent and much higher than a classical wt.gp160 plasmid. Mice immunized with syn.gp160 and wt.gp160 generated low and inconsistent ELISA antibody titres whereas the secreted gp120 consistently induced faster seroconversion and higher antibody titres. Due to a higher C + G content the numbers of putative CpG immune (Th1) stimulatory motifs were highest in the synthetic gp160 gene. However, both synthetic genes induced an equally strong and more pronounced Th2 response with higher IgG1/IgG2a and IFNgamma/IL-4 ratios than the wt.gp160 gene. As for induction of CTL, synthetic genes induced a somewhat earlier response but did not offer any advantage over wild type genes at a later time point. Thus, optimizing codon usage has the advantage of rendering the structural HIV genes Rev independent. For induction of antibodies the level of expression, while important, seems less critical than optimal contact with antigen presenting cells at locations reached by the secreted gp120 protein. A proposed Th1 adjuvant effect of the higher numbers of CpG motifs in the synthetic genes was not seen using gene gun immunization which may be due to the low amount of DNA used.

Generation of monoclonal antibodies to native human immunodeficiency virus type 1 envelope glycoprotein by immunization of mice with naked RNA

The Semliki Forest virus (SFV) vector system is a new approach for in vivo expression of heterologous proteins and can also be used to generate specific immune responses in animal models. HIV-1 envelope glycoprotein produced using the SFV expression system is correctly folded, cleaved, transported to the cell surface and exhibits functional activity. We evaluated a recombinant Semliki Forest virus naked RNA-based immunization protocol for generation of monoclonal antibodies against the HIV-1 envelope glycoprotein. In vitro-transcribed RNA encoding for the SFV replicase complex and Env protein of HIV-1 (HXB2 strain) was injected intramuscularly to mice. This approach elicited an Env-specific antibody response in four mice out of five and a monoclonal antibody, 12H2, directed against gp41 was produced. Our results show that recombinant SFV RNA immunization can potentially be used as a quick and direct method to produce monoclonal antibodies, with the particular advantage that vectored RNA, rather than purified antigen, delivers a complex oligomer produced correctly.

HIV-1 DNA vaccines

HIV-1 was among the original DNA vaccine targets and HIV DNA vaccines are now in human trials. Lack of strong correlates of protective immunity makes vaccine design difficult; however, DNA vaccines have the potential to be an ideal vaccine and therapeutic approach against HIV-1. DNA vaccines induce conformational-dependent antibodies, mimic live vaccines but without the pathogenic potential, and can easily be made polyvalent. Genes which encode important CTL and antibody epitopes can be included while those that confer pathogenicity, virulence, antibody enhancement or represent non-conserved epitopes can be excluded. In our hands pre-treatment of muscles with bupivacaine or cardiotoxin did not offer any advantage over no muscle pre-treatment or gene gun inoculation of skin although gene gun immunization seem to favour a Th2 type response. As DNA vaccine candidates we have compared vaccines encoding native HIV MN gp160 with Rev-independent synthetic genes encoding MNgp160 and MNgp120 using mammalian high expression codons. In these experiments the gene encoding secreted gp120 gave highest antibody neutralizing titers. High and fast antibody responses could also be obtained by transferring the HIV-1 MN V3 loop to the secreted HBsAg as a fusion gene vaccine. Thus, in the case of HIV-1 MN genes encoding secreted surface glycoproteins may be preferred instead of membrane bound envelopes. CTL responses were induced in all cases. However, in order to meet the high diversity of HIV and HLA types our approach is to include many CTL epitopes in a multivalent minigene vaccine. We found that gene gun DNA vaccination with minimal epitopes could induce specific CTL. Flanking sequences influenced the CTL response but was not needed. DNA vaccines encoding known and computer predicted CTL epitopes are now being developed.

Improved humoral and cellular immune responses against the gp120 V3 loop of HIV-1 following genetic immunization with a chimeric DNA vaccine encoding the V3 inserted into the hepatitis B surface antigen

The gp120-derived V3 loop of HIV-1 is involved in co-receptor interaction, it guides cell tropism, and contains an epitope for antibody neutralization. Thus, HIV-1 V3 is an attractive vaccine candidate. The V3 of the MN strain (MN V3) contains both B- and T-cell epitopes, including a known mouse H-2d-restricted cytotoxic T lymphocyte (CTL) epitope. In an attempt to improve the immunogenicity of V3 in DNA vaccines, a plasmid expressing MN V3 as a fusion protein with the highly immunogenic middle (pre-S2 + S) surface antigen of hepatitis B virus (HBsAg) was constructed. Epidermal inoculation by gene gun was used for genetic immunization in a mouse model. Antibody and CTL responses to MN V3 and HBsAg were measured and compared with the immune responses obtained after vaccination with plasmids encoding the complete HIV-1 MN gp160 and HBsAg (pre-S2 + S), respectively. DNA vaccination with the HIV MN gp160 envelope plasmid induced a slow and low titred anti-MN V3 antibody response at 12 weeks post-inoculation (p.i.) and a late appearing (7 weeks), weak and variable CTL response. In contrast, DNA vaccination with the HBsAg-encoding plasmid induced a rapid and high titred anti-HBsAg antibody response and a uniform strong anti-HBs CTL response already 1 week p.i. in all mice. DNA vaccination with the chimeric MN V3/HBsAg plasmid elicited humoral responses against both viruses within 3-6 weeks which peaked at 6-12 weeks and remained stable for at least 25 weeks. In addition, specific CTL responses were induced in all mice against both MN V3 and HBsAg already within the first 3 weeks, lasting at least 11 weeks. Thus, HBsAg acts as a 'genetic vaccine adjuvant' augmenting and accelerating the cellular and humoral immune response against the inserted MN V3 loop. Such chimeric HIV-HBsAg plasmid constructs may be useful in DNA immunizations as a 'carrier' of protein regions or minimal epitopes which are less exposed or poorly immunogenic.