Improved specificity of in vitro anti-HIV antibody production: implications for diagnosis and timing of transmission in infants born to HIV-seropositive mothers

Synthetic DNA vaccine strategies against persistent viral infections

The human body has developed an elaborate defense system against microbial pathogens and foreign antigens. However, particular microbes have evolved sophisticated mechanisms to evade immune surveillance, allowing persistence within the human host. In an effort to combat such infections, intensive research has focused on the development of effective prophylactic and therapeutic countermeasures to suppress or clear persistent viral infections. To date, popular therapeutic strategies have included the use of live-attenuated microbes, viral vectors and dendritic-cell vaccines aiming to help suppress or clear infection. In recent years, improved DNA vaccines have now re-emerged as a promising candidate for therapeutic intervention due to the development of advanced optimization and delivery technologies. For instance, genetic optimization of synthetic plasmid constructs and their encoded antigens, in vivo electroporation-mediated vaccine delivery, as well as codelivery with molecular adjuvants have collectively enhanced both transgene expression and the elicitation of vaccine-induced immunity. In addition, the development of potent heterologous prime-boost regimens has also provided significant contributions to DNA vaccine immunogenicity. Herein, the authors will focus on these recent improvements to this synthetic platform in relation to their application in combating persistent virus infection.

Nonviral delivery of cancer genetic vaccines

The potential use of genetic vaccines to address numerous diseases including cancer is promising, but currently unrealized. Here, we review advances in the nonviral delivery of antigen-encoded plasmid DNA for the purpose of treating cancer through the human immune system, as this disease has drawn the most attention in this field to date. Brief overviews of dendritic cell immunobiology and the mechanism of immune activation through genetic vaccines set the stage for the desirability of delivery technology. Several promising nonviral delivery techniques are discussed along with a mention of targeting strategies aimed at improving the potency of vaccine formulations. Implications for the future of genetic vaccines are also presented.

Enhancement of human immunodeficiency virus type 1-DNA vaccine potency through incorporation of T-helper 1 molecular adjuvants

It is clear that the development of a safe and effective vaccine for human immunodeficiency virus type 1 (HIV-1) remains a crucial goal for controlling the acquired immunodeficiency syndrome epidemic. At present, it is not clear what arm of the immune response correlates with protection from HIV-1 infection or disease. Therefore, a strong cellular and humoral immune response will likely be needed to control this infection. Among different vaccine alternatives, DNA vaccines appeared more than a decade ago, demonstrating important qualities of inducing both humoral and cellular immune responses in animal models. However, after several years and various clinical studies in humans, supporting the safety of the HIV-DNA vaccine strategies, it has become clear that their potency should be improved. One way to modulate and enhance the immune responses induced by a DNA vaccine is by including genetic adjuvants such as cytokines, chemokines, or T-cell costimulatory molecules as part of the vaccine itself. Particularly, vaccine immunogenicity can be modulated by factors that attract professional antigen-presenting cells, provide additional costimulation, or enhance the uptake of plasmid DNA. This review focuses on developments in the coadministration of molecular adjuvants for the enhancement of HIV-1 DNA-vaccine potency.

Predictive value of CD19 measurements for bacterial infections in children infected with human immunodeficiency virus

We investigated the predictive value of CD19 cell percentages (CD19%) for times to bacterial infections, using data from six pediatric AIDS Clinical Trials Group protocols and adjusting for other potentially prognostic variables, such as CD4%, CD8%, immunoglobulin (IgA) level, lymphocyte count, prior infections, prior zidovudine treatment, and age. In addition, we explored the combined effects of CD19% and IgG level in predicting time to infection. We found that a low CD19% is associated with a nonsignificant 1.2-fold increase in hazard of bacterial infection (95% confidence interval: 0.97, 1.49). In contrast, a high IgG level is associated with a nonsignificant 0.87-fold decrease in hazard of infection (95% confidence interval: 0.68, 1.12). CD4% was more prognostic of time to bacterial infection than CD19% or IgG level. Low CD19% and high IgG levels together lead to a significant (P < 0. 01) 0.50-fold decrease in hazard (95% confidence interval: 0.35, 0. 73) relative to low CD19% and low IgG levels. Similarly, in a model involving assay result changes (from baseline to 6 months) as well as baseline values, the effect of CD19% by itself is reversed from its effect in conjunction with IgG. In this model, CD19% that are increasing and high are associated with decreases in hazard of infection (P < 0.01), while increasing CD19% and increasing IgG levels are associated with significant (at the P = 0.01 level) fourfold increases in hazard of infection relative to stable CD19% and decreasing, stable, or increasing IgG levels. Our data suggest that CD19%, in conjunction with IgG level, provides a useful prognostic tool for bacterial infections. It is highly likely that T-helper function impacts on B-cell function; thus, inclusion of CD4% in such analyses may greatly enhance the assessment of risk for bacterial infection.

Approaches to new vaccines

The explosive technological advances in the fields of immunology and molecular biology in the last 5 years had an enormous impact on the identification of candidate vaccines against diseases, which until a few years ago seemed uncontrollable. Increased knowledge of the immune system has helped to define the mechanisms that underlie successful immunization and is now being exploited to develop improved versions of existing vaccines and new vaccines against emerging pathogens, tumors, or autoimmune diseases. An understanding of the mechanisms of action of novel adjuvants and the development of new vector and delivery systems will have a major impact on vaccine strategies. The use of DNA encoding antigens from pathogenic viruses, bacteria, and parasites as vaccines is a new approach that is receiving considerable attention. This and other innovative approaches, including vaccine production in plants, are appraised in this review. The successful eradication of smallpox and the imminent eradication of poliomyelitis by worldwide immunization campaigns provide positive examples of how the vaccine-mediated approach can lead to disease elimination; with the advent of new vaccines and improved delivery systems, there is no scientific reason why these successes cannot be repeated.

An HIV type 2 DNA vaccine induces cross-reactive immune responses against HIV type 2 and SIV

We have previously reported on the generation of specific functional immune responses after inoculation of animals with expression vectors encoding HIV-1 genes. This article provides the details of the first application of this new technology to induce immune responses against HIV-2. This virus is molecularly and serologically distinct from HIV-1 and is in fact more closely related to the simian immunodeficiency virus (SIV). Anti-HIV-2 and SIV antibodies were induced in mice of three different haplotypes following a single intramuscular inoculation with an HIV-2/ROD envelope glycoprotein expression vector (pcEnv-2). Boosting of animals with pcEnv-2 induced both anti-HIV-2 neutralizing antibodies and T cell-proliferative responses against HIV-2 and SIVmac proteins. We compared the humoral and cellular immune responses of mice injected with pcEnv-2 and then boosted with either the homologous DNA construct or a recombinant Env protein. Animals boosted with pcEnv-2 generated B and T cell immune responses as strong as those of mice boosted with recombinant gp140 protein in adjuvant. Finally, cellular immune responses were significantly increased with the coadministration of pcEnv-2 and a plasmid expressing interleukin 12. We therefore conclude that DNA plasmid inoculation induces cross-reactive anti-HIV-2 and anti-SIVmac immune responses in mice. This technology should be further investigated as a potential vaccine component for this human pathogen.

Induction of neutralizing antibodies against HTLV-I envelope proteins after combined genetic and protein immunizations in mice

Direct DNA inoculation can induce both protective humoral and cellular responses against several viruses. The HTLV-I envelope glycoproteins are the major antigens recognized by sera of HTLV-I infected patients that generate neutralizing immune responses in vitro and in vivo. We compared immune responses elicited after a single inoculation of two plasmids encoding the complete HTLV-I envelope proteins followed or not by gp62 Baculovirus recombinant protein boosts in BALB/c mice. First, we observe that the coexpression of env and rex genes is not sufficient to raise a detectable specific humoral response after a single DNA inoculation. Protein boosts generated a high antibody response in mice primed with DNA expressing HTLV-I envelope proteins as compared to naive and negative control vector primed groups. This humoral response presented high neutralizing antibody titers. These results suggest that a single inoculation of DNA expressing HTLV-I env gene can stimulate memory B-cell clones that are able to respond effectively to subsequent encounters with HTLV-I envelope proteins and a specific cellular T helper cell response in mice.

Engineering of in vivo immune responses to DNA immunization via codelivery of costimulatory molecule genes

Nucleic acid immunization is a novel vaccination technique to induce antigen-specific immune responses. We have developed expression cassettes for cell surface markers CD80 and CD86, two functionally related costimulatory molecules that play an important role in the induction of T cell-mediated immune responses. Coimmunization of these expression plasmids, along with plasmid DNA encoding for HIV-1 antigens, did not result in any significant change in the humoral response; however, we observed a dramatic increase in cytotoxic T-lymphocyte (CTL) induction as well as T-helper cell proliferation after the coadministration of CD86 genes. In contrast, coimmunization with a CD80 expression cassette resulted in a minor, but positive increase in T-helper cell or CTL responses. This strategy may be of value for the generation of rationally designed vaccines and immune therapeutics.

Protection of chimpanzees from high-dose heterologous HIV-1 challenge by DNA vaccination

Novel approaches for the generation of more effective vaccines for HIV-1 are of significant importance. In this report we analyze the immunogenicity and efficacy of an HIV-1 DNA vaccine encoding env, rev and gag/pol in a chimpanzee model system. The immunized animals developed specific cellular and humoral immune responses. Animals were challenged with a heterologous chimpanzee titered stock of HIV-1 SF2 virus and followed for 48 weeks after challenge. Polymerase chain reaction coupled with reverse transcription (RT-PCR) results indicated infection in the control animal, whereas those animals vaccinated with the DNA constructs were protected from the establishment of infection. These studies serve as an important benchmark for the use of DNA vaccine technology for the production of protective immune responses.

Comparative efficiency of feline immunodeficiency virus infection by DNA inoculation

Direct inoculation of genetic material in DNA form is a novel approach to vaccination that has proved efficacious for a number of viral agents. We are interested in the potential of this approach for the delivery of vaccines based on attenuated or replication-defective retroviruses. Toward this goal, we tested the effect of intramuscular inoculation of a plasmid containing the entire genome of feline immunodeficiency virus (FIV-Petaluma, F14 clone). DNA delivery was compared with intramuscular or intraperitoneal inoculation of virus reconstituted from the same molecular clone. The outcome was monitored by serological analysis and quantitative virus load determination over a 31-week period. DNA inoculation was found to be a reliable means of infection, although seroconversion and the rise in PBMC virus load were delayed relative to intramuscular or intraperitoneal inoculation of virus. At 31 weeks, similar levels of proviral DNA were detected in central lymphoid tissue of all infected animals. In conclusion, DNA inoculation of proviral DNA will be of use as a novel method of cell-free virus challenge and may have further potential for the delivery of lentiviral vaccines.

DNA vaccines

Observations in the early 1990s that plasmid DNA could directly transfect animal cells in vivo sparked exploration of the use of DNA plasmids to induce immune responses by direct injection into animals of DNA encoding antigenic proteins. This method, termed DNA immunization, now has been used to elicit protective antibody and cell-mediated immune responses in a wide variety of preclinical animal models for viral, bacterial, and parasitic diseases. DNA vaccination is particularly useful for the induction of cytotoxic T cells. This review summarizes current knowledge on the vectors, immune responses, immunological mechanisms, safety considerations, and potential for further application of this novel method of immunization.

DNA vaccines

Immunization with plasmid DNA encoding antigenic proteins elicits both antibody and cell-mediated immune responses. This method of producing the protein antigens of interest directly in host cells can provide appropriate tertiary structure for the induction of conformationally specific antibodies, and also facilitates the induction of cellular immune responses. DNA immunization has provided effective protective immunity in various animal models. The immune responses induced by DNA vaccines may in some instances be preferable to those produced by immunization using conventional methods. DNA vaccination appears to be applicable to a variety of pathogens and is a useful method of raising immune responses. Thus this approach to vaccination has the potential to be a successful method of rapidly screening for antigens capable of inducing protective immunity, and of inducing protective immunity against pathogens of clinical importance.

DNA inoculation as a novel vaccination method against human retroviruses with rheumatic disease associations

There are a number of rheumatologic manifestations of human retroviral infections associated with human immunodeficiency virus type I (HIV-I) and the human T-cell leukemia virus type I (HTLV-I) including arthritis, Sjøgren's syndrome-like symptoms as well as other varied autoimmune phenomena. Infection with HTLV-1 may be directly involved in the etiology and/or pathogenesis of an arthritic condition similar to rheumatoid arthritis. We have been characterizing a new vaccination strategy against human retroviral infections, designated DNA inoculation. This procedure involves the intramuscular injection of DNA plasmids which express specific human retroviral antigens. This technique results in the development of humoral and cellular immune responses against these proteins. Specifically, this method has been successfully used to develop immune responses against HIV-I and HTLV-I. The availability of rat and rabbit infection models for HTLV-I, coupled with the successful development of immune responses in these animals after DNA inoculation with an HTLV-I envelope expressing plasmid, will allow the efficacy of this vaccination technique to be evaluated with protection against in vivo viral challenge as an endpoint.