HIV-specific cytotoxic T-cells in HIV-exposed but uninfected Gambian women

Elicitation of immunity to HIV type 1 Gag is determined by Gag structure

The gag gene of the human immunodeficiency virus type 1 (HIV-1) encodes for viral proteins that self-assemble into viral particles. The primary Gag gene products (capsid, matrix, and nucleocapsid) elicit humoral and cellular immune responses during natural infection, and these proteins are included in many preclinical and clinical HIV/AIDS vaccines. However, the structure (particulate or soluble) of these proteins may influence the immunity elicited during vaccination. In this study, mice were inoculated with four different HIV-1 Gag vaccines to compare the elicitation of immune responses by the same Gag immunogen presented to the immune system in different forms. The immunity elicited by particles produced in vivo by DNA plasmid (pGag) was compared to these same proteins retained intracellularly (pGag(DMyr)). In addition, the elicitation of anti- Gag immunity by Gag(p55) virus-like particles (VLPs) or soluble, nonparticulate Gag(p55) proteins was compared. Enhanced cellular responses, but almost no anti-Gag antibodies, were elicited with intracellularly retained Gag proteins. In contrast, DNA vaccines expressing VLPs elicited both anti-Gag antibodies and cellular responses. Mice vaccinated with purified Gag(p55) VLPs elicited robust humoral and cellular immune responses, which were significantly higher than the immunity elicited by soluble, nonparticulate Gag(p55) protein. Overall, purified particles of Gag effectively elicited the broadest and highest titers of anti-Gag immunity. The structural form of Gag influences the elicited immune responses and should be considered in the design of HIV/AIDS vaccines.

SIV DNA vaccine co-administered with IL-12 expression plasmid enhances CD8 SIV cellular immune responses in cynomolgus macaques

Current evidence suggests that a strong induced CD8 human immunodeficiency virus type 1 (HIV-1)-specific cell mediated immune response may be an important aspect of an HIV vaccine. The response rates and the magnitude of the CTL responses induced by current DNA vaccines in humans need to be improved and cellular immune responses to DNA vaccines can be enhanced in mice by co-delivering DNA plasmids expressing immune modulators. Two reported to work well in the mouse systems are interleukin (IL)-12 and CD40L. We sought to compare these molecular adjuvants in a primate model system. The cDNA for macaque IL-12 and CD40L were cloned into DNA vectors. Groups of cynomolgus macaques were immunized with 2 mg of plasmid expressing SIVgag alone or in combination with either IL-12 or CD40L. CD40L did not appear to enhance the cellular immune response to SIVgag antigen. However, more robust results were observed in animals co-injected with the IL-12 molecular adjuvant. The IL-12 expanded antigen-specific IFN-gamma positive effector cells as well as granzyme B production. The vaccine immune responses contained both a CD8 component as well a CD4 component. The adjuvanted DNA vaccines illustrate that IL-12 enhances a CD8 vaccine immune response, however, different cellular profiles.

Therapeutic vaccination against HIV: current progress and future possibilities

Although effective in reducing mortality, current antiretroviral therapy for HIV infection involves complex and expensive drug regimens that are toxic and difficult to take. Eradication of HIV reservoirs is not possible with existing therapies. The concept of therapeutic vaccination has been investigated to increase the potency and breadth of anti-HIV immune responses in order to delay or reduce antiretroviral therapy use. A variety of approaches targeted to both cell- and antibody-mediated immunity have been developed, including whole inactivated HIV-1, protein subunits and synthetic peptides, DNA vaccines and a number of viral vectors expressing HIV-1. These investigations have occurred in the absence of a clear understanding of disease pathogenesis or the correlates of protective immunity. At this time, there is no licensed therapeutic vaccine for any viral disease, including HIV; however, this review will consider recent progress in the field and summarize the challenges faced in the development of a therapeutic HIV vaccine.

Low-level CD4+ T cell activation is associated with low susceptibility to HIV-1 infection

Different features have been associated with low susceptibility to HIV type 1 (HIV-1) infection in exposed seronegative individuals. These include genetic make-up such as homozygosity for the CCR5-Delta32 allele and the presence of HIV-specific CTLs. We studied immune activation and immune responsiveness in relation to HIV-1 susceptibility in 42 high-risk seronegative (HRSN) participants of the Amsterdam Cohort Studies and 54 men from the same cohort who were seronegative at the moment of analysis but later became HIV seropositive. HRSN had higher naive (CD45RO CD27) CD4 and CD8 T cell numbers and lower percentages of activated (HLADR CD38, CD70) CD4 and proliferating (Ki67) CD4 and CD8 T cells, irrespective of previous episodes of sexually transmittable infections. Furthermore, whole blood cultures from HRSN showed lower lymphoproliferative responses than healthy laboratory controls. These data suggest that low levels of immune activation and low T cell responsiveness may contribute to low HIV susceptibility.

Induction of serum and mucosal FIV-specific immune responses by intranasal immunization with p24Gag

We examined the ability of FIV p24Gag to induce systemic and mucosal FIV-specific immune responses when delivered as a nasal immunogen alone, or with a mucosal adjuvant, Escherichia coli heat labile toxin LT(R192G). Nasal immunization with p24Gag alone induced FIV-specific immune responses but overall responses were weak, transient, and/or present only in a few animals. Co-administration of LT(R192G) resulted in strong FIV-specific serum IgG and enhanced salivary IgA responses. Moreover, FIV-specific IgA was detected in vaginal wash fluid from 6/6 cats co-immunized with LT(R192G) and p24Gag versus 1/6 immunized with p24Gag alone. This is the first report detailing induction of systemic or mucosal FIV-specific immune responses by nasal immunization alone. As such, this study demonstrates that nasal immunization of cats can be a relevant and effective route for the delivery of candidate vaccines. However, while nasal immunization of cats with p24Gag induces antigen-specific systemic immune responses, development of strong systemic and mucosal immune responses requires co-administration of a mucosal adjuvant, such as LT(R192G).

Global human genetics of HIV-1 infection and China

Genetic polymorphisms in human genes can influence the risk for HIV-1 infection and disease progression, although the reported effects of these alleles have been inconsistent. This review highlights the recent discoveries on global and Chinese genetic polymorphisms and their association with HIV-1 transmission and disease progression.

The importance of standardisation of laboratory evaluations in HIV vaccine trials

It is important to evaluate HIV-1-specific immunological responses elicited by therapeutic or prophylactic vaccines using precise, standardised assays, so that the immunogenicity and putative efficacy of candidate vaccines may be compared. Different well-validated assays must be used to quantitate specific responses, to determine which particular strategies may be efficacious.

Mycobacterial immune reconstitution inflammatory syndrome in HIV-1 infection after antiretroviral therapy is associated with deregulated specific T-cell responses: beneficial effect of IL-2 and GM-CSF immunotherapy

BACKGROUND

With the advent of antiretroviral therapy (ART) cases of immune reconstitution inflammatory syndrome (IRIS) have increasingly been reported. IRIS usually occurs in individuals with a rapidly rising CD4 T-cell count or percentage upon initiation of ART, who develop a deregulated immune response to infection with or without reactivation of opportunistic organisms. Here, we evaluated rises in absolute CD4 T-cells, and specific CD4 T-cell responses in 4 HIV-1+ individuals presenting with mycobacterial associated IRIS who received in conjunction with ART, IL-2 plus GM-CSF immunotherapy.

METHODS

We assessed CD4 T-cell counts, HIV-1 RNA loads, phenotype for naïve and activation markers, and in vitro proliferative responses. Results were compared with those observed in 11 matched, successfully treated asymptomatic clinical progressors (CP) with no evidence of opportunistic infections, and uninfected controls.

RESULTS

Median CD4 T-cell counts in IRIS patients rose from 22 cells/microl before initiation of ART, to 70 cells/microl after 8 months of therapy (median 6.5 fold increase). This coincided with IRIS diagnosis, lower levels of naïve CD4 T-cells, increased expression of immune activation markers, and weak CD4 T-cell responses. In contrast, CP had a median CD4 T-cell counts of 76 cells/microl at baseline, which rose to 249 cells/microl 6 months post ART, when strong T-cell responses were seen in > 80% of patients. Higher levels of expression of immune activation markers were seen in IRIS patients compared to CP and UC (IRIS > CP > UC). Immunotherapy with IL-2 and GM-CSF paralleled clinical recovery.

CONCLUSION

These data suggest that mycobacterial IRIS is associated with inadequate immune reconstitution rather than vigorous specific T-cell responses, and concomitant administration of IL-2 and GM-CSF immunotherapy with effective ART may correct/augment T-cell immunity in such setting resulting in clinical benefit.

HIV-1 p24 vaccine protects cats against feline immunodeficiency virus infection

BACKGROUND

Based on previous analysis of feline immunodeficiency virus (FIV)-specific cross-reactive antibodies to HIV-1 p24, cats vaccinated with HIV-1 p24 were evaluated for cross-reactive immunity to FIV.

OBJECTIVE

: To determine the level of cross-reactivity that exists between HIV-1 and FIV p24 and its implications for vaccine prophylaxis.

METHODS

Specific-pathogen-free cats were immunized three times with HIV-1 p24 in Ribi adjuvant, with (n = 18) or without cytokine (n = 6). Control cats were immunized three times with adjuvant (n = 10) or phosphate-buffered saline (PBS; n = 5). All immunized cats were challenged with either subtypes B or A/B FIV, and monitored by virus isolation, proviral PCR, FIV-specific antibodies, and feline interferon-gamma ELISpot for T-cell activities.

RESULTS

Of 18 cats vaccinated with subtype B HIV-1 (HIV-1LAI/LAV, HIV-1UCD1) p24 in Ribi/cytokine adjuvant 14 (78%) were protected against FIV challenges (subtype Agag and Bgag) that infected all 15 adjuvant- or PBS-immunized cats. Furthermore, only three of six (50%) cats vaccinated with FIV p24 in Ribi/cytokine adjuvant were protected against similar FIV challenge. HIV-1 p24 vaccination induced weak cross-reactive antibodies to FIV p24, which did not correlate with vaccine efficacy. However, the peripheral blood mononuclear cells from HIV-1 p24-vaccinated/protected cats at 33-34 weeks post-FIV challenge responded to three T-cell responsive peptides at the carboxyl-terminus of the FIV p24, whereas those cells from the infected control cats had minimal to no responses to the same peptides.

CONCLUSIONS

These results suggest the importance of including lentiviral p24 as vaccine immunogen for human AIDS vaccine. Moreover, these results suggest the potential importance of evolutionarily conserved, cross-protective epitopes in vaccine protection.

Inhibition of HIV-1-specific T-cells and increase of viral load during immunosuppressive treatment in an HIV-1 infected patient with Chlamydia trachomatis induced arthritis

BACKGROUND

Studies in HIV-1 infected long-term non-progressors could demonstrate a strong HIV-1-specific CTL response, but it is difficult to prove that this strong CTL response actually is the cause of the efficient control of HIV-1 and not the consequence of low HIV-1 replication in these patients.

OBJECTIVE

Studies of HIV-1-specific immunity and viral replication in patients undergoing immunosuppressive therapy provide important opportunities to understand the role of HIV-1-specific T-cells.

RESULTS

In this report we describe an HLA B27 positive patient with normal CD4 counts and a low viral load of 200 copies/ml without antiretroviral therapy who exhibited a very strong HIV-1-specific CTL response. He had to be treated with steroids, NSAIDS and hydroxchloroquine because of a severe inflammatory reactive arthritis triggered by an acute Chlamydia trachomatis infection. Analysis of HIV-1 specific T-cells by gamma-IFN-ELISPOT revealed a high frequency of HIV-1 gag-specific CTL both in blood and synovial fluid, whereas gag-specific CD4-cells could be detected only in the peripheral blood. Further analysis revealed that the gag-specific T-cells were predominantly targeting the HLA B27-restricted CTL epitope KRWIILGLNK (KK10). Immunosuppressive therapy by prednisone was associated with a moderate increase of HIV-1 viremia and a decrease both in the number and in the gamma-IFN production of KK10-specific CTL indicating that inhibition of CTL function contributed to the increase of viral load.

CONCLUSIONS

This study is suggesting that HIV-1 specific CTL play an important role in the control of HIV-1, at least in this patient. Inhibition of CTL function by immunosuppressive therapy with prednisone may enhance viral replication. In addition, we could demonstrate for the first time the migration of HIV-1 specific T-cells into the synovial fluid.

The Effects of Allitridin on the Expression of Transcription Factors T-bet and GATA-3 in Mice Infected by Murine Cytomegalovirus

This study was designed to investigate the effects of allitridin on the expression of transcription factors T-bet and GATA-3 in mice infected by murine cytomegalovirus (MCMV). A BALB/c mouse model system of MCMV infection was established. Twenty mice were allocated randomly into an allitridin-treated group (n = 10) and a placebo control group (n = 10). The same dose (25 mg/kg/day) and regimen of allitridin were used in the treated group in the 24 hours after virus infection; the same volume of saline solution was injected in placebo control mice. In an additional blank control group (n = 10), the same volume of saline solution was injected. The expression levels of the transcription factors T-bet and GATA-3 were measured by reverse transcription-polymerase chain reaction. The expression levels of the T helper (Th) 1 cytokine interferon-gamma (IFN-gamma) and the Th2 cytokine interleukin (IL)-10 in supernatant of spleen cell culture were measured by enzyme-linked immunosorbent assay. MCMV infection markedly down-modulated the expression of IFN-gamma and T-bet and significantly up-modulated the expression of IL-10 and GATA-3. Allitridin induced significantly (P < .01) increased expression of the transcription factor T-bet and the Th1 cytokine IFN-gamma and markedly (P < .01) decreased expression of the transcription factor GATA-3 and the Th2 cytokine IL-10. Thus MCMV infection could lead to disequilibrium of Th1/Th2 cytokine expression: The level of the Th1 cytokine IFN-gamma was decreased significantly, and Th2 cytokine IL-10 was overexpressed markedly. Allitridin could up-regulate the expression of T-bet and IFN-gamma and inhibit the expression of GATA-3 and IL-10 in MCMV-infected mice, indicating a Th1 dominant state, which should enhance the specific cellular immune reactions against cytomegalovirus (CMV) and be helpful for clearance of CMV from the host.

Major histocompatibility complex class II (HLA-DRB and -DQB) allele frequencies in Botswana: association with human immunodeficiency virus type 1 infection

Southern Africa is facing an unprecedented public health crisis due to the high prevalence of human immunodeficiency virus type 1 (HIV-1). Vaccine development and testing efforts, mainly based on elicitation of HIV-specific T cells, are under way. To understand the role of human leukocyte antigen (HLA) class II alleles in HIV pathogenesis and to facilitate HLA-based HIV-1 vaccine design, we analyzed the frequencies of HLA class II alleles within the southern African country of Botswana. Common HLA class II alleles were identified within the Botswana population through the molecular genotyping of DRB and DQB1 loci. The DRB1 allele groups DRB1*01, DRB1*02/15, DRB1*03, DRB1*11, and DRB1*13 were encountered at frequencies above 20%. Within the DQB1 locus, DQB1*06 (47.7%) was the most common allele group, followed by DQB1*03 (39.2%) and DQB1*04 (25.8%). We found that DRB1*01 was more common in HIV-negative than in HIV-positive individuals and that those who expressed DRB1*08 had lower median viral loads. We demonstrate that the frequencies of certain HLA class II alleles in this Botswana population differ substantially from those in North American populations, including African-Americans. Common allele groups within Botswana cover large percentages of other African populations and could be targeted in regional vaccine designs.

Non-human primate models for AIDS vaccine research

Since the discovery of simian immunodeficiency viruses (SIV) causing AIDS-like diseases in Asian macaques, non-human primates (NHP) have played an important role in AIDS vaccine research. A multitude of vaccines and immunization approaches have been evaluated, including live attenuated viruses, DNA vaccines, viral and bacterial vectors, subunit proteins, and combinations thereof. Depending on the particular vaccine and model used, varying degrees of protection have been achieved, including prevention of infection, reduction of viral load, and amelioration of disease. In a few instances, potential safety concerns and vaccine-enhanced pathogenicity have also been noted. In the past decade, sophisticated methodologies have been developed to define the mechanisms of protective immunity. However, a clear road map for HIV vaccine development has yet to emerge. This is in part because of the intrinsic nature of the surrogate model and in part because of the improbability of any single model to fully capture the complex interactions of natural HIV infection in humans. The lack of standardization, the limited models available, and the incomplete understanding of the immunobiology of NHP contribute to the difficulty to extrapolate findings from such models to HIV vaccine development. Until efficacy data become available from studies of parallel vaccine concepts in humans and macaques, the predictive value of any NHP model remains unknown. Towards this end, greater appreciation of the utility and limitations of the NHP model and further developments to better mimic HIV infection in humans will likely help inform future AIDS vaccine efforts.

Efficacy of AIDS vaccine strategies in nonhuman primates

Since only a limited number of vaccines can be tested for efficacy in phase 3 studies in humans, a filter is needed allowing selection of the most promising ones. Although differences between HIV infection in humans and simian immunodeficiency virus infection in nonhuman primates (NHP) might limit the predictive value of these models, comparative efficacy studies in NHPs could facilitate ranking of vaccine candidates. While various forms of protein vaccines failed to induce consistent protection, live-attenuated vaccines, DNA vaccines and viral vector vaccines provided various levels of protection in NHPs. However, variability in the experimental models limits the conclusions that can be drawn with respect to the relative efficacy of vaccines not tested in the same experiment. Therefore, better standardization is an urgent necessity in order to exploit the full potential of nonhuman primate models in AIDS vaccine development.

The challenges of HIV vaccine development and testing

A vaccine against HIV remains the best hope for bringing the epidemic under control. An intensive global effort is underway to develop such a vaccine; however, the challenges are considerable. Several new vaccine technologies that have been developed and shown promise in animal models are now being tested in early phase safety trials in humans. Because there is no laboratory assay that will predict whether an HIV vaccine can protect humans from infection, clinical trials involving thousands of volunteers will need to be conducted to determine the efficacy of HIV vaccines. These trials need to take place in the developing countries that bear the burden of the epidemic, requiring a substantial amount of infrastructure development and capacity building.

Low levels of human immunodeficiency virus type 1 DNA in high-risk seronegative men

We detected human immunodeficiency virus type 1 (HIV-1) DNA at very low levels in sequential peripheral blood mononuclear cell samples of five out of six high-risk, seronegative, homosexual men and five out of five individuals 7.8 to 1.6 years prior to seroconversion. These data indicate a high prevalence of low-level HIV-1 DNA in exposed seronegative individuals.

HIV vaccine development by computer assisted design: the GAIA vaccine

The design of epitope-driven vaccines that address the global variability of HIV has been significantly hampered by concerns about conservation of the vaccine epitopes across clades of HIV. We developed two computer-driven methods for improving epitope-driven HIV vaccines: the Epi-Assembler, which derives representative or "immunogenic consensus sequence" (ICS) epitopes from multiple viral variants, and VaccineCAD, which reduces junctional immunogenicity when epitopes are aligned in a string-of-beads format for insertion in a DNA expression vector. In this study, we report on 20 ICS HIV-1 peptides. The core 9-mer contained in these consensus peptides was conserved in 105-2250 individual HIV-1 strains. Nineteen of the 20 ICS epitopes (95%) evaluated in this study were confirmed in ELISpot assays using peripheral blood monocytes obtained from 13 healthy HIV-1 infected subjects. Twenty-five ICS peptides (all 20 of the peptides evaluated in this study and 5 additional ICS epitopes) were then aligned in a pseudoprotein string using "VaccineCAD", an epitope alignment tool that eliminates immunogenicity created by the junctions between the epitopes. Reordering the construct reduced the immunogenicity of the junctions between epitopes as measured by EpiMatrix, an epitope mapping algorithm. The reordered construct was also a more effective immunogen in vivo when tested in HLA-DR transgenic mice. These data confirm the utility of bioinformatics tools to design novel vaccines containing "immunogenic consensus sequence" T cell epitopes for a globally relevant vaccine against HIV.

Identification and characterization of HIV-1-specific CD8+ T cell epitopes presented by HLA-A*2601

Since HLA-A*26 is one of the most common alleles in Asia, where approximately 20% of people have this allele, identification of HIV-1-specific epitopes presented by HLA-A*26 is necessary for studies on the immunopathogenesis of AIDS and vaccine development in Asia. As presented herein, we used the reverse immunogenetics approach to identify HIV-1 epitopes presented by HLA-A*2601, one of the major HLA-A*26 subtypes. We selected 24 HLA-A*2601-binding peptides out of 110 HIV-1 peptides by using a HLA-A*2601 stabilization assay. The ability of these HLA-A*2601-binding peptides to induce peptide-specific CD8(+) T cells was tested by stimulating PBMCs from HIV-1-infected individuals having HLA-A*2601 with these peptides. Four HLA-A*2601-binding peptides induced peptide-specific CD8 T cells. Analysis using HIV-1 recombinant vaccinia-infected C1R-A*2601 cells indicated that these four peptides were HIV-1 epitopes endogenously presented by HLA-A*2601. Two epitope-specific CD8(+) T cells were predominantly detected in HIV-1 infected individuals, suggesting that these epitopes may be useful for vaccine development.

Human immunodeficiency virus (HIV)-2-specific T lymphocyte proliferative responses in HIV-2-infected and in HIV-2-exposed but uninfected individuals in Guinea-Bissau

Human immunodeficiency virus (HIV)-2-specific T lymphocyte proliferative responses were determined in cultures of peripheral blood mononuclear cells from HIV-2-exposed uninfected individuals, HIV-2-infected individuals and HIV-negative controls in Guinea-Bissau. Increased HIV-2-specific T lymphocyte proliferative responses were detected in both groups compared to HIV-negative controls (healthy HIV-uninfected individuals without known exposure to an HIV-infected person); five out of 29 of the HIV-2-exposed uninfected and half (16 of 32) of the HIV-2-infected individuals had stimulation indexes >2, compared to one out of 49 of the HIV-negative controls (P = 0.003 and P < 0.0001, respectively). The exposed uninfected individuals had reactivity to a HIV-2 V3-peptide corresponding to amino acids 311-326 of the envelope glycoprotein, while the HIV-2-infected people reacted mainly to HIV-2 whole viral lysate. Thus, this study demonstrates a high degree of HIV-2-specific T helper cell activity, as measured by lymphocyte proliferation, in HIV-2-exposed uninfected individuals as well as in HIV-2-infected subjects. These immune responses could be important for resistance to the infection and for the control of established infection and, thus, play a role in the lower transmission and progression of HIV-2 compared to HIV-1.

Engineering immunogenic consensus T helper epitopes for a cross-clade HIV vaccine

Developing a vaccine that will stimulate broad HIV-specific T cell responses is difficult because of the variability in HIV T cell epitope sequences, which is in turn due to the high mutation rate and consequent strain diversity of HIV-1. We used a new Class II version of the EpiMatrix T cell epitope-mapping tool and Conservatrix to select highly conserved and promiscuous Class II HLA-restricted T cell epitopes from a database of 18,313 HIV-1 env sequences. Criteria for selection were: (1) number of HIV-1 strains represented as measured by Conservatrix; (2) EpiMatrix score; and (3) promiscuity (number of unique MHC motifs contained in the peptide). Using another vaccine design tool called the EpiAssembler, a new set of overlapping, conserved and immunogenic HIV-1 peptides were engineered creating extended "immunogenic consensus" sequences. Each overlapping 9-mer of the 20-23 amino acid long immunogenic consensus peptides was conserved in a large number (range 893-2254) of individual HIV-1 strains, although the novel peptides were not representative of any single strain of HIV. We synthesized nine representative peptides. T helper cell responses to the peptides were evaluated by ELISpot (gamma-interferon) assay, using peripheral blood monocytes (PBMC) obtained from 34 healthy long term non-progressor (LT) or moderate-progressor (MP) donors (median years infected = 8.88, median CD4 T cells = 595, median VL = 1044). Nine peptides were tested, of which eight were confirmed in ELISpot assays using PBMC from the LT/MP subjects. These epitopes were ranked by Conservation and EpiMatrix score 1, 2, 3, 5, 7, 11, and 14 out of the set of 9 original peptides. Five of these peptides were selected for inclusion in an epitope-driven cross-clade HIV-1 vaccine (the GAIA vaccine). These data confirm the utility of bioinformatics tools to select and construct novel "immunogenic consensus sequence" T cell epitopes for a globally relevant vaccine against HIV.

Functionally-inactive and immunogenic Tat, Rev and Nef DNA vaccines derived from sub-Saharan subtype C human immunodeficiency virus type 1 consensus sequences

The efficacy of cellular immune responses elicited by HIV vaccines is dependent on their strength, durability and antigenic breadth. The regulatory proteins are abundantly expressed early in the viral life cycle and CTL recognition may bring about early killing of infected cells. We synthesised DNA vaccine constructs that encode consensus HIV-1 subtype C Tat, Rev and Nef proteins. Proteins carrying inactivating mutations were tested for functional activity and highly expressing, inactive Tat, Rev and Nef mutants were identified and their reading frames fused into a TatRevNef cassette. Single- and polygene Tat, Rev and/or Nef constructs were immunogenic in BALB/c mice. These constructs may serve to increase the antigenic breadth for an HIV-1 vaccine that is relevant for sub-Saharan Africa.

Experimental Leishmania major infection suppresses HIV-1 DNA vaccine induced cellular immune response

The AIDS epidemic in the developing world represents a major global crisis and an effective vaccine is imperative. However, many parasites are common in developing countries and can result in a state of chronic immune activation that is polarized towards a Th2 profile and which can potentially impair responses to vaccines or other infectious challenges. In this study we demonstrate that experimental Leishmania major infection of BALB/c mice inhibits responses to a DNA-based HIV-1 gag vaccine. L. major infection in BALB/c results in a polarized Th2 immune response. In this study naïve BALB/c mice immunized with the HIV-1 gag DNA vaccine mounted a cellular immune response against the vaccine antigen, HIV-1 gag. CD8+ T lymphocytes were able to respond in vitro to HIV-1 gag stimulation and secrete interferon (IFN)-gamma. However, L. major-infected, vaccinated BALB/c mice had a significantly reduced number of IFN-gamma-producing CD8+ T cells following in vitro stimulation with gag antigen. These data suggest that parasitic infection, which results in a Th2 profile, reduces the efficacy of DNA vaccines that are designed to induce antiviral CD8+ T cell responses.

Antigen-specific beta-chemokine production and CD8 T-cell noncytotoxic antiviral activity in HIV-2-infected individuals

Human immunodeficiency virus-2 (HIV-2) is less pathogenic than HIV-1, and the disease progression in HIV-2-infected individuals seems to be similar to that seen in HIV-1-infected long-term nonprogressors. Cell-mediated immune responses and the production of noncytotoxic CD8+ T-cell antiviral factors (CAF) and beta-chemokines have been correlated to protection against HIV-1 and associated with asymptomatic infection and slower disease progression. We investigated the antigen-induced beta-chemokine production in HIV-2-infected patients living in Sweden and in Guinea-Bissau. We also compared in vitro CD8+ T-cell-mediated noncytotoxic antiviral activity against beta-chemokine-sensitive R5 virus (HIV-1Bal) and beta-chemokine-insensitive X4 virus (HIV-1IIIB) in HIV-2-infected patients with that in HIV-1-infected patients. HIV-2-specific beta-chemokine production was demonstrated in a majority of the HIV-2-infected subjects. CD8+ T cells of both HIV-1 and HIV-2-infected individuals suppressed R5 virus replication in vitro in a similar manner, while the inhibition of X4 virus replication seemed to be more frequent and of a higher magnitude among HIV-2-infected patients compared to HIV-1-infected subjects. Taken together, our results indicate that the production of CD8+ T-cell noncytotoxic antiviral factors may contribute to the low transmission of the virus and slower disease progression in HIV-2-infected patients.

Vaccine strategies for infectious diseases

Infectious diseases are the major cause of death worldwide; in developing countries such diseases are responsible for nearly half the burden of premature death and disability. Therefore, the need for the development of new vaccine strategies aimed at preventing or limiting disease is extremely urgent. Important successes have been achieved against some infectious diseases that were once endemic or, even, epidemic (e.g., polio, smallpox, diptheria). Advances in our knowledge of the pathogenesis and immune correlates of protections are needed to develop novel vaccinal approaches to diseases such as hepatitis C, AIDS and malaria. In this review we will analyse the biological problems associated with the prevention of development and/or improvement of vaccine strategies for infectious diseases, focusing on the difficulties facing the creation of new effective vaccines for HIV infection and malaria.

HIV-1 vaccines and co-infection

Vaccines are an economically efficient means of controlling viral infections, and it is likely that a vaccine against HIV-1 will be the most effective way of controlling the global AIDS crisis. However, an effective vaccine has not yet been attainable and in developing countries co-infection with protozoa and other chronic diseases adds another level of complexity to the design of an HIV-1 vaccine. Helminthic and protozoan infections can result in a constant state of immune activation that is characterised by a dominant T helper (Th)2 type of cytokine profile. Such an immune profile is likely to have an adverse impact on the efficacy of an HIV-1 vaccine CD8 cellular immune response and the corresponding Th1 cytokines that are most likely to be important for clearing viral infections.

Influence of host genetic variation on susceptibility to HIV type 1 infection

For this review of genetic susceptibility to human immunodeficiency virus type 1 infection, far more information was available on factors involved in acquisition of the virus by an uninfected "recipient" than on propagation by the infected "donor." Genetic variation presumably alters transmission from an infected host primarily by regulating the replication of virus and the concentration of particles circulating in blood and mucosal secretions of the potential donor. Thus, the effects of host genetic variation on transmission are inextricably bound to the well-established and powerful effects on virus load at different stages of infection. Teasing apart the effects in both donors and recipients has been and will continue to be quite difficult.

Strong cellular and humoral anti-HIV Env immune responses induced by a heterologous rhabdoviral prime-boost approach

Recombinant rhabdovirus vectors expressing human immunodeficiency virus (HIV) and/or simian immunodeficiency virus (SIV) proteins have been shown to induce strong immune responses in mice and rhesus macaques. However, the finding that such responses protect rhesus macaques from AIDS-like disease but not from infection indicates that further improvements for these vectors are needed. Here, we designed a prime-boost schedule consisting of a rabies virus (RV) vaccine strain and a recombinant vesicular stomatitis virus (VSV) both expressing HIV Envelope (Env). Mice were primed and boosted with the two vaccine vehicles by different routes and in different combinations. Mucosal and systemic humoral responses were assessed using enzyme linked immunosorbent assay (ELISA) while the cellular immune response was determined by an IFN-gamma ELISPOT assay. We found that an immunization combination of RV and VSV elicited the highest titers of anti-Env antibodies and the greatest amount of Env-specific IFN-gamma secreting cells pre- and post-challenge with a recombinant vaccinia virus expressing HIV(89.6) Env. Furthermore, intramuscular immunization did not induce antigen-specific mucosal antibodies while intranasal inoculation stimulated vector-specific IgA antibodies in vaginal washings and serum. Our results show that it is feasible to elicit robust cellular and humoral anti-HIV responses using two different live attenuated Rhabdovirus vectors to sequentially prime and boost.

Centralized immunogens as a vaccine strategy to overcome HIV-1 diversity

Genetic variation of HIV-1 represents a major obstacle for AIDS vaccine development. With the amino acid sequence divergence as high as 30% in envelopes between different subtypes among HIV-1 group M viruses, it is unlikely that cross-subtype protection will occur equally well among all subtypes. Computer programs have been used to generate 'centralized' HIV gene sequences: consensus, ancestor or center of the tree. These sequences can decrease the genetic distances between the 'centralized' and wild-type gene immunogens to half of those between any wild-type immuongens to each other. Recent studies demonstrated that an artificial group M consensus env gene is equidistant from any subtype and recombinants. It is biologically functional and preserves antigenicity similar to contemporary Env proteins. Most importantly, the group M consensus Env immunogen can elicit both T- and B-cell responses to wild-type HIV-1 isolates.

Therapeutic vaccination against HIV

The challenge for an immunotherapeutic vaccine is to increase antiviral responses in an increasingly immunocompromised host and to provide immunity to epitopes that have been neglected by the infected host. Therapeutic vaccination with structural and regulatory genes and proteins of HIV are reviewed. The most promising clinical results consist of short-term improvement in survival without antiretroviral therapy. Together with antiviral therapy, it is reported that immunization has provided a prolonged time to virological failure. It is clear, however, that additional help will be needed from adjuvants and/or modulators that activate natural killer and T-cells, or other immune molecules. Vaccine therapy should start early, while adequate reservoirs of appropriate T-helper and memory cells are available and still inducible.

Results of an ELISPOT proficiency panel conducted in 11 laboratories participating in international human immunodeficiency virus type 1 vaccine trials

We used an external quality assurance (EQA) panel to assess laboratory competency and comparability when performing ELISPOT assays in support of human immunodeficiency virus type 1 (HIV-1) vaccine trials. Cell recovery, viability, and frequency of interferon-gamma (IFN-gamma)-secreting cells after antigen stimulation were obtained from 11 laboratories on a coded panel of 11 peripheral blood mononuclear cell samples. The median recovery and viability before plating for all samples were 35% and 86%, respectively, with notable interlaboratory and intrasample variability. Empirical as well as statistical analysis methods were used to define positive ELISPOT responses. Remarkable concordance between laboratories was obtained in defining a qualitative assessment of responder/nonresponder status to antigens, but the frequency of responding cells varied among the laboratories. This study highlights the need for better standardization of protocols and reagents to obtain reliable and reproducible data that may support immunogenicity studies, vaccine regulatory submissions, and licensure.

Insights into the role of host genetic and T-cell factors in resistance to HIV transmission from studies of highly HIV-exposed Thais

Studies of resistance to HIV-1 transmission are likely to be valuable for the design of vaccines and other efforts to prevent HIV. Here, we review the T-cell and genetic factors associated with resistance to HIV-1 transmission in studies of highly exposed but persistently seronegative (HEPS) women from northern Thailand. Women were enrolled in two sex-worker studies and in a discordant couple study. We performed Cr51 cytotoxic T lymphocyte (CTL), interferon-gamma (IFN-gamma) ELISPOT, and proliferation assays as well as genetic studies, including HLA-class I typing. CTL and ELISPOT studies showed a skewing of T-cell responses to conserved HIV-1 proteins in HEPS, but not in HIV-1-seropositive women. T-cell responses were extremely long-lived in some HEPS women. In the two sex-worker studies, HLA-A11 was associated with resistance to HIV-1 transmission. These data provide promise for the ability of CTL to control HIV and emphasize the importance of developing HIV vaccines that stimulate strong, long-lasting Tcell responses.

DNA vaccines against human immunodeficiency virus type 1

Development of a vaccine against human immunodeficiency virus type 1 (HIV-1) is the main hope for controlling the acquired immunodeficiency syndrome pandemic. An ideal HIV vaccine should induce neutralizing antibodies, CD4+ helper T cells, and CD8+ cytotoxic T cells. While the induction of broadly neutralizing antibodies remains a highly challenging goal, there are a number of technologies capable of inducing potent cell-mediated responses in animal models, which are now starting to be tested in humans. Naked DNA immunization is one of them. This review focuses on the stimulation of HIV-specific T cells and discusses in the context of the current 'state-of-art' of DNA vaccines, the areas where this technology might assist either alone or as a part of more complex vaccine formulations in the HIV vaccine development.

Cellular immune responses in seronegative sexual contacts of acute hepatitis C patients

Acute hepatitis C virus (HCV) is typically defined as new viremia and antibody seroconversion. Rates and immunologic correlates of hepatitis C clearance have therefore been based on clearance of viremia only in individuals who initially had an antibody response. We sought to characterize the immunological correlates of clearance in patients with acute hepatitis C and their sexual contacts. We prospectively determined CD4(+) and CD8(+) cytotoxic T-lymphocyte responses in index patients with acute HCV and their sexual contacts who developed acute infection, either with or without spontaneous clearance, as well as those contacts who never developed viremia. Responses were measured using proliferation and ELISpot assays for CD4(+) and CD8(+) responses. We demonstrate in this prospective study that cellular immune responses can develop in exposed but persistently aviremic and antibody-negative individuals as well as those individuals with spontaneous clearance of acute HCV. These findings lend further credence to the importance of cellular immune responses in recovery from HCV and suggest that low exposure to HCV may lead to development of HCV-specific immune responses without ongoing HCV replication. This finding has important implications for HCV vaccine and therapeutic development.

Absence of immunodominant anti-Gag p17 (SL9) responses among Gag CTL-positive, HIV-uninfected vaccine recipients expressing the HLA-A*0201 allele

According to a number of previous reports, control of HIV replication in humans appears to be linked to the presence of anti-HIV-1 Gag-specific CD8 responses. During the chronic phase of HIV-1 infection, up to 75% of the HIV-infected individuals who express the histocompatibility leukocyte Ag (HLA)-A*0201 recognize the Gag p17 SLYNTVATL (aa residues 77-85) epitope (SL9). However, the role of the anti-SL9 CD8 CTL in controlling HIV-1 infection remains controversial. In this study we determined whether the pattern of SL9 immunodominance in uninfected, HLA-A*0201 HIV vaccine recipients is similar to that seen in chronically HIV-infected subjects. The presence of anti-SL9 responses was determined using a panel of highly sensitive cellular immunoassays, including peptide:MHC tetramer binding, IFN-gamma ELISPOT, and cytokine flow cytometry. Thirteen HLA-A*0201 vaccinees with documented anti-Gag CD8 CTL reactivities were tested, and none had a detectable anti-SL9 response. These findings strongly suggest that the pattern of SL9 epitope immunodominance previously reported among chronically infected, HLA-A*0201-positive patients is not recapitulated in noninfected recipients of Gag-containing canarypox-based candidate vaccines and may be influenced by the relative immunogenicity of these constructs.

Human immunodeficiency virus type 1 gag-specific mucosal immunity after oral immunization with papillomavirus pseudoviruses encoding gag

Mucosal surfaces are the primary portals for human immunodeficiency virus (HIV) transmission. Because systemic immunization, in general, does not induce effective mucosal immune responses, a mucosal HIV vaccine is urgently needed. For this study, we developed papillomavirus pseudoviruses that express HIV-1 Gag. The pseudoviruses are synthetic, nonreplicating viruses, yet they can produce antigens for a long time in the immune system. Here we show that oral immunization of mice by the use of papillomavirus pseudoviruses encoding Gag generated mucosal and systemic Gag-specific cytotoxic T lymphocytes that effectively lysed Gag-expressing target cells. Furthermore, the pseudoviruses generated Gag-specific gamma interferon-producing T cells and serum immunoglobulin G (IgG) and mucosal IgA. In contrast, oral immunization with plasmid DNA encoding HIV-1 Gag did not induce specific immune responses. Importantly, oral immunization with the pseudoviruses induced Gag-specific memory cytotoxic T lymphocytes and protected mice against a rectal mucosal challenge with a recombinant vaccinia virus expressing HIV-1 Gag. Thus, papillomavirus pseudoviruses encoding Gag are a promising mucosal vaccine against AIDS.

A consecutive priming-boosting vaccination of mice with simian immunodeficiency virus (SIV) gag/pol DNA and recombinant vaccinia virus strain DIs elicits effective anti-SIV immunity

To evaluate immunity induced by a novel DNA prime-boost regimen, we constructed a DNA plasmid encoding the gag and pol genes from simian immunodeficiency virus (SIV) (SIVgag/pol DNA), in addition to a replication-deficient vaccinia virus strain DIs recombinant expressing SIV gag and pol genes (rDIsSIVgag/pol). In mice, priming with SIVgag/pol DNA, followed by rDIsSIVgag/pol induced an SIV-specific lymphoproliferative response that was mediated by a CD4+-T-lymphocyte subset. Immunization with either vaccine alone was insufficient to induce high levels of proliferation or Th1 responses in the animals. The prime-boost regimen also induced SIV Gag-specific cellular responses based on gamma interferon secretion, as well as cytotoxic-T-lymphocyte responses. Thus, the regimen of DNA priming and recombinant DIs boosting induced Th1-type cell-mediated immunity, which was associated with resistance to viral challenge with wild-type vaccinia virus expressing SIVgag/pol, suggesting that this new regimen may hold promise as a safe and effective vaccine against human immunodeficiency virus type 1.

The HIV-1 HLA-A2-SLYNTVATL is a help-independent CTL epitope

The CTL response to the HLA-A*0201-restricted, HIV-1 p17 Gag(77-85) epitope (SLYNTVATL; SL9) has been extensively studied in patients. Although this reactivity is exceptionally prominent in chronically infected patients and inversely correlated to viral load, SL9-specific CTLs (SL9-CTLs) are rarely detected in acute infection. To explore the cellular basis for this unusual manifestation, SL9-CTLs primed ex vivo from naive circulating CD8(+) T cells of healthy, seronegative donors were generated and characterized. SL9 appeared to differ from other well-studied A*0201-restricted epitopes in several significant respects. In contrast to published reports for influenza and melanoma peptides and the HIV gag IV9 epitope studied here in parallel, SL9-CTLs were primed by immature but not mature autologous dendritic cells. Highly activated SL9-CTLs produce sufficient autocrine mediators to sustain clonal expansion and CTL differentiation for months without CD4(+) T cells or exogenous IL-2. Moreover, SL9-CTLs were sensitive to paracrine IL-2-induced apoptosis. IL-2 independence and sensitivity to paracrine IL-2 were also characteristic of SL9-CTLs immunized by dendritic cells transduced by a nonreplicating lentiviral vector encoding full-length Gag. In vitro-primed SL9-CTLs resembled those derived from patients in degeneracy of recognition and functional avidities for both SL9 and its natural mutations. Together, these data show that SL9 is a highly immunogenic, help-independent HIV epitope. The scarcity of SL9-CTLs in acute infection may result from cytokine-induced apoptosis with the intense activation of the innate immunity. In contrast, SL9-CTLs that constitutively produce autocrine help would predominate during CD4-diminished chronic infection.

Statistical considerations for the design and analysis of the ELISpot assay in HIV-1 vaccine trials

Effector T lymphocyte responses are considered critical for controlling human immunodeficiency virus type-1 (HIV-1) infection. The enzyme-linked immunospot (ELISpot) assay has emerged as a primary means of assessing HIV-specific T cell responses, and the development of objective methods that distinguish positive and negative ELISpot responses while properly controlling the rate of false positives is critical. In this paper, we consider several statistical methods that are helpful in defining such a positive criterion. Simulation results under a variety of scenarios suggest that a permutation-based criterion using a resampling adjustment for multiple comparisons yields the desired false positive rate while remaining competitive with other potential criteria in terms of sensitivity. These results also provide guidance on the effect of the number of experimental and negative control replicate wells on assay sensitivity. Application of different potential positive criteria using ELISpot assay results from IFN-gamma-secreting T cells of HIV-1 seropositive and seronegative donors confirmed several of the results obtained under simulation. Our findings support the application of statistically-based positive criteria such as the permutation-based resampling approach in assessing HIV vaccine-induced T cell responses. Moreover, the proposed methods have potential utility in related HIV immunopathogenesis studies and in non-HIV clinical vaccine trials.

Prospects for an AIDS vaccine: three big questions, no easy answers

The unremitting devastation created by the AIDS pandemic will probably only be controlled when a vaccine is developed that is safe, effective, affordable, and simple enough to permit implementation in developing countries where the impact of AIDS is most severe. Although formidable practical, political, economic, social, and ethical challenges face the AIDS vaccine development effort, the most fundamental challenges now reside at the level of the basic biology of HIV-1 infection and pathogenesis. Of these biological considerations, three questions loom especially large: can we design immunogens that will elicit neutralising antibodies that are reactive against a wide variety of primary HIV isolates; will vaccine-elicited cytotoxic T cells be fundamentally better at controlling HIV-1 replication and ameliorating disease progression than those responses that arise during natural HIV infection; and to what extent will the tremendous global genetic diversity of HIV-1 compromise the breadth of vaccine-elicited protective immunity and the overall effectiveness of an AIDS vaccine? Although these are three exceptionally challenging questions, they are now being approached with clear hypotheses whose testing is being facilitated by an ever-improving array of technologies for vaccine design and immunological characterisation. The extent to which the field of AIDS vaccine research can now come together to answer these questions in the best coordinated, most efficient manner will probably be an important determinant of how and when an effective AIDS vaccine will be developed.

Persistence of low levels of simian immunodeficiency virus in macaques that were transiently viremic by conventional testing

Transient SIV viremia after experimental SIV challenge has been documented. Whether SIV persists in these transiently viremic macaques remains unclear. In the present study, we applied a sensitive PCR and found persistent low levels of SIVmne infection (LLSI) (range: 0.1-5.3 SIV DNA copies/10(6) PBMC) in seven macaques that were transiently positive by conventional assays, which was 10(2)- to 10(6)-fold less than those of SIVmne infected monkeys with typical disease progression. SIV envelope V1 sequences remained homogeneous in these macaques for the 6-year study period, with a mean evolution rate of 0.005% per site per year, which was not different from zero (P = 0.612) and significantly lower than that (0.56-1.18%) in macaques with progressive infection of SIVmne. LLSI macaques have remained free from SIV-associated illness, and are still alive 10 years after virus inoculation. Understanding the mechanisms underlying this outcome may provide valuable insight into therapy and vaccine development.

Potent neutralizing serum immunoglobulin A (IgA) in human immunodeficiency virus type 2-exposed IgG-seronegative individuals

The mechanisms behind the resistance to human immunodeficiency virus type 2 (HIV-2) infection are still not fully understood. In the present study, we explored the HIV-2-specific humoral serum immunoglobulin A (IgA) immune response in HIV-2-exposed IgG-seronegative (EGSN) individuals. Serum samples from heterosexual EGSN individuals and their known HIV-2-infected partners, as well as controls originating from Guinea-Bissau in Africa, were studied. Antibody reactivity to native and recombinant envelope glycoproteins was investigated, and the capacity of purified serum IgA to neutralize HIV-2(SBL6669) was tested. Our results showed that 16 of 25 EGSN samples exhibited reactivity against whole HIV-2 antigen, 6 of 25 samples reacted with recombinant gp36 (rgp36), and 3 of 25 samples were positive against HIV-2 rgp105; no reactivity to native HIV-2 gp125 was detected. Purified serum IgA antibodies from both EGSN and HIV-2-positive individuals, but not that from the negative controls, exhibited neutralization of HIV-2(SBL6669). The most potent neutralization activity was exhibited by IgA purified from EGSN compared to infected individuals' IgA. The antigenic pattern of the HIV-2-positive partners showed that all serum IgA samples were reactive to whole HIV-2 antigen, and 14 of 15 reacted with rgp36. For rgp105 and gp125, 5 of 15 and 4 of 15 samples exhibited binding, respectively. The serum of the EGSN group had a higher mean IgA concentration than that of the negative controls (P < 0.05). Thus, we describe HIV-2-specific serum IgA antigen reactivity and show a more potent serum IgA-mediated HIV-2-neutralizing activity in EGSN individuals than in HIV-2-infected patients.

HIV type 1-specific inter- and intrasubtype cellular immune responses in HIV type 1-infected Ugandans

Investigations concerning the extent and nature of subtype-specific and intersubtype immune responses in HIV-1-infected persons are necessary for the development of appropriate candidate vaccines. In the cross-sectional study described here, 26 HIV-1-positive Ugandan patients were tested for their ability to mount HIV antigen-specific cellular immune responses. Subjects were infected with either HIV-1 subtypes A, C, or D. Recombinant vaccinia virus (rVV)-based and peptide-based enzyme-linked immunospot (Elispot) assays were used to evaluate HIV-1-specific gamma-interferon (IFN-gamma) cellular responses. rVV expressing gag, pol, or env proteins derived from HIV-1 subtypes A, B, and D were evaluated for their ability to induce whole HIV-1-protein-specific IFN-gamma responses in 14 patients. A panel of previously identified HLA class I-restricted peptides based on representative sequences from HIV-1 subtypes A, B, C, and D and restricted through HLA-A2, -A29, -B42, -B53, and -B57 alleles were used to evaluate the presence of HIV-1-peptide-specific T cells in 19 patients. Using rVV, 27 of a possible 38 subtype-specific responses (71%) and 56 of a possible 110 intersubtype responses (51%) were observed. When appropriate peptides were used 18 of 39 (46.2%) subtype-specific and 13 of 39 (33.3%) intersubtype responses were observed. Peptide responses were higher quantitatively than those seen when rVV were used. In 7 patients, both rVV and specific peptides were evaluated; in 3 of 7 individuals, global responses were seen despite a lack of measurable HLA-restricted peptide-specific responses demonstrating the need to evaluate a broader range of HIV-specific immune responses.

HLA-A and -B allele expression and ability to develop anti-Gag cross-clade responses in subtype C HIV-1–infected Ethiopians

A cohort of 35 human immunodeficiency virus type 1 (HIV-1) subtype C-infected Ethiopians was studied to define the HLA phenotype in all 35 subjects and highly conserved Gag protein regions involved in cross-clade cell-mediated immunity. Full-length Gag virus sequences were determined in 15 individuals. CD8 cell-mediated immune responses were detected by interferon-gamma ELISpot assay. HLA-A*03, -B*49, and -B*57 allelic frequencies were relatively higher than in other African populations. Anti-p17 (aa 1-60) CD8+ were detectable in the highest number of individuals. Anti-p17 (aa 1-60 and 51-110) cross-clade responses against subtype B and C were detected in 50% of the tested subjects. The p24 KF11 (aa 162-172) epitope was found to be immunodominant among the HLA-B*5703--positive individuals. These data represent the first report of correlating HLA phenotype and HIV-specific cell-mediated immune responses among infected Ethiopians and may be useful in designing cytotoxic T lymphocyte-inducing vaccines for this part of Africa.

Correlates of resistance to HIV-1 infection in homosexual men with high-risk sexual behaviour

OBJECTIVE

To investigate possible correlates of HIV resistance in participants from the Amsterdam Cohort of Homosexual men who have remained HIV seronegative despite high-risk sexual behaviour.

DESIGN/METHODS

We studied in vitro HIV-1 susceptibility and adaptive and innate immunity in 29 high-risk seronegative (HRSN) and 15 HIV-negative pre-seroconversion (pre-SC) homosexual men from the same Amsterdam Cohort Study (ACS) who seroconverted to HIV-1 positive during active follow-up. Host genetics were compared between HRSN and HIV-positive ACS participants.

RESULTS

We found lower in vitro susceptibility for a CCR5-using (R5) HIV-1 variant, higher RANTES production levels, but no difference in coreceptor expression in HRSN as compared with pre-SC controls. Reduced R5 in vitro susceptibility of two HRSN tested was restored to normal levels by addition of antibodies against beta-chemokines. A higher proportion of HRSN carried the SDF-1 3'A variant and HLA-A*11, A*31 and Cw*15 alleles. ELIspot analysis with HIV-1 peptide stimulation revealed low frequencies of HIV-1-specific CD8 interferon-gamma producing cytotoxic T cells in both HRSN and pre-SC controls.

CONCLUSIONS

Low in vitro R5 susceptibility of cells from the HRSN men was due to beta-chemokine mediated inhibition of virus replication. The presence of HIV-1 specific cytotoxic T cells in both HRSN and pre-SC participants may signify exposure to the virus rather than protection from infection. Host genetic characteristics and other factors affecting innate immunity may contribute to differential resistance to HIV-1 infection among exposed seronegative individuals.

Antiretroviral Drug Resistance Mutations Sustain or Enhance CTL Recognition of Common HIV-1 Pol Epitopes

Antiretroviral drug resistance and escape from CTL are major obstacles to effective control of HIV replication. To investigate the possibility of combining drug and immune-based selective pressures against HIV, we studied the effects of antiretroviral drug resistance mutations on CTL recognition of five HIV-1 Pol epitopes presented by common HLA molecules. We found that these common drug resistance mutations sustain or even enhance the antigenicity and immunogenicity of HIV-1 Pol CTL epitopes. Variable patterns of cross-reactive and selective recognition of wild-type and corresponding variant epitopes demonstrate a relatively diverse population of CD8(+) T cells reactive against these epitopes. Variant peptides with multiple drug resistance mutations still sustained CTL recognition, and some HIV-infected individuals demonstrated strong CD8(+) T cell responses against multiple CTL epitopes incorporating drug resistance mutations. Selective reactivity against variant peptides with drug resistance mutations reflected ongoing or previous exposure to the indicated drug, but was not dependent upon the predominance of the mutated sequence in endogenous virus. The frequency and diversity of CTL reactivity against the variant peptides incorporating drug resistance mutations and the ability of these peptides to activate and expand CTL precursors in vitro indicate a significant functional interface between the immune system and antiretroviral therapy. Thus, drug-resistant variants of HIV are susceptible to immune selective pressure that could be applied to combat transmission or emergence of antiretroviral drug-resistant HIV strains and to enhance the immune response against HIV.

DNA vaccine encoding human immunodeficiency virus-1 Gag, targeted to the major histocompatibility complex II compartment by lysosomal-associated membrane protein, elicits enhanced long-term memory response

Antigen presentation by major histocompatibility complex type II (MHC II) molecules and activation of CD4+ helper T cells are critical for the generation of immunological memory. We previously described a DNA vaccine encoding human immunodeficiency virus-1 p55Gag as a chimera with the lysosome-associated membrane protein (LAMP/gag). The LAMP/gag chimera protein traffics to the MHC II compartment of transfected cells and elicits enhanced immune responses as compared to a DNA vaccine encoding native gag not targeted to the MHC II compartment. We have now investigated the long-term responses of immunized mice and show that the LAMP/gag DNA vaccine promotes long-lasting B cell- and CD4+ and CD8+ T-cell memory responses induced by DNA encoding non-targeted Gag decay rapidly and elicit very low or undetectable levels of gag DNA is sufficient to generate T-cell memory. Following this initial priming immunization with LAMP/gag DNA, booster immunizations with native gag DNA or the LAMP/gag chimera are equally efficient in eliciting B- and T-cell secondary responses, results in accordance with observations that secondary expansion of CD8+ cells in the boost phase does not require additional CD4+ help. These findings underscore the significance of targeting DNA-encoded vaccine antigens to the MHC II processing compartments for induction of long-term immunological memory.

Designing and engineering of DNA-vaccine construction encoding multiple CTL-epitopes of major HIV-1 antigens

A synthetic T cell immunogen (TCI) has been designed as a candidate DNA-based vaccine against Human immunodeficiency virus (HIV)-1 using cytotoxic T lymphocytes (CD8(+) CTL) and T-helper lymphocytes (CD4(+) Th) epitopes retrieved from the Los Alamos HIV Molecular Immunology Database. The protein 392 amino acids in length contains about eighty CTL-epitopes, many of which are overlapping and are totally restricted by ten different HLA class I molecules. To be able to detect CTL responses induced by a DNA vaccine in experimental animals, additional epitopes, restricted by mouse and Macaque rhesus major histocompatibility complex (MHC) class I molecules, were included in the target immunogen. The gene encoding the TCI protein was assembled, cloned into vector plasmids and expressed in a prokaryotic and a eukaryotic system. The presence of HIV-1 protein fragments in the immunogen structure was ascertained by ELISA and immunoblotting using panels of HIV-1-positive sera and monoclonal antibodies to p24. It has been demonstrated that DNA vaccine can induce both specific T cell responses (CTL and blast transformation) and specific antibodies in mice immunized with pcDNA-TCI.

Poorly soluble peptides can mimic authentic ELISPOT responses

The ELISPOT assay is a specific, sensitive, quantitative assay for assessing cell-mediated immune responses to a variety of antigens including HIV-1 peptides. In an interferon (IFN)-gamma-ELISPOT assay, peripheral blood mononuclear cells (PBMC) from two HIV-1 exposed seronegative (ESN) individuals appeared to respond strongly to an HIV Gag peptide. Analysis of this peptide revealed that it was incompletely dissolved and induced non-specific spot formation, even in the absence of cells. In subsequent experiments, the peptide was found to interact with avidin and the ELISPOT membrane. Filtering the peptide prevented non-specific spot formation. These findings underscore the need for appropriate controls and proper peptide preparation in order to reduce the risk of false-positive ELISPOT responses.