Antigenic peptides recognized by T lymphocytes from AIDS viral envelope-immune humans

Comparison of the Biological Basis for Non-HIV Transmission to HIV-Exposed Seronegative Individuals, Disease Non-Progression in HIV Long-Term Non-Progressors and Elite Controllers

HIV-exposed seronegative individuals (HESIs) are a small fraction of persons who are multiply exposed to human immunodeficiency virus (HIV), but do not exhibit serological or clinical evidence of HIV infection. In other words, they are groups of people maintaining an uninfected status for a long time, even after being exposed to HIV several times. The long-term non-progressors (LTNPs), on the other hand, are a group of HIV-infected individuals (approx. 5%) who remain clinically and immunologically stable for an extended number of years without combination antiretroviral therapy (cART). Meanwhile, elite controllers are comprise a much lower number (0.5%) of HIV-infected persons who spontaneously and durably control viremia to below levels of detection for at least 12 months, even when using the most sensitive assays, such as polymerase chain reaction (PCR) in the absence of cART. Despite the fact that there is no universal agreement regarding the mechanisms by which these groups of individuals are able to control HIV infection and/or disease progression, there is a general consensus that the mechanisms of protection are multifaceted and include genetic, immunological as well as viral factors. In this review, we analyze and compare the biological factors responsible for the control of HIV in these unique groups of individuals.

Targeting HIV Env immunogens to B cell follicles in nonhuman primates through immune complex or protein nanoparticle formulations

Following immunization, high-affinity antibody responses develop within germinal centers (GCs), specialized sites within follicles of the lymph node (LN) where B cells proliferate and undergo somatic hypermutation. Antigen availability within GCs is important, as B cells must acquire and present antigen to follicular helper T cells to drive this process. However, recombinant protein immunogens such as soluble human immunodeficiency virus (HIV) envelope (Env) trimers do not efficiently accumulate in follicles following traditional immunization. Here, we demonstrate two strategies to concentrate HIV Env immunogens in follicles, via the formation of immune complexes (ICs) or by employing self-assembling protein nanoparticles for multivalent display of Env antigens. Using rhesus macaques, we show that within a few days following immunization, free trimers were present in a diffuse pattern in draining LNs, while trimer ICs and Env nanoparticles accumulated in B cell follicles. Whole LN imaging strikingly revealed that ICs and trimer nanoparticles concentrated in as many as 500 follicles in a single LN within two days after immunization. Imaging of LNs collected seven days postimmunization showed that Env nanoparticles persisted on follicular dendritic cells in the light zone of nascent GCs. These findings suggest that the form of antigen administered in vaccination can dramatically impact localization in lymphoid tissues and provides a new rationale for the enhanced immune responses observed following immunization with ICs or nanoparticles.

From therapeutic antibodies to immune complex vaccines

In recent years, therapeutic monoclonal antibodies have made impressive progress, providing great benefit by successfully treating malignant and chronic inflammatory diseases. Monoclonal antibodies with broadly neutralizing effects against specific antigens, or that target specific immune regulators, manifest therapeutic effects via their Fab fragment specificities. Subsequently therapeutic efficacy is mediated mostly by interactions of the Fc fragments of the antibodies with their receptors (FcR) displayed on cells of the immune system. These interactions can trigger a series of immunoregulatory responses, involving both innate and adaptive immune systems and including cross-presentation of antigens, activation of CD₈⁺ T cells and CD₄⁺ T cells, phagocytosis, complement-mediated antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). The nature of the triggered effector functions of the antibodies is markedly affected by the glycosylation patterns of the Fc fragments. These can cause differences in the conformation of the heavy chains of antibodies, with resultant changes in antibody binding affinity and activation of the complement system. Studies of the Fc glycosylation profiles together with the associated Fc effector functions and FcR/CR interactions promoted interest and progress in engineering therapeutic antibodies. Furthermore, because antigen–antibody immune complexes (ICs) have shown similar actions, in addition to certain novel immunoregulatory mechanisms that also reshape immune responses, the properties of ICs are being explored in new approaches for prevention and therapy of diseases. In this review, both basic studies and experimental/clinical applications of ICs leading to the development of preventive and therapeutic vaccines are presented.

Immune Complex Vaccination

Antibody/antigen binding results in immune complexes (IC) that have a variety of regulatory functions. One important feature is the enhanced host immune activation against antigen contained in the complex. ICs play important roles at several critical steps that lead to B and T cell activation, including antigen targeting/retention, facilitated antigen uptake, antigen presenting cell activation and proper balancing of positive and negative stimulatory signals. In both poultry industry and clinical health care, ICs have been used as preventive and therapeutic vaccines. With our deepening understanding of antibody biology, particularly in light of new revelations of regulatory functions of Fc receptors, mechanistically more precise engineering has spearheaded tailored use of this tool for infection control and cancer therapy. IC-based treatment and prophylaxis have been tested to different extents in HBV, HIV and influenza viral infection control and are actively examined as an alternative treatment for several forms of tumor. As a part of this book series, this chapter aims to discuss the mechanistic aspects of IC signaling and their impact on immune cells. We give samples how this old technology has been used by practitioners over the last several decades and suggest potential paths for future development of IC-based immune therapy.

Immunoregulatory functions of immune complexes in vaccine and therapy

Clinical and experimental preparations of IgG/soluble antigen complexes, as well as those formed following antibody therapy in vivo, are multifaceted immune regulators. These immune complexes (ICs) have been tested in humans and animal models, mostly in forms of experimental or clinical vaccination, for at least a century. With intensified research on Fcγ receptor-mediated immune modulation, as well as with immune complex-directed antigen processing, presentation, and inflammatory responses, there are renewed interests of using ICs in vaccines and immunotherapies. Currently, IC-based immune therapy has been broadly experimented in HBV and HIV viral infection control and antitumor treatments. However, mechanistic insights of IC-based treatments are relatively recent subjects of study; strong efforts are needed to establish links to connect laboratory findings with clinical practices. This review covers the history, mechanisms, and in vivo outcomes of this safe and effective therapeutic tool, with a clear aim to bridge laboratory findings with evolving clinical applications.

Converting monoclonal antibody-based immunotherapies from passive to active: bringing immune complexes into play

Monoclonal antibodies (mAbs), which currently constitute the main class of biotherapeutics, are now recognized as major medical tools that are increasingly being considered to fight severe viral infections. Indeed, the number of antiviral mAbs developed in recent years has grown exponentially. Although their direct effects on viral blunting have been studied in detail, their potential immunomodulatory actions have been overlooked until recently. The ability of antiviral mAbs to modulate antiviral immune responses in infected organisms has recently been revealed. More specifically, upon recognition of their cognate antigens, mAbs form immune complexes (ICs) that can be recognized by the Fc receptors expressed on different immune cells of infected individuals. This binding may be followed by the modulation of the host immune responses. Harnessing this immunomodulatory property may facilitate improvements in the therapeutic potential of antiviral mAbs. This review focuses on the role of ICs formed with different viral determinants and mAbs in the induction of antiviral immune responses in the context of both passive immunotherapies and vaccination strategies. Potential deleterious effects of ICs on the host immune response are also discussed.

Structural analysis of a novel rabbit monoclonal antibody R53 targeting an epitope in HIV-1 gp120 C4 region critical for receptor and co-receptor binding

The fourth conserved region (C4) in the HIV-1 envelope glycoprotein (Env) gp120 is a structural element that is important for its function, as it binds to both the receptor CD4 and the co-receptor CCR5/CXCR4. It has long been known that this region is highly immunogenic and that it harbors B-cell as well as T-cell epitopes. It is the target of a number of antibodies in animal studies, which are called CD4-blockers. However, the mechanism by which the virus shields itself from such antibody responses is not known. Here, we determined the crystal structure of R53 in complex with its epitope peptide using a novel anti-C4 rabbit monoclonal antibody R53. Our data show that although the epitope of R53 covers a highly conserved sequence (433)AMYAPPI(439), it is not available in the gp120 trimer and in the CD4-bound conformation. Our results suggest a masking mechanism to explain how HIV-1 protects this critical region from the human immune system.

Vaccine therapies for chronic hepatitis B: can we go further?

Chronic hepatitis B is a major health burden worldwide. In addition to the recent progress in antiviral treatment, therapeutic vaccination is a promising new strategy for the control of chronic hepatitis B. On the basis of the major specific and non-specific immune dysregulations and defects in chronic hepatitis B patients, this paper presents the peptide and protein-based, DNA-based, cell-based, and antigen-antibody-based therapeutic vaccines, which have undergone clinical trials. The advantages, disadvantages, and future perspectives for these therapeutic vaccines are discussed.

HIV-specific CD4 T cells and immune control of viral replication

PURPOSE OF REVIEW

To understand the role of HIV-specific CD4 T cells in viral control and highlight recent progress in the field.

RECENT FINDINGS

HIV-specific CD4 T cells show higher functional avidity in elite controllers than in patients with progressive infection. There is an attrition of the HIV-specific CD4 T-cell population in the digestive mucosa of antiretroviral therapy (ART)-treated patients that contrasts with robust responses in individuals with spontaneous viral control. Secretion of the cytokine IL-21, by HIV-specific CD4 T cells, is associated with disease control and enhances the capacity of HIV-specific CD8 T cells to suppress viral replication. Studies of the PD-1, IL-10, and Tim-3 pathways provided insight into mechanisms of HIV-specific CD4 T-cell exhaustion and new evidence that manipulation of these networks may restore immune functions. Robust, polyfunctional CD4 T-cell responses can be elicited with novel HIV and simian immunodeficiency virus (SIV) vaccines.

SUMMARY

These observations show that HIV-specific CD4 T-cell responses are different in elite controllers and individuals with progressive disease. Evidence suggests that HIV-specific CD4 T cells will be an important component of an effective HIV vaccine and significant efforts need to be made to further our understanding of HIV-specific CD4 T-cell functions in different body compartments.

Genome-wide analysis of primary CD4+ and CD8+ T cell transcriptomes shows evidence for a network of enriched pathways associated with HIV disease

BACKGROUND

HIV preferentially infects CD4+ T cells, and the functional impairment and numerical decline of CD4+ and CD8+ T cells characterize HIV disease. The numerical decline of CD4+ and CD8+ T cells affects the optimal ratio between the two cell types necessary for immune regulation. Therefore, this work aimed to define the genomic basis of HIV interactions with the cellular transcriptome of both CD4+ and CD8+ T cells.

RESULTS

Genome-wide transcriptomes of primary CD4+ and CD8+ T cells from HIV+ patients were analyzed at different stages of HIV disease using Illumina microarray. For each cell subset, pairwise comparisons were performed and differentially expressed (DE) genes were identified (fold change >2 and B-statistic >0) followed by quantitative PCR validation. Gene ontology (GO) analysis of DE genes revealed enriched categories of complement activation, actin filament, proteasome core and proton-transporting ATPase complex. By gene set enrichment analysis (GSEA), a network of enriched pathways functionally connected by mitochondria was identified in both T cell subsets as a transcriptional signature of HIV disease progression. These pathways ranged from metabolism and energy production (TCA cycle and OXPHOS) to mitochondria meditated cell apoptosis and cell cycle dysregulation. The most unique and significant feature of our work was that the non-progressing status in HIV+ long-term non-progressors was associated with MAPK, WNT, and AKT pathways contributing to cell survival and anti-viral responses.

CONCLUSIONS

These data offer new comparative insights into HIV disease progression from the aspect of HIV-host interactions at the transcriptomic level, which will facilitate the understanding of the genetic basis of transcriptomic interaction of HIV in vivo and how HIV subverts the human gene machinery at the individual cell type level.

In vitro priming recapitulates in vivo HIV-1 specific T cell responses, revealing rapid loss of virus reactive CD4 T cells in acute HIV-1 infection

BACKGROUND

The requirements for priming of HIV-specific T cell responses initially seen in infected individuals remain to be defined. Activation of T cell responses in lymph nodes requires cell-cell contact between T cells and DCs, which can give concurrent activation of T cells and HIV transmission.

METHODOLOGY

The study aim was to establish whether DCs pulsed with HIV-1 could prime HIV-specific T cell responses and to characterize these responses. Both infectious and aldrithiol-2 inactivated noninfectious HIV-1 were compared to establish efficiencies in priming and the type of responses elicited.

FINDINGS

Our findings show that both infectious and inactivated HIV-1 pulsed DCs can prime HIV-specific responses from naïve T cells. Responses included several CD4(+) and CD8(+) T cell epitopes shown to be recognized in vivo by acutely and chronically infected individuals and some CD4(+) T cell epitopes not identified previously. Follow up studies of acute and recent HIV infected samples revealed that these latter epitopes are among the earliest recognized in vivo, but the responses are lost rapidly, presumably through activation-induced general CD4(+) T cell depletion which renders the newly activated HIV-specific CD4(+) T cells prime targets for elimination.

CONCLUSION

Our studies highlight the ability of DCs to efficiently prime naïve T cells and induce a broad repertoire of HIV-specific responses and also provide valuable insights to the pathogenesis of HIV-1 infection in vivo.

Analysis of the immune responses in chimpanzees infected with HIV type 1 isolates

The mechanisms of resistance to AIDS development in HIV-1-infected chimpanzees have remained elusive. Unique among chimpanzees naturally or experimentally infected with HIV, several animals of the Yerkes cohort have progressed to clinical AIDS with selection of isolates showing increased pathogenicity for chimpanzees. We compared progressors vs. nonprogressors among the HIV-infected chimpanzees that made up this cohort, eight of which have been infected with HIV-1 for over 14 years. The additional two progressors were infected de novo with chimpanzee-pathogenic HIV, rapidly leading to a progressor status. Nonprogressors were characterized by normal CD4(+) T cell counts and the absence of detectable viremia. In contrast, progressor chimpanzees had relatively high plasma viral loads associated with a dramatic loss of CD4(+) T cells. The analysis of immune responses showed a similar amplitude and breadth of ELISPOT T cell responses in both groups. HIV-specific proliferative responses were, however, absent in the progressor animals, which also exhibited increased levels of immune activation characterized by elevated levels of the circulating chemokines IP-10 and MCP-1. Of interest was the conservation of potent NK cell activity in all animals, potentially contributing to the extended symptom-free survival of progressor animals. Modest anti-HIV antibody titers were detectable in the nonprogressor group, but these antibodies exhibited good neutralizing activity. In progressors, however, two sets of data were noted: in animals that gradually selected for pathogenic isolates, or that were superinfected, very high neutralizing antibody titers were observed, although none to the pathogenic HIV. In contrast, two animals infected de novo with chimpanzee pathogenic HIV failed to mount an extensive humoral response and both failed to develop neutralizing antibodies to the virus. Taken together, pathogenic HIV infection in chimpanzees is associated with rapid loss of CD4(+) T cells and proliferative responses as well as higher levels of immune activation.

Epitope Enhancement of a CD4 HIV Epitope toward the Development of the Next Generation HIV Vaccine

Virus-specific CD4+ T cell help and CD8+ cytotoxic T cell responses are critical for maintenance of effective immunity in chronic viral infections. The importance of CD4+ T cells has been documented in HIV infection. To investigate whether a stronger CD4+ T cell response can be induced by modifications to enhance the T1 epitope, the first CD4+ T cell epitope discovered in HIV-1-gp120, we developed a T1-specific CD4+ T cell line from a healthy volunteer immunized with a canarypox vector expressing gp120 and boosted with recombinant gp120. This T1-specific CD4+ T cell line was restricted to DR13, which is common in U.S. Caucasians and African-Americans and very frequent in Africans. Peptides with certain amino acid substitutions in key positions induced enhanced specific CD4+ T cell proliferative responses at lower peptide concentration than the original epitope. This relatively conserved CD4 epitope improved by the epitope enhancement strategy could be a component of a more effective second generation vaccine construct for HIV infection.

Generating neutralizing antibodies, Th1 response and MHC non restricted immunogenicity of HIV-I env and gag peptides in liposomes and ISCOMs with in-built adjuvanticity

For enhancing immunogenicity and develop vaccine strategies using peptide based constructs against HIV-1, a chimeric peptide containing V3 loop and transmembrane sequence of gp41 with two glycine motifs as spacer was constructed. The V3-gp41, gp41 peptide and p17 and p24 peptides separately or in a cocktail were entrapped with or without MA729 as an immunoadjuvant in liposomes or ISCOMs. The immunogenicity, antigen induced T-cell proliferation and cytokine profiles of various formulations were studied in four different inbred strains of mice of H-2^d, H-2^b, H-2^k and H-2^q haplotypes, keeping alum as a control adjuvant. Both liposomes and ISCOM preparations elicited high titer and long lasting antibody response (60 days and above). When compared to the alum formulation, the liposomes co-entrapped with MA729 produced high antibody levels, comparable with that induced by ISCOMs. Peptide in alum, liposomes and ISCOMs enhanced both antigen specific IgG2a and IgG2b isotypes and high T-cell stimulation index. Peptide formulations also induced antibodies with high affinity and in vitro neutralizated the formation of HIV-1 syncytia. T-cell supernatants contained high levels of IFN-γ and IL-2. Thus formulation in these adjuvants induced a predominant Th1 like response with MA729 as a versatile novel delivery vehicle for stimulating the appropriate arm of the immune response that can selectively modulate MHC class I or MHC class II response. The above peptide can be of wide vaccination interest as a means to improve immune responses to several other HIV-1 antigens and may serve as candidates for vaccine development.

Early induction and maintenance of Env-specific T-helper cells following human immunodeficiency virus type 1 infection

Mounting evidence points to a role for CD4+ T-helper (Th) cell activities in controlling human immunodeficiency virus type 1 (HIV-1) infection. To determine the induction and evolution of Th responses following acute infection, we prospectively analyzed Env- and Gag-specific Th responses longitudinally for 92 patients with acute (n = 28) or early (n = 64) HIV-1 infection (median, 55 days postinfection [DPI]). The probability of detecting HIV-1-specific lymphoproliferative responses was remarkably low, and when present, the responses were more likely to be Gag specific than Env specific (16 versus 5%). Env-specific responses were significantly more common in patients presenting at <30 DPI than in those presenting at 30 to 365 DPI (21 versus 0.5%, P = 0.001). By contrast, Gag-specific responses occurred with similar frequencies among subjects presenting at <30 DPI and 30 to 365 DPI (13 versus 17%, P = 0.6). After treatment, and regardless of the duration of infection before therapy, Gag-specific Th responses predominated. Furthermore, some acutely infected subjects lost detectable Env-specific Th proliferative responses, which failed to reemerge upon treatment. Detailed analysis for one such subject revealed Env-specific lymphoproliferation at 11 DPI but no detectable Env-specific lymphoproliferation or ex vivo gamma interferon (IFN-gamma) secretion at multiple subsequent time points. Env-specific CD4+ T-cell clones from 11 DPI recognized six epitopes in both conserved and variable regions within gp120 and gp41, exhibited major histocompatibility complex-restricted cytotoxicity, and secreted high levels of antiviral cytokines. T-cell receptor clonal transcript analyses and autologous virus sequencing revealed that Th cells induced during acute infection were maintained and there were no Th escape mutations. Subsequent analysis for this subject and six of seven others revealed detectable IFN-gamma-secreting cells, but only following in vitro gp160 stimulation. In summary, we conclude that Env-specific Th responses are elicited very early in acute infection and may precede Gag-specific responses. The inability to detect Env-specific Th responses over time and despite antiretroviral therapy may reflect low frequencies and impaired proliferative capacity, and viral escape is not necessary for this to occur.

A balanced type 1/type 2 response is associated with long-term nonprogressive human immunodeficiency virus type 1 infection

Previous reports have emphasized the requirements for strong type 1 cell-mediated responses in the control of human immunodeficiency virus type 1 (HIV-1). HIV-1 Gag p24-specific CD4 helper T-lymphocyte (HTL) responses have been shown to inversely correlate with viral burden in HIV-1-infected individuals. In this study, peripheral blood mononuclear cells from 70 individuals with chronic progressive HIV-1 infection (clinical progressors), 10 clinical nonprogressors, and 3 immunologically discordant progressors were assessed for HTL proliferation and type 1/type 2 cytokine production. Clinical progressors lacked functional HIV-1-specific HTLs with proliferative and cytokine-producing capacity. Clinical nonprogressors were found to respond to a wide range of HIV-1 antigens from different clades, producing both type 1 and type 2 cytokines. Immunologically discordant progressors responded strongly to clade B Gag p24 with a type 1 cytokine profile but not to other antigens. Thus, in contrast to clinical nonprogressors, neither progressors nor immunologically discordant progressors secreted interleukin-4 (IL-4) in response to HIV-1 antigens. Both clinical nonprogressors and immunologically discordant progressors responded broadly to B clade Gag p24-overlapping peptides. However, IL-4 production in the nonprogressors was restricted to a limited number of p24 peptides. No HIV-1-specific T-cell responses were seen in 20 seronegative controls. Additionally, we observed a rapid type 1 to type 2 shift in the response of one immunologically discordant progressor upon onset of clinical symptoms. These results suggest that a balanced type 1/type 2 profile correlates with successful long-term control of HIV-1.

Discordance between frequency of human immunodeficiency virus type 1 (HIV-1)-specific gamma interferon-producing CD4(+) T cells and HIV-1-specific lymphoproliferation in HIV-1-infected subjects with active viral replication

One hallmark of uncontrolled, chronic human immunodeficiency virus type 1 (HIV-1) infection is the absence of strong HIV-1-specific, CD4(+) T-cell-proliferative responses, yet the mechanism underlying this T helper (Th)-cell defect remains controversial. To better understand the impact of HIV-1 replication on Th-cell function, we compared the frequency of CD4(+) Th-cell responses based on production of gamma interferon to lymphoproliferative responses directed against HIV-1 proteins in HIV-1-infected subjects with active in vivo viral replication versus those on suppressed highly active antiretroviral therapy (HAART). No statistically significant differences in the frequencies of cytokine-secreting, HIV-1-specific CD4(+) T cells between the donor groups were found, despite differences in viral load and treatment status. However, HIV-1-specific lymphoproliferative responses were significantly greater in the subjects with HAART suppression than in subjects with active viral replication. Similar levels of HIV-1 RNA were measured in T-cell cultures stimulated with HIV-1 antigens regardless of donor in vivo viral loads, but only HIV-1-specific CD4(+) T cells from subjects with HAART suppression proliferated in vitro, suggesting that HIV-1 replication in vitro does not preclude HIV-1-specific lymphoproliferation. This study demonstrates a discordance between the frequency and proliferative capacity of HIV-1-specific CD4(+) T cells in subjects with ongoing in vivo viral replication and suggests that in vivo HIV-1 replication contributes to the observed defect in HIV-1-specific CD4(+) T-cell proliferation.

Detailed analysis of CD4+ Th responses to envelope and Gag proteins of simian immunodeficiency virus reveals an exclusion of broadly reactive Th epitopes from the glycosylated regions of envelope

Ag-specific CD4(+) Th cells play a key role in the development, maturation, and maintenance of pathogen-specific humoral and cellular immune responses. To define the fine specificity of broadly reactive Th responses associated with mature immunity in a lentiviral system, we analyzed peptide-specific Th responses in eight macaques chronically infected with a reference live attenuated SIV at 12-14 mo postinoculation. All macaques had stable immunocompetent Th cells at the time of analysis, and a unique array of Th responses to 20-mer overlapping peptides from envelope (Env) and Gag was identified for each macaque, which were then used to define a set of 31 broadly reactive peptide epitopes. Only 5 of the 31 broadly reactive Th epitope peptides mapped to the surface (SU) domain of Env. Interestingly, these were all confined to two conserved nonglycosylated regions toward the carboxyl terminus of SU, suggesting a structural influence of glycosylation on development of Th responses. Gag and the Env transmembrane proteins contained the majority of broadly reactive peptide epitopes (12 and 14 peptides, respectively), which were uniformly distributed throughout their sequence. This study defines for the first time broadly reactive Th epitope peptides of SIV Env and Gag proteins that are associated with enduring broadly protective vaccine immunity to attenuated SIV, which may be used for the design and evaluation of experimental vaccines. Moreover, the data suggest that extensive glycosylation of SU may provide yet another immune escape mechanism developed by lentiviruses to restrict the breadth of Th repertoire to SU, a major immunologically exposed protein of the virus.

Immune reconstitution in HIV-1-infected individuals treated with potent antiretroviral therapy

Potent combination antiretroviral therapy that was introduced in the mid-1990s for treatment of HIV-1 infection has resulted in unprecedented decreases in HIV-1 replication and increases in CD4+ T cell counts in many individuals. Coincident with the introduction of potent combination antiretroviral therapy, substantial declines in AIDS-related morbidity and mortality have been observed. Although these declines strongly suggest that significant immune reconstitution is occurring, increasing evidence suggests that immune reconstitution is neither uniform nor complete in all treated individuals. Clinical data suggest that some HIV-1-associated malignancies have not declined despite the new therapies, and that not all treated individuals reconstitute CD4+ T cell numbers to normal values. Laboratory studies reveal that immune responses to ubiquitous antigens are reconstituted, but that responses to rarely encountered antigens, such as tetanus, are not reconstituted without repeat vaccination. Many questions remain concerning the extent and clinical significance of the immune reconstitution that occurs in the setting of antiretroviral drug therapy. A better understanding of the nature of the immune reconstitution that results from potent antiretroviral therapy is critical to the optimal clinical management of HIV-1-infected individuals, and may provide important insights into the immunopathogenesis of HIV-1 infection as well.

Immune responses and reconstitution in HIV-1 infected individuals: impact of anti-retroviral therapy, cytokines and therapeutic vaccination

Most patients with chronic HIV-1 infection lack functional CD4(+) and CD8(+) HIV-1-specific T cells with proliferative and cytolytic capacity, respectively. This is despite being able to produce intracellular cytokines in response to viral antigens. Protease inhibitor (PI)-based highly active anti-retroviral therapy (HAART) is unable to completely eradicate virus and fails to enable total restoration of immunity including induction of anti-HIV-1 responses. We have taken novel approaches towards the treatment of chronic HIV-1 disease with the aim of instigating long-term non-progressor status and depletion of virus reservoirs. HIV-1-specific CD4(+) and CD8(+) T cell responses were measured following the administration of cytokines, during therapeutic vaccination, and following treatment interruption (TI) or drug therapy change. Administration of cytokines, with or without therapeutic vaccination, in HAART treated patients, improved both CD4(+) and CD8(+) HIV-1-specific T cell responses even in late-stage disease. Virus-specific T cell responses were also seen during TI or when transient viraemia was apparent, and following therapy change from a PI- to a non-nucleoside-based HAART regimen. Reconstitution of HIV-1-specific immune responses was found to be transient and reversal to the previous anergic state was rapid. Viral reservoirs in the latently infected resting CD4(+) T cells, on follicular dendritic cells of germinal centers or even in infected thymic epithelium may be involved in clonal suppression and anergy. These may present major obstacles to the maintenance of HIV-1-specific responses and the eventual eradication of HIV-1.

Detection and quantification of HIV-1 specific CD4 helper and CD8 cytotoxic cells: their role in HIV-1-infected individuals and vaccine recipients

There is a strong link between virus specific CD8 T-cell function and the efficiency of regulatory CD4 helper T cells. Controlling viraemia in HIV-1-infected individuals requires the maintenance of strong CD4 and CD8 T-cell responses. These responses should be elicited by prophylactic vaccination and by postexposure immunotherapy. This review will examine the methods that are available for the detection and quantification of HIV-1 specific CD4 and CD8 T-cell responses. We will also discuss the methods that should be used to identify these responses in HIV-1-infected individuals, seropositive recipients of immunotherapy and seronegative vaccinees. Finally, we will give examples of how responses observed in vitro relate to those known to occur in vivo.

Localization of CD4+ T cell epitope hotspots to exposed strands of HIV envelope glycoprotein suggests structural influences on antigen processing

The spectrum of immunogenic epitopes presented by the H2-IA(b) MHC class II molecule to CD4(+) T cells has been defined for two different (clade B and clade D) HIV envelope (gp140) glycoproteins. Hybridoma T cell lines were generated from mice immunized by a sequential prime and boost regime with DNA, recombinant vaccinia viruses, and protein. The epitopes recognized by reactive T cell hybridomas then were characterized with overlapping peptides synthesized to span the entire gp140 sequence. Evidence of clonality also was assessed with antibodies to T cell receptor Valpha and Vbeta chains. A total of 80 unique clonotypes were characterized from six individual mice. Immunogenic peptides were identified within only four regions of the HIV envelope. These epitope hotspots comprised relatively short sequences ( approximately 20-80 aa in length) that were generally bordered by regions of heavy glycosylation. Analysis in the context of the gp120 crystal structure showed a pattern of uniform distribution to exposed, nonhelical strands of the protein. A likely explanation is that the physical location of the peptide within the native protein leads to differential antigen processing and consequent epitope selection.

Development of virus-specific immune responses in SHIV(KU)-infected macaques treated with PMPA

Therapeutic intervention with highly active antiretroviral therapy (HAART) can lead to the suppression of HIV viremia below the threshold of detection for several years. However, impact of HAART on reconstitution of virus-specific immune responses remains poorly understood. In this study, four macaques were infected with pathogenic SHIV(KU). One week postinoculation two of the four animals were treated with PMPA [9-R-(2-phosphophomethoxypropyl)adenine] daily for 83 days. Two other macaques, that did not receive treatment, exhibited explosive virus replication accompanied by a near total loss of CD4(+) T cells and succumbed to AIDS-related complications within 6 months of infection. These animals did not develop any virus-specific immune responses. On the contrary, the animals that received PMPA showed transient loss of CD4(+) T cells that recovered during the treatment period. The virus burden declined below the level of detection that rebounded soon after cessation of PMPA therapy. The virus replicated productively for several weeks before both animals controlled the productive replication of virus. This control of virus replication was found to be associated with the development of virus-specific neutralizing antibodies, T-helper cells, and CTLs. Although PMPA did not eliminate virus from the animals, it provided them with enough time to mount virus-specific immune responses that eventually controlled the virus replication in the blood. Our results suggest that antiretroviral therapy, if initiated early during infection, would help the host in mounting virus-specific immune responses that might control productive replication of the virus.

Prolonged dominance of clonally restricted CD4(+) T cells in macaques infected with simian immunodeficiency viruses

The repertoire of functional CD4(+) T lymphocytes in human immunodeficiency virus type 1-infected individuals remains poorly understood. To explore this issue, we have examined the clonality of CD4(+) T cells in simian immunodeficiency virus (SIV)-infected macaques by assessing T-cell receptor complementarity-determining region 3 (CDR3) profiles and sequences. A dominance of CD4(+) T cells expressing particular CDR3 sequences was identified within certain Vbeta-expressing peripheral blood lymphocyte subpopulations in the infected monkeys. Studies were then done to explore whether these dominant CD4(+) T cells represented expanded antigen-specific cell subpopulations or residual cells remaining in the course of virus-induced CD4(+) T-cell depletion. Sequence analysis revealed that these selected CDR3-bearing CD4(+) T-cell clones emerged soon after infection and dominated the CD4(+) T-cell repertoire for up to 14 months. Moreover, inoculation of chronically infected macaques with autologous SIV-infected cell lines to transiently increase plasma viral loads in the monkeys resulted in the dominance of these selected CDR3-bearing CD4(+) T cells. Both the temporal association of the detection of these clonal cell populations with infection and the dominance of these cell populations following superinfection with SIV suggest that these cells may be SIV specific. Finally, the inoculation of staphylococcal enterotoxin B superantigen into SIV-infected macaques uncovered a polyclonal background underlying the few dominant CDR3-bearing CD4(+) T cells, demonstrating that expandable polyclonal CD4(+) T-cell subpopulations persist in these animals. These results support the notions that a chronic AIDS virus infection can induce clonal expansion, in addition to depletion of CD4(+) T cells, and that some of these clones may be SIV specific.

The role of CD4(+) T helper cells in the cytotoxic T lymphocyte response to HIV-1

Virus-specific CD4(+) T cell help and CD8(+) cytotoxic T cell (CTL) responses are critical for the maintenance of effective immunity in chronic viral infections. HIV-1 infection presents a unique situation in which HIV-1-specific T helper cell responses are characteristically impaired and virus-specific CTLs wane over time as disease progresses; a relationship exists between T cell help and CTL responses in HIV-1 infection.

Approaches to improve engineered vaccines for human immunodeficiency virus and other viruses that cause chronic infections

We used several approaches to develop enhanced vaccines for chronic viral infections such as human immunodeficiency virus (HIV) and hepatitis C virus (HCV). 1) Selected epitopes were used to avoid potentially harmful immune responses. 2) Linkage between helper and cytotoxic T-lymphocyte (CTL) epitopes was found to be important. 3) We developed an "epitope enhancement" approach modifying the sequences of epitopes to make more potent vaccines, including examples for HIV and HCV epitopes presented by murine class II and human class I major histocompatibility complex (MHC) molecules. 4) CTL avidity was found to be important for clearing viral infections in vivo, and the mechanism was examined. High-avidity CTLs, however, were found to undergo apoptosis when confronted with high-density antigen, through a mechanism involving tumor necrosis factor (TNF), TNF-RII, and a permissive state induced through the T-cell receptor. 5) We employed cytokines in the adjuvant to steer immune responses toward desired phenotypes, and showed synergy between cytokines. 6) Intrarectal immunization with peptide vaccine induced mucosal and systemic CTL. Local mucosal CTL were found to be critical for resistance to mucosal viral transmission and this resistance was enhanced with mucosally delivered interleukin-12. 7) We used an asymmetry in induction of mucosal and systemic immune responses to circumvent pre-existing vaccinia immunity for use of recombinant vaccinia vaccines.

Effects of IL-2 therapy in asymptomatic HIV-infected individuals on proliferative responses to mitogens, recall antigens and HIV-related antigens

The effects of IL-2 therapy on lymphoproliferative responses to mitogens, recall antigens and HIV epitopes were studied in asymptomatic HIV-infected patients enrolled in a phase II study of intermittent continuous intravenous (Ci.v.) IL-2 and subcutaneous infusions of polyethylene glycol-modified (PEG) IL-2. Sixteen consecutive patients randomized to receive Ci.v. IL-2 (n = 5), PEG IL-2 (n = 7) or anti-viral therapy alone (n = 4) were studied. All patients were vaccinated with tetanus toxoid (TT) before receiving therapy. Proliferative responses to phytohaemagglutinin (PHA), soluble anti-CD3, TT, streptokinase/streptodornase (SK/SD) and 11 previously described HIV-specific T-helper epitopes from gag and env were studied at weeks 0, 16, 30 and 48. Median CD4+ lymphocyte increases of 272 and 255CD4+ cells/microl were observed in the Ci.v. IL-2 and PEG IL-2 groups at week 48, while decreasing by 104 cells/microl in the anti-retroviral therapy alone group. At each time point proliferative responses to PHA, anti-CD3, TT and SK/SD were not different between treatment arms. Similarly, no differences in responses to HIV epitopes were found between the groups and no new responses to HIV epitopes were detected. IL-2 therapy results in a significant increase in peripheral blood CD4+ lymphocyte count, but this increase is not associated with quantifiable improvements in lymphoproliferative responses to mitogens, recall or HIV antigens.

Active immunization of patients with HIV infection: a study of the effect of VaxSyn, a recombinant HIV envelope subunit vaccine, on progression of immunodeficiency

Infection with the human immunodeficiency virus (HIV) leads to a progressive immunodeficiency characterized by decreasing levels of CD4+ T lymphocytes. VaxSyn, a vaccine based on the recombinant envelope glycoprotein subunit (rgp160) of HIV-1IIIB, was used to immunize HIV-infected patients to determine whether its administration was beneficial with respect to slowing disease progression. A 3-year multicenter, randomized, placebo-controlled, double-blinded, efficacy and safety trial of repeated immunization with VaxSyn was used to evaluate the long-term impact on the progression of immunodeficiency. VaxSyn in alum, or alum alone, was given to 278 HIV-infected asymptomatic individuals with initial CD4 counts of > or =500 cells/mm3. Clinical findings, the CD4 count, and both virological and immunological parameters were followed. No significant differences were observed between the treatment and placebo control groups in rate of CD4 T cell decline, time to initiation of antiretroviral therapy, incidence of opportunistic infections, HIV RNA plasma viremia, HIV viral infectivity as measured by quantitative HIV coculture assay, and death. This study revealed no effect on either clinical or laboratory virological parameters from the administration of VaxSyn.

Intracellular cytokine expression in the CD4+ and CD8+ T cells from intestinal mucosa of simian immunodeficiency virus infected macaques

Isolated intraepithelial lymphocytes (IEL) and lamina propria lymphocytes (LPL) from jejunum of SIV infected animals were examined for alterations in basal cytokine expression by RT-PCR. Remarkable changes in IFNgamma and IL-10 RNA levels were observed in IEL and LPL in SIV infection while IL-4 and IL-2 RNA levels remained unaltered. In addition, the CD4+ and CD8+ LPL were examined for intracellular cytokine production following mitogenic activation by flowcytometry. Both CD4+ and CD8+ T lymphocytes in intestinal mucosa retained the potential to produce IFNgamma in response to mitogenic stimulation in vitro, without a remarkable change in IL-4 production. The dominant IFNgamma cytokine response could be one of the major contributing factors in SIV associated enteropathy.

Vigorous HIV-1-specific CD4+ T cell responses associated with control of viremia

Virus-specific CD4+ T helper lymphocytes are critical to the maintenance of effective immunity in a number of chronic viral infections, but are characteristically undetectable in chronic human immunodeficiency virus-type 1 (HIV-1) infection. In individuals who control viremia in the absence of antiviral therapy, polyclonal, persistent, and vigorous HIV-1-specific CD4+ T cell proliferative responses were present, resulting in the elaboration of interferon-gamma and antiviral beta chemokines. In persons with chronic infection, HIV-1-specific proliferative responses to p24 were inversely related to viral load. Strong HIV-1-specific proliferative responses were also detected following treatment of acutely infected persons with potent antiviral therapy. The HIV-1-specific helper cells are likely to be important in immunotherapeutic interventions and vaccine development.

Enhanced immunogenicity of HIV-1 vaccine construct by modification of the native peptide sequence

Viral proteins are not naturally selected for high affinity major histocompatibility complex (MHC) binding sequences; indeed, if there is any selection, it is likely to be negative in nature. Thus, one should be able to increase viral peptide binding to MHC in the rational design of synthetic peptide vaccines. The T1 helper peptide from the HIV-1 envelope protein was made more immunogenic for inducing T cell proliferation to the native sequence by replacing a residue that exerts an adverse influence on peptide binding to an MHC class II molecule. Mice immunized with vaccine constructs combining the more potent Th helper (Th) epitope with a cytotoxic T lymphocyte (CTL) determinant developed greatly enhanced CTL responses. Use of class II MHC-congenic mice confirmed that the enhancement of CTL response was due to class II-restricted help. Thus, enhanced T cell help is key for optimal induction of CTL, and, by modification of the native immunogen to increase binding to MHC, it is possible to develop second generation vaccine constructs that enhance both Th cell activation and CTL induction.

Relationship between antigenicity and immunogenicity of chimeric hepatitis B virus core particles carrying HIV type 1 epitopes

We have developed a comparative study of antigenic and immunogenic properties of selected immunodominant HIV-1 epitopes from p24 and gp120 proteins added to C-terminally truncated hepatitis B virus (HBV) core protein and exposed on the surface of chimeric core particles. Inserted p24 (121-210) and gp120/MN (306-328) epitopes induced the appropriate humoral and cellular immune responses against HIV-1. Superficially exposed region 160-192 of p24 also showed maximal B cell immunogenicity whereas buried region 148-162 induced maximal T cell response. Both recombinant proteins were also able to be recognized in vitro by T lymphocytes of HIV-1 asymptomatic carriers.

Prediction of HIV peptide epitopes by a novel algorithm

Identification of promiscuous or multideterminant T cell epitopes is essential for HIV vaccine development, however, current methods for T cell epitope identification are both cost intensive and labor intensive. We have developed a computer-driven algorithm, named EpiMer, which searches protein amino acid sequences for putative MHC class I- and/or class II-restricted T cell epitopes. This algorithm identifies peptides that contain multiple MHC-binding motifs from protein sequences. To evaluate the predictive power of EpiMer, the amino acid sequences of the HIV-1 proteins nef, gp160, gag p55, and tat were searched for regions of MHC-binding motif clustering. We assessed the algorithm's predictive power by comparing the EpiMer-predicted peptide epitopes to T cell epitopes that have been published in the literature. The EpiMer method of T cell epitope identification was compared to the standard method of synthesizing short, overlapping peptides and testing them for immunogenicity (overlapping peptide method), and to an alternate algorithm that has been used to identify putative T cell epitopes from primary structure (AMPHI). For the four HIV-1 proteins analyzed, the in vitro testing of EpiMer peptides for immunogenicity would have required the synthesis of fewer total peptides than either AMPHI or the overlapping peptide method. The EpiMer algorithm proved to be more efficient and more sensitive per amino acid than both the overlapping peptide method and AMPHI. The EpiMer predictions for these four HIV proteins are described. Since EpiMer-predicted peptides have the potential to bind to multiple MHC alleles, they are strong candidates for inclusion in a synthetic HIV vaccine.

Statistical comparison of established T-cell epitope predictors against a large database of human and murine antigens

Identification of T-cell epitopes within a protein antigen is an important tool in vaccine design. The T-cell epitope prediction schemes often are exploited by workers but have proved unreliable in comparison with experimental techniques. We compared published T-cell epitope predictors against two databases of human and murine T-cell epitopes. Each predictor was assessed against random cyclic permutations of epitopes in order to determine significance. Predictor performance was expressed in terms of two parameters, specificity and sensitivity. Specificity is an expression of the quality of predictions, whereas sensitivity is an expression of the quantity of epitopes predicted. Against the human data set, the strip-of-hydrophobic helix algorithm [Stille et al., Molec. Immun. 24, 1021-1027 (1987)] was the only significant predictor (p < 0.05), whereas against murine data only, the Roth2 pattern [Rothbard and Taylor, EMBO J. 7, 93-100 (1988)] was significant (p < 0.05). Not only were the majority of algorithms no better than random against both data sets, against the murine data two schemes were significant (p < 0.05) anti-predictors. This report indicates which predictors are relevant statistically and is the first to describe anti-predictors which can themselves be useful in the identification of T-cell epitopes.

Kernel density analysis of variable and conserved regions of the envelope proteins of human immunodeficiency virus type 1 and associated epitopes

A new statistical approach to the study of conservation of amino acid and nucleotide sequences based on kernel density analysis is described that enables analysis of both conserved and highly variable HIV-1 protein sequences. The amino acid sequences of HIV-1 env proteins in 63 isolates were analysed to determine, first, whether the designations of regions identified in 1987 as conserved (C1-C6) or variable (V1-V5) were still valid. Even though the data base used was nine times larger, the designations that were based on seven isolates from five patients remain correct. Second, the new approach enabled the quantifications of the degree of conservation in reported B or T cell epitopes. Using this approach, highly conserved epitopes located in both gp41 and gp120 were identified.

Recombinant gp160 vaccination schedule and MHC HLA type as factors influencing cellular responses to HIV-1 envelope glycoprotein. NIAID AIDS Vaccine Clinical Trials Network

This study assessed (1) T-cell responses following vaccination of HIV-1 negative volunteers with HIV-1LAI recombinant gp160 (rgp160) vaccine, and (2) effects of vaccine injection schedule and MHC HLA type on those responses. In one trial, volunteers received rgp160 in two accelerated schedules (Groups 1 and 2). In the other trial, volunteers received rgp160 vaccine at 0, 1, 6, and 12 months and some received vaccine at 18 months (Groups 3 and 4). Peripheral blood mononuclear cells (PBMC) from vaccinees in Groups 3 and 4 were stimulated by more peptides representing envelope glycoprotein T-cell epitopes than Groups 1 and 2 (p = 0.01). Transient anti-envelope glycoprotein CTL activity was more frequently detectable in Groups 1 and 2 (p = 0.03). MHC HLA-Cw7, DR1 and DQw1 alleles appeared to be associated with PBMC responses to envelope glycoprotein.

Immunogenic targeting of recombinant peptide vaccines to human antigen-presenting cells by chimeric anti-HLA-DR and anti-surface immunoglobulin D antibody Fab fragments in vitro

To increase the inherently weak immunogenicity of synthetic peptide vaccines, we used recombinant DNA techniques to generate chimeras between immunogenic determinants of human immunodeficiency virus type 1 (HIV-1) gp120 and antibody Fab fragments reactive with surface structures displayed specifically on human antigen-presenting cells (APCs), including surface immunoglobulin D (sIgD) and class II major histocompatibility complex (MHC) molecules. Hybridomas producing anti-human MHC class II (HLA-DR) or surface immunoglobulin D monoclonal antibodies (MAbs) that recognize nonpolymorphic determinants were used to clone chimeric Fab gene fragments by employing an established procedure to generate antigen-binding Fab libraries in phagemid vector pComb3. Molecular and immunochemical analysis indicated that the expected chimeric Fab fragments expressing the HIV-1 epitopes were correctly cloned and expressed in Escherichia coli and retained the binding specificity of the native (hybridoma-derived) MAb. The chimeric Fab fragments targeted the linked HIV-1-derived antigenic determinants to the surface of human APCs in vitro, as evidenced by fluorescence-activated cell sorter analysis. Furthermore, such recombinant immunotargeted HIV-1 peptide antigens demonstrated improved immunogenicity over equivalent nonimmunotargeted control antigens, as shown by their ability to stimulate interleukin-2 production by CD4+ T-helper cells from human donors exposed to HIV-1 antigens. These data suggest that immunotargeting of recombinant peptide antigens via the attached Fab fragments facilitates uptake by human APCs with subsequent access to the MHC class II processing pathway, thereby validating the immunotargeting concept for such recombinant subunit vaccines in an in vitro human system.

Synthetic peptides representing sequences within gp41 of HIV as immunogens for murine T- and B-cell responses

Within the gp41 glycoprotein of the human immunodeficiency virus type 1 (HIV-1) there is a relatively conserved region which appears accessible to the immune system during the course of HIV infection and is recognised by antibody from virtually all patients with AIDS. This region has also been shown to function as a target for human T cells. We have examined synthetic peptides spanning this sequence, between residues 572 and 604, with a view to evaluating their potential as immunogens. Peptides 572GIKQLQARILAVERYLKDQQ591 and 579RILAVERYLKDQQLLGGIWGCSGK601 were good immunogens in two different strains of mice while peptide 576LQARILAVERYLKDQQ591 was an inferior immunogen, and peptide 593LGIWGCSGKLIC604 was non-immunogenic unless coupled to a carrier protein. For both antibody and T cell responses it was apparent that sequences that could function as determinants within one peptide could not do so in the context of a different peptide immunogen. It follows that by judicious choice of immunogen sequence it may be possible to direct the immune response towards a desired fine specificity. Unwanted responses by CD4+ T cells isolated from certain peptide-primed animals were also observed. These T cells showed an unusual reactivity in that they were incapable of recognising their determinant AVERYLKDQQ if it was extended at the C-terminal end with the native sequence and as such would not be expected to recognise the native molecule unless processing created the identical C-terminus.

Nef and Gag synthetic peptide priming of antibody responses to HIV type 1 antigens in mice and primates

T epitope mapping in human immunodeficiency virus proteins provides a useful tool for AIDS vaccine design. We have previously shown that four peptides selected from the Gag polyprotein of HIV-1 were able to prime mice for in vitro lymphoproliferative responses. These responses were shown to be MHC restricted, and a pool of these peptides was able to prime mice for a subsequent humoral response to HIV-1 Gag proteins. Here we show that two of these Gag peptides are able to prime the anti-HIV-1 IgG response to heat-inactivated HIV-1 in B10Sc.Cr mice. Furthermore, we extended this study in the nonhuman primate model, and show efficient priming of the IgG response to heat-inactivated HIV-1 using the pool of four Gag peptides in baboons. Further mapping of "nonself" peptides is extended to the HIV-1 Nef protein. Three potential Nef T epitopes located at positions 137-145, 98-107, and 81-95 are also shown to prime the IgG response to HIV-1 in the mouse model, although T cell proliferation to recall peptides in vitro was not detectable. Although they have not yet been defined as major helper T epitopes in humans, using classic in vitro stimulation assays, the fact that most of them are able to prime IgG responses in animals without detectable in vitro proliferative responses does not rule out their functional helper capacity in humans.

Human T-helper cell recognition of an immunodominant epitope of HIV-1 gp120 expressed on the surface of Streptococcus gordonii

Our genetic system for expression of heterologous proteins on the surface of the Gram-positive bacterium Streptococcus gordonii was used to express a human T-helper epitope of HIV-1 envelope glycoprotein gp120. In previous work on the naive repertoire of human T-helper cells, it was shown that a 15-amino acid synthetic peptide of the HIV-1 gp120 sequence contained an immunodominant T-helper epitope. Synthetic DNA coding for this peptide was cloned in frame within the gene for the streptococcal surface protein M6, and the gene fusion was integrated by transformation into the chromosome of S. gordonii. The expected M6-gp120 fusion protein was found to be expressed on the surface of the recombinant streptococci. To test whether the T epitope could be recognized by T cells when expressed on the bacterial surface within the context of M6, recombinant bacteria were used as antigen in proliferation assays to stimulate the 15-amino acid-specific human T-helper clone, in the presence of autologous antigen-presenting cells. Bacteria expressing the T epitope were efficiently recognized by the T cells in culture. In proliferation assays, 10(6)-10(7) bacteria induced responses comparable to those obtained by standard amounts of synthetic peptide (0.02-0.2 micrograms). Recombinant S. gordonii, a candidate for a live vaccine vector, appeared suitable for delivering T epitopes to the immune system.

Binding of glycoprotein 120 and peptides from the HIV-1 envelope by autoantibodies in mice with experimentally induced systemic lupus erythematosus and in patients with the disease

Systemic lupus erythematosus (SLE) and infection with the human immunodeficiency virus type 1 (HIV) are diseases that are characterized by immune dysregulation and autoantibody production. In this article we identify and characterize IgG antibodies from mice with SLE and SLE patients that bind HIV gp120 and HIV envelope-derived peptides. SLE can be induced in susceptible mouse strains by immunization with a human monoclonal anti-DNA antibody that bears a common idiotype designated 16/6 Id. We tested sera from various strains of mice in which experimental SLE was induced by this method, as well as from 93 patients with SLE and 31 controls (17 healthy controls, 14 patients with other autoimmune diseases) for the presence of antibodies reactive to gp120 by an ELISA. Antibodies reactive with gp120 were produced by BALB/c, C3H.SW, AKR, and DBA/2 mice, all of which were 16/6 Id immunized and had experimental SLE. C57BL/6 mice, which are resistant to induction of SLE by this method, did not produce antibodies reactive with gp120 despite 16/6 immunization. Forty-three percent of SLE patients made antibodies that bound to gp120 at titers greater than 1:40, whereas 12% of healthy control sera (p < or = 0.02) and 14% of patients with other autoimmune diseases contained such antibodies (p < or = 0.05). We delineated the specificity of this antibody activity by testing for reactivity to six HIV envelope peptides. In both mice and SLE patients, sera reactive with gp120 recognized the same three envelope peptides. Removal of the anti-DNA antibodies from the sera by DNA-agarose affinity purification did not change anti-gp120 specificity.

Kinetics and specificities of the T helper-cell response to gp120 in the asymptomatic stage of HIV-1 infection

Peripheral blood mononuclear cells from 36 asymptomatic HIV-1 seropositive individuals were tested longitudinally for in vitro T-cell proliferation and IL-2 production in response to synthetic peptides spanning the entire gp120 of HIV-1. At baseline, significant T-cell proliferative to pooled and individual peptides was observed in 15 of the 36 donors. After 12 months, proliferative responses to peptide pools were lost or decreased significantly in most donors. Responses appeared to fluctuate over time: at 12 months new recognition sites were detected in four of 10 donors showing T-cell proliferation at baseline, as well as in five of 15 donors with no previous proliferative responses. IL-2 production appeared to be a more sensitive and longer preserved parameter of T-helper cell function: at baseline the majority of donors with no T-cell proliferation produced IL-2 in response to pooled peptides. This response was not decreased significantly after 12 months. The overall patterns of response to both pooled and individual peptides were heterogeneous among donors. Multiple recognition sites were detected in both variable and conserved regions of gp120, but no pool or individual peptide was recognized by all responders. Functional T-cell responses were not statistically correlated to CD4+ cell percentile and absolute numbers.

Pathogenic disorders involved in immunosuppression and T cell depletion characterizing AIDS

Four cardinal immune disorders interacting with each other may promote the progressive T cell depletion and immunosuppression characterizing AIDS. Immune activation of HIV-1 infected T4 cells leads to virus release and premature cell death. Both virus release with its resulting viral load and dead cells are the source of gp120 stimulus. Anergy of non-infected CD4 cells, resulting in cytokine dysregulation may be promoted by impairing the CD4-MHC interaction during CD4 cell activation either directly through the SLWDQ pentapeptide identity with the CD4 molecule and the CD4 binding region or through a gp120-induced autoimmune reaction to CD4. Overproduction of IFN alpha, the known antiproliferative and cytolytic cytokine may promote in a paracrine manner to neighbouring cells the immunosuppression generated by the lack of IL2 secretion following CD4 cell anergy. Apoptosis of activated non infected T cells could be induced by effector components of the autoimmune reaction (CTL, Lymphotoxins or Abs?) directed towards the 2 consensus gp120 sequence identity/similarity (INCTR and FYCNST) shared with the APO/Fas molecule. These two sequences are known as immunodominant sites of the gp120. Furthermore, IFN alpha overproduction may also render circulating memory T cells competent to apoptosis by upregulating the cascade of metabolic events leading to programmed cell death.

Expression and immunogenicity of the V3 loop from the envelope of human immunodeficiency virus type 1 in an attenuated aroA strain of Salmonella typhimurium upon genetic coupling to two Escherichia coli carrier proteins

A peptide comprising residues glu293 to ser334 from the principal neutralization determinant (V3 loop) of the envelope of human immunodeficiency virus type 1 (HIV1 LAVBRU isolate) has been inserted within internal permissive sites of either LamB or MalE, two envelope proteins from Escherichia coli K12. The MalE hybrid protein (MalE133-V3 loop) was stably expressed in the periplasm of Escherichia coli K12, and the V3 loop peptide was detectable on the surface of the native protein by an anti-gp160 monoclonal antibody (mAb 110-A). The disulfide bridge between the two cysteines of the loop was formed. In contrast, genetic coupling to the outer membrane protein LamB did not allow the expression of a stable hybrid protein, and major proteolytic cleavage products of the LamB153-V3 loop were detected by mAb 110-A. The two plasmid-encoded hybrid genes were transferred to an aroA mutant of Salmonella typhimurium. Constitutive expression of the MalE133-V3 loop had no detectable effect on cell growth and on the survival in vivo of the recipient strain. The LamB153-V3 loop was not stably expressed in Salmonella, either in vitro or in vivo. Live recombinant salmonellas expressing MalE-V3 and LamB-V3 loop hybrids were used to immunize mice. The MalE-V3 loop hybrid induced anti-HIV1 envelope antibodies detectable by Western blot and ELISA, while the anti-HIV1 envelope antibodies induced by the LamB-V3 loop hybrid were only detectable by Western blot. In addition, purified MalE-V3 loop hybrid protein was able to stimulate in vitro and induce in vivo a V3 loop-specific T-cell proliferative response.

Identification of CD4 and major histocompatibility complex functional peptide sites and their homology with oligopeptides from human immunodeficiency virus type 1 glycoprotein gp120: role in AIDS pathogenesis

CD4 molecules interact with class II major histocompatibility complex molecules as a critical costimulatory signal in CD4+ cell immune activation. CD4 also recognizes a specific region of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120 forming a binding site for early stages of HIV-1 infection. We designed two software packages, AUTOMAT and CRITIC, which allowed us to identify similarities between regions of HIV-1 proteins and immunoregulatory protein sequences stored in data banks. In this report we have characterized (i) a pentapeptide, SLWDQ, found in both CD4 and HIV-1 gp120, which surprisingly had remained undetected in these two well-studied molecules until now, and (ii) an HLA sequence corresponding to the putative functional site of H2 I-A. We found that a region of gp120 (residues 254-263) known to be similar to a sequence in HLA class II beta chain overlaps this functional region. We showed experimentally that these two CD4 and HLA peptide segments inhibit CD4+ cell immune activation. There is strong inhibition (50% up to 80%) of immune activation by SLWDQ-containing gp120 segments and a lesser inhibition by the gp120 HLA-homologous segment. In addition, we found that SLWDQ induced in HIV-1-infected individuals a humoral (antibody) and cellular (cytotoxic T lymphocyte) immune reaction. We propose that these HIV-1 gp120 segments, together with the known CD4-binding region, may contribute to the HIV-1-induced immunosuppression by two mechanisms affecting CD4-HLA interaction during T-cell immune activation: autoimmune reaction toward CD4 and direct interference with the CD4-HLA costimulatory signal inducing CD4+ cell anergy with, as a consequence, generation of immunosuppression.