Anti-human immunodeficiency virus type 1 (HIV-1) CD8(+) T-lymphocyte reactivity during combination antiretroviral therapy in HIV-1-infected patients with advanced immunodeficiency

T-cell activation state differentially contributes to neuropsychiatric complications in women with HIV

Neuropsychiatric complications are common among women with HIV (WWH). The pathophysiological mechanisms underlying these complications are not fully known but likely driven in part by immune modulation. We examined associations between T-cell activation states which are required to mount an effective immune response (activation, co-stimulation/normal function, exhaustion, senescence) and neuropsychiatric complications in WWH. 369 WWH (78% HIV RNA undetectable/<20cp/mL) enrolled in the Women's Interagency HIV Study completed neuropsychological testing and measures of depression (Center for Epidemiological Studies Depression Scale-CES-D), self-reported stress levels (Perceived Stress Scale-10), and post-traumatic stress (PTSD Checklist-Civilian Scale). Multiparametric flow cytometry evaluated T-cell activation state. Partial least squares regressions were used to examine T-cell phenotypes and neuropsychiatric outcome associations after confounder adjustment. In the total sample and among virally suppressed (VS)-WWH, CD4+ T-cell exhaustion was associated with poorer learning and attention/working memory (P's < 0.05). In the total sample, CD4+ T-cell activation was associated with better attention/working memory and CD8+ T-cell co-stimulation and senescence was associated with poorer executive function (P's < 0.05). For mental health outcomes, in the total sample, CD4+ T-cell activation was associated with more perceived stress and CD4+ T-cell exhaustion was associated with less depressive symptoms (P's < 0.05). Among VS-WWH, CD4+ senescence was associated with less perceive stress and CD8+ T-cell co-stimulation and senescence was associated with higher depression (P's < 0.05). Together, results suggest the contribution of peripheral CD4+ and CD8+ T-cell activation status to neuropsychiatric complications in WWH.

STING Ligand-Mediated Priming of Functional CD8+ T Cells Specific for HIV-1-Protective Epitopes from Naive T Cells

Functional HIV-1-specific CD8+ T cells primed from naive T cells are expected to act as effector T cells in a "shock-and-kill" therapeutic strategy for an HIV-1 cure since less functional HIV-1-specific CD8+ T cells are elicited from memory T cells in HIV-1-infected individuals on combined antiretroviral therapy (cART). CD8+ T cells specific for HIV-1 conserved and protective epitopes are candidates for such T cells. We investigated the priming with STING ligand of CD8+ T cells specific for HLA-B*52:01 or HLA-C*12:02-restricted protective epitopes from naive T cells. STING ligand 3'3'-cGAMP effectively primed CD8+ T cells specific for 3 of 4 HLA-B*52:01-restricted epitopes but failed to prime those specific for all 3 HLA-C*12:02-restricted epitopes from the naive T cells of HIV-1-uninfected individuals having an HLA-B*52:01-C*12:02 protective haplotype. These HLA-B*52:01-restricted CD8+ T cells had a strong ability to suppress HIV-1 replication and expressed a high level of cytolytic effector molecules. The viral suppression ability of these T cells was significantly correlated with the expression level of perforin and showed a trend for a positive correlation with the expression level of CD107a. The present study highlighted the priming with STING ligand of functional CD8+ T cells specific for protective epitopes, which T cells would contribute as effector T cells to a shock-and-kill therapy. IMPORTANCE The current "shock-and-kill" therapeutic strategy for HIV cure has been directed toward eliminating latent viral reservoirs by reactivation of latent reservoirs with latency-reversing agents followed by eradication of these cells by immune-mediated responses. Although HIV-1-specific T cells are expected to eradicate viral reservoirs, the function of these T cells is reduced in HIV-1-infected individuals with long-term cART. Therefore, priming of HIV-1-specific T cells with high function from naive T cells is to be expected in these individuals. In this study, we demonstrated the priming with STING ligand 3'3'-cGAMP of CD8+ T cells specific for HIV-1-protective epitopes from naive T cells. cGAMP primed CD8+ T cells specific for 3 HLA-B*52:01-restricted protective epitopes, which cells expressed a high level of cytolytic effector molecules and effectively suppressed HIV-1 replication. The present study suggested that the priming with STING ligand of functional CD8+ T cells specific for protective epitopes would be useful in a therapy for an HIV-1 cure.

CD8+ T-Cell Response to HIV Infection in the Era of Antiretroviral Therapy

Although the combined antiretroviral therapy (cART) has decreased the deaths associated with the immune deficiency acquired syndrome (AIDS), non-AIDS conditions have emerged as an important cause of morbidity and mortality in HIV-infected patients under suppressive cART. Since these conditions are associated with a persistent inflammatory and immune activation state, major efforts are currently made to improve the immune reconstitution. CD8⁺ T-cells are critical in the natural and cART-induced control of viral replication; however, CD8⁺ T-cells are highly affected by the persistent immune activation and exhaustion state driven by the increased antigenic and inflammatory burden during HIV infection, inducing phenotypic and functional alterations, and hampering their antiviral response. Several CD8⁺ T-cell subsets, such as interleukin-17-producing and follicular CXCR5⁺ CD8⁺ T-cells, could play a particular role during HIV infection by promoting the gut barrier integrity, and exerting viral control in lymphoid follicles, respectively. Here, we discuss the role of CD8⁺ T-cells and some of their subpopulations during HIV infection in the context of cART-induced viral suppression, focusing on current challenges and alternatives for reaching complete reconstitution of CD8⁺ T-cells antiviral function. We also address the potential usefulness of CD8⁺ T-cell features to identify patients who will reach immune reconstitution or have a higher risk for developing non-AIDS conditions. Finally, we examine the therapeutic potential of CD8⁺ T-cells for HIV cure strategies.

Have Cells Harboring the HIV Reservoir Been Immunoedited?

Immunoediting is an important concept in oncology, delineating the mechanisms through which tumors are selected for resistance to immune-mediated elimination. The recent emergence of immunotherapies, such as checkpoint inhibitors, as pillars of cancer therapy has intensified interest in immunoediting as a constraint limiting the efficacy of these approaches. Immunoediting manifests at a number of levels for different cancers, for example through the establishment of immunosuppressive microenvironments within solid tumors. Of particular interest to the current review, selection also occurs at the cellular level; and recent studies have revealed novel mechanisms by which tumor cells acquire intrinsic resistance to immune recognition and elimination. While the selection of escape mutations in viral epitopes by HIV-specific T cells, which is a hallmark of chronic HIV infection, can be considered a form of immunoediting, few studies have considered the possibility that HIV-infected cells themselves may parallel tumors in having differential intrinsic susceptibilities to immune-mediated elimination. Such selection, on the level of an infected cell, may not play a significant role in untreated HIV, where infection is propagated by high levels of cell-free virus produced by cells that quickly succumb to viral cytopathicity. However, it may play an unappreciated role in individuals treated with effective antiretroviral therapy where viral replication is abrogated. In this context, an "HIV reservoir" persists, comprising long-lived infected cells which undergo extensive and dynamic clonal expansion. The ability of these cells to persist in infected individuals has generally been attributed to viral latency, thought to render them invisible to immune recognition, and/or to their compartmentalization in anatomical sites that are poorly accessible to immune effectors. Recent data from ex vivo studies have led us to propose that reservoir-harboring cells may additionally have been selected for intrinsic resistance to CD8+ T cells, limiting their elimination even in the context of antigen expression. Here, we draw on knowledge from tumor immunoediting to discuss potential mechanisms by which clones of HIV reservoir-harboring cells may resist elimination by CD8+ T cells. The establishment of such parallels may provide a premise for testing therapeutics designed to sensitize tumor cells to immune-mediated elimination as novel approaches aimed at curing HIV infection.

CD8+ lymphocyte control of SIV infection during antiretroviral therapy

CD8⁺ lymphocytes play an important role in suppressing in vivo viral replication in HIV infection. However, both the extent to which and the mechanisms by which CD8⁺ lymphocytes contribute to viral control are not completely understood. A recent experiment depleted CD8⁺ lymphocytes in simian immunodeficiency virus (SIV)-infected rhesus macaques (RMs) on antiretroviral treatment (ART) to study the role of CD8⁺ lymphocytes. CD8⁺ lymphocytes depletion resulted in temporary plasma viremia in all studied RMs. Viral control was restored when CD8⁺ lymphocytes repopulated. We developed a viral dynamic model to fit the viral load (VL) data from the CD8 depletion experiment. We explicitly modeled the dynamics of the latent reservoir and the SIV-specific effector cell population including their exhaustion and their potential cytolytic and noncytolytic functions. We found that the latent reservoir significantly contributes to the size of the peak VL after CD8 depletion, while drug efficacy plays a lesser role. Our model suggests that the overall CD8⁺ lymphocyte cytolytic killing rate is dynamically changing depending on the levels of antigen-induced effector cell activation and exhaustion. Based on estimated parameters, our model suggests that before ART or without ART the overall CD8 cytolytic killing rate is small due to exhaustion. However, after the start of ART, the overall CD8 cytolytic killing rate increases due to an expansion of SIV-specific CD8 effector cells. Further, we estimate that the cytolytic killing rate can be significantly larger than the cytopathic death rate in some animals during the second phase of ART-induced viral decay. Lastly, our model provides a new explanation for the puzzling findings by Klatt et al. and Wong et al. that CD8 depletion done immediately before ART has no noticeable effect on the first phase viral decay slope seen after ART initiation Overall, by incorporating effector cells and their exhaustion, our model can explain the effects of CD8 depletion on VL during ART, reveals a detailed dynamic role of CD8⁺ lymphocytes in controlling viral infection, and provides a unified explanation for CD8 depletion experimental data.

CD8⁺ lymphocytes play an important role in suppressing in vivo viral replication in HIV infection. However, both the extent to which and the mechanisms by which CD8⁺ lymphocytes contribute to viral control are not completely understood. By mathematically modeling data from a recent CD8 depletion experiment done in antiretroviral (ART) treated animals, our results suggest that the overall CD8⁺ lymphocyte cytolytic killing rate is dynamically changing depending on the levels of antigen-induced effector cell activation and exhaustion, i.e. before ART or without ART the overall CD8 cytolytic killing rate is small due to exhaustion. However, after the start of ART, the overall CD8 cytolytic killing rate increases due to an expansion of SIV-specific CD8 effector cells. By incorporating effector cells and their exhaustion, our model explains the effects on viral load of CD8 depletion done before ART or during ART, reveals a detailed dynamic role of CD8⁺ lymphocytes in controlling viral infection, and provides a unified explanation for CD8 depletion experimental data.

Lazarus and Group Psychotherapy: AIDS in the Era of Protease Inhibitors

A new class of medications, protease inhibitors, has dramatically improved the health of many people with Human Immunodeficiency Virus (HIV) and Acquired Immune Deficiency Syndrome (AIDS). This development has had a major impact on the lives of those affected by HIV/AIDS. This article considers how a group is affected by the larger systems of which it is a part. The article examines changes in the content, process, and salient leadership tasks of an ongoing therapy group for people with HIV and AIDS before and following the initial introduction of new medical treatments. It also considers how the group process continues to be affected by the more recent failure of these medications for many patients. Implications for research, practice, and training are discussed.

Effective Cytotoxic T Lymphocyte Targeting of Persistent HIV-1 during Antiretroviral Therapy Requires Priming of Naive CD8+ T Cells

Curing HIV-1 infection will require elimination of persistent cellular reservoirs that harbor latent virus in the face of combination antiretroviral therapy (cART). Proposed immunotherapeutic strategies to cure HIV-1 infection include enhancing lysis of these infected cells by cytotoxic T lymphocytes (CTL). A major challenge in this strategy is overcoming viral immune escape variants that have evaded host immune control. Here we report that naive CD8⁺ T cells from chronic HIV-1-infected participants on long-term cART can be primed by dendritic cells (DC). These DC must be mature, produce high levels of interleukin 12p70 (IL-12p70), be responsive to CD40 ligand (CD40L), and be loaded with inactivated, autologous HIV-1. These DC-primed CD8⁺ T cell responders produced high levels of gamma interferon (IFN-γ) in response to a broad range of both conserved and variable regions of Gag and effectively killed CD4⁺ T cell targets that were either infected with the autologous latent reservoir-associated virus or loaded with autologous Gag peptides. In contrast, HIV-1-specific memory CD8⁺ T cells stimulated with autologous HIV-1-loaded DC produced IFN-γ in response to a narrow range of conserved and variable Gag peptides compared to the primed T cells and most notably, displayed significantly lower cytolytic function. Our findings highlight the need to selectively induce new HIV-1-specific CTL from naive precursors while avoiding activation of existing, dysfunctional memory T cells in potential curative immunotherapeutic strategies for HIV-1 infection.

Current immunotherapeutic approaches aim to enhance antiviral immunity against the HIV-1 reservoir; however, it has yet to be shown whether T cells from persons on cART can recognize and eliminate virus-infected cells. We show that in persons on cART a personalized medicine approach using their dendritic cells to stimulate their naive T cells induces potent effector CTL in vitro that recognize and eradicate HIV-1-infected CD4⁺ T cells. Additionally, we show that the same stimulation of existing memory T cells results in cytokine secretion but limited effector function. Our study demonstrates that the naive T cell repertoire can recognize persistent HIV-1 during cART and supports immunotherapy strategies for an HIV-1 cure that targets naive T cells, rather than existing, dysfunctional, memory T cells.

HIV-specific CD8⁺ T cells and HIV eradication

After the success of combination antiretroviral therapy (cART) to treat HIV infection, the next great frontier is to cure infected persons, a formidable challenge. HIV persists in a quiescent state in resting CD4+ T cells, where the replicative enzymes targeted by cART are not active. Although low levels of HIV transcripts are detectable in these resting cells, little to no viral protein is produced, rendering this reservoir difficult to detect by the host CD8+ T cell response. However, recent advances suggest that this state of latency might be pharmacologically reversed, resulting in viral protein expression without the adverse effects of massive cellular activation. Emerging data suggest that with this approach, infected cells will not die of viral cytopathic effects, but might be eliminated if HIV-specific CD8+ T cells can be effectively harnessed. Here, we address the antiviral properties of HIV-specific CD8+ T cells and how these cells might be harnessed to greater effect toward achieving viral eradication or a functional cure.

Preserving HIV-specific T cell responses: does timing of antiretroviral therapy help?

PURPOSE OF REVIEW

HIV-specific T cell responses are likely to have an important role in HIV cure strategies that aim for long-lasting viral control without antiretroviral therapy (ART). An important issue in enhancing virus-specific T cell responses is whether timing of ART can influence their magnitude and breadth.

RECENT FINDINGS

Early ART is associated with lower T cell activation, preservation of T cell numbers, smaller DNA and RNA reservoir size, and, in a single study (VISCONTI), control of plasma viremia after treatment interruption. The prevention of T cell destruction by early ART is associated with relatively low anti-HIV CD8⁺ T cell responses but stronger CD4⁺ T helper function. The relatively lower CD8⁺T cell response, which is presumably due to rapid lowering of HIV antigen burden after early ART, appears sufficient to control residual viral replication as well as viral rebound upon treatment interruption.

SUMMARY

Available evidence of starting ART during acute or early HIV infection has shown benefit in both virologic and immunologic parameters despite the lower HIV-specific CD8⁺ T cell responses observed. Encouraging as this is, more extensive data are necessary to evaluate its role in combination with immunotherapeutic and latency activation strategies that are being assessed in various HIV cure-related studies.

Programming T cell Killers for an HIV Cure: Teach the New Dogs New Tricks and Let the Sleeping Dogs Lie

Despite the success of combination antiretroviral therapy (cART), a latent viral reservoir persists in HIV-1-infected persons. Unfortunately, endogenous cytotoxic T lymphocytes (CTLs) are unable to control viral rebound when patients are removed from cART. A "kick and kill" strategy has been proposed to eradicate this reservoir, whereby infected T cells are induced to express viral proteins via latency-inducing drugs followed by their elimination by CTLs. It has yet to be determined if stimulation of existing HIV-1-specific CTL will be sufficient, or if new CTLs should be primed from naïve T cells. In this review, we propose that dendritic cells (DCs), the most potent antigen presenting cells, act as dog trainers and can induce T cells (the dogs) to do magnificent tricks. We propose the hypothesis that an HIV-1 cure will require targeting of naïve T cells and will necessitate "teaching new dogs new tricks" while avoiding activation of potentially dysfunctional endogenous memory CTLs (letting the sleeping dogs lie).

The impact of viral evolution and frequency of variant epitopes on primary and memory human immunodeficiency virus type 1-specific CD8⁺ T cell responses

It is unclear if HIV-1 variants lose the ability to prime naïve CD8(+) cytotoxic T lymphocytes (CTL) during progressive, untreated infection. We conducted a comprehensive longitudinal analysis of viral evolution and its impact on primary and memory CD8(+) T cell responses pre-seroconversion (SC), post-SC, and during combination antiretroviral therapy (cART). Memory T cell responses targeting autologous virus variants reached a nadir by 8 years post-SC with development of AIDS, followed by a transient enhancement of anti-HIV-1 CTL responses upon initiation of cART. We show broad and high magnitude primary T cell responses to late variants in pre-SC T cells, comparable to primary anti-HIV-1 responses induced in T cells from uninfected persons. Despite evolutionary changes, CD8(+) T cells could still be primed to HIV-1 variants. Hence, vaccination against late, mutated epitopes could be successful in enhancing primary reactivity of T cells for control of the residual reservoir of HIV-1 during cART.

HIV-Specific CD8(+) T Lymphocytes in Blood of Long-Term HIV-Infected Hemophilia Patients

Hemophilia patients infected with human immunodeficiency virus (HIV) 30 years ago show increased proportions of activated CD8⁺DR⁺ blood lymphocytes. We hypothesized that this might indicate a cellular immune response directed against HIV and might be the reason for long-term clinical stability of these patients. CD8⁺ peripheral blood lymphocytes (PBL) reactive with six HIV and two cytomegalovirus (CMV) pentamers were determined in heparinized whole blood. Additional lymphocyte subsets as well as plasma cytokines and HIV-1 load were studied. Long-term HIV-infected hemophilia patients with (n=15) or without (n=33) currently detectable HIV-1 load in the plasma showed higher proportions of CD8⁺ lymphocytes reactive with HIV (p<0.001) and CMV pentamers (p=0.010) than healthy individuals. The cellular anti-HIV response tended to be stronger and more polyclonal in patients during periods of viral replication than in patients with retroviral quiescence (p=0.077). Anti-HIV CD8⁺ lymphocyte responses were strongest in patients with high counts of activated CD8⁺DR⁺ T (r=0.353; p=0.014) and low CD19⁺ B lymphocyte counts (r=−0.472; p=0.001). Patients with or without HIV-1 viral load showed normal Th1 and Th2 plasma cytokine levels and high plasma interleukin-6 (versus healthy controls, p=0.001) and tumor necrosis factor-α (p=0.020). Hemophilia patients who have been living with HIV for more than 30 years showed a polyclonal CD8⁺ T-cell response against HIV and CMV. This cellular antiviral immune response was strongest during periods of HIV-1 replication and remained detectable during periods of HIV-1 quiescence. We hypothesize that the consistent cellular anti-HIV-1 response in combination with highly active antiretroviral therapy ensures stability and survival of these chronically HIV-1–infected hemophilia patients.

Human Immunodeficiency Virus-Type 1 Specific Cellular Immunity in Chronic Infected Patients on Prolonged Highly Active Antiretroviral Treatment and on Structured Treatment Interruption

We have followed 15 HIV-1 chronically infected patients during prolonged highly active antiretroviral treatment (HAART) and subsequent long term structured treatment interruption (STI). We analyzed Nef, Tat, and p24 specific cellular immunity using IFN-gamma enzyme-linked immunospot assays and T cell proliferation assays. Eight HAART patients showed IFN-gamma responses to at least one antigen, but no positive responses were seen during STI. We observed retained or increased p24 specific IFN-gamma responses in most patients during HAART with viral suppression. These results showed persisting HIV-1 specific cellular immunity during HAART; however, in prolonged STI with viral rebound this immunity declined.

Professional antigen presenting cells in human herpesvirus 8 infection

Professional antigen presenting cells (APC), i.e., dendritic cells (DC), monocytes/macrophages, and B lymphocytes, are critically important in the recognition of an invading pathogen and presentation of antigens to the T cell-mediated arm of immunity. Human herpesvirus 8 (HHV-8) is one of the few human viruses that primarily targets these APC for infection, altering their cytokine profiles, manipulating their surface expression of MHC molecules, and altering their ability to activate HHV-8-specific T cells. This could be why T cell responses to HHV-8 antigens are not very robust. Of these APC, only B cells support complete, lytic HHV-8 infection. However, both complete and abortive virus replication cycles in APC could directly affect viral pathogenesis and progression to Kaposi's sarcoma (KS) and HHV-8-associated B cell cancers. In this review, we discuss the effects of HHV-8 infection on professional APC and their relationship to the development of KS and B cell lymphomas.

Dendritic cells reveal a broad range of MHC class I epitopes for HIV-1 in persons with suppressed viral load on antiretroviral therapy

Background

HIV-1 remains sequestered during antiretroviral therapy (ART) and can resume high-level replication upon cessation of ART or development of drug resistance. Reactivity of memory CD8⁺ T lymphocytes to HIV-1 could potentially inhibit this residual viral replication, but is largely muted by ART in relation to suppression of viral antigen burden. Dendritic cells (DC) are important for MHC class I processing and presentation of peptide epitopes to memory CD8⁺ T cells, and could potentially be targeted to activate memory CD8⁺ T cells to a broad array of HIV-1 epitopes during ART.

Principal Findings

We show for the first time that HIV-1 peptide-loaded, CD40L-matured DC from HIV-1 infected persons on ART induce IFN gamma production by CD8⁺ T cells specific for a much broader range and magnitude of Gag and Nef epitopes than do peptides without DC. The DC also reveal novel, MHC class I restricted, Gag and Nef epitopes that are able to induce polyfunctional T cells producing various combinations of IFN gamma, interleukin 2, tumor necrosis factor alpha, macrophage inhibitory protein 1 beta and the cytotoxic de-granulation molecule CD107a.

Significance

There is an underlying, broad antigenic spectrum of anti-HIV-1, memory CD8⁺ T cell reactivity in persons on ART that is revealed by DC. This supports the use of DC-based immunotherapy for HIV-1 infection.

Regulatory T cell suppression of Gag-specific CD8 T cell polyfunctional response after therapeutic vaccination of HIV-1-infected patients on ART

We tested the hypothesis that therapeutic vaccination against HIV-1 can increase the frequency and suppressive function of regulatory, CD4⁺ T cells (Treg), thereby masking enhancement of HIV-1-specific CD8⁺ T cell response. HIV-1-infected subjects on antiretroviral therapy (N = 17) enrolled in a phase I therapeutic vaccine trial received 2 doses of autologous dendritic cells (DC) loaded with HIV-1 peptides. The frequency of CD4⁺CD25^hiFOXP3⁺ Treg in blood was determined prior to and after vaccination in subjects and normal controls. Polyfunctional CD8⁺ T cell responses were determined pre- and post-vaccine (N = 7) for 5 immune mediators after in vitro stimulation with Gag peptide, staphylococcal enterotoxin B (SEB), or medium alone. Total vaccine response (post-vaccine–pre-vaccine) was compared in the Treg(+) and Treg-depleted (Treg-) sets. After vaccination, 12/17 subjects showed a trend of increased Treg frequency (P = 0.06) from 0.74% to 1.2%. The increased frequency did not correlate with CD8⁺ T cell vaccine response by enzyme linked immunosorbent assay for interferon γ production. Although there was no significant change in CD8⁺ T cell polyfunctional response after vaccination, Treg depletion increased the polyfunctionality of the total vaccine response (P = 0.029), with a >2-fold increase in the percentage of CD8⁺ T cells producing multiple immune mediators. In contrast, depletion of Treg did not enhance polyfunctional T cell response to SEB, implying specificity of suppression to HIV-1 Gag. Therapeutic immunization with a DC-based vaccine against HIV-1 caused a modest increase in Treg frequency and a significant increase in HIV-1-specific, Treg suppressive function. The Treg suppressive effect masked an increase in the vaccine-induced anti-HIV-1-specific polyfunctional response. The role of Treg should be considered in immunotherapeutic trials of HIV-1 infection.

Utilizing the FIV model to understand dendritic cell dysfunction and the potential role of dendritic cell immunization in HIV infection

Dendritic cells (DC) are potent antigen presenting cells which initiate and coordinate the immune response making them central targets of and attractive candidates for manipulation in chronic lentiviral infections. Emerging evidence suggests that DC immune function is disrupted during both acute and chronic infection with human immunodeficiency virus (HIV), simian immunodeficiency virus (SIV), and feline immunodeficiency virus (FIV). Despite some early promising data, the use of DC for lentiviral immunotherapy has not fulfilled its expected potential and has been complicated by the large number of variables involved in DC harvesting, purifying, and antigen loading. Pre-clinical studies aimed at identifying successful strategies for DC augmentation of current HIV treatment protocols are needed. Over the past two decades, the FIV model for HIV infection has increased the understanding of retroviral pathogenesis, and studies have begun using the FIV model to study DC dysfunction and DC-mediated immunotherapy. Careful consideration of the many variables involved in DC function and therapy should help develop protocols to explore the potential of DC vaccine-based therapies for lentiviral infection.

Production of a dendritic cell-based vaccine containing inactivated autologous virus for therapy of patients with chronic human immunodeficiency virus type 1 infection

In preparation for a pilot clinical trial in patients with chronic human immunodeficiency virus type 1 (HIV-1) infection, a novel dendritic cell (DC)-based vaccine is being manufactured. The trial will test the hypothesis that isolated endogenous virus presented by DCs serves as a potent immunogen for activation of CD8(+) and CD4(+) T cells specific for a broad range of autologous HIV-1 antigens. Production of the vaccine under good manufacture practice conditions involves (i) autologous virus isolation; (ii) superinfection of CD4(+) T cells with the virus; (iii) inactivation of the virus in CD4(+) T cells, T-cell apoptosis, and coincubation of T cells with autologous DCs; and (iv) product testing and release. Endogenous virus was isolated from peripheral blood-derived CD4(+) T cells of three HIV-1-positive subjects by coincubation with autologous OKT-3-stimulated CD4(+) T cells. CD4(+) T-cell supernatants were tested for p24 levels by enzyme-linked immunosorbent assay (>25 ng/ml) and for the 50% tissue culture infective doses (TCID(50); which ranged from 4,642 to 46,416/ml on day 19 of culture). Autologous CD4(+) T cells that were separated on immunobeads (>95% purity) and superinfected with virus-expressed p24 (28 to 54%) had TCID(50) of >400/ml on days 5 to 10. Virus inactivation with psoralen (20 microg/ml) and UVB irradiation (312 nm) reduced the TCID(50) of the supernatants from 199,986 to 11/ml (>99%). 7-Amino-actinomycin D-positive, annexin V-positive CD4(+) T cells were fed to autologous DCs generated by using the Elutra cell separation system and the Aastrom system. Flow analysis showed that DC loading was complete in 24 h. On the basis of these translational results and experience with the generation of DCs from HIV-1-infected patients in a previous clinical trial, the Investigational New Drug application for clinical vaccination was submitted and approved by the FDA (application no. BB-IND-13137).

Dendritic cell-based human immunodeficiency virus vaccine

Dendritic cells (DC) have profound abilities to induce and coordinate T-cell immunity. This makes them ideal biological agents for use in immunotherapeutic strategies to augment T-cell immunity to HIV infection. Current clinical trials are administering DC-HIV antigen preparations carried out ex vivo as proof of principle that DC immunotherapy is safe and efficacious in HIV-infected patients. These trials are largely dependent on preclinical studies that will provide knowledge and guidance about the types of DC, form of HIV antigen, method of DC maturation, route of DC administration, measures of anti-HIV immune function and ultimately control of HIV replication. Additionally, promising immunotherapy approaches are being developed based on targeting of DC with HIV antigens in vivo. The objective is to define a safe and effective strategy for enhancing control of HIV infection in patients undergoing antiretroviral therapy.

Generation of HIV-1-specific T cells by electroporation of T-cell receptor RNA

BACKGROUND

HIV-1-specific cytotoxic T lymphocytes, which recognize conserved epitopes of the virus, are correlated with prolonged survival of infected individuals. Unfortunately, most HIV-1-infected patients are unable to generate such an immune response. Antigen-specific cytotoxic T lymphocytes can be generated by T-cell receptor transfer. This is commonly done by retroviral transduction, which is complicated and poses the threat of stable genetic alteration of autologous cells.

METHODS

We reprogrammed primary CD8+ T cells by electroporation of RNA, which encoded an HIV-1-pol- and an HIV-1-gag-specific T-cell receptor recognizing the human leukocyte antigen-A2 restricted epitopes ILKEPVHGV and SLYNTVATL, respectively.

RESULTS

These reprogrammed cells specifically produced the proinflammatory cytokines interleukin-2, tumor necrosis factor-alpha, and interferon-gamma after stimulation with target cells that presented the corresponding peptides, and were able to lyse these targets efficiently and specifically. The lytic avidities of the HIV-1-pol- and HIV-1-gag-TCR-RNA-electroporated CD8+ T cells were within the same range than those of the parental cytotoxic T lymphocytes. Most importantly, HIV-1-gag-reprogrammed T cells recognized target cells that presented endogenously processed antigen, which resulted in cytokine production and lysis.

CONCLUSION

It is shown here for the first time that functional transfer of virus-specific T-cell receptors by RNA electroporation is feasible, and represents an innovative, safe, and easy method to generate virus-specific T cells, avoiding the risks of retroviral transduction.

Availability of a diversely avid CD8+ T cell repertoire specific for the subdominant HLA-A2-restricted HIV-1 Gag p2419-27 epitope

HLA-A2-restricted CTL responses to immunodominant HIV-1 epitopes do not appear to be very effective in the control of viral replication in vivo. In this study, we studied human CD8+ T cell responses to the subdominant HLA-A2-restricted epitope TV9 (Gag p24(19-27), TLNAWVKVV) to explore the possibility of increasing its immune recognition. We confirmed in a cohort of 313 patients, infected by clade B or clade C viruses, that TV9 is rarely recognized. Of interest, the functional sensitivity of the TV9 response can be relatively high. The potential T cell repertoires for TV9 and the characteristics of constituent clonotypes were assessed by ex vivo priming of circulating CD8+ T cells from healthy seronegative donors. TV9-specific CTLs capable of suppressing viral replication in vitro were readily generated, suggesting that the cognate T cell repertoire is not limiting. However, these cultures contained multiple discrete populations with a range of binding avidities for the TV9 tetramer and correspondingly distinct functional dependencies on the CD8 coreceptor. The lack of dominant clonotypes was not affected by the stage of maturation of the priming dendritic cells. Cultures primed by dendritic cells transduced to present endogenous TV9 were also incapable of clonal maturation. Thus, a diffuse TCR repertoire appeared to be an intrinsic characteristic of TV9-specific responses. These data indicate that subdominance is not a function of poor immunogenicity, cognate TCR repertoire availability, or the potential avidity properties thereof, but rather suggest that useful responses to this epitope are suppressed by competing CD8+ T cell populations during HIV-1 infection.

Pediatric HIV-1-specific cytotoxic T-lymphocyte responses suggesting ongoing viral replication despite combination antiretroviral therapy

Human immunodeficiency virus-1 (HIV-1)-specific cytotoxic T-lymphocyte (CTL) responses are common in infected adults and usually exhibit rapid decay after combination antiretroviral therapy (ART). CTLs develop later in the first year of life, and the fate of HIV-1-specific responses in perinatally infected children after ART is less well described. HIV-1-specific CTL responses were measured in 17 perinatally infected children and adolescents (ages 3-20 y) receiving combination ART. Seven had prolonged viral suppression (<400 copies/mL) for 2.5-5.3 y and 10 had persistent viremia (median, 77,550 copies/mL). HIV-1-specific CTL responses were tested by interferon (IFN)-gamma enzyme-linked immunospot (ELIS-pot) assays using 53 overlapping peptide pools spanning the entire HIV-1 proteome. HIV-1-specific CTL responses were detected in 14 of 17 individuals. Responses to one to four viral proteins were found in eight of 10 individuals with persistent viremia and six of seven with prolonged viral suppression. The magnitude and breadth of CTL responses were similar between groups. HIV-1-specific CTL responses were present in the majority of perinatally infected subjects, irrespective of viremia at evaluation. Because ART-treated infected adults usually have rapid decay of responses, these data suggest viral replication below the limits of detection is more persistent in combination ART-treated perinatally infected pediatric subjects. The long-term clinical implications of these findings remain to be determined.

Large HIV-specific CD8 cytotoxic T-lymphocyte (CTL) clones reduce their overall size but maintain high frequencies of memory CTL following highly active antiretroviral therapy

Cytotoxic T-lymphocytes (CTL) play an important role in the control of human immunodeficiency virus (HIV) and of human cytomegalovirus (HCMV) infection. Following highly active antiretroviral therapy (HAART), most studies have demonstrated a decline in the frequency of HIV-specific CTL. We analysed the effect of HAART on the size, phenotype and function of individual HIV- and HCMV-specific CTL clones, using clonotypic oligonucleotide probing specific for the T-cell receptor (TCR) beta-chain hypervariable sequence of defined immunodominant CTL clones specific for peptides of HIV or HCMV, and quantified the limiting dilution analysis frequencies of CTL precursors (CTLp) specific for the same viral peptides. We found that the clonal composition of CD8+ T cells specific for HIV gag and env epitopes was highly focused and did not change after HAART. Following HAART, there was progressive contraction of HIV-specific CD8+ clones, especially in the CD28- CD27- subpopulation--the remaining cells of contracting HIV-specific clones were predominantly CD28- CD27+ CD45RO(hi). We observed maintenance of strong functional HIV-specific CD8+ T-cell responses in limiting dilution analysis following HAART, indicating preferential loss of HIV-specific cells that have reduced cloning efficiency in vitro. Following HAART, we also observed selective expansion of HCMV-specific CD8+ clones. Most HCMV-specific CD8+ clones were predominantly CD28- CD27+/- CD45RA(hi) following HAART. In one subject, a Vbeta6.4+ clone specific for HCMV pp65 selectively expanded following HAART, without expansion of two other Vbeta6.4+ clones, indicating that individual clonotypes specific for the same peptide can show different kinetics and phenotypes in response to antiretroviral therapy.

CD8+ cell noncytotoxic anti-HIV response: restoration by HAART in the late stage of infection

Highly active antiretroviral therapy (HAART) is currently the best HIV infection management strategy. However, its effects on the CD8+ T cell noncytotoxic anti-HIV response (CNAR) are not well known. We investigated if HAART has different effects on CNAR in patients at the intermediate and late stages of HIV infection. Untreated healthy HIV-infected subjects with a mean CD4+ T cell count of 606 cells/microl were examined as a reference group. Plasma viral load, CD4+ T cell count, and CNAR activity were measured at baseline and regular intervals for at least 48 weeks following initiation of HAART. Baseline CNAR activity in all subjects correlated inversely with viral load and directly with CD4 T+ cell counts. The level of CNAR in the latestage group was significantly lower than in the intermediate-stage and the healthy reference group (p < 0.01). Following initiation of HAART, substantial increases in CD4+ T cell counts and decreases in viral loads were observed in both groups, indicating treatment success. CNAR activity was found to be increased significantly during HAART, but only in the late-stage group (p < 0.01). This increase in CD8+ cell function was seen within 4 weeks of treatment initiation and resulted in levels of CNAR activity almost equal to those observed in the healthy reference subjects. Our findings suggest a beneficial effect on CNAR in those individuals with reduced activity, typically in late-stage infection.

Parallel human immunodeficiency virus type 1-specific CD8+ T-lymphocyte responses in blood and mucosa during chronic infection

Gut-associated lymphoid tissue is the major reservoir of lymphocytes and human immunodeficiency virus type 1 (HIV-1) replication in vivo, yet little is known about HIV-1-specific CD8+ T-lymphocyte (CTL) responses in this compartment. Here we assessed the breadth and magnitude of HIV-1-specific CTL in the peripheral blood and sigmoid colon mucosa of infected subjects not on antiretroviral therapy by enzyme-linked immunospot analysis with 53 peptide pools spanning all viral proteins. Comparisons of blood and mucosal CTL revealed that the magnitude of pool-specific responses is correlated within each individual (mean r2 = 0.82 +/- 0.04) and across all individuals (r2 = 0.75; P < 0.001). Overall, 85.1% of screened peptide pools yielded concordant negative or positive results between compartments. CTL targeting was also closely related between blood and mucosa, with Nef being the most highly targeted (mean of 2.4 spot-forming cells [SFC[/10(6) CD8+ T lymphocytes/amino acid [SFC/CD8/aa]), followed by Gag (1.5 SFC/CD8/aa). Finally, comparisons of peptide pool responses seen in both blood and mucosa (concordant positives) versus those seen only in one but not the other (discordant positives) showed that most discordant results were likely an artifact of responses being near the limit of detection. Overall, these results indicate that HIV-1-specific CTL responses in the blood mirror those seen in the mucosal compartment in natural chronic infection. For protective or immunotherapeutic vaccination, it will be important to determine whether immunity is elicited in the mucosa, which is a key site of initial infection and subsequent HIV-1 replication in vivo.

Processing and presentation of exogenous HLA class I peptides by dendritic cells from human immunodeficiency virus type 1-infected persons

Dendritic cells (DCs) loaded with viral peptides are a potential form of immunotherapy of human immunodeficiency virus type 1 (HIV-1) infection. We show that DCs derived from blood monocytes of subjects with chronic HIV-1 infection on combination antiretroviral drug therapy have increases in expression of HLA, T-cell coreceptor, and T-cell activation molecules in response to the DC maturation factor CD40L comparable to those from uninfected persons. Mature DCs (mDCs) loaded with HLA A*0201-restricted viral peptides of the optimal length (9-mer) were more efficient at activating antiviral CD8(+) T cells than were immature DCs or peptide alone. Optimal presentation of these exogenous peptides required uptake and vesicular trafficking and was comparable in DCs derived from HIV-1-infected and uninfected persons. Furthermore, DCs from HIV-1-infected and uninfected persons had similar capacities to process viral peptides with C-terminal and N-terminal extensions through their proteasomal and cytosolic pathways, respectively. We conclude that DCs derived from HIV-1-infected persons have similar abilities to process exogenous peptides for presentation to CD8(+) T cells as those from uninfected persons. This conclusion supports the use of DCs loaded with synthetic peptides in immunotherapy of HIV-1 infection.

Macaques infected long-term with attenuated simian immunodeficiency virus (SIVmac) remain resistant to wild-type challenge, despite declining cytotoxic T lymphocyte responses to an immunodominant epitope

To further investigate mechanisms of protective immunity that are induced by live, attenuated simian immunodeficiency virus (SIV), three macaques were infected with SIVmacGX2, a nef-disrupted molecular clone. In two of these animals, which expressed the MamuA*01 major histocompatibility complex class I allele, loss of functional activity against an SIV-Gag-encoded immunodominant cytotoxic T lymphocyte (CTL) epitope was observed following prolonged infection. Nonetheless, all three animals were resistant to challenge with an uncloned pool of wild-type SIVmac, whereas four naïve controls became infected. Tetramer staining revealed the rapid generation of CD8+ T-cell responses against gag- and tat-encoded immunodominant epitopes in MamuA*01+ challenge controls. The dynamics of these T-cell responses to the wild-type virus were similar to those observed following primary infection of the vaccine group with attenuated virus. In contrast, neither tetramer staining nor gamma interferon ELISpot assay revealed an immediate, systemic, anamnestic response in the wild-type-challenged, attenuated SIV-infected animals. Functional CTL capacity had not been lost in this group, as lytic activity was still evident 17 weeks after challenge. Both attenuated and wild-type viruses induced a disseminated CD8+ T-cell response, which was of a higher magnitude in lymphoid tissues than in the periphery. These results suggest that, at least as measured in the periphery, protection against wild-type infection that is induced by live, attenuated SIV is not dependent on a rechallenge-driven expansion of immunodominant epitope-specific CD8+ T cells and, therefore, pre-existing activity may be sufficient to prevent superinfection.

Use of well-defined HIV-derived epitopes to evaluate CD4(+) and CD8(+) T cell responses in patients with chronic HIV-1 infection treated with HAART

Highly active antiretroviral therapy (HAART) is associated with a dramatic clinical benefit to HIV-infected patients through significant plasma viremia reduction and CD4(+) T cells increase. In previous reports, HIV-specific CD4(+) and/or CD8(+) T cell responses have been studied separately during HAART; therefore the relationship between these two virus-specific populations is currently not well understood. In this study, both HIV-specific CD4(+) and CD8(+) T cell responses were investigated using a large panel of well-defined T cell epitope peptides in 24 HIV-1-infected patients undergoing HAART, with undetectable viral load and CD4(+) T cell count >/= 350/mm(3). One-third of the patients had CD4(+) T cells able to proliferate when exposed to HIV-1 protein fragments but only two patients displayed polyclonal responses. In addition the majority (78%) of HAART-treated patients displayed no or monospecific CD8(+) T cell responses and the phenotypic analysis of these HIV-specific CD8(+) T cells demonstrated the absence of terminally differentiated effectors. In conclusion, the experimental approach used in this study shows that CD4(+) T cell responses may persist during HAART but are not associated with strong CD8(+) T cell responses

A novel MHCp binding prediction model

Many statistical and molecular mechanics models have been developed and tested for major histocompatibility complex peptide (MHCp) binding predictions during the last decade. The statistical model prediction using pooled peptide sequence data and three-dimensional modeling prediction by molecular mechanics calculations have been assessed for efficiency and human leukocyte antigen diversity coverage. We describe a novel predictive model using information gleaned from 29 human MHCp crystal structures. The validation for the new model is performed using four different sets of data: (1) MHCp crystal structures, (2) peptides with known IC(50) binding values, (3) peptides tested positive by tetramer staining, (4) peptides with known binding information at the MHCBN database. The model produces high prediction efficiencies (average 60 %) with good sensitivity (approximately 50%-73%) and specificity (52%-58%) values. The average positive predictive value of the model is 89%, while the average negative predictive value is only 18%. The efficiency is very high in predicting binders and very low in predicting nonbinders. This model is superior to many existing methods because of its potential application to any given MHC allele whose sequence is clearly defined.

A simian replication-defective adenoviral recombinant vaccine to HIV-1 gag

In animal models, E1-deleted human adenoviral recombinants of the serotype 5 (AdHu5) have shown high efficacy as vaccine carriers for different Ags including those of HIV-1. Humans are infected by common serotypes of human adenovirus such as AdHu5 early in life and a significant percentage has high levels of neutralizing Abs to these serotypes, which will very likely impair the efficacy of recombinant vaccines based on the homologous virus. To circumvent this problem, a novel replication-defective adenoviral vaccine carrier based on an E1-deleted recombinant of the chimpanzee adenovirus 68 (AdC68) was developed. An AdC68 construct expressing a codon-optimized, truncated form of gag of HIV-1 induces CD8(+) T cells to gag in mice which at the height of the immune response encompass nearly 20% of the entire splenic CD8(+) T cell population. The vaccine-induced immune response provides protection to challenge with a vaccinia gag recombinant virus. Induction of transgene-specific CD8(+) T cells and protection against viral challenge elicited by the AdC68 vaccines is not strongly inhibited in animals preimmune to AdHu5 virus. However, the response elicited by the AdHu5 vaccine is greatly attenuated in AdHu5 preimmune animals.

Functional discrepancies in HIV-specific CD8+ T-lymphocyte populations are related to plasma virus load

The potent ability of current antiretroviral drug regimens to control human immunodeficiency Virus-1 (HIV-1) replication, in conjunction with the clinical practice of structured therapeutic interruptions, provides a system in which virus levels are manipulated during a persistent infection in humans. Here, we exploit this system to examine the impact of variable plasma virus load (pVL) on the functionality of HIV-specific CD8+ T-lymphocyte populations. Using both ELISpot methodology and intracellular cytokine staining for interferon (IFN)-gamma to assess functional status, together with fluorochrome-labeled peptide-major histocompatibility complex (pMHC) class I tetramer analysis to detect the physical presence of CD8+ T lymphocytes expressing cognate T-cell receptors (TCRs), we observed that the proportion of HIV-specific CD8+ T lymphocytes capable of mounting an effector response to antigen challenge directly ex vivo is related to the kinetics of virus exposure. Specifically, (a) after prolonged suppression of pVL with antiretroviral therapy (ART), physical and functional measures of HIV-specific CD8+ T-lymphocyte frequencies approximated; and (b) the percentage of functionally responsive cells in the HIV-specific CD8+ T lymphocyte populations declined substantially when therapy was discontinued and pVL recrudesced in the same patients. These results corroborate and extend observations in animal models that describe nonresponsive CD8+ T lymphocytes in the presence of high levels of antigen load and have implications for the interpretation of quantitative data generated by methods that rely on functional readouts.

Differences between T cell epitopes recognized after immunization and after infection

Evidence suggests that cellular immune responses play a crucial role in the control of HIV and SIV replication in infected individuals. Several vaccine strategies have therefore targeted these CD8(+) and CD4(+) responses. Whether vaccination induces the same repertoire of responses seen after infection is, however, a key unanswered question in HIV vaccine development. We therefore compared the epitope specificity induced by vaccination to that present postchallenge in the peripheral blood. Intracellular cytokine staining of PBMC stimulated with overlapping 15/20-mer peptides spanning the proteins of SIV were measured after DNA/modified vaccinia Ankara vaccination of eight rhesus macaques. Lymphocytes from 8 animals recognized a total of 39 CD8 epitopes and 41 CD4 epitopes encoded by the vaccine. T cell responses were again monitored after challenge with SIVmac239 to investigate the evolution of these responses. Only 57% of all CD8(+) T cell responses and 19% of all CD4(+) T cell responses present after vaccination were recalled after infection as measured in the peripheral blood. Interestingly, 29 new CD8 epitopes and 5 new CD4 epitopes were recognized by PBMC in the acute phase. These new epitopes were not detected after vaccination, and only some of them were maintained in the chronic phase (33% of CD8 and no CD4 responses). Additionally, 24 new CD8 epitopes and 7 new CD4 epitopes were recognized by PBMC in the chronic phase of infection. The repertoire of the immune response detected in the peripheral blood after immunization substantially differed from the immune response detected in the peripheral blood after infection.

Early and late effects of highly active antiretroviral therapy: a 2 year follow-up of antiviral-treated and antiviral-naive chronically HIV-infected patients

BACKGROUND

Control of HIV replication can be observed in highly active antiretroviral therapy (HAART)-treated and, occasionally, in HAART-naive patients. The immunological correlates of these situations were examined in a longitudinal study.

DESIGN

A prospective study. Immunovirological analyses in 16 chronically HIV-infected, HAART-naive patients (time 0) who started HAART. Fifteen patients (short-term HAART) were re-evaluated after 24 months (time 1). Results were compared with those of 30 patients who received HAART for more than 12 months before the study period (long-term HAART) and were analysed at the same timepoints. Fifteen patients who were antiviral therapy naive (naive) at both timepoints were also studied.

RESULTS

Over a 24-month period CD4 and CD8 cell counts and viraemia remained unchanged in naive and long-term HAART patients; CD4 cell counts increased and viraemia diminished in short-term HAART individuals. Antigen-stimulated proliferation was unmodified in naive and short-term HAART patients, but improved in long-term HAART individuals. Gp160-stimulated IL-2 and IFN-gamma production was augmented in long-term HAART patients and marginally modified in other patients. IL-7 production was unmodified in naive individuals, augmented in short-term HAART patients, and diminished in long-term HAART patients. Chemokine production was similar in all patients. Naive patients showed the highest CD8 cell counts at both timepoints.

CONCLUSION

HAART has a major impact on the outcome of HIV infection, even if functional immune modulation in HAART-treated patients is evident only after long periods of therapy. Low but detectable HIV replication in HAART-naive patients with preserved immune functions might not be associated with CD4 cell reduction, functional immune defects, or changes in viraemia.

CD8+ T-cell immunity to HIV infection

Fifteen years after the first, definitive reports of HIV-1-specific, CD8+ T cells [147,148], there is ample evidence for the importance of these cells in control of HIV-1 infection. As much is known of their role in the natural history of HIV-1 infection and their cellular and molecular mechanisms of reactivity than of T-cell responses to any other human virus. Indeed, HIV-1-related research has led the scientific field in revealing many new, fundamental principles of cellular immunity in the last 15 years. From these data, there are multiple, posited mechanisms for loss of CD8+ T-cell control of HIV-1 infection. These include both intrinsic defects in T-cell function and loss of T-cell recognition of HIV-1 because of its extraordinary genetic diversity and disruption of antigen presentation. Efforts have begun on devising approaches to reverse these immune defects in infected individuals and develop vaccines that induce T-cell immunity for protection from infection. Combination antiretroviral drug regimens now provide exceptional, long-lasting control of HIV-1 infection, even though they do not restore anti-HIV-1 T-cell immunity fully in persons with chronic HIV-1 infection. Very encouraging results show that such treatment can maintain normal T-cell reactivity specific for this virus in some persons with early HIV-1 infection. Unfortunately, the antiviral treatment does not cure the host of this persistent, latent virus. This has led to new strategies for immunotherapeutic intervention to enhance the level and breadth of the T-cell repertoire specific for the host's residual virus in persons with chronic HIV-1 infection. Although the principles of immunotherapy stem from early in the last century, modern era approaches are integrating highly sophisticated, molecular and cell biology reagents and methods for control of HIV-1 infection. The most promising immunotherapies are autologous virus activated in vivo by STI or administered in autologous DC that have been engineered ex vivo. There are also compelling rationales supported by animal models and early clinical trials for use of cytokines and chemokines as recombinant proteins or DNA to augment anti-HIV-1 T-cell reactivity and trafficking of T cells and APC to tissue sites of infection. For prevention of HIV-1 infection, the discouragingly poor results of vaccine development in the late 1980s and early 1990s have led to very encouraging, recent studies in monkeys that show partially protective and possibly sterilizing immunity. Finally, clinical trials of new-generation DNA and live vector vaccines already have indications of improved induction of HIV-1-specific T-cell responses. Knowledge of HIV-1-specific T-cell immunity and its role in protection from HIV-1 infection and disease must continue to expand until the goal of complete control of HIV-1 infection is accomplished.

Involvement of Bcl-2 and IL-2R in HIV-positive patients whose CD4 cell counts fail to increase rapidly with highly active antiretroviral therapy

OBJECTIVE

Combination antiretroviral therapy in a subset of HIV-infected patients, here called CD4-low responders (CD4-LR), fails to produce a rapid rise in CD4 cell counts despite effective control of plasma viral load (< 50 copies/ml). The mechanism responsible for this failure was investigated.

DESIGN AND METHODS

CD4-LR patients (n = 13) included in the study had been receiving stable antiretroviral therapy for > 9 months, resulting in undetectable viral load, but nontheless showed a CD4 cell count of < 200 x 106 cells/l. Samples from these patients were analysed for intracellular expression of the anti-apoptotic molecule Bcl-2 and the in vitro apoptosis of their CD4 lymphocytes. Since interleukin-2 (IL-2) induces Bcl-2 and participates in the control of lymphocyte apoptosis, we also investigated the IL-2/IL-2 receptor (IL-2R) system in these CD4-LR patients. All these investigations were performed before and after the CD4-LR patients received IL-2 therapy.

RESULTS

CD4 T lymphocytes from these patients underexpressed the anti-apoptotic molecule Bcl-2 and were more susceptible to spontaneous apoptosis. Peripheral CD4 T lymphocytes from the CD4-LR patients showed a regulatory dysfunction in the IL-2R system that resulted in a lack of reactivity to IL-2. Overall, the results obtained with CD4-LR patients differed radically from those in patients undergoing successful antiretroviral therapy. Finally, an increase in Bcl-2 expression and IL-2 reactivity was observed in the CD4 T lymphocytes of CD4-LR patients receiving IL-2 immunotherapy. This correlated with a reduction in their apoptosis.

CONCLUSION

Our study characterizes the defective maintenance of peripheral CD4 T lymphocytes in CD4-LR patients, probably resulting from Bcl-2 underexpression and dysregulation of the IL-2R system.

Identification of an HLA A*0201-restricted CD8(+) T-cell epitope for the glycoprotein B homolog of human herpesvirus 8

Human herpesvirus 8 (HHV-8; Kaposi sarcoma-associated herpesvirus)-specific cytotoxic T-lymphocyte (CTL) and interferon-gamma (IFN-gamma) responses to proteins produced during the lytic cycle of HHV-8 replication are mediated by HLA class I-restricted, CD8(+) T cells. We have characterized the fine specificity of the CD8(+) T-cell response to 25 peptides derived from 5 HHV-8 lytic cycle proteins based on a prediction model for HLA A*0201 binding motifs. One of the 25 HLA A*0201 peptides derived from the glycoprotein B (gB) homolog of Epstein-Barr virus (gB(492-500); LMWYELSKI; single-letter amino acid codes) bound to HLA A*0201 and stimulated IFN-gamma responses in CD8(+) T cells from HHV-8(+), HLA A*0201 persons, but not HHV-8-seronegative or non-HLA A*0201 persons. The peptide also induced IFN-gamma and CTL reactivity to naturally processed gB protein. The peptide was a major immunogenic epitope of HHV-8 as indicated by induction of IFN-gamma responses in peripheral blood mononuclear cells from 5 of 5 HHV-8 seropositive, HLA A*0201 persons when gB(492-500) was presented by autologous dendritic cells. T-cell reactivity to gB(492-500) was not related to detectable HHV-8 DNA in the blood. These data show that CD8(+) T cells recognize an HLA A*0201-restricted epitope for HHV-8 lytic cycle protein gB, particularly when presented by dendritic cells. This epitope may be important in control of HHV-8 infection by CD8(+) T cells.

Induction of anti-human immunodeficiency virus type 1 (HIV-1) CD8(+) and CD4(+) T-cell reactivity by dendritic cells loaded with HIV-1 X4-infected apoptotic cells

T-cell responses to X4 strains of human immunodeficiency virus type 1 (HIV-1) are considered important in controlling progression of HIV-1 infection. We investigated the ability of dendritic cells (DC) and various forms of HIV-1 X4 antigen to induce anti-HIV-1 T-cell responses in autologous peripheral blood mononuclear cells from HIV-1-infected persons. Immature DC loaded with HIV-1 IIIB-infected, autologous, apoptotic CD8(-) cells and matured with CD40 ligand induced gamma interferon production in autologous CD8(+) and CD4(+) T cells. In contrast, mature DC loaded with HIV-1 IIIB-infected, necrotic cells or directly infected with cell-free HIV-1 IIIB were poorly immunogenic. Thus, HIV-1-infected cells undergoing apoptosis serve as a rich source of X4 antigen for CD8(+) and CD4(+) T cells by DC. This may be an important mechanism of HIV-1 immunogenicity and provides a strategy for immunotherapy of HIV-1-infected patients on combination antiretroviral therapy.

Residual viral replication during antiretroviral therapy boosts human immunodeficiency virus type 1-specific CD8+ T-cell responses in subjects treated early after infection

Human immunodeficiency virus type 1 (HIV-1)-infected subjects treated early after infection have preserved HIV-1-specific CD4+ T-cell function. We studied the effect of highly active antiretroviral therapy (HAART) on the frequency of HIV-1-specific CD8+ T cells in patients treated during early (n = 31) or chronic (n = 23) infection. The degree of viral suppression and time of initiation of treatment influenced the magnitude of the CD8+ T-cell response. HIV-1-specific CD8+ T cells can increase in number after HAART in subjects treated early after infection who have episodes of transient viremia.

Vaccine protection against functional CTL abnormalities in simian human immunodeficiency virus-infected rhesus monkeys

Accumulating evidence suggests that HIV-specific CD8(+) CTL are dysfunctional in HIV-infected individuals with progressive clinical disease. In the present studies, cytokine production by virus-specific CTL was assessed in the rhesus monkey model for AIDS to determine its contribution to the functional impairment of CTL. CTL from monkeys infected with nonpathogenic isolates of simian and simian-human immunodeficiency virus expressed high levels of IFN-gamma, TNF-alpha, and IL-2 after in vitro exposure to a nonspecific mitogen or the optimal peptide representing a dominant virus-specific CTL epitope. However, similarly performed studies assessing these capabilities in CTL from monkeys infected with pathogenic immunodeficiency virus isolates demonstrated a significant dysfunction in the ability of the CTL to produce IL-2 and TNF-alpha. Importantly, CTL from vaccinated monkeys that effectively controlled the replication of a highly pathogenic simian-human immunodeficiency virus isolate following challenge demonstrated a preserved capacity to produce these cytokines. These experiments suggest that defects in cytokine production may contribute to CTL dysfunction in chronic HIV or SIV infection. Moreover, an AIDS vaccine that confers protection against clinical disease evolution in this experimental model also preserves the functional capacity of these CTL to produce both IL-2 and TNF-alpha.

Distribution of the natural killer-related receptor for HLA-C during highly active antiretroviral therapy for human immunodeficiency virus infection

Receptors interacting with Major Histocompatibility Complex class I molecules have been initially found on the surface of human natural killer (NK) cells, where they deliver inhibitory signals to the lysis, being thus defined killer inhibitory receptors (KIR). Subsequently, they were detected also on the surface of T-CD8(+) lymphocytes and are particularly expanded during human immunodeficiency virus (HIV) infection, where they downregulate HIV-specific cytolysis. The expression of KIR recognizing human leukocyte antigen-C alleles was assessed in HIV-infected patients, undergoing highly active antiretroviral therapy (HAART). To this end, the combined expression of CD16/CD56, of CD3 and CD8 as well as of KIR (CD158a and CD158b) surface molecules was analyzed on peripheral blood mononuclear cells by monoclonal antibodies, and flow cytometry. An increase of CD3(+)CD8(+)CD158b(+) cells was found after 6 months of HAART. This finding may have implications for the regulation of T-cell mediated cytolysis during HAART.

Structured antiretroviral treatment interruptions in chronically HIV-1-infected subjects

The risks and benefits of structured treatment interruption (STI) in HIV-1-infected subjects are not fully understood. A pilot study was performed to compare STI with continuous highly active antiretroviral therapy (HAART) in chronic HIV-1-infected subjects with HIV-1 plasma RNA levels (VL) <400 copies per ml and CD4(+) T cells >400 per microl. CD4(+) T cells, VL, HIV-1-specific neutralizing antibodies, and IFN-gamma-producing HIV-1-specific CD8(+) and CD4(+) T cells were measured in all subjects. STIs of 1-month duration separated by 1 month of HAART, before a final 3-month STI, resulted in augmented CD8(+) T cell responses in all eight STI subjects (P = 0.003), maintained while on HAART up to 22 weeks after STI, and augmented neutralization titers to autologous HIV-1 isolate in one of eight subjects. However, significant decline of CD4(+) T cell count from pre-STI level, and VL rebound to pre-HAART baseline, occurred during STI (P = 0.001 and 0.34, respectively). CD4(+) T cell counts were regained on return to HAART. Control subjects (n = 4) maintained VL <400 copies per ml and stable CD4(+) T cell counts, and showed no enhancement of antiviral CD8(+) T cell responses. Despite increases in antiviral immunity, no control of VL was observed. Future studies of STI should proceed with caution.

Decay kinetics of human immunodeficiency virus-specific CD8+ T cells in peripheral blood after initiation of highly active antiretroviral therapy

We measured the longitudinal responses to 95 HLA class I-restricted human immunodeficiency virus (HIV) epitopes and an immunodominant HLA A2-restricted cytomegalovirus (CMV) epitope in eight treatment-naive HIV-infected individuals, using intracellular cytokine staining. Patients were treated with highly active antiretroviral therapy (HAART) for a median of 78 weeks (range, 34 to 121 weeks). Seven of eight patients maintained an undetectable viral load for the duration of therapy. A rapid decline in HIV-specific CD8(+) T-cell response was observed at initiation of therapy. After an undetectable viral load was achieved, a slower decrease in HIV-specific CD8(+) T-cell response was observed that was well described by first-order kinetics. The median half-life for the rate of decay was 38.8 (20.3 to 68.0) weeks when data were expressed as percentage of peripheral CD8(+) T cells. In most cases, data were similar when expressed as the number of responding CD8(+) T cells per microliter of blood. In subjects who responded to more than one HIV epitope, rates of decline in response to the different epitopes were similar and varied by a factor of 2.2 or less. Discontinuation of treatment resulted in a rapid increase in HIV-specific CD8(+) T cells. Responses to CMV increased 1.6- and 2.8-fold within 16 weeks of initiation of HAART in two of three patients with a measurable CMV response. These data suggest that HAART quickly starts to restore CD8(+) T-cell responses to other chronic viral infections and leads to a slow decrease in HIV-specific CD8(+) T-cell response in HIV-infected patients. The slow decrease in the rate of CD8(+) T-cell response and rapid increase in response to recurrent viral replication suggest that the decrease in CD8(+) T-cell response observed represents a normal memory response to withdrawal of antigen.

Restoration of anti-human immunodeficiency virus type 1 (HIV-1) responses in CD8+ T cells from late-stage patients on prolonged antiretroviral therapy by stimulation in vitro with HIV-1 protein-loaded dendritic cells

We demonstrate that dendritic cells loaded in vitro with human immunodeficiency virus type 1 (HIV-1) protein-liposome complexes activate HLA class I-restricted anti-HIV-1 cytotoxic T-lymphocyte and gamma interferon (IFN-gamma) responses in autologous CD8+ T cells from late-stage HIV-1-infected patients on prolonged combination drug therapy. Interleukin-12 enhanced this effect through an interleukin-2- and IFN-gamma-mediated pathway. This suggests that dendritic cells from HIV-1-infected persons can be engineered to evoke stronger anti-HIV-1 CD8+ T-cell reactivity as a strategy to augment antiretroviral therapy.

T cell responses to recall antigens, alloantigen, and mitogen of HIV-infected patients receiving long-term combined antiretroviral therapy

The effect of highly active antiretroviral therapy (HAART) on T cell responses in 30 HIV-infected patients was studied. Lymphocyte proliferation in response to influenza A virus, HIV-1 p24, gp160, allogeneic leukocytes, and mitogen, as well as influenza-specific cytotoxic T lymphocyte (CTL) responses, were measured. AIDS patients had decreased T cell-proliferative responses to influenza and alloantigen compared with asymptomatic patients. Absence of positive proliferative responses of HIV-infected patients to HIV-1 antigens was not associated with increased interleukin 10 production. Correlation was observed between influenza-specific CTL response and T cell proliferation, as well as CD4+ T lymphocyte counts, indicating the importance of CD4+ helper T cells for generating antiviral CTL responses. Finally, these results show that HAART-treated asymptomatic patients, but not AIDS patients, have T cell responses comparable to those of control individuals. It remains to be determined whether immune-based therapy will contribute any additional benefit to patients who received HAART.

A significant number of human immunodeficiency virus epitope-specific cytotoxic T lymphocytes detected by tetramer binding do not produce gamma interferon

Despite the seemingly important role of cytotoxic T-lymphocyte (CTL) responses in human immunodeficiency virus (HIV) disease pathogenesis, their measurement has relied on a variety of different techniques. We utilized three separate methodologies for the detection of CTLs in a cohort of HIV-infected individuals who were also human leukocyte antigen A2 (HLA-A2) positive. Among the different CTL assays, a correlation was seen only when the Gag epitope-specific HLA A*0201-restricted tetramer assay was compared with the ELISPOT assay performed after stimulation with the Gag epitope; however, this correlation was of borderline statistical significance. On average, the tetramer reagent detected a 10-fold-higher number of cells than were seen to produce gamma interferon by the ELISPOT assay. The implications of this CTL assay comparison and the possibility of phenotypic differences in HIV-specific CD8(+) T lymphocytes are discussed.

Immunofluorescence analysis of T-cell responses in health and disease

The use of flow cytometry to study the functional responses of T cells by immunofluorescent staining for intracellular cytokines and other markers is a growing field of clinical interest. In this article, we describe methods for the rapid evaluation of T-cell responses to mitogens and specific antigens and explore how these assays might be valuable in various clinical settings.

CD8(+) T-cell gamma interferon production specific for human immunodeficiency virus type 1 (HIV-1) in HIV-1-infected subjects

The CD8(+)-T-cell response to human immunodeficiency virus type 1 (HIV-1) is considered to be important in host control of infection and prevention of AIDS. We have developed a single-cell enzyme immunoassay (enzyme-linked immunospot assay) specific for gamma interferon (IFN-gamma) production stimulated by either autologous B-lymphoblastoid cell lines (B-LCL) infected with vaccinia virus vectors expressing HIV-1 proteins or synthetic peptides representing known HIV-1 CD8(+) cytotoxic T-lymphocyte (CTL) epitopes. Single-cell IFN-gamma production stimulated by HIV-1 Gag-, Pol-, and Env-expressing B-LCL was a reliable measure of HIV-1-specific T-cell immunity in peripheral blood CD8(+) T cells from HIV-1 infected individuals. This method was more sensitive than stimulation of IFN-gamma by direct infection of the cultures with HIV-1-vaccinia virus vectors. Comparable results were found for IFN-gamma production in CD8(+) T cells from HIV-1-negative, cytomegalovirus (CMV)-seropositive, healthy donors stimulated with B-LCL expressing the CMV pp65 lower matrix protein. HIV-1 peptides were immunodominant for both CD8(+) single-cell IFN-gamma production and CTL precursor frequencies. The number of cells producing IFN-gamma decreased in individuals with late-stage HIV-1 infection and was temporally enhanced during combination antiretroviral therapy with two reverse transcriptase nucleoside inhibitors and a protease inhibitor.