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

Dramatic rise in plasma viremia after CD8(+) T cell depletion in simian immunodeficiency virus-infected macaques

To determine the role of CD8(+) T cells in controlling simian immunodeficiency virus (SIV) replication in vivo, we examined the effect of depleting this cell population using an anti-CD8 monoclonal antibody, OKT8F. There was on average a 99.9% reduction of CD8 cells in peripheral blood in six infected Macaca mulatta treated with OKT8F. The apparent CD8 depletion started 1 h after antibody administration, and low CD8 levels were maintained until day 8. An increase in plasma viremia of one to three orders of magnitude was observed in five of the six macaques. The injection of a control antibody to an infected macaque did not induce a sustained viral load increase, nor did it significantly reduce the number of CD8(+) T cells. These results demonstrate that CD8 cells play a crucial role in suppressing SIV replication in vivo.

Clonal Dominance Patterns of CD8 T Cells in Relation to Disease Progression in HIV-Infected Children

CD8 T cells are important mediators of cellular immune responses as evidenced by clonal expansions in the CD8 TCR Vβ repertoire during primary HIV infection in adults. This study investigated the CD8 TCR Vβ repertoire by complementarity-determining region 3 length analysis using multiplex PCR in purified peripheral blood CD8 T cells of 22 HIV-infected children (age range was 0.75–15 yr, mean was 8.2 ± 4.1 yr). Evidence of clonal dominance in one or more Vβ families was obtained in 15 of 22 children. The patterns of clonal dominance were designated as major, minor, single, and none to indicate the involvement of three or more, two, one, or no Vβ families, respectively. A pattern of major or minor clonal dominance was observed in 12 children (group 1), whereas 10 children had single or no clonal dominance (group 2). In comparison with group 2, the children in group 1 had a higher percentage of CD4 cells (28.3 ± 11.6 vs 8.6 ± 4.8, p < 0.001); a higher stimulation index in lymphoproliferative responses to Candida (92.0 ± 59.5 vs 12.3 ± 14.4, p = 0.002), tetanus (76.3 ± 51.2 vs 11.2 ± 12.7, p = 0.002), and alloantigens (178.3 ± 298.9 vs 32.9 ± 35.2, p < 0.001); and a lower percentage of CD8+HLA-DR+CD38+ cells (37.4 ± 13.1 vs 54.6 ± 14.2, p < 0.01). The number of dominant CD8 T cell clones was significantly correlated with the percentage of CD4 T cells (r = 0.669, p < 0.001) but not with plasma HIV RNA. Compared with group 1, patients in group 2 had a 4.8 times greater probability of having <15% CD4 cells. These findings indicate that CD8 clonal dominance in HIV-infected children reflects robustness of immune responses, regardless of time since infection and virus load.

HLA and HIV-1: heterozygote advantage and B*35-Cw*04 disadvantage

A selective advantage against infectious disease associated with increased heterozygosity at the human major histocompatibility complex [human leukocyte antigen (HLA) class I and class II] is believed to play a major role in maintaining the extraordinary allelic diversity of these genes. Maximum HLA heterozygosity of class I loci (A, B, and C) delayed acquired immunodeficiency syndrome (AIDS) onset among patients infected with human immunodeficiency virus-type 1 (HIV-1), whereas individuals who were homozygous for one or more loci progressed rapidly to AIDS and death. The HLA class I alleles B*35 and Cw*04 were consistently associated with rapid development of AIDS-defining conditions in Caucasians. The extended survival of 28 to 40 percent of HIV-1-infected Caucasian patients who avoided AIDS for ten or more years can be attributed to their being fully heterozygous at HLA class I loci, to their lacking the AIDS-associated alleles B*35 and Cw*04, or to both.

Enhanced cellular immunity to hepatitis C virus nonstructural proteins by codelivery of granulocyte macrophage-colony stimulating factor gene in intramuscular DNA immunization

Hepatitis C virus (HCV) nonstructural (NS) proteins appeared to be important targets for HCV vaccine development, since NS-specific T-helper-cell responses are associated with clearance from acute HCV infection. In this report, we have constructed a plasmid, pTV-NS345, that encodes the HCV NS3, NS4 and NS5 proteins (NS345) and a bicistronic plasmid, PTV-NS345/GMCSF, in which the HCV NS345 polyprotein and GMCSF are translated independently. Intramuscular inoculation with pTV-NS345 plasmid DNA into the Buffalo rats generated both antibody and T-cell proliferative responses to each NS protein. The expression of GMCSF, together with HCV NS345 proteins, appeared to significantly increase T-cell proliferative responses. In particular, the inoculation of a bicistronic plasmid generated higher T-cell proliferative responses to each NS protein than did the coinjection of two separate plasmids, pTV-NS345 and pTV-GMCSF. These results demonstrate that the codelivery of GMCSF augmented HCV NS345-specific cellular immunity and that the intensity of the immunity was differed depending on how GMCSF gene is codelivered.

HLA class I homozygosity accelerates disease progression in human immunodeficiency virus type 1 infection

Polymorphic products of HLA class I genes restrict cytotoxic T lymphocyte responses to the constantly evolving spectrum of HIV-1 antigens. Accordingly, homozygosity at class I loci can reduce the repertoire for such HLA-dependent interactions, leading to accelerated disease progression. To test this hypothesis we studied subjects from two distinct HIV/AIDS cohorts: 140 Dutch homosexual men and 202 Rwandan heterosexual women followed up to 13 years from HIV-1 seroconversion. We performed intermediate- and selective high-resolution molecular typing at HLA class I (A, B, and C) and high-resolution typing at HLA class II DRB1 and DQB1. Homozygosity at the HLA-A or -B locus or both was found at increasingly high frequency among individuals with successively more rapid progression to late-stage HIV-1-related conditions. In the combined cohorts (n = 342) the odds ratio (OR) due to HLA-A or -B antigen homozygosity in rapid versus slow progressors was 3.8 (p = 0.003); for Dutch men alone the OR was 3.5 (p = 0.102), and for Rwandan women the OR was 4.1 (p = 0.009). In contrast, homozygous genotypes at either HLA-C, DRB1, or DQB1 alone, or DRB1-DQB1 haplotypes, did not exert any deleterious effect on HIV-1 disease progression. These findings suggest strongly that diversity in addition to sequence specificity at HLA-A and -B loci can influence the rate of disease progression following HIV-1 infection.

HIV-1-Specific CTL Responses Primed In Vitro by Blood-Derived Dendritic Cells and Th1-Biasing Cytokines

Vaccine strategies designed to elicit strong cell-mediated immune responses to HIV Ags are likely to lead to protective immunity against HIV infection. Dendritic cells (DC) are the most potent APCs capable of priming both MHC class I- and II-restricted, Ag-specific T cell responses. Utilizing a system in which cultured DC from HIV-seronegative donors were used as APC to present HIV-1 Ags to autologous T cells in vitro, the strength and specificity of primary HIV-specific CTL responses generated to exogenous HIV-1 Nef protein as well as intracellularly expressed nef transgene product were investigated. DC expressing the nef gene were able to stimulate Nef-specific CTL, with T cells from several donors recognizing more than one epitope restricted by a single HLA molecule. Primary Nef-specific CTL responses were also generated in vitro using DC pulsed with Nef protein. T cells primed with Nef-expressing DC (via protein or transgene) were able to lyse MHC class I-matched target cells pulsed with defined Nef epitope peptides as well as newly identified peptide epitopes. The addition of Th1-biasing cytokines IL-12 or IFN-α, during priming with Nef-expressing DC, enhanced the Nef-specific CTL responses generated using either Ag-loading approach. These results suggest that this in vitro vaccine model may be useful in identifying immunogenic epitopes as vaccine targets and in evaluating the effects of cytokines and other adjuvants on Ag-specific T cell induction. Successful approaches may provide information important to the development of prophylactic HIV vaccines and are envisioned to be readily translated into clinical DC-based therapeutic vaccines for HIV-1.

Construction and characterization of recombinant VLPs and Semliki-Forest virus live vectors for comparative evaluation in the SHIV monkey model

For testing of recombinant virus-like particles (VLPs) in the SHIV monkey model, SIVmac239 Pr56gag precursor-based pseudovirions were modified by HIV-1 gp160 derived peptides. First, well-characterized epitopes from the HIV-1 envelope glycoprotein were inserted into the Pr56gag precursor by replacing defined regions that were shown to be dispensable for virus particle formation. Expression of these chimeric proteins in a baculovirus expression system resulted in efficient assembly and release of non-infectious, hybrid VLPs. In a second approach the HIV-1IIIB external glycoprotein gp120 was covalently linked to an Epstein-Barr virus derived transmembrane domain. Coexpression of the hybrid envelope derivative with the Pr56gag precursor yielded recombinant SIV derived Pr56gag particles with the HIV-1 gp120 firmly anchored on the VLP surface. Immunization of rhesus monkeys with either naked VLPs or VLPs adsorbed to alum induced substantial serum antibody titers and promoted both T helper cell and cytotoxic T lymphocyte responses. Furthermore, priming macaques with the corresponding set of recombinant Semliki-Forest viruses tended to enhance the immunological outcome. Challenge of the immunized monkeys with chimeric SHIV resulted in a clearly accelerated reduction of the plasma viremia as compared to control animals.

Acute effects of pathogenic simian-human immunodeficiency virus challenge on vaccine-induced cellular and humoral immune responses to Gag in rhesus macaques

Simian-human immunodeficiency virus (SHIV) infection in macaques provides a convenient model for testing vaccine efficacy and for understanding viral pathogenesis in AIDS. We immunized macaques with recombinant, Salmonella typhimurium (expressing Gag) or soluble Gag in adjuvant to generate T-cell-dependent lymphoproliferative or serum antibody responses. Immunized animals were challenged by intrarectal inoculation with SHIV89.6PD. Virus infection was accompanied by rapid losses of lymphoproliferative responses to Gag or phytohemagglutinin. By 8 weeks, mitogen responses recovered to near normal levels but antigen-specific immunity remained at low or undetectable levels. Serum antibody levels were elevated initially by virus exposure but soon dropped well below levels achieved by immunization. Our studies show a rapid depletion of preexisting Gag-specific CD4(+) T cells that prevent or limit subsequent antiviral cellular and humoral immune responses during acute SHIV infection.

Rapid Death of Adoptively Transferred T Cells in Acquired Immunodeficiency Syndrome

Human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) probably play the major role in controlling HIV replication. However, the value of adoptive transfer of HIV-specific CTL expanded in vitro to HIV+ patients has been limited: this contrasts with the success of CTL therapy in treating or preventing Epstein-Barr virus and cytomegalovirus disease after bone marrow transplantation (BMT). We investigated the fate of expanded HIV-specific CTL clones in vivo following adoptive transfer to a patient with acquired immunodeficiency syndrome (AIDS). Two autologous CTL clones specific for HIV Gag and Pol were expanded to large numbers (>109) in vitro and infused into an HIV-infected patient whose viral load was rising despite antiretroviral therapy. The fate of one clone was monitored by staining peripheral blood mononuclear cells (PBMCs) with T-cell receptor–specific tetrameric major histocompatibility complex (MHC)-peptide complexes. Although the CTL transfer was well tolerated, there were no significant changes in CD4 and CD8 lymphocyte counts and virus load. By tracking an infused clone using soluble MHC-peptide complexes, we show that cells bearing the Gag-specific T-cell receptors were rapidly eliminated within hours of infusion through apoptosis. Thus, the failure of adoptively transferred HIV-specific CTL to reduce virus load in AIDS may be due to rapid apoptosis of the infused cells, triggered by a number of potential mechanisms. Further trials of adoptive transfer of CTL should take into account the susceptibility of infused cells to in vivo apoptosis.

Rapid Death of Adoptively Transferred T Cells in Acquired Immunodeficiency Syndrome

Human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) probably play the major role in controlling HIV replication. However, the value of adoptive transfer of HIV-specific CTL expanded in vitro to HIV+ patients has been limited: this contrasts with the success of CTL therapy in treating or preventing Epstein-Barr virus and cytomegalovirus disease after bone marrow transplantation (BMT). We investigated the fate of expanded HIV-specific CTL clones in vivo following adoptive transfer to a patient with acquired immunodeficiency syndrome (AIDS). Two autologous CTL clones specific for HIV Gag and Pol were expanded to large numbers (>109) in vitro and infused into an HIV-infected patient whose viral load was rising despite antiretroviral therapy. The fate of one clone was monitored by staining peripheral blood mononuclear cells (PBMCs) with T-cell receptor–specific tetrameric major histocompatibility complex (MHC)-peptide complexes. Although the CTL transfer was well tolerated, there were no significant changes in CD4 and CD8 lymphocyte counts and virus load. By tracking an infused clone using soluble MHC-peptide complexes, we show that cells bearing the Gag-specific T-cell receptors were rapidly eliminated within hours of infusion through apoptosis. Thus, the failure of adoptively transferred HIV-specific CTL to reduce virus load in AIDS may be due to rapid apoptosis of the infused cells, triggered by a number of potential mechanisms. Further trials of adoptive transfer of CTL should take into account the susceptibility of infused cells to in vivo apoptosis.

Nef-induced CD4 and major histocompatibility complex class I (MHC-I) down-regulation are governed by distinct determinants: N-terminal alpha helix and proline repeat of Nef selectively regulate MHC-I trafficking

The Nef protein of primate lentiviruses triggers the accelerated endocytosis of CD4 and of class I major histocompatibility complex (MHC-I), thereby down-modulating the cell surface expression of these receptors. Nef acts as a connector between the CD4 cytoplasmic tail and intracellular sorting pathways both in the Golgi and at the plasma membrane, triggering the de novo formation of CD4-specific clathrin-coated pits (CCP). The downstream partners of Nef in this event are the adapter protein complex (AP) of CCP and possibly a subunit of the vacuolar ATPase. Whether Nef-induced MHC-I down-regulation stems from a similar mechanism is unknown. By comparing human immunodeficiency virus type 1 (HIV-1) Nef mutants for their ability to affect either CD4 or MHC-I expression, both in transient-transfection assays and in the context of HIV-1 infection, it was determined that Nef-induced CD4 and MHC-I down-regulation constitute genetically and functionally separate properties. Mutations affecting only CD4 regulation mapped to residues previously shown to mediate the binding of Nef to this receptor, such as W57 and L58, as well as to an AP-recruiting dileucine motif and to an acidic dipeptide in the C-terminal region of the protein. In contrast, mutation of residues in an alpha-helical region in the proximal portion of Nef and amino acid substitutions in a proline-based SH3 domain-binding motif selectively affected MHC-I down-modulation. Although both the N-terminal alpha-helix and the proline-rich region of Nef have been implicated in recruiting Src family protein kinases, the inhibitor herbimycin A did not block MHC-I down-regulation, suggesting that the latter process is not mediated through an activation of this family of tyrosine kinases.

DNA inoculations with HIV-1 recombinant genomes that express cytokine genes enhance HIV-1 specific immune responses

Vaccination with HIV-1 DNA sequences induce both humoral and cellular immune responses in experimental animals. However, these responses are relatively weak and are often only transient in their nature. In order to enhance the level of HIV-1 specific immunity, we have engineered HIV-1 DNA constructs which contained various cytokine genes such as interleukin-2 (IL-2), granulocyte-macrophage colony stimulating factor (GM-CSF) and interferon-gamma (IFN-gamma) gene. These constructs have deleted the tat and nmf genes of HIV-1 to eliminate their immunosuppressive effects. Immunizations with these recombinant constructs elicited moderate proliferative T cell responses but poor antibody responses in rats. However, inoculations of HIV-1 DNA that contained the GM-CSF or the IL-2 gene significantly enhanced humoral and proliferative T cell responses, respectively. Thus, recombinant HIV-1 genomes such as those described here may increase the efficacy of DNA vaccination.

Presence of HLA-C-restricted cytotoxic T-lymphocyte responses in long-term nonprogressors infected with human immunodeficiency virus

Approximately 5% of people with human immunodeficiency virus type 1 (HIV-1) infection remain free of disease for 10 or more years. These long-term nonprogressors (LTNPs) exhibit lower viral loads and stable CD4+ lymphocyte counts. The immunologic basis for this disease-free condition is not known. Because cytotoxic T lymphocytes (CTLs) constitute a major immune defense mechanism for sustained recovery from viral infections, we analyzed HIV-specific CTL responses in three asymptomatic LTNPs. We observed the presence of HIV-1 envelope-specific CTL responses mediated by HLA class I C-restricted CD8+ cells in these individuals. Using autologous target cells and a panel of HLA-matching and -mismatching B-cell lines as targets, we determined that HLA-Cw7 is the restricting element for the observed CTL activity. Additionally, we identified three peptides, one previously not reported, from conserved regions in the envelope protein as CTL epitopes. We previously reported these peptides to be efficient in inducing HIV-specific cellular immune responses in murine and nonhuman primate models. Our results support the role of the HLA-C locus in generating CTL responses and constitute the first report of an HLA-Cw7-restricted HIV-1 envelope-specific CTL response in HIV+ LTNPs, which may be important in the control of HIV replication in vivo.

A synthetic peptide from the first conserved region in the envelope protein gp160 is a strong T-cell epitope in HIV-infected chimpanzees and humans

We reported earlier that synthetic peptides corresponding to highly conserved regions in the envelope protein gp160 of the human immunodeficiency virus type 1 (HIV-1), in particular an 11-amino acid sequence (peptide 104) from the first conserved region at the amino-terminus, were capable of inducing strong HIV-specific T-cell proliferative responses in several inbred mouse strains as well as in outbred Rhesus monkeys. We have now obtained evidence of the presence of significant levels of proliferative response to peptide 104 in 7 of 9 chimpanzees chronically infected with HIV-1 (p < or = 0.05) and 8 of 17 HIV+ individuals (p < or = 0.001). Further, four other conserved HIV envelope-derived peptides, identified previously in our murine and Rhesus monkey model systems, were widely recognized as T-cell epitopes in both chimpanzees and humans infected with HIV-1. In none of the infected subjects did peripheral blood mononuclear cells show proliferative responses to unrelated control peptides. Also, neither the control normal chimpanzees nor HIV-seronegative individuals showed proliferative responses to the conserved peptides. With respect to the humoral responses, serum samples from none of the chimpanzees showed reactivity with any of the conserved peptides, and only low levels of antibody responses against peptide 104 were observed in 3 of the 17 patients (p > 0.05). Importantly, three of the conserved envelope-derived peptides, including peptide 104, overlap with sequences that were reported in the literature to be epitopes for virus-induced cytotoxic T lymphocytes in asymptomatic HIV+ individuals. These observations, together with our results in multiple animal models and humans, establish that these conserved HIV envelope-derived peptides, particularly peptide 104, are significant T-cell epitopes with potential usefulness for induction of HIV-specific cell-mediated immune responses in humans.

Therapeutic vaccination with p24-VLP and zidovudine augments HIV-specific cytotoxic T lymphocyte activity in asymptomatic HIV-infected individuals

This study evaluates the impact of therapeutic vaccination with p24-VLP and zidovudine on the induction or maintenance of HIV-specific cytotoxic lymphocyte activity in a cohort of asymptomatic patients with CD4 counts greater than 400 cells/microl. In a dummy, randomized, phase II clinical trial of the therapeutic vaccine, participants were randomized to one of three arms for 6 months: p24-VLP (500 microg) in alum monthly plus zidovudine 200 mg tds, alum adjuvant plus zidovudine, or p24-VLP plus placebo. Subjects were studied for a total of 52 weeks from baseline. Monitoring included viral load, CD4 and CD8 counts, markers of immune activation, delayed-type hypersensitivity (DTH) skin testing, and cytotoxic T lymphocyte (CTL) measurement. The nine subjects who received p24-VLP and zidovudine had an augmentation and/or broadening of their CTL response compared with baseline (p = 0.004). The eight subjects receiving p24-VLP and seven subjects receiving zidovudine did not have a statistically significant increase or broadening of CTL activity. The augmentation of the CTL response in the subjects who received p24-VLP and zidovudine was not associated with a decline in viral load or an increase in CD8 counts. This study suggests that HIV-specific CTL activity can be augmented in HIV-infected individuals receiving p24-VLP and zidovudine, supporting the hypothesis of therapeutic vaccination in the presence of antiretroviral therapy.

Protease inhibitors as initial therapy for individuals with an intermediate risk of HIV disease progression: is more necessarily better?

OBJECTIVE

To compare three possible therapeutic strategies for the treatment of patients with an intermediate risk of HIV disease progression.

DESIGN

Mathematical modeling based on assumptions derived from published data.

METHODS

A parametric survival model was fitted to empirical data to describe the survival trajectory of untreated individuals. It was assumed that successful treatment decreases the risk of disease progression curing the first year after its introduction by a constant that is dependent on the magnitude of the initial drop in HIV viral load. Thereafter, individual members of the treatment cohort follow different pathways, depending on the duration of the initial response or, in case of virologic failure, the response to a new drug regimen.

RESULTS

Sub-groups of patients starting therapy with two nucleoside reverse transcriptase inhibitors (NRTI) or two NRTI and a protease inhibitor had the highest instantaneous risk of disease progression at the end of the 5-year follow-up period. Patients who started therapy with two NRTI and a non-NRTI had the lowest likelihood of progression to AIDS or death at 5 years of follow-up. This is because, in the case of the subgroup whose initial treatment included a protease inhibitor, failure rates due to non-adherence to therapy are high and response to salvage therapy is limited by past protease inhibitor experience.

CONCLUSIONS

Despite the superior virologic potency of the protease inhibitor-containing regimens, in this analysis other strategies performed equally well or even better. In the absence of solid empirical data and until the advent of antiretroviral regimens that are shown to be safe, simple to take, and maximally suppress viral load, caution may be required in selecting the long-term therapy for patients with less advanced HIV disease.

Serum HIV-1 p24 antibody, HIV-1 RNA copy number and CD4 lymphocyte percentage are independently associated with risk of mortality in HIV-1-infected children. National Institute of Child Health and Human Development Intravenous Immunoglobulin Clinical Trial Study Group

OBJECTIVE

The role of HIV-1 antibody in modulating disease progression must be assessed in the context of other immune and viral load markers. We evaluated the association between HIV-1 p24 antibody, HIV-1 RNA, immune complex-dissociated (ICD) p24 antigen, CD4 cell percentage, and mortality in a cohort of 218 HIV-infected children enrolled in a trial of intravenous immunoglobulin prophylaxis of bacterial infections.

METHODS

CD4 cell percentage was measured and sera collected and stored at baseline and every 3 months on study (1988-1991). Stored sera were assayed for HIV-1 p24 antibody, HIV-1 RNA, and ICD p24 antigen. Mortality was recorded during the trial and updated through 1996 (mean total follow-up, 6.3 years).

RESULTS

Eighty-one (37%) children died; probability of mortality for children with baseline HIV-1 p24 antibody concentrations of undetectable (< 1), 1-4, 5-124, and > or = 125 reciprocal titer units (RTU) was 61, 50, 24, and 10%, respectively. A 3.5-fold increase in the relative risk (RR) of death [95% confidence interval (CI), 2.2-5.5] was observed among children with baseline HIV-1 p24 antibody concentration < 5 RTU compared with > or = 5 RTU. In multivariate analyses, p24 antibody, HIV-1 RNA, and CD4 cell percentage but not ICD p24 antigen were independently associated with mortality; the RR of death increased by 1.7 (95% CI, 1.3-2.1) for each log10 decrement in baseline HIV-1 p24 antibody.

CONCLUSIONS

HIV-1 p24 antibody, HIV-1 RNA and CD4 cell percentage independently predict mortality amongst infected children. Whereas CD4 cell percentage provides an estimate of the general degree of immune suppression, HIV-1 p24 antibody could provide an easily obtained, inexpensive assessment of CD4 cell function and could augment prognostic information provided by CD4 cell count and viral load for clinical management of infected children.

Decay kinetics of human immunodeficiency virus-specific effector cytotoxic T lymphocytes after combination antiretroviral therapy

Little is known of the changes in human immunodeficiency virus type 1 (HIV-1)-specific effector cytotoxic T lymphocytes (CTL) after potent antiretroviral therapy. Using HLA/peptide tetrameric complexes, we show that after starting treatment, there are early rapid fluctuations in the HIV-1-specific CTL response which last 1 to 2 weeks. These fluctuations are followed by an exponential decay (median half-life, 45 days) of HIV-1-specific CTL which continues while viremia remains undetectable. These data have implications for the immunological control of drug-resistant virus.

Cytokine molecular adjuvants modulate immune responses induced by DNA vaccine constructs for HIV-1 and SIV

DNA or nucleic acid immunization has been shown to induce both antigen-specific cellular and humoral immune responses in vivo. Moreover, immune responses induced by DNA immunization can be enhanced and modulated by the use of molecular adjuvants. To further engineer the immune response in vivo, we investigated the induction and regulation of immune responses from the codelivery of Thl cytokines (interleukin-2 [IL-2] and IL-12), Th2 cytokines (IL-4 and IL-10), and granulocyte-macrophage colony-stimulating factor (GM-CSF) genes along with a DNA vaccine construct encoding for simian immunodeficiency virus (SIV) gag/pol proteins. We observed that coinjection with IL-2, IL-4, IL-10, and GM-CSF resulted in increased levels of antigen-specific antibodies. In addition, we found that coinjection with cytokine genes drove the immune responses toward a more Thl or Th2 phenotype. We also observed that coadministration of IL-2, IL-12, and GM-CSF genes resulted in a dramatic enhancement of Th proliferation responses. Moreover, coimmunization with IL-12 genes resulted in a dramatic enhancement of antigen-specific cytotoxic T lymphocyte (CTL) responses. These results support the potential utility of molecular adjuvants in DNA vaccine regimens.

Effect of protease therapy on cytokine secretion by peripheral blood mononuclear cells (PBMC) from HIV-infected subjects

The viral load reduction seen in patients with late stage HIV infection treated with the protease inhibitor, ritonavir, is accompanied by increases in the in vitro proliferative responses generated by PBMC. The present study was undertaken to investigate which lymphocyte subsets generated these responses and the effects of therapy on cytokine production. Lymphoproliferation following phytohaemagglutinin (PHA) stimulation was studied by thymidine incorporation, and production of IL-2, interferon-gamma (IFN-gamma) and IL-4 was assessed by ELISA in 12 patients receiving ritonavir and seven receiving placebo in the context of randomized, blinded clinical trials. CD4+ cell-depleted and CD8+ cell-depleted subsets were obtained from PBMC by immunomagnetic bead depletion. At week 4 of therapy a two-fold or greater increase in proliferative responses was observed in 9/12 subjects receiving therapy, compared with 0/7 receiving placebo. Similarly there was a significant increase in IL-2 and IFN-gamma production of 2.7-fold (P = 0.02) and 1.7-fold (P = 0.03), respectively, in the treatment group compared with those receiving placebo. No change in IL-4 production was observed. Despite these increases, cytokine responses post-therapy were still reduced compared with both healthy controls and asymptomatic HIV-infected subjects. Increases in proliferative response and IL-2 production were greater in the CD8+ cell-depleted population than in the CD4+ cell-depleted population, whereas increases in IFN-gamma production were derived from the CD4+ cell-depleted population.

Induction and Maintenance Treatment Regimens for HIV-1 Infection in Vitro

Can aggressive anti-human immunodeficiency virus (HIV) induction regimens be simplified after sufficient virus suppression is achieved? In vitro studies were conducted to evaluate the hypothesis that aggressive induction regimens could be followed by less aggressive maintenance regimens. A clinical HIV-1 isolate and lymphoblastoid cell line (H9) were employed. Virus multiplicities were varied, as were drug inhibitory concentrations (IC90, IC99) and induction periods (1, 2 and 3 weeks) of a three-drug regimen (zidovudine plus lamivudine and indinavir), following which maintenance regimens (no drug, zidovudine alone, indinavir alone, zidovudine plus lamivudine) were employed. After 1 week inductions at IC99 concentrations, viral rebound occurred on none or one-drug maintenance regimens but not on a two-drug regimen. After 2 week inductions, viral rebound occurred with no-drug maintenance, but not with one- and two-drug regimens. After 3 week inductions, viral rebound did not occur in zero-, one-, or two-drug maintenance regimens, although HIV-1 DNA persisted in cultured cells. These studies suggest that although some induction–maintenance regimens will fail, after a sufficient period of HIV-1 suppression with a three-drug antiretroviral regimen, maintenance on fewer drugs may be feasible.

Enhancement of cellular immune response in HIV-1 seropositive individuals: A DNA-based trial

A DNA-based vaccine containing HIV-1 Env and Rev genes was tested for safety and host immune response in 15 HIV-infected asymptomatic patients with CD4-positive lymphocyte counts >/=500/microl of blood and receiving no antiviral therapy. Successive groups of patients received three doses of vaccine at 30, 100, or 300 microg at 10-week intervals in a dose-escalation trial. Some changes were noted in cytotoxic T-lymphocyte activity against gp160-bearing targets. Importantly, enhanced specific lymphocyte proliferative activity against HIV-1 envelope was observed in multiple patients. Three of three patients in the 300-microg dose group also developed increased MIP-1alpha levels which were detectable in their serum. Interestingly patients in the lowest dose group showed no overall changes in the immune parameters measured. The majority of patients who exhibited increases in any immune parameters were contained within the 300 microg, which was the highest dose group. These studies support further investigation of this technology for the production of antigen-specific immune responses in humans.

In vivo migration and function of transferred HIV-1-specific cytotoxic T cells

The persistence of HIV replication in infected individuals may reflect an inadequate host HIV-specific CD8+ cytotoxic T lymphocyte (CTL) response. The functional activity of HIV-specific CTLs and the ability of these effector cells to migrate in vivo to sites of infection was directly assessed by expanding autologous HIV-1 Gag-specific CD8+ CTL clones in vitro and adoptively transferring these CTLs to HIV-infected individuals. The transferred CTLs retained lytic function in vivo, accumulated adjacent to HIV-infected cells in lymph nodes and transiently reduced the levels of circulating productively infected CD4+ T cells. These results provide direct evidence that HIV-specific CTLs target sites of HIV replication and mediate antiviral activity, and indicate that the development of immunotherapeutic approaches to sustain a strong CTL response to HIV may be a useful adjunct to treatment of HIV infection.

Strong human immunodeficiency virus (HIV)-specific cytotoxic T-lymphocyte activity in Sydney Blood Bank Cohort patients infected with nef-defective HIV type 1

Proposals for the use of live attenuated human immunodeficiency virus (HIV) type 1 (HIV-1) as a vaccine candidate in humans have been based on the protection afforded by attenuated simian immunodeficiency virus in the macaque model. Although it is not yet known if this strategy could succeed in humans, a study of the Sydney Blood Bank Cohort (SBBC), infected with an attenuated HIV-1 quasispecies with natural nef and nef/long terminal repeat deletions for up to 17 years, could provide insights into the long-term immunological consequences of living with an attenuated HIV-1 infection. In this study, HIV-specific cytoxic T-lymphocyte (CTL) responses in an SBBC donor and six recipients were examined over a 3-year period with enzyme-linked immunospot, tetrameric complex binding, direct CTL lysis, and CTL precursor level techniques. Strong HIV-specific CTL responses were detected in four of seven patients, including one patient with an undetectable viral load. Two of seven patients had weak CTL responses, and in one recipient, no HIV-specific CTLs were detected. High levels of circulating effector and memory HIV-specific CTLs can be maintained for prolonged periods in these patients despite very low viral loads.

Identification of a Conserved Universal Th Epitope in HIV-1 Reverse Transcriptase That Is Processed and Presented to HIV-Specific CD4+ T Cells by at Least Four Unrelated HLA-DR Molecules

CD4+ Th cells play an important role in the induction and maintenance of specific T cell immunity. Indications for a protective role of CD4+ T cells against HIV-1 infection were found in subjects who were able to control HIV-1 viremia as well as in highly HIV-1-exposed, yet seronegative, individuals. This study describes the identification of an HIV-1-specific Th epitope that exhibits high affinity binding as well as high immunogenicity in the context of at least four different HLA-DR molecules that together cover 50–60% of the Caucasian, Oriental, and Negroid populations. This HIV-1 reverse transcriptase-derived peptide (RT171–190) is highly conserved among different HIV-1 isolates. Importantly, stimulation of PBL cultures from HIV-1 seronegative donors with this peptide resulted in Th1-type lymphocytes capable of efficient recognition of HIV-1-pulsed APCs. Taken together, these data indicate that peptide RT171–190 constitutes an attractive component of vaccines aiming at induction or enhancement of HIV-1-specific T cell immunity.

Viral immune evasion due to persistence of activated T cells without effector function

We examined the regulation of virus-specific CD8 T cell responses during chronic lymphocytic choriomeningitis virus (LCMV) infection of mice. Our study shows that within the same persistently infected host, different mechanisms can operate to silence antiviral T cell responses; CD8 T cells specific to one dominant viral epitope were deleted, whereas CD8 T cells responding to another dominant epitope persisted indefinitely. These virus-specific CD8 T cells expressed activation markers (CD69(hi), CD44(hi), CD62Llo) and proliferated in vivo but were unable to elaborate any antiviral effector functions. This unresponsive phenotype was more pronounced under conditions of CD4 T cell deficiency, highlighting the importance of CD8- CD4 T cell collaboration in controlling persistent infections. Importantly, in the presence of CD4 T cell help, adequate CD8 effector activity was maintained and the chronic viral infection eventually resolved. The persistence of activated virus-specific CD8 T cells without effector function reveals a novel mechanism for silencing antiviral immune responses and also offers new possibilities for enhancing CD8 T cell immunity in chronically infected hosts.

Viral immune evasion due to persistence of activated T cells without effector function

We examined the regulation of virus-specific CD8 T cell responses during chronic lymphocytic choriomeningitis virus (LCMV) infection of mice. Our study shows that within the same persistently infected host, different mechanisms can operate to silence antiviral T cell responses; CD8 T cells specific to one dominant viral epitope were deleted, whereas CD8 T cells responding to another dominant epitope persisted indefinitely. These virus-specific CD8 T cells expressed activation markers (CD69(hi), CD44(hi), CD62Llo) and proliferated in vivo but were unable to elaborate any antiviral effector functions. This unresponsive phenotype was more pronounced under conditions of CD4 T cell deficiency, highlighting the importance of CD8- CD4 T cell collaboration in controlling persistent infections. Importantly, in the presence of CD4 T cell help, adequate CD8 effector activity was maintained and the chronic viral infection eventually resolved. The persistence of activated virus-specific CD8 T cells without effector function reveals a novel mechanism for silencing antiviral immune responses and also offers new possibilities for enhancing CD8 T cell immunity in chronically infected hosts.

Role of preimmunization virus sequences in cellular immunity in HIV-infected patients during HIV type 1 MN recombinant gp160 immunization

The effect of patient preimmunization virus sequences on CTL responses during gp160 immunization were studied. Ten HLA-A2+, HIV+ asymptomatic patients with CD4+ T cells >500/mm3 were given two courses of HIV-1 MN rgp160 vaccine over a 2-year period. Envelope epitope-specific CTL responses, using PBMCs, were measured against peptide-coated autologous B lymphoblastoid cell lines. Optimum CTL epitopes were determined by HLA-A2-binding affinity of 9- to 10-mer peptides containing the HLA-A2.1-binding motif. Ten of the high- or intermediate-binding peptides were conserved among >50% of reported clade B HIV strains. These peptide-specific CTL activities and the patient virus sequences in peptide-coding regions were monitored. Six patients showed envelope peptide-specific CTL responses, which correlated with the presence of whole envelope antigen-specific CTL responses. Five of these patients, who showed responses to epitopes in the gp41 region (aa 814-824), had preimmunization virus similar to the vaccine sequence in this region. Three patients who did not show these epitope-specific responses had initially different sequences in the HIV gene encoding that region. The epitope-specific CTL responses appear to reflect recall responses, as only patients infected with virus containing the vaccine sequence developed them and they could be recalled with a second set of vaccine injections. This appears to be reminiscent of the concept of T cell "original antigenic sin." This vaccine was also immunogenic as measured by gp160-specific lymphocyte-proliferative responses. However, increased immune responses did not impact the HIV load or CTL epitope sequences during therapy.

Safety and immunogenicity of HIV recombinant envelope vaccines in HIV-infected infants and children. National Institutes of Health-sponsored Pediatric AIDS Clinical Trials Group (ACTG-218)

Study objectives were to evaluate the safety and immunogenicity of three HIV recombinant glycoproteins in HIV-infected infants and children between 1 month and 18 years of age with asymptomatic (P-1) infection. Using Chiron rgp 120 (SF-2) 15 or 50 microg; MicroGeneSys rgp 160 (IIIB) 40 or 320 microg; Genentech rgp120 (MN) 75 or 300 microg; or adjuvant control (Alum or MF-59), children were randomized to a double-blind, placebo-controlled, dose-escalating study of vaccine administered intramuscularly at entry and 1, 2, 3, 4, and 6 months later. No adverse events were attributed to study vaccines. Between 30% and 56% of volunteers exhibited a lymphoproliferative response as defined in terms of stimulation index (SI) to vaccine antigens; 65% of vaccinees but none of placebo recipients exhibited moderate or strong responses after enzyme immunoassay to HIV specific antigens. CD4 cell counts and quantitative HIV culture did not differ significantly among vaccine and control groups, nor were differences found among groups in HIV disease progression. The rgp160 and gp120 subunit vaccines were safe and immunogenic in this population.

The optimization of helper T lymphocyte (HTL) function in vaccine development

Helper T lymphocyte (HTL) responses play an important role in the induction of both humoral and cellular immune responses. Therefore, HTL epitopes are likely to be a crucial component of prophylactic and immunotherapeutic vaccines. For this reason, Pan DR helper T cell epitopes (PADRE), engineered to bind most common HLA-DR molecules with high affinity and act as powerful immunogens, were developed. Short linear peptide constructs comprising PADRE and Plasmodium-derived B cell epitopes induced antibody responses comparable to more complex multiple antigen peptides (MAP) constructs in mice. These antibody responses were composed mostly of the IgG subclass, reactive against intact sporozoites, inhibitory of schizont formation in liver invasion assays, and protective against sporozoite challenge in vivo. The PADRE HTL epitope has also been shown to augment the potency of vaccines designed to stimulate a cellular immune response. Using a HBV transgenic murine model, it was found that CTL tolerance was broken by PADRE-CTL epitope lipopeptide, but not by a similar construct containing a conventional HTL epitope. There are a number of prophylactic vaccines that are of limited efficacy, require multiple boosts, and/or confer protection to only a fraction of the immunized population. Also, in the case of virally infected or cancerous cells, new immunotherapeutic vaccines that induce strong cellular immune responses are desirable. Therefore, optimization of HTL function by use of synthetic epitopes such as PADRE or pathogen-derived, broadly crossreactive epitopes holds promise for a new generation of highly efficacious vaccines.

Diverse host responses and outcomes following simian immunodeficiency virus SIVmac239 infection in sooty mangabeys and rhesus macaques

Sooty mangabeys naturally infected with simian immunodeficiency virus (SIV) do not develop immunodeficiency despite the presence of viral loads of 10(5) to 10(7) RNA copies/ml. To investigate the basis of apathogenic SIV infection in sooty mangabeys, three sooty mangabeys and three rhesus macaques were inoculated intravenously with SIVmac239 and evaluated longitudinally for 1 year. SIVmac239 infection of sooty mangabeys resulted in 2- to 4-log-lower viral loads than in macaques and did not reproduce the high viral loads observed in natural SIVsmm infection. During acute SIV infection, polyclonal cytotoxic T-lymphocyte (CTL) activity coincident with decline in peak plasma viremia was observed in both macaques and mangabeys; 8 to 20 weeks later, CTL activity declined in the macaques but was sustained and broadly directed in the mangabeys. Neutralizing antibodies to SIVmac239 were detected in the macaques but not the mangabeys. Differences in expression of CD38 on CD8(+) T lymphocytes or in the percentage of naive phenotype T cells expressing CD45RA and CD62L-selection did not correlate with development of AIDS in rhesus macaques. In macaques, the proportion of CD4(+) T lymphocytes expressing CD25 declined during SIV infection, while in mangabeys, CD25-expressing CD4(+) T lymphocytes increased. Longitudinal evaluation of cytokine secretion by flow cytometric analysis of unstimulated lymphocytes revealed elevation of interleukin-2 and gamma interferon in a macaque and only interleukin-10 in a concurrently infected mangabey during acute SIV infection. Differences in host responses following experimental SIVmac239 infection may be associated with the divergent outcome in sooty mangabeys and rhesus macaques.

Enhanced T-cell immunogenicity and protective efficacy of a human immunodeficiency virus type 1 vaccine regimen consisting of consecutive priming with DNA and boosting with recombinant fowlpox virus

The induction of human immunodeficiency virus (HIV)-specific T-cell responses is widely seen as critical to the development of effective immunity to HIV type 1 (HIV-1). Plasmid DNA and recombinant fowlpox virus (rFPV) vaccines are among the most promising safe HIV-1 vaccine candidates. However, the immunity induced by either vaccine alone may be insufficient to provide durable protection against HIV-1 infection. We evaluated a consecutive immunization strategy involving priming with DNA and boosting with rFPV vaccines encoding common HIV-1 antigens. In mice, this approach induced greater HIV-1-specific immunity than either vector alone and protected mice from challenge with a recombinant vaccinia virus expressing HIV-1 antigens. In macaques, a dramatic boosting effect on DNA vaccine-primed HIV-1-specific helper and cytotoxic T-lymphocyte responses, but a decline in HIV-1 antibody titers, was observed following rFPV immunization. The vaccine regimen protected macaques from an intravenous HIV-1 challenge, with the resistance most likely mediated by T-cell responses. These studies suggest a safe strategy for the enhanced generation of T-cell-mediated protective immunity to HIV-1.

HIV-1 variation diminishes CD4 T lymphocyte recognition

Effective long-term antiviral immunity requires specific cytotoxic T lymphocytes and CD4(+) T lymphocyte help. Failure of these helper responses can be a principle cause of viral persistence. We sought evidence that variation in HIV-1 CD4(+) T helper epitopes might contribute to this phenomenon. To determine this, we assayed fresh peripheral blood mononuclear cells from 43 asymptomatic HIV-1(+) patients for proliferative responses to HIV-1 antigens. 12 (28%) showed a positive response, and we went on to map dominant epitopes in two individuals, to p24 Gag restricted by human histocompatibility leukocyte antigen (HLA)-DR1 and to p17 Gag restricted by HLA-DRB52c. Nine naturally occurring variants of the p24 Gag epitope were found in the proviral DNA of the individual in whom this response was detected. All variants bound to HLA-DR1, but three of these peptides failed to stimulate a CD4(+) T lymphocyte line which recognized the index sequence. Antigenic variation was also detected in the p17 Gag epitope; a dominant viral variant present in the patient was well recognized by a specific CD4(+) T lymphocyte line, whereas several natural mutants were not. Importantly, variants detected at both epitopes also failed to stimulate fresh uncultured cells while index peptide stimulated successfully. These results demonstrate that variant antigens arise in HIV-1(+) patients which fail to stimulate the T cell antigen receptor of HLA class II-restricted lymphocytes, although the peptide epitopes are capable of being presented on the cell surface. In HIV-1 infection, naturally occurring HLA class II-restricted altered peptide ligands that fail to stimulate the circulating T lymphocyte repertoire may curtail helper responses at sites where variant viruses predominate.

CD8 T cells in HIV infection: mechanisms of immunity

CD8 lymphocytes probably play a key role in the immunologic defense against HIV. The evidence is that they control viral replication by at least two mechanisms: direct antigen-specific cytolysis, which appears to be required for optimal suppression, and release of soluble antiviral factors. New therapeutic strategies are taking into account mechanisms by which the virus may evade CD8 control.

Regulation of Hepatitis B Virus mRNA Expression in a Hepatitis B Surface Antigen Transgenic Mouse Model by IFN-γ-Secreting T Cells After DNA-Based Immunization

The immunotherapeutic effect of DNA-mediated immunization against chronic hepatitis B virus (HBV) infection has been evaluated in transgenic mice expressing the sequences that code for the envelope proteins of HBV in the liver. In this model of HBV chronic carriers, a single i.m. injection of plasmid DNA encoding HBV envelope proteins is sufficient to generate specific immune responses leading to the clearance of the transgene expression product and the control of HBV mRNA. The relative contributions of the T cell subpopulations induced by DNA immunization were examined using adoptive transfer experiments. It was shown that either CD8+ or CD4+ T lymphocytes from immunocompetent DNA-immunized animals were sufficient to control viral gene expression in the livers of the recipient transgenic mice. This effect was mediated by a cytokine-dependent mechanism common to both T cell subpopulations; this mechanism did not require cell lysis, but did involve the production of IFN-γ by the activated T cells.

HIV-specific cytotoxic T-lymphocyte activity in immunologically normal HIV-infected persons

BACKGROUND

CD8+ T-cell counts usually increase soon after infection with HIV, whereas CD4+ cell counts decrease. The result of these changes in T-cell subpopulation subsets in most HIV-infected subjects is inversion of the CD4 : CD8 ratio from greater than 1.0 typical of uninfected persons to less than 1.0 after infection.

SUBJECTS

Six HIV-infected individuals were identified in whom the CD4 : CD8 ratio remained normal throughout follow-up (4.0-11.25 years). They all maintained levels of CD4+ cells above 500 x 10(6)/l and had never received antiretroviral therapy. Because HIV-specific cytotoxic T lymphocytes (CTL) have been implicated in control of HIV during the asymptomatic phase of disease, we screened these individuals for the presence of HIV-specific CTL activity.

METHODS

CTL activity was assessed in freshly isolated peripheral blood mononuclear cells (PBMC) and in phytohaemagglutinin-stimulated interleukin-2 expanded cell lines established from PBMC. Cytotoxicity to HIV-1 env, gag, pol and nef gene products was surveyed in a 4 h 51Cr-release assay using autologous Epstein-Barr virus (EBV) transformed B cells infected with vaccinia constructs expressing each of these HIV genes. The immunodominant CTL epitope and MHC class I antigen restriction specificity of HIV-specific CTL was mapped when present. Plasma viral load was assessed by branched DNA assay. Attempts were made to isolate virus from these individuals by the PBMC coculture assay.

RESULTS

None of the six immunologically normal HIV-infected (INHI) subjects exhibited direct HIV-specific CTL activity in their freshly isolated PBMC compared with 16 (47%) out of 34 HIV disease progressors (P = 0.03, chi2 test) and one out of 10 seronegative subjects. Three of the six INHI subjects had detectable memory HIV-specific precursor CTL (pCTL) activity in in vitro-activated T-cell lines compared with 25 (73.5%) out of 34 HIV-1 disease progressors and in none out of 10 seronegative individuals. All three INHI subjects had Gag-specific pCTL, and none had reverse transcriptase-specific pCTL. Plasma HIV viraemia in all six INHI subjects was below the level of detection by branched DNA assay (< 500 copies/ml). Virus could not be isolated from four of these individuals despite multiple attempts to do so by PBMC coculture assays.

CONCLUSION

Direct HIV-specific CTL activity mediated by activated circulating PBMC was undetectable in six INHI individuals under conditions where it is frequently observed in HIV disease progressors. Despite the absence of cells activated for killing HIV-infected targets in the circulation of these individuals, they appeared able to control their HIV infection by maintaining normal levels of CD4 and CD8 cells and low viral load.

The role of in vitro-induced lymphocyte apoptosis in feline immunodeficiency virus infection: correlation with different markers of disease progression

Human immunodeficiency virus infection is characterized by a progressive decline in the number of peripheral blood CD4(+) T lymphocytes, which finally leads to AIDS. This T-cell decline correlates with the degree of in vitro-induced lymphocyte apoptosis. However, such a correlation has not yet been described in feline AIDS, caused by feline immunodeficiency virus (FIV) infection. We therefore investigated the intensity of in vitro-induced apoptosis in peripheral blood lymphocytes from cats experimentally infected with a Swiss isolate of FIV for 1 year and for 6 years and from a number of long-term FIV-infected cats which were coinfected with feline leukemia virus. Purified peripheral blood lymphocytes were either cultured overnight under nonstimulating conditions or stimulated with phytohemagglutinin and interleukin-2 for 60 h. Under stimulating conditions, the isolates from the infected cats showed significantly higher relative counts of apoptotic cells than did those from noninfected controls (1-year-infected cats, P = 0.01; 6-year-infected cats, P = 0.006). The frequency of in vitro-induced apoptosis was inversely correlated with the CD4(+) cell count (P = 0. 002), bright CD8(+) cell count (P = 0.009), and CD4/CD8 ratio (P = 0. 01) and directly correlated with the percentage of bright major histocompatibility complex class II-positive peripheral blood lymphocytes (P = 0.004). However, we found no correlation between in vitro-induced apoptosis and the viral load in serum samples. Coinfection with feline leukemia virus enhanced the degree of in vitro-induced apoptosis compared with that in FIV monoinfected cats. We concluded that the degree of in vitro-induced apoptosis was closely related to FIV-mediated T-cell depletion and lymphocyte activation and could be used as an additional marker for disease progression in FIV infection.

Human immunodeficiency virus type 1 infection of antigen-specific CD4 cytotoxic T lymphocytes

The effect of macrophage (M)-tropic and T cell line (T)-tropic human immunodeficiency virus type 1 (HIV-1) infection on antigen-specific CD4 cytotoxic T lymphocytes (CTLs) has been studied using a CD4 CTL line specific for a peptide from influenza B virus hemagglutinin. In the absence of antigen presentation, the production of CC chemokines was low. Both the M-tropic HIV-1 strain (HIV-1AD) and the T-tropic HIV-1 strain (HIV-1LAI) established productive infections in the CD4 CTLs, decreasing antigen-specific cytotoxicity. Peptide presented to the CD4 CTLs increased their secretion of RANTES and MIP-1beta, suppressed M-tropic HIV-1 replication, downmodulated CCR5 expression, and preserved CTL recognition. The suppression of M-tropic HIV-1 replication and downmodulation of the CCR5 receptor likely resulted from CC chemokine secretion since antibodies to CC chemokines restored M-tropic HIV-1 replication. Antigen presentation did not protect CD4 CTLs from T-tropic HIV-1 infection or preserve their CTL recognition. Thus, these CD4 CTLs do not make suppressor factors that inhibit the T-tropic HIV-1LAI isolate. The results indicate that these CD4 CTLs can either harbor or suppress M-tropic HIV-1 infection, depending on whether antigen is present. CD4 CTLs might therefore provide some protection in the early stages of HIV-1 infection when M-tropic isolates are present.

Progressive loss of IL-2-expandable HIV-1-specific cytotoxic T lymphocytes during asymptomatic HIV infection

In HIV-1 infection, circulating HIV-1-specific cytotoxic T lymphocytes (CTL) exist in different states of activation, including activated cytotoxic cells and memory cells. We report that a subpopulation of HIV-1-specific CTL is capable of clonal expansion upon culture with IL-2 without exogenous antigen. The IL-2-expandable HIV-1-specific CTL precursor frequency was reduced in patients with advancing infection, although HIV-1-specific memory CTL could still be detected by stimulation in vitro with allele-specific HIV-1 peptide. Longitudinal analysis during advancing infection showed a progressive decline in the IL-2-expandable HIV-1-specific CTL precursor (CTLp) frequency without a decline in Epstein-Barr virus (EBV)-specific or allo-specific CTLp frequencies. To address mechanisms that may contribute to the decline in the IL-2-expandable HIV-specific CTL response, the requirements for in vitro generation of HIV-1-specific and EBV-specific effector CTL were examined. In the absence of exogenous IL-2 in limiting dilution, generation of EBV-specific CD8+ effector CTL was dependent upon help from CD4+ cells. CD4+ help for EBV-specific CD8+ CTL was observed in asymptomatic HIV infection but not in advanced infection. In the presence of exogenous IL-2, CD4+ cells could also provide help for the optimal generation of HIV-1 peptide-specific CD8+ CTL, because in vitro depletion of CD4+ cells prior to culture using stimulation with an MHC class I-restricted HIV-1 peptide reduced the peptide-specific CD8+ CTL response. We conclude that there is a decline in the IL-2-expandable HIV-1-specific CTL response during advancing infection. There are a number of possible mechanisms for this decline, including a reduction in CD4+ T cell help for in vivo antigen-activated CD8+ T cells.

Requirement for CD4(+) T cells in the Friend murine retrovirus neutralizing antibody response: evidence for functional T cells in genetic low-recovery mice

Recovery from infection with the Friend murine leukemia retrovirus complex (FV) requires T-helper cells and cytotoxic T cells as well as neutralizing antibodies. Several host genes, including genes of the major histocompatibility complex (H-2) and an H-2-unlinked gene, Rfv-3, influence these FV-specific immune responses. (B10.A x A/Wy)F1 mice, which have the H-2(a/a) Rfv-3(r/s) genotype, fail to mount a detectable FV-specific T-cell proliferative response but nevertheless produce FV-specific neutralizing immunoglobulin M (IgM) antibodies and can eliminate FV viremia. Thus, this IgM response, primarily influenced by the Rfv-3 gene, may be T-cell independent. To test this idea, mice were depleted of either CD4(+) or CD8(+) T-cell populations in vivo and were monitored for the effect on the neutralizing antibody response following FV infection. Surprisingly, mice in which CD4(+) cells were depleted showed undetectable FV-neutralizing antibody responses and high viremia levels compared to nondepleted or CD8-depleted animals. In addition to knocking out the FV antibody response, CD4(+) T-cell depletion reduced survival time significantly, further indicating the importance of CD4(+) T cells. These studies revealed the first evidence for a functional T-cell response following FV infection in these low-recovery mice and showed that CD4(+) T-helper cells are required for the Rfv-3-controlled FV antibody response.

An inhibitor of HIV-1 protease modulates proteasome activity, antigen presentation, and T cell responses

Inhibitors of the protease of HIV-1 have been used successfully for the treatment of HIV-1-infected patients and AIDS disease. We tested whether these protease inhibitory drugs exerted effects in addition to their antiviral activity. Here, we show in mice infected with lymphocytic choriomeningitis virus and treated with the HIV-1 protease inhibitor ritonavir a marked inhibition of antiviral cytotoxic T lymphocyte (CTL) activity and impaired major histocompatibility complex class I-restricted epitope presentation in the absence of direct effects on lymphocytic choriomeningitis virus replication. A potential molecular target was found: ritonavir selectively inhibited the chymotrypsin-like activity of the 20S proteasome. In view of the possible role of T cell-mediated immunopathology in AIDS pathogenesis, the two mechanisms of action (i.e., reduction of HIV replication and impairment of CTL responses) may complement each other beneficially. Thus, the surprising ability of ritonavir to block the presentation of antigen to CTLs may possibly contribute to therapy of HIV infections but potentially also to the therapy of virally induced immunopathology, autoimmune diseases, and transplantation reactions.