Cross-reactions between the cytotoxic T-lymphocyte responses of human immunodeficiency virus-infected African and European patients

The great variability of protein sequences from human immunodeficiency virus (HIV) type 1 (HIV-1) isolates represents a major obstacle to the development of an effective vaccine against this virus. The surface protein (Env), which is the predominant target of neutralizing antibodies, is particularly variable. Here we examine the impact of variability among different HIV-1 subtypes (clades) on cytotoxic T-lymphocyte (CTL) activities, the other major component of the antiviral immune response. CTLs are produced not only against Env but also against other structural proteins, as well as some regulatory proteins. The genetic subtypes of HIV-1 were determined for Env and Gag from several patients infected either in France or in Africa. The cross-reactivities of the CTLs were tested with target cells expressing selected proteins from HIV-1 isolates of clade A or B or from HIV type 2 isolates. All African patients were infected with viruses belonging to clade A for Env and for Gag, except for one patient who was infected with a clade A Env-clade G Gag recombinant virus. All patients infected in France were infected with clade B viruses. The CTL responses obtained from all the African and all the French individuals tested showed frequent cross-reactions with proteins of the heterologous clade. Epitopes conserved between the viruses of clades A and B appeared especially frequent in Gag p24, Gag p18, integrase, and the central region of Nef. Cross-reactivity also existed among Gag epitopes of clades A, B, and G, as shown by the results for the patient infected with the clade A Env-clade G Gag recombinant virus. These results show that CTLs raised against viral antigens from different clades are able to cross-react, emphasizing the possibility of obtaining cross-immunizations for this part of the immune response in vaccinated individuals.     

Cross-clade human immunodeficiency virus (HIV)-specific cytotoxic T-lymphocyte responses in HIV-infected Zambians

We have examined cross-clade HIV-specific cytotoxic T-lymphocyte (CTL) activity in peripheral blood of eight Zambian individuals infected with non-B-clade human immunodeficiency virus type 1 (HIV-1). Heteroduplex mobility assay and partial sequence analysis of env and gag genes strongly suggests that all the HIV-infected subjects were infected with clade C HIV-1. Six of eight C-clade HIV-infected individuals elicited CTL activity specific for recombinant vaccinia virus-infected autologous targets expressing HIV gag-pol-env derived from B-clade HIV-1 (IIIB). Recognition of individual recombinant HIV-1 B-clade vaccinia virus-infected targets expressing gag, pol, or env was variable among the patients tested, indicating that cross-clade CTL activity is not limited to a single HIV protein. These data demonstrate that HIV clade C-infected individuals can mount vigorous HIV clade B-reactive CTL responses.     

Human immunodeficiency virus (HIV)-specific cytotoxic T lymphocyte activity in HIV-exposed seronegative persons

Repeated exposure to human immunodeficiency virus (HIV) does not always result in seroconversion. Understanding the conditions that permit or protect against progressive infection with HIV is important for vaccine development. Nineteen subjects at risk for HIV infection were CCR-5 genotyped and screened for virus-specific memory cytotoxic T lymphocytes (CTL). None had the Delta32CCR-5/Delta32CCR-5 genotype associated with HIV resistance. HIV-specific CTL were detected in 7 (41.1%) of 17 exposed uninfected subjects versus 0 of 14 seronegative subjects with no HIV risk factors (P=.006, chi2 test). Recognition of virus by CTL in exposed uninfected subjects was major histocompatibility complex class I-restricted and multispecific, and specificity could change with time. Activity could persist up to 34 months after the last virus exposure. The presence of HIV-specific CTL in a greater proportion of seronegative HIV-exposed versus unexposed subjects supports the notion that in some cases, virus exposure induces HIV immunity without seroconversion or disease progression.     

Longitudinal and cross-sectional analysis of cytotoxic T lymphocyte responses and their relationship to vertical human immunodeficiency virus transmission. ARIEL Project Investigators

The ARIEL Project for the Prevention of HIV Transmission from Mother to Infant was established to evaluate virologic and immunologic parameters during vertical transmission. To determine the strength and breadth of the cytotoxic T lymphocyte (CTL) response and its correlation with human immunodeficiency virus (HIV) transmission, a cross-sectional study was done of 31 HIV-infected pregnant women, of whom 15 transmitted and 16 did not transmit HIV to their infants. The precursor frequencies of CTL specific for HIV-1 gag, pol, nef, and env from 5 different isolates of the clade B of HIV-1 were determined by limiting dilution analysis. Results showed that variable levels of HIV-specific CTL response were present in HIV-infected pregnant women during and after pregnancy. In addition, CTL precursor frequencies specific for pol and nef were higher during pregnancy in nontransmitters than in transmitters. Thus, CTL responding to different HIV antigens may not be contributing equally to the prevention of vertical transmission.     

Distinct recognition of non-clade B human immunodeficiency virus type 1 epitopes by cytotoxic T lymphocytes generated from donors infected in Africa

We present detailed studies of human immunodeficiency virus (HIV)-specific cytotoxic T-lymphocyte (CTL) responses to clade A or C HIV type 1 in three donors infected in East Africa. We define several novel non-clade B CTL epitopes, including some restricted by HLA alleles common in Africans. Although cross-clade CTL recognition of these epitopes does occur, recognition can also be highly clade specific.     

New mechanisms of viral persistence in primary human immunodeficiency virus (HIV) infection

Viruses, including the Human Immunodeficiency Virus (HIV), have evolved multiple strategies to overcome host immune defenses, allowing them to persist in the host. Molecular and cellular approaches were simultaneously used to provide sensitive and unbiased delineation of the diversity and dynamics of the immune response, and to study the relative compartimentalization of HIV-specific CTL clones in patients undergoing primary HIV infection. This approach revealed that some HIV-specific CTL clones can be deleted in presence of high levels of antigen, a phenomenon analogous to high-dose tolerance or clonal exhaustion described in murine models of persistent viral infections. Also, HIV-specific CTL clones were found to accumulate preferentially in peripheral blood as compared to lymph nodes, even though the large majority of viral replication during primary HIV infection takes place within lymph nodes. These two mechanisms may decrease the effectiveness of the host cell-mediated immune responses, and favor the establishment of virus persistence during primary HIV infection.     

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.     

Cross-clade cytotoxic T cell response to human immunodeficiency virus type 1 proteins among HLA disparate North Americans and Thais

A globally effective vaccine will need to elicit cytotoxic T lymphocytes (CTL) capable of recognizing diverse human immunodeficiency virus type 1 (HIV-1) clades. Study of the cellular immune responses of HIV-1-infected persons may allow predictions to be made regarding useful vaccine antigen components. The frequency and magnitude of CTL responses to clade E and B Gag, Pol-RT, Env, and Nef proteins were compared in 12 HLA-characterized, clade E-infected Thais and in 10 clade B-infected North Americans using vaccinia recombinant constructs for protein expression. While responses were detected against all proteins, they were most frequent and cross-reactive to Gag in both groups. Pol-RT was recognized less frequently in Thais than North Americans. Cross-clade protein recognition was common but not uniformly present among these HLA-disparate individuals. Population-specific CTL data are needed to adequately prepare for vaccine trials outside of North America and Europe.     

Cytotoxic T lymphocytes in asymptomatic long-term nonprogressing HIV-1 infection. Breadth and specificity of the response and relation to in vivo viral quasispecies in a person with prolonged infection and low viral load

Although vigorous activated and memory CTL have been associated with HIV-1 infection, data are lacking regarding the breadth of epitopes recognized in a given individual and the relationship to the viral quasispecies present in vivo. In this study we performed a detailed analysis of the HIV-1-specific CTL response in a seropositive person with documented HIV-1 infection of 15 yr duration, stable CD4 counts above 500 cells/ml, and viral load persistently below 500 molecules of RNA/ml of plasma. Epitope mapping studies revealed the presence of HLA class I-restricted CTL responses to six different epitopes in p17, p24, RT, Env, and Nef, which conferred broadly cross-reactive recognition of reported HIV-1 variants. Sequence analysis of autologous viruses revealed the absence of immune escape variants within five of the six epitopes. Despite consistently low viral RNA levels in plasma and viral DNA levels in PBMC, in vivo-activated circulating CTL were detected against three of the epitopes. Five of the six epitopes, including the three dominant epitopes, have been detected in persons with progressive disease, suggesting that nonprogressors may not target unique epitopes. This study demonstrates that HIV-1-specific CTL can be highly activated and broadly directed in the setting of an extremely low viral load, and that neither high viral load nor antigenic diversity is required for the generation of a multispecific CTL response. Although the detection of strong CTL responses, low viral load, and lack of immune escape are consistent with the hypothesis that CTL may contribute to lack of disease progression in this individual, the contribution of these responses to maintenance of the asymptomatic state remains to be determined.     

T lymphocytes and their cytokines in human immunodeficiency virus (HIV) infection: implications for associated neoplasias

Infection with the human immunodeficiency virus (HIV) results in gradual immunosuppression due to the loss of CD4+ T cells. In the wake of immune system breakdown, infected individuals may acquire multiple opportunistic infections and develop certain malignancies which ultimately account for the vast majority of deaths in these persons. A limited number of malignancies are directly associated with HIV infection and suggest a common tie between these tumors. Inappropriate immune surveillance resulting in insufficient inhibition of virus replication and inadequate control of the growth of transformed cells may contribute to the development of malignancies in HIV-infected individuals. Alternatively, malignancies in HIV infection may be the consequence of immune dysregulation. Cellular immune responses mediated by antigen-specific cytotoxic T lymphocytes (CTL) are of particular importance for immunologic control of viral infections and substantial information has been gathered about theses cells in HIV infection. The goal of this review is therefore to summarize recent findings regarding the cellular immune response to HIV with a particular focus on cytokines released by HIV-specific CTL.     

Accumulation of human immunodeficiency virus-specific cytotoxic T lymphocytes away from the predominant site of virus replication during primary infection

Down-regulation of the initial burst of viremia during primary human immunodeficiency virus (HIV) infection is thought to be mediated predominantly by HIV-specific CD8+ cytotoxic T lymphocytes (CTL). This response is associated with major perturbations in the T cell receptor (TCR) repertoire. To investigate the failure of the cellular immune response to adequately control viral spread and replication and to prevent establishment of HIV infection, changes in the TCR repertoire and in the distribution of virus-specific CTL between blood and lymph node were analyzed in three patients with primary infection. By the combined use of clonotype-specific polymerase chain reaction and analysis of the frequency of in vivo activated HIV-specific CTL, it was shown that HIV-specific CTL clones preferentially accumulated in blood as opposed to lymph node. Accumulation of HIV-specific CTL in blood occurred prior to effective down-regulation of virus replication in both blood and lymph node. These findings should provide new insights into how HIV, and possibly other viruses, elude the immune response of the host during primary infection.     

Participation of a sialic acid-specific lectin from freshwater prawn Macrobrachium rosenbergii hemocytes in the recognition of non-self cells

Recombinant vaccinia virus (VV) vectors that express the envelope (Env) protein of the human immunodeficiency virus-type 1 (HIV-1) have been previously shown to elicit HIV-specific cytotoxic T-lymphocyte (CTL) and weak antibody responses in non-human primate studies and clinical trials. In first clinical trials, single Env proteins were presented to the immune system by VV recombinants and other vectors, but individuals were not protected against later exposures to heterologous HIV. It is likely that the generation of protective immune responses against diverse HIV will require that vaccines encompass proteins from not just one, but multiple distinct HIV isolates. Here is described the simple construction of numerous new VV, each expressing a unique, truncated, Env protein (VVenv). Mouse experiments were performed to evaluate the ability of these VVenv to elicit immune responses. HIV-1-specific antibodies appeared within one month following one intraperitoneal inoculation of mice with single or mixed VVenv, reaching plateau levels by 4 months. The magnitude of antibody production was poor at the dose of 10(5) p.f.u. VVenv per animal, but improved with increasing doses of VVenv up to 10(7) p.f.u. per animal. The subcutaneous route of VV immunization, previously proven safe in human trials, was also effective for administering VVenv. These results highlight the strengths of recombinant VV constructs as vehicles for the presentation of multiple HIV-1-Env proteins to the naive immune system.     

Quantitation of HIV-1-specific cytotoxic T lymphocytes and plasma load of viral RNA

Although cytotoxic T lymphocytes (CTLs) are thought to be involved in the control of human immunodeficiency virus-type 1 (HIV-1) infection, it has not been possible to demonstrate a direct relation between CTL activity and plasma RNA viral load. Human leukocyte antigen-peptide tetrameric complexes offer a specific means to directly quantitate circulating CTLs ex vivo. With the use of the tetrameric complexes, a significant inverse correlation was observed between HIV-specific CTL frequency and plasma RNA viral load. In contrast, no significant association was detected between the clearance rate of productively infected cells and frequency of HIV-specific CTLs. These data are consistent with a significant role for HIV-specific CTLs in the control of HIV infection and suggest a considerable cytopathic effect of the virus in vivo.     

Perceived importance of clinical teaching characteristics for nurse anesthesia clinical faculty

Cancer-related, mucin-type carbohydrate epitopes, principally mannose and sialo-syl residues, are expressed on the envelope protein gp 160 of the human immunodeficiency virus (HIV). Anticarbohydrate antibodies directed toward these and other carbohydrate epitopes are known to neutralize HIV-1 infection by cell-free virus. Carbohydrates, however, being T cell-independent antigens, typically elicit diminished immune responses. To overcome this potential draw back, we have examined the ability of peptides that mimic such epitopes to elicit immune responses that cross-react with carbohydrate structures. We report that mouse polyclonal antisera generated against peptides that mimic mucin-related carbohydrate epitopes have anti-HIV-1 activity. Generation of antibodies was not lr-gene restricted, as at least two different strains of mice. Balb/c (H-2d) and C57Bl/6 (H-2b), responded equally to the peptides. The antipeptide sera displayed neutralizing activity against HIV-I/MN and HIV-I/3B viral strains. This neutralization was as good as human anti-HIV sera. These results indicate that peptide mimics of carbohydrates provide a novel strategy for the further development of reagents that elicit immune responses to carbohydrate epitopes associated with many infectious organisms and tumor cells.     

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.     

Safety and immunogenicity of REMUNE in HIV-infected Thai subjects

The safety and immunogenicity of REMUNE, an HIV-specific immune based therapy for HIV infection, was evaluated in a cohort of 30 HIV infected subjects in Thailand. This therapy utilizes a gp120 depleted inactivated virus (HZ321), which exhibits a high degree of conservation with the core antigens of both type B' and E strains of HIV, the predominant Thailand isolates. The treatment was well tolerated, with no serious adverse events reported over the course of the 4-month trial. Treatment in which four doses were administered with REMUNE appeared to boost HIV-specific immune responses, with approximately 75% of the treated subjects demonstrating an increase in either the repertoire or the intensity of the serological response to HIV as measured by Western blot. CD4%, viral load, and weight remained stable over the course of the 4-month study relative to baseline values. Viral subtyping of this cohort revealed a predominance of type 'E'. These data suggest that REMUNE is safe and immunogenic in seropositive Thai subjects and supports further study of the therapeutic potential of REMUNE to treat HIV-1 infection.     

Factors affecting the immunogenicity and potency of tetanus toxoid: implications for the elimination of neonatal and non-neonatal tetanus as public health problems

The neutralizing activity of anti-V3 monoclonal antibodies (MAbs) and anti-HIV-1 immune sera was tested against HIV-1 laboratory strains and African primary isolates. Neutralization was investigated in Phytohaemagglutinin (PHA)-stimulated peripheral blood mononuclear cell (PBMC) cultures by means of two distinct viral titer reduction assays. In these assays, virus was detected by means of either p24 antigen measurement using ELISA or HIV provirus synthesis using PCR, respectively. Anti-V3 MAbs and anti-HIV-1 immune sera neutralized efficiently the homologous laboratory HIV-1 strains used for eliciting immune response but showed no neutralizing activity against most primary isolates. The two neutralization assays used provided similar results. However, a PCR-based assay circumvented the limitations due to low levels of virus replication. The mechanism of resistance of the primary isolates to neutralizing antibodies was complex and was not simply predicted by partial sequence determination of the epitopes. This points out the need for reliable neutralization assays of HIV-1 primary isolates in order to evaluate the role of humoral immunity during HIV-1 infection and for future vaccine strategies.