Role of cellular immunity in protection against HIV infection

An Early Th1 Response Is a Key Factor for a Favorable COVID-19 Evolution

The Th1/Th2 balance plays a crucial role in the progression of different pathologies and is a determining factor in the evolution of infectious diseases. This work has aimed to evaluate the early, or on diagnosis, T-cell compartment response, T-helper subsets and anti-SARS-CoV-2 antibody specificity in COVID-19 patients and to classify them according to evolution based on infection severity. A unicenter, randomized group of 146 COVID-19 patients was divided into four groups in accordance with the most critical events during the course of disease. The immunophenotype and T-helper subsets were analyzed by flow cytometry. Asymptomatic SARS-CoV-2 infected individuals showed a potent and robust Th1 immunity, with a lower Th17 and less activated T-cells at the time of sample acquisition compared not only with symptomatic patients, but also with healthy controls. Conversely, severe COVID-19 patients presented with Th17-skewed immunity, fewer Th1 responses and more activated T-cells. The multivariate analysis of the immunological and inflammatory parameters, together with the comorbidities, showed that the Th1 response was an independent protective factor for the prevention of hospitalization (OR 0.17, 95% CI 0.03–0.81), with an AUC of 0.844. Likewise, the Th1 response was found to be an independent protective factor for severe forms of the disease (OR 0.09, 95% CI: 0.01–0.63, p = 0.015, AUC: 0.873). In conclusion, a predominant Th1 immune response in the acute phase of the SARS-CoV-2 infection could be used as a tool to identify patients who might have a good disease evolution.

T-Scan: A Genome-wide Method for the Systematic Discovery of T Cell Epitopes

T cell recognition of specific antigens mediates protection from pathogens and controls neoplasias, but can also cause autoimmunity. Our knowledge of T cell antigens and their implications for human health is limited by the technical limitations of T cell profiling technologies. Here, we present T-Scan, a high-throughput platform for identification of antigens productively recognized by T cells. T-Scan uses lentiviral delivery of antigen libraries into cells for endogenous processing and presentation on major histocompatibility complex (MHC) molecules. Target cells functionally recognized by T cells are isolated using a reporter for granzyme B activity, and the antigens mediating recognition are identified by next-generation sequencing. We show T-Scan correctly identifies cognate antigens of T cell receptors (TCRs) from viral and human genome-wide libraries. We apply T-Scan to discover new viral antigens, perform high-resolution mapping of TCR specificity, and characterize the reactivity of a tumor-derived TCR. T-Scan is a powerful approach for studying T cell responses.

Timing of CD8 T cell effector responses in viral infections

CD8 T cell or cytotoxic T lymphocyte (CTL) responses are an important branch of the immune system in the fight against viral infections. The dynamics of anti-viral CTL responses have been characterized in some detail, both experimentally and with mathematical models. An interesting experimental observation concerns the timing of CTL responses. A recent study reported that in pneumonia virus of mice the effector CTL tended to arrive in the lung only after maximal virus loads had been achieved, an observation that seems at first counterintuitive because prevention of pathology would require earlier CTL-mediated activity. A delay in CTL-mediated effector activity has also been quoted as a possible explanation for the difficulties associated with CTL-based vaccines. This paper uses mathematical models to show that in specific parameter regimes, delayed CTL effector activity can be advantageous for the host in the sense that it can increase the chances of virus clearance. The increased ability of the CTL to clear the infection, however, is predicted to come at the cost of acute pathology, giving rise to a trade-off, which is discussed in the light of evolutionary processes. This work provides a theoretical basis for understanding the described experimental observations.

Design and preclinical development of a recombinant protein and DNA plasmid mixed format vaccine to deliver HIV-derived T-lymphocyte epitopes

Coordinated interactions between helper and cytotoxic T-lymphocytes (HTL and CTL) are needed for optimal effector cell functions and the establishment of immunological memory. We, therefore, designed a mixed format vaccine based on the use of highly conserved HIV-derived T-lymphocyte epitopes wherein the HTL epitopes were delivered as a recombinant protein and the CTL epitopes which were encoded in a DNA vaccine plasmid. Immunogenicity testing in HLA transgenic mice and GLP preclinical safety testing in rabbits and guinea pigs were used to document the utility of this approach and to support Phase 1 trial clinical testing. Both vaccine components were immunogenic and safely co-administered.

Immunologic features of HIV-1-infected women on HAART at delivery

BACKGROUND

The conjoint effect of HIV infection and pregnancy on the immune system of women submitted to the prophylactic antiretroviral therapy presently recommended is still poorly understood.

METHODS

We evaluated 44 HIV-infected women (HIV) and 45 HIV-negative women (CT) at parturition and we compared them to 20 healthy nonpregnant women (NP). Immunophenotyping of lymphocytes was done by four-color flow cytometry.

RESULTS

All HIV-infected women received HAART during pregnancy and 56.8% had viral load <50 copies/mL at delivery. CD4+T cells/mm(3) were lower in HIV (447) than CT (593) and NP (738) (P < 0.05). CD8+T cells/mm(3) were higher in HIV (799) than CT (384) and NP (395) (P < 0.05). NK cells/mm(3) were lower in HIV (146) than in CT (253) and NP (198) (P < 0.05). CD38 expression on CD4+T and on CD8+T cells was higher in HIV (CD4:12.1; CD8:14.9) than in CT(CD4:9.2; CD8:10.2) and NP(CD4:8.6; CD8:6.0) (P < 0.05). However, CD56 expression on CD8+T cells (a marker of cytolytic effector function) was lower in HIV(7%) than in CT(12%) and NP(9%) (P < 0.05).

CONCLUSIONS

Even with low levels of viremia, HIV-infected women at delivery showed a different immunologic profile from both healthy non-HIV-infected women in the puerperium and nonpregnant women, with lower CD4+T and higher CD8+T cells, high levels of CD38 expression, but low CD56 expression on CD8+T cells and low NK cell numbers.

Efficient in vitro expansion of human immunodeficiency virus (HIV)-specific T-cell responses by gag mRNA-electroporated dendritic cells from treated and untreated HIV type 1-infected individuals

Developing an immunotherapy to keep human immunodeficiency virus type 1 (HIV-1) replication suppressed while discontinuing highly active antiretroviral therapy (HAART) is an important challenge. In the present work, we evaluated in vitro whether dendritic cells (DC) electroporated with gag mRNA can induce HIV-specific responses in T cells from chronically infected subjects. Monocyte-derived DC, from therapy-naïve and HAART-treated HIV-1-seropositive subjects, that were electroporated with consensus codon-optimized HxB2 gag mRNA efficiently expanded T cells, secreting gamma interferon (IFN-gamma) and interleukin 2 (IL-2), as well as other cytokines and perforin, upon restimulation with a pool of overlapping Gag peptides. The functional expansion levels after 1 week of stimulation were comparable in T cells from HAART-treated and treatment-naïve patients and involved both CD4(+) and CD8(+) T cells, with evidence of bifunctionality in T cells. Epitope mapping of p24 showed that stimulated T cells had a broadened response toward previously nondescribed epitopes. DC, from HAART-treated subjects, that were electroporated with autologous proviral gag mRNA equally efficiently expanded HIV-specific T cells. Regulatory T cells did not prevent the induction of effector T cells in this system, whereas the blocking of PD-L1 slightly increased the induction of T-cell responses. This paper shows that DC, loaded with consensus or autologous gag mRNA, expand HIV-specific T-cell responses in vitro.

Robust CD4+ and CD8+ T cell responses to SIV using mRNA-transfected DC expressing autologous viral Ag

A potentially powerful strategy for therapeutic HIV vaccination is the use of DC transfected with mRNA encoding autologous viral Ag, as epitopes presented by transfected DC would exactly reflect those expressed by infected cells in the individual. Using human and rhesus macaque monocyte-derived DC, we show that nucleofection is a superior method for mRNA transfection, resulting in high-level protein expression and DC maturation. DC transfected with SIV gag isolated from an infected monkey stimulated robust Ag-specific recall T cell responses of similar magnitude to those induced by peptide-pulsed PBMC that were predominantly CD8+ T cell mediated. Enhanced CD4+ T cell responses were stimulated when Gag was redirected into the lysosomal pathway via the targeting signal derived from lysosome-associated membrane protein-1 (LAMP-1). Rhesus DC transfected with lysosome-targeted gag encoding an escape mutation in an immunodominant CTL epitope stimulated CD4+ and CD8+ T cell responses of almost equivalent magnitude directed towards undefined epitopes outside of the mutated region. Finally, gag-transfected DC from SIV-infected monkeys stimulated significant Ag-specific recall T cell responses in an entirely autologous system. These findings demonstrate that mRNA-transfected DC expressing SIV Ag derived from infected monkeys stimulate broad and relevant T cell responses, supporting this approach for therapeutic HIV vaccine development.

In vivo effects of HIV-1 exposure in the presence and absence of single-dose nevirapine on cellular plasma activation markers of infants born to HIV-1-seropositive mothers

Short-course antiretroviral drug regimens reduce the risk of mother-to-child transmission of HIV-1, but mechanisms affording protection of such interventions remain poorly defined. Because T-cell activation is an important factor in productive HIV-1 infection, we tested the hypothesis that single-dose nevirapine (NVP) reduces immune activation, which in turn reduces the likelihood of transmission. We compared concentrations of cord and maternal blood plasma immune activation markers, neopterin, beta2-microglobulin, and soluble l-selectin, in 2 groups of HIV-1-exposed newborns whose mothers either received NVP at the onset of labor or who only received NVP as postexposure prophylaxis within 72 hours of birth and among HIV-unexposed controls. In utero exposure of the infant to HIV-1, regardless of NVP exposure, led to demonstrable increases in immune activation markers, this being most notable in the presence of preexisting infection. Contrary to what was hypothesized, immune activation was increased by prebirth exposure to single-dose NVP, with this effect being enhanced in infants already infected at birth. Our data suggest that reductions in immune activation do not explain transmission prevention effects of single-dose NVP. Our data also suggest a biological explanation for why HIV-1-infected infants exposed perinatally to antiretroviral drugs might experience hastened disease progression, namely, in some HIV-1-infected individuals, NVP may synergize with HIV-1 to enhance an environment that favors increased HIV-1 replication.

A novel assay for assessment of HIV-specific cytotoxicity by multiparameter flow cytometry

BACKGROUND

Assessment of CD8(+) T-cell activity is of significant importance for the evaluation of cellular immune responses to viral infections, especially in HIV. We present a new assay for the assessment of HIV-specific cytotoxicity by multiparameter flow cytometry.

METHODS

Target cells, pulsed with peptide pools (Gag or Nef), were stained with 5- (and -6)-carboxyfluorescein diacetate succinimidyl ester (CFSE), cultured with specific or nonspecific effector cells, and finally stained with propidium iodide (PI). Determination of cytolysis is based on the enumeration of viable target cells (CFSE(hi)PI(-)) in the test sample (target and specific effector cells) as compared with that of the viable target cells in the control sample (target and nonspecific effector cells). The (51)Cr-release assay and IFN-gamma ELISpot were performed by standard procedures.

RESULTS

A comparison with the Cr-release showed that the two assays were strongly correlated (r = 0.67; P < 0.001) but the sensitivity of the flow cytometric assay was significantly higher (P < 0.05), and the reproducibility good (CV, 7.7%). Good correlation was also found with the ELISpot assay (r = 0.66; P < 0.01).

CONCLUSION

This new assay provides both specific and sensitive results when employed for the detection of HIV-specific CTL and can be a valuable tool for the evaluation of cytolytic activity in vaccine trials or in HIV-infected subjects, especially if such responses are present at low levels.

In vivo induction of cellular and humoral immune responses by hybrid DNA vectors encoding simian/human immunodeficiency virus/hepatitis B surface antigen virus particles in BALB/c and HLA-A2-transgenic mice

To improve the immunogenicity of epitopes derived from Gag proteins of simian immunodeficiency virus (SIV) and from the envelope (Env) protein of human immunodeficiency virus type 1 (HIV-1), we have designed hybrid DNA vaccines by inserting sequences encoding antigenic domains of SIV and HIV-1 into the hepatitis B virus envelope gene. This gene encodes the hepatitis B surface antigen (HBsAg) capable of spontaneous assembly into virus-like particles that were used here as carrier. Injections of hybrid vectors encoding B-cell epitopes from the gp41 and the gp120 envelope proteins of HIV-1 induced specific humoral responses in BALB/c mice. Furthermore, high frequencies of IFN-gamma-secreting CD8+ T cells specific for various antigenic determinants of SIV-Gag were observed after intramuscular injections of hybrid DNA vectors in BALB/c mice. Genetic immunization of HLA-A2.1-transgenic mice with HIV-Env/HBsAg-encoding DNA generated a strong CTL response and IFN-gamma-secreting CD8+ T lymphocytes specific for HIV-1 envelope-derived peptide. H-2d-restricted HBs-specific T-cell responses dominated over SIV-Gag responses in BALB/c mice whereas HLA-A2-restricted HIV-Env response was enhanced after fusion with HBsAg. These data demonstrate that different B and T-cell epitopes of vaccine-relevant viral antigens can be expressed in vivo as fusion proteins with HBsAg but that the optimal immunogenicity may differ strikingly between individual epitopes.

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HLA antigens as predictors of disease progression in HIV-infected haemophilia patients (a 22 years' follow up)

Our objective was to assess the influence of genetic factors such as HLA classes I and II antigens and other clinical and laboratory variables on the progression of HIV disease in a cohort of 118 HIV infected haemophilic subjects of Greek origin who had been typed for HLA antigens and were followed up prospectively for 22 years since seroconversion. At the end of the follow up we compared two groups of patients: 22 patients who had a fast progression to AIDS (median 6 years since seroconversion) vs. 33 patients who remained asymptomatic in stage A2 for up to 22 years (median 15 years). The results showed that the two groups did not differ significantly in age at seroconversion or baseline CD4+ T cell count. However there was a difference in the frequencies of certain HLA antigens in the two groups. The fast progressors had a higher frequency of HLA-A28, B21 and DR3, which was statistically significant (P = 0.02, 0.04, 0.05, respectively) compared to the slow progressors. These findings based on classical HLA typing techniques confirm other published observations and support the effect of genetic background in the progression of HIV infection in haemophilics.

DNA prime Listeria boost induces a cellular immune response to SIV antigens in the rhesus macaque model that is capable of limited suppression of SIV239 viral replication

DNA vaccines and recombinant Listeria monocytogenes that express and secrete SIV Gag and Env antigens were combined in a nonhuman primate prime-boost immunogenicity study followed by a challenge with SIV239. We report that recombinant DNA vaccine delivered intramuscularly, and recombinant L. monocytogenes delivered orally each individually have the ability to induce CD8+ and CD4+ T cell immune responses in a nonhuman primate. Four rhesus monkeys were immunized at weeks 0, 4, 8, and 12 with the pCSIVgag and pCSIVenv DNA plasmids and boosted with SIV expressing L. monocytogenes vaccines at weeks 16, 20, and 28. Four rhesus monkeys received only the L. monocytogenes vaccines at weeks 16, 20, and 28. A final group of monkeys served as a control group. Blood samples were taken before vaccination and 2 weeks post each injection and analyzed by ELISPOT for CD4+ and CD8+ T cell responses. Moderate vaccine induced SIV-specific cellular immune responses were observed following immunization with either DNA or L. monocytogenes vectors. However, the SIV antigen-specific immune responses were significantly increased when Rhesus macaques were primed with SIV DNA vaccines and boosted with the SIV expressing L. monocytogenes vectors. In addition, the combined vaccine was able to impact SIV239 viral replication following an intrarectal challenge. This study demonstrates for the first time that oral L. monocytogenes can induce a cellular immune response in a nonhuman primate and is able to enhance the efficacy of a DNA vaccine as well as provide modest protection against SIV239 challenge.

Novel and promiscuous CTL epitopes in conserved regions of Gag targeted by individuals with early subtype C HIV type 1 infection from southern Africa

Characterization of optimal CTL epitopes in Gag can provide crucial information for evaluation of candidate vaccines in populations at the epicenter of the HIV-1 epidemic. We screened 38 individuals with recent subtype C HIV-1 infection using overlapping consensus C Gag peptides and hypothesized that unique HLA-restricting alleles in the southern African population would determine novel epitope identity. Seventy-four percent of individuals recognized at least one Gag peptide pool. Ten epitopic regions were identified across p17, p24, and p2p7p1p6, and greater than two-thirds of targeted regions were directed at: TGTEELRSLYNTVATLY (p17, 35%); GPKEPFRDYVDRFFKTLRAEQATQDV (p24, 19%); and RGGKLDKWEKIRLRPGGKKHYMLKHL (p17, 15%). After alignment of these epitopic regions with consensus M and a consensus subtype C sequence from the cohort, it was evident that the regions targeted were highly conserved. Fine epitope mapping revealed that five of nine identified optimal Gag epitopes were novel: HLVWASREL, LVWASRELERF, LYNTVATLY, PFRDYVDRFF, and TLRAEQATQD, and were restricted by unique HLA-Cw*08, HLA-A*30/B*57, HLA-A*29/B*44, and HLA-Cw*03 alleles, respectively. Notably, three of the mapped epitopes were restricted by more than one HLA allele. Although these epitopes were novel and restricted by unique HLA, they overlapped or were embedded within previously described CTL epitopes from subtype B HIV-1 infection. These data emphasize the promiscuous nature of epitope binding and support our hypothesis that HLA diversity between populations can shape fine epitope identity, but may not represent a constraint for universal recognition of Gag in highly conserved domains.

Optimization of a multi-gene HIV-1 recombinant subtype CRF02_AG DNA vaccine for expression of multiple immunogenic forms

We developed an AIDS vaccine for Western and West-Central Africa based on a DNA plasmid vector expressing HIV-1 recombinant subtype CRF02_AG gag, pol, and env genes. To optimize the production of noninfectious HIV-like particles (VLPs) and potentially improve the effectiveness of the vaccine, we generated four potential vaccine constructs: the parental (IC2) and three modifications (IC25, IC48, and IC90) containing mutations within the HIV protease. While the parental construct IC2 expressed aggregates of Gag proteins, the IC25 construct resulted in the production of immature VLPs (the core comprises unprocessed Pr(55Gag)). The remaining two constructs (IC48 and IC90) produced mature VLPs (the core comprises processed capsid p24) in addition to immature VLPs and aggregates of Gag proteins. VLPs incorporated significant levels of mature gp120 envelope glycoprotein. Importantly, the mature VLPs were fusion competent and entered coreceptor-specific target cells. The production of multiple antigenic forms, including fusion-competent VLPs, by candidate DNA vaccine constructs may provide immunologic advantages for induction of protective cellular and humoral responses against HIV-1 proteins.

Effector HIV-specific cytotoxic T-lymphocyte activity in long-term nonprogressors: associations with viral replication and progression

Ex vivo effector cytotoxic T-lymphocyte (CTL) activity was assessed in 27 members of the Australian Long-Term Nonprogressor cohort and correlated with genetic, virological, and immunological markers. The 27 individuals were antiretroviral naive with CD4(+) T-cell counts of >500 cells/ microl for more than 8 years after human immunodeficiency virus type 1 (HIV-1) infection. Effector CTL activity was determined using a standard ex vivo chromium release assay. Individuals with CTL activity (HIV-1 env(IIIB) or pol or gag) were then compared to those without CTL activity in relation to plasma HIV-1 RNA, ICD p24 antigen, beta(2)-microglobulin, CD4 and CD8 T-cell counts, CCR5 and CCR2b genotypes, and progression to CD4 <500 cells/microl or commencement of antiretroviral treatment. Of the 27 individuals examined, 19 had no detectable effector CTL activity. The eight individuals with detectable CTL activity had significantly higher plasma levels of HIV-1 RNA (P = 0.014), immune complex dissociated p24 antigen (P = 0.006), and beta(2)-microglobulin (P = 0.009). There was increased risk of progression within 4 years of study entry in individuals with detectable effector CTL activity, higher plasma levels of HIV-1 RNA, higher beta(2)-microglobulin levels, and higher immune complex dissociated p24 antigen levels at enrollment (P = 0.017, P = 0.004, P = 0.027, P = 0.008 respectively). Multivariate analysis demonstrated viral load remained the strongest predictor of disease progression within this group (P = 0.017). There were no significant associations between CTL response and chemokine receptor genotype. These findings demonstrate the importance of HIV replication in generating an effector CTL response and show that effector CTL activity may be an early predictor of progression in people with long-term asymptomatic HIV infection.

Yeast-derived human immunodeficiency virus type 1 p55(gag) virus-like particles activate dendritic cells (DCs) and induce perforin expression in Gag-specific CD8(+) T cells by cross-presentation of DCs

To evaluate the immunogenicity of human immunodeficiency virus (HIV) type 1 p55(gag) virus-like particles (VLPs) released by budding from yeast spheroplasts, we have analyzed the effects of yeast VLPs on monocyte-derived dendritic cells (DCs). Yeast VLPs were efficiently incorporated into DCs via both macropinocytosis and endocytosis mediated by mannose-recognizing receptors, but not the mannose receptor. The uptake of yeast VLPs induced DC maturation and enhanced cytokine production, notably, interleukin-12 p70. We showed that yeast membrane components may contribute to DC maturation partly through Toll-like receptor 2 signaling. Thus, Gag particles encapsulated by yeast membrane may have an advantage in stimulating Gag-specific immune responses. We found that yeast VLPs, but not the control yeast membrane fraction, were able to activate both CD4(+) and CD8(+) T cells of HIV-infected individuals. We tested the effect of cross-presentation of VLP by DCs in two subjects recruited into a long-term nonprogressor-slow progressor cohort. When yeast VLP-loaded DCs of these patients were cocultured with peripheral blood mononuclear cells for 7 days, approximately one-third of the Gag-specific CD8(+) T cells were activated and became perforin positive. However, some of the Gag-specific CD8(+) T cells appeared to be lost during in vitro culture, especially in a patient with a high virus load. Our results suggest that DCs loaded with yeast VLPs can activate Gag-specific memory CD8(+) T cells to become effector cells in chronically HIV-infected individuals, but there still remain unresponsive Gag-specific T-cell populations in these patients.

Shared modes of protection against poxvirus infection by attenuated and conventional smallpox vaccine viruses

The concern about bioterrorism with smallpox has raised the possibility of widespread vaccination, but the greater prevalence of immunocompromised individuals today requires a safer vaccine, and the mechanisms of protection are not well understood. Here we show that, at sufficient doses, the protection provided by both modified vaccinia Ankara and NYVAC replication-deficient vaccinia viruses, safe in immunocompromised animals, was equivalent to that of the licensed Wyeth vaccine strain against a pathogenic vaccinia virus intranasal challenge of mice. A similar variety and pattern of immune responses were involved in protection induced by modified vaccinia Ankara and Wyeth viruses. For both, antibody was essential to protect against disease, whereas neither effector CD4+ nor CD8+ T cells were necessary or sufficient. However, in the absence of antibody, T cells were necessary and sufficient for survival and recovery. Also, T cells played a greater role in control of sublethal infection in unimmunized animals. These properties, shared with the existing smallpox vaccine, provide a basis for further evaluation of these replication-deficient vaccinia viruses as safer vaccines against smallpox or against complications from vaccinia virus.

Specific nature of cellular immune responses elicited by chimpanzees against HIV-1

Recent epidemiologic and phylogenetic analyses suggest that in the human population human immunodeficiency virus (HIV-1) is a relatively new pathogen that arose by zoonotic transmission from chimpanzees. In humans the morbidity and mortality figures due to HIV infection are extremely high. In a very small percentage of the human population, however, individuals have been identified who were infected for more than 20 years and have no evidence of disease progression. In contrast to most infected humans, almost all chimpanzees appear to be resistant to the pathologic effects caused by lentiviruses such as HIV-1. Here we review the characteristics of the HIV-1-specific cell-mediated immune responses mounted by chimpanzees, and we postulate the mechanisms that have evolved that facilitate their resistance to acquired immunodeficiency syndrome.

Differential proteasomal processing of hydrophobic and hydrophilic protein regions: contribution to cytotoxic T lymphocyte epitope clustering in HIV-1-Nef

HIV proteins contain a multitude of naturally processed cytotoxic T lymphocyte (CTL) epitopes that concentrate in clusters. The molecular basis of epitope clustering is of interest for understanding HIV immunogenicity and for vaccine design. We show that the CTL epitope clusters of HIV proteins predominantly coincide with hydrophobic regions, whereas the noncluster regions are predominantly hydrophilic. Analysis of the proteasomal degradation products of full-length HIV-Nef revealed a differential sensitivity of cluster and noncluster regions to proteasomal processing. Compared with the epitope-scarce noncluster regions, cluster regions are digested by proteasomes more intensively and with greater preference for hydrophobic P1 residues, resulting in substantially greater numbers of fragments with the sizes and COOH termini typical of epitopes and their precursors. Indeed, many of these fragments correspond to endogenously processed Nef epitopes and/or their potential precursors. The results suggest that differential proteasomal processing contributes importantly to the clustering of CTL epitopes in hydrophobic regions.

The influence of HLA genotype on AIDS

Genetic resistance to infectious diseases is likely to involve a complex array of immune-response and other genes with variants that impose subtle but significant consequences on gene expression or protein function. We have gained considerable insight into the genetic determinants of HIV-1 disease, and the HLA class I genes appear to be highly influential in this regard. Numerous reports have identified a role for HLA genotype in AIDS outcomes, implicating many HLA alleles in various aspects of HIV disease. Here we review the HLA associations with progression to AIDS that have been consistently affirmed and discuss the underlying mechanisms behind some of these associations based on functional studies of immune cell recognition.

The induction of HIV Gag-specific CD8+ T cells in the spleen and gut-associated lymphoid tissue by parenteral or mucosal immunization with recombinant Listeria monocytogenes HIV Gag

The induction of mucosal immunity is crucial in controlling viral replication during HIV infection. In this study we compare the ability of a recombinant Listeria monocytogenes that expresses and secretes the HIV Ag Gag to induce CD8(+) T cells against this Ag in the spleen, mesenteric lymph nodes, and Peyer's patches and the ability to provide effector Gag-specific CD8(+) T cells to the lamina propria after i.v., oral, or rectal administration of the vaccine. The levels of Ag-specific CD8(+)-activated T cells were measured ex vivo using intracellular cytokine staining for IFN-gamma and H-2K(d) Gag peptide tetramer staining. We found that all routes of immunization induced Gag-specific CD8(+) T cells in the spleen. After secondary infection, we observed substantial increases in splenic levels of CD8(+) T cells, and levels of Gag-specific cells were similar to those against listeriolysin O, the immunodominant Ag of L. monocytogenes. Both primary and secondary oral immunization resulted in abundant Gag-specific CD8(+)-activated T cells in the lamina propria that constituted approximately 35% of the CD8 compartment. However, significant levels of Gag and listeriolysin O-specific CD8(+) T cells were observed in mucosal lymphoid tissue only after two immunizations, perhaps because they had already entered the lamina propria compartment after a single immunization. In the context of HIV, a mucosally administered vaccine seems best calculated to prompt an immune response that is capable of preventing infection. The data presented in this report demonstrate that mucosally administered Listeria can prompt such a response and that booster doses can maintain this response.

Simian-human immunodeficiency virus SHIV89.6-induced protection against intravaginal challenge with pathogenic SIVmac239 is independent of the route of immunization and is associated with a combination of cytotoxic T-lymphocyte and alpha interferon responses

Attenuated primate lentivirus vaccines provide the most consistent protection against challenge with pathogenic simian immunodeficiency virus (SIV). Thus, they provide an excellent model to examine the influence of the route of immunization on challenge outcome and to study vaccine-induced protective anti-SIV immune responses. In the present study, rhesus macaques were immunized with live nonpathogenic simian-human immunodeficiency virus (SHIV) 89.6 either intravenously or mucosally (intranasally or intravaginally) and then challenged intravaginally with pathogenic SIVmac239. The route of immunization did not affect mucosal challenge outcome after a prolonged period of systemic infection with the nonpathogenic vaccine virus. Further, protection from the SIV challenge was associated with the induction of multiple host immune effector mechanisms. A comparison of immune responses in vaccinated-protected and vaccinated-unprotected animals revealed that vaccinated-protected animals had higher frequencies of SIV Gag-specific cytotoxic T lymphocytes and gamma interferon (IFN-gamma)-secreting cells during the acute phase postchallenge. Vaccinated-protected animals also had a more pronounced increase in peripheral blood mononuclear cell IFN-alpha mRNA levels than did the vaccinated-unprotected animals in the first few weeks after challenge. Thus, innate as well as cellular anti-SIV immune responses appeared to contribute to the SHIV89.6-induced protection against intravaginal challenge with pathogenic SIVmac239.

A push-pull approach to maximize vaccine efficacy: abrogating suppression with an IL-13 inhibitor while augmenting help with granulocyte/macrophage colony-stimulating factor and CD40L

Although a role for CD4(+) helper cells in CD8(+) cytotoxic T lymphocyte (CTL) induction by vaccines is widely recognized, much less is known about a counterbalancing role of CD4(+) T cells in down-modulating this response, or about ways to optimize vaccine responses through abrogation of this negative regulatory mechanism. Here, we discovered a synergistic enhancement of vaccine-mediated CTL induction and protection by the relief of suppression through depletion of regulatory CD4(+) cells, including CD4(+) NKT cells, or blockade of IL-13 made by these cells, combined with the cytokine granulocyte/macrophage colony-stimulating factor and the costimulatory molecule CD40L. Indeed, in the absence of helper epitopes, granulocyte/macrophage colony-stimulating factor and the helper-mimetic molecule CD40L are not sufficient to replace help to induce CTL without abrogation of CD4(+) T cell-mediated suppression, suggesting a role for T cell help in overcoming suppression. The increased CTL induction translated to striking protection against viral infection by a vaccine by using this synergistic combined approach. These results argue for a push-pull approach to maximize vaccine efficacy, especially for HIV and cancer.

Cross-clade HIV-1-specific neutralizing IgA in mucosal and systemic compartments of HIV-1-exposed, persistently seronegative subjects

There is an urgent need for a universally effective HIV-1 vaccine, but whether a vaccine will be able to protect against HIV-1 of different clades is a significant concern. IgA from HIV-1-exposed, persistently seronegative (HEPS) subjects has been shown to neutralize HIV-1 and to block epithelial HIV-1 transcytosis, and it may target novel HIV-1 epitopes. We have tested the ability of plasma and mucosal IgA purified from HEPS subjects to neutralize HIV-1 primary isolates of different viral clades and phenotypes. IgA from two groups of HEPS subjects was tested: sex workers from Nairobi, Kenya, where clades A and D predominate, and the heterosexual partners of individuals infected by clade B virus. HIV-1-infected and low-risk uninfected individuals were included as controls. IgA purified from the blood, genital tract, and saliva of most HEPS sex workers demonstrated significant cross-clade HIV-1 neutralization, whereas a more clade-restricted pattern of neutralization was found in partners of clade B-infected individuals. IgA purified from HIV-1-infected individuals also mediated cross-clade neutralization, whereas IgA from uninfected controls lacked neutralizing activity. In conclusion, mucosal and plasma IgA from HEPS subjects neutralizes HIV-1 of different clades. This ability to induce HIV-1-specific systemic and mucosal IgA may be an important feature of an effective prophylactic HIV-1 vaccine.

Immunological functions of the proteasome

Proteasomes are highly abundant cytosolic and nuclear protease complexes that degrade most intracellular proteins in higher eukaryotes and appear to play a major role in the cytosolic steps of MHC class I antigen processing. This review summarizes the knowledge of the role of proteasomes in antigen processing and the impact of proteasomal proteolysis on T cell-mediated immunity.

Dynamics of T cell responses in HIV infection

Cytotoxic CD8(+) T cells play a major role in the immune response against viruses. However, the dynamics of CD8(+) T cell responses during the course of a human infection are not well understood. Using tetrameric complexes in combination with a range of intracellular and extracellular markers, we present a detailed analysis of the changes in activation and differentiation undergone by Ag-specific CD8(+) T cells, in relation to Ag-specific CD4(+) T cell responses, in the context of a human infection: HIV-1. During primary HIV-1 infection, the initial population of HIV-specific CD8(+) T cells is highly activated and prone to apoptosis. The Ag-specific cells differentiate rapidly from naive to cells at a perforin low intermediate stage of differentiation, later forming a stable pool of resting cells as viral load decreases during chronic infection. These observations have significant implications for our understanding of T cell responses in human viral infections in general and indicate that the definition of effector and memory subsets in humans may need revision.

HIV type 1-specific IgE in serum of long-term surviving children inhibits HIV type 1 production in vitro

We previously identified a group of long-term pediatric survivors who had acquired HIV-1 through maternal transmission; had not received antiretroviral therapy; are now >8 years old, in good health, and with no opportunistic infections; and have not failed to thrive, although they have greatly decreased numbers of blood CD4+ T cells (<500/mm(3)). All the children have elevated total serum IgE levels (210-2475 IU/ml) and make anti-HIV-1 IgE or IgE directed against non-HIV-1 specificities (radioimmunoassay, Western blot assay); they have no detectable antigenemia. We have now studied the ability of anti-HIV-1 IgE in serum obtained from these children to regulate (1) production of HIV-1 by interleukin 2/phytohemagglutinin (IL-2/PHA)-stimulated peripheral blood mononuclear cells (PBMCs) taken from HIV-1-seronegative donors and infected with a T cell-tropic clone of HIV-1, and (2) transmission of a primary HIV-1 strain from adult AIDS patients to uninfected IL-2/PHA-stimulated PBMCs (p24 core antigen production). High levels of HIV-1 production were observed when PBMCs were cultured for 5 days in the presence of HIV-1-seronegative donor serum that was either IgE positive or IgE negative (IgE, >100 or <100 IU/ml, respectively). HIV-1 production also was observed when PBMCs were cultured with HIV-1-infected donor serum that either contained IgE directed against non-HIV-1 specificities or was IgE negative; these levels were 40% less than those seen with sera from the HIV-1-seronegative donors. Far greater inhibition of virus production was observed if the serum in culture contained anti-HIV-1 IgE (>95%). Virus neutralization did not appear to account for the inhibition obtained with anti-HIV-1 IgE-containing serum because virus production was not suppressed in cultures to which serum was added immediately preinfection (<10%), but was strongly suppressed when serum was added 1.5 hr postinfection (>95%). The inhibition of virus production obtained with serum containing anti-HIV-1 IgE was reversed when (1) serum was depleted of IgE (immunoaffinity), but not when it was depleted of IgG (protein G-Sepharose) before inclusion in culture postinfection, (2) anti-IgE, but not anti-IgG, was included in culture, or (3) serum was heat treated before culture. The results indicate that serum from certain HIV-1-infected pediatric long-term survivors contains agents that inhibit HIV-1 production in vitro, and that these agents include anti-HIV-1 IgE. They suggest that a cytotoxic event, rather than virus neutralization, plays an important role in anti-HIV-1 IgE-mediated inhibition of virus production.

Purification and characterization of oligomeric envelope glycoprotein from a primary R5 subtype B human immunodeficiency virus

Human immunodeficiency virus (HIV) continues to be a major public health problem throughout the world, with high levels of mortality and morbidity associated with AIDS. Considerable efforts to develop an effective vaccine for HIV have been directed towards the generation of cellular, humoral, and mucosal immune responses. A major emphasis of our work has been toward the evaluation of oligomeric (o-gp140) forms of the HIV type 1 (HIV-1) envelope protein for their ability to induce neutralizing antibody responses. We have derived stable CHO cell lines expressing o-gp140 envelope protein from the primary non-syncytium-inducing (R5) subtype B strain HIV-1(US4). We have developed an efficient purification strategy to purify oligomers to near homogeneity. Using a combination of three detectors measuring intrinsic viscosity, light scattering, and refractive index, we calculated the molecular mass of the oligomer to be 474 kDa, consistent with either a trimer or a tetramer. The hydrodynamic radius (R(h)) of o-gp140 was determined to be 8.40 nm, compared with 5.07 nm for the monomer. The relatively smaller R(h) of the oligomer suggests that there are indeed differences between the foldings of o-gp140 and gp120. To assess the structural integrity of the purified trimers, we performed a detailed characterization of the glycosylation profile of o-gp140, its ability to bind soluble CD4, and also its ability to bind to a panel of monoclonal antibodies with known epitope specificities for the CD4 binding site, the CD4 inducible site, the V3 loop, and gp41. Immunogenicity studies with rabbits indicated that the purified o-gp140 protein was highly immunogenic and induced high-titer, high-avidity antibodies directed predominantly against conformational epitopes. These observations confirm the structural integrity of purified o-gp140 and its potential as a vaccine antigen.

Magnitude of functional CD8+ T-cell responses to the gag protein of human immunodeficiency virus type 1 correlates inversely with viral load in plasma

The importance of CD8+ T-cell responses in the control of human immunodeficiency virus type 1 (HIV-1) infection has been demonstrated, yet few studies have been able to correlate these responses with markers of HIV-1 disease progression. This study measured cell-mediated immune responses using peripheral blood mononuclear cells (PBMC) obtained from 27 patients with chronic HIV-1 infection, the majority of whom were off antiretroviral therapy. The ELISPOT assay was used to detect gamma interferon-secreting PBMC after stimulation with overlapping HIV-1 peptides spanning the Gag, Pol, Env, and Nef proteins in addition to the baculovirus-derived p24 and gp160 proteins. All volunteers had responses to at least one HIV-1-specific peptide. All but one of the subjects (96%) responded to the Gag peptide pool, and 86% responded to the Pol and/or Nef peptide pools. The magnitude and the breadth of T-cell responses directed to either the Gag or p24 peptide pools correlated inversely with viral load in plasma (r = -0.60, P < 0.001 and r = -0.52, P < 0.005, respectively) and directly with absolute CD4+ T-cell counts (r = 0.54, P < 0.01 and r = 0.39, P < 0.05, respectively) using the Spearman rank correlation test. Responses to the Pol and integrase peptide pools also correlated with absolute CD4+ T-cell counts (r = 0.45, P < 0.05 and r = 0.49, P < 0.01, respectively). No correlation with markers of disease progression was seen with specific T-cell responses directed toward the Env or Nef peptides. These data serve as strong evidence that major histocompatibility complex class I presentation of Gag peptides is an essential feature for any HIV-1 vaccine designed to elicit optimal CD8+ T-cell responses.

Human immunodeficiency virus (HIV)-specific cellular immune responses in newborns exposed to HIV in utero

Significant immunological changes are associated with intrauterine human immunodeficiency virus (HIV) encounter among uninfected infants of HIV-infected mothers. Peripheral blood cells of more than one-third of these exposed-uninfected infants proliferate and produce IL-2 after stimulation with HIV, and HIV-specific CD4+ T helper cell responses can be quantified in nearly all when sensitive intracellular cytokine assays are used. HIV-specific CD8+ cytotoxic T lymphocyte responses can be elicited in some, although less frequently. It is difficult to demonstrate that these responses are components of protective immunity and not simply epiphenomena of exposure. However, HIV-specific responses are associated with lack of infection, even with prolonged reexposure through breast-feeding. Elevations in nonspecific markers of immune activation provide further corroboration, as do similar findings in adults, consistent across all known routes of HIV transmission. Many questions remain, but much can be learned from this special population that may be informative for development of effective immunity in response to HIV vaccines.

TCRBV CDR3 diversity of CD4+ and CD8+ T-lymphocytes in HIV-infected individuals

TCRBV CDR3 repertoire diversity was analyzed in a cross-sectional study of HIV-infected individuals by CDR3 fingerprinting/spectratyping and single strand conformation polymorphism (SSCP). Most TCRBV families were detected in CD4+ cells of HIV-infected patients with CD4 counts ranging from 35 to 1103. In patients with CD4 counts >500, CD4+ TCRBV CDR3 fingerprinting profiles contained subtle variations with generally gaussian-distributed sizes. Lower CD4 counts coincided with more fragmented TCRBV CDR3 repertoires, containing dominant bands and bands missing from the CDR3 profiles. The CD8+ population of the same patients exhibited skewed CDR3 profiles of the majority of TCR BV families at CD4 counts >500. Irregularity of CD8+ CDR3 size distribution was most profound at low CD4 counts and suggested domination of the CD8+ TCRBV repertoire by a limited number of clones. Skewed patterns of CDR3 diversity probably reflect (oligo)clonal expansion of particular CD4+ and CD8+ cell populations during chronic infection with HIV. In addition, irregular CDR3 profiles of CD4+ and CD8+ at low CD4 counts suggest diminished TCR repertoire diversity, which may contribute to immunodeficiency.

Immunology and the REACH study: HIV immunology and preliminary findings. Reaching for Excellence in Adolescent Care and Health

This review paper presents the immunology findings in human immunodeficiency virus (HIV) infected and uninfected youth in the Reaching for Excellence in Adolescent Care and Health (REACH) Project within the context of basic and HIV immunology concepts. Methods employed in the study for specimen collection, management, and laboratory analysis are presented. This paper reviews published analyses of cross-sectional data; longitudinal analyses are underway. These preliminary data extend the work of others in demonstrating the potential for substantial thymic reserve in youth. This finding in HIV infected adolescents has implications for a fuller response to antiretroviral or immune-based therapies compared to that seen in adults. Dysregulation in mucosal immunity may appear before systemic HIV effects are seen and requires attention particularly to screening and treatment of genital co-infections. REACH has demonstrated gender differences in immunologic measures irrespective of HIV infection status.

Cytotoxic T-cell abundance and virus load in human immunodeficiency virus type 1 and human T-cell leukaemia virus type 1

The correlation between virus load and specific cytotoxic T-lymphocyte (CTL) frequency during the chronic phase in human immunodeficiency virus type 1 (HIV-1) infection has been found to be negative in cross-sectional studies. We report here that, in infection with the related retrovirus human T-cell leukaemia virus type 1 (HTLV-1), the correlation is positive in asymptomatic carriers and zero in patients with the associated inflammatory disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). We demonstrate that the direction of the correlation may depend on the efficacy of the CTL response using mathematical models. We conclude that the CTL response is effective in asymptomatic carriers of HTLV-1, but ineffective in patients with HAM/TSP. Virus-mediated impairment of specific CTL production in HIV-1 infection can account for the negative correlation observed.

Cellular HIV-1 immune responses in natural infection and after genetic immunization

By eliminating infected cells, virus-specific cytotoxic T-lymphocytes (CTL) play a central role in host protection. Many studies to date seem to support the concept that human immunodeficiency virus (HIV)-specific CTL responses contribute to the control of viral replication, and thus delay the onset of disease. The feasibility of improving the virus-specific T-cell immunity by immunizing during the asymptomatic phase of infection has been studied in man. DNA vaccination is a novel strategy, involving direct inoculation of genetic material that is capable of producing antigen intracellularly for presentation to CTL. Such DNA-based immunization has been shown in animal models to be effective for the induction of both cellular and humoral immune responses as well as for protection from infectious challenge. This article reviews the cell-mediated immune responses in natural HIV-1 infection and the induction by DNA vaccination in humans.

MHC-I-restricted presentation of HIV-1 virion antigens without viral replication

Dendritic cells and macrophages can process extracellular antigens for presentation by MHC-I molecules. This exogenous pathway may have a crucial role in the activation of CD8+ cytotoxic T lymphocytes during human viral infections. We show here that HIV-1 epitopes derived from incoming virions are presented through the exogenous MHC-I pathway in primary human dendritic cells, and to a lower extent in macrophages, leading to cytotoxic T-lymphocyte activation in the absence of viral protein synthesis. Exogenous antigen presentation required adequate virus-receptor interactions and fusion of viral and cellular membranes. These results provide new insights into how anti-HIV cytotoxic T lymphocytes can be activated and have implications for anti-HIV vaccine design.

Positive and negative aspects of the human immunodeficiency virus protease: development of inhibitors versus its role in AIDS pathogenesis

In this review we summarize multiple aspects of the human immunodeficiency virus (HIV) protease from both structural and functional viewpoints. After an introductory overview, we provide an up-to-date status report on protease inhibitors (PI). This proceeds from a discussion of PI structural design, to how PI are optimally utilized in highly active antiretroviral triple therapy (one PI along with two reverse transcriptase inhibitors), the emergence of PI resistance, and the natural role of secretory leukocyte PI. Then we switch to another focus: the interaction of HIV protease with other genes in acute and persistent infection, which in turn may have an effect on AIDS pathogenesis. We conclude with a discussion on future directions in HIV treatment, involving multiple-target anti-HIV therapy, vaccine development, and novel reactivation-inhibitory reagents.

Transfer of specificity for human immunodeficiency virus type 1 into primary human T lymphocytes by introduction of T-cell receptor genes

The introduction of genes encoding T-cell receptor (TCR) chains specific for human immunodeficiency virus into T cells of infected patients represents a means to quantitatively and qualitatively improve immunity to the virus. Our results demonstrate that the high level of TCR expression required for physiologic functioning can be reproducibly achieved with retroviral vectors encoding full-length unmodified TCR chains under the control of a strong internal constitutive phosphoglycerate kinase promoter.

Creating HIV-1 reverse transcriptase cytotoxic T lymphocyte target structures by HLA-A2 heavy chain modifications

Vigorous HIV-1-specific CD8(+) cytotoxic T lymphocyte (CTL) responses play an important role in the control of HIV-1 replication and the induction of a strong, broadly cross-reactive CTL response remains an important goal of HIV vaccine development. It is known that the display of high levels of class I MHC-viral peptide complexes at the cell surface of target cells is necessary to elicit a strong CTL response. We now report two strategies to enhance the presentation of defined HIV-1 epitope-specific CTL target structures, by incorporating subdominant HIV-1 reverse transcriptase (RT) CTL epitope sequences into the human class I MHC molecule HLA-A2. We show that either incorporation of HIV-1 CTL epitopes into the signal sequence of HLA or tethering of epitopes to the HLA-A2 heavy chain provide simple ways to create effective CTL target structures that can be recognized and lysed by human HLA-A2-restricted RT-specific CD8(+) CTL. Moreover, cells expressing these epitope-containing HLA-A2 constructs stimulated the generation of primary epitope-specific CTL in vitro. These strategies offer new options in the design of plasmid DNA-based vaccines or immunotherapeutics for the induction of CTL responses against subdominant HIV-1 epitopes.

Anti-major histocompatibility complex antibody responses in macaques via intradermal DNA immunizations

In simian immunodeficiency virus (SIV) models, immunization of macaques with uninfected human cells or human major histocompatibility complex (MHC) proteins can induce xenogeneic immune responses which can protect the animals from subsequent SIV challenges. These studies suggest that the induction of anti-MHC immune responses can be a viable vaccine strategy against human immunodeficiency virus type 1 (HIV-1). We have previously shown in mouse studies that DNA immunization with class I and class II MHC-encoding plasmids can elicit both xenogeneic and allogeneic antibody responses against conformationally intact MHC molecules (Vaccine 17 (1999) 2479-92). Here we take these observations one step closer to human applications and report that intradermal needle immunizations of non-human primates with plasmid DNA encoding human MHC alleles can safely elicit xenogeneic anti-MHC antibody responses. Moreover, injecting macaques with DNA encoding a specific macaque allogeneic MHC induced anti-allogeneic MHC antibodies production. These studies show that DNA immunization with MHC-encoding vectors can indeed be used to induce specific anti-human xenogeneic, as well as anti-macaque allogeneic MHC immunity in non-human primates. This strategy could thus be used to mobilize anti-MHC antibody response which may be useful as part of an anti-HIV-1 vaccination approach.

Interleukin-12 (IL-12) enhancement of the cellular immune response against human immunodeficiency virus type 1 env antigen in a DNA prime/vaccinia virus boost vaccine regimen is time and dose dependent: suppressive effects of IL-12 boost are mediated by nitric oxide

We previously demonstrated that codelivery of interleukin-12 (IL-12) with the human immunodeficiency virus type 1 (HIV-1) Env antigen from a recombinant vaccinia virus (rVV) can enhance the specific anti-Env cell-mediated immune (CMI) response. In the present study, we have investigated the effects of IL-12 in mice when it is expressed in a DNA prime/VV boost vaccine regimen. The delivery of IL-12 and Env product during priming with a DNA vector, followed by a booster with VV expressing the Env gene (rVVenv), was found to trigger the optimal CMI response compared with other immunization schedules studied. Significantly, if IL-12 is also delivered as a booster from the viral vector, an impairment of the effects of IL-12 was observed involving nitric oxide (NO), since it was overcome by specific inhibitors of inducible NO synthase. NO caused transient immunosuppression rather than impairment of viral replication. Moreover, at certain viral doses, coadministration of the NO inhibitor during the booster resulted in IL-12-mediated enhancement of the specific CD8(+) T-cell response. In addition, the dose of the IL-12-encoding plasmid (pIL-12) and the route of administration of both vectors were relevant factors for optimal CMI responses. Maximal numbers of Env-specific CD8(+) gamma interferon-secreting cells were obtained when 50 microg of pIL-12 was administered intramuscularly at priming, followed by an intravenous rVVenv boost. Our results demonstrate, in a murine model, critical parameters affecting the success of vaccination schedules based on a combination of DNA and VV vectors in conjunction with immunomodulators.

Genetic characterization and phylogenetic analysis of HIV-1 subtype C from Uganda

To better understand the emergence of subtype C and its potential impact on vaccine efforts in Uganda, we have characterized subtype C sequences from Uganda (n = 13), Zimbabwe (n = 11), Mozambique (n = 5), South Africa (n = 4), and India (n = 3). Phylogenetic analysis of subtype C sequences in the env gp41 gene region revealed multiple subclusters within subtype C. Further, while most Ugandan specimen subclustered together, other subclusters did not reflect a clear geographic location. The nucleotide divergence within the Ugandan subset was 8.2% (6.1-9.8%) compared with 9.5% (2.5-15%) for the other subtype C gp41 sequences. The protein sequence alignment revealed marked sequence conservation of major immunodominant epitopes within the gp41 region.

Memory CD8+ T cells in HIV infection

Cytotoxic T lymphocytes (CTLs) play a central role in the control of persistent HIV infection in humans. The kinetics and general features of the CTL response are similar to those found during other persisting virus infections in humans. During chronic infection there are commonly between 0.1 and 1.0% of all CD8+ T cells in the blood that are specific for immunodominant virus epitopes, as measured by HLA class I peptide tetramers. These figures are greatly in excess of the numbers found by limiting dilution assays; the discrepancy may arise because in the latter assay, CTLs have to divide many times to be detected and many of the HIV-specific CD8+ T cells circulating in infected persons may be incapable of further division. Many tetramer-positive T cells make interferon-gamma, beta-chemokines and perforin, so are probably functional. It is not known how fast these T cells turn over, but in the absence of antigen they decay in number. Impairment of CTL replacement, because CD4+ T helper cells are depleted by HIV infection, may play a major role in the development of AIDS.

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.

Challenges in the development of an effective HIV vaccine: current approaches and future directions

OBJECTIVE

The intent of this review is to investigate and discuss why developing a successful HIV vaccine has been so challenging, first by examining the molecular biology of the virus and how HIV interacts with the immune system, and then reviewing past viral vaccine successes as well as future directions for HIV vaccine research.

BACKGROUND

Since HIV appeared in the United States in the early 1980s, an estimated 40 million people worldwide have been infected with the virus. Despite promising advances in the pharmacotherapy of HIV infection, it is apparent that the best, most cost-effective strategy for controlling the further spread of the virus is through synthesis of a protective vaccine. Almost 2 decades into the epidemic, there are few prospects for a truly effective vaccine entering the market in the foreseeable future.

METHODS

MEDLINE was searched for articles written between 1966 and June 1999. Search terms used were AIDS, HIV vaccine, HIV-1, HIV-2, vaccines, and human immunodeficiency virus.

RESULTS

Only 2 candidates for an HIV vaccine are currently in phase III clinical trials (1 in the United States and 1 in Thailand). The efficacy of these vaccines when applied to the population as a whole is widely questioned, largely because they induce protection by an antibody response only. Several studies have suggested that this approach will likely be ineffective in providing any real protection from viral infection. It appears that a strong cellular immune response is necessary in addition to a strong antibody response.

Human immunodeficiency virus type 1 envelope-specific cytotoxic T lymphocytes response dynamics after prime-boost vaccine regimens with human immunodeficiency virus type 1 canarypox and pseudovirions

Virus-specific cytotoxic T lymphocytes (CTLs) may represent significant immune mechanisms in the control of human immunodeficiency virus (HIV) infection and, therefore, CTL induction may be a fundamental goal in the development of an efficacious acquired immunodeficiency syndrome (AIDS) vaccine. In the current study, prime-boost protocols were used to investigate the potential of noninfectious human immunodeficiency virus type 1 (HIV-1) pseudovirions (HIV PSV) in enhancing HIV-specific CTL responses in Balb/c mice primed with the recombinant canarypox vector, vCP205, encoding HIV-1 gp120 (MN strain) in addition to Gag/Protease (HIB strain). The prime-boost immunization regimens were administered intramuscularly and involved injections of vCP205 followed by boosts with HIV PSV. Previous vaccination strategies solely involving vCP205 had induced good cellular immune responses in uninfected human volunteers, despite some limitations. The use of genetically engineered HIV PSV was a logical step in the evaluation of whole noninfectious virus or inactivated virus vaccine strategies, particularly as a potential boosting agent for vCP205-primed recipients. Based on this current study, HIV PSV appeared to have the capability to effectively induce and boost cell-mediated HIV-1-specific responses. In order to observe the immune effects of HIV PSV in a prime-boost immunization strategy, both HIV vaccine immunogens required careful titration in vivo. This suggests that careful consideration should be given to the optimization of immunization protocols destined for human use.