HIV-specific Immune Responses Research Articles

Phenotype and function of protective T cell immune responses in HIV

Definition of T cell immune correlates in HIV infection remains a lofty goal towards our understanding of the HIV-specific immune response. This review will focus upon recent developments and controversies in our understanding of protective T cell responses against HIV. It has become clear that multiple functions and phenotypic markers of T cells must be assessed to accurately characterize the complexity of CD4 and CD8 T cell responses. While evidence indicates that a hallmark of protective immune responses in HIV infection is the presence of 'polyfunctional' T cell responses, a disconnect remains between the function and phenotype of effective HIV-specific T cells. Moreover, there may be inherent differences in the ability of specific human leukocyte antigen class I families to promote CD8 T cell effector versus polyfunctional responses. It remains to be determined how polyfunctional responses arise in HIV infection, which functions are important for control, and whether surface phenotype markers provide an indication of protective capacity. Polyfunctional and phenotypic assessment of T cell responses have clearly advanced our understanding of HIV specific immune responses. Critical questions remain, however, especially whether polyfunctional T cell responses control, or are controlled by, HIV replication.

HIV-1/AIDS vaccine development: are we in the darkness before the dawn?

HIV-1/AIDS vaccine development: are we in the darkness before the dawn?

Human immunodeficiency virus (HIV)-specific T helper responses fail to predict CD4+ T cell decline following short-course treatment at primary HIV-1 infection

Early anti-retroviral treatment (ART) in primary human immunodeficiency virus (HIV) infection (PHI) may have unique, restorative immunological and virological benefits which could enhance clinical outcomes. However, the sustainability of these HIV-specific immune responses and their impact on clinical outcome remains unclear. We present a 3-year longitudinal clinical and immunological follow-up of a single-arm, prospective study assessing the long-term impact of a short-course of ART (SCART) during PHI. Twenty-eight subjects with defined PHI received 3 months of SCART at HIV-1 seroconversion. HIV-specific interferon-gamma+ CD4+ T cell responses, CD4 cell counts and plasma viral loads were assessed prospectively. Clinical outcome was defined as the time taken from PHI to a fall in CD4 cell counts <350 cells/mul on two or more occasions. Of 28 patients, 25 (89%) had detectable HIV-specific CD4+ helper responses at baseline. Five of 11 (45%) patients had preserved HIV-specific CD4+ responses 3 years after stopping SCART. Neither the presence nor magnitude of HIV-1-specific T helper responses either at baseline or 3 years following SCART cessation predicted clinical outcome. Rebound viraemia associated with stopping SCART did not diminish HIV-1-specific CD4+ responses. Long-term (>3 years) preservation of virus-specific CD4+ cells occurred in 45% of patients receiving SCART in PHI. There was no correlation between either the presence or magnitude of these responses and clinical outcome.

Delayed early antiretroviral treatment is associated with an HIV-specific long-term cellular response in HIV-1 vertically infected infants

Antiviral T-cell immune responses appear to be crucial to control HIV replication. Infants treated before the third month of life with highly active antiretroviral treatment (HAART) did not develop a persistent HIV-specific immune response. We evaluated how delayed initiation of HAART after 3 months of age influences the development of HIV-1-specific T-cell responses during long-term follow-up in 9 HIV-1 vertically infected infants. These data suggest that a longer antigenic stimulation, due to a larger window for therapeutic intervention with HAART, is associated with the establishment of a persistent specific HIV immune response resulting in a long-term viral control of vertically infected infants.

Supraphysiologic TCRs Generate Polyfunctional CD8 T Cells That Effectively Re‐directed the CD8 T cell Immune Response

We evaluated how increased TCR affinity for its cognate antigen affects its ability to redirect an HIV‐1 and tumor specific immune response. TCRs differing in affinity for the HIVgag epitope SL9 were introduced into primary human CD8 T cells and the ability of these cells to proliferate, produce cytokines, and control HIV infection was studied. Increased avidity did not alter the ability of CD8 T cells to expand in response to antigen stimulation. In contrast, CD8 T cells transduced with high affinity, supraphysiologic SL9 TCRs were more likely to have a polyfunctional cytokine profile following antigen stimulation. The most notable difference was the ability of CD8 T cells transduced with supraphysiologic SL9 TCRs to produce IL‐2, a cytokine whose expression correlates closely with CD8 T cell antiviral activity during the natural progression of HIV‐1 disease. Importantly, high affinity SL9‐specific TCR expressing cells more effectively controlled HIV‐1 infection than cells expressing the wildtype SL9‐specific TCR receptor. This difference was most pronounced when viruses that contained known SL9 escape mutations were used. Similar experiments using hTERT TCRs were performed. These data indicate that engineered TCRs with antibody‐like‐affinities for antigen can induce a polyfunctional phenotype to CD8 T cells and that use of supraphysiologic TCRs in adoptive T cell therapy is attractive.

Immune modulators and treatment interruption

This article reviews the relevance of sudden immune activation in HIV pathogenesis and summarizes the strategies that could prevent the high peaks of viral replication after antiretroviral therapy interruption. Systemic immune activation could have both beneficial and harmful effects in chronic infection. Recent findings suggest that in addition to viral replication other factors could drive immune activation. The changes in natural regulatory T cell number or function and microbial translocation have been hypothesized as potential causes. Immune activation after antiretroviral therapy interruption could play a critical role in the increase in the rates of AIDS-defining and non-AIDS-defining malignancies or cardiovascular events between patients on a CD4 T-cell-guided intermittent antiretroviral therapy strategy in the SMART study. The use of a cytostatic drug would help T lymphocytes to remain quiescent, becoming refractory to productive HIV-1-infection and thus avoiding high peaks of viral replication after antiretroviral interruption without blunting HIV-1 specific immune responses. This has been the rationale for the use of immunomodulators (such as corticosteroids, hydroxyurea, mycophenolate mofetil, thalidomide, and cyclosporin A) as adjuvant to antiretroviral therapy in structured treatment interruption strategies.

Planned Multiple Exposures to Autologous Virus in HIV Type 1-Infected Pediatric Populations Increases HIV-Specific Immunity and Reduces HIV Viremia

We tested to determine if planned multiple exposures to autologous HIV in pediatric patients with HIV-1 infection will induce cellular immunity that controls viremia. A prospective multicenter study of aviremic pediatric patients on highly active antiretroviral therapy who underwent progressively longer antiretroviral treatment interruptions in cycles starting with 3 days, increasing by 2 days in length each consecutive cycle, was conducted. Eight individuals became viremic and reached Cycle 13 or greater with an "off-therapy" interval of >or=27 days. HIV-specific interferon-gamma (IFN-gamma) production to inactivated HIV and vaccinia vectors expressing gag, env, nef, and pol increased (>10-fold) from baseline in six of eight subjects. The HIV-specific lymphoproliferative response as measured by the median stimulation index (SI) increased in the treatment group from 1 at baseline to 16, 12, 4, and 3 at Cycles 7, 10, 13, and 17, respectively. Median plasma RNA levels peaked at Cycle 7 (4.45 log) and declined to levels <10(4) cp/ml after Cycle 10 (4.1, 3.5, and 3.4 at Cycles 10, 13, and 17). In a subset of five patients who reached Cycle 17, HIV-specific IFN-gamma frequencies were 4- to 30-fold higher and median RNA levels were 0.32-2.10 (median 1.3) log lower than at comparable days off treatment at Cycle 8 (17 days off therapy). A second group of children, not undergoing drug interruption, did not develop significant increases in either HIV-specific IFN-gamma production or SI. Increased HIV-specific immune responses and decreased HIV RNA were seen in those children who have had >10 cycles of antiretroviral discontinuations of increasing durations acting as autologous virus vaccinations. Other studies may have failed due to an insufficient number of exposures to HIV; most of the studies had fewer than six drug interruptions.

Aerosol immunization with NYVAC and MVA vectored vaccines is safe, simple, and immunogenic

Each year, approximately five million people die worldwide from putatively vaccine-preventable mucosally transmitted diseases. With respect to mass vaccination campaigns, one strategy to cope with this formidable challenge is aerosol vaccine delivery, which offers potential safety, logistical, and cost-saving advantages over traditional vaccination routes. Additionally, aerosol vaccination may elicit pivotal mucosal immune responses that could contain or eliminate mucosally transmitted pathogens in a preventative or therapeutic vaccine context. In this current preclinical non-human primate investigation, we demonstrate the feasibility of aerosol vaccination with the recombinant poxvirus-based vaccine vectors NYVAC and MVA. Real-time in vivo scintigraphy experiments with radiolabeled, aerosol-administered NYVAC-C (Clade C, HIV-1 vaccine) and MVA-HPV vaccines revealed consistent mucosal delivery to the respiratory tract. Furthermore, aerosol delivery of the vaccines was safe, inducing no vaccine-associated pathology, in particular in the brain and lungs, and was immunogenic. Administration of a DNA-C/NYVAC-C prime/boost regime resulted in both systemic and anal-genital HIV-specific immune responses that were still detectable 5 months after immunization. Thus, aerosol vaccination with NYVAC and MVA vectored vaccines constitutes a tool for large-scale vaccine efforts against mucosally transmitted pathogens.

Structured treatment interruptions (STIs) in HIV-1 infected pediatric populations increases interferon gamma production and reduces viremia

We assessed the effect of progressively longer antiretroviral structured treatment interruptions (STIs) starting with 3 days, increasing by 2 days in length each cycle on HIV-specific immune responses. As well, we correlated these responses with control of HIV viremia. Eight individuals became viremic and reached cycle 13 with an STI of ≥27 days. HIV-specific gamma-interferon production to inactivated HIV and vaccinia vectors expressing gag, env, nef, and pol increased (>10-fold) in six of eight subjects. Median plasma RNA levels peaked @ cycle 7 and declined to levels <10 4 cp/ml after cycle 10. In a subset of five who reached cycle 17, HIV-specific IFN-gamma frequencies increased from cycle 8 to cycle 17 with evidence of improved virologic control over comparable periods off antiretroviral therapy. This allowed us to conclude that exposure to autologous virus increased HIV-specific immune responses and decreased HIV RNA were seen in those who have had >13 interruptions, with STI intervals that exceeded 27 days.

Microtransfusion and viral exposure in uninfected infants born to HIV-infected women

Background HIV-specific cellular immune responses have been detected in some uninfected infants born to HIV-infected women, indicating transient virus exposure or replication has occurred. Small quantities of maternal blood pass into the infant's circulation during childbirth, termed “microtransfusion”, potentially facilitating viral exposure. We sought to determine the occurrence of microtransfusion and HIV-specific immune responses as an indicator of viral exposure in a cohort of uninfected infants born to HIV-infected women, in the context of interventions.

Su.39. Loss of Virus-specific Memory T Cells in Coxsackievirus B3 and B4-Infected Mice

Given the limited success of clinical HIV vaccine trials, new vaccine strategies are needed for the HIV pipeline. The present study explored the novel concept that a live enteric virus, with limited disease potential, is a suitable vaccine vector to elicit HIV-specific immune responses in the gut mucosa of immunized mice. Two coxsackievirus B4 (CVB4) vaccine vectors were designed to induce HIV-specific B or T cell responses. A B cell immunogen, CVB4/gp41(2F5), was constructed by expressing an epitope from the membrane proximal external region (MPER) of gp41 as a structural peptide within a surface loop of a capsid protein of CVB4. The T cell immunogen, CVB4/p24(733), was constructed previously by expressing a gag p24 sequence as a non-structural peptide at the amino-terminus of the CVB4 polyprotein. The CVB4/gp41(2F5) recombinant was antigenic in mice and elicited anti-gp41 antibodies in both the mucosal and systemic compartments. The route of immunization affected the antibody response since oral delivery of CVB4/gp41(2F5) induced anti-gp41 antibodies in the mucosal but not in the systemic compartment while parenteral delivery induced anti-gp41 antibodies in both compartments. In contrast, oral immunization with CVB4/p24(733) elicited both mucosal and systemic gag p24-specific T cell responses. Since coxsackieviruses are ubiquitous in the human population, a key question is whether pre-existing vector immunity will inhibit the ability of a CVB4-based vaccine to induce HIV-specific immune responses. We show that pre-existing vector immunity did not preclude the development of mucosal anti-gp41 antibodies or gag p24-specific T cell responses after oral immunization with the CVB4/HIV recombinants. We suggest that the CVB4/HIV recombinants have the potential to be a viable vaccine product because of ease of delivery, safety, immunogenicity, ease of large-scale production, and storage conditions requiring cold-chain temperatures provided by refrigeration.

Relationship between T Cell Activation and CD4+T Cell Count in HIV‐Seropositive Individuals with Undetectable Plasma HIV RNA Levels in the Absence of Therapy

Although untreated human immunodeficiency virus (HIV)-infected patients maintaining undetectable plasma HIV RNA levels (elite controllers) have high HIV-specific immune responses, it is unclear whether they experience abnormal levels of T cell activation, potentially contributing to immunodeficiency. We compared percentages of activated (CD38(+)HLA-DR(+)) T cells between 30 elite controllers, 47 HIV-uninfected individuals, 187 HIV-infected individuals with undetectable viremia receiving antiretroviral therapy (antiretroviral therapy suppressed), and 66 untreated HIV-infected individuals with detectable viremia. Because mucosal translocation of bacterial products may contribute to T cell activation in HIV infection, we also measured plasma lipopolysaccharide (LPS) levels. Although the median CD4(+) cell count in controllers was 727 cells/mm(3), 3 (10%) had CD4(+) cell counts <350 cells/mm(3) and 2 (7%) had acquired immunodeficiency syndrome. Controllers had higher CD4(+) and CD8(+) cell activation levels (P < .001 for both) than HIV-negative subjects and higher CD8(+) cell activation levels than the antiretroviral therapy suppressed (P = .048). In controllers, higher CD4(+) and CD8(+) T cell activation was associated with lower CD4(+) cell counts (P = .009 and P = .047). Controllers had higher LPS levels than HIV-negative subjects (P < .001), and in controllers higher LPS level was associated with higher CD8(+) T cell activation (P = .039). HIV controllers have abnormally high T cell activation levels, which may contribute to progressive CD4(+) T cell loss even without measurable viremia.

Increased Sequence Diversity Coverage Improves Detection of HIV-Specific T Cell Responses

The accurate identification of HIV-specific T cell responses is important for determining the relationship between immune response, viral control, and disease progression. HIV-specific immune responses are usually measured using peptide sets based on consensus sequences, which frequently miss responses to regions where test set and infecting virus differ. In this study, we report the design of a peptide test set with significantly increased coverage of HIV sequence diversity by including alternative amino acids at variable positions during the peptide synthesis step. In an IFN-gamma ELISpot assay, these "toggled" peptides detected HIV-specific CD4(+) and CD8(+) T cell responses of significantly higher breadth and magnitude than matched consensus peptides. The observed increases were explained by a closer match of the toggled peptides to the autologous viral sequence. Toggled peptides therefore afford a cost-effective and significantly more complete view of the host immune response to HIV and are directly applicable to other variable pathogens.

Mucosal priming with replicative Tiantan vaccinia and systemic boosting with DNA vaccine raised strong mucosal and systemic HIV-specific immune responses

An effective vaccine strategy for HIV-1 will probably require the induction and maintenance of both humoral and cellular immunity at mucosal and systemic sites. We tested a new prime-boost approach of intranasal priming with 3 × 10 6 PFU of replicative recombinant Tiantan vaccinia virus (rTTV) and intramuscular boosting with 100 μg DNA plasmid expressing HIV-1 Gag in BALB/c mice along with other strategies. Our data demonstrated that intranasal priming with replicative recombinant Tiantan vaccinia and intramuscular boosting with DNA vaccine raised the highest vaginal IgA and systemic T-cell responses, and modest lung IgA and sera IgG responses among all vaccination regimens; each vaccination regimen generated its own imprint of the most preferential T-cell receptor usage of Vβ. These results demonstrate that the combination of intranasal priming with replicative recombinant Tiantan vaccinia and intramuscular boosting with DNA vaccine is a preferable regimen for induction of both T-cell and humoral immune responses at mucosal and systemic sites.

Induction of HIV-specific functional immune responses by a multiclade HIV-1 DNA vaccine candidate in healthy Ugandans

A phase I randomized, double blind, placebo-controlled trial to assess the immunogenicity of a multiclade HIV-1 DNA plasmid vaccine was conducted in 31 HIV-1-negative Ugandans. Following immunization with DNA at 0, 1, and 2 months, the frequency of HIV-specific immune responses was assessed up to 10 months using a standard chromium release assay (CRA), lymphoproliferative assay (LPA), and antibody dependent cell-mediated cytotoxicity assay (ADCC). Seven of 15 (47%) vaccinees demonstrated CTL activity using the CRA to HIV-1 Env B with responses observed 1 month following the second vaccination and as late as 7 months following complete immunization. Additionally, lymphoproliferative reponses were observed in 14/15 vaccinees against p24. No CTL or LPA responses were observed at baseline or in the placebo group. ADCC activity was minimally induced by DNA vaccination. This study demonstrates that immunization with DNA alone induces CTL and lymphoproliferative responses in a population that will participate in a phase IIb study evaluating HIV-1 DNA priming followed by boosting with a replication-defective recombinant adenovirus vector.

Biological mechanisms of vertical human immunodeficiency virus (HIV‐1) transmission

In the absence of interventions, 30-45% of exposed infants acquire human immunodeficiency virus type 1 (HIV-1) through mother-to-child transmission. It remains unclear why some infants become infected while others do not, despite significant exposure to HIV-1 in utero, during delivery and while breastfeeding. Here we discuss the correlates of vertical transmission with an emphasis on factors that increase maternal HIV-1 levels, either systemically or locally in genital secretions and breast milk. Immune responses may influence maternal viral load, and data suggest that maternal neutralising antibodies reduce infection rates. In addition, infants may be capable of mounting HIV-specific cellular immune responses. We propose that both humoral and cellular responses are necessary to reduce infection because cell-free as well as cell-associated virus appears to play a role in vertical transmission. These distinct forms of the virus may be targeted most effectively by different components of the immune system. We also discuss the use of antiretrovirals to reduce transmission, focusing on the mechanisms of action of regimens currently used in developing country settings. We conclude that prevention relies not only on reducing maternal HIV-1 levels within blood, genital tract and breast milk, but also on pre- and/or post-exposure prophylaxis to the infant. However, HIV-1 has the capacity to mutate under drug pressure and rapidly acquires mutations conferring antiretroviral resistance. This review concludes with data on persistence of low-level resistance after delivery as well as recent guidelines for maternal and infant regimens designed to limit resistance.

Gene Therapeutic Approaches for Immune Modulation in AIDS

Antiviral drug therapy can effectively suppress HIV replication, but emerging viral resistance and drug toxicity limit long-term therapeutic efficacy. In addition, regeneration of the T helper cell repertoire is often incomplete. The current major challenges in the treatment of HIV infection are therefore the reconstitution of cellular immunity, and especially of the HIV-specific immune response, and the suppression of virus replication in patients with HAART failure. Several gene therapeutic strategies for immune reconstitution of AIDS patients have been described. Preclinical and clinical studies have examined the safety and efficacy of two basic approaches: firstly, the transfer of autologous T cells armed with recombinant receptors that target HIV antigens to specifically increase antiviral immunity and, secondly, the transfer of genetically modified T cells or hematopoietic progenitor cells that express an antiviral gene. However, for both approaches, engraftment levels of gene-modified cells have not been sufficient to reconstitute cellular immunity and to effectively reduce the overall viral load in patients. Strategies to improve the technologies and procedures involved in gene therapeutic immune reconstitution of AIDS patients are discussed. Keywords: HIV infection, stem cell transplantation, T cell therapy, immune reconstitution

Chimeric adenovirus 5/35 vector containing the clade C HIV gag gene induces a cross-reactive immune response against HIV

Most of the recent HIV studies have focused on the clade B virus subtype. However, it is estimated that half the HIV patients in developing countries are infected with virus belonging to clade C. Therefore, a vaccine against HIV clade C is urgently required. In this study, we evaluate the immunogenicity and protective immunity of an adenovirus vector (Ad) in BALB/c mice and cynomolgus monkeys. We developed an HIV vaccine containing the HIV clade C gag gene using a replication-defective chimeric adenovirus type 5 (Ad5) vector incorporating Ad35 fiber (Ad5/35); this vector has exhibited low hepatotoxicity in animal models. We observed that immunization with the Ad5/35 vaccine generated heightened HIV-specific immune responses in both mice and monkeys. Furthermore, the Ad5/35 vector vaccine produced a cross-immunity against challenge with recombinant vaccinia viruses expressing HIV clade B gag. These results demonstrate that Ad5/35 vaccines expressing HIV clade C gag may be promising candidates for clinical trials.

A dendritic cell‐based vaccine for treating HIV infection: background and preliminary results

Antibody response against human immunodeficiency virus-1 (HIV) is ineffective and cellular immune response is not strong enough to achieve the complete suppression or at least a strong control of viral replication in HIV- infected patients. In 2001, we showed in vitro that dendritic cells (DCs) of HIV-infected patients loaded with autologous HIV chemically inactivated by aldrithiol-2 were capable of raising an HIV-specific cellular immune response powerful enough to allow the destruction of autologous HIV- infected CD4 T cells. In 2003, we showed that simian immunodeficiency virus (SIV)-infected macaques vaccinated with inactivated SIV-loaded autologous DCs raised a strong SIV-specific cellular response. Ten months after vaccination, plasma viral load of 7 out of the 10 vaccinated monkeys remained 1000-fold lower than initially. In December 2004, we published results observed in 18 untreated HIV-infected patients vaccinated with autologous monocyte-derived DCs loaded with autologous inactivated HIV. A year following vaccination, 8 patients had a plasma viral load decrease >90%; among them, 4 had viral load <1000 copies mL(-1). Moreover, by one year, the viral load decline of the 18 patients was significantly correlated with their percentage of HIV-1-gag-specific CD8(+) T cells expressing perforin and that of HIV-1-specific CD4(+) T(H)1 cells. This is the first demonstration of the capacity of a therapeutic vaccine to induce an effective HIV-specific T cell response associated with sustained viral suppression in untreated viremic patients. The manipulation of antigen presenting cells to elicit virus-specific cellular responses is a promising tool to control persistant viral infections.

A dual color ELISPOT method for the simultaneous detection of IL-2 and IFN-γ HIV-specific immune responses

The single color IFN-γ ELISPOT assay has become a standard for assessing HIV-specific immune responses in HIV-infected subjects. However, recent data suggests that single cytokine detection for immune monitoring of HIV-infected individuals may not be sufficient to fully describe virus-specific immune responses. Here, we have designed and validated a dual color ELISPOT assay capable of detecting both IL-2 and IFN-γ secreting cells simultaneously in response to HIV antigens. We found that a cell input number of 200,000 cells/well provided a good balance between limited availability of cells due to blood volume restrictions and ability to detect all cytokine secretion patterns. The simultaneous detection of IL-2 and IFN-γ resulted in a decreased magnitude of IFN-γ but not IL-2 responses. Measures of intra- and inter-assay variability for the dual color ELISPOT assay were comparable to that seen for single cytokine ELISPOT assay with coefficients of variation below 20% for IL-2, IFN-γ and dual secretion. Although CD8+ T cells mediated most HIV-specific responses in infected subjects, CD4+ T cells mediated responses to HIV were also detected. Features of this assay such as high throughput, cell number requirement and cytokine choice should make this assay a valuable tool for screening for HIV-specific immune responses in several clinically relevant settings.