IL-15 drives CD8 T cell cycling and differentiation in chronic HIV-1 infection (VIR6P.1162)

HIV-1 infection is characterized by sustained CD8 T cell expansion that is linked to morbid outcomes even after HIV replication is controlled with antiretroviral therapy (ART). The drivers of this persistent CD8 expansion in HIV-1 infection are not well understood. Here we show that cycling frequency is increased in memory CD8 T cells in untreated HIV-1 infected patients and cycling CD8 T cells have a broad T cell receptor repertoire tightly linked to the repertoire of non-cycling cells suggesting that they are largely driven into cycle by bystander mechanisms. In HIV-1 infection, cycling and granzyme B expression were increased among CD8 T cells binding viral peptide/HLA tetramers and this enriched cycling/cytolytic phenotype among virus-reactive CD8 T cells could be generated in vitro by exposure to interleukin (IL)-15. Lymph nodes of HIV-1 infected untreated patients were enriched for interleukin-15 expression that correlated with circulating CD8 T cell counts and normalized with drug-induced control of HIV-1 replication. The determinants of persistent CD8 T cell expansion and the mechanisms whereby this expansion is linked to increased morbidity merit further examination.

Immune activation alters cellular and humoral responses to yellow fever 17D vaccine

BACKGROUND

Defining the parameters that modulate vaccine responses in African populations will be imperative to design effective vaccines for protection against HIV, malaria, tuberculosis, and dengue virus infections. This study aimed to evaluate the contribution of the patient-specific immune microenvironment to the response to the licensed yellow fever vaccine 17D (YF-17D) in an African cohort.

METHODS

We compared responses to YF-17D in 50 volunteers in Entebbe, Uganda, and 50 volunteers in Lausanne, Switzerland. We measured the CD8+ T cell and B cell responses induced by YF-17D and correlated them with immune parameters analyzed by flow cytometry prior to vaccination.

RESULTS

We showed that YF-17D-induced CD8+ T cell and B cell responses were substantially lower in immunized individuals from Entebbe compared with immunized individuals from Lausanne. The impaired vaccine response in the Entebbe cohort associated with reduced YF-17D replication. Prior to vaccination, we observed higher frequencies of exhausted and activated NK cells, differentiated T and B cell subsets and proinflammatory monocytes, suggesting an activated immune microenvironment in the Entebbe volunteers. Interestingly, activation of CD8+ T cells and B cells as well as proinflammatory monocytes at baseline negatively correlated with YF-17D-neutralizing antibody titers after vaccination. Additionally, memory T and B cell responses in preimmunized volunteers exhibited reduced persistence in the Entebbe cohort but were boosted by a second vaccination.

CONCLUSION

Together, these results demonstrate that an activated immune microenvironment prior to vaccination impedes efficacy of the YF-17D vaccine in an African cohort and suggest that vaccine regimens may need to be boosted in African populations to achieve efficient immunity.

TRIAL REGISTRATION

Registration is not required for observational studies.

FUNDING

This study was funded by Canada's Global Health Research Initiative, Defense Threat Reduction Agency, National Institute of Allergy and Infectious Diseases, Bill & Melinda Gates Foundation, and United States Agency for International Development.

Quantifying and predicting the effect of exogenous interleukin-7 on CD4+ T cells in HIV-1 infection

Exogenous Interleukin-7 (IL-7), in supplement to antiretroviral therapy, leads to a substantial increase of all CD4⁺ T cell subsets in HIV-1 infected patients. However, the quantitative contribution of the several potential mechanisms of action of IL-7 is unknown. We have performed a mathematical analysis of repeated measurements of total and naive CD4⁺ T cells and their Ki67 expression from HIV-1 infected patients involved in three phase I/II studies (N = 53 patients). We show that, besides a transient increase of peripheral proliferation, IL-7 exerts additional effects that play a significant role in CD4⁺ T cell dynamics up to 52 weeks. A decrease of the loss rate of the total CD4⁺ T cell is the most probable explanation. If this effect could be maintained during repeated administration of IL-7, our simulation study shows that such a strategy may allow maintaining CD4⁺ T cell counts above 500 cells/µL with 4 cycles or fewer over a period of two years. This in-depth analysis of clinical data revealed the potential for IL-7 to achieve sustained CD4⁺ T cell restoration with limited IL-7 exposure in HIV-1 infected patients with immune failure despite antiretroviral therapy.

HIV infection is characterized by a decrease of CD4⁺ T-lymphocytes in the blood. Whereas antiretroviral treatment succeeds to control viral replication, some patients fail to reconstitute their CD4⁺ T cell count to normal value. IL-7 is a promising cytokine under evaluation for its use in HIV infection, in supplement to antiretroviral therapy, as it increases cell proliferation and survival. Here, we use data from three clinical trials testing the effect of IL-7 on CD4⁺ T-cell recovery in treated HIV-infected individuals and use a simple mathematical model to quantify IL-7 effects by estimating the biological parameters of the model. We show that the increase of peripheral proliferation could not explain alone the long-term dynamics of T cells after IL-7 injections underlining other important effects such as the improvement of cell survival. We also investigate the feasibility and the efficiency of repetitions of IL-7 cycles and argue for further evaluation through clinical trials.

Microarray analysis reveals novel insights into immunity to H1N1/09 influenza vaccine in aviremic HIV infected children and adolescents in IMPAACT P1088 (VIR2P.1024)

HIV infected persons often exhibit poor responses to influenza vaccine despite effective HAART-mediated viral suppression. The goal of the present study was to identify gene expression profiles that characterize vaccine driven antibody responses in aviremic pediatric and adolescent HIV infected patients (4-25 yrs) given two doses of Novartis/H1N1 09 vaccine 21 days apart during the pandemic H1N1 influenza outbreak in 2009. Blood samples were collected in Paxgene tubes on days 0, 21, and 31 post-vaccination for microarray analysis. Supervised clustering analysis for contrasts between vaccine responders (R) and vaccine non-responders (NR) was performed and top pathways were ranked by Ingenuity Pathway analysis. Cutoffs for fold change (<-1.3, >1.3) and p value (0.05) were applied to assess the top upregulated and downregulated genes in pathways. Patients were segregated by age into 2 groups for analysis: 1) <12 yrs, n=16 and 2) ≥13 yrs, n=28. In group 1, R showed upregulation of genes related to cell growth and metabolism at both d0 and d21. At d21, B cell differentiation, cell survival and stress response pathways were also upregulated. In group 2, R showed upregulation of innate signaling pathways at d0, and at d21 showed reduced TNF and upregulation of genes involved in T helper differentiation and B cell signaling pathways. Our results reveal signatures of successful vaccine response in HIV infected subjects and may identify favorable targets for improved vaccine design.

Myeloid dendritic cells induce HIV-1 latency in non-proliferating CD4+ T cells

Latently infected resting CD4⁺ T cells are a major barrier to HIV cure. Understanding how latency is established, maintained and reversed is critical to identifying novel strategies to eliminate latently infected cells. We demonstrate here that co-culture of resting CD4⁺ T cells and syngeneic myeloid dendritic cells (mDC) can dramatically increase the frequency of HIV DNA integration and latent HIV infection in non-proliferating memory, but not naïve, CD4⁺ T cells. Latency was eliminated when cell-to-cell contact was prevented in the mDC-T cell co-cultures and reduced when clustering was minimised in the mDC-T cell co-cultures. Supernatants from infected mDC-T cell co-cultures did not facilitate the establishment of latency, consistent with cell-cell contact and not a soluble factor being critical for mediating latent infection of resting CD4⁺ T cells. Gene expression in non-proliferating CD4⁺ T cells, enriched for latent infection, showed significant changes in the expression of genes involved in cellular activation and interferon regulated pathways, including the down-regulation of genes controlling both NF-κB and cell cycle. We conclude that mDC play a key role in the establishment of HIV latency in resting memory CD4⁺ T cells, which is predominantly mediated through signalling during DC-T cell contact.

Current antiretroviral drugs significantly prolong life and reduce morbidity but are unable to cure HIV. While on treatment, the virus is able to hide in resting memory T cells in a silent or “latent” form. These latently infected cells are rare and thus are hard to study using blood from HIV-infected individuals on treatment. Therefore, it is very important to have laboratory models that can closely mimic what is going on in the body. We have developed a novel model of HIV latency in the laboratory. Using this model we have shown that the presence of dendritic cells, an important type of immune cell that can regulate T cell activation, at the time of infection allows for the infection of resting T cells and the establishment of latency. We have demonstrated that this is predominantly mediated by direct cell-to-cell interactions. Further exploration of the mechanisms behind HIV latency could lead to new ways to treat and possibly eradicate HIV.

Temporal effect of HLA-B*57 on viral control during primary HIV-1 infection

Background

HLA-B alleles are associated with viral control in chronic HIV-1 infection, however, their role in primary HIV-1 disease is unclear. This study sought to determine the role of HLA-B alleles in viral control during the acute phase of HIV-1 infection and establishment of the early viral load set point (VLSP).

Findings

Individuals identified during primary HIV-1 infection were HLA class I typed and followed longitudinally. Associations between HLA-B alleles and HIV-1 viral replication during acute infection and VLSP were analyzed in untreated subjects. The results showed that neither HLA-B*57 nor HLA-B*27 were significantly associated with viral control during acute HIV-1 infection (Fiebig stage I-IV, n=171). HLA-B*57 was however significantly associated with a subsequent lower VLSP (p<0.001, n=135) with nearly 1 log₁₀ less median viral load. Analysis of a known polymorphism at position 97 of HLA-B showed significant associations with both lower initial viral load (p<0.01) and lower VLSP (p<0.05). However, this association was dependent on different amino acids at this position for each endpoint.

Conclusions

The effect of HLA-B*57 on viral control is more pronounced during the later stages of primary HIV-1 infection, which suggests the underlying mechanism of control occurs at a critical period in the first several months after HIV-1 acquisition. The risk profile of polymorphisms at position 97 of HLA-B are more broadly associated with HIV-1 viral load during primary infection and may serve as a focal point in further studies of HLA-B function.

GenePattern flow cytometry suite

BACKGROUND

Traditional flow cytometry data analysis is largely based on interactive and time consuming analysis of series two dimensional representations of up to 20 dimensional data. Recent technological advances have increased the amount of data generated by the technology and outpaced the development of data analysis approaches. While there are advanced tools available, including many R/BioConductor packages, these are only accessible programmatically and therefore out of reach for most experimentalists. GenePattern is a powerful genomic analysis platform with over 200 tools for analysis of gene expression, proteomics, and other data. A web-based interface provides easy access to these tools and allows the creation of automated analysis pipelines enabling reproducible research.

RESULTS

In order to bring advanced flow cytometry data analysis tools to experimentalists without programmatic skills, we developed the GenePattern Flow Cytometry Suite. It contains 34 open source GenePattern flow cytometry modules covering methods from basic processing of flow cytometry standard (i.e., FCS) files to advanced algorithms for automated identification of cell populations, normalization and quality assessment. Internally, these modules leverage from functionality developed in R/BioConductor. Using the GenePattern web-based interface, they can be connected to build analytical pipelines.

CONCLUSIONS

GenePattern Flow Cytometry Suite brings advanced flow cytometry data analysis capabilities to users with minimal computer skills. Functionality previously available only to skilled bioinformaticians is now easily accessible from a web browser.

Intrinsic role of FoxO3a in the development of CD8+ T cell memory

CD8(+) T cells undergo rapid expansion during infection with intracellular pathogens, which is followed by swift and massive culling of primed CD8(+) T cells. The mechanisms that govern the massive contraction and maintenance of primed CD8(+) T cells are not clear. We show in this study that the transcription factor, FoxO3a, does not influence Ag presentation and the consequent expansion of CD8(+) T cell response during Listeria monocytogenes infection, but plays a key role in the maintenance of memory CD8(+) T cells. The effector function of primed CD8(+) T cells as revealed by cytokine secretion and CD107a degranulation was not influenced by inactivation of FoxO3a. Interestingly, FoxO3a-deficient CD8(+) T cells displayed reduced expression of proapoptotic molecules BIM and PUMA during the various phases of response, and underwent reduced apoptosis in comparison with wild-type cells. A higher number of memory precursor effector cells and memory subsets was detectable in FoxO3a-deficient mice compared with wild-type mice. Furthermore, FoxO3a-deficient memory CD8(+) T cells upon transfer into normal or RAG1-deficient mice displayed enhanced survival. These results suggest that FoxO3a acts in a cell-intrinsic manner to regulate the survival of primed CD8(+) T cells.

Short communication: human immunodeficiency virus rebound in blood and seminal plasma following discontinuation of antiretroviral therapy

Although there is discordance between human immunodeficiency virus (HIV) blood plasma and seminal plasma viral loads (VL), little is known about the dynamics of VL rebound in these compartments upon discontinuation of highly active antiretroviral therapy (HAART). Therefore, we sought to examine the relationship between blood and semen VL rebound after discontinuation of HAART. Participants in this substudy were men enrolled from two centers of a multicenter, placebo-controlled randomized trial of HIV therapeutic vaccination using ALVAC with or without Remune. With at least 2 years of sustained virologic suppression and following a 20-week vaccination course, subjects underwent structured HAART interruption. Fourteen men provided semen samples. Seven to 12 weeks after HAART interruption, all 14 men had detectable blood VLs whereas 8 of 14 had detectable seminal VLs. There was a significant correlation between blood and seminal VLs (Spearman r=0.58, p=0.03) at the time of semen collection. An earlier time to detectable blood VL after HAART interruption was associated with higher seminal VL (Spearman r=-0.64, p=0.02). These findings support the compartmentalization of HIV and underscore the importance of understanding the genital tract as an HIV reservoir in the quest to minimize HIV transmission.

Type I IFN induced by adenovirus serotypes 28 and 35 has multiple effects on T cell immunogenicity

Recombinant adenovirus (rAd) vectors are being investigated as vaccine delivery vehicles in preclinical and clinical studies. rAds constructed from different serotypes differ in receptor usage, tropism, and ability to activate cells, aspects of which likely contribute to their different immunogenicity profiles. In this study, we compared the infectivity and cell stimulatory capacity of recombinant adenovirus serotype 5 (rAd5), recombinant adenovirus serotype 28 (rAd28), and recombinant adenovirus serotype 35 (rAd35) in association with their respective immunogenicity profiles. We found that rAd28 and rAd35 infected and led to the in vitro maturation and activation of both human and mouse dendritic cells more efficiently compared with rAd5. In stark contrast to rAd5, rAd28 and rAd35 induced production of IFN-α and stimulated IFN-related intracellular pathways. However, the in vivo immunogenicity of rAd28 and rAd35 was significantly lower than that of rAd5. Deletion of IFN-α signaling during vaccination with rAd28 and rAd35 vectors increased the magnitude of the insert-specific T cell response to levels induced by vaccination with rAd5 vector. The negative impact of IFN-α signaling on the magnitude of the T cell response could be overcome by increasing the vaccine dose, which was also associated with greater polyfunctionality and a more favorable long-term memory phenotype of the CD8 T cell response in the presence of IFN-α signaling. Taken together, our results demonstrate that rAd-induced IFN-α production has multiple effects on T cell immunogenicity, the understanding of which should be considered in the design of rAd vaccine vectors.

Effects of recombinant human interleukin 7 on T-cell recovery and thymic output in HIV-infected patients receiving antiretroviral therapy: results of a phase I/IIa randomized, placebo-controlled, multicenter study

BACKGROUND

The immune deficiency of human immunodeficiency virus (HIV) infection is not fully corrected with ARV therapy. Interleukin-7 (IL-7) can boost CD4 T-cell counts, but optimal dosing and mechanisms of cellular increases need to be defined.

METHODS

We performed a randomized placebo-controlled dose escalation (10, 20 and 30 µg/kg) trial of 3 weekly doses of recombinant human IL-7 (rhIL-7) in ARV-treated HIV-infected persons with CD4 T-cell counts between 101 and 400 cells/µL and plasma HIV levels <50 copies/mL. Toxicity, activity and the impact of rhIL-7 on immune reconstitution were monitored.

RESULTS

Doses of rhIL-7 up to 20 µg/kg were well tolerated. CD4 increases of predominantly naive and central memory T cells were brisk (averaging 323 cells/µL at 12 weeks) and durable (up to 1 year). Increased cell cycling and transient increased bcl-2 expression were noted. Expanded cells did not have the characteristics of regulatory or activated T cells. Transient low-level HIV viremia was seen in 6 of 26 treated patients; modest increases in total levels of intracellular HIV DNA were proportional to CD4 T-cell expansions. IL-7 seemed to increase thymic output and tended to improve the T-cell receptor (TCR) repertoire in persons with low TCR diversity.

CONCLUSIONS

Three weekly doses of rhIL-7 at 20 µg/kg are well tolerated and lead to a dose-dependent CD4 T-cell increase and the broadening of TCR diversity in some subjects. These data suggest that this rhIL-7 dose could be advanced in future rhIL-7 clinical studies.

CLINICAL TRIALS REGISTRATION

NCT0047732.

Clonotype and repertoire changes drive the functional improvement of HIV-specific CD8 T cell populations under conditions of limited antigenic stimulation

Persistent exposure to cognate Ag leads to the functional impairment and exhaustion of HIV-specific CD8 T cells. Ag withdrawal, attributable either to antiretroviral treatment or the emergence of epitope escape mutations, causes HIV-specific CD8 T cell responses to wane over time. However, this process does not continue to extinction, and residual CD8 T cells likely play an important role in the control of HIV replication. In this study, we conducted a longitudinal analysis of clonality, phenotype, and function to define the characteristics of HIV-specific CD8 T cell populations that persist under conditions of limited antigenic stimulation. Ag decay was associated with dynamic changes in the TCR repertoire, increased expression of CD45RA and CD127, decreased expression of programmed death-1, and the emergence of polyfunctional HIV-specific CD8 T cells. High-definition analysis of individual clonotypes revealed that the Ag loss-induced gain of function within HIV-specific CD8 T cell populations could be attributed to two nonexclusive mechanisms: 1) functional improvement of persisting clonotypes; and 2) recruitment of particular clonotypes endowed with superior functional capabilities.

Ex vivo measurement of the cytotoxic capacity of human primary antigen-specific CD8 T cells

The major function of CD8 T cells is to kill specifically target cells. Moreover in certain incurable diseases, antigen-specific human CD8 T cells are impaired, and assessment of their cytolytic activity could bring insights into their physiopathological role and ways to restore immune dysfunctions for immunotherapeutic purposes. Despite this, T cell cytolytic function has been seldom analyzed thoroughly in humans, due to the lack of approaches well suited for ex vivo assessment of T cell cytotoxicity. Current techniques require prior in vitro expansion of antigen-specific CD8 T cell populations and the use of immortalized cells as targets to measure the cell-mediated killing. Furthermore, bulk cytotoxic activity is frequently measured using percentage of specific lysis calculations that do not quantify actual target cell death and effector numbers at the single cell level. Here we established a new flow cytometry-based assay that allows accurate single-cell analysis of cytotoxic capacity of primary antigen-specific CD8 T cells generated in vivo in humans after antigenic exposure without in vitro amplification that can be used for specificities restricted by different HLAs as target cells are autologous cells. We show that this assay is robust, highly sensitive irrespective of the frequency of antigen-specific CD8 T cells, and allows accurate calculation of the index of cytotoxic capacity in lytic units. This new assay provides a sensitive method to measure the intrinsic cytotoxic activity of antigen-specific CD8 T cells directly ex vivo on human primary cells.

Peripheral blood CCR4+CCR6+ and CXCR3+CCR6+CD4+ T cells are highly permissive to HIV-1 infection

There is limited knowledge on the identity of primary CD4(+) T cell subsets selectively targeted by HIV-1 in vivo. In this study, we established a link between HIV permissiveness, phenotype/homing potential, and lineage commitment in primary CD4(+) T cells. CCR4(+)CCR6(+), CCR4(+)CCR6(-), CXCR3(+)CCR6(+), and CXCR3(+)CCR6(-) T cells expressed cytokines and transcription factors specific for Th17, Th2, Th1Th17, and Th1 lineages, respectively. CCR4(+)CCR6(+) and CXCR3(+)CCR6(+) T cells expressed the HIV coreceptors CCR5 and CXCR4 and were permissive to R5 and X4 HIV replication. CCR4(+)CCR6(-) T cells expressed CXCR4 but not CCR5 and were permissive to X4 HIV only. CXCR3(+)CCR6(-) T cells expressed CCR5 and CXCR4 but were relatively resistant to R5 and X4 HIV in vitro. Total CCR6(+) T cells compared with CCR6(-) T cells harbored higher levels of integrated HIV DNA in treatment-naive HIV-infected subjects. The frequency of total CCR6(+) T cells and those of CCR4(+)CCR6(+) and CXCR3(+)CCR6(+) T cells were diminished in chronically infected HIV-positive subjects, despite viral-suppressive therapy. A high-throughput analysis of cytokine profiles identified CXCR3(+)CCR6(+) T cells as a major source of TNF-alpha and CCL20 and demonstrated a decreased TNF-alpha/IL-10 ratio in CXCR3(+)CCR6(-) T cells. Finally, CCR4(+)CCR6(+) and CXCR3(+)CCR6(+) T cells exhibited gut- and lymph node-homing potential. Thus, we identified CCR4(+)CCR6(+) and CXCR3(+)CCR6(+) T cells as highly permissive to HIV replication, with potential to infiltrate and recruit more CCR6(+) T cells into anatomic sites of viral replication. It is necessary that new therapeutic strategies against HIV interfere with viral replication/persistence in discrete CCR6(+) T cell subsets.

A comparative analysis of gene expression patterns and cell phenotypes between cervical and peripheral blood mononuclear cells

Studies of the immunological environment in the female genital tract (FGT) are critical for the development of vaccines or microbicides to halt the spread of sexually transmitted infections. Challenges arise due to the difficulties of sampling from this site, and the majority of studies have been conducted utilising peripheral blood mononuclear cells. Identifying functional differences between immune cells of the FGT and peripheral blood would aid in our understanding of mucosal immunology. We compared the gene expression profile of mononuclear cells at these two sites. Messenger RNA expression analysis was performed using gene expression arrays on matched cervical mononuclear cells and peripheral blood mononuclear cells. Further cellular phenotyping was done by 10 colour flow cytometry. Of the 22,185 genes expressed by these samples, 5345 genes were significantly differentially expressed between the cell populations. Most differences can be explained by significantly lower levels of T and B cells and higher levels of macrophages and dendritic cells in the FGT compared with peripheral blood. Several immunologically relevant pathways such as apoptosis and innate immune signalling, and a variety of cytokines and cytokine receptors were differentially expressed. This study highlights the importance of the unique immunological environment of the FGT and identifies important differences between systemic and mucosal immune compartments.

FuGEFlow: data model and markup language for flow cytometry

Background

Flow cytometry technology is widely used in both health care and research. The rapid expansion of flow cytometry applications has outpaced the development of data storage and analysis tools. Collaborative efforts being taken to eliminate this gap include building common vocabularies and ontologies, designing generic data models, and defining data exchange formats. The Minimum Information about a Flow Cytometry Experiment (MIFlowCyt) standard was recently adopted by the International Society for Advancement of Cytometry. This standard guides researchers on the information that should be included in peer reviewed publications, but it is insufficient for data exchange and integration between computational systems. The Functional Genomics Experiment (FuGE) formalizes common aspects of comprehensive and high throughput experiments across different biological technologies. We have extended FuGE object model to accommodate flow cytometry data and metadata.

Methods

We used the MagicDraw modelling tool to design a UML model (Flow-OM) according to the FuGE extension guidelines and the AndroMDA toolkit to transform the model to a markup language (Flow-ML). We mapped each MIFlowCyt term to either an existing FuGE class or to a new FuGEFlow class. The development environment was validated by comparing the official FuGE XSD to the schema we generated from the FuGE object model using our configuration. After the Flow-OM model was completed, the final version of the Flow-ML was generated and validated against an example MIFlowCyt compliant experiment description.

Results

The extension of FuGE for flow cytometry has resulted in a generic FuGE-compliant data model (FuGEFlow), which accommodates and links together all information required by MIFlowCyt. The FuGEFlow model can be used to build software and databases using FuGE software toolkits to facilitate automated exchange and manipulation of potentially large flow cytometry experimental data sets. Additional project documentation, including reusable design patterns and a guide for setting up a development environment, was contributed back to the FuGE project.

Conclusion

We have shown that an extension of FuGE can be used to transform minimum information requirements in natural language to markup language in XML. Extending FuGE required significant effort, but in our experiences the benefits outweighed the costs. The FuGEFlow is expected to play a central role in describing flow cytometry experiments and ultimately facilitating data exchange including public flow cytometry repositories currently under development.

Therapeutic vaccination with simian immunodeficiency virus (SIV)-DNA + IL-12 or IL-15 induces distinct CD8 memory subsets in SIV-infected macaques

DNA vaccination is an invaluable approach for immune therapy in that it lacks vector interference and thus permits repeated vaccination boosts. However, by themselves, DNA-based vaccines are typically poor inducers of Ag-specific immunity in humans and non-human primates. Cytokines, such as IL-12 and IL-15, have been shown to be potent adjuvants for the induction and maintenance of cellular immune responses, in particular during HIV infection. In this study, we examined the ability of therapeutic vaccination with SIV-DNA+IL-12 or IL-15 as molecular adjuvants to improve DNA vaccine potency and to enhance memory immune responses in SIV-infected macaques. Our results demonstrate that incorporating IL-12 into the vaccine induces SIV-specific CD8 effector memory T cell (T(EM)) functional responses and enhances the capacity of IFN-gamma-producing CD8 T(EM) cells to produce TNF. Lower levels of PD-1 were expressed on T cells acquiring dual function upon vaccination as compared with mono-functional CD8 T(EM) cells. Finally, a boost with SIV-DNA+IL-15 triggered most T cell memory subsets in macaques primed with either DNA-SIV or placebo but only CD8 T(EM) in macaques primed with SIV-DNA+IL-12. These results indicate that plasmid IL-12 and IL-15 cytokines represent a significant addition to enhance the ability of therapeutic DNA vaccines to induce better immunity.

Transcription factor FOXO3a controls the persistence of memory CD4(+) T cells during HIV infection

The persistence of central memory CD4(+) T cells (T(CM) cells) is a major correlate of immunological protection in HIV/AIDS, as the rate of T(CM) cell decline predicts HIV disease progression. In this study, we show that T(CM) cells and effector memory CD4(+) T cells (T(EM) cells) from HIV(+) elite controller (EC) subjects are less susceptible to Fas-mediated apoptosis and persist longer after multiple rounds of T cell receptor triggering when compared to T(CM) and T(EM) cells from aviremic successfully treated (ST) subjects or from HIV(-) donors. We show that persistence of T(CM) cells from EC subjects is a direct consequence of inactivation of the FOXO3a pathway. Silencing the transcriptionally active form of FOXO3a by small interfering RNA or by introducing a FOXO3a dominant-negative form (FOXO3a Nt) extended the long-term survival of T(CM) cells from ST subjects to a length of time similar to that of T(CM) cells from EC subjects. The crucial role of FOXO3a in the survival of memory cells will help shed light on the underlying immunological mechanisms that control viral replication in EC subjects.

The failed HIV Merck vaccine study: a step back or a launching point for future vaccine development?

The world of human immunodeficiency virus (HIV) vaccines has suffered a baffling setback. The first trial of a vaccine designed to elicit strong cellular immunity has shown no protection against infection. More alarmingly, the vaccine appeared to increase the rate of HIV infection in individuals with prior immunity against the adenovirus vector used in the vaccine. A new study in this issue suggests that a different vaccine approach—using a DNA prime/poxvirus boost strategy—induces polyfunctional immune responses to an HIV immunogen. The disappointing results of the recent vaccine trial suggest that a more thorough assessment of vaccine-induced immune responses is urgently needed, and that more emphasis should be placed on primate models before efficacy trials are undertaken.

Inhibition of HIV-1 transmission in trans from dendritic cells to CD4+ T lymphocytes by natural antibodies to the CRD domain of DC-SIGN purified from breast milk and intravenous immunoglobulins

The present study demonstrates that human breast milk and normal human polyclonal immunoglobulins purified from plasma [intravenous immunoglobulins (IVIg)] contain functional natural immunoglobulin A (IgA) and IgG antibodies directed against the carbohydrate recognition domain (CRD) domain of the dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) molecule, which is involved in the binding of human immunodeficiency virus (HIV)-1 to dendritic cells (DCs). Antibodies to DC-SIGN CRD were affinity-purified on a matrix to which a synthetic peptide corresponding to the N-terminal CRD domain (amino-acid 342-amino-acid 371) had been coupled. The affinity-purified antibodies bound to the DC-SIGN peptide and to the native DC-SIGN molecule expressed by HeLa DC-SIGN+ cells and immature monocyte-derived dendritic cells (iMDDCs), in a specific and dose-dependent manner. At an optimal dose of 200 microg/ml, natural antibodies to DC-SIGN CRD peptide purified from breast milk and IVIg stained 25 and 20% of HeLa DC-SIGN+ cells and 32 and 12% of iMDDCs, respectively. Anti-DC-SIGN CRD peptide antibodies inhibited the attachment of virus to HeLa DC-SIGN by up to 78% and the attachment to iMDDCs by only 20%. Both breast milk- and IVIg-derived natural antibodies to the CRD peptide inhibited 60% of the transmission in trans of HIV-1(JRCSF), an R5-tropic strain, from iMDDCs to CD4+ T lymphocytes. Taken together, these observations suggest that the attachment of HIV to DCs and transmission in trans to autologous CD4+ T lymphocytes occur through two independent mechanisms. Our data support a role of natural antibodies to DC-SIGN in the modulation of postnatal HIV transmission through breast-feeding and in the natural host defence against HIV-1 in infected individuals.

Filter selection for five color flow cytometric analysis with a single laser

Flow cytometry has evolved from single- and two-color analysis to the current use of 11-16 colors. The relatively bright excitation spectra of most fluorochromes have made color compensation a challenge especially when performed manually. We describe how by choosing filters with narrower bandwidths results in the color compensation values between FITC, PE, PE-TxR (ECD), PE-Cy5, and PE-Cy7 that range from 0 % to 50% depending on the combination of fluorochromes. Peripheral blood mononuclear cells were stained with alpha-CD4-FITC, alpha-CD27-PE, alpha-CD62L-ECD, alpha-CD45RA-PE-Cy5 and alpha-CD3-PE-Cy7. The samples were acquired on a MO Flo. The initial (first) and second filter sets for our experiments consisted of 530/30 or 519/20 for FITC, 580/30 or 575/20for PE, 630/30 or 630/22 for PE-TxR (ECD), 670/30 or 675/20 for PE-Cy5 and 740LP or 780/40 for PE-Cy7. Nonstained cells were used to adjust the threshold values of detection for each photo multiplier tube (PMT) for each filter set. The mean fluorescent intensity (MFI) of each fluorochrome was not reduced to any great extent by either filter set. However, the compensation value between PE and PE-TxR (ECD) with the first filter selection ranged from 84% to 89% and with the second set of filters it was 25-36%. In addition, the compensation between PE-TxR (ECD) and PE-Cy5 were reduced to 30.2% from 44.2% with the second filter set. The reduction of filter bandwidths that results in minimizing spectral overlaps without lost of signal provides a method by which discrimination of signals between PE containing fluorochromes can be achieved.

Recognition of a defined region within p24 gag by CD8+ T cells during primary human immunodeficiency virus type 1 infection in individuals expressing protective HLA class I alleles

Human immunodeficiency virus type 1 (HIV-1)-specific immune responses during primary HIV-1 infection appear to play a critical role in determining the ultimate speed of disease progression, but little is known about the specificity of the initial HIV-1-specific CD8(+) T-cell responses in individuals expressing protective HLA class I alleles. Here we compared HIV-1-specific T-cell responses between subjects expressing the protective allele HLA-B27 or -B57 and subjects expressing nonprotective HLA alleles using a cohort of over 290 subjects identified during primary HIV-1 infection. CD8(+) T cells of individuals expressing HLA-B27 or -B57 targeted a defined region within HIV-1 p24 Gag (amino acids 240 to 272) early in infection, and responses against this region contributed over 35% to the total HIV-1-specific T-cell responses in these individuals. In contrast, this region was rarely recognized in individuals expressing HLA-B35, an HLA allele associated with rapid disease progression, or in subjects expressing neither HLA-B57/B27 nor HLA-B35 (P < 0.0001). The identification of this highly conserved region in p24 Gag targeted in primary infection specifically in individuals expressing HLA class I alleles associated with slower HIV-1 disease progression provides a rationale for vaccine design aimed at inducing responses to this region restricted by other, more common HLA class I alleles.

The Duration of Exposure to HIV Modulates the Breadth and the Magnitude of HIV-Specific Memory CD4+T Cells

The impact of exposure to Ag on the development and maintenance of human CD4(+) memory T cells in general and HIV infection in particular is partially understood. In this study, we measured HIV-specific CD4(+) T cell proliferative responses against HIV proteins and derived peptides one year after highly active antiretroviral therapy initiation in 39 HIV-infected patients who initiated therapy at different times following infection. We show that a brief exposure to HIV of <1 month does not allow the generation of significant detectable frequencies of HIV-specific CD4(+) memory T cells. Patients having prolonged cumulative exposure to high viral load due to therapy failures also demonstrated limited HIV-specific CD4(+) T cell responses. In contrast, patients exposed to significant levels of virus for periods ranging from 3 to 18 mo showed brisk and broad HIV-specific CD4(+) T cell responses 1 year following the onset of therapy intervention. We also demonstrate that the nadir CD4(+) T cell count before therapy initiation correlated positively with the breadth and magnitude of these responses. Our findings indicate that the loss of proliferative HIV-specific CD4(+) T cell responses is associated with the systemic progression of the disease and that a brief exposure to HIV does not allow the establishment of detectable frequencies of HIV-specific memory CD4(+) T cells.

Convergence of TCR and cytokine signaling leads to FOXO3a phosphorylation and drives the survival of CD4+ central memory T cells

The molecular events involved in the establishment and maintenance of CD4⁺ central memory and effector memory T cells (T_CM and T_EM, respectively) are poorly understood. In this study, we demonstrate that ex vivo isolated T_CM are more resistant to both spontaneous and Fas-induced apoptosis than T_EM and have an increased capacity to proliferate and persist in vitro. Using global gene expression profiling, single cell proteomics, and functional assays, we show that the survival of CD4⁺ T_CM depends, at least in part, on the activation and phosphorylation of signal transducer and activator of transcription 5a (STAT5a) and forkhead box O3a (FOXO3a). T_CM showed a significant increase in the levels of phosphorylation of STAT5a compared with T_EM in response to both IL-2 (P < 0.04) and IL-7 (P < 0.002); the latter is well known for its capacity to enhance T cell survival. Moreover, ex vivo T_CM express higher levels of the transcriptionally inactive phosphorylated forms of FOXO3a and concomitantly lower levels of the proapoptotic FOXO3a target, Bim. Experiments aimed at blocking FOXO3a phosphorylation confirmed the role of this phosphoprotein in protecting T_CM from apoptosis. Our results provide, for the first time in humans, an insight into molecular mechanisms that could be responsible for the longevity and persistence of CD4⁺ T_CM.

Slow disease progression and robust therapy-mediated CD4+ T-cell recovery are associated with efficient thymopoiesis during HIV-1 infection

In chronic HIV infection, most untreated patients lose naive CD4+ and CD8+ T cells, whereas a minority preserve them despite persistent high viremia. Although antiretroviral therapy (ART)–mediated viral suppression generally results in a rise of naive and total CD4+ T cells, certain patients experience very little or no T-cell reconstitution. High peripheral T-cell activation has been linked to poor clinical outcomes, interfering with previous evaluations of thymic function in disease progression and therapy-mediated T-cell recovery. To circumvent this, we used the sj/βTREC ratio, a robust index of thymopoiesis that is independent of peripheral T-cell proliferation, to evaluate the thymic contribution to the preservation and restoration of naive CD4+ T cells. We show that the loss of naive and total CD4+ T cells is the result of or is exacerbated by a sustained thymic defect, whereas efficient thymopoiesis supports naive and total CD4+ T-cell maintenance in slow progressor patients. In ART-treated patients, CD4+ T-cell recovery was associated with the normalization of thymopoiesis, whereas the thymic defect persisted in aviremic patients who failed to recover CD4+ T-cell counts. Overall, we demonstrate that efficient thymopoiesis is key in the natural maintenance and in therapy-mediated recovery of naive and total CD4+ T cells.

Upregulation of PD-1 expression on HIV-specific CD8+ T cells leads to reversible immune dysfunction

The engagement of programmed death 1 (PD-1) to its ligands, PD-L1 and PD-L2, inhibits proliferation and cytokine production mediated by antibodies to CD3 (refs. 5,6,7). Blocking the PD-1-PD-L1 pathway in mice chronically infected with lymphocytic choriomeningitis virus restores the capacity of exhausted CD8(+) T cells to undergo proliferation, cytokine production and cytotoxic activity and, consequently, results in reduced viral load. During chronic HIV infection, HIV-specific CD8(+) T cells are functionally impaired, showing a reduced capacity to produce cytokines and effector molecules as well as an impaired capacity to proliferate. Here, we found that PD-1 was upregulated on HIV-specific CD8(+) T cells; PD-1 expression levels were significantly correlated both with viral load and with the reduced capacity for cytokine production and proliferation of HIV-specific CD8(+) T cells. Notably, cytomegalovirus (CMV)-specific CD8(+) T cells from the same donors did not upregulate PD-1 and maintained the production of high levels of cytokines. Blocking PD-1 engagement to its ligand (PD-L1) enhanced the capacity of HIV-specific CD8(+) T cells to survive and proliferate and led to an increased production of cytokines and cytotoxic molecules in response to cognate antigen. The accumulation of HIV-specific dysfunctional CD8(+) T cells in the infected host could prevent the renewal of a functionally competent HIV-specific CD8(+) repertoire.

IL-4 influences the differentiation and the susceptibility to activation-induced cell death of human naive CD8+ T cells

It is now well established that the cytokine environment influences the activation, differentiation, proliferation and death of T lymphocytes during the primary response to antigen. Using an in vitro model, we investigated the influence of IL-4, added at the onset of TCR stimulation, on phenotypic and functional markers of naive CD8+ T cell activation including the up-regulation of activation markers, proliferation as well as the susceptibility to activation-induced cell death (AICD). We report that IL-4, unlike IL-2 added at the onset of repeated TCR stimulation of naive CD8+ T cells prevents AICD, in part due to its ability to maintain the level of the survival-related protein Bcl-2. Moreover, TCR-triggered activation of naive CD8+ T cells in the presence of IL-4 leads to the development of a CD8+ T cell subset that proliferates normally, but which fails to exhibit characteristic activation parameters such as the up-regulation of CD25 and Granzyme B. Taken together, these results demonstrate that exposure to IL-4 during primary activation influences CD8+ T cell differentiation by inducing the development of a sub-population of AICD-resistant, proliferation-competent cells that do not show some of the typical features of CD8+ T cell activation.

Evaluation of OX40 Ligand as a Costimulator of Human Antiviral Memory CD8 T Cell Responses: Comparison with B7.1 and 4-1BBL

CTL are important effectors of antiviral immunity. Designing adjuvants that can induce strong cytotoxic T cell responses in humans would greatly improve the effectiveness of an antiviral vaccination or therapeutic strategy. Recent evidence suggests that, in addition to its well-established role in costimulation of CD4 T cell responses, OX40L (CD134) can directly costimulate mouse CD8 T cells. In this study, we evaluated the role of OX40L in costimulation of human antiviral CD8 T cell responses and compared it with two other important costimulators, B7.1 (CD80) and 4-1BBL (CD137L). Delivery of OX40L to human monocytes using a recombinant replication-defective adenovirus led to greater expansion, up-regulation of perforin, enhanced cytolytic activity, and increased numbers of IFN-gamma- and TNF-alpha-producing antiviral memory CD8 T cells in cultures of total T cells. Synergistic or additive effects were observed when OX40L costimulation was combined with 4-1BBL (CD137L) or B7.1 (CD80) costimulation. In total T cell cultures, at low Ag dose, 4-1BBL provided the most potent costimulus for influenza-specific CD8 T cell expansion, followed by B7.1 (CD80) and then OX40L. For isolated CD8 T cells, 4-1BBL was also the most consistent costimulator, followed by B7.1. In contrast, OX40L showed efficacy in direct activation of memory CD8 T cells in only one of seven donors. Thus, OX40L costimulates human antiviral memory CD8 T cell responses largely through indirect effects and can enhance anti-influenza, anti-EBV, and anti-HIV responses, particularly in combination with 4-1BBL or B7.

Enhancement of HIV-Specific CD8 T Cell Responses by Dual Costimulation with CD80 and CD137L

HIV-specific CD8 T cell responses are defective in chronic HIV infection. In this study, we report that costimulation with either CD137L (4-1BBL) or CD80 (B7.1) enhanced the Ag-specific expansion and acquisition of effector function by HIV-specific memory CD8 T cells. Ag-specific T cells from recently infected donors showed maximal expansion with single costimulatory molecules. Dual costimulation of T cells from recently infected donors or from healthy donors responding to influenza epitopes led to enhanced responses when the accumulation of cytokines was measured. However, accumulation of regulatory cytokines, particularly IFN-gamma, led to inhibition of further Ag-specific CD8 T cell expansion in the cultures. This inhibition was relieved by neutralization of IFN-gamma or of IFN-gamma, TNF, and IL-10. Thus, strong costimulation of T cells in vitro can lead to induction of regulatory cytokines at levels that limit further T cell expansion. In marked contrast, T cells from long-term (>4 years) infected HIV+ donors exhibited reduced Ag-specific CD8 T cell expansion, reduced CD4 T cell responses, and minimal cytokine accumulation. Dual costimulation with both 4-1BBL and B7.1 enhanced responses of T cells from long-term infected subjects to a level similar to that obtained with T cells from early in HIV infection. Experiments with purified CD8 T cells showed that B7.1 and 4-1BBL could act directly and synergistically on CD8 T cells. Taken together, these data suggest that 4-1BBL and B7.1 have additive or synergistic effects on HIV-specific CD8 T cell responses and represent a promising combination for therapeutic vaccination for HIV.

Caspase-3 is a component of Fas death-inducing signaling complex in lipid rafts and its activity is required for complete caspase-8 activation during Fas-mediated cell death

Since its discovery, caspase-8 has been placed at the apex of the proteolytic cascade triggered by death receptor (DR) cross-linking. Because of its capacity to interact with the cytoplasmic portion of DR, it has been suggested that caspase-8 acts independently of other caspases in the initiation of Fas and other DR signaling. In this study, we demonstrate that in Jurkat cells, caspase-3 cleavage is an early step during Fas-induced apoptosis. We show that caspase-3 processing into its p20 occurs rapidly after Fas cross-linking, in the absence of mitochondrial depolarization and caspase-9 activation. Moreover, caspase-3 is present in lipid rafts of untreated Jurkat cells and peripheral T lymphocytes. Caspase-3, caspase-8, and Fas-associated death domain are further recruited to lipid rafts of Jurkat cells following anti-Fas treatment. Fas immunoprecipitation reveals that caspase-3 is a component of the death-inducing signaling complex, suggesting that this cysteine protease is in close proximity to caspase-8. Furthermore, transduction of Jurkat cells with a caspase-3 dominant-negative form inhibits caspase-8 processing and results in inhibition of apoptosis, suggesting that caspase-3 activity is required for caspase-8 activation. Overall, these findings support a model whereby caspase-3 is a component of the death-inducing signaling complex located in lipid rafts, and as such, is involved in the amplification of caspase-8 activity by the mitochondrion.

HIV-1 viremia prevents the establishment of interleukin 2-producing HIV-specific memory CD4+ T cells endowed with proliferative capacity

CD4⁺ T cell responses are associated with disease control in chronic viral infections. We analyzed human immunodeficiency virus (HIV)-specific responses in ten aviremic and eight viremic patients treated during primary HIV-1 infection and for up to 6 yr thereafter. Using a highly sensitive 5-(and-6)-carboxyfluorescein diacetate-succinimidyl ester–based proliferation assay, we observed that proliferative Gag and Nef peptide-specific CD4⁺ T cell responses were 30-fold higher in the aviremic patients. Two subsets of HIV-specific memory CD4⁺ T cells were identified in aviremic patients, CD45RA⁻ CCR7⁺ central memory cells (Tcm) producing exclusively interleukin (IL)-2, and CD45RA⁻ CCR7⁻ effector memory cells (Tem) that produced both IL-2 and interferon (IFN)-γ. In contrast, in viremic, therapy-failing patients, we found significant frequencies of Tem that unexpectedly produced exclusively IFN-γ. Longitudinal analysis of HIV epitope–specific CD4⁺ T cells revealed that only cells that had the capacity to produce IL-2 persisted as long-term memory cells. In viremic patients the presence of IFN-γ–producing cells was restricted to periods of elevated viremia. These findings suggest that long-term CD4⁺ T cell memory depends on IL-2–producing CD4⁺ T cells and that IFN-γ only–producing cells are short lived. Our data favor a model whereby competent HIV-specific Tcm continuously arise in small numbers but under persistent antigenemia are rapidly induced to differentiate into IFN-γ only–producing cells that lack self-renewal capacity.

Changes in immunological and virological parameters in HIV-1 infected subjects following leukapheresis

In order to assess immune responses during HIV-1 therapeutic immunization, a large number of blood mononuclear cells (PBMC) are needed. Clinical tolerance and safety, as well as changes in immunological and virological parameters, were assessed, following leukapheresis in HIV-1 infected subjects with CD4(+) cell count >200 x 10(6)/l. PBMC were collected using a Fenwal CS3000 cell separator in 29 subjects with mean CD4(+) cell counts of 503 x 10(6)/l (range 172-1,119) and viral load of 2.5 log(10) copies/ml (range <1.7-5.4). Twenty-four (83%) subjects were on antiretroviral therapy while 5 (17%) were untreated. The blood volume processed was 7 L over a period of 3 hours. A mean value (+/- standard error) of 82 +/- 26 x 10(9)/l lymphocytes was collected by a single apheresis in a mean volume of 200 +/- 1.8 ml, containing 9.0 +/- 1.3 x 10(9)/l CD4(+) and 10.2 +/- 1.3 x 10(9)/l CD8(+) cells. The leukapheresis procedures were well tolerated and no immediate or delayed side effects were observed within 90 days of follow-up. No changes from blood pre-leukapheresis values were detected for white blood cells, lymphocytes, monocytes, CD8(+), CD34(+), naive and memory CD4(+) cell counts immediately after, 1 h, 7 days, or within 90 days after leukapheresis. However, absolute CD4(+) cell counts and percentage significantly increased from pre-leukapheresis values after 1 h (530 +/- 43 vs. 700 +/- 75 cell x 10(6)/l; 32.6 +/- 1.6 vs. 36.9 +/- 1.9%; P < 0.001 for both paired t-tests) before returning to pre-leukapheresis levels on day 7. No significant changes in viral load from pre-leukapheresis levels in treated or untreated subjects were detected at any time points. We conclude that leukapheresis in HIV-1 infected subjects with CD4(+) cell counts >200 x 10(6)/l is safe and induces a transient increase in the absolute and percentage of CD4(+) cell count without enhancing viral replication.

Diminished proliferation of human immunodeficiency virus-specific CD4+ T cells is associated with diminished interleukin-2 (IL-2) production and is recovered by exogenous IL-2

Virus-specific CD4(+) T-cell function is thought to play a central role in induction and maintenance of effective CD8(+) T-cell responses in experimental animals or humans. However, the reasons that diminished proliferation of human immunodeficiency virus (HIV)-specific CD4(+) T cells is observed in the majority of infected patients and the role of these diminished responses in the loss of control of replication during the chronic phase of HIV infection remain incompletely understood. In a cohort of 15 patients that were selected for particularly strong HIV-specific CD4(+) T-cell responses, the effects of viremia on these responses were explored. Restriction of HIV replication was not observed during one to eight interruptions of antiretroviral therapy in the majority of patients (12 of 15). In each case, proliferative responses to HIV antigens were rapidly inhibited during viremia. The frequencies of cells that produce IFN-gamma in response to Gag, Pol, and Nef peptide pools were maintained during an interruption of therapy. In a subset of patients with elevated frequencies of interleukin-2 (IL-2)-producing cells, IL-2 production in response to HIV antigens was diminished during viremia. Addition of exogenous IL-2 was sufficient to rescue in vitro proliferation of DR0101 class II Gag or Pol tetramer(+) or total-Gag-specific CD4(+) T cells. These observations suggest that, during viremia, diminished in vitro proliferation of HIV-specific CD4(+) T cells is likely related to diminished IL-2 production. These results also suggest that relatively high frequencies of HIV-specific CD4(+) T cells persist in the peripheral blood during viremia, are not replicatively senescent, and proliferate when IL-2 is provided exogenously.

HIV-1 protease processes procaspase 8 to cause mitochondrial release of cytochrome c, caspase cleavage and nuclear fragmentation

Infection of T cells with HIV-1 induces apoptosis and modulates apoptosis regulatory molecules. Similar effects occur following treatment of cells with individual HIV-1 encoded proteins. While HIV-1 protease is known to be cytotoxic, little is known of its effect on apoptosis and apoptosis regulatory molecules. The ability of HIV-1 protease to kill cells, coupled with the degenerate substrate specificity of HIV-1 protease, suggests that HIV-1 protease may activate cellular factor(s) which, in turn, induce apoptosis. We demonstrate that HIV-1 protease directly cleaves and activates procaspase 8 in T cells which is associated with cleavage of BID, mitochondrial release of cytochrome c, activation of the downstream caspases 9 and 3, cleavage of DFF and PARP and, eventually, to nuclear condensation and DNA fragmentation that are characteristic of apoptosis. The effect of HIV-1 protease is not seen in T cell extracts which have undetectable levels of procaspase 8, indicating a specificity and requirement for procaspase 8.

Persistence and fitness of multidrug-resistant human immunodeficiency virus type 1 acquired in primary infection

This study examines the persistence and fitness of multidrug-resistant (MDR) viruses acquired during primary human immunodeficiency virus infection (PHI). In four individuals, MDR infections persisted over the entire study period, ranging from 36 weeks to 5 years, in the absence of antiretroviral therapy. In stark contrast, identified source partners in two cases showed expected outgrowth of wild-type (WT) virus within 12 weeks of treatment interruption. In the first PHI case, triple-class MDR resulted in low plasma viremia (1.6 to 3 log copies/ml) over time compared with mean values obtained for an untreated PHI group harboring WT infections (4.1 to 4.3 log copies/ml). Increasing viremia in PHI patient 1 at week 52 was associated with the de novo emergence of a protease inhibitor-resistant variant through a recombination event involving the original MDR virus. MDR infections in two other untreated PHI patients yielded viremia levels typical of the untreated WT group. A fourth patient's MDR infection yielded low viremia (<50 to 500 copies/ml) for 5 years despite his having phenotypic resistance to all antiretroviral drugs in his treatment regimen. In two of these PHI cases, a rebound to higher levels of plasma viremia only occurred when the M184V mutation in reverse transcriptase could no longer be detected and, in a third case, nondetection of M184V was associated with an inability to isolate virus. To further evaluate the fitness of MDR variants acquired in PHI, MDR and corresponding WT viruses were isolated from index and source partners, respectively. Although MDR viral infectivity (50% tissue culture infective dose) was comparable to that observed for WT viruses, MDR infections in each case demonstrated 2-fold and 13- to 23-fold reductions in p24 antigen and reverse transcriptase enzymatic activity, respectively. In dual-infection competition assays, MDR viruses consistently demonstrated a marked replicative disadvantage compared with WT virus. These results indicate that MDR viruses that are generated following PHI can establish persistent infections as dominant quasispecies despite their impaired replicative competence.

Substantial differences in specificity of HIV-specific cytotoxic T cells in acute and chronic HIV infection

Cytotoxic T lymphocytes (CTLs) play a vital part in controlling viral replication during human viral infections. Most studies in human infections have focused on CTL specificities in chronic infection and few data exist regarding the specificity of the initial CTL response induced in acute infection. In this study, HIV-1 infection in persons expressing human histocompatibility leukocyte antigen (HLA)-A*0201 was used as a means of addressing this issue. In chronic infection, the dominant HLA-A*0201-restricted CTL response is directed towards the epitope SLYNTVATL ("SL9") in p17 Gag (residues 77-85). This epitope is targeted by 75% of HLA-A*0201-positive adults, and the magnitude of this A*0201-SL9 response shows a strong negative association with viral load in progressive infection. Despite using the highly sensitive peptide-major histocompatibility complex tetramer and intracellular cytokine assays, responses to the SL9 epitope were not detectable in any of 11 HLA-A*0201-positive subjects with acute HIV-1 infection (P = 2 x 10(-6)), even when assays were repeated using the SL9 peptide variant that was encoded by their autologous virus. In contrast, multiple responses (median 3) to other epitopes were evident in 7 of the 11 A*0201-positive subjects. Longitudinal study of two subjects confirmed that the A*0201-SL9 response emerged later than other CTL responses, and after viral set point had been reached. Together, these data show that the CTL responses that are present and that even may dominate in chronic infection may differ substantially from those that constitute the initial antiviral CTL response. This finding is an important consideration in vaccine design and in the evaluation of vaccine candidates.

Resistance to antiretroviral drugs in patients with primary HIV-1 infection. Investigators of the Quebec Primary Infection Study

The widespread use of antiretroviral agents (ARVs) and the growing occurrence of HIV strains resistant to these drugs have given rise to serious concerns regarding the transmission of resistant viruses to newly infected persons. Plasma viral RNA from 80 individuals newly infected between 1997 and 1999 was genotyped by automated sequencing to analyze the profile of viruses resistant to nucleoside and non-nucleoside reverse transcriptase inhibitors (NRTIs and NNRTIs) and to protease inhibitors (PIs). The prevalence of mutations that conferred primary resistance to PIs (L10I, D30Y, V82A, L90M) was 15% of the cohort. RT genotypic variants, associated with high-level resistance to ARVs, were observed in 21% of individuals, including NRTI, NNRTI and multidrug (MDR) resistance in 6, 5, and 10% of cases, respectively. The phenotypic susceptibility of viral isolates to ARVs was also assayed and showed transmission of high-level resistance to ZDV, 3TC, and PIs in those individuals with MDR. The transmission of drug-resistant HIV genotypic variants is a serious problem that merits further attention by public health officials, virologists, and clinicians.

Identification of dominant optimal HLA-B60- and HLA-B61-restricted cytotoxic T-lymphocyte (CTL) epitopes: rapid characterization of CTL responses by enzyme-linked immunospot assay

Human immunodeficiency virus type 1 (HIV-1)-specific cytotoxic T-lymphocyte (CTL) responses play a major role in the antiviral immune response, but the relative contribution of CTL responses restricted by different HLA class I molecules is less well defined. HLA-B60 or the related allele B61 is expressed in 10 to 20% of Caucasoid populations and is even more highly prevalent in Asian populations, but yet no CTL epitopes restricted by these alleles have been defined. Here we report the definition of five novel HLA-B60-restricted HIV-1-specific CTL epitopes, using peripheral blood mononuclear cells in enzyme-linked immunospot (Elispot) assays and using CTL clones and lines in cytolytic assays. The dominant HLA-B60-restricted epitope, Nef peptide KEKGGLEGL, was targeted by all eight subjects with B60 and also by both subjects with B61 studied. This study additionally establishes the utility of the Elispot assay as a more rapid and efficient method of defining novel CTL epitopes. This approach will help to define new CTL epitopes that may play an important role in the immune control of HIV-1.

Comparison of clinical features of acute HIV-1 infection in patients infected sexually or through injection drug use. The Investigators of the Québec Primary HIV Infection Study

Acute HIV-1 infection (AHI) may present with a clinical picture that represents a diagnostic challenge. We tested the hypothesis that two different routes of infection, that is, sexual versus parenteral, might be associated with a difference in the clinical features of AHI. A prospective cohort of seroconvertors was established in Montréal in private medical clinics and hospitals from February 1996 to May 1999. The prevalence of the symptomatic presentation was almost overlapping within the two groups of newly infected individuals 69% (42 of 61) for men having sex with men (MSM) and 69% (18 of 26) for injection drug users (IDUs; p =.98). Comparison of all types of symptoms and signs as well as their duration was also similar in both groups. Of particular interest, the site of lymph node enlargement was not different despite the estimated sites of intravenous inoculation. Oral and anal ulcers were more frequently observed in MSM than in IDUs (6 versus 0 and 4 versus 1, respectively). Neither the mean CD4+ count (514.8 and 414.7 cells/mm3; p =.14) nor the mean viral load (4.45 and 4.70 log copies/ml; p =.40) were different between the two groups at the time of the first study visit. Our study results clearly indicate that health care workers can expect similar clinical presentation of AHI in MSM and in IDUs despite the different routes of infection.

The extracellular domain of CD4 regulates the initiation of T cell activation

To assess the respective contribution of the extracellular and intracellular domains of CD4 in regulating early T cell activation events, we have used a CD4-independent murine T cell clone transfected with human CD4. Stimulation of CD4 positive clones could only be observed if CD4 molecules associated to lck were co-aggregated with the TCR complex, confirming that the simultaneous interaction of MHC class II molecules with the CD4/lck complex and the TCR is required to initiate T cell activation. To assess the involvement of the extracellular portion of CD4 in this process, we transfected a chimeric molecule (EGFRCD4) consisting of the extracellular portion of the epidermal growth factor receptor (EGFR), and of the transmembrane and cytoplasmic domains of human CD4. Although this chimeric molecule associates with lck, transfected clones were induced to proliferate by mAb specific for TCR in the absence of co-aggregation. A new regulatory role for the extracellular domain of CD4 which is independent of its interaction with MHC class II molecules is thus revealed in these experiments. Taken together, our results demonstrate that, in a CD4-independent cell line, two domains of CD4 regulate early T cell activation events: (1) its association with lck and (2) its extracellular domain, independently of its interaction with MHC class II molecules.

Prevalence of HIV-1 resistant to antiretroviral drugs in 81 individuals newly infected by sexual contact or injecting drug use. Investigators of the Quebec Primary Infection Study

OBJECTIVE

Prolonged treatment with antiretroviral drugs results in the selection of HIV-1 variants with mutations conferring resistance to nucleoside and non-nucleoside reverse transcriptase inhibitors (NRTI and NNRTI) or to protease inhibitors (PI). There is serious concern about transmission of resistant viruses to newly infected persons. This study monitored the prevalence of resistant viruses in individuals undergoing primary HIV infection.

DESIGN

Resistance testing was performed on 81 individuals infected between 1997 and 1999 by injecting drug use (n =21), sexual (n = 56), or unknown (n = 4) transmission.

METHODS

Automated sequencing was used to genotype the reverse transcriptase (RT) and protease regions of virus isolated from patients' plasma. The phenotypic susceptibility of stimulated peripheral blood mononuclear cells to antiretroviral drugs was assayed. Line probe assays detected quasispecies variations in wild-type and mutated RT codons.

RESULTS

A high prevalence of PI and RT genotypic variants, associated with high-level resistance to antiretroviral drugs, was observed in individuals newly infected by injecting drug use (PI = 24%, RT = 24%) or sexual transmission (PI = 12%, RT = 22%). The PI mutations, L101, V82A, and L90M, were found in 10.5, 3 and 4% of cases, respectively; whereas for RT, primary mutations at positions T215Y (zidovudine), M184V (lamivudine), T69D/A (zalcitabine), and K103N (multi-NNRTI) were present in 8, 5, 4, and 4% of subjects, respectively. Resistance to NRTI was demonstrated by phenotypic, genotypic, and line probe analyses. Transmission of multidrug (NRTI/NNRTI/PI) resistance in eight subjects (9.9%) was confirmed by showing that source partners possessed viruses of similar genotype.

CONCLUSIONS

The transmission of drug-resistant HIV is a serious problem that merits further attention by public health officials as well as virologists and clinicians.