Magnitude and complexity of rectal mucosa HIV-1-specific CD8+ T-cell responses during chronic infection reflect clinical status

First-in-human immunoPET imaging of COVID-19 convalescent patients using dynamic total-body PET and a CD8-targeted minibody

With most of the T cells residing in the tissue, not the blood, developing noninvasive methods for in vivo quantification of their biodistribution and kinetics is important for studying their role in immune response and memory. This study presents the first use of dynamic positron emission tomography (PET) and kinetic modeling for in vivo measurement of CD8+ T cell biodistribution in humans. A 89Zr-labeled CD8-targeted minibody (89Zr-Df-Crefmirlimab) was used with total-body PET in healthy individuals (N = 3) and coronavirus disease 2019 (COVID-19) convalescent patients (N = 5). Kinetic modeling results aligned with T cell-trafficking effects expected in lymphoid organs. Tissue-to-blood ratios from the first 7 hours of imaging were higher in bone marrow of COVID-19 convalescent patients compared to controls, with an increasing trend between 2 and 6 months after infection, consistent with modeled net influx rates and peripheral blood flow cytometry analysis. These results provide a promising platform for using dynamic PET to study the total-body immune response and memory.

Analysis on epidemiological characters and HIV care continuum of HIV-infected students: a retrospective cohort study in Shandong province, China

BACKGROUD

The proportion of HIV-infected students in China showed an increasing trend. This study aimed to identify the epidemiological characteristics and the HIV care continuum for HIV-infected students in Shandong Province, China.

METHODS

Case report and follow-up data of HIV-infected students were obtained from the National HIV/AIDS comprehensive response information management system. Logistic regression analyses were used to analyze the associating factors of HIV-infected students accepting CD4 + T cells (CD4) test and antiviral therapy (ART) in 30 days, and ArcGIS software was used for the spatial anlysis.

RESULTS

From 2017 to 2019, 403 HIV-infected students were reported in Shandong Province. The majority of them were male (99.5%) and transmitted through homosexual sexual activity(92.1%). Most of them lived in Jinan city and Qingdao city. 68.5% (276 cases) accepted CD4 test in 30 days, and 48.6% (196 cases) started ART in 30 days. The heterosexual transmitted cases (AOR = 0.458, 95%CI: 0.210-0.998), patients accepting HIV care in western area (AOR = 0.266,95%CI: 0.147-0.481) were less likely to test CD4 within 30 days; patients aged 23-25 (AOR = 2.316, 95%CI: 1.009-5.316) and patients who had tested CD4 within 30 days (AOR = 4.377; 95%CI: 2.572-7.447) prefered to receive ART within 30 days; patients accepted HIV care in central area (AOR = 0.407; 95%CI: 0.251-0.657) and western area (AOR = 0.508; 95%CI: 0.261-0.989) and patients diagnosed by voluntary blood donation (AOR = 0.352; 95%CI: 0.144-0.864) were less willing to receive ART in 30 days.

CONCLUSIONS

The HIV care continuum of HIV-infected students in Shandong Province still needed strenghthing. More health education and case management should be done for cases transmitted through heterosexual behavior, accepted HIV care in central and western area, and diagnosed by voluntary blood donation.

First-in-human immunoPET imaging of COVID-19 convalescent patients using dynamic total-body PET and a CD8-targeted minibody

With the majority of CD8+ T cells residing and functioning in tissue, not blood, developing noninvasive methods for in vivo quantification of their biodistribution and kinetics in humans offers the means for studying their key role in adaptive immune response and memory. This study is the first report on using positron emission tomography (PET) dynamic imaging and compartmental kinetic modeling for in vivo measurement of whole-body biodistribution of CD8+ T cells in human subjects. For this, a 89Zr-labeled minibody with high affinity for human CD8 (89Zr-Df-Crefmirlimab) was used with total-body PET in healthy subjects (N=3) and in COVID-19 convalescent patients (N=5). The high detection sensitivity, total-body coverage, and the use of dynamic scans enabled the study of kinetics simultaneously in spleen, bone marrow, liver, lungs, thymus, lymph nodes, and tonsils, at reduced radiation doses compared to prior studies. Analysis and modeling of the kinetics was consistent with T cell trafficking effects expected from immunobiology of lymphoid organs, suggesting early uptake in spleen and bone marrow followed by redistribution and delayed increasing uptake in lymph nodes, tonsils, and thymus. Tissue-to-blood ratios from the first 7 h of CD8-targeted imaging showed significantly higher values in the bone marrow of COVID-19 patients compared to controls, with an increasing trend between 2 and 6 months post-infection, consistent with net influx rates obtained by kinetic modeling and flow cytometry analysis of peripheral blood samples. These results provide the platform for using dynamic PET scans and kinetic modelling to study total-body immunological response and memory.

Differential localization and limited cytotoxic potential of duodenal CD8+ T cells

The duodenum is a major site of HIV persistence during suppressive antiretroviral therapy despite harboring abundant tissue-resident memory (Trm) CD8⁺ T cells. The role of duodenal Trm CD8⁺ T cells in viral control is still not well defined. We examined the spatial localization, phenotype, and function of CD8⁺ T cells in the human duodenal tissue from people living with HIV (PLHIV) and healthy controls. We found that Trm (CD69⁺CD103^hi) cells were the predominant CD8⁺ T cell population in the duodenum. Immunofluorescence imaging of the duodenal tissue revealed that CD103⁺CD8⁺ T cells were localized in the intraepithelial region, while CD103^–CD8⁺ T cells and CD4⁺ T cells were mostly localized in the lamina propria (LP). Furthermore, HIV-specific CD8⁺ T cells were enriched in the CD69⁺CD103^–/lo population. However, the duodenal HIV-specific CD8⁺ Trm cells rarely expressed canonical molecules for potent cytolytic function (perforin and granzyme B) but were more polyfunctional than those from peripheral blood. Taken together, our results show that duodenal CD8⁺ Trm cells possess limited perforin-mediated cytolytic potential and are spatially separated from HIV-susceptible LP CD4⁺ T cells. This could contribute to HIV persistence in the duodenum and provides critical information for the design of cure therapies.

The TLR7 agonist vesatolimod induced a modest delay in viral rebound in HIV controllers after cessation of antiretroviral therapy

Toll-like receptor 7 (TLR7) agonists, in combination with other therapies, can induce sustained control of simian-human immunodeficiency virus (SHIV) or simian immunodeficiency virus (SIV) in nonhuman primates. Here, we report the results of a randomized, double-blind, placebo-controlled phase 1b clinical trial of an oral TLR7 agonist, vesatolimod, in HIV-1-infected controllers on antiretroviral therapy (ART). We randomized participants 2:1 to receive vesatolimod (n = 17) or placebo (n = 8) once every other week for a total of 10 doses while continuing on ART. ART was then interrupted, and the time to viral rebound was analyzed using the Kaplan-Meier method. Vesatolimod was associated with induction of immune cell activation, decreases in intact proviral DNA during ART, and a modest increase in time to rebound after ART was interrupted. The delayed viral rebound was predicted by the lower intact proviral DNA at the end of vesatolimod treatment (13 days after the final dose). Inferred pathway analysis suggested increased dendritic cell and natural killer cell cross-talk and an increase in cytotoxicity potential after vesatolimod dosing. Larger clinical studies will be necessary to assess the efficacy of vesatolimod-based combination therapies aimed at long-term control of HIV infection.

TCF-1 regulates HIV-specific CD8+ T cell expansion capacity

Although many HIV cure strategies seek to expand HIV-specific CD8+ T cells to control the virus, all are likely to fail if cellular exhaustion is not prevented. A loss in stem-like memory properties (i.e., the ability to proliferate and generate secondary effector cells) is a key feature of exhaustion; little is known, however, about how these properties are regulated in human virus-specific CD8+ T cells. We found that virus-specific CD8+ T cells from humans and nonhuman primates naturally controlling HIV/SIV infection express more of the transcription factor TCF-1 than noncontrollers. HIV-specific CD8+ T cell TCF-1 expression correlated with memory marker expression and expansion capacity and declined with antigenic stimulation. CRISPR-Cas9 editing of TCF-1 in human primary T cells demonstrated a direct role in regulating expansion capacity. Collectively, these data suggest that TCF-1 contributes to the regulation of the stem-like memory property of secondary expansion capacity of HIV-specific CD8+ T cells, and they provide a rationale for exploring the enhancement of this pathway in T cell-based therapeutic strategies for HIV.

The importance of advanced cytometry in defining new immune cell types and functions relevant for the immunopathogenesis of HIV infection

: In the last years, novel, exciting immunological findings of interest for HIV research and treatment were identified thanks to different cytometric approaches. The analysis of the phenotypes and functionality of cells belonging to the immune system could clarify their role in the immunopathogenesis of HIV infection, and to elaborate key concepts, relevant in the treatment of this disease. Important discoveries have been made concerning cells that are important for protective immunity like lymphocytes that display polyfunctionality, resident memory T cells, innate lymphoid cells, to mention a few. The complex phenotype of myeloid-derived suppressor cells has been investigated, and relevant changes have been reported during chronic and primary HIV infection, in correlation with changes in CD4 T-cell number, T-cell activation, and with advanced disease stage. The search for markers of HIV persistence present in latently infected cells, namely those molecules that are important for a functional or sterilizing cure, evidenced the role of follicular helper T cells, and opened a discussion on the meaning and use of different surface molecules not only in identifying such cells, but also in designing new strategies. Finally, advanced technologies based upon the simultaneous detection of HIV-RNA and proteins at the single cell level, as well as those based upon spectral cytometry or mass cytometry are now finding new actors and depicting a new scenario in the immunopathogenesis of the infection, that will allow to better design innovative therapies based upon novel drugs and vaccines.

Parallel studies of mucosal immunity in the reproductive and gastrointestinal mucosa of HIV-infected women

PROBLEM

The effects of HIV on the gastrointestinal tract (GIT), including CD4 depletion, epithelial disruption, and collagen deposition, are well documented and only partially reversed by combination antiretroviral therapy (cART). However, the effects of HIV on the female reproductive tract (FRT) are poorly understood, and most studies have focused on ectocervix and vagina without assessing the upper tract. Here, we investigated CD4⁺ T-cell frequency, phenotype, and HIV-specific T-cell responses in the endocervix and endometrium of HIV-infected women, comparing these tissues to the GIT.

METHOD OF STUDY

Mucosal samples and blood were obtained from 18 women: four who were HIV-positive and not on cART for at least 3 years prior to sampling, including two natural controllers (viral load [VL] undetectable and CD4 >350); nine women on cART with low to undetectable VL; and five HIV-uninfected women. Mucosal samples included terminal ileum, sigmoid colon, endocervical cytobrush, endocervical curettage, and endometrial biopsy. T-cell frequency, phenotypes, and HIV-specific T-cell responses were analyzed by multiparameter flow cytometry.

RESULTS

T-cell activation, measured by CD38/HLA-DR co-expression, remained significantly elevated in endometrium following cART, but was lower in gastrointestinal tissues. HIV-specific CD8⁺ T-cell responses were detected in ileum, colon, and endometrial tissues of women both on and off cART, and were of higher magnitude on those not on cART.

CONCLUSION

Our findings reveal differences in CD4⁺ T-cell frequencies, immune activation, and HIV-specific T-cell responses between the gastrointestinal and reproductive tracts, and highlight differences between HIV controllers and women on cART.

Tissue issues: mucosal T-cell responses in HIV-1 infection

PURPOSE OF REVIEW

This review summarizes our current understanding of HIV-1-specific T-cell responses in mucosal tissues, emphasizing recent work and specifically highlighting papers published over the past 18 months.

RECENT FINDINGS

Recent work has improved the standardization of tissue sampling approaches and provided new insights on the abundance, phenotype and distribution of HIV-1-specific T-cell populations in mucosal tissues. In addition, it has recently been established that some lymphocytes exist in tissues as "permanent resident" memory cells that differ from their counterparts in blood.

SUMMARY

HIV-1-specific T-cell responses have been extensively characterized; however, the vast majority of reports have focused on T-cells isolated from peripheral blood. Mucosal tissues of the genitourinary and gastrointestinal tracts serve as the primary sites of HIV-1 transmission, and provide "front line" barrier defenses against HIV-1 and other pathogens. In addition, the gastrointestinal tract remains a significant viral reservoir throughout the chronic phase of infection. Tissue-based immune responses may be critical in fighting infection, and understanding these defenses may lead to improved vaccines and immunotherapeutic strategies.

CD8+ T-Cell Response to HIV Infection in the Era of Antiretroviral Therapy

Although the combined antiretroviral therapy (cART) has decreased the deaths associated with the immune deficiency acquired syndrome (AIDS), non-AIDS conditions have emerged as an important cause of morbidity and mortality in HIV-infected patients under suppressive cART. Since these conditions are associated with a persistent inflammatory and immune activation state, major efforts are currently made to improve the immune reconstitution. CD8⁺ T-cells are critical in the natural and cART-induced control of viral replication; however, CD8⁺ T-cells are highly affected by the persistent immune activation and exhaustion state driven by the increased antigenic and inflammatory burden during HIV infection, inducing phenotypic and functional alterations, and hampering their antiviral response. Several CD8⁺ T-cell subsets, such as interleukin-17-producing and follicular CXCR5⁺ CD8⁺ T-cells, could play a particular role during HIV infection by promoting the gut barrier integrity, and exerting viral control in lymphoid follicles, respectively. Here, we discuss the role of CD8⁺ T-cells and some of their subpopulations during HIV infection in the context of cART-induced viral suppression, focusing on current challenges and alternatives for reaching complete reconstitution of CD8⁺ T-cells antiviral function. We also address the potential usefulness of CD8⁺ T-cell features to identify patients who will reach immune reconstitution or have a higher risk for developing non-AIDS conditions. Finally, we examine the therapeutic potential of CD8⁺ T-cells for HIV cure strategies.

Mucosal Immunity in HIV/SIV Infection: T Cells, B Cells and Beyond

As our understanding of mucosal immunity increases, it is becoming clear that the host response to HIV-1 is more complex and nuanced than originally believed. The mucosal landscape is populated with a variety of specialized cell types whose functions include combating infectious agents while preserving commensal microbiota, maintaining barrier integrity, and ensuring immune homeostasis. Advances in multiparameter flow cytometry, gene expression analysis and bioinformatics have allowed more detailed characterization of these cell types and their roles in host defense than was previously possible. This review provides an overview of existing literature on immunity to HIV-1 and SIVmac in mucosal tissues of the female reproductive tract and the gastrointestinal tract, focusing on major effector cell populations and briefly summarizing new information on tissue resident memory T cells, T_reg, Th17, Th22 and innate lymphocytes (ILC), subsets that have been studied primarily in the gastrointestinal mucosa.

Cryopreservation of human mucosal tissues

Background

Cryopreservation of leukocytes isolated from the cervicovaginal and colorectal mucosa is useful for the study of cellular immunity (see Hughes SM et al. PLOS ONE 2016). However, some questions about mucosal biology and sexually transmitted infections are better addressed with intact mucosal tissue, for which there is no standard cryopreservation protocol.

Methods and findings

To find an optimal preservation protocol for mucosal tissues, we tested slow cooling (1°C/min) with 10% dimethylsulfoxide (designated “cryopreservation”) and fast cooling (plunge in liquid nitrogen) with 20% dimethylsulfoxide and 20% ethylene glycol (“vitrification”). We compared fresh and preserved human cervicovaginal and colorectal tissues in a range of assays, including metabolic activity, human immunodeficiency virus infection, cell phenotype, tissue structure by hematoxylin-and-eosin staining, cell number and viability, production of cytokines, and microbicide drug concentrations. Metabolic activity, HIV infectability, and tissue structure were similar in cryopreserved and vitrified vaginal tissues. However, vitrification led to poor cell recovery from the colorectal mucosa, with 90% fewer cells recovered after isolation from vitrified colorectal tissues than from cryopreserved. HIV infection rates were similar for fresh and cryopreserved ectocervical tissues, whereas cryopreserved colorectal tissues were less easily infected than fresh tissues (hazard ratio 0.7 [95% confidence interval 0.4, 1.2]). Finally, we compared isolation of cells before and after cryopreservation. Cell recoveries were higher when cells were isolated after freezing and thawing (71% [59–84%]) than before (50% [38–62%]). Cellular function was similar to fresh tissue in both cases. Microbicide drug concentrations were lower in cryopreserved explants compared to fresh ones.

Conclusions

Cryopreservation of intact cervicovaginal and colorectal tissues with dimethylsulfoxide works well in a range of assays, while the utility of vitrification is more limited. Cell yields are higher from cryopreserved intact tissue pieces than from thawed cryopreserved single cell suspensions isolated before freezing, but T cell functions are similar.

Detection of HIV-1-specific gastrointestinal tissue resident CD8+ T-cells in chronic infection

Tissue-resident memory (TRM) CD8+ T-cells are non-recirculating, long-lived cells housed in tissues that can confer protection against mucosal pathogens. Human immunodeficiency virus-1 (HIV-1) is a mucosal pathogen and the gastrointestinal tract is an important site of viral pathogenesis and transmission. Thus, CD8+ TRM cells may be an important effector subset for controlling HIV-1 in mucosal tissues. This study sought to determine the abundance, phenotype, and functionality of CD8+ TRM cells in the context of chronic HIV-1 infection. We found that the majority of rectosigmoid CD8+ T-cells were CD69+CD103+S1PR1- and T-betLowEomesoderminNeg, indicative of a tissue-residency phenotype similar to that described in murine models. HIV-1-specific CD8+ TRM responses appeared strongest in individuals naturally controlling HIV-1 infection. Two CD8+ TRM subsets, distinguished by CD103 expression intensity, were identified. CD103Low CD8+ TRM primarily displayed a transitional memory phenotype and contained HIV-1-specific cells and cells expressing high levels of Eomesodermin, whereas CD103High CD8+ TRM primarily displayed an effector memory phenotype and were EomesoderminNeg. These findings suggest a large fraction of CD8+ T-cells housed in the human rectosigmoid mucosa are tissue-resident and that TRM contribute to the anti-HIV-1 immune response. Further exploration of CD8+ TRM will inform development of anti-HIV-1 immune-based therapies and vaccines targeted to the mucosa.

Resistance of HIV-infected macrophages to CD8+ T lymphocyte-mediated killing drives activation of the immune system

CD4⁺ T lymphocytes are the principal target of human immunodeficiency virus (HIV), but infected macrophages also contribute to viral pathogenesis. The killing of infected cells by CD8⁺ cytotoxic T lymphocytes (CTLs) leads to control of viral replication. Here we found that the killing of macrophages by CTLs was impaired relative to the killing of CD4⁺ T cells by CTLs, and this resulted in inefficient suppression of HIV. The killing of macrophages depended on caspase-3 and granzyme B, whereas the rapid killing of CD4⁺ T cells was caspase independent and did not require granzyme B. Moreover, the impaired killing of macrophages was associated with prolonged effector cell-target cell contact time and higher expression of interferon-γ by CTLs, which induced macrophage production of pro-inflammatory chemokines that recruited monocytes and T cells. Similar results were obtained when macrophages presented other viral antigens, suggestive of a general mechanism for macrophage persistence as antigen-presenting cells that enhance inflammation and adaptive immunity. Inefficient killing of macrophages by CTLs might contribute to chronic inflammation, a hallmark of chronic disease caused by HIV.

Differential Expression of CD8+ T Cell Cytotoxic Effector Molecules in Blood and Gastrointestinal Mucosa in HIV-1 Infection

We previously reported that CD8⁺ T cells in human gastrointestinal mucosa exhibit reduced perforin expression and weak or impaired cytotoxic capacity compared with their counterparts in blood. Nevertheless, these cells degranulate and express cytokines and chemokines in response to cognate Ag. In addition to weak expression of perforin, earlier studies suggested differential regulation of perforin and granzymes (Gzms), with GzmA and B expressed by significantly higher percentages of mucosal CD8⁺ T cells than perforin. However, this topic has not been fully explored. The goal of this study was to elucidate the expression and coexpression patterns of GzmA, B, and K in conjunction with perforin in rectosigmoid CD8⁺ T cells during HIV-1 infection. We found that expression of both perforin and GzmB, but not GzmA or GzmK, was reduced in mucosa compared with blood. A large fraction of rectosigmoid CD8⁺ T cells either did not express Gzms or were single-positive for GzmA. Rectosigmoid CD8⁺ T cells appeared skewed toward cytokine production rather than cytotoxic responses, with cells expressing multiple cytokines and chemokines generally lacking in perforin and Gzm expression. These data support the interpretation that perforin and Gzms are differentially regulated, and display distinct expression patterns in blood and rectosigmoid T cells. These studies may help inform the development of strategies to combat HIV-1 and other mucosal pathogens.

Predominance of weakly cytotoxic, T-betLowEomesNeg CD8+ T-cells in human gastrointestinal mucosa: implications for HIV infection

The gastrointestinal mucosa is an important site of HIV acquisition, viral replication, and pathogenesis. Immune cells in mucosal tissues frequently differ in phenotype and function from their non-mucosal counterparts. Although perforin-mediated cytotoxicity as measured in blood is a recognized correlate of HIV immune control, its role in gastrointestinal tissues is unknown. We sought to elucidate the cytotoxic features of rectal mucosal CD8⁺ T-cells in HIV infected and uninfected subjects. Perforin expression and lytic capacity were significantly reduced in rectal CD8⁺ T-cells compared with their blood counterparts, regardless of HIV clinical status; granzyme B (GrzB) was reduced to a lesser extent. Mucosal perforin and GrzB expression were higher in participants not on antiretroviral therapy compared with those on therapy and controls. Reduction in perforin and GrzB was not explained by differences in memory/effector subsets. Expression of T-bet and Eomesodermin was significantly lower in gut CD8⁺ T-cells compared with blood, and in vitro neutralization of TGF-β partially restored perforin expression in gut CD8⁺ T-cells. These findings suggest that rectal CD8⁺ T-cells are primarily non-cytotoxic, and phenotypically shaped by the tissue microenvironment. Further elucidation of rectal immune responses to HIV will inform the development of vaccines and immunotherapies targeted to mucosal tissues.

Higher Frequency of NK and CD4+ T-Cells in Mucosa and Potent Cytotoxic Response in HIV Controllers

HIV infection induces immune alterations, mainly in gut mucosa, where the main target cells reside. However, the evolution of the infection is variable among infected individuals, as evidenced by HIV controllers who exhibit low or undetectable viral load in the absence of treatment. The aim of this study was to evaluate the frequency, phenotype and activity of T and NK cells in peripheral blood and gut mucosa in a cohort of Colombian HIV controllers. Blood and gut biopsies were included. The frequency and the activation status of T and NK cells were performed by flow cytometry. In addition, Gag-stimulated CD8⁺ T-cells and cytokine-stimulated NK cells were tested for cytotoxic activity. Finally, microbial translocation was measured by plasma lipopolysaccharide quantification. Compared with HIV-progressors, HIV controllers exhibited higher frequency of CD4⁺ T and NK cells, and lower expression of activation molecules in blood and mucosal immune cells, as well as lower microbial translocation. An increased production of molecules associated with cytotoxic activity of CD8⁺ T-cells in blood and mucosa and a higher percentage of polyfunctional CD8⁺ T cells in blood were also observed in HIV controllers. In addition, an increased activity of NK cells was observed in blood. These findings suggest that HIV controllers have a potent immune response, mainly mediated by cytotoxic cells that control HIV replication, which contribute to reducing alterations at the gut mucosa.

Heterologous prime-boost regimens with a recombinant chimpanzee adenoviral vector and adjuvanted F4 protein elicit polyfunctional HIV-1-specific T-Cell responses in macaques

HIV-1-specific CD4+ and CD8+ T lymphocytes are important for HIV-1 replication control. F4/AS01 consists of F4 recombinant fusion protein (containing clade B Gag/p24, Pol/RT, Nef and Gag/p17) formulated in AS01 Adjuvant System, and was shown to induce F4-specific polyfunctional CD4+ T-cell responses in humans. While replication-incompetent recombinant HIV-1/SIV antigen-expressing human adenoviral vectors can elicit high-frequency antigen-specific CD8+ T-cell responses, their use is hampered by widespread pre-existing immunity to human serotypes. Non-human adenovirus serotypes associated with lower prevalence may offer an alternative strategy. We evaluated the immunogenicity of AdC7-GRN ('A'), a recombinant chimpanzee adenovirus type 7 vector expressing clade B Gag, RT and Nef, and F4/AS01 ('P'), when delivered intramuscularly in homologous (PP or AA) and heterologous (AAPP or PPAA) prime-boost regimens, in macaques and mice. Vaccine-induced HIV-1-antigen-specific T cells in peripheral blood (macaques), liver, spleen, and intestinal and genital mucosa (mice) were characterized by intracellular cytokine staining. Vaccine-specific IgG antibodies (macaques) were detected using ELISA. In macaques, only the heterologous prime-boost regimens induced polyfunctional, persistent and balanced CD4+ and CD8+ T-cell responses specific to each HIV-1 vaccine antigen. AdC7-GRN priming increased the polyfunctionality of F4/AS01-induced CD4+ T cells. Approximately 50% of AdC7-GRN-induced memory CD8+ T cells exhibited an effector-memory phenotype. HIV-1-specific antibodies were detected with each regimen. In mice, antigen-specific CD4+ and CD8+ T-cell responses were detected in the mucosal and systemic anatomical compartments assessed. When administered in heterologous prime-boost regimens, AdC7-GRN and F4/AS01 candidate vaccines acted complementarily in inducing potent and persistent peripheral blood HIV-1-specific CD4+ and CD8+ T-cell responses and antibodies in macaques. Besides, adenoviral vector priming modulated the cytokine-expression profile of the protein-induced CD4+ T cells. Each regimen induced HIV-1-specific T-cell responses in systemic/local tissues in mice. This suggests that prime-boost regimens combining adjuvanted protein and low-seroprevalent chimpanzee adenoviral vectors represent an attractive vaccination strategy for clinical evaluation.

Vaginal type-II mucosa is an inductive site for primary CD8⁺ T-cell mucosal immunity

The structured lymphoid tissues are considered the only inductive sites where primary T-cell immune responses occur. The naïve T cells in structured lymphoid tissues, once being primed by antigen-bearing dendritic cells, differentiate into memory T cells and traffic back to the mucosal sites through the bloodstream. Contrary to this belief, here we show that the vaginal type-II mucosa itself, despite the lack of structured lymphoid tissues, can act as an inductive site during primary CD8(+) T-cell immune responses. We provide evidence that the vaginal mucosa supports both the local immune priming of naïve CD8(+) T cells and the local expansion of antigen-specific CD8(+) T cells, thereby demonstrating a different paradigm for primary mucosal T-cell immune induction.

Induction of Potent and Long-Lived Antibody and Cellular Immune Responses in the Genitorectal Mucosa Could be the Critical Determinant of HIV Vaccine Efficacy

The field of HIV prevention has indeed progressed in leaps and bounds, but with major limitations of the current prevention and treatment options, the world remains desperate for an HIV vaccine. Sadly, this continues to be elusive, because more than 30 years since its discovery there is no licensed HIV vaccine. Research aiming to define immunological biomarkers to accurately predict vaccine efficacy have focused mainly on systemic immune responses, and as such, studies defining correlates of protection in the genitorectal mucosa, the primary target site for HIV entry and seeding are sparse. Clearly, difficulties in sampling and analysis of mucosal specimens, as well as their limited size have been a major deterrent in characterizing the type (mucosal antibodies, cytokines, chemokines, or CTL), threshold (magnitude, depth, and breadth) and viral inhibitory capacity of HIV-1-specific immune responses in the genitorectal mucosa, where they are needed to immediately block HIV acquisition and arrest subsequent virus dissemination. Nevertheless, a few studies document the existence of HIV-specific immune responses in the genitorectal mucosa of HIV-infected aviremic and viremic controllers, as well as in highly exposed persistently seronegative (HEPS) individuals with natural resistance to HIV-1. Some of these responses strongly correlate with protection from HIV acquisition and/or disease progression, thus providing significant clues of the ideal components of an efficacious HIV vaccine. In this study, we provide an overview of the key features of protective immune responses found in HEPS, elite and viremic controllers, and discuss how these can be achieved through mucosal immunization. Inevitably, HIV vaccine development research will have to consider strategies that elicit potent antibody and cellular immune responses within the genitorectal mucosa or induction of systemic immune cells with an inherent potential to home and persist at mucosal sites of HIV entry.

Phenotype and functionality of CD4+ and CD8+ T cells in the upper reproductive tract of healthy premenopausal women

PROBLEM

The goal of this study was to investigate the phenotype and functional responsiveness of CD4(+) and CD8(+) T-cells in the upper reproductive tract of healthy premenopausal women. The lower reproductive tract is frequently studied as a site of sexually transmitted infections; however, the upper reproductive tract may also be a portal of entry and dissemination for pathogens, including HIV-1.

METHOD OF STUDY

Endometrial biopsy, endocervical curettage, cytobrush, and blood were collected during mid-luteal phase from 23 healthy women. T-cells were isolated and analyzed by flow cytometry.

RESULTS

As compared with their counterparts in blood, endometrial and endocervical T-cells had enhanced CCR5 expression, and were enriched for activated, effector memory cells. Endometrial T-cells were more responsive to polyclonal stimuli, producing a broad range of cytokines and chemokines.

CONCLUSION

These findings underscore the responsiveness of endometrial T-cells to stimulation, and reveal their activated phenotype. These findings also suggest susceptibility of the upper reproductive tract to HIV-1 infection.

Longitudinal analysis of distribution and function of plasmacytoid dendritic cells in peripheral blood and gut mucosa of HIV infected patients

Aberrant activation of plasmacytoid dendritic cells (pDCs) with excessive production of interferon alpha (IFNα) represents one of the hallmarks of immune activation during chronic phase of human immunodeficiency virus (HIV) infection. A number of studies have shown that disruption of mucosal integrity in the gut is a cause of persistent immune activation. However, little is known about the role that pDCs play in this process, and our current understanding comes from the simian immunodeficiency virus macaque model. Thus, in the present study we sought to investigate the frequency and function of pDCs in peripheral blood and gut samples from HIV-infected individuals before and 6 months after initiation of antiretroviral therapy (ART). We show that circulating pDCs were depleted in ART-naive HIV+ patients, and upregulated the gut-homing receptor CD103 compared with uninfected controls. By converse, pDCs accumulated in the terminal ileum of ART-naive HIV individuals compared with controls. Baseline levels of IFNα production and markers of immune activation in gut samples of ART-naive HIV subjects were elevated. All these parameters declined after 6 months of ART. Our results suggest that in chronic HIV infection, pDCs migrate from peripheral blood to the gut-associated lymphatic tissue, where they may contribute to immune activation.

Prospective antiretroviral treatment of asymptomatic, HIV-1 infected controllers

The study of HIV-infected "controllers" who are able to maintain low levels of plasma HIV RNA in the absence of antiretroviral therapy (ART) may provide insights for HIV cure and vaccine strategies. Despite maintaining very low levels of plasma viremia, controllers have elevated immune activation and accelerated atherosclerosis. However, the degree to which low-level replication contributes to these phenomena is not known. Sixteen asymptomatic controllers were prospectively treated with ART for 24 weeks. Controllers had a statistically significant decrease in ultrasensitive plasma and rectal HIV RNA levels with ART. Markers of T cell activation/dysfunction in blood and gut mucosa also decreased substantially with ART. Similar reductions were observed in the subset of "elite" controllers with pre-ART plasma HIV RNA levels below conventional assays (<40 copies/mL). These data confirm that HIV replication persists in controllers and contributes to a chronic inflammatory state. ART should be considered for these individuals (ClinicalTrials.gov NCT01025427).

Incomplete normalization of regulatory t-cell frequency in the gut mucosa of Colombian HIV-infected patients receiving long-term antiretroviral treatment

INTRODUCTION

To evaluate the effect of late initiation of HAART and poor immune reconstitution on the frequency of regulatory T-cells (Treg) in the peripheral blood and gut of HIV-infected patients, we studied Colombian HIV-infected patients who had been on suppressive HAART for at least one year. They had undetectable viremia but were either immunological responders (HIR); (CD4 counts >500 cells/µl) or non-immunological responders (NIR); (CD4 T-cell count <300 cells/µl). Untreated HIV-infected patients and uninfected controls from the same region were also evaluated.

METHODS

Frequency and phenotype of regulatory T-cells (Treg) were analyzed in gut biopsies and blood samples. The functional effect of Treg depletion on CMV and HIV responses was determined. Markers of immune activation and circulating LPS levels were quantified.

RESULTS

Untreated patients exhibited high Treg frequency in PBMC and gut, and their Treg express high levels of CTLA-4 and PD-1. Although HAART significantly decreased mucosal Treg frequency, it did not normalize it in any of the treated groups (HIR and NIR patients). Treg normalization was observed in the blood of HIR patients following HAART, but did not occur in NIR patients. Treg from HIV-infected patients (treated or not) suppressed HIV and hCMV-specific T-cells from gut and blood. Plasma LPS levels and percentage of HLA-DR+CD38+ T-cells were significantly elevated in all infected groups compared to controls.

CONCLUSIONS

These findings suggest that control of viral replication is not sufficient to normalize gut Treg frequency in patients, independent of their response to HAART. Furthermore, persistence of functional Treg in the gut appears to be associated with the failure of HAART to repair mucosal damage.

CD8(+) T-cell effector function and transcriptional regulation during HIV pathogenesis

A detailed understanding of the immune response to human immunodeficiency virus (HIV) infection is needed to inform prevention and therapeutic strategies that aim to contain the acquired immunodeficiency syndrome (AIDS) pandemic. The cellular immune response plays a critical role in controlling viral replication during HIV infection and will likely need to be a part of any vaccine approach. The qualitative feature of the cellular response most closely associated with immunological control of HIV infection is CD8(+) T-cell cytotoxic potential, which is responsible for mediating the elimination of infected CD4(+) T cells. Understanding the underlying mechanisms involved in regulating the elicitation and maintenance of this kind of effector response can provide guidance for vaccine design. In this review, we discuss the evidence for CD8(+) T cells as correlates of protection, the means by which their antiviral capacity is evaluated, and transcription factors responsible for their function, or dysfunction, during HIV infection.

Administration of a Toll-like receptor 9 agonist decreases the proviral reservoir in virologically suppressed HIV-infected patients

Toll-like receptor (TLR) agonists can reactivate HIV from latently infected cells in vitro. We aimed to investigate the TLR-9 agonist, CPG 7909's in vivo effect on the proviral HIV reservoir and HIV-specific immunity. This was a post-hoc analysis of a double-blind randomized controlled vaccine trial. HIV-infected adults were randomized 1∶1 to receive pneumococcal vaccines with or without 1 mg CPG 7909 as adjuvant at 0, 3 and 9 months. In patients on suppressive antiretroviral therapy we quantified proviral DNA at 0, 3, 4, 9, and 10 months (31 subjects in the CPG group and 37 in the placebo-adjuvant group). Furthermore, we measured HIV-specific antibodies, characterized T cell phenotypes and HIV-specific T cell immunity. We observed a mean reduction in proviral DNA in the CPG group of 12.6% (95% CI: −23.6–0.0) following each immunization whereas proviral DNA in the placebo-adjuvant group remained largely unchanged (6.7% increase; 95% CI: −4.2–19.0 after each immunization, p = 0.02). Among participants with additional cryo-preserved PBMCs, HIV-specific CD8+ T cell immunity as indicated by increased expression of degranulation marker CD107a and macrophage inflammatory protein 1β (MIP1β) tended to be up-regulated following immunization with CPG 7909 compared with placebo as adjuvant. Further, increasing proportion of HIV-specific CD107a and MIP1β-expressing CD8+ T cells were strongly correlated with decreasing proviral load. No changes were observed in T cell phenotype distribution, HIV-specific CD4+ T cell immunity, or HIV-specific antibodies. TLR9-adjuvanted pneumococcal vaccination decreased proviral load. Reductions in proviral load correlated with increasing levels of HIV specific CD8+ T cells. Further investigation into the potential effect of TLR9 agonists on HIV latency is warranted.

Cell-Mediated Immunity in Elite Controllers Naturally Controlling HIV Viral Load

The natural course of human immunodeficiency virus (HIV) infection is characterized by high viral load, depletion of immune cells, and immunodeficiency, ultimately leading to acquired immunodeficiency syndrome phase and the occurrence of opportunistic infections and diseases. Since the discovery of HIV in the early 1980s a naturally selected population of infected individuals has been emerged in the last years, characterized by being infected for many years, with viremia constantly below detectable level and poor depletion of immune cells. These individuals are classified as “elite controllers (EC) or suppressors” and do not develop disease in the absence of anti-retroviral therapy. Unveiling host factors and immune responses responsible for the elite status will likely provide clues for the design of therapeutic vaccines and functional cures. Scope of this review was to examine and discuss differences of the cell-mediated immune responses between HIV+ individuals with disease progression and EC.

Impact of highly active antiretroviral therapy initiation on CD4(+) T-cell repopulation in duodenal and rectal mucosa

OBJECTIVE

The objective of this study was to assess the effects of HAART initiation on CD4(+) T-cell repopulation and T-cell immune activation in rectal and duodenal mucosa.

DESIGN

The effects of HAART on the gastrointestinal tract remain controversial, and studies have reached different conclusions regarding its effectiveness at restoring mucosal CD4(+) T cells depending upon time of initiation, duration of treatment and gastrointestinal tract region studied.

METHODS

We obtained blood, rectal biopsies and duodenal biopsies from 14 chronically infected individuals at baseline and at 4-9 months post-HAART initiation. We examined CD4(+) T-cell frequencies in blood, rectum and duodenum at both time points, and performed a detailed assessment of CD4(+) T-cell phenotype, immune activation marker expression and HIV-specific CD8(+) T-cell responses in blood and rectal mucosa.

RESULTS

CD4(+) T-cell percentages increased significantly in blood, rectal and duodenal mucosa after 4-9 months of HAART (P = 0.02, 0.0005, 0.0002), but remained lower than in uninfected controls. HIV-specific CD8(+) T-cell responses in blood and rectal mucosa declined following HAART initiation (P = 0.0015, 0.021). CD8(+) T-cell coexpression of CD38 and HLA-DR in blood and mucosa, as well as plasma sCD14, declined significantly. CD28 expression on blood and mucosal CD8(+) T cells increased, whereas programmed death receptor-1 expression on blood HIV-specific CD4(+) and CD8(+) T cells decreased.

CONCLUSION

Within the first months of HAART, limited CD4(+) T-cell reconstitution occurs in small and large intestinal mucosa. Nevertheless, decreased immune activation and increased CD28 expression suggest rapid immunological benefits of HAART despite incomplete CD4(+) T-cell reconstitution.

HIV-specific CD8+ T cells from elite controllers are primed for survival

HIV-specific cytotoxic T lymphocytes (CTL) are preferentially primed for apoptosis, and this may represent a viral escape mechanism. We hypothesized that HIV-infected individuals that control virus to undetectable levels without antiretroviral therapy (ART) (elite controllers [EC]) have the capacity to upregulate survival factors that allow them to resist apoptosis. To address this, we performed cross-sectional and longitudinal analysis of proapoptotic (cleaved caspase-3) and antiapoptotic (Bcl-2) markers of cytomegalovirus (CMV) and HIV-specific CD8 T cells in a cohort of HIV-infected subjects with various degrees of viral control on and off ART. We demonstrated that HIV-specific CTL from EC are more resistant to apoptosis than those with pharmacologic control (successfully treated patients [ST]), despite similar in vivo conditions. Longitudinal analysis of chronically infected persons starting ART revealed that the frequency of HIV-specific T cells prone to death decreased, suggesting that this phenotype is partially reversible even though it never achieves the levels present in EC. Elucidating the apoptotic factors contributing to the survival of CTL in EC is paramount to our development of effective HIV-1 vaccines. Furthermore, a better understanding of cellular markers that can be utilized to predict response durability in disease- or vaccine-elicited responses will advance the field.

Human immunodeficiency virus and the gastrointestinal immune system: does highly active antiretroviral therapy restore gut immunity?

While only partial immune reconstitution in gut-associated lymphoid tissue typically occurs following initiation of highly active antiretroviral therapy (HAART) in human immunodeficiency virus (HIV) infection, near-complete immune reconstitution has occasionally been described. This review highlights findings from studies examining the effects of HAART and the timing of its initiation on gastrointestinal (GI) CD4+ T-cell recovery. Its effects on specific CD4+ T-cell subtypes, CD8+ T cells, natural killer cells, and immunoglobulins are also described. Finally, the ability of HAART to restore the intestinal epithelial barrier and lymphatic tissue architecture and reduce microbial translocation is addressed. Determining whether HAART has the ability to prevent permanent GI immune damage when commenced in acute HIV infection has implications for the optimal timing of HAART initiation.

Large intestine-targeted, nanoparticle-releasing oral vaccine to control genitorectal viral infection

Both rectal and vaginal mucosal surfaces serve as transmission routes for pathogenic microorganisms. Vaccination through large intestinal mucosa, previously proven protective for both of these mucosal sites in animal studies, can be achieved successfully by direct intracolorectal (i.c.r.) administration, but this route is clinically impractical. Oral vaccine delivery seems preferable but runs the risk of the vaccine's destruction in the upper gastrointestinal tract. Therefore, we designed a large intestine-targeted oral delivery with pH-dependent microparticles containing vaccine nanoparticles, which induced colorectal immunity in mice comparably to colorectal vaccination and protected against rectal and vaginal viral challenge. Conversely, vaccine targeted to the small intestine induced only small intestinal immunity and provided no rectal or vaginal protection, demonstrating functional compartmentalization within the gut mucosal immune system. Therefore, using this oral vaccine delivery system to target the large intestine, but not the small intestine, may represent a feasible new strategy for immune protection of rectal and vaginal mucosa.

Measurements of immune responses for establishing correlates of vaccine protection against HIV

Well-defined correlates of protective immunity are an essential component of rational vaccine development. Despite years of basic science and three HIV vaccine efficacy trials, correlates of immunological protection from HIV infection remain undefined. In December 2010, a meeting of scientists engaged in basic and translational work toward developing HIV-1 vaccines was convened. The goal of this meeting was to discuss current opportunities and optimal approaches for defining correlates of protection, both for ongoing and future HIV-1 vaccine candidates; specific efforts were made to engage young scientists. We discuss here the highlights from the meeting regarding the progress made and the way forward for a protective HIV-1 vaccine.

The HIV-1 transactivator factor (Tat) induces enterocyte apoptosis through a redox-mediated mechanism

The intestinal mucosa is an important target of human immunodeficiency virus (HIV) infection. HIV virus induces CD4+ T cell loss and epithelial damage which results in increased intestinal permeability. The mechanisms involved in nutrient malabsorption and alterations of intestinal mucosal architecture are unknown. We previously demonstrated that HIV-1 transactivator factor (Tat) induces an enterotoxic effect on intestinal epithelial cells that could be responsible for HIV-associated diarrhea. Since oxidative stress is implicated in the pathogenesis and morbidity of HIV infection, we evaluated whether Tat induces apoptosis of human enterocytes through oxidative stress, and whether the antioxidant N-acetylcysteine (NAC) could prevent it. Caco-2 and HT29 cells or human intestinal mucosa specimens were exposed to Tat alone or combined with NAC. In an in-vitro cell model, Tat increased the generation of reactive oxygen species and decreased antioxidant defenses as judged by a reduction in catalase activity and a reduced (GSH)/oxidized (GSSG) glutathione ratio. Tat also induced cytochrome c release from mitochondria to cytosol, and caspase-3 activation. Rectal dialysis samples from HIV-infected patients were positive for the oxidative stress marker 8-hydroxy-2'-deoxyguanosine. GSH/GSSG imbalance and apoptosis occurred in jejunal specimens from HIV-positive patients at baseline and from HIV-negative specimens exposed to Tat. Experiments with neutralizing anti-Tat antibodies showed that these effects were direct and specific. Pre-treatment with NAC prevented Tat-induced apoptosis and restored the glutathione balance in both the in-vitro and the ex-vivo model. These findings indicate that oxidative stress is one of the mechanism involved in HIV-intestinal disease.

CD4 T cell depletion at the cervix during HIV infection is associated with accumulation of terminally differentiated T cells

In blood, the accumulation of terminally differentiated (TD) T cells during HIV infection is associated with CD4 T cell loss and HIV disease progression. Here, we investigated the maintenance and functional characteristics of memory T cells at the cervix. We found that CD4 T cell depletion at the cervix mirrors CD4 depletion in blood. In all women, depletion of CD4 T cells at the cervix was associated with significant reductions in CD45RA- CCR7+ (central memory [CM]) T cells and the accumulation of CD45RA+ CCR7- (TD T cells). We determined whether inflammation in the genital tract was associated with the local differentiation of T cells at the cervix. In uninfected women, genital tract inflammation was associated with the accumulation of CD45RA- CCR7+ CM CD4 T cells and reduced frequencies of CD45RA+ CCR7- TD cells at the cervix. This finding may reflect the fact that, in the absence of HIV infection, TD T cells may be slowly lost in the presence of genital inflammation, while CD45RA- CCR7+ CM T cells are recruited to replenish the diminishing CD4 T cell pool. Following global stimulation with phorbol myristate acetate (PMA)-ionomycin, we noted a significant interleukin 2 (IL-2) deficit in both cervical and blood CD4 T cells from HIV-infected women compared to uninfected women, while gamma interferon (IFN-γ) production was similar, irrespective of HIV status. Few HIV-infected women had detectable IFN-γ and IL-2 HIV-specific T cell responses at the cervix, and these responses were significantly lower in magnitude than the corresponding responses in blood. These data suggest that CD4 depletion was associated with the accumulation of terminally differentiated T cell phenotypes at the cervical mucosa defective in their ability to produce IL-2. CD4 depletion and compromised immunity at the cervix may be accompanied by progressive decline of central memory-like T cells and development of T cells toward terminally differentiated phenotypes.

CD8(+)T-cell-mediated control of HIV-1 and SIV infection

A detailed understanding of the cellular response to human immunodeficiency virus (HIV-1) infection is needed to inform prevention and therapeutic strategies that aim to contain the AIDS pandemic. The cellular immune response plays a critical role in reducing viral load in HIV-1 infection and in the nonhuman primate model of SIV infection. Much of this virus suppressive activity has been ascribed to CD8(+)T-cell-directed cytolysis of infected CD4(+)T cells. However, emerging evidence suggests that CD8(+)T cells can maintain a lowered viral burden through multiple mechanisms. A thorough understanding of the CD8(+)T-cell functions in HIV-1 infection that correlate with viral control, the populations responsible for these functions, and the elicitation and maintenance of these responses can provide guidance for vaccine design and potentially the development of new classes of antiretroviral therapies. In this review, we discuss the CD8(+)T-cell correlates of protection in HIV-1 and SIV infection and recent advances in this field.

Mucosal immunity in HIV controllers: the right place at the right time

PURPOSE OF REVIEW

The phenomenon of long-term nonprogression in HIV infection has been recognized for some time, and the ability of rare individuals, designated 'elite controllers', to control HIV in the absence of therapy is the focus of numerous ongoing studies. This review focuses on studies of HIV-specific immune responses in mucosal tissues as a potential correlate of immune control, with an emphasis on recently published work.

RECENT FINDINGS

Genetic studies have implicated a role for elements localized to the major histocompatibility complex (MHC) on chromosome 6 in the immune control of HIV infection. In parallel, functional studies have strongly implicated MHC class I-restricted, CD8+ T-cell responses as a major contributor to elite control. In addition, the localization of HIV-specific CD8+ and CD4+ T cells with respect to the major sites of virus replication in the body may be critical in determining clinical outcome.

SUMMARY

Recent findings suggest that MHC class I-restricted, CD8+ T cells are a major component of immune control in 'elite controllers'. In addition, the presence of these effector cells at or near critical viral reservoirs, such as mucosal tissues, may be critical in determining their effectiveness at limiting viral replication and dissemination.

A randomized, controlled trial of raltegravir intensification in antiretroviral-treated, HIV-infected patients with a suboptimal CD4+ T cell response

BACKGROUND

Some human immunodeficiency virus (HIV)-infected individuals are not able to achieve a normal CD4(+) T cell count despite prolonged, treatment-mediated viral suppression. We conducted an intensification study to assess whether residual viral replication contributes to replenishment of the latent reservoir and whether mucosal HIV-specific T cell responses limit the reservoir size.

METHODS

Thirty treated subjects with CD4(+) T cell counts of <350 cells/mm(3) despite viral suppression for ≥ 1 year were randomized to add raltegravir (400 mg twice daily) or matching placebo for 24 weeks. The primary end points were the proportion of subjects with undetectable plasma viremia (determined using an ultrasensitive assay with a lower limit of detection of <.3 copy/mL) and a change in the percentage of CD38(+)HLA-DR(+)CD8(+) T cells in peripheral blood mononuclear cells (PBMCs).

RESULTS

The proportion of subjects with undetectable plasma viremia did not differ between the 2 groups (P = .42). Raltegravir intensification did not have a significant effect on immune activation or HIV-specific responses in PBMCs or gut-associated lymphoid tissue.

CONCLUSIONS

Low-level viremia is not likely to be a significant cause of suboptimal CD4(+) T cell gains during HIV treatment.

CLINICAL TRIALS REGISTRATION

NCT00631449.

Relationship between functional profile of HIV-1 specific CD8 T cells and epitope variability with the selection of escape mutants in acute HIV-1 infection

In the present study, we analyzed the functional profile of CD8⁺ T-cell responses directed against autologous transmitted/founder HIV-1 isolates during acute and early infection, and examined whether multifunctionality is required for selection of virus escape mutations. Seven anti-retroviral therapy-naïve subjects were studied in detail between 1 and 87 weeks following onset of symptoms of acute HIV-1 infection. Synthetic peptides representing the autologous transmitted/founder HIV-1 sequences were used in multiparameter flow cytometry assays to determine the functionality of HIV-1-specific CD8⁺ T memory cells. In all seven patients, the earliest T cell responses were predominantly oligofunctional, although the relative contribution of multifunctional cell responses increased significantly with time from infection. Interestingly, only the magnitude of the total and not of the poly-functional T-cell responses was significantly associated with the selection of escape mutants. However, the high contribution of MIP-1β-producing CD8⁺ T-cells to the total response suggests that mechanisms not limited to cytotoxicity could be exerting immune pressure during acute infection. Lastly, we show that epitope entropy, reflecting the capacity of the epitope to tolerate mutational change and defined as the diversity of epitope sequences at the population level, was also correlated with rate of emergence of escape mutants.

An important role for the polyfunctional T-cell fraction of anti-HIV CD8 responses during chronic HIV infection has previously been suggested. This study characterized the role of polyfunctional T-cells directed against the transmitted/founder virus in the selection of viral escape mutants during acute HIV-1 infection within a unique cohort of individuals recruited within 3 weeks from the onset of symptoms at the time when the virus load was still declining. For the first time, the sequences of the transmitted/founder virus isolated from each patient were used. Interestingly, polyfunctionality was not found to be a pre-requisite for selection of escape mutations. A novel significant correlation is found between the order of appearance of escape mutations in different epitope sequences and both the magnitude of the CD8⁺ T-cell responses and the degree of entropy of the individual epitopes. A high proportion of the T-cells participating in the total response produced MIP-1β, suggesting that mechanisms not limited to the killing of infected cells might play a relevant role in early infection. This highlights the importance of measuring the quality of the CD8⁺ lymphocyte response and the sequence of the transmitted virus isolates to better understand the mechanisms of control of HIV replication during acute infection.

Impaired memory CD8 T cell responses against an immunodominant retroviral cryptic epitope

The immunodominant cryptic epitope SYNTGRFPPL, encoded within open reading frame 2 of the LP-BM5 retroviral gag gene, is critical for protection against retroviral-induced pathogenesis. The goal of this study was to dissect the memory response against this unique immunodominant cryptic epitope. Unlike the protective acute effector population of SYNTGRFPPL-specific CD8 T cells, long-lived SYNTGRFPPL-specific CD8 T cells lacked the ability to protect susceptible mice infected with LP-BM5 retrovirus. Compared to memory CD8 T cells against a conventional epitope with similar MHC-I specificity, primed and restimulated using similar conditions, long-lived SYNTGRFPPL-specific CD8 T cells were impaired in their ability to recall against antigen, with reduced cytolytic capabilities and cytokine production. Since similar priming and restimulation regimes were utilized to generate each effector CD8 T cell population, this study has potentially broad implications with regard to the selection criteria of potent, highly conserved cryptic epitopes for use in epitope-based vaccines.

Immune responses to HIV and SIV in mucosal tissues: 'location, location, location'

PURPOSE OF REVIEW

This review summarizes research literature regarding mucosal immunity to HIV and simian immunodeficiency virus (SIV), with an emphasis on work published within the past 18 months.

RECENT FINDINGS

Notable recent studies have focused on the pivotal events occurring within mucosal tissues during acute HIV/SIV infection that serve to establish a balance between detrimental immune activation and beneficial adaptive responses. In cervicovaginal mucosa, an early inflammatory response leads to recruitment of susceptible target cells. At this acute stage, the in-vivo ratio between CD8 effector cells and infected CD4 T-cells may be critical for limiting viral dissemination. Acute infection is also accompanied by loss of germinal center architecture and T/B cell apoptosis in Peyer's patches of the gastrointestinal tract. During chronic infection, mucosal CD8 T-cells may play a role in immune control, as suggested by studies of elite controllers.

SUMMARY

Mucosal tissues serve as the major portal of entry for HIV, and house a majority of the body's lymphocytes, including CD4 T-cells that are targets for infection. Recent studies have focused renewed attention on events occurring immediately after transmission, and underscore the concept that the balance between inflammation and protective immunity is established by host responses in mucosal tissues.

HIV controllers with HLA-DRB1*13 and HLA-DQB1*06 alleles have strong, polyfunctional mucosal CD4+ T-cell responses

A small percentage of human immunodeficiency virus (HIV)-infected individuals, termed elite controllers, are able to spontaneously control HIV replication in blood. As the gastrointestinal mucosa is an important site of HIV transmission and replication as well as CD4+ T-cell depletion, it is important to understand the nature of the immune responses occurring in this compartment. Although the role of the HIV-specific CD8+ T-cell responses in mucosal tissues has been described, few studies have investigated the role of mucosal HIV-specific CD4+ T cells. In this study, we assessed HIV-specific CD4+ T-cell responses in the rectal mucosa of 28 "controllers" (viral load [VL] of <2,000 copies/ml), 14 "noncontrollers" (VL of >10,000 copies/ml), and 10 individuals on highly active antiretroviral therapy (HAART) (VL of <75 copies/ml). Controllers had higher-magnitude Gag-specific mucosal CD4+ T-cell responses than individuals on HAART (P<0.05), as measured by their ability to produce gamma interferon (IFN-γ), interleukin-2 (IL-2), tumor necrosis factor alpha (TNF-α), and macrophage inflammatory protein 1β (MIP-1β). The frequency of polyfunctional mucosal CD4+ T cells was also higher in controllers than in noncontrollers or individuals on HAART (P<0.05). Controllers with the strongest HIV-specific CD4+ T-cell responses possessed class II HLA alleles, HLA-DRB1*13 and/or HLA-DQB1*06, previously associated with a nonprogression phenotype. Strikingly, individuals with both HLA-DRB1*13 and HLA-DQB1*06 had highly polyfunctional mucosal CD4+ T cells compared to individuals with HLA-DQB1*06 alone or other class II alleles. The frequency of polyfunctional CD4+ T cells in rectal mucosa positively correlated with the magnitude of the mucosal CD8+ T-cell response (Spearman's r=0.43, P=0.005), suggesting that increased CD4+ T-cell "help" may be important in maintaining strong CD8+ T-cell responses in the gut of HIV controllers.

Persistence of genital tract T cell responses in HIV-infected women on highly active antiretroviral therapy

Initiation of highly active antiretroviral therapy (HAART) for HIV-infected individuals is associated with control of viremia, improved CD4 counts, and declining systemic HIV-specific immune responses. While HAART effectively reduces plasma viremia, it remains unclear how effectively antiretroviral drugs reach mucosal surfaces, such as those of the genital tract. The aim of this study was to determine the effect of HAART on genital tract CD4 T cell reconstitution, HIV shedding, and HIV-specific T cell responses. Cervical cytobrush and blood specimens were obtained from 35 HIV-infected, HAART-naïve women and 27 women on HAART in order to investigate HIV Gag-specific T cell responses by intracellular gamma interferon (IFN-γ) staining. Interleukin 1β (IL-1β), IL-6, and IL-8 concentrations were measured by enzyme-linked immunosorbent assays (ELISA). We show that for HIV-infected women, HAART is associated with significantly improved CD4 T cell counts both in blood and at the cervix. While HAART effectively suppressed both blood and cervical viremia, HIV-specific CD8 T cell responses in blood were lost, while those at the cervix were preserved.

Immunodominant HIV-specific CD8+ T-cell responses are common to blood and gastrointestinal mucosa, and Gag-specific responses dominate in rectal mucosa of HIV controllers

Previous studies have suggested that polyfunctional mucosal CD8(+) T-cell responses may be a correlate of protection in HIV controllers. Mucosal T-cell breadth and/or specificity may also contribute to defining protective responses. In this study, rectal CD8(+) T-cell responses to HIV Gag, Env, and Nef were mapped at the peptide level in four subject groups: elite controllers (n = 16; viral load [VL], <75 copies/ml), viremic controllers (n = 14; VL, 75 to 2,000 copies/ml), noncontrollers (n = 14; VL, >10,000 copies/ml), and antiretroviral-drug-treated subjects (n = 8; VL, <75 copies/ml). In all subject groups, immunodominant CD8(+) T-cell responses were generally shared by blood and mucosa, although there were exceptions. In HIV controllers, responses to HLA-B27- and HLA-B57-restricted epitopes were common to both tissues, and their magnitude (in spot-forming cells [SFC] per million) was significantly greater than those of responses restricted by other alleles. Furthermore, peptides recognized by T cells in both blood and rectal mucosa, termed "concordant," elicited higher median numbers of SFC than discordant responses. In magnitude as well as breadth, HIV Gag-specific responses, particularly those targeting p24 and p7, dominated in controllers. Responses in noncontrollers were more evenly distributed among epitopes in Gag, Env, and Nef. Viremic controllers showed significantly broader mucosal Gag-specific responses than other groups. Taken together, these findings demonstrate that (i) Gag-specific responses dominate in mucosal tissues of HIV controllers; (ii) there is extensive overlap between CD8(+) T cells in blood and mucosal tissues, with responses to immunodominant epitopes generally shared by both sites; and (iii) mucosal T-cell response breadth alone cannot account for immune control.

Towards developing standardized protocols for evaluation of cellular mucosal immune responses - Recommendations from a DAIDS/NIH workshop, June 15-16, 2009

Although 80% of HIV infections occur through mucosal routes and vaccine strategies need to be designed for inducing protective immune responses at the site of the viral entry, it has proven to be very challenging to measure these responses. A 2-day workshop was convened by Division of AIDS, National Institutes of Health on June 15-16, 2009 to address the challenges encountered in the evaluation of mucosal T cell immune responses. The goal of the workshop was to obtain recommendations/consensus for developing standardized protocols for the assessment of mucosal immunity. This report summarizes the areas of consensus and recommendations that should assist in developing standardized methodologies for the evaluation of mucosal immune responses.

Quality of the transgene-specific CD8+ T cell response induced by adenoviral vector immunization is critically influenced by virus dose and route of vaccination

Adenoviral vectors have been widely used for experimental gene therapy and vaccination, yet there is a surprising lack of knowledge connecting the route and dose of adenovirus administration to the induced transgene-specific immune response. We have recently demonstrated polyfunctional CD8(+) T cells and protective memory responses using adenoviral vectors, which seem to contrast with recent reports suggesting that an exhausted CD8(+) T cell phenotype is induced by inoculation with adenoviral vectors. Accordingly, we investigated the route and dose interrelationship for transgene-specific CD8(+) T cells using adenoviral vectors encoding beta-galactosidase applied either s.c. or i.v. Irrespective of the route of inoculation, most of the adenoviral inoculum was found to disseminate systemically as the dose was raised beyond 10(9) particles. The number of transgene-specific CD8(+) T cells correlated positively with dissemination, whereas the functional capacity of the generated T cells correlated inversely with vector dissemination. A comparison of the immune response to s.c. or i.v. administration at moderate doses revealed that inoculation by both routes induced a transient peak of IFN-gamma-producing CD8(+) T cells 2 to 3 wk postinfection, but following i.v. administration, these cells were only detected in the liver. Two to four months after systemic, but not peripheral, immunization, dysfunctional transgene-specific CD8(+) T cells impaired in both cytokine production and important in vivo effector functions, accumulated in the spleen. These findings indicate that the localization of the adenoviral inoculum and not the total Ag load determines the quality of the CD8(+) T cell response induced with adenoviral vaccines.

HIV Infection and Gut Mucosal Immune Function: Updates on Pathogenesis with Implications for Management and Intervention

HIV is primarily a sexually transmitted infection. However, given that the gastrointestinal tract (GIT) houses most of the body’s lymphocytes, including activated memory CD4⁺ T cells that are preferential targets for HIV, recent research has focused on the role of the GIT in transmission and pathogenesis. In health, the GIT maintains a balance between immune tolerance and rapid responsiveness. A complex network of innate and adaptive responses maintains this balance, which is severely perturbed in HIV infection. Recent studies have focused on mechanisms of GIT CD4⁺ T-cell depletion and epithelial disruption in HIV infection, the role of inflammation in accelerating viral dissemination, the kinetics of the adaptive response following transmission, and the extent of T-cell reconstitution following antiretroviral therapy. This review summarizes the results of recent investigations that may have important implications for the development of vaccines, microbicides, and therapeutic interventions for HIV and other mucosal pathogens.

CTL quality and the control of human retroviral infections

The CTL response plays a central part in deciding the outcome of viral infections. Evidence from host and viral genetics, gene expression microarrays and assays of T-cell phenotype and function indicate that individual differences in the efficiency of the virus-specific CTL response strongly determine the outcome of infection with the human retroviruses HTLV-1 and HIV-1. It is now believed that differences in anti-viral CTL efficiency or "quality" at the single-cell level are critical in determining the efficacy of the host response to viruses. However, it is difficult to identify and quantify the reasons for this apparent individual variation in CTL efficiency, because of the chronic course of infection and the dynamical complexity of the equilibrium that is established between the virus and the host immune response. Specifically, it is unclear whether the observed variations among infected hosts, i.e. in the frequency, phenotype and function or quality of T cells, are the causes or effects - or both - of the variation in the efficiency of virus control.

An African perspective on mucosal immunity and HIV-1

HIV prevention mandates an understanding of the mechanisms of mucosal immunity with attention to some unique features of the epidemic and mucosal environment in the developing world. An effective vaccine will have to induce mucosal protection against a highly diverse virus, which is equipped with a number of immune evasion strategies. Its development will require assessment of mucosal immune responses, and it will have to protect a mucosal environment where inflammation and altered immune responses are common because of the presence of other mucosal infections, such as sexually transmitted infections and parasites, and where nutritional status may also be compromised. Ideally, not only prevention methods would protect adults but also provide cover against gastrointestinal transmission through maternal milk. Prevention might also be complemented by microbicides and circumcision, two alternative approaches to mucosal protection. It seems unlikely that a single solution will work in all instances and intervention might have to act at multiple levels and be tailored to local circumstances. We review here some of the mucosal events associated with HIV infection that are most relevant in an African setting.

Mucosal T-cell responses to HIV: responding at the front lines

Mucosal surfaces of the body serve as the major portal of entry for human immunodeficiency virus (HIV). These tissues also house a majority of the body's lymphocytes, including the CD4(+) T cells that are the major cellular target for HIV infection. Mucosal surfaces are defended by innate and adaptive immune mechanisms, including secreted antibodies and CD8(+) cytotoxic T cells (CTL). CTL in mucosal lymphoid tissues may serve to limit viral replication, decreasing the host's viral burden as well as reducing the likelihood of sexual transmission to a naïve host. This review summarizes recent literature on HIV-specific T-cell responses in mucosal tissues, with an emphasis on the gastrointestinal tract.

Mucosal immune responses to HIV-1 in elite controllers: a potential correlate of immune control

There exists a unique group of persons who are able to durably control HIV in the absence of therapy. The mechanisms of control in these persons remain poorly defined. In this study, we examined CD8(+) T-cell responses in blood and rectal mucosa from 17 "elite controllers" (viral load < 75 copies/mL), 11 "viremic controllers" (75-2000 copies/mL), 14 noncontrollers (> 10,000 copies/mL), and 10 antiretroviral-treated persons (< 75 copies/mL). Production of interferon-gamma, interleukin-2, tumor necrosis factor-alpha, macrophage inflammatory protein-1 beta, and CD107a by CD8(+) T cells in response to HIV-1 Gag stimulation was measured using flow cytometry. Our hypothesis was that "polyfunctional" T cells producing multiple antiviral factors would be most abundant in mucosal tissues of HIV controllers. Mucosal CD8(+) T-cell responses were significantly stronger and more complex in controllers than in antiretroviral-suppressed persons (P = .0004). The frequency of 4-function responses in rectal mucosa was higher in controllers than in noncontrollers and patients on therapy (P < .0001). Mucosal responses in controllers were frequently stronger and more complex than blood responses. These findings demonstrate that many controllers mount strong, complex HIV-specific T-cell responses in rectal mucosa. These responses may play an important role in mucosal immune surveillance, as suggested by their relative enrichment among persons who control HIV in the absence of therapy.