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Special Report For reprint orders, please contact: [email protected] Biomarkers of immune dysfunction following combination antiretroviral therapy for HIV infection Combination antiretroviral therapy (cART) has significantly reduced morbidity and mortality of HIV‑infected patients, yet their life expectancy remains reduced compared with the general population. Most HIV‑infected patients receiving cART have some persistent immune dysfunction characterized by chronic immune activation and premature aging of the immune system. Here we review biomarkers of T‑cell activation (CD69, -25 and -38, HLA-DR, and soluble CD26 and -30); generalized immune activation (C‑reactive protein, IL‑6 and D‑dimer); microbial translocation (lipopolysaccharide, 16S rDNA, lipopolysaccharide-binding protein and soluble CD14); and immune dysfunction of specific cellular subsets (T cells, natural killer cells and monocytes) in HIV-infected patients on cART and their relationship to adverse clinical outcomes including impaired CD4 T-cell recovery, as well as non-AIDS clinical events, such as cardiovascular disease. KEYWORDS: antiretroviral therapy n HIV n immune activation n immune dysfunction n immune senescence n microbial translocation n non-AIDS illness A large number of biomarkers have been evaluated in HIV-infected patients and have largely been used to predict clinical outcome, including AIDS and death. Given the widespread availability of combination antiretroviral therapy (cART) and the ability of cART to reduce morbidity and mortality, this article primarily focuses on biomarkers of interest in HIV-infected patients receiving cART, with an emphasis on the effect of microbial translocation and immune activation. Following cART, many patients continue to demonstrate ongoing immune abnormalities and patients are at an increased risk of non-AIDS events including cardiovascular disease (CVD) and malignancy. Some of these biomarkers are in early clinical development while others have been evaluated in larger clinical trials and cohorts to determine whether they can predict adverse clinical outcomes in patients on cART. Most of these biomarkers are not yet used in routine clinical practice but are currently being evaluated to understand the pathogenesis of immune dysfunction in patients on cART, identify patients at highest risk of immune dysfunction and nonAIDS events, such as CVD and malignancy, and develop novel immunotherapeutic approaches that could be used in addition to cART. HIV pathogenesis & response to cART The physiological hallmark of HIV infection is the destruction of CD4 + T cells and persistent immune activation. HIV predominantly infects activated CD4 + T cells, resulting in productive viral infection [1] , and a rapid and profound depletion of GI tract-associated CD4 + T cells, leading to loss of integrity of the intestinal mucosa [2,3] . The depletion of GI tract CD4 + T cells has been associated with increased translocation of microbial products from the intestinal lumen into the blood stream, which can trigger the innate immune system to produce proinflammatory cytokines and chronic immune activation [3] . However, the pathogenesis of immune activation is complex and multifactorial. In addition to the translocation of microbial products, immune activation is believed to be driven by direct infection of CD4 + T cells and release of cytokines, a combination of innate and adaptive immune responses against viral antigens and/or secondary infections, and an imbalance in the immune response caused by the loss of T regulatory and central memory T cells (reviewed in [4]). Combination antiretroviral therapy has led to a dramatic reduction in mortality and morbidity in HIV-infected patients [5,6] . Despite long-term suppression of HIV RNA and recovery of the total number of CD4 + T cells in most patients following cART, full life expectancy of patients is restored in some [7] , but not all, patients [6,8] . The chance of an HIV-infected patient reaching the age of 70 years is still approximately 50% that of HIV-uninfected controls [8] . HIVinfected patients experience higher rates of CVD, non-AIDS malignancies, dementia, liver 10.2217/BMM.11.15 © 2011 Future Medicine Ltd Biomarkers Med. (2011) 5(2), 171–186 Gregor F Lichtfuss1,2, Jennifer Hoy2,3, Reena Rajasuriar1,2,4, Marit Kramski5, Suzanne M Crowe1,2,3 & Sharon R Lewin†1,2,3 Centre for Virology, Burnet Institute, Melbourne, Australia 2 Department of Medicine, Monash University, Melbourne, Australia 3 Infectious Diseases Unit, The Alfred Hospital, Melbourne, Australia 4 Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia 5 Department of Microbiology & Immunology, University of Melbourne, Melbourne, Australia † Author for correspondence: Tel.: +61 390 768 491 [email protected] 1 ISSN 1752-0363 171 Special Report Lichtfuss, Hoy, Rajasuriar, Kramski, Crowe & Lewin disease, renal diseases and bone disorders [9,10] . Factors that drive ongoing morbidity include a combination of immune activation, aging of the immune system and cART toxicity (reviewed in [11]). Biomarkers in HIV-infected patients & the effect of cART Immune activation A detailed overview of markers of persistent immune activation in HIV-infected patients has recently been published [12] . Here we will focus only on measures of immune activation in patients receiving cART (summarized in Table 1) with a focus on larger prospective studies that have aimed to identify associations between the relevant biomarker and clinical outcomes. T‑cell activation: cellular markers CD69, -25 & -38, & HLA-DR T‑cell activation can be monitored using either cell-associated or soluble markers. T‑cell activation is identified by increased expression of CD69, -25 and -38, and HLA-DR. CD69, a transmembrane C‑type lectin, is an early marker of activation [13] and is followed by increased expression of CD25, the a‑chain of the IL‑2 receptor [14] . The MHC class II antigen, HLA-DR, is expressed in later phases of T‑cell activation, while CD38 (an extracellular ADP-ribose cyclase) is expressed constitutively in activated T cells [15] . CD69 expression is a useful tool to monitor T‑cell activation in vitro [16] ; however, expression of CD69 from freshly isolated blood is low and is similar in HIV-infected and HIVuninfected patients [16,17] , potentially because of the transient expression of these markers or sequestration of CD69 + T cells in lymph nodes and other organs. CD25, although a marker of T‑cell activation and used as such in vitro, is also expressed on regulatory T cells [18] , often in combination with other intracellular markers such as FoxP3 [19] . Most studies characterizing T‑cell activation during HIV infection in vivo have therefore focused on expression of CD38 and HLA-DR [20–22] . Increased expression of CD38 and HLA-DR on CD4 + and CD8 + T cells in untreated HIV infection has been associated with shorter survival and faster disease progression [23–25] . However, expression of CD38 on CD8 + T cells before the initiation of cART was not predictive for clinical outcomes in patients receiving cART [26] . Following cART, expression of CD38 and HLA-DR on both CD4 + and CD8 + T cells 172 Biomarkers Med. (2011) 5(2) declines significantly but remains higher than in uninfected controls [27] . Persistent elevation of CD38 and HLA-DR on both CD4 + and CD8 + T cells has been associated with impaired magnitude and speed of CD4 + T‑cell recovery [27–29] , and higher levels of expression of CD38 on CD8 + T cells was observed in patients on cART at the time of an opportunistic infection or death [26] . T‑cell activation markers were significantly higher in HIV-infected patients from Africa compared with the USA and were associated with poorer CD4 + T‑cell recovery and increased mortality following cART in this Ugandan-based prospective study [30] . T‑cell activation: soluble markers Plasma markers for T‑cell activation are of potential interest, as these can be more easily measured than cell-associated markers in clinical practice. Activated T cells express a number of proteins on their surface that are shed, including CD26, -27 and -30, and the ligand of the CD40 receptor, leading to increased levels of their soluble forms in plasma. Th1 cells predominantly express and release CD26, while Th2 cells express and release CD30. Therefore, these plasma markers have been investigated in conditions that are defined by either a Th1 [31] or a Th2 environment [32,33] . While soluble (s)CD30 is directly quantified in plasma using a standard ELISA, sCD26 is usually indirectly detected through its enzymatic activity [34] . A decrease of enzymatic activity of sCD26 had been inversely correlated with HIV RNA in untreated HIV-infected patients [35] . In patients receiving cART, there was no significant elevation in sCD26 compared with uninfected individuals, regardless of whether patients had detectable HIV RNA [34] . Despite the potential use of sCD26 as a diagnostic or prognostic marker in other diseases [36] , its value as a marker in the context of HIV infection has not been established and, therefore, requires further investigation. Plasma levels of sCD30 are elevated during the early phase of HIV infection and decrease following seroconversion, correlating with detectable HIV p24 antigen [37] , and were associated with faster progression to AIDS in untreated HIV-infected patients [38,39] . Data regarding changes in sCD30 in untreated HIVinfected patients are inconsistent, with some studies reporting higher levels [40,41] or levels similar to uninfected subjects [34] . However, a recent large retrospective cohort study (n = 290) future science group Biomarkers of immune dysfunction following combination antiretroviral therapy demonstrated a significant decrease of sCD30 following initiation of cART, even in the absence of virological control. sCD30 also correlated with hypergammaglobulinemia, an indicator of B-cell activation [42] . In a separate cohort study of patients receiving cART (n = 276), higher baseline levels of sCD30 prior to cART initiation were associated with higher HIV RNA [43] . In patients who achieved virological suppression (<500 copies/ml), a faster decrease of sCD30 in the first 6 months predicted a higher risk of subsequent viral rebound [43] . To date, no studies have evaluated the relationship between sCD30 and clinical outcome on cART. Receptors of the TNF receptor (TNFR) superfamily include CD27 expressed on T cells, CD40 expressed on antigen presenting cells and TNFR‑1, which is widely expressed across cell types. The TNFR superfamily are involved in pathways regulating a wide array of cellular functions, such as cell proliferation, differentiation and survival, and are often shed following receptor engagement. The CD40 ligand (CD40L) is expressed and shed by activated T cells. Plasma levels of sCD27 [44,45] and sCD40L are elevated in untreated HIV infection [46] . Combination antiretroviral therapy leads to a significant reduction of plasma levels of sCD27 [42] , while increased levels of sCD40L do not appear to be affected by cART [47] . In a recent case–control study of treatmentnaive patients initiating cART, pretreatment levels of sTNFR‑1, sCD27 and sCD40L were each significantly associated with the risk of an AIDS-defining malignancy or death [26] . These clinical events presented a median of 51 weeks after cART initiation, by which time the majority of subjects had over 200 circulating CD4 cells/mm3 and had suppressed plasma viremia to less than 50 copies/ml. Therefore, these markers may potentially identify patients at the highest risk of an AIDS-defining malignancy or death on cART [26] . Generalized immune activation & thrombotic risk: C-reactive protein, IL‑6 & D‑dimer C-reactive protein (CRP), IL‑6 and D‑dimer have been extensively studied as biomarkers of persistent immune activation and increased thrombotic risk in patients on cART [12] . The interest in these biomarkers started following the Strategic Management of Antiretroviral Therapy (SMART) study. The SMART study was a randomized controlled trial comparing the effect of intermittent CD4-guided cART versus future science group Special Report continuous cART on morbidity and mortality [48] . SMART was one of the first studies to identify a relationship between viral replication, immune activation and non-AIDS events, and several substudies of SMART have identified multiple biomarkers that are associated with non-AIDS events [49–53] and mortality [54] . C-reactive protein, generally measured using a high-sensitivity assay and, therefore, referred to as highly sensitive (hs)CRP, is an acute-phase protein produced by hepatocytes in response to IL‑6 and is involved in complement formation [55] . Elevated CRP has been associated with CVD in over 30 prospective cohort and case–control studies in previously healthy middle-aged and elderly populations [56,57] . In the setting of HIV infection, levels of hsCRP are higher than age- and sex-matched HIVnegative controls [52] , and increased levels of CRP have been demonstrated to be associated with a greater risk of development of opportunistic infection [50,58] , and cardiovascular or allcause mortality [49,59] ; although the association with cardiovascular risk was not reported in all studies [49,59,60] . Following initiation of cART, most studies have reported little or no change in hsCRP, although one study demonstrated a significant reduction in hsCRP [42,51,61–63] . However, increased levels of hsCRP in plasma of patients receiving cART was associated with increased carotid intima media thickness, a predictor for CVD [64] . IL‑6 is a proinflammatory cytokine produced mainly by monocytes, endothelial cells and lymphoc ytes, [65] . IL‑6 levels increase with age in the general population and have been associated with increased CVD and mortality in the elderly [57,66,67] . Compared with the general population, IL‑6 levels are significantly increased in HIV infection [52] . In untreated HIV-infected patients, IL‑6 levels are elevated and associated with markers of vascular dysfunction (reduced small artery elasticity) and some plasma markers of endothelial function, including E-selectin and soluble ICAM‑1 [52,68] . As with the observations for hsCRP, cART did not lead to a significant reduction in IL‑6 [51] , not even after 3 years of continuous cART [42] . However, when cART was interrupted, IL‑6 levels significantly increased, and the magnitude of the increase correlated with levels of HIV RNA [49] . Increased baseline levels of IL‑6, before the initiation of cART, was the strongest predictor of all-cause mortality in the SMART study [49] and was also associated with the development of opportunistic disease [26,50] . www.futuremedicine.com 173 Special Report Lichtfuss, Hoy, Rajasuriar, Kramski, Crowe & Lewin Table 1. Biomarkers commonly used to assess HIV-infected patients on combination antiretroviral therapy and their relationship with clinical outcomes. Biomarker Marker Assay type Specimen Function HIV infection Naive On cART Reduced but slow/no normalization Unclear T‑cell activation CD38/HLA-DR – Flow cytometry WB/PBMC sCD26 (Th1) Plasma sCD27 sCD30 sCD40L sTNFR‑1 – (Th2) – – Enzymatic activity assay ELISA ELISA ELISA ELISA Elevated on CD4 + and CD8 + T cells Reduced Plasma Plasma Plasma Plasma Elevated Elevated Elevated Elevated Reduced Reduced/elevated in IRD No change – Inflammation/immune activation CRP IL‑6 – – ELISA ELISA Plasma Plasma Elevated Elevated Reduced in some studies No change D‑dimer – ELISA Plasma Elevated – LPS – Enzymatic activity assay Plasma Elevated Reduced but slow/no normalization 16S rDNA – PCR Plasma Elevated Reduced Microbial translocation Immune response to bacterial products LBP – ELISA Plasma Elevated – sCD14 – ELISA Plasma Elevated EndoCAb – ELISA Plasma Elevated Reduced but slow/no normalization Reduced CD28/CD57 Senescence Flow cytometry WB/PBMC Elevated No normalization Antigen-specific dysfunction Against CMV Abnormal immune restoration – – – – – Functional assay† WB/PBMC Elevated Elevated Against Mtb – Functional assay† WB/PBMC Reduced Against HBV – Functional assay† WB/PBMC Reduced Variable increase, can be excessive No normalization Immune activation Flow cytometry WB/PBMC Elevated No normalization T‑cell dysfunction NK cell dysfunction HLA-DR on NK All associations are positive correlations unless otherwise specified. † Incubation with specific antigen or peptides and cytokine production measured by enzyme-linked immunospot (ELISpot) or intracellular cytokine staining. ‡ Functional assay requires ex vivo stimulation and intracellular staining. § CD107a expression elevated if measured by surface expressioin ex vivo but reduced if measured in response to experimental stimulus. ¶ Cell bound TF measured by flow cytometry. sTF requires an Enzymatic Activity Assay. ADCC: Antibody-dependent cell cytotoxicity; BMD: Bone mineral density; cART: Combination antiretroviral therapy; CMV: Cytomegalovirus; CRP: C-reactive protein; CVD: Cardiovascular disease; EndoCAb: Endotoxin core antibody; HBV: Hepatitis B virus; HCV: Hepatitis C virus; IRD: Immune restoration disease; LBP: Lipopolysaccharide-binding protein; LPS: Lipopolysaccharide; Mtb: Mycobacterium tuberculosis; NHL: Non-Hodgkin’s lymphoma; NK: Natural killer; PBMC: Peripheral blood mononuclear cell; s: Soluble; TF: Tissue factor; TNFR: TNF receptor; WB: Whole blood. 174 Biomarkers Med. (2011) 5(2) future science group Biomarkers of immune dysfunction following combination antiretroviral therapy Association with other biomarkers Naive Association with clinical outcome Ref. Naive (HIV ) On cART (HIV ) HIV un‑infected LPS, 16S rDNA, sCD14, inverse – correlation with CD28/CD57, TF Inverse correlation with HIV RNA – Mortality, disease progression – – – [23–29] – – [34–36] sTNFR‑1, IL‑6, CD4 count HIV RNA sTNFR‑1 sCD27, IL‑6, HIV RNA inverse correlation with CD4 count – – – – – NHL – – – – – – – NHL – – HIV RNA, CD4 count – – – TF HIV RNA, TF – Vascular dysfunction, endothelial dysfunction – CVD, mortality CVD, BMD Mortality, Age, mortality opportunistic disease and NHL, reduced BMD Mortality, CVD, mortality opportunistic disease 16S rDNA, LBP, sCD14, CD8 + T‑cell activation 16S rDNA, sCD14, CD8 + T-cell activation LPS, CD8 + T-cell activation Opportunistic infection, dementia, liver disease progression (HCV) – Inverse correlation with CD4 + T‑cell recovery – [3,77,80–89,91,101] Inverse correlation with CD4 + T‑cell recovery – [77] LPS, sCD14 – – – [3,91] LPS, CD8 + T‑cell activation, NK activation Inverse correlation with LPS LPS Faster CD4 + T‑cell recovery Mortality Faster disease progression, dementia – – – [3,48,54,78,83,89–91,94,95] – [3,54] Inverse correlation with HLA-DR – on CD4 + T‑cells – Increase of CD28 with AIDS – Lower arterial distensibility – Aging – – – CVD – – – Carotid intima thickness, CVD Severe Mtb disease – [118,119] – – – – – [117] sCD14 – – – – [Lichtfuss GF, Lewin SR, HIV RNA, CD8 + T‑cell activation On cART Special Report – + + [26,42,44–46] [34,37–43] [26,46,47] [26] [42,49,50,52,56–64] [26,42,49–52,57, 6–68] [49–52,69,71–73] [105,106, 111–114,160] – [121–125] Jaworwski A, Crowe SM, Unpublished Data] future science group www.futuremedicine.com 175 Special Report Lichtfuss, Hoy, Rajasuriar, Kramski, Crowe & Lewin Table 1. Biomarkers commonly used to assess HIV-infected patients on combination antiretroviral therapy and their relationship with clinical outcomes (cont.). Biomarker Marker Assay type Specimen Function HIV infection Naive On cART NK cell dysfunction (cont.) CD107a on NK CD16 on NK NK cell activity Flow cytometry‡ NK cell ADCC capacity Flow cytometry WB/PBMC WB/PBMC Elevated/reduced§ Reduced/no normalization Reduced No normalization WB/PBMC WB/PBMC WB/PBMC/ plasma Elevated Elevated Elevated Monocyte dysfunction CD14 + CD16 ++ monocytes CD38 on monocytes TF Monocyte activation Immune response to bacterial products Flow cytometry Flow cytometry Flow cytometry ¶ Normalized Reduced/no normalization – All associations are positive correlations unless otherwise specified. † Incubation with specific antigen or peptides and cytokine production measured by enzyme-linked immunospot (ELISpot) or intracellular cytokine staining. ‡ Functional assay requires ex vivo stimulation and intracellular staining. § CD107a expression elevated if measured by surface expressioin ex vivo but reduced if measured in response to experimental stimulus. ¶ Cell bound TF measured by flow cytometry. sTF requires an Enzymatic Activity Assay. ADCC: Antibody-dependent cell cytotoxicity; BMD: Bone mineral density; cART: Combination antiretroviral therapy; CMV: Cytomegalovirus; CRP: C-reactive protein; CVD: Cardiovascular disease; EndoCAb: Endotoxin core antibody; HBV: Hepatitis B virus; HCV: Hepatitis C virus; IRD: Immune restoration disease; LBP: Lipopolysaccharide-binding protein; LPS: Lipopolysaccharide; Mtb: Mycobacterium tuberculosis; NHL: Non-Hodgkin’s lymphoma; NK: Natural killer; PBMC: Peripheral blood mononuclear cell; s: Soluble; TF: Tissue factor; TNFR: TNF receptor; WB: Whole blood. D‑dimer is a fibrin degradation product, which has been associated with CVD and death in the general population and is elevated in untreated HIV-infected patients [69] . D‑dimer has also been investigated as a marker for predicting the development of opportunistic disease and mortality in patients receiving cART [70] . Following initiation of cART, there was a significant reduction in plasma levels of D‑dimer [51,69,71] . Increased baseline plasma levels of D‑dimer before initiating cART and elevated levels immediately preceding an event were associated with the development of an opportunistic infection [50,52] . In the SMART trial, increased baseline levels of D‑dimer were also associated with a higher risk of CVD and allcause mortality [72] . The magnitude of change in D‑dimer levels following interruption of cART in the SMART study correlated with changes in HIV RNA [49] , suggesting that viral replication may drive the production of D‑dimer. D‑dimer levels have also been correlated with levels of tissue factor (TF) expressed on activated monocytes, which were associated with both the level of HIV RNA and markers of microbial translocation [73] . Microbial translocation & associated immune reponse With the emergence of the hypothesis that microbial translocation through the GI tract might be a driving factor for immune activation in HIV-infected patients, soluble markers of microbial translocation have recently been studied as novel biomarkers in HIV infection [74–76] . 176 Biomarkers Med. (2011) 5(2) Microbial translocation can be measured in plasma by direct quantification of bacterial products, including lipopolysaccharide (LPS), a major component of the Gram-negative bacterial cell wall [3] , bacterial DNA fragments using PCR-based assays [77] or other microbe-specific compounds (e.g., peptidoglycan, a component of the Gram-positive bacterial cell wall) [78] . In vivo, LPS binds to LPS-binding protein (LBP), which is expressed at high concentrations by numerous cell types during the acute phase of the innate immune response to bacterial infection [79] . The LPS/LBP complex is then bound by CD14 and the Toll-like receptor 4 on monocytes. This leads to monocyte activation and release of sCD14 into the circulation. Therefore, measure ment of sCD14 and LBP can also indirectly quantify the effects of microbial translocation. Direct measurement of bacterial products in vivo The most commonly used method to quantify LPS in plasma is the limulus amebocyte lysate assay, which utilizes a series of enzymatic reactions that mimic the coagulation cascade. This cascade sequence results in the amplification of the initial stimulus and accounts for the high sensitivity of the assay (down to 1 pg/ml endotoxin) [80] . Since this assay is so sensitive, contamination during sample preparation and during the conduct of the assay can easily occur. Furthermore, the enzymatic reactions are critically time and temperature dependent [81] , and may be affected by numerous inhibitors present in plasma [82] . These issues all contribute to the future science group Biomarkers of immune dysfunction following combination antiretroviral therapy Association with other biomarkers Special Report Association with clinical outcome Naive On cART Naive (HIV+) On cART (HIV+) HIV uninfected – sCD14 – – – – – – – – – – HIV RNA, sCD14, CD8 + T‑cell activation, D‑dimer – – – – – – – – – – – Myocardial infarction poor reproducibility of the assay with reported interassay variability ranging from 25 to 30% [77,83] . Therefore, multiple levels of quality control need to be in place when utilizing the assay for clinical studies. Plasma LPS is elevated in HIV-infected patients not receiving cART [3,83,84] . Following cART, LPS levels significantly reduce but do not return to levels of healthy controls [83–85] . In HIV-infected patients living in Africa, the relationship between elevated levels of LPS and HIV disease progression is less clear. Some studies have reported elevated levels of LPS [85–87] and sCD14 [85] , while another study has demon strated no change in either of these markers over time in untreated HIV infection [88] . In this latter study, although LPS and sCD14 levels were not significantly elevated compared with normal controls, LBP levels were raised and correlated (albeit weakly) with the increase in proinflammatory cytokines IL‑6 and TNF‑a. It is unknown why the relationship between LPS and clinical outcome might be different in this African cohort to other studies from the USA, but one possible explanation might be that the higher prevalence of co-infections may drive immune activation and, therefore, obscure the associations usually seen between LPS and disease progression. In addition, differences in markers of microbial translocation may also be confounded by ethnic differences in the patient population [88,89] and should be taken into account during analysis. The 16S genomic rDNA can also be quantified in plasma using PCR-based techniques. This is a technically challenging assay and persistent DNA future science group Ref. [130,131,142] [142–144] [147,149] [150] [3,151] is often detected in negative controls, as a result of bacterial DNA contamination from the environment and reagents such as Taq polymerase. It is also likely that there is a ‘normal’ background level of 16S rDNA in healthy humans. We, and others, have demonstrated that 16S rDNA was increased in untreated HIV-infected patients and levels were reduced, but not normalized in patients receiving cART [Kramski M, Purcell DFJ, Unpublished Data] [77] . Elevated levels of 16S rDNA have also been associated with higher HIV RNA and poor CD4 + T‑cell recovery [77] . Indirect measures of microbial translocation: endotoxin-specific immune response Plasma LBP levels may measure exposure to LPS more reliably than direct measurement of LPS [90] . LBP levels are increased in untreated HIV-infected patients [3] and patients with AIDS [91] . However, to our knowledge, the effect of cART on LBP has not been studied so far. Endotoxin core antibodies (EndoCAb) are produced by B cells in response to LPS and can bind to LPS to neutralize its activity [92] . EndoCAb titers are significantly reduced in HIV-infected patients compared with healthy controls [3,54] . Levels of EndoCAb were significantly lower in patients receiving cART compared with untreated patients [54] . Although levels of EndoCAb have been found to be inversely correlated with LPS [3] , the levels of EndoCAb may also be affected by B-cell dysfunction in HIV [93] and, therefore, may not be a realiable indirect measure of LPS function. www.futuremedicine.com 177 Special Report Lichtfuss, Hoy, Rajasuriar, Kramski, Crowe & Lewin Plasma levels of sCD14 are measured by ELISA. Therefore, unlike the LPS and 16S rDNA assays, which are both technically challenging, quantification of sCD14 is highly reproducible and could potentially be reliably used in large-scale clinical studies. sCD14 levels are elevated in untreated HIV-infected patients, and are elevated in patients with faster progression to AIDS [3,94] . Similar to LPS, cART leads to a significant reduction in sCD14, but levels remain significantly elevated compared with healthy controls [83,95] . Using detailed longitudinal assessment of LPS and sCD14 in patients on cART together with mathematical modeling, we recently demonstrated that both markers will eventually normalize in patients on long-term cART [83] . Relationship of markers of microbial translocation to each other A direct correlation between all markers for microbial translocation would be expected; however, the relationship between LPS and the immunological response, involving membranebound CD14, sCD14, LBP and EndoCAb, are complex, and the interaction among these components may differ in patients who are on and off cART [96,97] . Studies have demonstrated a significant correlation between 16S DNA and LPS [77] ; LPS and LBP [91] ; and LPS and sCD14 [3,83,91] . LBP itself also correlates with sCD14 [3] . In addition, 16S rDNA, LPS and sCD14 have all been demonstrated to correlate with T‑cell activation (defined as expression of CD38 +HLA-DR+ on CD8 + T cells) [Lichtfuss GF, Lewin SR, Jaworwski A, Crowe SM, Unpublished Data] [3,77] . Clinical relevance of microbial translocation The effects of microbial translocation on reconstitution of CD4 + T cells following cART has been examined in several studies [3,77,83,98,99] . Some of these studies demonstrated an inverse association between CD4 + T‑cell increase and the amount of circulating microbial products as measured by levels of LPS [3] or 16S rDNA [77] . We recently examined the relationship between LPS, sCD14 and long-term CD4 recovery in a cohort of 96 patients initiating cART, and used multivariate analysis to determine factors associated with the speed of CD4 + T‑cell recovery to over 500 cells/µl [83] . Faster restoration to CD4 + T‑cell counts of over 500 cells/µl was associated with, in addition to other factors, higher baseline CD4 + T‑cell counts, lower baseline LPS levels and paradoxically higher baseline sCD14 levels, 178 Biomarkers Med. (2011) 5(2) highlighting the complexity of LPS and sCD14 interactions, which can be both pro- and antiinflammatory [100] . In addition, we did not find that the level of LPS or sCD14 in patients on cART was associated with the speed of CD4 + T‑cell recovery [83] . Increased microbial translocation has also been associated with several adverse HIV-related clinical outcomes, including HIV disease progression, dementia, liver disease and mortality. In cART-naive patients, development of an opportunistic infection was associated with elevated LPS [85] . Higher plasma levels of LPS and sCD14 were also associated with HIV-associated dementia in patients who had either failed or never received cART [91] . In patients with HIV–hepatitis C virus (HCV) co-infection, elevated LPS was associated with more rapid progression of liver disease [101] . Patients with an LPS in the upper quartile (>42 pg/ml) had a 19‑fold greater risk of liver disease progression (p = 0.018). By contrast, in a small cross-sectional study of patients with HIV–hepatitis B virus (HBV) co-infection (n = 55), we found that LPS was not associated with an increased risk of liver disease (measured by liver biopsy) [102] . Whether elevated LPS in the setting of HIV–HCV co-infection is a cause or a consequence of liver disease remains uncertain, but it appears that the impact of HCV–HBV co-infection is different. Finally, a recent prospective substudy of patients enrolled in the SMART study demon strated that subjects with sCD14 levels in the highest quartile had a sixfold higher risk of death than those in the lowest quartile (95% CI: 2.2–16.1; p = 0.0004), with minimal change after adjustment for inflammatory markers, CD4 + T‑cell count and HIV RNA [54] . Immune dysfunction T cells HIV not only significantly reduces the number of CD4 + T cells and causes the expansion of CD8 + T cells, but also has a profound effect on T‑cell function. While the total number of CD4 + T cells is often normalized following cART, the composition of the T‑cell populations and their function are not. In patients receiving cART, naive CD4 + T cells often do not return to normal levels [103,104] and the number of activated and senescent cells is elevated [105] . Senescent cells have shortened telomere length and are defined as CD28-CD57+, which are both established biomarkers for immuno logical aging in a healthy aging population [106] . future science group Biomarkers of immune dysfunction following combination antiretroviral therapy The activating co-receptor, CD28, expressed on CD4 + and CD8 + T cells, promotes cell survival, IL‑2 production, metabolic activity and clonal expansion [107–110] . Therefore, loss of CD28 is accompanied by phenot ypic changes that inhibit T‑cell function and the accumulation of CD28T cells is a hallmark of immunologic aging [111] . In untreated HIV-infected patients, an increase in CD8 + CD28 - T cells and a decrease in CD4 +CD28 + and CD8 +CD28 + T cells was associated with progression to AIDS [112] , and loss of CD28 inversely correlated with an increase in HLA-DR expression on CD4 + T cells [113] . Patients receiving suppressive cART showed increased proportions of senescent T cells, similar to levels found in the elderly (defined as CD8 + CD57+ CD28-) [105,106] , and higher numbers of CD57+ CD28 - senescent T cells were associated with lower arterial distensibility [114] . Recovery of antigen-specific T‑cell responses can also be impaired or dysregulated following cART, especially in patients who initiate cART at low CD4 + T‑cell counts [115,116] . In HIV–HBV co-infected patients we recently described little or no recovery in HBV-specific CD8 + T cells despite HBV-active cART, which successfully suppressed both HIV and HBV [117] . In HIVinfected patients co-infected with Mycobacterium tuberculosis, recovery of M. tuberculosis-specific cells is variable and can be associated with an excessive T‑cell-mediated immune response against M. tuberculosis antigens, often leading to severe clinical disease [118,119] . In HIV-infected patients, cytomegalovirus (CMV)-specific T cells account for close to 10% of all antigen-specific CD4 + and CD8 + T cells [120] , and there has been recent interest in the role of these cells in immune activation and non-AIDS events. The number of CMVspecific T cells was significantly higher in HIVinfected patients on cART compared with uninfected controls [121,122] and in patients naive to cART [123] . The percentage of CMV-specific IFN‑g‑producing CD8 + T cells was also positively correlated with carotid intima thickness in both HIV patients and uninfected control subjects, suggesting that an increased inflammatory response to CMV may be contributing to CVD [124] . Interventions that reduce CMV replication, such as valganciclovir, have recently been demonstrated to reduce CD8 + T‑cell activation in HIV-infected patients receiving cART [125] . This novel strategy requires further evaluation but may have some role in the future to reduce inflammation and potentially reduce the risk of CVD. future science group Special Report In conclusion, not all T‑cell subsets recover equally following cART and this imbalance may contribute to ongoing immune dysfunction, even in patients with a normal total CD4 + T‑cell count. Natural killer cells Natural killer (NK) cells are traditionally defined as CD3 -CD56 + cells, and are further differentiated by the level of expression of CD56 and whether there is expression of the Fc receptor, CD16, also known as the receptor for antibody-dependent cell cytotoxicity. Therefore, NK cells can be grouped into the smaller regulating CD3 - CD56 bright CD16 -, the larger, predominately cytolytic CD3-CD56dimCD16 + [126] and the functionally inert CD3 -CD56 -CD16 + subsets [127] . Activity of NK cells can also be assessed by expression of HLA-DR as a marker of activation [128] and CD107a as a marker of active degranulation [129–131] . Early studies in treatment-naive HIV-infected patients demonstrated a significant reduction in the total number of NK cells compared with healthy controls [131–135] . However, recent studies have also demonstrated an altered distribution of NK cell subsets, with an increase in CD3 - CD56 - CD16 + NK cells compared with uninfected controls [136] . In addition, in treatment-naive HIV-infected patients, NK cells had reduced expression of activating surface receptors, and reduced cytotoxicity and cytokine production with little improvement following cART (reviewed in [137]). Following cART, the expanded functionally inert CD3-CD56 -CD16 + NK cells persist [138] and restoration of CD56 + NK cell numbers occurs, although at a slower rate than CD4 + T cells [139–141] . We and others have observed that NK cells in HIV-infected patients naive to cART express high levels of CD107a consistent with active degranulation, a marker for high cytolytic activity [130,131,142] . Following cART, we observed a reduction of CD107a expression while the coexpression of CD38 and HLA-DR remained elevated, consistent with persistent NK cell activation [Lichtfuss GF, Lewin SR, Jaworwski A, Crowe SM, Unpublished Data] . In addition, expression of CD16 on NK cells was low in patients with HIV [143] and did not return to normal levels following cART [142,144] , possibly as a direct result of NK cell activation [144,145] . The relationship between persistent NK cell dysfunction on cART and long-term clinical outcomes has not been determined but is an area of interest for future research. www.futuremedicine.com 179 Special Report Lichtfuss, Hoy, Rajasuriar, Kramski, Crowe & Lewin Monocytes Monocytes in peripheral blood are characterized by the combination of CD14 and -16 surface antigen expression. The majority of monocytes express CD14 without detectable expression of CD16 (CD14++CD16- monocytes). A minor subset representing 5–15% of monocytes expresses CD16 and variable levels of CD14, and these cells are phenotypically described as CD14 +CD16 ++ [146] . HIV preferentially infects these CD14 +CD16 ++ monocytes [147,148] . Although this subset was reported to be expanded in HIV‑infected individuals in the pre-cART era [149] , our more recent data show that the CD14 +CD16 ++ monocyte population was not significantly increased in HIV‑infected individuals in the setting of cART [147] . Hallmarks of monocyte activation include the shedding of CD14, production of IL‑6 and catalysis of D‑dimer, and have been discussed in the previous sections. Similar to T‑cell activation markers, monocyte activation continues for significant periods of time following suppression of HIV RNA with cART. One measure of monocyte activation, the surface expression of CD38, declines following cART, although levels remain significantly higher than in uninfected controls [150] . Recent evidence suggests that persistence of markers of monocyte activation may be independent of persistent T‑cell activation. In the presence of LPS and other Toll-like receptor ligands, the surface expression of TF (thrombo plastin and CD142) is elevated in untreated HIVinfected patients and correlates with the activation of the monocyte coagulation cascade, eventually leading to the cleavage of fibrinogen into D‑dimer. Chronic monocyte activation may directly contribute to the elevated risk of CVD, as heightened expression of TF has been linked to myocardial infarction and angina in HIV-uninfected patients [151] . Activated monocytes are crucial cells in the pathogenesis of atherosclerosis: they are the precursors of fat-laden foam cells, which are the major cells found within the atheromatous plaque, potentially contributing to the increased risk of CVD in HIV-infected patients, even in those with virologic suppression (reviewed in [152,153]). Studies to determine the precise role of monocytes in the pathogenesis of non-AIDS morbidity and mortality in HIV-infected patients with virologic suppression on cART are ongoing. Biomarkers & clinical disease in HIV-infected patients on cART Biomarkers of inflammation and coagulation have been most extensively studied regarding their relationship with overall mortality, CVD 180 Biomarkers Med. (2011) 5(2) and cardiovascular mortality. There are far fewer studies examining the relationship between persistent immune dysfunction and inflammation, and other non-AIDS clinical diseases, including malignancy. There is a clear relationship between lower total CD4 + T‑cell counts and rates of malignancy (both HIV related and non-HIV related) [154] , and the cytokines, IL6, IL‑10 and sCD30, have all been associated with an increased risk of non-Hodgkin’s lymphoma [155] . HIV-infected adults have a higher prevalence of low bone mineral density (BMD; 40–83%) compared with HIV-uninfected subjects, and HIV-infected patients receiving cART have a lower BMD than HIV-infected patients naive to cART [156] . Baseline levels of hsCRP and IL‑6, as well as change in IL‑6, are associated with lower BMD in the general population [157] , and also associated with greater risk of fragility fracture [158] . There are currently no data evaluating levels of inflammatory cytokines or immune activation on the prevalence of osteopenia or osteo porosis, or change in BMD in HIV patients; given the importance of this complication of cART, further studies are warranted. Conclusion Despite control of viral replication and CD4 + T‑cell reconstitution following cART, HIVinfected patients experience high rates of nonAIDS events, including CVD, malignancy and premature death. Current research on biomarkers in HIV infection is focusing on the potential links between persisting immune activation and dysfunction, and adverse clinical outcomes following cART. While a number of biomarkers have been evaluated in large clinical prospective studies, none of these biomarkers are used in routine clinical practise. Further work is still needed to define the cause and effect of the relationship between the relevant biomarker and clinical outcome, and whether reduction of a specific biomarker following a therapeutic intervention leads to improved clinical outcomes. Future perspective After years of success in the use of cART to manage HIV infection, clinicians now face the challenge of reducing non-AIDS events in patients on cART. Unfortunately, CD4 + T‑cell count and HIV RNA as sole biomarkers are unable to fully predict health outcomes in HIV-infected patients on cART. The recent clinical trials of IL‑2 clearly demonstrated that an increase in total CD4+ T‑cell count did not correlate with improved health outcomes for patients receiving IL‑2 in addition to future science group Biomarkers of immune dysfunction following combination antiretroviral therapy cART [159] . In addition to conventional biomarkers used in HIV-uninfected patients that predict diseases such as CVD, novel biomarkers that are highly reproducible will be needed to monitor ongoing immune activation and dysfunction in patients on cART. Larger longitudinal clinical studies are necessary to convincingly demonstrate clear associations between biomarkers and clinical outcomes. In addition, continuing efforts in fundamental immunology research are needed to understand the mechanistic links between biomarkers and clinical disease. These studies will also potentially enable the development of therapeutic interventions beyond cART to reduce the incidence of non-AIDS events. Special Report Financial & competing interests disclosure GF Lichtfuss is funded by scholarships from Monash University, the Burnet Institute and The Alfred Hospital. R Rajasuriar is a recipient of the Kings Scholarship by the Malaysia government. SM Crowe is a National Health and Medical Research Council (NHMRC) of Australia Principal Research Fellow. SR Lewin is a NHMRC practitioner fellow. This work was supported by the NHMRC and the Alfred Foundation. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript. Executive summary HIV-infected patients receiving combination antiretroviral treatment continue to experience worse health outcomes compared with the uninfected population Combination antiretroviral treatment (cART) successfully suppresses HIV RNA and restores the total number of CD4+ T cells to normal levels in most patients. HIV-infected patients on long-term cART experience higher rates of cardiovascular disease (CVD), non-AIDS malignancy, neurocognitive impairment, and liver, kidney and bone disease. HIV-infected patients on long-term cART have a shorter life expectancy compared with the general population. cART fails to normalize generalized immune activation of HIV patients Cellular markers for immune activation (e.g., CD38/HLA-DR coexpression on CD4+ and CD8+ T cells) are elevated in patients on cART and has been linked to impaired CD4+ T‑cell recovery and increased mortality. Plasma markers for inflammation (e.g. C-reactive protein, IL-6 and D‑dimer) are elevated in patients on cART, and are associated with increased CVD, opportunistic disease and all-cause mortality. HIV is associated with elevated circulating microbial products. In HIV-infected patients on or off cART, microbial products (e.g., lipopolysaccharide or bacterial 16S rDNA in plasma) are significantly elevated, and these correlate with markers of T‑cell activation. Elevated levels of microbial products are associated with the development of opportunistic disease, slower T‑cell recovery and faster progression of liver disease in patients co-infected with hepatitis C virus. The immunological response specific for microbial products can be measured (e.g., soluble CD14, lipopolysaccharide-binding protein or endotoxin core antibody), and in HIV-infected patients receiving cART, elevated soluble CD14 been associated with an increased risk of mortality. cART fails to normalize the composition of the T‑cell compartment Overall, total CD4+ T‑cell numbers return to normal following cART, but there is skewed recovery of some CD4+ T‑cell subpopulations. HIV-infected patients receiving cART have increased proportions of CD28-CD57+ T cells, a sign of immunological senescence which is associated with increased CVD. The repertoire of antigen-specific T cells is altered in some patients receiving cART and is skewed towards particular common pathogens (e.g., cytomegalovirus). cART fails to normalize phenotype & function of other immune cells Natural killer cells, which are important for antiviral immune response and tumor surveillance, are altered by HIV infection and are characterized by increased activation and a large functionally inert subpopulation that is only slowly restored following cART. Monocytes, the source of several plasma markers of immune activation (e.g., sCD14), show increased expression of tissue factor, which mediates the catalysis of D‑dimer, which can enhance coagulation. The role of natural killer cells and monocytes in the pathogenesis of disease in cART patients is currently being investigated, and they are potentially linked to enhanced CVD. Conclusion Increased morbidity and mortality in HIV patients receiving cART is associated with incomplete restoration of immune function. Biomarkers for immune activation and immune dysfunction are useful research tools to understand pathogenesis of and increased risk for non-AIDS events. Further research of these biomarkers is required to reliably predict adverse health outcomes and to develop novel interventions to be used in addition to cART for the management of HIV infection. future science group www.futuremedicine.com 181 Special Report Lichtfuss, Hoy, Rajasuriar, Kramski, Crowe & Lewin Bibliography Papers of special note have been highlighted as: n of interest nn of considerable interest 1 2 3 n 4 5 6 n 7 8 9 10 Kahn JO, Walker BD: Acute human immunodeficiency virus type 1 infection. N. Engl. J. Med. 339(1), 33–39 (1998). Mehandru S, Poles M, Tenner-Racz K et al.: Primary HIV‑1 infection is associated with preferential depletion of CD4 + T lymphocytes from effector sites in the gastrointestinal tract. J. Experiment. Med. 200(6), 761–770 (2004). Brenchley JM, Price DA, Schacker TW et al.: Microbial translocation is a cause of systemic immune activation in chronic HIV infection. Nat. Med. 12(12), 1365–1371 (2006). Key paper that was the first to establish a link between microbial translocation and immune activation in HIV infection. 11 n Collaboration ATC: Life expectancy of individuals on combination antiretroviral therapy in high-income countries: a collaborative analysis of 14 cohort studies. Lancet 372(9635), 293–299 (2008). Lohse N, Hansen A-BE, Pedersen G et al.: Survival of persons with and without HIV infection in Denmark, 1995–2005. Ann. Intern. Med. 146(2), 87–95 (2007). Collaboration ATC: Causes of death in HIV‑1-infected patients treated with antiretroviral therapy, 1996–2006: collaborative analysis of 13 HIV cohort studies. Clin. Infect. Dis. 50(10), 1387–1396 (2010). Smith C; Data Collection on Adverse Events of Anti-HIV drugs (D:A:D) Study Group: Factors associated with specific causes of death amongst HIV‑positive individuals in the D:A:D Study. AIDS 24(10), 1537–1548 (2010). 182 22 Coetzee L, Tay S, Lawrie D, Janossy G, Glencross D: From research tool to routine test: CD38 monitoring in HIV patients. Cytometry B Clin Cytom. 76(6), 375–384 (2009). immune dysfunction in HIV. Curr. Opin. HIV AIDS 5(6), 498–503 (2010). nn Detailed review of current biomarkers in HIV. 23 Giorgi JV, Hultin LE, McKeating JA et al.: Shorter survival in advanced human immunodeficiency virus type 1 infection is more closely associated with T lymphocyte activation than with plasma virus burden or virus chemokine coreceptor usage. J. Infect. Dis. 179(4), 859–870 (1999). 13 Santis AG, Campanero MR, Alonso JL et al.: Tumor necrosis factor-a production induced in T lymphocytes through the AIM/CD69 activation pathway. Eur. J. Immunol. 22(5), 1253–1259 (1992). 14 Thèze J, Alzari PM, Bertoglio J: Interleukin 2 and its receptors: recent advances and new immunological functions. Immunol. Today 17(10), 481–486 (1996). 15 Reinherz EL, Kung PC, Goldstein G, Levey RH, Schlossman SF: Discrete stages of human intrathymic differentiation: analysis of normal thymocytes and leukemic lymphoblasts of T‑cell lineage. Proc. Natl Acad. Sci. USA 77(3), 1588–1592 (1980). 16 Krowka JF, Cuevas B, Maron DC, Steimer KS, Ascher MS, Sheppard HW: Expression of CD69 after in vitro stimulation: a rapid method for quantitating impaired lymphocyte responses in HIV-infected individuals. J. Acquir. Immune Defic. Syndr. Hum. Retrovirol. 11(1), 95–104 (1996). 24 Cao W, Jamieson BD, Hultin LE, Hultin PM, Detels R: Regulatory T cell expansion and immune activation during untreated HIV type 1 infection are associated with disease progression. AIDS Res. Hum. Retroviruses 25(2), 183–191 (2009). 25 Deeks SG, Kitchen CMR, Liu L et al.: Immune activation set point during early HIV infection predicts subsequent CD4 + T‑cell changes independent of viral load. Blood 104(4), 942–947 (2004). 26 Kalayjian RC, Machekano RN, Rizk N et al.: Pretreatment levels of soluble cellular receptors and interleukin-6 are associated with HIV disease progression in subjects treated with highly active antiretroviral therapy. J. Infect. Dis. 201(12), 1796–1805 (2010). 27 Hunt PW, Martin JN, Sinclair E et al.: T cell activation is associated with lower CD4 + T cell gains in human immunodeficiency virusinfected patients with sustained viral suppression during antiretroviral therapy. J. Infect. Dis. 187(10), 1534–1543 (2003). 17 Pitsios C, Dimitrakopoulou A, Tsalimalma K, Kordossis T, ChoremiPapadopoulou H: Expression of CD69 on T‑cell subsets in HIV‑1 disease. Scand. J. Clin. Lab. Invest. 68(3), 233–241 (2008). 18 Aandahl EM, Michaëlsson J, Moretto WJ, Hecht FM, Nixon DF: Human CD4 + CD25 + regulatory T cells control T‑cell responses to human immunodeficiency virus and cytomegalovirus antigens. J. Virol. 78(5), 2454–2459 (2004). 28 Solomon A, Cameron PU, Bailey M et al.: Weiss L, Letimier FA, Carriere M et al.: In vivo expansion of naive and activated CD4 + CD25 +FOXP3 + regulatory T cell populations in interleukin‑2-treated HIV patients. Proc. Natl Acad. Sci. USA 107(23), 10632–10637 (2010). 29 Fernandez S, Price P, McKinnon EJ, Large prospective cohort study on life expectancy of HIV-infected patients on combination antiretroviral therapy (cART). Lewden C, Chene G, Morlat P et al.: HIV-infected adults with a CD4 cell count greater than 500 cells/mm3 on long-term combination antiretroviral therapy reach same mortality rates as the general population. J. Acquir. Immune Defic. Syndr. 46(1), 72–77 (2007). Concise and detailed overview of current complications of cART. follow-up. The Los Angeles Center, Multicenter AIDS Cohort Study. J. Acquir. Immune Defic. Syndr. 6(8), 904–912 (1993). 12 Nixon DE, Landay AL: Biomarkers of Sodora D, Silvestri G: Immune activation and AIDS pathogenesis. AIDS 22(4), 439–446 (2008). Palella FJ, Delaney KM, Moorman AC et al.: Declining morbidity and mortality among patients with advanced human immunodeficiency virus infection. HIV Outpatient Study Investigators. N. Engl. J. Med. 338(13), 853–860 (1998). Volberding PA, Deeks SG: Antiretroviral therapy and management of HIV infection. Lancet 376(9734), 49–62 (2010). 19 20 Ho HN, Hultin LE, Mitsuyasu RT et al.: Circulating HIV-specific CD8 + cytotoxic T cells express CD38 and HLA-DR antigens. J. Immunol. 150(7), 3070–3079 (1993). 21 Giorgi JV, Liu Z, Hultin LE, Cumberland WG, Hennessey K, Detels R: Elevated levels of CD38 + CD8 + T cells in HIV infection add to the prognostic value of low CD4 + T cell levels: results of 6 years of Biomarkers Med. (2011) 5(2) n First study to clearly demonstrate persisting T‑cell activation in HIV-infected patients receiving cART. Immunological and virological failure after antiretroviral therapy is associated with enhanced peripheral and thymic pathogenicity. J. Infect. Dis. 187(12), 1915–1923 (2003). Nolan RC, French MA: Low CD4 + T‑cell counts in HIV patients receiving effective antiretroviral therapy are associated with CD4 + T‑cell activation and senescence but not with lower effector memory T‑cell function. Clin. Immunol. 120(2), 163–170 (2006). 30 Hunt P, Martin J, Ssewanyana I et al.: Impact of CD8 + T cell activation on CD4 + T cell recovery and mortality in HIV‑infected Ugandans initiating ART. Presented at: 17th Conference on Retroviruses and Opportunistic Infections. San Francisco, CA, USA, 16–19 February 2010. future science group Biomarkers of immune dysfunction following combination antiretroviral therapy 31 Scheel-Toellner D, Richter E, Toellner KM et al.: CD26 expression in leprosy and other granulomatous diseases correlates with the production of interferon‑g. Lab. Invest. 73(5), 685–690 (1995). 32 Chilosi M, Facchetti F, Notarangelo LD et al.: CD30 cell expression and abnormal soluble CD30 serum accumulation in Omenn’s syndrome: evidence for a T helper 2-mediated condition. Eur. J. Immunol. 26(2), 329–334 (1996). 42 Regidor DL, Detels R, Breen EC et al.: 43 Biswas P, Cozzi-Lepri A, Delfanti F et al.: Significant link between sCD30 changes and HIV viremia in patients treated with HAART. J. Med. Virol. 78(12), 1513–1519 (2006). Aberrant expression of CD27 and soluble CD27 (sCD27) in HIV infection and in AIDS-associated lymphoma. Clin. Immunol. 93(2), 114–123 (1999). Type 2 helper T‑cell predominance and high CD30 expression in systemic sclerosis. Am. J. Pathol. 151(6), 1751–1758 (1997). French MA: An evaluation of serum soluble CD30 levels and serum CD26 (DPPIV) enzyme activity as markers of type 2 and type 1 cytokines in HIV patients receiving highly active antiretroviral therapy. Clin. Exp. Immunol. 126(1), 111–116 (2001). 35 45 Kordossis T: Levels of soluble CD40 ligand (CD154) in serum are increased in human immunodeficiency virus type 1-infected patients and correlate with CD4 + T‑cell counts. Clin. Diagn. Lab. Immunol. 9(3), 558–561 (2002). Battegay M, Study SHC: Antiretroviral therapy reduces markers of endothelial and coagulation activation in patients infected with human immunodeficiency virus type 1. J. Infect. Dis. 185(4), 456–462 (2002). et al.; Strategies for Management of Antiretroviral Therapy (SMART) Study Group: CD4 + count-guided interruption of antiretroviral treatment. N. Engl. J. Med. 355(22), 2283–2296 (2006). 38 Pizzolo G, Vinante F, Morosato L et al.: High serum level of the soluble form of CD30 molecule in the early phase of HIV‑1 infection as an independent predictor of progression to AIDS. AIDS 8(6), 741–745 (1994). 39 Rizzardi GP, Barcellini W, Tambussi G et al.: Plasma levels of soluble CD30, tumour necrosis factor (TNF)‑a and TNF receptors during primary HIV‑1 infection: correlation with HIV‑1 RNA and the clinical outcome. AIDS 10(13), F45–F50 (1996). n 49 Kuller LH, Tracy R, Belloso W et al.: Inflammatory and coagulation biomarkers and mortality in patients with HIV infection. PLoS Med. 5(10), e203 (2008). 41 Sadeghi M, Süsal C, Daniel V et al.: Short communication: decreasing soluble CD30 and increasing IFN‑g plasma levels are indicators of effective highly active antiretroviral therapy. AIDS Res. Hum. Retroviruses 23(7), 886–890 (2007). future science group 54 Sandler NG, Wand H, Roque A et al.: Plasma levels of soluble CD14 independently predict mortality in HIV infection. J. Infect. Dis. 203(6), 780–790 (2011). n 55 Activation and coagulation biomarkers are independent predictors of the development of opportunistic disease in patients with HIV infection. J. Infect. Dis. 200(6), 973–983 (2009). 51 Baker JV, Neuhaus J, Duprez D et al.: Changes in inflammatory and coagulation biomarkers: a randomized comparison of immediate versus deferred antiretroviral therapy in patients with HIV infection. J. Acquir. Immune Defic. Syndr. 56(1), 36–43 (2011). www.futuremedicine.com Important substudy of the SMART study that established an association between elevated soluble CD14 and increased mortality in HIV‑infected patients receiving cART. Gabay C, Kushner I: Acute-phase proteins and other systemic responses to inflammation. N. Engl. J. Med. 340(6), 448–454 (1999). 56 Hingorani AD, Shah T, Casas JP, Humphries SE, Talmud PJ: C‑reactive protein and coronary heart disease: predictive test or therapeutic target? Clin. Chem. 55(2), 239–255 (2009). 57 Luc G, Bard J-M, Juhan-Vague I et al.: C‑reactive protein, interleukin‑6, and fibrinogen as predictors of coronary heart disease: the PRIME study. Arterioscler. Thromb. Vasc. Biol. 23(7), 1255–1261 (2003). 58 Lau B, Sharrett AR, Kingsley LA et al.: C‑reactive protein is a marker for human immunodeficiency virus disease progression. Arch. Intern. Med. 166(1), 64–70 (2006). 59 Triant VA, Meigs JB, Grinspoon SK: Association of C‑reactive protein and HIV infection with acute myocardial infarction. J. Acquir. Immune Defic. Syndr. 51(3), 268–273 (2009). 50 Rodger AJ, Fox Z, Lundgren JD et al.: 40 Mostafa H-M-H, Ali-Akbar P, Zahra S et al.: Soluble CD26 and CD30 plasma levels in HIV infected patients with and without GB virus type C co-infection. Pak. J. Biol. Sci. 10(12), 2014–2019 (2007). Provided the main body of evidence for biomarkers of immune activation and non-AIDS events in HIV-infected patients receiving cART Neuhaus J, Jacobs DR, Baker JV et al.: Markers of inflammation, coagulation, and renal function are elevated in adults with HIV infection. J. Infect. Dis. 201(12), 1788–1795 (2010). Interruption of antiretroviral therapy and risk of cardiovascular disease in persons with HIV‑1 infection: exploratory analyses from the SMART trial. Antivir. Ther. (Lond.) 13(2), 177–187 (2008). 48 El-Sadr WM, Lundgren JD, Neaton JD serum level of soluble CD30 in acute primary HIV‑1 infection. Clin. Exp. Immunol. 108(2), 251–253 (1997). Important substudy of Strategies for the Management of Antiretroviral Therapy (SMART) that investigated the relationship of C-reactive protein, IL‑6 and d-dimer as biomarkers in HIV-infected patients receiving cART. 53 Phillips AN, Carr A, Neuhaus J et al.: 47 Wolf K, Tsakiris DA, Weber R, Erb P, De Meester I: Dipeptidyl-peptidase IV from bench to bedside: an update on structural properties, functions, and clinical aspects of the enzyme DPP IV. Crit. Rev. Clin. Lab. Sci. 40(3), 209–294 (2003). 37 Pizzolo G, Vinante F, Nadali G et al.: High Messele T, Brouwer M, Girma M et al.: Plasma levels of viro-immunological markers in HIV-infected and non-infected Ethiopians: correlation with cell surface activation markers. Clin. Immunol. 98(2), 212–219 (2001). 46 Sipsas NV, Sfikakis PP, Kontos A, Hosono O, Homma T, Kobayashi H et al.: Decreased dipeptidyl peptidase IV enzyme activity of plasma soluble CD26 and its inverse correlation with HIV‑1 RNA in HIV‑1 infected individuals. Clin. Immunol. 91(3), 283–295 (1999). 36 Lambeir A-M, Durinx C, Scharpé S, 52 44 Widney D, Gundapp G, Said JW et al.: 33 Mavalia C, Scaletti C, Romagnani P et al.: 34 Keane NM, Price P, Lee S, Stone SF, nn Effect of highly active antiretroviral therapy on biomarkers of B‑lymphocyte activation and inflammation. AIDS 25(3), 303–314 (2011). Special Report 60 Chaudhary M, Kashyap B, Gautam H, Saini S, Bhalla P: Role of C‑reactive protein in HIV infection: a pilot study. Viral Immunol. 21(2), 263–266 (2008). 61 van Vonderen MGA, Hassink EAM, van Agtmael MA et al.: Increase in carotid artery intima-media thickness and arterial stiffness but improvement in several markers of endothelial function after initiation of antiretroviral therapy. J. Infect. Dis. 199(8), 1186–1194 (2009). 183 Special Report Lichtfuss, Hoy, Rajasuriar, Kramski, Crowe & Lewin 62 Funderburg N, Kalinowska M, Eason J et al.: Effects of maraviroc and efavirenz on markers of immune activation and inflammation and associations with CD4 + cell rises in HIVinfected patients. PLoS One 5(10), e13188 (2010). 63 Shikuma CM, Ribaudo HJ, Zheng Y et al.: Change in high-sensitivity C‑reactive protein (hsCRP) levels following initiation of efavirenz-based antiretroviral regimens in HIV‑infected individuals. AIDS Res. Hum. Retroviruses (2010) (Epub ahead of print). nn 74 65 Kishimoto T: Interleukin-6: from basic science to medicine – 40 years in immunology. Ann. Rev. Immunol. 23, 1–21 (2005). Collagen deposition limits immune reconstitution in the gut. J. Infect. Dis. 198(4), 456–464 (2008). 67 Harris TB, Ferrucci L, Tracy RP et al.: Cycling of gut mucosal CD4 + T cells decreases after prolonged anti-retroviral therapy and is associated with plasma LPS levels. Mucosal Immunol. 3(2), 172–181 (2010). Interleukin‑6 and D‑dimer levels are associated with vascular dysfunction in patients with untreated HIV infection. HIV Med. 11(9), 608–609 (2010). 69 Jong E, Louw S, Meijers JCM et al.: The hemostatic balance in HIV-infected patients with and without antiretroviral therapy: partial restoration with antiretroviral therapy. AIDS Patient Care STDS 23(12), 1001–1007 (2009). 70 Cohen HJ, Harris T, Pieper CF: Coagulation and activation of inflammatory pathways in the development of functional decline and mortality in the elderly. Am. J. Med. 114(3), 180–187 (2003). 71 Calmy A, Gayet-Ageron A, Montecucco F et al.: HIV increases markers of cardiovascular risk: results from a randomized, treatment interruption trial. AIDS 23(8), 929–939 (2009). 72 Duprez DA, Kuller LH, Tracy R et al.: Lipoprotein particle subclasses, cardiovascular disease and HIV infection. Atherosclerosis 207(2), 524–529 (2009). 73 Funderburg NT, Mayne E, Sieg SF et al.: Increased tissue factor expression on circulating monocytes in chronic HIV infection: relationship to in vivo coagulation and immune activation. Blood 115(2), 161–167 (2010). 184 86 Trøseid M, Nowak P, Nyström J, Lindkvist A, Abdurahman S, Sönnerborg A: Elevated plasma levels of lipopolysaccharide and high mobility group box‑1 protein are associated with high viral load in HIV‑1 infection: reduction by 2‑year antiretroviral therapy. AIDS 24(11), 1733–1737 (2010). 87 Lester RT, Yao X-D, Ball TB et al.: HIV‑1 RNA dysregulates the natural TLR response to subclinical endotoxemia in Kenyan female sex-workers. PLoS One 4(5), e5644 (2009). 88 Redd AD, Dabitao D, Bream JH et al.: Microbial translocation, the innate cytokine response, and HIV‑1 disease progression in Africa. Proc. Natl Acad. Sci. USA 106(16), 6718–6723 (2009). 77 Jiang W, Lederman MM, Hunt P et al.: Plasma levels of bacterial DNA correlate with immune activation and the magnitude of immune restoration in persons with antiretroviral-treated HIV infection. J. Infect. Dis. 199(8), 1177–1185 (2009). 89 Miller MA, McTernan PG, Harte AL et al.: Ethnic and sex differences in circulating endotoxin levels: a novel marker of atherosclerotic and cardiovascular risk in a British multi-ethnic population. Atherosclerosis 203(2), 494–502 (2009). 78 Brenchley J: Microbial translocation and T cell dysfunction. Presented at: 4th International AIDS Society Conference. Sydney, Australia, 22–25 June 2007 (Abstract TUSY402). Associations of elevated interleukin‑6 and C‑reactive protein levels with mortality in the elderly. Am. J. Med. 106(5), 506–512 (1999). 68 Baker J, Quick H, Hullsiek KH et al.: Persistent microbial translocation and immune activation in HIV‑1-infected South Africans receiving combination antiretroviral therapy. J. Infect. Dis. 202(5), 723–733 (2010). 76 Ciccone EJ, Read SW, Mannon PJ et al.: 66 Franceschi C, Capri M, Monti D et al.: Inflammaging and anti-inflammaging: a systemic perspective on aging and longevity emerged from studies in humans. Mech. Ageing Dev. 128(1), 92–105 (2007). Brenchley J, Schacker T, Ruff L et al.: CD4 + T cell depletion during all stages of HIV disease occurs predominantly in the gastrointestinal tract. J. Exp. Med. 200(6), 749 (2004). 85 Cassol E, Malfeld S, Mahasha P et al.: 75 Estes J, Baker JV, Brenchley JM et al.: 64 Ross AC, Rizk N, O’Riordan MA et al.: Relationship between inflammatory markers, endothelial activation markers, and carotid intima-media thickness in HIV‑infected patients receiving antiretroviral therapy. Clin. Infect. Dis. 49(7), 1119–1127 (2009). Important study that investigated the association between microbial translocation, immune activation and cardiovascular disease in HIV-infected patients receiving cART. 90 Opal SM, Scannon PJ, Vincent JL et al.: Relationship between plasma levels of lipopolysaccharide (LPS) and LPS-binding protein in patients with severe sepsis and septic shock. J. Infect. Dis. 180(5), 1584–1589 (1999). 79 Villar J, Pérez-Méndez L, Espinosa E et al.: Serum lipopolysaccharide binding protein levels predict severity of lung injury and mortality in patients with severe sepsis. PLoS One 4(8), e6818 (2009). 80 Hurley JC: Endotoxemia: methods of detection and clinical correlates. Clin. Microbiol. Rev. 8(2), 268–292 (1995). 81 Thomas LL, Sturk A, Kahlé LH, ten Cate JW: Quantitative endotoxin determination in blood with a chromogenic substrate. Clin. Chim. Acta 116(1), 63–68 (1981). 82 Novitsky TJ, Roslansky PF, Siber GR, Warren HS: Turbidimetric method for quantifying serum inhibition of Limulus amoebocyte lysate. J. Clin. Microbiol. 21(2), 211–216 (1985). 83 Rajasuriar R, Booth D, Solomon A et al.: Biological determinants of immune reconstitution in HIV-infected patients receiving antiretroviral therapy: the role of interleukin 7 and interleukin 7 receptor a and microbial translocation. J. Infect. Dis. 202(8), 1254–1264 (2010). 84 Anselmi A, Vendrame D, Rampon O, Giaquinto C, Zanchetta M, De Rossi A: Immune reconstitution in human immunodeficiency virus type 1-infected children with different virological responses to anti-retroviral therapy. Clin. Exp. Immunol. 150(3), 442–450 (2007). Biomarkers Med. (2011) 5(2) 91 Ancuta P, Kamat A, Kunstman KJ et al.: Microbial translocation is associated with increased monocyte activation and dementia in AIDS patients. PLoS One 3(6), e2516 (2008). 92 Cross AS, Opal SM, Warren HS et al.: Active immunization with a detoxified Escherichia coli J5 lipopolysaccharide group B meningococcal outer membrane protein complex vaccine protects animals from experimental sepsis. J. Infect. Dis. 183(7), 1079–1086 (2001). 93 Titanji K, De Milito A, Cagigi A et al.: Loss of memory B cells impairs maintenance of long-term serologic memory during HIV‑1 infection. Blood 108(5), 1580–1587 (2006). 94 Lien E, Aukrust P, Sundan A, Müller F, Frøland SS, Espevik T: Elevated levels of serum-soluble CD14 in human immunodeficiency virus type 1 (HIV‑1) infection: correlation to disease progression and clinical events. Blood 92(6), 2084–2092 (1998). 95 Wallet MA, Rodriguez CA, Yin L et al.: Microbial translocation induces persistent macrophage activation unrelated to HIV‑1 levels or T‑cell activation following therapy. AIDS 24(9), 1281–1290 (2010). future science group Biomarkers of immune dysfunction following combination antiretroviral therapy 96 Hamann L, Alexander C, Stamme C, Zähringer U, Schumann RR: Acute-phase concentrations of lipopolysaccharide (LPS)-binding protein inhibit innate immune cell activation by different LPS chemotypes via different mechanisms. Infect. Immun. 73(1), 193–200 (2005). 97 Fan H, Cook JA: Molecular mechanisms of endotoxin tolerance. J. Endotoxin Res. 10(2), 71–84 (2004). 98 Marchetti G, Bellistrì GM, Borghi E et al.: Microbial translocation is associated with sustained failure in CD4 + T‑cell reconstitution in HIV-infected patients on long-term highly active antiretroviral therapy. AIDS 22(15), 2035–2038 (2008). 99 Baroncelli S, Galluzzo CM, Pirillo MF et al.: Microbial translocation is associated with residual viral replication in HAARTtreated HIV+ subjects with <50 copies/ml HIV‑1 RNA. J. Clin. Virol. 46(4), 367–370 (2009). 100 Kitchens RL, Thompson PA: Modulatory effects of sCD14 and LBP on LPS–host cell interactions. J. Endotoxin Res. 11(4), 225–229 (2005). 101 Balagopal A, Philp FH, Astemborski J et al.: Human immunodeficiency virus-related microbial translocation and progression of hepatitis C. Gastroenterology 135(1), 226–233 (2008). 102 Crane M, Rajasuriar R, Avahingsanon A et al.: LPS, immune activation and liver disease in HIV‑HBV co-infection and the effects of HBV-active HAART. Presented at: 18th Conference on Retroviruses and Opportunistic Infections. Boston, MA, USA, 27 February–22 March 2011. 103 Robbins GK, Spritzler JG, Chan ES et al.: Incomplete reconstitution of T cell subsets on combination antiretroviral therapy in the AIDS Clinical Trials Group protocol 384. Clin. Infect. Dis. 48(3), 350–361 (2009). 104 Sakai K, Gatanaga H, Takata H, Oka S, Takiguchi M: Comparison of CD4 + T‑cell subset distribution in chronically infected HIV+ patients with various CD4 nadir counts. Microbes Infect. 12(5), 374–381 (2010). 105 Hunt P, Sinclair E, Epling L et al.: T cell senescence and proliferation defects persist in treated HIV-infected individuals maintaining viral suppression and are associated with poor CD4+ T cell recovery. Presented at:17th Conference on Retroviruses and Opportunistic Infections. San Francisco, CA, USA, 16–19 February 2010 (Abstract 316). 106 Desai S, Landay A: Early immune senescence in HIV disease. Curr. HIV/AIDS Rep. 7(1), 4–10 (2010). future science group 107 Boise LH, Minn AJ, Noel PJ et al.: CD28 costimulation can promote T cell survival by enhancing the expression of Bcl-xL. Immunity. 1995. 3: 87–98. J. Immunol. 185(7), 3788–3799 (2010). 108 Thompson CB, Lindsten T, Ledbetter JA et al.: CD28 activation pathway regulates the production of multiple T‑cell-derived lymphokines/cytokines. Proc. Natl Acad. Sci. USA 86(4), 1333–1337 (1989). 109 Sperling AI, Auger JA, Ehst BD, Rulifson IC, Thompson CB, Bluestone JA: CD28/B7 interactions deliver a unique signal to naive T cells that regulates cell survival but not early proliferation. J. Immunol. 157(9), 3909–3917 (1996). 110 Frauwirth KA, Riley JL, Harris MH et al.: The CD28 signaling pathway regulates glucose metabolism. Immunity 16(6), 769–777 (2002). 111 Vallejo AN: CD28 extinction in human T cells: altered functions and the program of T‑cell senescence. Immunol. Rev. 205, 158–169 (2005). 112 Choremi-Papadopoulou H, Panagiotou N, Samouilidou E et al.: CD28 costimulation and CD28 expression in T lymphocyte subsets in HIV-1 infection with and without progression to AIDS. Clin. Exp. Immunol. 119(3), 499–506 (2000). 113 Choi B-S, Park Y-K, Lee J-S: The CD28/ HLA-DR expressions on CD4 + T but not CD8 + T cells are significant predictors for progression to AIDS. Clin. Exp. Immunol. 127(1), 137–144 (2002). 114 Kaplan RC, Sinclair E, Landay AL et al.: T cell activation and senescence predict subclinical carotid artery disease in HIV-infected women. J. Infect. Dis. 203(4), 452–463 (2011). 115 Lange CG, Valdez H, Medvik K, Asaad R, Lederman MM: CD4 + T‑lymphocyte nadir and the effect of highly active antiretroviral therapy on phenotypic and functional immune restoration in HIV‑1 infection. Clin. Immunol. 102(2), 154–161 (2002). 116 Lange CG, Lederman MM: Immune reconstitution with antiretroviral therapies in chronic HIV‑1 infection. J. Antimicrobial Chemother. 51(1), 1–4 (2003). 117 Crane M, Sirivichayakul S, Chang JJ et al.: No increase in hepatitis B virus (HBV)specific CD8 + T cells in patients with HIV‑1–HBV co-infections following HBV-active highly active antiretroviral therapy. J. Virol. 84(6), 2657–2665 (2010). 118 Bourgarit A, Carcelain G, Samri A et al.: Tuberculosis-associated immune restoration syndrome in HIV‑1-infected patients involves tuberculin-specific CD4 Th1 cells and KIR-negative gd T cells. J. Immunol. 183(6), 3915–3923 (2009). www.futuremedicine.com Special Report 119 Elliott J, Vohith K, Saramony S et al.: Immunopathogenesis and diagnosis of tuberculosis and tuberculosis-associated immune reconstitution inflammatory syndrome during early antiretroviral therapy. J. Infect. Dis. 200(11), 1736–1745 (2009). 120 Sylwester AW, Mitchell BL, Edgar JB et al.: Broadly targeted human cytomegalovirusspecific CD4 + and CD8 + T cells dominate the memory compartments of exposed subjects. J. Exp. Med. 202(5), 673–685 (2005). 121 Stone SF, Price P, Khan N, Moss PA, French MA: HIV patients on antiretroviral therapy have high frequencies of CD8 T cells specific for immediate early protein‑1 of cytomegalovirus. AIDS 19(6), 555–562 (2005). 122 Singh KP, Howard JL, Wild SP, Jones SL, Hoy J, Lewin SR: Human cytomegalovirus (CMV)-specific CD8 + T cell responses are reduced in HIV‑infected individuals with a history of CMV disease despite CD4 + T cell recovery. Clin. Immunol. 124(2), 200–206 (2007). 123 Naeger DM, Martin JN, Sinclair E et al.: Cytomegalovirus-specific T cells persist at very high levels during long-term antiretroviral treatment of HIV disease. PLoS One 5(1), e8886 (2010). 124 Hsue PY, Hunt PW, Sinclair E et al.: Increased carotid intima-media thickness in HIV patients is associated with increased cytomegalovirus-specific T‑cell responses. AIDS 20(18), 2275–2283 (2006). 125 Hunt P, Martin J, Sinclair E et al.: Valganciclovir reduces CD8 + T cell activation among HIV-infected patients with suboptimal CD4 + T cell recovery during antiretroviral therapy. Presented at:17th Conference on Retroviruses and Opportunistic Infections. San Francisco, CA, USA, 16–19 February 2010 (Abstract 380). 126 Baume DM, Robertson MJ, Levine H, Manley TJ, Schow PW, Ritz J: Differential responses to interleukin 2 define functionally distinct subsets of human natural killer cells. Eur. J. Immunol. 22(1), 1–6 (1992). 127 Mavilio D, Lombardo G, Benjamin J et al.: Characterization of CD56 - /CD16 + natural killer (NK) cells: a highly dysfunctional NK subset expanded in HIV‑infected viremic individuals. Proc. Natl Acad. Sci. USA 102(8), 2886–2891 (2005). 128 Fogli M, Costa P, Murdaca G et al.: Significant NK cell activation associated with decreased cytolytic function in peripheral blood of HIV‑1-infected patients. Eur. J. Immunol. 34(8), 2313–2321 (2004). 185 Special Report Lichtfuss, Hoy, Rajasuriar, Kramski, Crowe & Lewin 129 Aktas E, Kucuksezer UC, Bilgic S, Erten G, Deniz G: Relationship between CD107a expression and cytotoxic activity. Cell Immunol. 254(2), 149–154 (2009). 130 Alter G, Malenfant JM, Delabre RM et al.: Increased natural killer cell activity in viremic HIV‑1 infection. J. Immunol. 173(8), 5305–5311 (2004). 131 Eller MA, Eller LA, Ouma BJ et al.: Elevated natural killer cell activity despite altered functional and phenotypic profile in Ugandans with HIV‑1 clade A or clade D infection. J. Acquir. Immune Defic. Syndr. 51(4), 380–389 (2009). 132 Hu PF, Hultin LE, Hultin P et al.: Natural killer cell immunodeficiency in HIV disease is manifest by profoundly decreased numbers of CD16 + CD56 + cells and expansion of a population of CD16dimCD56 - cells with low lytic activity. J. Acquir. Immune Defic. Syndr. Hum Retrovirol 10(3), 331–340 (1995). 133 Lucia B, Jennings C, Cauda R, Ortona L, Landay AL: Evidence of a selective depletion of a CD16 + CD56 + CD8 + natural killer cell subset during HIV infection. Cytometry 22(1), 10–15 (1995). 134 Plaeger-Marshall S, Spina CA, Giorgi JV et al.: Alterations in cytotoxic and phenotypic subsets of natural killer cells in acquired immune deficiency syndrome (AIDS). J. Clin. Immunol. 7(1), 16–23 (1987). 135 Sirianni MC, Mezzaroma I, Aiuti F, Moretta A: Analysis of the cytolytic activity mediated by natural killer cells from acquired immunodeficiency syndrome patients in response to phytohemagglutinin or anti-CD16 monoclonal antibody. Eur. J. Immunol. 24(8), 1874–1878 (1994). 136 Björkström NK, Ljunggren H-G, Sandberg JK: CD56 negative NK cells: origin, function, and role in chronic viral disease. Trends Immunol. 31(11), 401–406 (2010). 137 Ward J, Barker E: Role of natural killer cells in HIV pathogenesis. Curr. HIV/AIDS Rep. 5(1), 44–50 (2008). 138 Brunetta E, Hudspeth KL, Mavilio D: Pathologic natural killer cell subset redistribution in HIV‑1 infection: new insights in pathophysiology and clinical outcomes. J. Leukocyte Biol. 88(6), 1119–1130 (2010). 139 Villanueva JL, Caballero J, Del Nozal M et al.: Peripheral blood natural killer cell reconstitution after highly active antiretroviral therapy. AIDS 14(4), 473–474 (2000). 140 Chehimi J, Azzoni L, Farabaugh M et al.: Baseline viral load and immune activation determine the extent of reconstitution of 186 innate immune effectors in HIV‑1-infected subjects undergoing antiretroviral treatment. J. Immunol. 179(4), 2642–2650 (2007). 141 Xie J, Qiu Z-F, Han Y: [The reconstitutional profiles of peripheral blood natural killer cell, gd T lymphocyte and CD(4) + T cell in human immunodeficiency virus infected patients during one-year antiretroviral therapy]. Zhonghua Nei Ke Za Zhi 47(9), 750–753 (2008). 142 Lichtfuss GF, Meehan AC, Cheng W-J et al.: Inhibition of early signal transduction events in NK cells which are important for antibody-dependent cellular cytotoxicity in both antiretroviral therapy naive HIV patients and patients receiving ART. Presented at: Keystone Symposium on NK and NKT Cell Biology: Specificity and Redundancy of Innate Responses. Breckenridge, CO, USA, 9–14 January 2011 (Abstract 209). 143 Lichtfuss GF, Meehan AC, Cheng W-J et al.: HIV inhibits early signal transduction events triggered by CD16 cross-linking on NK cells, which are important for antibody-dependent cellular cytotoxicity. J. Leukocyte Biol. 89(1), 149–158 (2010). 144 Liu Q, Sun Y, Rihn S et al.: Matrix metalloprotease inhibitors restore impaired NK cell-mediated antibody-dependent cellular cytotoxicity in human immunodeficiency virus type 1 infection. J. Virol. 83(17), 8705–8712 (2009). 145 Grzywacz B, Kataria N, Verneris MR: CD56(dim)CD16 + NK cells downregulate CD16 following target cell induced activation of matrix metalloproteinases. Leukemia 21(2), 356–359; author reply 359 (2007). 146 Ziegler-Heitbrock L, Ancuta P, Crowe S et al.: Nomenclature of monocytes and dendritic cells in blood. Blood 116(16), e74–e80 (2010). 147 Ellery PJ, Tippett E, Chiu Y-L et al.: The CD16 + monocyte subset is more permissive to infection and preferentially harbors HIV‑1 in vivo. J. Immunol. 178(10), 6581–6589 (2007). 148 Jaworowski A, Kamwendo DD, Ellery P et al.: CD16 + monocyte subset preferentially harbors HIV‑1 and is expanded in pregnant Malawian women with Plasmodium falciparum malaria and HIV‑1 infection. J. Infect. Dis. 196(1), 38–42 (2007). 149 Thieblemont N, Weiss L, Sadeghi HM, Estcourt C, Haeffner-Cavaillon N: CD14lowCD16high: a cytokine-producing monocyte subset which expands during human immunodeficiency virus infection. Eur. J. Immunol. 25(12), 3418–3424 (1995). Biomarkers Med. (2011) 5(2) 150 Almeida M, Cordero M, Almeida J, Orfao A: Relationship between CD38 expression on peripheral blood T‑cells and monocytes, and response to antiretroviral therapy: a one-year longitudinal study of a cohort of chronically infected ART-naive HIV‑1+ patients. Cytometry B Clin. Cytom. 72(1), 22–33 (2007). 151 Leatham EW, Bath PM, Tooze JA, Camm AJ: Increased monocyte tissue factor expression in coronary disease. Br. Heart J. 73(1), 10–13 (1995). 152 Crowe SM, Westhorpe CLV, Mukhamedova N, Jaworowski A, Sviridov D, Bukrinsky M: The macrophage: the intersection between HIV infection and atherosclerosis. J. Leukocyte Biol. 87(4), 589–598 (2010). 153 Maisa A, Westhorpe C, Elliott J et al.: Premature onset of cardiovascular disease in HIV‑infected individuals: the drugs and the virus. HIV Ther. 4(6), 675–692 (2011). 154 Monforte ADA, Abrams D, Pradier C et al.: HIV-induced immunodeficiency and mortality from AIDS-defining and non-AIDS-defining malignancies. AIDS 22(16), 2143–2153 (2008). 155 Ambinder RF, Bhatia K, Martinez-Maza O, Mitsuyasu R: Cancer biomarkers in HIV patients. Curr. Opin. HIV AIDS 5(6), 531–537 (2010). 156 Brown TT, Qaqish RB: Antiretroviral therapy and the prevalence of osteopenia and osteoporosis: a meta-analytic review. AIDS 20(17), 2165–2174 (2006). 157 Ding C, Parameswaran V, Udayan R, Burgess J, Jones G: Circulating levels of inflammatory markers predict change in bone mineral density and resorption in older adults: a longitudinal study. J. Clin. Endocrinol. Metab. 93(5), 1952–1958 (2008). 158 Cauley JA, Danielson ME, Boudreau RM et al.: Inflammatory markers and incident fracture risk in older men and women: the Health Aging and Body Composition Study. J. Bone Miner. Res. 22(7), 1088–1095 (2007). 159 Group I-ES, Committee SS, Abrams D et al.: Interleukin‑2 therapy in patients with HIV infection. N. Engl. J. Med. 361(16), 1548–1559 (2009). 160 Kaplan RC, Sinclair E, Landay AL et al.: T‑cell senescence and T‑cell activation predict carotid atherosclerosis in HIV‑infected women. Presented at: 17th Conference on Retroviruses and Opportunistic Infections. San Francisco, CA, USA, 16–19 February 2010 (Abstract 709). future science group