Julie C. Gaardbo

Incomplete immune recovery in HIV infection: mechanisms, relevance for clinical care, and possible solutions.

Treatment of HIV-infected patients with highly active antiretroviral therapy (HAART) usually results in diminished viral replication, increasing CD4+ cell counts, a reversal of most immunological disturbances, and a reduction in risk of morbidity and mortality. However, approximately 20% of all HIV-infected patients do not achieve optimal immune reconstitution despite suppression of viral replication. These patients are referred to as immunological nonresponders (INRs). INRs present with severely altered immunological functions, including malfunction and diminished production of cells within lymphopoetic tissue, perturbed frequencies of immune regulators such as regulatory T cells and Th17 cells, and increased immune activation, immunosenescence, and apoptosis. Importantly, INRs have an increased risk of morbidity and mortality compared to HIV-infected patients with an optimal immune reconstitution. Additional treatment to HAART that may improve immune reconstitution has been investigated, but results thus far have proved disappointing. The reason for immunological nonresponse is incompletely understood. This paper summarizes the known and unknown factors regarding the incomplete immune reconstitution in HIV infection, including mechanisms, relevance for clinical care, and possible solutions.

Microbial translocation in HIV infection is associated with dyslipidemia, insulin resistance, and risk of myocardial infarction.

Objective:Microbial translocation has been suggested to be a driver of immune activation and inflammation. It is hypothesized that microbial translocation may be related to dyslipidemia, insulin resistance, and the risk of coronary heart disease in HIV-infected individuals. Design:Cross-sectional study of 60 HIV-infected patients on combination antiretroviral therapy with viral suppression >2 years and 31 healthy age-matched controls. Methods:Lipopolysaccharide (LPS) was analyzed by limulus amebocyte lysate colorimetric assay. Lipids, including cholesterol, low-density lipoprotein (LDL), and triglycerides, were measured. Glucose metabolism was determined using an oral glucose tolerance test. Body composition was determined using whole-body dual-energy x-ray absorptiometry scans and magnetic resonance imaging. The Framingham risk score was used to assess risk of cardiovascular disease and myocardial infarction. Results:HIV-infected patients had higher level of LPS compared with controls (64 pg/mL vs. 50 pg/mL, P = 0.002). Likewise, HIV-infected patients had higher triglycerides, LDL, and fasting insulin as well as evidence of lower insulin sensitivity compared with controls. Among HIV-infected patients, high LPS was associated with a higher level of triglycerides and LDL and with lower insulin sensitivity. Importantly, among HIV-infected patients, high LPS was associated with a higher Framingham risk score. Conclusions:HIV-infected patients with suppressed viral replication had increased level of microbial translocation as measured by LPS. LPS was associated with cardiometabolic risk factors and increased Framingham risk score. Hence, the gastrointestinal mucosal barrier may be a potential therapeutic target to prevent dyslipidemia and future cardiovascular complications in HIV infection.

Increased levels of regulatory T cells (Tregs) in human immunodeficiency virus-infected patients after 5 years of highly active anti-retroviral therapy may be due to increased thymic production of naive Tregs.

This study determines levels of regulatory T cells (Tregs), naive Tregs, immune activation and cytokine patterns in 15 adult human immunodeficiency virus (HIV)‐infected patients receiving prolonged highly active anti‐retroviral therapy (HAART) who have known thymic output, and explores if naive Tregs may represent recent thymic emigrant Tregs. HIV‐infected patients treated with HAART with a median of 1 and 5 years were compared with healthy controls. Percentages of Tregs (CD3+CD4+CD25+CD127low), naive Tregs (CD3+CD4+CD25+CD45RA+) and activation markers (CD38+human leucocyte antigen D‐related) were determined by flow cytometry. Forkhead box P3 mRNA expression and T cell receptor excision circles (TREC) content in CD4+ cells were determined by polymerase chain reaction and cytokines analysed with Luminex technology. Levels of Tregs were significantly higher in HIV‐infected patients compared with controls, both after 1 and 5 years of HAART (P < 0·001), despite fully suppressed HIV‐RNA and normalization of both CD4 counts, immune activation and cytokine patterns. Furthermore, levels of naive Tregs were elevated significantly in HIV‐infected patients (P < 0·001) and were associated with thymic output measured as the TREC frequency in CD4+ cells (P = 0·038). In summary, Treg levels in HIV‐infected patients are elevated even after 5 years of HAART. Increased thymic production of naive Tregs may contribute to higher Treg levels in HIV‐infection.

Persisting inflammation and chronic immune activation but intact cognitive function in HIV-infected patients after long-term treatment with combination antiretroviral therapy.

Objectives:Impaired cognitive function in HIV-infected patients has been suggested. Treatment with combination antiretroviral therapy (cART) restores CD4+ cell counts and suppresses viral replication, but immune activation and inflammation may persist. The aim of the study was to examine if cognitive function in HIV-infected patients was related to immune activation and inflammation. Methods:Sixty-one HIV-infected patients and 31 healthy controls were included. All patients were on treatment with cART, had suppressed viral replication, and had a mean CD4+ cell count of 522 cells/&mgr;L. Cognitive function was assessed using a test battery of neurocognitive tests. Plasma concentrations of interleukin-6 (IL-6), tumor necrosis factor-&agr; (TNF-&agr;), and &bgr;-2-microglobulin were measured. Immune activation (CD8+HLR-DR+CD38+ cells) was determined using flow cytometry. Multiple linear regression analysis was performed to identify relationship between cognitive scores and markers of inflammation and immune activation. Results:HIV-infected patients had intact cognitive function compared with healthy controls. Higher levels of TNF-&agr;, &bgr;-2-microglobulin, and chronic activated CD8+ cells were found in HIV-infected patients (P = 0.0002, P < 0.0001, and P = 0.021, respectively). Weak negative correlations were found between chronic activated CD8+ cells (&bgr;-coefficient = −0.277, P = 0.044), IL-6 (&bgr;-coefficient = −0.280, P = 0.014), and memory and learning. Conclusions:HIV-infected patients on cART with undetectable viral load had an increased level of inflammation and immune activation. However, intact cognitive function was found, and only weak correlations were found between cognitive function and markers of inflammation and immune activation, indicating that peripheral inflammation and immune activation are not major drivers of cognitive decay in HIV-infected patients.

CD4+ and CD8+ Regulatory T Cells (Tregs) are Elevated and Display an Active Phenotype in Patients with Chronic HCV Mono‐Infection and HIV/HCV Co‐Infection

The aim of this study was to examine regulatory T cells (Tregs) in peripheral blood and liver tissue in patients with chronic hepatitis C virus (HCV) mono‐infection and in patients with HIV/HCV co‐infection. In a cross‐sectional study were included 51 patients with chronic HCV infection, 24 patients with HIV/HCV co‐infection and 24 healthy individuals. CD4+ and CD8+ Tregs were determined using flow cytometry. Fibrosis was examined by transient elastography. Inflammation, fibrosis and Tregs were determined in liver biopsies from 12 patients. Increased frequency of CD4+ and CD8+ Tregs was found in HIV/HCV co‐infected patients [median: 6.4% (IQR: 5.7–6.9) and 1.0% (0.7–1.2), respectively] compared to HCV mono‐infected patients [5.6% (4.2–6.3), P = 0.01 and 0.5% (0.3–0.7), P < 0.001, respectively]. Furthermore, HCV mono‐infected patients had increased frequencies of Tregs compared with healthy controls (P < 0.05). However, no associations between the frequency of Tregs and fibrosis were found. Furthermore, characterization of CD4+ Tregs using CD45RA demonstrated a higher frequency of activated Tregs in both HCV mono‐infected and HIV/HCV co‐infected patients compared with healthy controls. Finally, number of intrahepatic Tregs was associated with both peripheral CD8+ Tregs and intrahepatic inflammation. In conclusion, HCV mono‐infected patients and particularly HIV/HCV co‐infected patients have increased the frequency of CD4+ and CD8+ Tregs compared with healthy controls. Furthermore, CD4+ Tregs in infected patients displayed an active phenotype. Tregs were not associated with fibrosis, but a positive correlation between intrahepatic Tregs and inflammation was found. Taken together, these results suggest a role for Tregs in the pathogenesis of chronic HCV infection.

Thirty Years with HIV Infection—Nonprogression Is Still Puzzling: Lessons to Be Learned from Controllers and Long-Term Nonprogressors

In the early days of the HIV epidemic, it was observed that a minority of the infected patients did not progress to AIDS or death and maintained stable CD4+ cell counts. As the technique for measuring viral load became available it was evident that some of these nonprogressors in addition to preserved CD4+ cell counts had very low or even undetectable viral replication. They were therefore termed controllers, while those with viral replication were termed long-term nonprogressors (LTNPs). Genetics and virology play a role in nonprogression, but does not provide a full explanation. Therefore, host differences in the immunological response have been proposed. Moreover, the immunological response can be divided into an immune homeostasis resistant to HIV and an immune response leading to viral control. Thus, non-progression in LTNP and controllers may be due to different immunological mechanisms. Understanding the lack of disease progression and the different interactions between HIV and the immune system could ideally teach us how to develop a functional cure for HIV infection. Here we review immunological features of controllers and LTNP, highlighting differences and clinical implications.

Increased Tryptophan Catabolism Is Associated With Increased Frequency of CD161+Tc17/MAIT Cells and Lower CD4+ T-Cell Count in HIV-1 Infected Patients on cART After 2 Years of Follow-Up.

Background:HIV infection is associated with increased ratio between kynurenine and tryptophan (KTR) in plasma, increased microbial translocation, expansion of regulatory T cells (Tregs), and depletion of Tc17/mucosa-associated invariant T (MAIT) cells. The association between these parameters and the impact of KTR on CD4+ T-cell recovery in HIV-infected patients on combination antiretroviral therapy (cART) after 2 years of follow-up was investigated. Methods:Forty-one HIV-infected individuals treated with cART for a minimum of 2 years were included. Tregs, CD161+Tc17/MAIT cells, naive cells, immune activation, senescence, and apoptosis were measured using flow cytometry. Soluble CD14 (sCD14), lipopolysaccharide, and tryptophan metabolites in plasma were measured retrospectively before cART and at inclusion initiation using Limulus Amebocyte Lysate colometric assay, enzyme-linked immunosorbent assay, and tandem mass spectrometry, respectively. KTR was calculated, and patients were divided into 2 groups defined by high vs. low KTR. CD4+ T-cell count was determined at inclusion and after 2 years of follow-up. Results:KTR decreased after cART initiation. Patients on cART with high KTR displayed an immunological profile with high sCD14, high percentage Tregs, low percentage CD161+Tc17/MAIT cells, low percentage naive cells, low CD4/CD8 ratio, and poor immune reconstitution after 2 years of follow-up compared with patients with low KTR. Conclusions:Our results support the hypothesis that tryptophan catabolism, indoleamine 2,3-dioxygenase 1 (IDO1) activation, microbial translocation, and perturbed distribution of Tregs and CD161+Tc17/MAIT cells are part of a vicious circle that perpetuates exhaustion of the immune system and progression of untreated HIV infection and challenge immune reconstitution in patients on cART.

Immunoregulatory T cells may be involved in preserving CD4 T cell counts in HIV-infected long-term nonprogressors and controllers.

Background:HIV-infected controllers control viral replication and maintain normal CD4 T cell counts. Long-term nonprogressors (LTNPs) also maintain normal CD4 T cell counts but have ongoing viral replication. We hypothesized that immunoregulatory mechanisms are involved in preserved CD4 T cell counts in controllers and in LTNPs. Methods:Twenty HIV-infected viremic controllers, 5 elite controllers (ECs), and 14 LTNPs were included in this cross-sectional study. For comparison, 25 progressors and 34 healthy controls were included. Regulatory T cells (Tregs), Treg subpopulations, CD161+Th17 cells, and CD3+CD8+CD161highTc17 cells in peripheral blood were measured using flow cytometry. Tregs in lymphoid tissue were determined in tonsil biopsies and evaluated using immunolabeling. The production of transforming growth factor beta (TGF-&bgr;), interleukin (IL)-10, and IL-17 upon stimulation with phytohemagglutinin in peripheral blood was determined by Luminex. Results:All groups of HIV-infected patients displayed similar percentages of Tregs in both peripheral blood and lymphoid tissue. However, a larger percentage of Tregs in ECs and LTNPs were activated compared with that in controls, progressors, and viremic controllers. Further, ECs as the only group of HIV-infected patients, displayed elevated percentages of CD161+Th17 cells, preserved CD3+CD8+CD161highTc17 cells, and preserved IL-10 production. Conclusions:Overall, Treg percentage was similar in both blood and lymphoid tissue in all groups of patients and controls. However, both ECs and LTNPs displayed a large proportion of activated Tregs suggesting immunoregulatory mechanisms to be involved in preserving CD4 T cell counts in HIV-infected nonprogressors.

Impaired thymic output in patients with chronic hepatitis C virus infection.

Altered T cell homeostasis in chronic hepatitis C virus (HCV) infection has been demonstrated. However, it is unknown whether fibrosis is associated with more perturbed T cell homeostasis in chronic HCV infection. The aim of this study was to examine and compare T cell subsets including recent thymic emigrants (RTE), naive, memory, senescent, apoptotic and IL‐7 receptor α (CD127) expressing CD4+ and CD8+ T cells as well as telomere length and interferon‐γ production in HCV‐infected patients with (n = 25) and without (n = 26) fibrosis as well as in healthy controls (n = 24). Decreased proportions of CD4+ and CD8+ RTE were found in HCV‐infected patients, especially in HCV‐infected patients with fibrosis (14.3% (9.7–23.0) and 28.8% (16.1–40.5), respectively) compared with healthy controls (24.2% (16.3–32.1), P = 0.004 and 39.1% (31.6–55.0), P = 0.010, respectively). Furthermore, HCV‐infected patients with fibrosis presented with a higher proportion of CD4+ T cells expressing CD127 compared with HCV‐infected patients without fibrosis [88.4% (84.5–91.0) versus 83.8% (79.9–86.8), P = 0.016]. Thus, impaired thymic output in HCV infection was found, and high proportion of CD127+ T cells may illustrate a compensatory mechanism to preserve T cell counts.

CD3+CD8+CD161high Tc17 cells are depleted in HIV-infection.

CD8+ Tc17 cells with pro-inflammatory properties have only recently been acknowledged, and Tc17 cells in HIV-infection are not described. CD3+CD8+CD161high Tc17 cells and the production of interleukin (IL)-17 were examined in untreated and treated HIV-infected patients, HIV–hepatitis C virus co-infected patients, and healthy controls. Depletion of CD3+CD8+CD161high Tc17 cells and diminished production of IL-17 in HIV-infected patients were found. The level of Tc17 cells was associated with the CD4+ cell count in treated patients.