PTG-100, an Oral α4ß7 Antagonist Peptide: Preclinical Development and Phase 1 and 2a Studies in Ulcerative Colitis.

BACKGROUND & AIMS: Oral therapies targeting the integrin α4ß7 may offer unique advantages for the treatment of inflammatory bowel disease. We characterized the oral α4ß7 antagonist peptide PTG-100 in preclinical models and established safety, pharmacokinetic/pharmacodynamic relationships, and efficacy in a phase 2a trial in patients with ulcerative colitis (UC). METHODS: In vitro studies measured binding properties of PTG-100. Mouse studies measured biomarkers and drug concentrations in blood and tissues. The phase 1 study involved healthy volunteers. In phase 2a, patients with moderate to severe active UC were randomized to receive PTG-100 (150, 300, or 900 mg) or placebo once daily for 12-weeks. RESULTS: PTG-100 potently and selectively blocks α4ß7. Oral dosing of PTG-100 in mice showed high levels of target engagement and exposure in gut-associated lymphoid tissues. In healthy volunteers, PTG-100 showed dose-dependent increases in plasma exposure and blood target engagement. Although this phase 2a study initially did not meet the primary endpoint, a blinded reread of the endoscopy videos by a third party indicated clinical efficacy in conjunction with histologic remission at doses correlating with less than 100% receptor occupancy in peripheral blood. CONCLUSIONS: PTG-100 showed local gastrointestinal tissue target engagement and inhibition of memory T-cell trafficking in mice. It was safe and well tolerated in phase 1 and 2 studies. Phase 2a data are consistent with biological and clinical response and showed a dose response reflecting similar activities in preclinical models and healthy individuals. These data suggest that local gut activity of an oral α4ß7 integrin antagonist, distinct from full target engagement in blood, are important for efficacy and the treatment of UC. (ClinicalTrials.gov, Number NCT02895100; EudraCT, Number 2016-003452-75).

Sofosbuvir and ribavirin in adolescents 12-17 years old with hepatitis C virus genotype 2 or 3 infection.

Children with chronic hepatitis C virus infection have limited treatment options. We evaluated the all-oral combination of sofosbuvir and ribavirin in adolescents aged 12-17 with hepatitis C virus genotype 2 or 3 (ClinicalTrials.gov NCT02175758). Fifty-two patients received sofosbuvir 400 mg once daily and weight-based ribavirin twice daily for 12 (genotype 2) or 24 (genotype 3) weeks. The pharmacokinetics of sofosbuvir and its metabolite GS-331007 were evaluated by intensive plasma sampling at day 7 in the first 10 patients enrolled and by sparse sampling in all patients throughout treatment. The primary efficacy endpoint was the percentage of patients with a sustained virologic response 12 weeks after treatment (SVR12). The median age of patients was 15 years, and 75% had genotype 3. Eighty-three percent of patients were treatment-naive, and 73% were infected by vertical transmission. Forty percent were assessed as not having cirrhosis; the remainder did not have a cirrhosis determination. Overall, SVR12 was achieved by 98% of patients (51/52; 95% confidence interval, 90%-100%). SVR12 rates were 100% (13/13) for patients with genotype 2 and 97% (38/39) for those with genotype 3. The single patient who did not achieve SVR12 was lost to follow-up after achieving SVR4. The most commonly reported adverse events were nausea (27%) and headache (23%). When compared with the exposure in adults treated in phase 2 and 3 sofosbuvir studies, the area under the curve and maximum concentration for sofosbuvir and GS-331007 in adolescents were within predefined pharmacokinetic equivalence boundaries of 50%-200%. CONCLUSION: Sofosbuvir and ribavirin was safe and highly effective in adolescents with chronic hepatitis C virus genotype 2 or 3 infection. (Hepatology 2017;66:1102-1110).

The safety and effectiveness of ledipasvir-sofosbuvir in adolescents 12-17 years old with hepatitis C virus genotype 1 infection.

No all-oral, direct-acting antiviral regimens have been approved for children with chronic hepatitis C virus (HCV) infection. We conducted a phase 2, multicenter, open-label study to evaluate the efficacy and safety of ledipasvir-sofosbuvir in adolescents with chronic HCV genotype 1 infection. One hundred patients aged 12-17 years received a combination tablet of 90 mg ledipasvir and 400 mg sofosbuvir once daily for 12 weeks. On the tenth day following initiation of dosing, 10 patients underwent an intensive pharmacokinetic evaluation of the concentrations of sofosbuvir, ledipasvir, and the sofosbuvir metabolite GS-331007. The primary efficacy endpoint was the percentage of patients with a sustained virologic response at 12 weeks posttreatment. Median age of patients was 15 years (range 12-17). A majority (80%) were HCV treatment-naive, and 84% were infected through perinatal transmission. One patient had cirrhosis, and 42 did not; in 57 patients the degree of fibrosis was unknown. Overall, 98% (98/100; 95% confidence interval 93%-100%) of patients reached sustained virologic response at 12 weeks. No patient had virologic failure. The 2 patients who did not achieve sustained virologic response at 12 weeks were lost to follow-up either during or after treatment. The three most commonly reported adverse events were headache (27% of patients), diarrhea (14%), and fatigue (13%). No serious adverse events were reported. Area under the concentration-time curve (tau) and maximum concentration values for sofosbuvir, ledipasvir, and GS-331007 were within the predefined pharmacokinetic equivalence boundaries of 50%-200% when compared with adults from phase 2 and 3 studies of ledipasvir and sofosbuvir. CONCLUSION: Ledipasvir-sofosbuvir was highly effective at treating adolescents with chronic HCV genotype 1 infection; the dose of ledipasvir-sofosbuvir currently used in adults was well tolerated in adolescents and had an appropriate pharmacokinetic profile. (Hepatology 2017;66:371-378).

Sofosbuvir plus pegylated interferon and ribavirin in patients with genotype 1 hepatitis C virus in whom previous therapy with direct-acting antivirals has failed.

UNLABELLED: Retreatment of patients who have not achieved sustained virological response (SVR) after treatment with investigational direct-acting antiviral agents (DAAs) has not been extensively studied. We conducted an open-label trial to assess the efficacy and safety of sofosbuvir (SOF) plus pegylated interferon (Peg-IFN) and ribavirin (RBV) in patients with genotype 1 hepatitis C virus (HCV) who participated in previous studies of one or more Gilead investigational DAAs in combination with RBV with or without Peg-IFN. We enrolled 80 patients at 40 sites. All patients received SOF 400 mg once daily plus Peg-IFN-α 180 µg/week and weight-based ribavirin (1,000 or 1,200 mg/day) for 12 weeks. The efficacy endpoint was the proportion of patients with SVR 12 weeks after discontinuation of therapy (SVR12). Of the 80 patients enrolled, 36 (45%) had received two or more courses of earlier treatment for HCV and 74 (93%) had at least one resistance-associated variant (RAV) at baseline. SVR12 was achieved by 63 of the 80 patients (79%) treated. Rates of SVR12 were similar across patient subgroups. Presence of RAVs at baseline did not appear to be associated with treatment failure. Seventy-one of eighty patients (89%) experienced at least one adverse event (AE), but most events were mild to moderate in severity. The most common AEs were fatigue, headache, and nausea. No patients discontinued all treatment because of AEs. CONCLUSION: These findings suggest that SOF plus Peg-IFN and RBV for 12 weeks is effective and safe in patients who have not achieved SVR with earlier regimens of one or more DAAs plus Peg-IFN and RBV.

Simtuzumab treatment of advanced liver fibrosis in HIV and HCV-infected adults: results of a 6-month open-label safety trial.

BACKGROUND: Chronic liver injury can result in fibrosis that may progress over years to end-stage liver disease. The most effective anti-fibrotic therapy is treatment of the underlying disease, however when not possible, interventions to reverse or slow fibrosis progression are needed. AIM: The aim of this study was to study the safety and tolerability of simtuzumab, a monoclonal antibody directed against lysyl oxidase-like 2 (LOXL2) enzyme, in subjects with hepatitis C virus (HCV), human immunodeficiency virus (HIV), or HCV-HIV co-infection and advanced liver disease. METHODS: Eighteen subjects with advanced liver fibrosis received simtuzumab 700 mg intravenously every 2 weeks for 22 weeks. Transjugular liver biopsies were performed during screening and at the end of treatment to measure hepatic venous pressure gradient (HVPG) and to stage fibrosis. RESULTS: Treatment was well-tolerated with no discontinuations due to adverse events. No significant changes were seen in HVPG or liver biopsy fibrosis score after treatment. Exploratory transcriptional and protein profiling using paired pre- and post-treatment liver biopsy and serum samples suggested up-regulation of TGF-ß3 and IL-10 pathways with treatment. CONCLUSION: In this open-label, pilot clinical trial, simtuzumab treatment was well-tolerated in HCV- and HIV-infected subjects with advanced liver disease. Putative modulation of TGF-ß3 and IL-10 pathways during simtuzumab treatment merits investigation in future trials.

All-oral combination of ledipasvir, vedroprevir, tegobuvir, and ribavirin in treatment-naïve patients with genotype 1 HCV infection.

UNLABELLED: This phase II trial assessed the efficacy and safety of a combination regimen of the nonstructural protein (NS)5A inhibitor ledipasvir (LDV), NS3 protease inhibitor vedroprevir (VDV), non-nucleoside NS5B inhibitor tegobuvir (TGV), and ribavirin (RBV) in treatment-naïve patients with chronic hepatitis C virus (HCV) genotype 1 without cirrhosis. Patients were randomized 1:2 to LDV 30 mg once daily (QD; Arm 1; n = 46) or LDV 90 mg QD (Arm 2; n = 94); patients in both arms also received VDV 200 mg QD, TGV 30 mg twice-daily, and RBV 1,000-1,200 mg/day. Patients in Arm 2 with vRVR, defined as HCV RNA below the lower limit of quantification (LLOQ) from treatment weeks 2 to 10, were randomized 1:1 to stop treatment at 12 weeks or continue for 24 weeks. Sustained virologic response 12 weeks after treatment (SVR12) was higher in patients receiving 90 mg of LDV for 24 weeks (63%), compared with LDV 90 mg for 12 weeks (54%) and LDV 30 mg for 24 weeks (48%). In patients with very rapid virologic response (vRVR) in Arm 2, SVR12 was achieved by 68% and 81% of patients treated for 12 and 24 weeks, respectively. Virologic breakthrough was more common in patients with HCV genotype 1a and was associated with resistance-associated variants for all three direct-acting antiviral agents (DAAs); however, in all but 1 patient who relapsed, resistance-associated variants directed against only one or two of the DAAs were detected. The most common adverse events were fatigue, headache, nausea, rash, and diarrhea. CONCLUSION: In patients with HCV genotype 1, an interferon-free regimen containing LDV/VDV/TGV/RBV was well tolerated and led to SVR12 in up to 63% of patients. LDV 90 mg is currently being investigated in combination with the nucleotide polymerase inhibitor, sofosbuvir.

Therapeutic helminth infection of macaques with idiopathic chronic diarrhea alters the inflammatory signature and mucosal microbiota of the colon.

Idiopathic chronic diarrhea (ICD) is a leading cause of morbidity amongst rhesus monkeys kept in captivity. Here, we show that exposure of affected animals to the whipworm Trichuris trichiura led to clinical improvement in fecal consistency, accompanied by weight gain, in four out of the five treated monkeys. By flow cytometry analysis of pinch biopsies collected during colonoscopies before and after treatment, we found an induction of a mucosal T(H)2 response following helminth treatment that was associated with a decrease in activated CD4(+) Ki67+ cells. In parallel, expression profiling with oligonucleotide microarrays and real-time PCR analysis revealed reductions in T(H)1-type inflammatory gene expression and increased expression of genes associated with IgE signaling, mast cell activation, eosinophil recruitment, alternative activation of macrophages, and worm expulsion. By quantifying bacterial 16S rRNA in pinch biopsies using real-time PCR analysis, we found reduced bacterial attachment to the intestinal mucosa post-treatment. Finally, deep sequencing of bacterial 16S rRNA revealed changes to the composition of microbial communities attached to the intestinal mucosa following helminth treatment. Thus, the genus Streptophyta of the phylum Cyanobacteria was vastly increased in abundance in three out of five ICD monkeys relative to healthy controls, but was reduced to control levels post-treatment; by contrast, the phylum Tenericutes was expanded post-treatment. These findings suggest that helminth treatment in primates can ameliorate colitis by restoring mucosal barrier functions and reducing overall bacterial attachment, and also by altering the communities of attached bacteria. These results also define ICD in monkeys as a tractable preclinical model for ulcerative colitis in which these effects can be further investigated.

Correlating cellular and molecular signatures of mucosal immunity that distinguish HIV controllers from noncontrollers.

HIV "controllers" are persons infected with human immunodeficiency virus, type I (HIV) who maintain long-term control of viremia without antiviral therapy and who usually do not develop the acquired immune deficiency syndrome (AIDS). In this study, we have correlated results from polychromatic flow cytometry and oligonucleotide expression arrays to characterize the mucosal immune responses of these subjects in relation to untreated HIV(+) persons with high viral loads and progressive disease ("noncontrollers"). Paired peripheral blood and rectosigmoid biopsies were analyzed from 9 controllers and 11 noncontrollers. Several cellular immune parameters were found to be concordant between the 2 compartments. Compared with noncontrollers, the mucosal tissues of controllers had similar levels of effector T cells and fewer regulatory T cells (Tregs). Using principal component analysis to correlate immunologic parameters with gene expression profiles, transcripts were identified that accurately distinguished between controllers and noncontrollers. Direct 2-way comparison also revealed genes that are significantly different in their expression between controllers and noncontrollers, all of which had reduced expression in controllers. In addition to providing an approach that integrates flow cytometry datasets with transcriptional profiling analysis, these results underscore the importance of the sustained inflammatory response that attends progressive HIV disease.

Cytokine profiles in peripheral blood of children and adults with Crohn disease.

BACKGROUND: Increasing evidence suggests that cytokine dysregulation in T-helper 1 and T-helper 2 (TH1/TH2) subsets contributes to the pathogenesis of Crohn disease (CD). The present pilot study examines the hypothesis that cytokine profiles differ between pediatric and adult patients with CD. METHODS: Production of TH1 cytokines interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α) and of TH2 cytokines interleukin-4 (IL-4) and IL-6 was analyzed in peripheral blood of patients with CD and healthy controls (n=20) using flow cytometry after in vitro stimulation. RESULTS: In both pediatric and adult subjects, frequencies of TNF-α CD4+ T cells were higher in patients with CD than in controls (P=0.009 and P=0.047, respectively). Percentages of cells expressing IL-4 were slightly increased (P=0.036), whereas those for IFN-γ were decreased (P=0.009) in pediatric patients with CD compared with controls. As expected, the overall production of TH1 cytokines was higher in adults compared with pediatric subjects. When memory CD4+CD45RO+ T cells were considered, lower IFN-γ expression was observed in pediatric subjects with CD compared with controls (P=0.009), matching the trend seen in the general CD4+ T cell population. The percentage of CD4+CD45RO+ T cells was increased in adult patients with CD compared with pediatric patients with CD (P=0.016). CONCLUSIONS: The present study describes a peripheral blood TH1/TH2 cytokine imbalance in CD and suggests different immunological mechanisms in children and adults for disease pathogenesis.

Transcriptional profiling in pathogenic and non-pathogenic SIV infections reveals significant distinctions in kinetics and tissue compartmentalization.

Simian immunodeficiency virus (SIV) infection leads to AIDS in experimentally infected macaques, whereas natural reservoir hosts exhibit limited disease and pathology. It is, however, unclear how natural hosts can sustain high viral loads, comparable to those observed in the pathogenic model, without developing severe disease. We performed transcriptional profiling on lymph node, blood, and colon samples from African green monkeys (natural host model) and Asian pigtailed macaques (pathogenic model) to directly compare gene expression patterns during acute pathogenic versus non-pathogenic SIV infection. The majority of gene expression changes that were unique to either model were detected in the lymph nodes at the time of peak viral load. Results suggest a shift toward cellular stress pathways and Th1 profiles during pathogenic infection, with strong and sustained type I and II interferon responses. In contrast, a strong type I interferon response was initially induced during non-pathogenic infection but resolved after peak viral load. The natural host also exhibited controlled Th1 profiles and better preservation of overall cell homeostasis. This study identified gene expression patterns that are specific to disease susceptibility, tissue compartmentalization, and infection duration. These patterns provide a unique view of how host responses differ depending upon lentiviral infection outcome.

Critical loss of the balance between Th17 and T regulatory cell populations in pathogenic SIV infection.

Chronic immune activation and progression to AIDS are observed after SIV infection in macaques but not in natural host primate species. To better understand this dichotomy, we compared acute pathogenic SIV infection in pigtailed macaques (PTs) to non-pathogenic infection in African green monkeys (AGMs). SIVagm-infected PTs, but not SIVagm-infected AGMs, rapidly developed systemic immune activation, marked and selective depletion of IL-17-secreting (Th17) cells, and loss of the balance between Th17 and T regulatory (Treg) cells in blood, lymphoid organs, and mucosal tissue. The loss of Th17 cells was found to be predictive of systemic and sustained T cell activation. Collectively, these data indicate that loss of the Th17 to Treg balance is related to SIV disease progression.

Persistent systemic inflammation and atypical enterocolitis in patients with NEMO syndrome.

The NEMO syndrome is a primary immunodeficiency with immune and non-immune manifestations. The immune deficiency is heterogeneous showing defects in humoral, innate, and cell-mediated immunity. While the clinical aspects of the immunodeficiency are increasingly well understood, little is known about autoimmune manifestations in NEMO patients. We therefore sought to examine serologic markers of systemic inflammation and intestinal pathology in a kindred of patients with the NEMO syndrome. We observed persistent elevation of erythrocyte sedimentation rates in five patients, and two were symptomatic, with a chronic but atypical enterocolitis. Though pathologic lesions in these two patients were consistent with acute inflammation, sustained clinical improvement was only achieved with systemic and/or topical glucocorticoid therapy. Our data suggest that some patients with the NEMO syndrome exhibit persistent elevation of inflammatory markers similar to systemic autoimmune diseases and may subsequently develop an atypical enterocolitis.

In vivo imaging of mucosal CD4+ T cells using single photon emission computed tomography in a murine model of colitis.

Immune responses that occur in the context of human infectious and inflammatory diseases are usually studied by sampling cells from peripheral blood, from biopsies, or by end-point harvests at necropsy. These approaches are likely to yield information that is incomplete and/or non-representative. Here, we report the development and validation of a non-invasive method to localize and to quantitate the disposition of specific subpopulations of cells in vivo. In a murine model of dextran sulfate sodium (DSS)-induced colitis, CD4+ T cells were visualized in the colon by single photon emission computed tomography (SPECT-CT) after injection of monoclonal, non-depleting, indium-111 (111In) labeled anti-CD4+ antibodies. The SPECT-CT colon uptake ratio (CUR) was found to correlate (p<0.01) with the number of total CD4+ T cells and with standard measures of pathology (colon length, cell counts, and histopathologic evidence of apoptosis, edema, and cellular infiltrates) as assessed by direct examination of diseased colon. Each of these parameters, including the SPECT-CT signal uptake, increased as a function of DSS dose (p<0.05). We conclude that CT-SPECT imaging using an 111In-labeled anti-CD4+ antibody is reflective of traditional parameters of pathology in this experimental model of murine colitis. This approach should be readily applicable to the imaging of discrete cell subpopulations in non-human primates and in humans, thus augmenting our understanding of infectious diseases and inflammation in vivo.

Identification of cinnabarinic acid as a novel endogenous aryl hydrocarbon receptor ligand that drives IL-22 production.

The aryl hydrocarbon receptor (AHR) binds to environmental toxicants including synthetic halogenated aromatic hydrocarbons and is involved in a diverse array of biological processes. Recently, the AHR was shown to control host immunity by affecting the balance between inflammatory T cells that produce IL-17 (Th17) and IL-22 versus regulatory T cells (Treg) involved in tolerance. While environmental AHR ligands can mediate this effect, endogenous ligands are likely to be more relevant in host immune responses. We investigated downstream metabolites of tryptophan as potential AHR ligands because (1) tryptophan metabolites have been implicated in regulating the balance between Th17 and Treg cells and (2) many of the AHR ligands identified thus far are derivatives of tryptophan. We characterized the ability of tryptophan metabolites to bind and activate the AHR and to increase IL-22 production in human T cells. We report that the tryptophan metabolite, cinnabarinic acid (CA), is an AHR ligand that stimulates the differentiation of human and mouse T cells producing IL-22. We compare the IL-22-stimulating activity of CA to that of other tryptophan metabolites and define stimulation conditions that lead to CA production from immune cells. Our findings link tryptophan metabolism to AHR activation and define a novel endogenous AHR agonist with potentially broad biological functions.

Genome-wide association study to characterize serum bilirubin elevations in patients with HCV treated with GS-9256, an HCV NS3 serine protease inhibitor.

BACKGROUND: Protease inhibitors for the treatment of HCV can cause mild and reversible elevations of unconjugated bilirubin. We sought to characterize genetic determinants of bilirubin elevations using a genome-wide approach among patients with genotype 1 HCV who received combination therapy that included GS-9256, a novel potent inhibitor of HCV NS3 serine protease, as part of a Phase IIb trial. METHODS: Of the 200 patients sampled, 176 had confirmed European ancestry and were included in the analysis. Infinium HumanOmni5BeadChip (Illumina, Inc., San Diego, CA, USA) was used for genotyping. A categorical analysis of low (grade 0-1) versus high (grade 2-4) bilirubin toxicity grade and a quantitative trait locus mapping of peak bilirubin concentrations was performed. RESULTS: A total of 4,466,809 genetic markers were analysed. No single variant showed a statistically significant association with observed bilirubin elevations in this patient population. In a targeted analysis of single nucleotide polymorphisms in genes known to be involved in bilirubin transport, no significant differences in allele frequency between high and low bilirubin toxicity grade were observed. CONCLUSIONS: These results indicate that risk for bilirubin elevation in patients receiving GS-9256 is unlikely to be strongly influenced by common genetic variants with large effects. The current study cannot rule out a role for common variants of weak effect, or a more complex model, including multiple contributing factors, such as rare variants and as yet unidentified environmental influences.

SIV replication in the infected rhesus macaque is limited by the size of the preexisting TH17 cell compartment.

The mechanisms by which some HIV-infected subjects resist disease progression, whereas others progress rapidly, are incompletely understood. Viral and host genetic factors, such as nef deletions and major histocompatibility complex alleles, explain a portion of the observed variability. However, it has been difficult to identify host immune functions that may be present before infection and that allow resistance to lentiviral disease progression. Here, we show that simian immunodeficiency virus replication in the infected rhesus macaque is limited by the size of the preexisting T helper 17 (T(H)17) cell compartment: Animals with a high representation of such cells in blood and intestinal tissue before infection experienced peak and set-point viral loads about one log unit lower than those with a lower representation of T(H)17 cells. Reciprocally, treatment of macaques with interleukin-2 and granulocyte colony-stimulating factor before infection led to depletion of T(H)17 cells, reduction of the ratio between T(H)17 cells and CD3(+)CD4(+)CD25(+)CD127(low) regulatory T cells, and higher viral loads for 6 months after infection. These results demonstrate that the composition of the host immune system before infection has an influence on the course of disease after infection. Furthermore, to the extent that this influence shapes and interacts with T cell-mediated responses to virus, our findings provide a new framework for understanding interindividual variation in responses to therapies and vaccines against HIV.

Th17 and regulatory T cells: implications for AIDS pathogenesis.

PURPOSE OF REVIEW: The present review discusses recent reports showing that reciprocal changes in T helper interleukin-17-secreting CD4 Th17 cells and CD4CD25FoxP3 regulatory T cells (Tregs) may play a role in the progressive disease caused by the HIV and by simian immunodeficiency virus. RECENT FINDINGS: Studies in nonhuman primate models of lentiviral infection and in HIV-infected human individuals have shown that pathogenic infection is associated with loss of Th17 cells and an increase in the frequency of Tregs. Because interleukin-17 serves to maintain the integrity of the mucosal barrier, loss of Th17 cells may permit the increase in microbial translocation across the gastrointestinal mucosa that is observed in pathogenic lentiviral disease. It remains unclear, however, whether Th17 cells are preferentially infected or if, instead, their loss is induced by bystander effects of lentiviral infection, for example, the induction of indoleamine 2,3-dioxygenase. SUMMARY: Progressive lentiviral disease is associated with preferential depletion of Th17 cells and loss of Th17/Treg balance. Further analysis of such changes in the composition of subset CD4 T helper and Tregs may shed new light on the immunopathology of HIV disease and suggest new strategies for therapeutic and preventive interventions.

Tryptophan catabolism by indoleamine 2,3-dioxygenase 1 alters the balance of TH17 to regulatory T cells in HIV disease.

The pathogenesis of human and simian immunodeficiency viruses is characterized by CD4(+) T cell depletion and chronic T cell activation, leading ultimately to AIDS. CD4(+) T helper (T(H)) cells provide protective immunity and immune regulation through different immune cell functional subsets, including T(H)1, T(H)2, T regulatory (T(reg)), and interleukin-17 (IL-17)-secreting T(H)17 cells. Because IL-17 can enhance host defenses against microbial agents, thus maintaining the integrity of the mucosal barrier, loss of T(H)17 cells may foster microbial translocation and sustained inflammation. Here, we study HIV-seropositive subjects and find that progressive disease is associated with the loss of T(H)17 cells and a reciprocal increase in the fraction of the immunosuppressive T(reg) cells both in peripheral blood and in rectosigmoid biopsies. The loss of T(H)17/T(reg) balance is associated with induction of indoleamine 2,3-dioxygenase 1 (IDO1) by myeloid antigen-presenting dendritic cells and with increased plasma concentration of microbial products. In vitro, the loss of T(H)17/T(reg) balance is mediated directly by the proximal tryptophan catabolite from IDO metabolism, 3-hydroxyanthranilic acid. We postulate that induction of IDO may represent a critical initiating event that results in inversion of the T(H)17/T(reg) balance and in the consequent maintenance of a chronic inflammatory state in progressive HIV disease.