Interleukin 21 Drives a Hypermetabolic State and CD4+ T-Cell-Associated Pathogenicity in Chronic Intestinal Inflammation.

BACKGROUND & AIMS: Incapacitated regulatory T cells (Tregs) contribute to immune-mediated diseases. Inflammatory Tregs are evident during human inflammatory bowel disease; however, mechanisms driving the development of these cells and their function are not well understood. Therefore, we investigated the role of cellular metabolism in Tregs relevant to gut homeostasis. METHODS: Using human Tregs, we performed mitochondrial ultrastructural studies via electron microscopy and confocal imaging, biochemical and protein analyses using proximity ligation assay, immunoblotting, mass cytometry and fluorescence-activated cell sorting, metabolomics, gene expression analysis, and real-time metabolic profiling utilizing the Seahorse XF analyzer. We used a Crohn's disease single-cell RNA sequencing dataset to infer the therapeutic relevance of targeting metabolic pathways in inflammatory Tregs. We examined the superior functionality of genetically modified Tregs in CD4+ T-cell-induced murine colitis models. RESULTS: Mitochondria-endoplasmic reticulum appositions, known to mediate pyruvate entry into mitochondria via voltage-dependent anion channel 1 (VDAC1), are abundant in Tregs. VDAC1 inhibition perturbed pyruvate metabolism, eliciting sensitization to other inflammatory signals reversible by membrane-permeable methyl pyruvate supplementation. Notably, interleukin (IL) 21 diminished mitochondria-endoplasmic reticulum appositions, resulting in enhanced enzymatic function of glycogen synthase kinase 3 ß, a putative negative regulator of VDAC1, and a hypermetabolic state that amplified Treg inflammatory response. Methyl pyruvate and glycogen synthase kinase 3 ß pharmacologic inhibitor (LY2090314) reversed IL21-induced metabolic rewiring and inflammatory state. Moreover, IL21-induced metabolic genes in Tregs in vitro were enriched in human Crohn's disease intestinal Tregs. Adoptively transferred Il21r-/- Tregs efficiently rescued murine colitis in contrast to wild-type Tregs. CONCLUSIONS: IL21 triggers metabolic dysfunction associated with Treg inflammatory response. Inhibiting IL21-induced metabolism in Tregs may mitigate CD4+ T-cell-driven chronic intestinal inflammation.

G9a Modulates Lipid Metabolism in CD4 T Cells to Regulate Intestinal Inflammation.

BACKGROUND & AIMS: Although T-cell intrinsic expression of G9a has been associated with murine intestinal inflammation, mechanistic insight into the role of this methyltransferase in human T-cell differentiation is ill defined, and manipulation of G9a function for therapeutic use against inflammatory disorders is unexplored. METHODS: Human naive T cells were isolated from peripheral blood and differentiated in vitro in the presence of a G9a inhibitor (UNC0642) before being characterized via the transcriptome (RNA sequencing), chromatin accessibility (assay for transposase-accessible chromatin by sequencing), protein expression (cytometry by time of flight, flow cytometry), metabolism (mitochondrial stress test, ultrahigh performance liquid chromatography-tandem mas spectroscopy) and function (T-cell suppression assay). The in vivo role of G9a was assessed using 3 murine models. RESULTS: We discovered that pharmacologic inhibition of G9a enzymatic function in human CD4 T cells led to spontaneous generation of FOXP3+ T cells (G9a-inibitors-T regulatory cells [Tregs]) in vitro that faithfully reproduce human Tregs, functionally and phenotypically. Mechanistically, G9a inhibition altered the transcriptional regulation of genes involved in lipid biosynthesis in T cells, resulting in increased intracellular cholesterol. Metabolomic profiling of G9a-inibitors-Tregs confirmed elevated lipid pathways that support Treg development through oxidative phosphorylation and enhanced lipid membrane composition. Pharmacologic G9a inhibition promoted Treg expansion in vivo upon antigen (gliadin) stimulation and ameliorated acute trinitrobenzene sulfonic acid-induced colitis secondary to tissue-specific Treg development. Finally, Tregs lacking G9a expression (G9a-knockout Tregs) remain functional chronically and can rescue T-cell transfer-induced colitis. CONCLUSION: G9a inhibition promotes cholesterol metabolism in T cells, favoring a metabolic profile that facilitates Treg development in vitro and in vivo. Our data support the potential use of G9a inhibitors in the treatment of immune-mediated conditions including inflammatory bowel disease.

Child-Turcotte-Pugh versus MELD-XI identify distinct high-risk populations for heart transplantation following ventricular assist device placement.

BACKGROUND: Patients with end-stage heart failure frequently have significant congestive hepatopathy requiring hepatology assessment prior to heart transplantation listing. An elevated Model for End-stage Liver Disease score with modification to exclude INR (MELD-XI) has been associated with increased mortality following heart transplantation (HT). This study's primary aim was to examine whether Child-Turcotte-Pugh (CTP) classification is associated with post-transplant mortality in patients bridged to transplant with left ventricular assist devices. METHODS AND RESULTS: We conducted a retrospective analysis of 134 patients from our center. Age, CTP class, and MELD-XI at HT were included in the multivariate model for the primary outcome, which demonstrated a significant association between 1-year mortality and CTP class (CTP-A HR: .08, CI .01-.46, P < .01; CTP-B HR: .25, CI .05-1.2, P = .08; reference group CTP-C), and MELD-XI (HR: 1.15; CI: 1.03-1.28; P = .01), but no significant difference for age (HR: .97; CI: .93-1.01; P = .15). Only 13/33 patients with CTP improvement after assist device also had improvement in MELD-XI. CONCLUSIONS: Patients with relatively low MELD-XI scores with discordantly high CTP classification may be a distinct subset for whom MELD-XI underestimates the risk of mortality after heart transplantation compared to CTP.

Brief treatment with a highly selective immunoproteasome inhibitor promotes long-term cardiac allograft acceptance in mice.

Constitutive proteasomes (c-20S) are ubiquitously expressed cellular proteases that degrade polyubiquitinated proteins and regulate cell functions. An isoform of proteasome, the immunoproteasome (i-20S), is highly expressed in human T cells, dendritic cells (DCs), and B cells, suggesting that it could be a potential target for inflammatory diseases, including those involving autoimmunity and alloimmunity. Here, we describe DPLG3, a rationally designed, noncovalent inhibitor of the immunoproteasome chymotryptic subunit ß5i that has thousands-fold selectivity over constitutive ß5c. DPLG3 suppressed cytokine release from blood mononuclear cells and the activation of DCs and T cells, diminished accumulation of effector T cells, promoted expression of exhaustion and coinhibitory markers on T cells, and synergized with CTLA4-Ig to promote long-term acceptance of cardiac allografts across a major histocompatibility barrier. These findings demonstrate the potential value of using brief posttransplant immunoproteasome inhibition to entrain a long-term response favorable to allograft survival as part of an immunomodulatory regimen that is neither broadly immunosuppressive nor toxic.

Molecular autopsy in maternal-fetal medicine.

PurposeThe application of genomic sequencing to investigate unexplained death during early human development, a form of lethality likely enriched for severe Mendelian disorders, has been limited.MethodsIn this study, we employed exome sequencing as a molecular autopsy tool in a cohort of 44 families with at least one death or lethal fetal malformation at any stage of in utero development. Where no DNA was available from the fetus, we performed molecular autopsy by proxy, i.e., through parental testing.ResultsPathogenic or likely pathogenic variants were identified in 22 families (50%), and variants of unknown significance were identified in further 15 families (34%). These variants were in genes known to cause embryonic or perinatal lethality (ALPL, GUSB, SLC17A5, MRPS16, THSD1, PIEZO1, and CTSA), genes known to cause Mendelian phenotypes that do not typically include embryonic lethality (INVS, FKTN, MYBPC3, COL11A2, KRIT1, ASCC1, NEB, LZTR1, TTC21B, AGT, KLHL41, GFPT1, and WDR81) and genes with no established links to human disease that we propose as novel candidates supported by embryonic lethality of their orthologs or other lines of evidence (MS4A7, SERPINA11, FCRL4, MYBPHL, PRPF19, VPS13D, KIAA1109, MOCS3, SVOPL, FEN1, HSPB11, KIF19, and EXOC3L2).ConclusionOur results suggest that molecular autopsy in pregnancy losses is a practical and high-yield alternative to traditional autopsy, and an opportunity for bringing precision medicine to the clinical practice of perinatology.

BCL6 controls Th9 cell development by repressing Il9 transcription.

The transcriptional repressor B cell lymphoma 6 (BCL6) is required for the development of Th follicular cells, and it has been shown to suppress Th2 cell differentiation. We demonstrate that BCL6 is a key regulator of Th9 cell development. BCL6 expression is transiently downregulated in polarized Th9 cells, and forced expression of BCL6 in Th9 cells impairs Th9 cell differentiation. In contrast, BCL6 knockdown upregulated IL-9 production in Th9 cells. The function of BCL6 in Th9 cells is under the control of IL-2/JAK3/STAT5 signaling pathway. Using chromatin immunoprecipitation, we show that, in Th9 cells, BCL6 and STAT5 bind to adjacent motifs in the Il9 promoter. Furthermore, we found that STAT5 binding was associated with the abundance of a permissive histone mark at the Il9 promoter, whereas under conditions in which BCL6 binding was predominant, a repressive histone mark was prevalent. The effects of STAT5 and BCL6 on IL-9 transcription were further demonstrated using an IL-9 luciferase reporter assay in which BCL6 repressed STAT5-mediated Il9 transactivation. In experimental autoimmune encephalomyelitis, forced expression of BCL6 in myelin oligodendrocyte glycoprotein35-55-specific Th9 cells resulted in decreased IL-9 production and induction of IFN-γ, causing an exacerbation of the clinical disease. Our findings demonstrate a novel role of BCL6 in the regulation of Th9 cell development and their encephalitogenicity.

Effect of consanguinity on birth defects in Saudi women: results from a nested case-control study.

BACKGROUND: The role of consanguinity in the etiology of structural birth defects outside of chromosomal and inherited disorders has always been debated. We studied the independent role of consanguinity on birth defects in Saudi women with a high prevalence of consanguineous marriages. METHODS: This case and control study was nested within a 3-year prospective cohort study to examine patterns of fetal and neonatal malformations in Saudi women at Prince Sultan Military Medical City (PSMMC), Riyadh -Saudi Arabia. Consanguineous marriages were defined as marriages with first or second cousins (related); unions beyond second cousins (distant relatives) were considered unrelated for this study. RESULTS: During the 3-year study (July 2010 through June 2013), there were 28,646 total births; of these, we included 1,179 babies with major birth defects, and 1,262 babies as their controls. The consanguinity prevalence for all included women was 49.6%. The consanguinity among babies with major Birth Defects (BDs) was 54.5% and 45.2% for controls (P < 0.0002). The prevalence of major birth defects was 41.1 per 1000 total births. Univariate analysis showed that consanguinity had a statistically significant contribution in babies born with genetic syndromes, isolated renal defects, and isolated other defects (P < 0.05). Multivariate logistic regression analyses showed that consanguinity was an independent risk factor for this high prevalence of birth defects in the study population (P < 0.0002). CONCLUSION: The prevalence of major birth defects in the study population is higher than what is reported from European countries. Consanguinity is a significant independent risk factor for the high prevalence of birth defects.

Vaginoscopic resection of vaginal septum.

We report the resection of a vaginal septum while preserving the virginity of a 12-year-old girl with Herlyn-Werner-Wunderlich Syndrome (HWWS) having a didelphys uterus, obstructed hemivagina, and an ipsilateral renal agenesis with follow-up at 18 months. Successful resection of the vaginal septum with conservation of the hymenal ring and complete drainage of both the hematocolpos and the hematometra were achieved. Cyclic dysmenorrhea and pelvic pain were completely resolved on follow-up visits at 4, 6, and 18 months. Office hysteroscopy performed during the last follow-up visit revealed a patent vaginal vault without evidence of adenosis or recurrence of the vaginal septum. Vaginoscopy is a safe, convenient, and efficient diagnostic and therapeutic modality that can be used in the management of patients with an obstructed hemivagina. It maintains the patient's virginity and it is useful in patients with a restrictive vaginal opening or narrow vaginal canal. Furthermore, the hysteroscopic excision of the vaginal septum offers minimal risk of recurrence of the septal defect.

Harlequin Ichthyosis: A Fatal Case Report in Al-Medina, Saudi Arabia.

Harlequin ichthyosis (HI) is an autosomal recessive disorder. It is a fatal disease and many infants born with HI die shortly after birth. The incidence is extremely rare and is reported to be about 1 in 300,000 births. The hallmark of the disease is alligator-like horned skin that is severely keratinized. Several cases of fetal HI have been reported, but to contribute to the collective knowledge of this rare severe skin disorder, we report the first case, from Medina, Saudi Arabia, of a 45-year-old woman who delivered a newborn infant with HI and has a previous history of six infants who died from a similar condition. Obtaining a prenatal diagnosis, in this case, is critical to alleviate the physical and mental suffering experienced by parents and relatives. Management is mainly supportive until now, as no curable therapy has been proven. Genetic counseling of the ABCA12 gene is advised in consanguinity marriage with positive family history.

Detection of Anal Intraepithelial Neoplasia and Anal Squamous Cell Carcinoma on Colonoscopy.

The purpose of this case series is to review the endoscopic detection of anal intraepithelial neoplasia and anal squamous cell carcinoma including the role of rectal retroflexion and narrow-band imaging. Four cases of anal intraepithelial neoplasia were incidentally discovered in women aged 55-71 years. Anal lesions identified included sessile polyps, nodular mucosa, and circumferential polyps. A fifth patient, who presented with abdominal pain, was found to have a 3 cm anal squamous cell carcinoma on diagnostic colonoscopy, despite a negative colonoscopy 21 months earlier. In the absence of contraindications, retroflexion should be performed on all patients. Suspicious anal mucosa warrants biopsy.

Synovitis, Acne, Pustulosis, Hyperostosis, and Osteitis Syndrome Diagnosis in Adolescent and Isotretinoin as a Possible Serious Exacerbating Factor.

Synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome is a rare auto-inflammatory condition involving cutaneous and osteoarticular manifestations. This study presents a case where a 16-year-old male with glucose-6-phosphate dehydrogenase (G6PD) deficiency presented with severe nodulocystic acne after three weeks of isotretinoin therapy. In addition to worsening acne, the patient had bone and joint pain with movement restriction. The patient's workup showed elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), bilateral symmetrical sacroiliitis on magnetic resonance imaging (MRI), and multiple bony lesions on bone scintigraphy. A diagnosis of SAPHO syndrome possibly induced by isotretinoin was made. Isotretinoin discontinuation, analgesia, topical acne medications, prednisolone, and adalimumab yielded considerable clinical improvement.

Evaluation of Charcot Triad, Reynolds Pentad, and Tokyo Guidelines for Diagnosis of Cholangitis Secondary to Choledocholithiasis Across Patient Age Groups.

OBJECTIVE: To determine the prevalence of Charcot triad, Reynolds pentad, and Tokyo Guidelines criteria and clinical outcomes among patients with cholangitis across different age groups. PATIENTS AND METHODS: We conducted a retrospective analysis of 257 consecutive hospitalized adult patients with acute cholangitis due to endoscopic retrograde cholangiopancreatography-confirmed choledocholithiasis between January 1, 2015, and December 31, 2019. Patients were divided into 3 age groups: less than 65 years, 65 to 79 years, and 80 years or older. Symptoms, vital signs, and laboratory data on admission were collected. Outcomes included length of hospitalization, intensive care unit stay, and 3-month mortality. Nominal variables were tested with the Pearson χ2 test, and continuous variables were tested with the Wilcoxon rank sum test. RESULTS: Charcot triad decreased with older ages. In the group that was age 80 years or older, malaise was the most common symptom; 33.6% (37 of 110) presented with altered sensorium, 9.1% (10 of 110) had no pain, fever, or jaundice, and positive blood culture results were more frequent. Tokyo cholestasis criterion was present in 96.0% (247 of 257), while inflammation (considered essential for diagnosis) was present in 75.9% (195 of 257). Patients 80 years or older had significantly higher mean length of hospital stay (P<.001) and mean length of intensive care unit stay (P=.021). CONCLUSION: Compared with patients in younger age groups, patients with cholangitis who are 80 years or older are less likely to have Charcot triad, are more likely to have features of Reynolds pentad, or present with unexplained malaise. Within the Tokyo Guidelines, cholestasis should replace inflammation as an essential diagnostic criterion.

Fetal aortic valvuloplasty: first report of two cases from Saudi Arabia.

BACKGROUND: Fetal aortic stenosis may progress to hypoplastic left heart syndrome (HLHS), which carries a poor prognosis. We report two infants with fetal aortic stenosis successfully treated with fetal aortic valvuloplasty (FAV) using balloon dilatation. CASE PRESENTATION: Of five fetuses with aortic stenosis fulfilling the FAV criteria of severe aortic stenosis with a left ventricular length Z-score of ≥ - 2, retrograde flow in the transverse aortic arch, left-to-right flow across the foramen ovale, monophasic mitral inflow, and significant left ventricular dysfunction, we obtained permission for FAV in two fetuses. FAV was performed successfully under echocardiographic guidance using balloon dilatation. Both fetuses survived to birth. During FAV, mild pericardial effusion developed when introducing the stylet needle in the second fetus, and this resolved within 48 h. No intraprocedural complications occurred in the first patient, and no maternal complications occurred. The first infant underwent the Ross procedure after birth and is currently 7 years old and doing well. The second patient underwent aortic and mitral valve repair with endocardial fibroelastosis resection approximately 2 weeks after birth, which temporarily addressed the mitral valve stenosis; high doses of inotropes were subsequently required. The infant died of sepsis at 2 months of age. CONCLUSION: FAV using balloon dilatation to treat fetal aortic stenosis was successful in our two patients, with subsequent neonatal biventricular repair resulting in long-term survival in one patient and death secondary to sepsis in the second patient.

Congenital anomalies and associated risk factors in a Saudi population: a cohort study from pregnancy to age 2 years.

OBJECTIVE: To assess the three key issues for congenital anomalies (CAs) prevention and care, namely, CA prevalence, risk factor prevalence and survival, in a longitudinal cohort in Riyadh, Saudi Arabia. SETTING: Tertiary care centre, Riyadh, Saudi Arabia. PARTICIPANTS: Saudi women enrolled during pregnancy over 3 years and their 28 646 eligible pregnancy outcomes (births, stillbirths and elective terminations of pregnancy for foetal anomalies). The nested case-control study evaluated the CA risk factor profile of the underlying cohort. All CA cases (1179) and unaffected controls (1262) were followed through age 2 years. Referred mothers because of foetal anomaly and mothers who delivered outside the study centre and their pregnancy outcome were excluded. PRIMARY OUTCOME MEASURES: Prevalence and pattern of major CAs, frequency of CA-related risk factors and survival through age 2 years. RESULTS: The birth prevalence of CAs was 412/10 000 births (95% CI 388.6 to 434.9), driven mainly by congenital heart disease (148 per 10 000) (95% CI 134 to 162), renal malformations (113, 95% CI 110 to 125), neural tube defects (19, 95% CI 25.3 to 38.3) and chromosomal anomalies (27, 95% CI 21 to 33). In this study, the burden of potentially modifiable risk factors included high rates of diabetes (7.3%, OR 1.98, 95% CI 1.04 to 2.12), maternal age >40 years (7.0%, OR 2.1, 95% CI 1.35 to 3.3), consanguinity (54.5%, OR 1.5, 95% CI 1.28 to 1.81). The mortality for live births with CAs at 2 years of age was 15.8%. CONCLUSIONS: This study documented specific opportunities to improve primary prevention and care. Specifically, folic acid fortification (the neural tube defect prevalence was >3 times that theoretically achievable by optimal fortification), preconception diabetes screening and consanguinity-related counselling could have significant and broad health benefits in this cohort and arguably in the larger Saudi population.

Prevalence and pattern of alternative medicine use: the results of a household survey.

BACKGROUND AND OBJECTIVES: Alternative medicine (AM) encompasses all forms of therapies that fall outside the mainstream of medical practice. Its popularity is on the increase. Because previous surveys were limited and not generalizable, we estimated the prevalence, pattern and factors associated with use of AM in the community. SUBJECTS AND METHODS: A multistage cluster cross-sectional household survey was conducted among Saudi residents of the Riyadh region. Data were collected in 2003 by trained interviewers from primary health care centers using a specially designed questionnaire. RESULTS: Of 1408 individuals participating in the study, 39% were men. The mean (+/-SD) age for the study population was 35.5 (+/-13.9) years. Sixty-eight percent of the respondents had used AM during the last 12 months. The Holy Quran as a therapy was the most frequently used AM (50.3%), followed by honey (40.1%), black seed (39.2%) and myrrh (35.4%). The health belief model was found to be the most important determinant of AM use. Factors independently associated with AM use included perceived failure of medical treatment, the perceived success of AM, a preference for natural materials, and long appointment intervals to see physicians. CONCLUSIONS AND RECOMMENDATIONS: There is a high prevalence of AM use in the Riyadh region and the most important determinant of AM use was the perceived failure of medical treatment. The study results call for intensive health education campaigns in the media addressing wrong beliefs regarding AM and modern medicine. The popularity of AM in this community should alert decision makers to look at the difficult accessibility to the health system.

IBD Journal Editorial Fellowship: A Practical Guide for Future Fellows.

Inflammatory Bowel Diseases offers an editorial fellowship for GI and IBD fellows with a background in clinical, translational, and basic research and who are interested to experience the editorial process. Herein, the inaugural fellows compile their experience as a guide for future applicants on the fellowship's responsibilities and highlights.

Antibody-Dependent Cellular Phagocytosis by Macrophages is a Novel Mechanism of Action of Elotuzumab.

Elotuzumab, a recently approved antibody for the treatment of multiple myeloma, has been shown to stimulate Fcγ receptor (FcγR)-mediated antibody-dependent cellular cytotoxicity by natural killer (NK) cells toward myeloma cells. The modulatory effects of elotuzumab on other effector cells in the tumor microenvironment, however, has not been fully explored. Antibody-dependent cellular phagocytosis (ADCP) is a mechanism by which macrophages contribute to antitumor potency of monoclonal antibodies. Herein, we studied the NK cell independent effect of elotuzumab on tumor-associated macrophages using a xenograft tumor model deficient in NK and adaptive immune cells. We demonstrate significant antitumor efficacy of single-agent elotuzumab in immunocompromised xenograft models of multiple myeloma, which is in part mediated by Fc-FcγR interaction of elotuzumab with macrophages. Elotuzumab is shown in this study to induce phenotypic activation of macrophages in vivo and mediates ADCP of myeloma cells though a FcγR-dependent manner in vitro Together, these findings propose a novel immune-mediated mechanism by which elotuzumab exerts anti-myeloma activity and helps to provide rationale for combination therapies that can enhance macrophage activity. Mol Cancer Ther; 17(7); 1454-63. ©2018 AACR.

Human regulatory T cells undergo self-inflicted damage via granzyme pathways upon activation.

Tregs hold great promise as a cellular therapy for multiple immunologically mediated diseases, given their ability to control immune responses. The success of such strategies depends on the expansion of healthy, suppressive Tregs ex vivo and in vivo following the transfer. In clinical studies, levels of transferred Tregs decline sharply in the blood within a few days of the transfer. Tregs have a high rate of apoptosis. Here, we describe a new mechanism of Treg self-inflicted damage. We show that granzymes A and -B (GrA and GrB), which are highly upregulated in human Tregs upon stimulation, leak out of cytotoxic granules to induce cleavage of cytoplasmic and nuclear substrates, precipitating apoptosis in target cells. GrA and GrB substrates were protected from cleavage by inhibiting granzyme activity in vitro. Additionally, we show - by using cytometry by time of flight (CYTOF) - an increase in GrB-expressing Tregs in the peripheral blood and renal allografts of transplant recipients undergoing rejection. These GrB-expressing Tregs showed an activated phenotype but were significantly more apoptotic than non-GrB expressing Tregs. This potentially novel finding improves our understanding of Treg survival and suggests that manipulating Gr expression or activity might be useful for designing more effective Treg therapies.

Tiam1/Rac1 complex controls Il17a transcription and autoimmunity.

RORγt is a master transcription factor of Th17 cells and considered as a promising drug target for the treatment of autoimmune diseases. Here, we show the guanine nucleotide exchange factor, Tiam1, and its cognate Rho-family G protein, Rac1, regulate interleukin (IL)17A transcription and autoimmunity. Whereas Tiam1 genetic deficiency weakens IL-17A expression partially and inhibits the development of experimental autoimmune encephalomyelitis (EAE), deletion of Rac1 in T cells exhibits more robust effects on Th17 cells and EAE. We demonstrate Tiam1 and Rac1 form a complex with RORγt in the nuclear compartment of Th17 cells, and together bind and activate the Il17 promoter. The clinical relevance of these findings is emphasized by pharmacological targeting of Rac1 that suppresses both murine and human Th17 cells as well as EAE. Thus, our findings highlight a regulatory pathway of Tiam1/Rac1 in Th17 cells and suggest that it may be a therapeutic target in multiple sclerosis.