Prednisolone and rapamycin reduce the plasma cell gene signature and may improve AAV gene therapy in cynomolgus macaques.

Adeno-associated virus (AAV) vector gene therapy is a promising approach to treat rare genetic diseases; however, an ongoing challenge is how to best modulate host immunity to improve transduction efficiency and therapeutic outcomes. This report presents two studies characterizing multiple prophylactic immunosuppression regimens in male cynomolgus macaques receiving an AAVrh10 gene therapy vector expressing human coagulation factor VIII (hFVIII). In study 1, no immunosuppression was compared with prednisolone, rapamycin (or sirolimus), rapamycin and cyclosporin A in combination, and cyclosporin A and azathioprine in combination. Prednisolone alone demonstrated higher mean peripheral blood hFVIII expression; however, this was not sustained upon taper. Anti-capsid and anti-hFVIII antibody responses were robust, and vector genomes and transgene mRNA levels were similar to no immunosuppression at necropsy. Study 2 compared no immunosuppression with prednisolone alone or in combination with rapamycin or methotrexate. The prednisolone/rapamycin group demonstrated an increase in mean hFVIII expression and a mean delay in anti-capsid IgG development until after rapamycin taper. Additionally, a significant reduction in the plasma cell gene signature was observed with prednisolone/rapamycin, suggesting that rapamycin's tolerogenic effects may include plasma cell differentiation blockade. Immunosuppression with prednisolone and rapamycin in combination could improve therapeutic outcomes in AAV vector gene therapy.

Efficacy and Safety of Abrilumab in a Randomized, Placebo-Controlled Trial for Moderate-to-Severe Ulcerative Colitis.

BACKGROUND & AIMS: The α4ß7 integrin is a validated target in inflammatory bowel disease. This randomized, phase 2b, placebo-controlled, double-blind study evaluated the efficacy and safety of the anti-α4ß7 antibody abrilumab in patients with moderate-to-severe ulcerative colitis despite treatment with conventional therapies. METHODS: Patients (total Mayo Score 6-12, recto-sigmoidoscopy score ≥2) with inadequate response or intolerance to conventional therapies were randomized to receive subcutaneous abrilumab (7, 21, or 70 mg) on day 1, weeks 2 and 4, and every 4 weeks; abrilumab 210 mg on day 1; or placebo. The primary end point was remission (total Mayo Score ≤2 points, no individual sub-score >1 point) for the 2 highest dosages at week 8. Key secondary end points were response and mucosal healing (centrally read) at week 8. RESULTS: For 354 patients who received ≥1 dose of investigational product (placebo, n = 116; 7 mg, n = 21; 21 mg, n = 40; 70 mg, n = 98; 210 mg, n = 79), non-adjusted remission rates at week 8 were 4.3%, 13.3%, and 12.7% for the placebo and abrilumab 70-mg and 210-mg groups, respectively (P < .05 for 70 and 210 mg vs placebo); odds of achieving remission were significantly greater with abrilumab 70 mg (odds ratio 3.35; 90% CI 1.41-7.95; P = .021) and 210 mg (odds ratio 3.33; 90% confidence interval 1.34-8.26; P = .030) than with placebo. Response and mucosal healing rates with these dosages also were significantly greater than with placebo. Higher baseline α4ß7 levels on naïve CD4+ T cells were a prognostic indicator for overall outcome, but not a predictive biomarker of abrilumab response. There were no cases of progressive multifocal leukoencephalopathy or deaths. CONCLUSIONS: Abrilumab treatment for 8 weeks induced remission, clinical response, and mucosal healing in patients with moderate-to-severe ulcerative colitis. ClinicalTrials.gov, number NCT01694485.

Acid test: lipid antigens get into the groove.

How do CD1 molecules load lipid antigens? In this issue of Immunity, Relloso et al. (2008) uncover how lysosomal pH targets amino acids in CD1b, causing it to open and attain a conformation more receptive to lipid antigens.

Clinical pharmacology of AMG 181, a gut-specific human anti-α4ß7 monoclonal antibody, for treating inflammatory bowel diseases.

AIMS: AMG 181 pharmacokinetics/pharmacodynamics (PK/PD), safety, tolerability and effects after single subcutaneous (s.c.) or intravenous (i.v.) administration were evaluated in a randomized, double-blind, placebo-controlled study. METHODS: Healthy male subjects (n= 68) received a single dose of AMG 181 or placebo at 0.7, 2.1, 7, 21, 70 mg s.c. (or i.v.), 210 mg s.c. (or i.v.), 420 mg i.v. or placebo. Four ulcerative colitis (UC) subjects (n= 4, male : female 2:2) received 210 mg AMG 181 or placebo s.c. (3:1). AMG 181 concentration, anti-AMG 181-antibody (ADA), α4 ß7 receptor occupancy (RO), target cell counts, serum C-reactive protein, fecal biomarkers and Mayo score were measured. Subjects were followed 3-9 months after dose. RESULTS: Following s.c. dosing, AMG 181 was absorbed with a median tmax ranging between 2-10 days and a bioavailability between 82% and 99%. Cmax and AUC increased dose-proportionally and approximately dose-proportionally, respectively, within the 70-210 mg s.c. and 70-420 mg i.v. ranges. The linear ß-phase t1/2 was 31 (range 20-48) days. Target-mediated disposition occurred at serum AMG 181 concentrations of less than 1 µg ml(-1) . The PD effect on α4 ß7 RO showed an EC50 of 0.01 µg ml(-1) . Lymphocytes, eosinophils, CD4+ T cells and subset counts were unchanged. AMG 181-treated UC subjects were in remission with mucosal healing at weeks 6, 12 and/or 28. The placebo-treated UC subject experienced colitis flare at week 6. No ADA or AMG 181 treatment-related serious adverse events were observed. CONCLUSIONS: AMG 181 has PK/PD, safety, and effect profiles suitable for further testing in subjects with inflammatory bowel diseases.

Mechanisms for glycolipid antigen-driven cytokine polarization by Valpha14i NKT cells.

Certain glycolipid Ags for Valpha14i NKT cells can direct the overall cytokine balance of the immune response. Th2-biasing OCH has a lower TCR avidity than the most potent agonist known, alpha-galactosylceramide. Although the CD1d-exposed portions of OCH and alpha-galactosylceramide are identical, structural analysis indicates that there are subtle CD1d conformational differences due to differences in the buried lipid portion of these two Ags, likely accounting for the difference in antigenic potency. Th1-biasing C-glycoside/CD1d has even weaker TCR interactions than OCH/CD1d. Despite this, C-glycoside caused a greater downstream activation of NK cells to produce IFN-gamma, accounting for its promotion of Th1 responses. We found that this difference correlated with the finding that C-glycoside/CD1d complexes survive much longer in vivo. Therefore, we suggest that the pharmacokinetic properties of glycolipids are a major determinant of cytokine skewing, suggesting a pathway for designing therapeutic glycolipids for modulating invariant NKT cell responses.

A CD1d-dependent antagonist inhibits the activation of invariant NKT cells and prevents development of allergen-induced airway hyperreactivity.

The prevalence of asthma continues to increase in westernized countries, and optimal treatment remains a significant therapeutic challenge. Recently, CD1d-restricted invariant NKT (iNKT) cells were found to play a critical role in the induction of airway hyperreactivity (AHR) in animal models and are associated with asthma in humans. To test whether iNKT cell-targeted therapy could be used to treat allergen-induced airway disease, mice were sensitized with OVA and treated with di-palmitoyl-phosphatidyl-ethanolamine polyethylene glycol (DPPE-PEG), a CD1d-binding lipid antagonist. A single dose of DPPE-PEG prevented the development of AHR and pulmonary infiltration of lymphocytes upon OVA challenge, but had no effect on the development of OVA-specific Th2 responses. In addition, DPPE-PEG completely prevented the development of AHR after administration of alpha-galactosylceramide (alpha-GalCer) intranasally. Furthermore, we demonstrate that DPPE-PEG acts as antagonist to alpha-GalCer and competes with alpha-GalCer for binding to CD1d. Finally, we show that DPPE-PEG completely inhibits the alpha-GalCer-induced phosphorylation of ERK tyrosine kinase in iNKT cells, suggesting that DPPE-PEG specifically blocks TCR signaling and thus activation of iNKT cells. Because iNKT cells play a critical role in the development of AHR, the inhibition of iNKT activation by DPPE-PEG suggests a novel approach to treat iNKT cell-mediated diseases such as asthma.

Safety and Biological Activity of Rozibafusp alfa, a Bispecific Inhibitor of Inducible Costimulator Ligand and B Cell Activating Factor, in Patients With Rheumatoid Arthritis: Results of a Phase 1b, Randomized, Double-Blind, Placebo-Controlled, Multiple Ascending Dose Study.

OBJECTIVE: To assess the safety and biological activity of rozibafusp alfa, a first-in-class bispecific antibody-peptide conjugate targeting inducible costimulator ligand (ICOSL) and B cell activating factor (BAFF), in patients with rheumatoid arthritis (RA). METHODS: This phase 1b, double-blind, placebo-controlled, multiple ascending dose study included 34 patients (18-75 years; 82.4% female) with active RA (Disease Activity Score of 28 joints-C-reactive protein [DAS28-CRP] >2.6, on stable methotrexate) randomized 3:1 to receive rozibafusp alfa (n = 26, in four ascending dose cohorts of 70, 140, 210, and 420 mg) or a placebo (n = 8) subcutaneously once every 2 weeks for 10 weeks (six total doses), with 24 weeks of follow-up. The primary end point was the incidence of treatment-emergent adverse events (TEAEs). Additional assessments included serum pharmacokinetics (PK), pharmacodynamics (PD), immunogenicity, and RA disease activity measures (DAS28-CRP, Patient Global Assessment of Disease, and Physician Global Assessment of Disease). RESULTS: TEAEs occurred in 96.2% and 87.5% of patients receiving rozibafusp alfa and the placebo, respectively; most were mild or moderate in severity. Two (7.7%) patients treated with rozibafusp alfa reported serious TEAEs; none were considered treatment related. Multiple doses of rozibafusp alfa showed nonlinear PK (mean t1/2  = 4.6-9.5 days) and dose-related, reversible PD (>90% ICOSL receptor occupancy in 210- and 420-mg cohorts; reduction in naïve B cells and increase in memory B cells in all cohorts). Five (20%) patients developed anti-rozibafusp alfa antibodies, with no apparent impact on safety. RA disease activity showed greater numerical improvement from baseline with rozibafusp alfa versus the placebo in the 210- and 420-mg cohorts. CONCLUSION: Multiple ascending doses of rozibafusp alfa were well tolerated, with PK and PD reflecting dual ICOSL and BAFF blockade. Findings support further clinical evaluation of rozibafusp alfa in autoimmune disease.

Prednisolone reduces the interferon response to AAV in cynomolgus macaques and may increase liver gene expression.

Ornithine transcarbamylase deficiency is a rare X-linked genetic urea cycle disorder leading to episodes of acute hyperammonemia, adverse cognitive and neurological effects, hospitalizations, and in some cases death. DTX301, a non-replicating, recombinant self-complimentary adeno-associated virus vector serotype 8 (scAAV8)-encoding human ornithine transcarbamylase, is a promising gene therapy for ornithine transcarbamylase deficiency; however, the impact of sex and prophylactic immunosuppression on ornithine transcarbamylase gene therapy outcomes is not well characterized. This study sought to describe the impact of sex and immunosuppression in adult, sexually mature female and male cynomolgus macaques through day 140 after DTX301 administration. Four study groups (n = 3/group) were included: male non-immunosuppressed; male immunosuppressed; female non-immunosuppressed; and female immunosuppressed. DTX301 was well tolerated with and without immunosuppression; no notable differences were observed between female and male groups across outcome measures. Prednisolone-treated animals exhibited a trend toward greater vector genome and transgene expression, although the differences were not statistically significant. The hepatic interferon gene signature was significantly decreased in prednisolone-treated animals, and a significant inverse relationship was observed between interferon gene signature levels and hepatic vector DNA and transgene RNA. These observations were not sustained upon immunosuppression withdrawal. Further studies may determine whether the observed effect can be prolonged.

Immune Complex Formation Is Associated With Loss of Tolerance and an Antibody Response to Both Drug and Target.

AMG 966 is a bi-specific, heteroimmunoglobulin molecule that binds both tumor necrosis factor alpha (TNFα) and TNF-like ligand 1A (TL1A). In a first-in-human clinical study in healthy volunteers, AMG 966 elicited anti-drug antibodies (ADA) in 53 of 54 subjects (98.1%), despite a paucity of T cell epitopes observed in T cell assays. ADA were neutralizing and bound to all domains of AMG 966. Development of ADA correlated with loss of exposure. In vitro studies demonstrated that at certain drug-to-target ratios, AMG 966 forms large immune complexes with TNFα and TL1A, partially restoring the ability of the aglycosylated Fc domain to bind FcγRIa and FcγRIIa, leading to the formation of ADA. In addition to ADA against AMG 966, antibodies to endogenous TNFα were also detected in the sera of subjects dosed with AMG 966. This suggests that the formation of immune complexes between a therapeutic and target can cause loss of tolerance and elicit an antibody response against the target.

Efficacy and safety of abrilumab, an α4ß7 integrin inhibitor, in Japanese patients with moderate-to-severe ulcerative colitis: a phase II study.

BACKGROUND/AIMS: Inhibition of α4ß7 integrin has been shown to be effective for induction and maintenance therapy in patients with ulcerative colitis (UC). We investigated the effects of varying doses of the α4ß7 inhibitor abrilumab in Japanese patients with moderate-to-severe UC despite conventional treatments. METHODS: In this randomized, double-blind, placebocontrolled study, 45 UC patients were randomized to abrilumab 21 mg (n=11), 70 mg (n=12), 210 mg (n=9), or placebo (n=13) via subcutaneous (SC) injection for 12 weeks. The double-blind period was followed by a 36-week open-label period, in which all patients received abrilumab 210 mg SC every 12 weeks, and a 28-week safety follow-up period. The primary efficacy variable was clinical remission at week 8 (total Mayo score ≤2 points with no individual subscore >1 point). RESULTS: Clinical remission at week 8 was 4 out of 31 (12.9%) overall in the abrilumab groups versus 0 out of 13 in the placebo group (abrilumab 21 mg, 1/10 [10.0%]; 70 mg, 2/12 [16.7%]; 210 mg, 1/9 [11.1%]). In both the double-blind and open-label periods, fewer patients in the abrilumab groups experienced ≥1 adverse event compared with those in the placebo group. There were no cases of progressive multifocal leukoencephalopathy and no deaths. CONCLUSIONS: Abrilumab 70 mg and 210 mg yielded numerically better results in terms of clinical remission rate at Week 8 than placebo, with the 210 mg dose showing more consistent treatment effects. Abrilumab was well tolerated in Japanese patients with UC.

Activation or anergy: NKT cells are stunned by alpha-galactosylceramide.

Invariant natural killer T (iNKT) cells are T lymphocytes that behave similarly to cells of the innate immune system. The glycolipid alpha-galactosylceramide (alpha-GalCer) is a potent and specific activator of mouse and human iNKT cells and has been used in cancer clinical trials to drive NKT cell-mediated immune responses. However, little is known about the dynamics of the iNKT cell response to alpha-GalCer in vivo. In this issue of the JCI, Parekh and colleagues demonstrate that administration of alpha-GalCer causes iNKT cells to become unresponsive, for at least 1 month, in mice. This leads us to ask, should sequential administration of alpha-GalCer still be used to activate iNKT cells given the anergic state it has been shown here to induce? This intriguing article raises the issue of the avoidance of anergy induction in the design of treatment regimens that use alpha-GalCer as a specific activator of iNKT cells.

Brief Report: A Randomized, Double-Blind, Parallel-Group, Placebo-Controlled, Multiple-Dose Study to Evaluate AMG 557 in Patients With Systemic Lupus Erythematosus and Active Lupus Arthritis.

OBJECTIVE: To evaluate the safety and potential efficacy of AMG 557, a fully human antibody directed against the inducible T cell costimulator ligand (ICOSL) in patients with systemic lupus erythematosus (SLE) with arthritis. METHODS: In this phase Ib, randomized, double-blind, placebo-controlled study, patients received AMG 557 210 mg (n = 10) or placebo (n = 10) weekly for 3 weeks, then every other week for 10 additional doses. The corticosteroid dosage was tapered to ≤7.5 mg/day by day 85, and immunosuppressants were discontinued by day 29. Primary end points on day 169 were safety, immunogenicity, the Lupus Arthritis Response Index (LARI; defined by a reduction in the tender and swollen joint counts), ≥1-letter improvement in the musculoskeletal domain of the British Isles Lupus Assessment Group (BILAG) index, and medication discontinuation. The secondary/exploratory end points were changes in the tender and swollen joint counts, BILAG index scores (musculoskeletal, global), and the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI). RESULTS: The incidence of adverse events, most of which were mild, was similar between groups. LARI responses occurred in 3 of 10 patients receiving AMG 557 and 1 of 10 patients receiving placebo (P = 0.58). More patients in the AMG 557 group achieved a ≥4-point improvement in the SLEDAI score on day 169 (7 of 10 patients) compared with the placebo group (2 of 10 patients) (P = 0.07). Patients treated with AMG 557 (versus placebo) had greater improvements from baseline in the global BILAG index scores (-36.3% versus -24.7%) and the SLEDAI score (-47.8% versus -10.7%) and in tender (-22.8% versus -13.5%) and swollen (-62.1% versus -7.8%) joint counts on day 169. CONCLUSION: AMG 557 showed safety and potential efficacy, supporting further evaluation of the clinical efficacy of ICOSL blockade in patients with SLE.

Brief Report: Pharmacodynamics, Safety, and Clinical Efficacy of AMG 811, a Human Anti-Interferon-γ Antibody, in Patients With Discoid Lupus Erythematosus.

OBJECTIVE: Interferon-γ (IFNγ) is implicated in the pathogenesis of discoid lupus erythematosus (DLE). This study sought to evaluate a single dose of AMG 811, an anti-IFNγ antibody, in patients with DLE. METHODS: The study was designed as a phase I randomized, double-blind, placebo-controlled crossover study of the pharmacodynamics, safety, and clinical efficacy of AMG 811 in patients with DLE. Patients received a single subcutaneous dose of AMG 811 (180 mg) or placebo. The patients in sequence 1 received AMG 811 followed by placebo, while those in sequence 2 received placebo followed by AMG 811. Pharmacodynamic end points included global transcriptional analyses of lesional and nonlesional skin, IFNγ blockade signature (IGBS) transcriptional scores in the skin and blood, keratinocyte IFNγ RNA scores, and serum levels of CXCL10 protein. Additional end points were efficacy outcome measures, including the Cutaneous Lupus Erythematosus Disease Area and Severity Index, and safety outcome measures. RESULTS: Sixteen patients with DLE were enrolled in the study (9 in sequence 1 and 7 in sequence 2). AMG 811 treatment reduced the IGBS score (which was elevated in DLE patients at baseline) in both the blood and lesional skin. The keratinocyte IFNγ RNA score was not affected by administration of AMG 811. Serum CXCL10 protein levels (which were elevated in the blood of DLE patients) were reduced with AMG 811 treatment. The AMG 811 treatment was well tolerated but did not lead to statistically significant improvements in any of the efficacy outcome measures. CONCLUSION: AMG 811 treatment led to changes in IFNγ-associated biomarkers and was well tolerated, but no significant clinical benefit was observed in patients with DLE.

Safety, pharmacokinetics and pharmacodynamics of AMG 811, an anti-interferon-γ monoclonal antibody, in SLE subjects without or with lupus nephritis.

OBJECTIVE: To evaluate safety, pharmacokinetics and pharmacodynamics of anti-interferon (IFN)-γ monoclonal antibody AMG 811 in subjects with SLE without or with lupus nephritis (LN). METHODS: In this phase Ib, randomised, multiple-dose escalation study (NCT00818948), subjects without LN were randomised to subcutaneous AMG 811 (6, 20 or 60 mg) or placebo and subjects with LN were randomised to subcutaneous AMG 811 (20, 60 or 120 mg) or placebo every four weeks for three total doses. Outcomes included incidence of adverse events (AEs); pharmacokinetics; levels of serum proteins (CXCL-10, interleukin 18, monocyte chemotactic protein-1); changes in gene transcript profiles and clinical parameters (Safety of Estrogen in Lupus Erythematosus National Assessment-Systemic Lupus Erythematosus Disease Activity Index (SELENA-SLEDAI) scores, proteinuria, anti-double-stranded DNA (anti-dsDNA) antibodies, C3 complement, C4 complement). RESULTS: Fifty-six subjects enrolled (28 SLE without LN; 28 with LN). Baseline mean SELENA-SLEDAI scores were 2.2 and 12.0 for SLE subjects without and with LN, respectively. Most subjects reported an AE; no meaningful imbalances were observed between AMG 811 and placebo. Pharmacokinetic profiles were similar and mostly dose-proportional in subjects without or with LN. AMG 811 treatment reduced CXCL-10 protein levels and blood-based RNA IFN-γ Blockade Signature compared with placebo. Reductions were less pronounced and not sustained in subjects with LN, even at the highest dose tested, compared with subjects without LN. No effect on SELENA-SLEDAI scores, proteinuria, C3 or C4 complement levels, or anti-dsDNA antibodies was observed. CONCLUSION: AMG 811 demonstrated favourable pharmacokinetics and acceptable safety profile but no evidence of clinical impact. IFN-γ-associated biomarkers decreased with AMG 811; effects were less pronounced and not sustained in LN subjects. TRIAL REGISTRATION NUMBER: NCT00818948; results.

A modified alpha-galactosyl ceramide for staining and stimulating natural killer T cells.

CD1d presentation of alpha-galactosyl ceramides to natural killer T cells has been a focal point of the study of regulatory T cells. KRN7000, an alpha-galactosyl ceramide originally generated from structure activity studies of antitumor properties of marine sponge glycolipids, is currently the most commonly used agonist ligand and is used to stain NKT cells. However, this glycolipid suffers from poor solubility and availability. We have developed an alpha-galactosyl ceramide with improved solubility over KRN7000 that effectively stains NKT cells, both mouse and human, and stimulates cytokine release at low concentrations.

Qa-1, a nonclassical class I histocompatibility molecule with roles in innate and adaptive immunity.

Qa-1, a nonclassical class I histocompatibility molecule expressed in mice, predominantly assembles with a single nonameric peptide, Qdm, derived from the signal sequence of certain class Ia molecules. The Qa-1/Qdm complex is the primary ligand for CD94/NKG2A inhibitory receptors expressed on a major fraction of natural killer (NK) cells. Cells become susceptible to killing by NK cells under conditions where surface expression of the Qa-1/Qdm inhibitory ligand is reduced. The CD94/NKG2 "missing-self" recognition system serves as mechanism for removing cells that have abnormalities in the intracellular machinery required for assembly and expression of class I-peptides complexes, as a consequence of viral infection, for example. Despite its highly focused peptide-binding specificity, Qa-1 also has a capacity to act as an antigen-presentation molecule for CD8+ T cells. It appears that a small subpopulation of these T cells undergoes positive selection by interaction with Qa-1 in the thymus, and they maintain their specificity for Qa-1 after maturation. The role of these unusual T cells in adaptive immune responses remains to be defined.

Co-receptor choice by V alpha14i NKT cells is driven by Th-POK expression rather than avoidance of CD8-mediated negative selection.

Mouse natural killer T (NKT) cells with an invariant V alpha14-J alpha18 rearrangement (V alpha14 invariant [V alpha14i] NKT cells) are either CD4(+)CD8(-) or CD4(-)CD8(-). Because transgenic mice with forced CD8 expression in all T cells exhibited a profound NKT cell deficit, the absence of CD8 has been attributed to negative selection. We now present evidence that CD8 does not serve as a coreceptor for CD1d recognition and that the defect in development in CD8 transgene homozygous mice is the result of a reduction in secondary T cell receptor alpha rearrangements. Thymocytes from mice hemizygous for the CD8 transgene have a less severe rearrangement defect and have functional CD8(+) V alpha14i NKT cells. Furthermore, we demonstrate that the transcription factor Th, Poxviruses and Zinc finger, and Krüppel family (Th-POK) is expressed by V alpha14i NKT cells throughout their differentiation and is necessary both to silence CD8 expression and for the functional maturity of V alpha14i NKT cells. We therefore suggest that Th-POK expression is required for the normal development of V alpha14i NKT cells and that the absence of CD8 expression by these cells is a by-product of such expression, as opposed to the result of negative selection of CD8-expressing V alpha14i NKT cells.

Identification of pre- and postselection TCRalphabeta+ intraepithelial lymphocyte precursors in the thymus.

The immune system preserves and makes use of autoreactive lymphocytes with specialized functions. Here we showed that one of these populations, CD8alphaalpha(+)TCRalphabeta(+) intestinal intraepithelial lymphocytes (IELs), arose from a unique subset of double-positive thymocytes. This subset of cells was precommitted to preferentially give rise to CD8alphaalpha(+)TCRalphabeta(+) IELs, but they required exposure to self-agonist peptides. The agonist-selected TCRalphabeta(+) thymocytes are CD4 and CD8 double-negative, and their final maturation, including the induction of CD8alphaalpha expression, appeared to occur only after thymus export in the IL-15-rich environment of the gut. These developmental steps, including precommitment of immature thymocytes, TCR-mediated agonist selection, and postthymic differentiation promoted by cytokines, define a unique pathway for the generation of CD8alphaalpha(+)TCRalphabeta(+) IEL.

Immediate antigen-specific effector functions by TCR-transgenic CD8+ NKT cells.

Only recently have natural antigens for CD1d-dependent, invariant Valpha14+ natural killer T (iNKT) cells been identified. Similar data for CD1d-independent and CD8+ NKT cell populations are still missing. Here, we show that the MHC class I-restricted CD8+ TCR-transgenic mouse lines OT-I, P14 and H-Y contain a significant proportion of transgenic CD8+ NK1.1+ T cells. In liver, most of NK1.1+ T cells express CD8alphaalpha homodimers. Transgenic NKT cells did not bind invariant Valpha14-to-Jalpha18 TCR rearrangement (Valpha14i)-specific CD1d/alpha-galactosylceramide tetramers and the frequency of iNKT cells was severely reduced. The activated cell surface phenotype and the distribution of transgenic NKT cells in vivo were similar to that reported for iNKT cells. The OT-I and P14 CD8+ NKT cells recognized their cognate antigen in the context of H2-Kb and produced cytokines shortly after TCR stimulation. Importantly, transgenic NKT cells exerted immediate antigen-specific cytotoxicity in vitro and in vivo. Our results demonstrate the presence of transgenic CD8+ NKT cells in MHC class I-restricted TCR-transgenic animals, which are endowed with rapid antigen-specific effector functions. These data imply that experiments studying naive T cell function in TCR-transgenic animals should be interpreted with caution, and that such animals could be utilized for studying CD8+ NKT cell function in an antigen-specific manner.

Design of natural killer T cell activators: structure and function of a microbial glycosphingolipid bound to mouse CD1d.

Natural killer T (NKT) cells provide an innate-type immune response upon T cell receptor interaction with CD1d-presented antigens. We demonstrate through equilibrium tetramer binding and antigen presentation assays with Valpha14i-positive NKT cell hybridomas that the Sphingomonas glycolipid alpha-galacturonosyl ceramide (GalA-GSL) is a NKT cell agonist that is significantly weaker than alpha-galactosylceramide (alpha-GalCer), the most potent known NKT agonist. For GalA-GSL, a shorter fatty acyl chain, an absence of the 4-OH on the sphingosine tail and a 6'-COOH group on the galactose moiety account for its observed antigenic potency. We further determined the crystal structure of mCD1d in complex with GalA-GSL at 1.8-A resolution. The overall binding mode of GalA-GSL to mCD1d is similar to that of the short-chain alpha-GalCer ligand PBS-25, but its sphinganine chain is more deeply inserted into the F' pocket due to alternate hydrogen-bonding interactions between the sphinganine 3-OH with Asp-80. Subsequently, a slight lateral shift (>1 A) of the galacturonosyl head group is noted at the CD1 surface compared with the galactose of alpha-GalCer. Because the relatively short C(14) fatty acid of GalA-GSL does not fully occupy the A' pocket, a spacer lipid is found that stabilizes this pocket. The lipid spacer was identified by GC/MS as a mixture of saturated and monounsaturated palmitic acid (C(16)). Comparison of available crystal structures of alpha-anomeric glycosphingolipids now sheds light on the structural basis of their differential antigenic potency and has led to the design and synthesis of NKT cell agonists with enhanced cell-based stimulatory activities compared with alpha-GalCer.