Clinical translation of anti-inflammatory effects of Prevotella histicola in Th1, Th2, and Th17 inflammation

Introduction

EDP1815 is a non-colonizing pharmaceutical preparation of a single stain of Prevotella histicola isolated from the duodenum of a human donor. We report here preclinical and clinical studies showing that the action of EDP1815, an orally delivered and gut restricted single strain of commensal bacteria can regulate inflammatory responses throughout the body.

Methods

Supported by evidence for anti-inflammatory activity in three preclinical mouse models of Th1-, TH2-, and Th17-mediated inflammation, EDP1815 was tested clinically in three Phase 1b studies in patients with psoriasis, patients with atopic dermatitis, and healthy volunteers in a KLH skin challenge model.

Results

Preclinically, EDP1815 was efficacious in all three mouse models of inflammation, showing reduction in skin inflammation as well as related tissue cytokines. In the Phase 1b studies, EDP1815 was found to be well tolerated by participants, with a safety profile comparable to placebo, including no severe or consistent side-effects reported, and no evidence of immunosuppression with no opportunistic infection occurring in these studies. In psoriasis patients, signs of clinical efficacy were seen after 4 weeks of treatment, which continued beyond the treatment period in the higher-dose cohort. In atopic dermatitis patients, improvements were seen throughout the key physician-and patient-reported outcomes. In a healthy-volunteer study of a KLH-induced skin inflammatory response, consistent anti-inflammatory effects were seen in two cohorts through imaging-based measures of skin inflammation.

Discussion

This is the first report demonstrating clinical effects from targeting peripheral inflammation with a non-colonizing gut-restricted single strain of commensal bacteria, providing proof of concept for a new class of medicines. These clinical effects occur without systemic exposure of EDP1815 or modification of the resident gut microbiota, and with placebo-like safety and tolerability. The breadth of these clinical effects of EDP1815, combined with its excellent safety and tolerability profile and oral administration, suggests the potential for a new type of effective, safe, oral, and accessible anti-inflammatory medicine to treat the wide range of diseases driven by inflammation.Clinical Trial Registration: EudraCT # 2018-002807-32; EudraCT # 2018-002807-32; NL8676; https://clinicaltrials.gov/ct2/show/NCT03733353; http://www.trialregister.nl.

Impact of oral administration of single strain Lactococcus lactis spp. cremoris on immune responses to keyhole limpet hemocyanin immunization and gut microbiota: A randomized placebo-controlled trial in healthy volunteers

Introduction

Lactococcus lactis spp. cremoris has been associated with promising immunomodulatory results in preclinical trials. The aim of this study was to investigate the pharmacodynamic (PD) effects of three monoclonal microbial formulations of L. lactis spp. cremoris (EDP1066) on the immune response to keyhole limpet hemocyanin (KLH). Potential effects on the gut microbiota were also investigated.

Methods

The trial was registered on Netherlands Trial Register (trial ID NL7519, https://trialsearch.who.int). Eighty-one healthy subjects (median 28, range 18-59 years) were randomized to 28 days of enteric-coated capsules at five doses (n = 13) (1.5 * 1012 total cells daily), freeze-dried powder at one dose (n = 12) (3.0 * 1011 total cells daily) or five doses (n = 12), minitablets at one dose (n = 12) or five doses (n = 12), or placebo (n = 20) prior to KLH immunization. Antibody responses and circulating regulatory T cells (Tregs) were measured after KLH immunization, and skin responses were evaluated after a KLH rechallenge by laser speckle contrast imaging and multispectral imaging. Ex vivo lymphocyte (phytohemagglutinin) and monocyte (lipopolysaccharide (LPS)) cytokine release assays were explored in the minitablet-treated groups only. The prevalence of L. lactis spp. cremoris in the gastrointestinal tract and the impact on the fecal microbiota were assessed by qPCR and 16S rRNA sequencing, respectively.

Results

Repeated-measures analysis of covariances revealed no significant treatment effects on the antibody responses to KLH, number of Tregs, or KLH skin rechallenge outcomes. Ex vivo LPS-driven cytokine responses in whole blood were lower in the low dose minitablet group compared to placebo: tumor necrosis factor (estimated difference (ED) from placebo: -44.2%, 95% confidence interval (CI) -65.3% to -10.3%), interleukin (IL)-1β (ED -41.4%, 95% CI -63.5% to -5.8%), and IL-6 (ED -39.2%, 95% CI -56.8% to -14.5%). The fecal presence of L. lactis spp. cremoris increased during treatment by all EDP1066 formulations and normalized 5 days after the last dose. Microbiome α-diversity did not change by the treatments compared to placebo.

Discussion

The EDP1066 formulations did not affect the immune response to KLH immunization in healthy individuals. However, exposure to L. lactis spp. cremoris in minitablet formulation impacted ex vivo whole blood LPS cytokine response. The clinical impact of these effects awaits further investigations.

Netherlands Trial Register

trialsearch.who.int, trial ID NL7519.

Harnessing the small intestinal axis to resolve systemic inflammation

This Perspective presents the potential of the Small Intestinal Axis, a sub-division of the Gut-immune Axis, to modulate systemic inflammation based on sensing contents of the gut lumen. Gut mucosal immunity regulates tolerance to food and gut contents and is a significant factor in maintaining systemic homeostasis without compromising immunity to pathogens. This is achieved through anatomical structures and signaling pathways that link the tolerogenic potential of the proximal small intestine to systemic immunity. Non-live preparations of microbes isolated from human small intestinal mucosa, and the extracellular vesicles (EVs) which they shed, can resolve systemic inflammation without systemic exposure after oral delivery. The mechanism involves primary interactions with pattern recognition receptors followed by trafficking of immune cells through mesenteric lymph nodes. This generates in the periphery a population of circulating CD4+ T cells which have regulatory function but an atypical FoxP3- phenotype. There is no modification of the resident gut microbiome. Discoveries using this novel approach of targeting mucosal microbial elements to the tolerogenic proximal regions of the small intestine are revealing some of the mysteries of the relationship between the gut and immune system.

Treatment with an orally delivered non-replicating, non-colonizing strain of Veillonella parvula resolves systemic inflammation in murine models of disease

Introduction

The mucosal immune system comprises of a complex network of intestinal epithelial cells and immune cells. We report that an orally delivered microbial strain of Veillonella parvula (EDP1867) that is non-replicating and non-colonizing acts through pattern recognition receptor mediated modulation of small intestinal immune responses to induce potent systemic inflammation resolution.

Methods

EDP1867 is a strain of Veillonella parvula isolated from mucosal tissue of a human donor and rendered non replicating by gamma irradiation. In vitro experiments were performed in primary human immune cells. In vivo efficacy was done using mouse models of delayed-type hypersensitivity (DTH) and psoriasis. Fluorescently labeled EDP1867 was used in biodistribution experiments.

Results

EDP1867 induced IL-10 in primary human immune cells. In a DTH model, orally delivered EDP1867 reduced inflammation and diminished production of pro-inflammatory cytokines ex vivo. Fluorescently labeled EDP1867 transited through the gut without systemic exposure in biodistribution studies to demonstrate gut restriction. EDP1867 activity is dependent on TLR2 and migration of immune cells through the gut. In an imiquimod-induced psoriasis model, EDP1867 reduced skin inflammation and psoriasis score and Th17 cytokines in the skin.

Conclusions

EDP1867 drives broad based resolution of inflammation and can reestablish normal homeostasis. These data demonstrate that EDP1867 can act as a new oral anti-inflammatory drug that is gut restricted and dependent on local immune recognition within the small intestine, to induce systemic anti-inflammatory effects. EDP1867 is currently in clinical development for treatment of inflammatory diseases.

Regulation of Peripheral Inflammation by a Non-Viable, Non-Colonizing Strain of Commensal Bacteria

The gastrointestinal tract represents one of the largest body surfaces that is exposed to the outside world. It is the only mucosal surface that is required to simultaneously recognize and defend against pathogens, while allowing nutrients containing foreign antigens to be tolerated and absorbed. It differentiates between these foreign substances through a complex system of pattern recognition receptors expressed on the surface of the intestinal epithelial cells as well as the underlying immune cells. These immune cells actively sample and evaluate microbes and other particles that pass through the lumen of the gut. This local sensing system is part of a broader distributed signaling system that is connected to the rest of the body through the enteric nervous system, the immune system, and the metabolic system. While local tissue homeostasis is maintained by commensal bacteria that colonize the gut, colonization itself may not be required for the activation of distributed signaling networks that can result in modulation of peripheral inflammation. Herein, we describe the ability of a gut-restricted strain of commensal bacteria to drive systemic anti-inflammatory effects in a manner that does not rely upon its ability to colonize the gastrointestinal tract or alter the mucosal microbiome. Orally administered EDP1867, a gamma-irradiated strain of Veillonella parvula, rapidly transits through the murine gut without colonization or alteration of the background microbiome flora. In murine models of inflammatory disease including delayed-type hypersensitivity (DTH), atopic dermatitis, psoriasis, and experimental autoimmune encephalomyelitis (EAE), treatment with EDP1867 resulted in significant reduction in inflammation and immunopathology. Ex vivo cytokine analyses revealed that EDP1867 treatment diminished production of pro-inflammatory cytokines involved in inflammatory cascades. Furthermore, blockade of lymphocyte migration to the gut-associated lymphoid tissues impaired the ability of EDP1867 to resolve peripheral inflammation, supporting the hypothesis that circulating immune cells are responsible for promulgating the signals from the gut to peripheral tissues. Finally, we show that adoptively transferred T cells from EDP1867-treated mice inhibit inflammation induced in recipient mice. These results demonstrate that an orally-delivered, non-viable strain of commensal bacteria can mediate potent anti-inflammatory effects in peripheral tissues through transient occupancy of the gastrointestinal tract, and support the development of non-living bacterial strains for therapeutic applications.

Orally-delivered microbial extracellular vesicle induces anti-inflammatory activity in mice

The small intestinal axis is a network of anatomical and functional connections linking the small intestine with the rest of the body. It senses external signals in the gut lumen and translates them into systemic immune effects. We have previously shown that an oral microbial drug candidate induces anti-inflammatory activity in preclinical models of inflammation by acting directly on host cells without colonization of the gut or modulation of the microbiome. We now extend these observations to EDP2939, a bacterial extracellular vesicle (EV), that has potent anti-inflammatory activity in preclinical models. EVs are non-replicating bacterial membrane vesicles with approximately 1/1000th the volume of the parent cell. EDP2939 was orally delivered and gut-restricted in distribution, it acts by modulation of innate and adaptive immunity within the small intestine to attenuate systemic inflammatory responses.

We observed significantly decreased ear swelling and inflammation in a delayed-type hypersensitivity model, showing that EDP2939 modulates systemic inflammatory responses. Activity of EDP2939 is dependent upon both TLR2 signaling and the presence of local immune cells. In vitro results show TLR2 agonism and induction of anti-inflammatory cytokine responses in immune cells by EVs. This is the first report of striking anti-inflammatory effects of an orally delivered microbial extracellular vesicle. EDP2939 induces broad-based resolution of inflammation across multiple pathways via a novel mechanism of systemic pharmacology without systemic exposure. EVs are particularly effective at engaging host cells in the gut to modulate distal inflammation. These data point to oral EVs as a new class of immunotherapeutic drugs.

3-Amido pyrrolopyrazine JAK kinase inhibitors: development of a JAK3 vs JAK1 selective inhibitor and evaluation in cellular and in vivo models

The Janus kinases (JAKs) are involved in multiple signaling networks relevant to inflammatory diseases, and inhibition of one or more members of this class may modulate disease activity or progression. We optimized a new inhibitor scaffold, 3-amido-5-cyclopropylpyrrolopyrazines, to a potent example with reasonable kinome selectivity, including selectivity for JAK3 versus JAK1, and good biopharmaceutical properties. Evaluation of this analogue in cellular and in vivo models confirmed functional selectivity for modulation of a JAK3/JAK1-dependent IL-2 stimulated pathway over a JAK1/JAK2/Tyk2-dependent IL-6 stimulated pathway.

Isoform-selective thiazolo[5,4-b]pyridine S1P1 agonists possessing acyclic amino carboxylate head-groups

Replacement of the azetidine carboxylate of an S1P(1) agonist development candidate, AMG 369, with a range of acyclic head-groups led to the identification of a novel, S1P(3)-sparing S1P(1) agonist, (-)-2-amino-4-(3-fluoro-4-(5-(1-phenylcyclopropyl)thiazolo[5,4-b]pyridin-2-yl)phenyl)-2-methylbutanoic acid (8c), which possessed good in vivo efficacy and pharmacokinetic properties. A 0.3mg/kg oral dose of 8c produced a statistically significant reduction in blood lymphocyte counts 24h post-dosing in female Lewis rats.

Discovery of a Potent, S1P3-Sparing Benzothiazole Agonist of Sphingosine-1-Phosphate Receptor 1 (S1P1)

Optimization of a benzofuranyl S1P1 agonist lead compound (3) led to the discovery of 1-(3-fluoro-4-(5-(2-fluorobenzyl)benzo[d]thiazol-2-yl)benzyl)azetidine-3-carboxylic acid (14), a potent S1P1 agonist with minimal activity at S1P3. Dosed orally at 0.3 mg/kg, 14 significantly reduced blood lymphocyte counts 24 h postdose and attenuated a delayed type hypersensitivity (DTH) response to antigen challenge.

Discovery of AMG 369, a Thiazolo[5,4-b]pyridine Agonist of S1P1 and S1P5

The optimization of a series of thiazolopyridine S1P1 agonists with limited activity at the S1P3 receptor is reported. These efforts resulted in the discovery of 1-(3-fluoro-4-(5-(1-phenylcyclopropyl)thiazolo-[5,4-b]pyridin-2-yl)benzyl)azetidine-3-carboxylic acid (5d, AMG 369), a potent dual S1P1/S1P5 agonist with limited activity at S1P3 and no activity at S1P2/S1P4. Dosed orally at 0.1 mg/kg, 5d is shown to reduce blood lymphocyte counts 24 h postdose and delay the onset and reduce the severity of experimental autoimmune encephalomyelitis in rat.

INFLUENCE OF TEMPERATURE AND HYDROGEN ION CONCENTRATION UPON THE SPORE CYCLE OF BACILLUS SUBTILIS

1. At 5 degrees C. no germination took place. 2. At 25 degrees C. and at 37 degrees C. germination occurs if the hydrogen ion concentration of the broth is kept between pH 5 and pH 10, but not at higher or lower pH values. 3. The completion of the spore cycle likewise requires a hydrogen ion concentration between pH 5 and pH 10. 4. The spores can germinate when the pH value is 10, although after germination the vegetative cells multiply only to a very slight extent and soon pass into spores. 5. The slight growth and multiplication of vegetative cells in broth of pH 10 suggest that the formation of endospores in this medium must be caused largely by the unfavorable reaction of the medium rather than by the accumulation of metabolic products. 6. Automatic adjustment of the medium seems to play a rôle in the completion of the spore cycle. 7. The results are not only of theoretical importance but they have a practical application to the preservation of food by canning and by other methods.

Dibutyl phthalate-induced thymic stromal lymphopoietin is required for Th2 contact hypersensitivity responses

Thymic stromal lymphopoietin (TSLP) is an IL-7-related cytokine, produced by epithelial cells, that has been linked to atopic dermatitis and asthma; however, it remains unclear how TSLP shapes the adaptive immune response that causes these allergic disorders. In this study, we demonstrate a role for TSLP in a Th2 model of contact hypersensitivity in mice. TSLP is required for the development of Th2-type contact hypersensitivity induced by the hapten FITC in combination with the sensitizing agent dibutyl phthalate. TSLPR-deficient mice exhibited a dramatically reduced response, including markedly reduced local infiltration by eosinophils, Th2 cytokine production, and serum IgE levels, following FITC sensitization and challenge. The reduced response by TSLPR-deficient mice is likely due to decreased frequency and reduced T cell stimulatory function of skin-derived Ag-bearing FITC(+)CD11c(+) dendritic cells in draining lymph nodes following FITC sensitization. These data suggest that skin-derived dendritic cells are direct or indirect targets of TSLP in the development of type 2 immune responses in the skin, where TSLP drives their maturation, accumulation in skin draining lymph nodes, and ability to induce proliferation of naive allergen-specific T cells.

Antagonists of CD117 (cKit) signaling inhibit mast cell accumulation in healing skin wounds

Mast cells (MCs) have important functional roles in leukocyte recruitment, pain, and wound healing, and increased tissue resident MC function has been associated with several fibrotic diseases. Consequently, the study of MCs in situ can be a direct approach to studying the pharmacodynamic impact of MC-directed therapeutics in tissues. Here we describe an automated laser scanning cytometry assay that was used to characterize the kinetics of MC accumulation in healing skin wounds and to study the effect of inhibiting CD117 (cKit) signaling. The number of tryptase-positive MCs approximately doubled 14 days after cutaneous injury in nonhuman primates. Treatment of animals with anti-CD117 or imatinib mesylate (Gleevec) reduced MC accumulation at the edge of healing wounds in mice and nonhuman primates, respectively. In translating this MC assay to become a biomarker for human studies, no differences in dermal MC numbers were evident between genders, ages or body mass index from 20 healthy donors. These data suggest that skin is a practical and useful tissue for tracking pharmacodynamic effects of MC-directed therapies.

The effect of c-Kit inhibition on mast cells in skin, colon, and lung (39.46)

Stem Cell Factor (SCF) signaling via its receptor tyrosine kinase, c-Kit, is vital for mast cell development, function and survival. The effect of inhibition of c-Kit function using subcutaneous administration of a specific blocking monoclonal antibody weekly for up to 28 days was examined in African Green monkeys (Cercopithecus aethiops sabaeus). Treatment-related effects on mast cell populations were evaluated in tissue samples collected from wounded skin and colon biopsies on days 0, 7, 14, 21, and 28 (colon only) and skin, lung, and gastrointestinal tract collected at necropsy on day 28. Mast cells were visualized by Astra blue staining and immunohistochemistry for CD117, tryptase, and/or chymase. Specific c-Kit inhibition resulted in depletion of mast cells in unchallenged skin, colon, and lung after 28 days. Additionally, c-Kit antibody treatment inhibited the injury-induced expansion of dermal mast cells adjacent to wounded skin. Mast cells have been implicated as important mediators in a wide range of inflammatory diseases including asthma, rheumatoid arthritis, inflammatory bowel disease, and fibrosis. This is the first report of use of an antibody to deplete tissue mast cells in relevant organs in non-human primates.

Discovery of aryl aminoquinazoline pyridones as potent, selective, and orally efficacious inhibitors of receptor tyrosine kinase c-Kit

Inhibition of c-Kit has the potential to treat mast cell associated fibrotic diseases. We report the discovery of several aminoquinazoline pyridones that are potent inhibitors of c-Kit with greater than 200-fold selectivity against KDR, p38, Lck, and Src. In vivo efficacy of pyridone 16 by dose-dependent inhibition of histamine release was demonstrated in a rodent pharmacodynamic model of mast cell activation.

CCR6-dependent recruitment of blood phagocytes is necessary for rapid CD4 T cell responses to local bacterial infection

The contribution of CCR6 and phagocyte recruitment to the initiation of T cell responses to a local pathogen is unclear. CD4 T cell activation to an injected soluble antigen occurred rapidly and was completely CCR6-independent. In marked contrast, the tempo of pathogen-specific CD4 T cell activation depended on whether the antigen was secreted or cell-associated. Furthermore, lymph node pathogen-specific CD4 T cell activation required CCR6 and cell migration from the site of infection. Surprisingly, adoptive transfer of wild-type blood phagocytes rescued bacteria-specific T cell activation in CCR6-deficient mice, even when these cells were unable to participate in direct antigen presentation. These data demonstrate that T cell responses to a local bacterial infection follow a distinct tempo, largely determined by bacterial protein secretion, and that CCR6-mediated blood phagocyte recruitment to the site of infection is a critical step in the initiation of pathogen-specific immune responses in skin draining lymph nodes.

In vivo activation of antigen-specific CD4 T cells

Physical detection of antigen-specific CD4 T cells has revealed features of the in vivo immune response that were not appreciated from in vitro studies. In vivo, antigen is initially presented to naïve CD4 T cells exclusively by dendritic cells within the T cell areas of secondary lymphoid tissues. Anatomic constraints make it likely that these dendritic cells acquire the antigen at the site where it enters the body. Inflammation enhances in vivo T cell activation by stimulating dendritic cells to migrate to the T cell areas and display stable peptide-MHC complexes and costimulatory ligands. Once stimulated by a dendritic cell, antigen-specific CD4 T cells produce IL-2 but proliferate in an IL-2--independent fashion. Inflammatory signals induce chemokine receptors on activated T cells that direct their migration into the B cell areas to interact with antigen-specific B cells. Most of the activated T cells then die within the lymphoid tissues. However, in the presence of inflammation, a population of memory T cells survives. This population is composed of two functional classes. One recirculates through nonlymphoid tissues and is capable of immediate effector lymphokine production. The other recirculates through lymph nodes and quickly acquires the capacity to produce effector lymphokines if stimulated. Therefore, antigenic stimulation in the presence of inflammation produces an increased number of specific T cells capable of producing effector lymphokines throughout the body.

Highly efficient selection of CD4 and CD8 lineage thymocytes supports an instructive model of lineage commitment

We undertook a kinetic analysis of the generation of mature T cells in TCR and coreceptor transgenic mice using BrdU labeling. We observed that the selection efficiency of mature CD4-CD8+ and CD4+CD8- thymocytes could be as high as 40% and 90% of CD4+CD8+ precursors, respectively. The surprisingly high efficiency of selection favors an instructional model of lineage commitment and is incompatible with a stochastic model in which the efficiency of selection would be no greater than 100% in both lineages combined.

The Cytoplasmic Domain of CD8β Regulates Lck Kinase Activation and CD8 T Cell Development

Previous studies have shown that CD8β plays a role in both enhancing CD8α-associated Lck kinase activity and promoting the development of CD8-lineage T cells. To examine the role of this enhancement in the maturation of CD8-lineage cells, we assessed CD8α-associated Lck kinase activity in both T cell hybridomas and thymocytes of mice expressing CD8β mutations known to impair CD8 T cell development. Lack of CD8β expression or expression of a cytoplasmic domain-deleted CD8β resulted in a severalfold reduction in CD8α-associated Lck kinase activity compared with that observed with cells expressing wild-type CD8β chain. This analysis indicated a critical role for the cytoplasmic domain of CD8β in the regulation of CD8α-associated Lck activity. Decreased CD8α-associated Lck activity observed with the various CD8β mutations also correlated with diminished in vivo cellular tyrosine phosphorylation. In addition, analysis of CD8β mutant mice (CD8β−/− or cytoplasmic domain-deleted CD8β transgenic) indicated that the degree of reduction in CD8α-associated Lck activity associated with each mutation correlated with the severity of developmental impairment. These results support the importance of CD8β-mediated enhancement of CD8α-associated Lck kinase activity in the differentiation of CD8 single-positive thymocytes.

The cytoplasmic domain of CD8 beta regulates Lck kinase activation and CD8 T cell development

Previous studies have shown that CD8 beta plays a role in both enhancing CD8 alpha-associated Lck kinase activity and promoting the development of CD8-lineage T cells. To examine the role of this enhancement in the maturation of CD8-lineage cells, we assessed CD8 alpha-associated Lck kinase activity in both T cell hybridomas and thymocytes of mice expressing CD8 beta mutations known to impair CD8 T cell development. Lack of CD8 beta expression or expression of a cytoplasmic domain-deleted CD8 beta resulted in a severalfold reduction in CD8 alpha-associated Lck kinase activity compared with that observed with cells expressing wild-type CD8 beta chain. This analysis indicated a critical role for the cytoplasmic domain of CD8 beta in the regulation of CD8 alpha-associated Lck activity. Decreased CD8 alpha-associated Lck activity observed with the various CD8 beta mutations also correlated with diminished in vivo cellular tyrosine phosphorylation. In addition, analysis of CD8 beta mutant mice (CD8 beta-/- or cytoplasmic domain-deleted CD8 beta transgenic) indicated that the degree of reduction in CD8 alpha-associated Lck activity associated with each mutation correlated with the severity of developmental impairment. These results support the importance of CD8 beta-mediated enhancement of CD8 alpha-associated Lck kinase activity in the differentiation of CD8 single-positive thymocytes.

An activated form of Notch influences the choice between CD4 and CD8 T cell lineages

Notch is a transmembrane receptor that controls cell fate decisions in Drosophila and whose role in mammalian cell fate decisions is beginning to be explored. We are investigating the role of Notch in a well-studied mammalian cell fate decision: the choice between the CD8 and CD4 T cell lineages. Here we report that expression of an activated form of Notch1 in developing T cells of the mouse leads to both an increase in CD8 lineage T cells and a decrease in CD4 lineage T cells. Expression of activated Notch permits the development of mature CD8 lineage thymocytes even in the absence of class I major histocompatability complex (MHC) proteins, ligands that are normally required for the development of these cells. However, activated Notch is not sufficient to promote CD8 cell development when both class I and class II MHC are absent. These results implicate Notch as a participant in the CD4 versus CD8 lineage decision.

The cytoplasmic domain of CD4 promotes the development of CD4 lineage T cells

Thymocytes must bind major histocompatibility complex (MHC) proteins on thymic epithelial cells in order to mature into either CD8+ cytotoxic T cells or CD4+ helper T cells. Thymic precursors express both CD8 and CD4, and it has been suggested that the intracellular signals generated by CD8 or CD4 binding to class I or II MHC, respectively, might influence the fate of uncommitted cells. Here we test the notion that intracellular signaling by CD4 directs the development of thymocytes to a CD4 lineage. A hybrid protein consisting of the CD8 extracellular and transmembrane domains and the cytoplasmic domain of CD4 (CD884) should bind class I MHC but deliver a CD4 intracellular signal. We find that expression of a hybrid CD884 protein in thymocytes of transgenic mice leads to the development of large numbers of class I MHC-specific, CD4 lineage T cells. We discuss these results in terms of current models for CD4 and CD8 lineage commitment.

Functional commitment to helper T cell lineage precedes positive selection and is independent of T cell receptor MHC specificity

Thymocyte differentiation proceeds from double positive CD4+CD8+ to single positive T cells. It has been proposed that this process occurs by an instructive or a stochastic mechanism. In this report, we show that in recombination-deficient mice (RAG-1-I-) constitutive expression of a CD8 transgene allows maturation of CD4+(CD8tg+) cells, which express mature levels of a transgenic class I-restricted T cell receptor, F5. Rescued F5+CD4+(CD8tg+) cells have equivalent levels of T cell receptor expression as CD8end+ cells, respond to cognate antigen and, upon stimulation, they exhibit a phenotype characteristic of CD4+ helper T cells. These data are consistent with a model of differentiation that predicts that thymocytes become functionally committed to a helper or cytotoxic lineage before the final step of positive selection and independently of MHC specificity of their T cell receptor.

A role for the cytoplasmic tail of the beta chain of CD8 in thymic selection

The CD8 coreceptor plays a critical role in the recognition of foreign antigens by mature T cells and in the development of class I-restricted T cells. CD8 can be expressed on the surface of T cells as either a heterodimer composed of an alpha and beta chain, or as a homodimer composed of two alpha chains. In this report, we show that a CD8 beta transgene that lacks a cytoplasmic domain can suppress expression of wild-type endogenous CD8 beta and act as a dominant negative mutation. We show that this dominant negative CD8 beta transgene interferes with the development of mature CD8 T cells to different extents depending on the individual class I-restricted TCR. These data suggest CD8 beta plays a role in thymic development, and that different class I-restricted TCRs differ in their dependence on the cytoplasmic tail of CD8 beta.

Constitutive CD8 expression allows inefficient maturation of CD4+ helper T cells in class II major histocompatibility complex mutant mice

Although mature CD4+ T cells bear T cell receptors (TCRs) that recognize class II major histocompatibility complex (MHC) and mature CD8+ T cells bear TCRs that recognize class I MHC, it is possible that the initial commitment of an immature thymocyte to a CD4 or CD8 lineage is made without regard to the specificity of the TCR. According to this model, CD4+ cells with class I TCR do not mature because the CD8 coreceptor is required for class I MHC recognition and positive selection. If this model is correct, constitutive expression of CD8 should allow CD4+ T cells with class I-specific TCRs to develop. In this report, we show that mature peripheral CD4+ cells are present in class II MHC-deficient mice that express a constitutive CD8.1 transgene. These cells share a number of properties with the major class II MHC-selected CD4 population, including the ability to express CD40 ligand upon activation. Although mature CD4 cells are also detectable in the thymus of class II MHC mutant/CD8.1 transgenic mice, they represent a small fraction of the mature CD4 cells found in mice that express class II MHC. These results indicate that some T cells choose the CD4 helper lineage independent of their antigen receptor specificity; however, the inefficiency of generating class I-specific CD4 cells leaves open the possibility that an instructive signal generated upon MHC recognition may bias lineage commitment.

Stochastic component to development of class I major histocompatibility complex-specific T cells

The mechanism by which an initially uncommitted cell chooses between alternative fates is a central issue in developmental biology. In the mammalian thymus, CD4 helper T cells and CD8 cytotoxic T cells arise from a common precursor that expresses both CD4 and CD8. The choice between the CD4 and CD8 lineage is linked to the specificity of the T-cell antigen receptor expressed by a thymocyte, but whether lineage commitment is stochastic or instructed has not been definitively resolved. We present evidence that expression of a constitutive CD8 transgene during thymic selection permits development of mature CD4 cells bearing the class I-restricted F5 T-cell antigen receptor. These results suggest that there is a stochastic component to the development of class I major histocompatibility complex-restricted T cells.

Chronic murine experimental myasthenia gravis: strength testing and serology

CB6 (Balb/c x C57Bl/6 F1) and C57Bl/6 (B6) mice were hyperimmunized with Torpedo acetylcholine receptor (AChR) for 7 months. Control groups were hyperimmunized with bovine serum albumin. Antibody titers against Torpedo AChR rose quickly, reaching plateau levels by 3-4 months, while antibody to mouse AChR lagged by a few months, reaching plateau levels in 5 months. After the last immunization the mice maintained a state of stable autoimmunity for 9 months with high levels of antibodies against Torpedo and mouse AChR. Fatigability was measured on a programmable treadmill and remained present through the 9 months after the last immunization. CB6 mice had less weakness than the B6 mice, but the latter strain when immunized with BSA had more "false-positive" weakness. Titers of antibodies did not correlate with the degree of weakness measured on the treadmill. Despite the weakness and the high titers of anti-AChR antibodies, sera from myasthenic mice, in contrast to sera from myasthenic humans, were not able to block bungarotoxin binding to native AChR on the surface of BC3H1 cells.

Olfactory classical conditioning in neonates

One-day-old, awake infants underwent an olfactory classical conditioning procedure to assess associative learning within the olfactory system of newborns. Experimental infants received ten 30-second pairings of a novel olfactory conditioned stimulus (a citrus odor of neutral value) and tactile stimulation provided by stroking as the reinforcing unconditioned stimulus (a stimulus with positive properties). Control babies received only the odor, only the stroking, or the stroking followed by the odor presentation. The next day, all infants, in either the awake or sleep state, were given five 30-second presentations of the odor. Results were analyzed from video tapes scored by an observer unaware of the infants' training condition. The results indicate that only those infants who received the forward pairings of the odor and stroking exhibited conditioned responding (head turning toward the odor) to the citrus odor. The performance of the conditioned response was not affected by the state of the baby during testing, because both awake and sleeping infants exhibited conditioned responses. Furthermore, the expression of the conditioned response was odor specific; a novel floral odor presented during testing did not elicit conditioned responses in the experimental babies. These results suggest that complex associative olfactory learning is seen in newborns within the first 48 hours of life. These baseline findings may serve as normative data against which observation from neonates at risk for neurological sequelae may be compared.

Borrelia burgdorferi infection of the brain: characterization of the organism and response to antibiotics and immune sera in the mouse model

To learn more about the neurologic involvement in Lyme disease, we inoculated inbred mice with the causative agent of Lyme disease, Borrelia burgdorferi. We cultured brains and other organs, and measured anti-B burgdorferi antibody titers. We further studied a brain isolate for its plasmid DNA content and its response in vitro to immune sera and antibiotics. One strain of B burgdorferi, N40, was consistently infective for mice, and resulted in chronic infection of the bladder and spleen. SJL mice developed fewer culture-positive organs and had lower antibody titers than Balb/c and C57Bl/6 mice. Organism was cultured from the brain early in the course of infection, and this isolate, named N40Br, was further studied in vitro. The plasmid content of N40Br was different from that of the infecting strain, implying either a highly selective process during infection or DNA rearrangement in the organism in vivo. N40Br was very sensitive to antibiotics, but only after prolonged incubation. Immune sera from both mice and humans infected with B burgdorferi were unable to completely kill the organism by complement-mediated cytotoxicity. These data demonstrate that B burgdorferi infects the brain of experimental animals, and is resistant to immune sera in vitro but sensitive to prolonged treatment with antibiotics.