The CD6-ALCAM pathway selectively modulates pathogenic T cell migration

CD6 is a costimulatory receptor on T cells that, through binding to its ligand ALCAM, modulates both the activity and trafficking of effector T cells (Teff). ALCAM has been seen to be overexpressed on various tissues during inflammation and is associated with increased infiltration of pathogenic CD6high CD4+ T cells in patients with autoimmune and inflammatory diseases. However, the role of the CD6-ALCAM pathway in the chemotaxis of pathogenic T cells into inflamed tissues is not yet clear.

Here, we investigate the contribution of CD6 in mediating chemokine-induced migration of Teff cells through the endothelial barrier by using itolizumab, a humanized anti-CD6 monoclonal antibody that inhibits the CD6-ALCAM interaction and reduces CD6 levels on T cells in the presence of monocytes. The migration of Teff cells from PBMCs or in vitro polarized TH17 cells expressing high levels of CD6, was tested under static conditions using a Boyden chamber assay incorporating human umbilical vein endothelial cells (HUVEC) which express high levels of ALCAM.

Analysis of migrating CD4+ T cells from total PBMCs showed that cells expressing higher levels of CD6 preferentially migrated through the HUVEC layer in response to CXCL12. Blocking the CD6-ALCAM pathway reduces the migration of CD4+ CCR7− CD45RA− TEM cells by ~60%. Furthermore, itolizumab treatment reduced the migration of pathogenic TH17 when co-cultured with monocytes.

This data demonstrates that the CD6-ALCAM pathway contributes to the chemokine-driven migration of Teff cells into inflamed organs through the endothelial layers. Consequently, blockade of this pathway will not only inhibit the activity of Teff but may also selectively affect their infiltration into inflamed organs.

CD6 – a costimulatory receptor at the nexus of Teff / Treg development

The balance of proinflammatory effector T cells (Teff) and anti-inflammatory regulatory T cells (Treg) is associated with autoimmune and inflammatory diseases. CD6 is a costimulatory receptor expressed on T cells with its greatest expression on pathogenic Teff cells, while Tregs are CD6low. Notably T cells from CD6knockout mice fail to differentiate to Th17 cells but were seen to skew to a Treg phenotype more rapidly. Although the role of CD6 in Teff development is well characterized, here we sought to investigate the role of CD6 in the development of Treg cells.

Itolizumab, a humanized anti-CD6 monoclonal antibody that modulates cell surface levels of CD6, was used to generate CD6low naïve T cells, after which itolizumab was removed and Tregs were differentiated using a standard protocol. Tregs derived from CD6low cells had greater co-expression of FOXP3 and HELIOS (~2-fold) vs. Tregs derived from isotype-treated CD6high. These Tregs possessed greater suppressive function, with increased inhibition of proliferation and cytokine release by stimulated T responder cells by at least 50% more than Tregs derived from CD6high cells; this was verified in three different donors. Similar observations were made when measuring levels of cytokines. CD6low Tregs were able to suppress T responder’s production of proinflammatory cytokines by 60–90% compared to CD6high Tregs.

This is the first study to directly characterize the role of CD6 in the development and activity of Treg cells. These data suggest that reduced levels of cell surface CD6 facilitate the development of Treg cells with greater stability and suppressive activity and that modulating the levels of CD6 may decrease the Teff/Treg ratio in patients with autoimmune and inflammatory diseases.

Modulating levels of cell surface CD6 is a novel mechanism for regulating T cell activity

CD6 is a co-stimulatory receptor expressed on the surface of T cells that promotes immune synapse formation, T cell activation, and migration into tissues by engaging its ligand, ALCAM. CD6high cells have been described to be more pathogenic relative to CD6low cells. Furthermore, T cells in CD6 knockout mice have decreased proliferation and inflammatory responses. Hence, a therapeutic that can modulate surface levels of CD6 may have favorable outcomes for autoimmune/inflammatory conditions. We recently demonstrated that the anti-CD6 mAb, itolizumab, induces proteolytic cleavage of cell surface CD6. The goal of the work shown here is to characterize the mechanism of cleavage and the downstream functional consequences of reduced cell surface CD6. Treatment of PBMCs with itolizumab induces CD6 cleavage from the cell surface and a concomitant increase in the soluble form detected in the supernatant. Itolizumab-induced loss of CD6 was not observed with isolated T cells, however CD6 levels were reduced by 87% when T cells and monocytes were cocultured with itolizumab. The cleavage of CD6 is initiated through rapid cell-to-cell contact between T cells and monocytes via FcγRI. The dose-dependent reduction in surface levels of CD6 positively correlates with decreases in T cell activation markers such as CD25, PD-1, and CD71 (Pearson, p<0.001) and cytokine production including IL-2 (p<0.01) and TNFα (p<0.05). Itolizumab-treated cells are also less alloreactive as shown by a reduction in proliferation and cytokine production of responder cells in a mixed-lymphocyte reaction. This data further supports targeting CD6 as an effective means to inhibit pathogenic T cell activity in the treatment of autoimmune and inflammatory diseases.

Phenotypic and functional characterization of the CD6-ALCAM T cell costimulatory pathway after allogeneic cell transplantation

CD6 is a co-stimulatory receptor expressed on T cells that binds activated leukocyte cell adhesion molecule (ALCAM), expressed on antigen presenting cells, epithelial and endothelial tissues. The CD6-ALCAM pathway plays an integral role in modulating T-cell activation, proliferation, and trafficking. In this study we examined expression of CD6 by reconstituting T cells in 95 patients after allogeneic cell transplantation and evaluated the effects of itolizumab, an anti-CD6 monoclonal antibody, on T-cell activation. CD6 T cells reconstituted early after transplant with CD4 regulatory T cells (Treg)-expressing lower levels of CD6 compared to conventional CD4 T cells (Tcon) and CD8 T cells. After onset of acute graft-versus-host disease (aGvHD), CD6 expression was further reduced in Treg and CD8 T cells compared to healthy donors, while no difference was observed for Tcon. ALCAM expression was highest in plasmacytoid dendritic cells (pDC), lowest in myeloid dendritic cells (mDC) and intermediate in monocytes and was generally increased after aGvHD onset. Itolizumab inhibited CD4 and CD8 T-cell activation and proliferation in preGvHD samples, but inhibition was less prominent in samples collected after aGvHD onset, especially for CD8 T cells. Functional studies showed that itolizumab did not mediate direct cytolytic activity or antibody-dependent cytotoxicity in vitro. However, itolizumab efficiently abrogated the costimulatory activity of ALCAM on T-cell proliferation, activation and maturation. Our results identify the CD6-ALCAM pathway as a potential target for aGvHD control and a phase I/II study using itolizumab as first line treatment in combination with steroids for patients with aGvHD is currently ongoing (clinicaltrials gov. Identifier: NCT03763318).

The CD6/ALCAM pathway promotes lupus nephritis via T cell-mediated responses

T cells are central to the pathogenesis of lupus nephritis (LN), a common complication of systemic lupus erythematosus (SLE). CD6 and its ligand, activated leukocyte cell adhesion molecule (ALCAM), are involved in T cell activation and trafficking. Previously, we showed that soluble ALCAM is increased in urine (uALCAM) of patients with LN, suggesting that this pathway contributes to disease. To investigate, uALCAM was examined in 1038 patients with SLE and LN from 5 ethnically diverse cohorts; CD6 and ALCAM expression was assessed in LN kidney cells; and disease contribution was tested via antibody blockade of CD6 in murine models of SLE and acute glomerulonephritis. Extended cohort analysis offered resounding validation of uALCAM as a biomarker that distinguishes active renal involvement in SLE, irrespective of ethnicity. ALCAM was expressed by renal structural cells whereas CD6 expression was exclusive to T cells, with elevated numbers of CD6+ and ALCAM+ cells in patients with LN. CD6 blockade in models of spontaneous lupus and immune-complex glomerulonephritis revealed significant decreases in immune cells, inflammatory markers, and disease measures. Our data demonstrate the contribution of the CD6/ALCAM pathway to LN and SLE, supporting its use as a disease biomarker and therapeutic target.

Serum-circulating His-tRNA synthetase inhibits organ-targeted immune responses

His-tRNA synthetase (HARS) is targeted by autoantibodies in chronic and acute inflammatory anti-Jo-1-positive antisynthetase syndrome. The extensive activation and migration of immune cells into lung and muscle are associated with interstitial lung disease, myositis, and morbidity. It is unknown whether the sequestration of HARS is an epiphenomenon or plays a causal role in the disease. Here, we show that HARS circulates in healthy individuals, but it is largely undetectable in the serum of anti-Jo-1-positive antisynthetase syndrome patients. In cultured primary human skeletal muscle myoblasts (HSkMC), HARS is released in increasing amounts during their differentiation into myotubes. We further show that HARS regulates immune cell engagement and inhibits CD4+ and CD8+ T-cell activation. In mouse and rodent models of acute inflammatory diseases, HARS administration downregulates immune activation. In contrast, neutralization of extracellular HARS by high-titer antibody responses during tissue injury increases susceptibility to immune attack, similar to what is seen in humans with anti-Jo-1-positive disease. Collectively, these data suggest that extracellular HARS is homeostatic in normal subjects, and its sequestration contributes to the morbidity of the anti-Jo-1-positive antisynthetase syndrome.

Itolizumab-induced antigenic modulation of CD6 inhibits T cell activity

CD6 is an immunomodulatory receptor on T cells that promotes immune synapse formation, T-cell activation, and cell migration into tissues by binding activated leukocyte cell adhesion molecule (ALCAM). Excessive activation through the CD6-ALCAM pathway has been implicated in the pathogenesis of multiple autoimmune and inflammatory diseases. Hence, the ability to modulate the level of activation is beneficial to disease resolution. Itolizumab is a humanized anti-CD6 monoclonal antibody that is specific for the membrane distal domain 1 of CD6. Previously, itolizumab was believed to sterically hinder the CD6-ALCAM interaction, thereby blocking T-cell co-stimulation. Here we describe antigenic modulation as an additional mechanism whereby binding of itolizumab to CD6 induces proteolytic cleavage of the extracellular portion of CD6. Upon treatment with itolizumab, surface levels of CD6 decreased in a dose- and time-dependent manner, as monitored by flow cytometry using a noncompetitive anti-CD6 monoclonal antibody. This loss was inhibited in the presence of protease inhibitors and the decrease in surface levels of CD6 was accompanied by an increase in levels of soluble CD6 in the supernatant. Furthermore, we assessed the effect of surface levels of CD6 on the response of cells to T cell stimulation in the presence of ALCAM. CD6low cells showed reduced T-cell activity compared to CD6highcells as measured by cell surface activation makers, including CD25, CD69 and PD-1, and cytokine production. These findings demonstrate that CD6 is an important regulator of T-cell activity and that modulating surface levels of CD6 is an effective method for fine-tuning the activity of T-cells.

Blockade of the CD6-ALCAM pathway modulates effector T cell function

CD6 is a T-cell costimulatory receptor predominantly expressed on T cells and promotes immune synapse formation, T-cell activation, and T-cell migration via interaction with activated leukocyte cell adhesion molecule (ALCAM). The CD6-ALCAM pathway has been linked to the pathogenesis of multiple autoimmune and inflammatory diseases. While the contribution of CD6 to T cell activation has been well described, less is known regarding the expression levels and role of CD6 on effector and memory T cells which contribute to ongoing disease. Consequently, the aim of this study was to determine the role of CD6 specifically on Th1, Th2 and Th17 effector T cells (Teff). Blockade of the CD6 pathway using itolizumab, a humanized mAb currently being tested in the clinic, during restimulation of fully differentiated Th1, Th2 or Th17 Teff cells in the presence of ALCAM inhibited multiple effector functions, including proliferation and changes in cell size. An average 40% decrease in proliferation was observed across multiple donors. Furthermore, treatment of Teff cells with itolizumab resulted in a significant decrease in relevant cytokines such as IFNγ and TNFα for Th1, IL-4 and IL-13 for Th2, TNFα and IL-17 for Th17, as well as in expression levels of T cell markers of activation and exhaustion such as CD69, CD25, and PD-1. This effect was exclusively observed in the presence of ALCAM, indicating that the effect was specific to blockade of the CD6-ALCAM pathway. This study is the first to characterize the CD6-ALCAM pathway as a key regulator of effector Teff cell function. As these are the cells that drive disease pathogenicity, these data support targeting the CD6-ALCAM pathway to inhibit effector Teff cell populations in autoimmune and inflammatory diseases.

An Assay to Monitor the Engagement and Modulation of CD6 on T cells as a Clinical Biomarker of Treatment with Itolizumab

Itolizumab is a novel first-in-class monoclonal antibody that selectively targets the co-stimulatory molecule CD6, a receptor that is highly expressed on CD4 and CD8 T cells and plays an important role in activation and migration. Monitoring target engagement and changes in receptor levels is critically important to interpreting clinical data. To evaluate the pharmacodynamic properties of itolizumab treatment on T cells in patients including those with graft versus host disease (GvHD), Precision for Medicine has developed and validated a 10-color flow cytometry assay to assess the engagement and modulation of cell-surface CD6.

The assay was validated using whole blood from healthy donors. Blood was spiked with five concentrations of drug selected based on expected PK in the clinical study. The assay conditions were optimized for sensitivity, signal: noise ratio, detection of free receptor, receptor-bound itolizumab and total surface CD6. Itolizumab was detected using a fluorochrome conjugated α-human IgG1 antibody while total surface CD6 expression was assessed using an antibody to a non-competing site on CD6. For validation, pre-set criteria were used to assess inter-assay, intra-assay, inter-operator precision and post-staining stability. Technical validation was successfully met; and the assay performs within acceptable precision parameters.

Measuring cell-based receptor engagement and fate in patients on immuno-modulatory therapies is very challenging. This assay was designed and validated to be both sensitive and selective in the quantification of CD6 receptor occupancy and modulation to facilitate the determination of an optimal therapeutic dose in autoimmune and inflammatory diseases.

CD6 modulation ameliorates immune complex-mediated glomerulonephritis

Lupus nephritis (LN) is a serious end organ complication of systemic lupus erythematosus (SLE) in which T cells are thought to play an essential role. CD6 is a co-stimulatory receptor on T cells, that binds to activated leukocyte cell adhesion molecule (ALCAM), a ligand expressed on antigen presentation cells and epithelial and endothelial tissues. The CD6-ALCAM pathway plays an integral role in modulating T cell activation and trafficking, and increased levels of CD6 are associated with pathogenic T cell responses. To assess the role of the CD6-ALCAM pathway in LN pathogenesis, we tested a monoclonal antibody against CD6 in a short-term, validated, inducible murine model of lupus nephritis known as nephrotoxic serum nephritis (NTN). NTN mice were treated 3× per week with an anti-CD6 mAb (10D12, 60ug/dose, n=23) or with vehicle control (n=23). Healthy mice were also included as a control (n=12). Mice treated with the anti-CD6 mAb displayed decreased levels of proteinuria (p<0.001) and significantly improved BUN levels (p<0.01) compared to vehicle control mice. Histology also significantly improved with anti-CD6 treatment (p<0.05). RT-PCR revealed significantly decreased levels of VCAM and RANTES in the kidneys of treated mice, while anti-inflammatory IL-10 was increased, compared to vehicle control mice. Flow cytometry analysis indicated decreased accumulation of both renal-infiltrating activated T cells (CD4+CD25+CD69+, p <0.01) inflammatory macrophages (p<0.05). Overall, these results indicate that the CD6-ALCAM pathway is an important driver of inflammation and pathology in LN and, thus, a promising therapeutic option that is more selective than the immunosuppressive therapies currently offered.

CD6-ALCAM signaling regulates multiple effector/memory T cell functions

CD6 is a T-cell costimulatory receptor that has been implicated in the pathogenesis of multiple autoimmune and inflammatory diseases. Primarily expressed on CD4 T cells, CD6 promotes immune synapse formation, T-cell activation and T-cell migration via interaction with its ligand activated leukocyte cell adhesion molecule (ALCAM). While the contribution of CD6 to T cell activation has been well described, less is known regarding the role of CD6 on effector and memory T cells (Teff). Thus, to better characterize this, we examined phosphorylation signaling patterns during CD6 co-stimulation together with the impact of CD6 on differentiated Teff functions. Profiling of ~100 phosphorylation targets associated with T-cell receptor signaling revealed that CD6 co-stimulation on T cells activates factors in pathways involved in actin polymerization, motility, integrin activation and T-cell activation. Comparison of Tnaive cells vs. Teff demonstrated differing levels of phosphorylation in response to CD6 stimulation. Furthermore, CD6 signaling on Teff sustained phosphorylation of these pathways at later timepoints compared to CD28 stimulation. Blockade of the CD6 pathway, using the clinically tested anti-CD6 mAb itolizumab during re-stimulation of CD4 Teff cells in the presence of ALCAM, inhibited multiple effector functions including proliferation and changes in blast size. This effect was observed exclusively in the presence of ALCAM, indicating that the effect was specific to blockade of the CD6-ALCAM pathway. These findings demonstrate that the CD6-ALCAM pathway is a key regulator of effector T-cell functions and further support targeting this pathway to directly inhibit both naïve and effector T cell populations.

Amelioration of skin and kidney disease in a spontaneous murine lupus model via CD6 modulation

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease that can affect multiple organ systems, including the kidneys, skin, and brain. T cells are an important mediator in this end organ damage. CD6 is a co-stimulatory receptor, predominantly expressed on T cells, which binds with activated leukocyte cell adhesion molecule (ALCAM), a ligand expressed on antigen presentation cells and various epithelial and endothelial tissues. This signaling pathway is vital for T cell activation, proliferation, differentiation and trafficking. We found increased expression of both CD6 and ALCAM in the kidneys of MRL/lpr mice (a spontaneous model of SLE) versus healthy control B6 mice. In a separate experiment, female MRL/lpr mice were aged to 9–10 weeks of age, at which point we began treating with either anti-CD6 antibody (60 ug/dose, intraperitoneally twice per week), isotype control (60 ug/dose, twice per week), or cyclophosphamide (25 mg/kg, once per week). We also included a no treatment group and a group of MRL/MpJ mice, a congenic healthy control strain. Mice treated with anti-CD6 show lower levels of proteinuria and BUN (p<0.05), improved survival rates, and decreased renal pathology compared to isotype control mice. Flow cytometry revealed decreased numbers of activated and effector T cells within the kidneys of anti-CD6 treated mice compared to isotype control mice. While there was no difference in anti-DNA levels, anti-CD6 treatment significant improved the spontaneous skin lesions associated with disease progression. Overall, these results indicate that targeting CD6-ALCAM interactions may have promising therapeutic potential within the context of different end organ pathologies within lupus.

Abstract 3834: Antibodies targeting Resokine, a soluble immune modulator, inhibit tumor growth in syngeneic mouse models

A number of non-canonical functions have been established for proteins generated from the tRNA synthetase gene family. One of these, termed Resokine, is derived from histidyl tRNA synthetase and plays an important role in controlling immune cell activation. Circulating levels are sufficient to down-regulate the extent of T cell activation that can be achieved in vitro. A panel of specific monoclonal antibodies have been generated and tested for their anti-tumor activity in mouse syngeneic tumor models. Antibodies to Resokine demonstrated anti-tumor activity across three different tumor models. Treatment of subcutaneous CT26 tumors resulted in improved efficacy compared to treatment with antibodies that block the PD-1/PD-L1 interaction. Significant efficacy was also observed in the difficult to treat subcutaneous B16F10 melanoma and 4T1 breast tumor models. In addition anti-Resokine demonstrated significant activity in a tumor seeding model using B16F10 melanoma which resulted in inhibition of tumor nodules in the lung, and was more efficacious than a combination of antibodies to PD-L1 and CTLA-4. Combinations of anti-Resokine antibody with either anti-PD-1 or anti-PD-L1 demonstrated at least additive, and potentially synergistic activity in these models. Animals with long-term tumor regressions were re-implanted with viable tumor cells, and demonstrated long-term immune memory with rejection of the newly implanted tumors. To understand the mechanism of anti-Resokine antibody therapy, cell depletion studies were carried out in the B16F10 tumor model. In these experiments activity of anti-Resokine antibodies was demonstrated to be dependent upon the presence of CD8 T cells and also NK cells, but independent of CD4 T cells. The immune based mechanism of antibodies to Resokine was further demonstrated by re-challenge of mice that had regressed tumors upon treatment. Tumor re-growth was not observed even in the absence of further treatment whereas control mice grew tumors at the normal rate, suggesting that immune memory had been induced. Antibodies to Resokine offer an exciting new potential option for immunotherapy of cancer, which has significant activity as monotherapy and is compatible with more established modalities. Anti-Resokine antibodies are currently being developed to initiate clinical evaluation.

Citation Format: Kathy Ogilvie, Cherie Ng, Leslie Nangle, Jeanette Ampudia, Joon Chang, Andrea Cubitt, David J. King, John Mendlein. Antibodies targeting Resokine, a soluble immune modulator, inhibit tumor growth in syngeneic mouse models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3834.

Identification of a T cell immunomodulatory domain in histidyl-tRNA synthetase

Histidyl-tRNA synthetase (HARS) is the autoantigen target of Jo-1 antibodies, which occur in the major form of anti-synthetase syndrome. These patients are characterized by an autoimmune myositis and interstitial lung disease. Circulating extracellular HARS is detected in healthy individuals, but is reduced or undetectable in Jo-1-positive individuals. Administration of ATYR1940, a recombinant form of HARS, ameliorates lung fibrosis and reduces T cell cytokine production in the bleomycin-induced lung injury model. Similar effects were observed with the N-terminal domain of HARS (the iMod domain) conjugated to IgG Fc, suggesting that this domain confers the immunomodulatory activity of HARS.

To confirm primary immune effects of ATYR1940 and ATYR1923 (iMod.Fc), human T cells were isolated from PBMC from healthy individuals and stimulated with anti-CD3/anti-CD28. Proteins containing the HARS iMod domain reduced in vitro activation of human CD4+ and CD8+ T cells, as evidenced by reduced secretion of IL-2, IFNγ, TNFα, IL-17, IL-13, and granzyme B, as well as decreased upregulation of activation markers such as CD69 and CD40L. ATYR1940 and ATYR1923 also inhibited cytokine release after ex vivo stimulation of human memory T cells in a NSG mouse xenogeneic GVHD model. T cell inhibition by ATYR1940 was dependent on its iMod domain, as demonstrated using an iMod-specific blocking monoclonal antibody. The ATYR1940-induced T cell gene signature reflected a general inhibitory effect on activation as well as on cell cycle protein expression. These results suggest that circulating levels of HARS may act to control the threshold stimulatory signal required to activate T cells. We propose circulating HARS as a soluble immune set-point modulator.

Allelic exclusion of TCR α-chains upon severe restriction of Vα repertoire

Development of thymocytes through the positive selection checkpoint requires the rearrangement and expression of a suitable T cell receptor (TCR) α-chain that can pair with the already-expressed β-chain to make a TCR that is selectable. That is, it must have sufficient affinity for self MHC-peptide to induce the signals required for differentiation, but not too strong so as to induce cell death. Because both alleles of the α-chain continue to rearrange until a positively-selectable heterodimer is formed, thymocytes and T cells can in principle express dual α-chains. However, cell-surface expression of two TCRs is comparatively rare in mature T cells because of post-transcriptional regulatory mechanisms termed “phenotypic allelic exclusion”. We produced mice transgenic for a rearranged β-chain and for two unrearranged α-chains on a genetic background where endogenous α-chains could not be rearranged. Both Vα3.2 and Vα2 containing α-chains were efficiently positively selected, to the extent that a population of dual α-chain-bearing cells was not distinguishable from single α-chain-expressors. Surprisingly, Vα3.2-expressing cells were much more frequent than the Vα2 transgene-expressing cells, even though this Vα3.2-Vβ5 combination can reconstitute a known selectable TCR. In accord with previous work on the Vα3 repertoire, T cells bearing Vα3.2 expressed from the rearranged minilocus were predominantly selected into the CD8⁺ T cell subpopulation. Because of the dominance of Vα3.2 expression over Vα2 expressed from the miniloci, the peripheral T cell population was predominantly CD8⁺ cells.

Coreceptor affinity for MHC defines peptide specificity requirements for TCR interaction with coagonist peptide-MHC

The requirement for the TCR to interact with coagonists, endogenous MHC–peptide complexes which do not themselves activate the T cell, decreases as the strength of the CD8–class I interaction increases.

Recent work has demonstrated that nonstimulatory endogenous peptides can enhance T cell recognition of antigen, but MHCI- and MHCII-restricted systems have generated very different results. MHCII-restricted TCRs need to interact with the nonstimulatory peptide–MHC (pMHC), showing peptide specificity for activation enhancers or coagonists. In contrast, the MHCI-restricted cells studied to date show no such peptide specificity for coagonists, suggesting that CD8 binding to noncognate MHCI is more important. Here we show how this dichotomy can be resolved by varying CD8 and TCR binding to agonist and coagonists coupled with computer simulations, and we identify two distinct mechanisms by which CD8 influences the peptide specificity of coagonism. Mechanism 1 identifies the requirement of CD8 binding to noncognate ligand and suggests a direct relationship between the magnitude of coagonism and CD8 affinity for coagonist pMHCI. Mechanism 2 describes how the affinity of CD8 for agonist pMHCI changes the requirement for specific coagonist peptides. MHCs that bind CD8 strongly were tolerant of all or most peptides as coagonists, but weaker CD8-binding MHCs required stronger TCR binding to coagonist, limiting the potential coagonist peptides. These findings in MHCI systems also explain peptide-specific coagonism in MHCII-restricted cells, as CD4–MHCII interaction is generally weaker than CD8–MHCI.

Initiation of TCR phosphorylation and signal transduction. (P5041)

Recognition of antigen by the T cell receptor (TCR) is the key event for the T cell activation. The earliest molecular events in T cell recognition have not yet been fully described, and the TCR triggering mechanism remains a subject of controversy. By using supported lipid bilayers to present peptide MHC class I complexes to CD8+ cells, we can monitor the molecular events occurring at the immune synapse. The lipid bilayer technology mimics the signaling environment for T cell activation as judged by Ca2+ flux, total phospho-Tyr levels, and IL-2 secretion. Using TIRF/FRET microscopy we have observed an early (> 1 min) interaction between CD3ζ and the coreceptor CD8 that is independent of the MHC-CD8 binding, but requires CD8 association with Lck. Later (< 10 min) CD3ζ-CD8 interactions require CD8-MHC binding. This suggests that, upon antigen recognition, TCR may be initially phosphorylated by Lck not associated with coreceptor, followed by MHC dependent recruitment of CD8-Lck complexes. We have now additional evidences that free Lck is the responsible for the initial TCR phosphorylation. We are currently working on elucidating the proposed different roles of unbound and coreceptor associated Lck during the early stages of antigen recognition.

Trem-like 4-expressing dendritic cells and macrophages exhibit distinct inflammatory chemokine receptors (173.33)

Trem-like 4 (Treml4) is a recently identified type I transmembrane protein, member of the Trem (Triggering receptor expressed on myeloid cells) family. It is mainly expressed on splenic CD8α+ dendritic cells (DCs) and marginal metallophilic and red pulp macrophages. The natural ligand of Treml4 remains to be identified, but a fusion protein containing the extracellular domains of Treml4 is able to bind apoptotic and necrotic cells, suggesting it potentially plays a role in the clearance of dead cells, a process associated with anti-inflammatory and immunosuppressive effects. To further characterize the cell subsets expressing Treml4, we stained splenic DCs and macrophages with various flourochrome conjugated antibodies, including the anti-Treml4 antibody, 16E5. Our data demonstrated that both Treml4+ DCs and macrophages also express CCR6, but neither population expresses CXCR2 nor CCR5. In addition, Treml4+ DCs, but not Treml4+ macrophages, express CXCR3. Conversely, Treml4+ macrophages, but not Treml4+ DCs, express the receptor for the anaphylatoxin C5a. Taken together, these findings suggest that Treml4+ DCs and Treml4+ macrophages might be recruited to inflammation sites depending on the different chemoattractants produced.

Protein kinase C η is required for T cell activation and homeostatic proliferation

Protein kinase C η (PKCη) is abundant in T cells and is recruited to the immunological synapse that is formed between a T cell and an antigen-presenting cell; however, its function in T cells is unknown. We showed that PKCη was required for the activation of mature CD8+ T cells through the T cell receptor. Compared with wild-type T cells, PKCη-/- T cells showed poor proliferation in response to antigen stimulation, a trait shared with T cells deficient in PKCθ, which is the most abundant PKC isoform in T cells and was thought to be the only PKC isoform with a specific role in T cell activation. In contrast, only PKCη-deficient T cells showed defective homeostatic proliferation, which requires self-antigen recognition. PKCη was dispensable for thymocyte development; however, thymocytes from mice doubly deficient in PKCη and PKCθ exhibited poor development, indicating some redundancy between the PKC isoforms. Deficiency in PKCη or PKCθ had opposing effects on the relative numbers of CD4+ and CD8+ T cells. PKCη-/- mice had a higher ratio of CD4+ to CD8+ T cells compared to that of wild-type mice, whereas PKCθ-/- mice had a lower ratio. Mice deficient in both isoforms exhibited normal cell ratios. Together, these data suggest that PKCη shares some redundant roles with PKCθ in T cell biology and also performs nonredundant functions that are required for T cell homeostasis and activation.

A single-chain MHC-class I system to investigate the role of non-stimulatory peptides in T-cell recognition (35.39)

Recent work has demonstrated that endogenous or non-stimulatory peptides can enhance T-cell recognition, a finding that is unexplained by the classical model of CD8, TCR, and MHC interaction. To investigate this phenomenon, we have developed a tetracycline-inducible CHO cell system where cognate single-chain MHC-peptide is expressed at low levels and non-stimulatory single-chain MHC-peptide is constitutively expressed. Mutations in the CD8 binding site of stimulatory or non-stimulatory MHCp enable us to distinguish between different binding models in this system. Preliminary results indicate that CD8 binding to the non-stimulatory MHC is necessary for efficient activation.

Supported by NIH R01 GM065230

Visualizing intermolecular interactions in T cells

The use of appropriate fluorescent proteins has allowed the use of FRET microscopy for investigation of intermolecular interactions in living cells. This method has the advantage of both being dynamic and of working at the subcellular level, so that the time and place where proteins interact can be visualized. We have used FRET microscopy to analyze the interactions between the T cell antigen receptor and the coreceptors CD4 and CD8. This chapter reviews data on how these coreceptors are recruited to the immunological synapse, and how they interact when the T cell is stimulated by different ligands.

Maternal glucose tolerance status influences the risk of macrosomia in male but not in female fetuses

OBJECTIVE

To elucidate whether the risk of macrosomia, large for gestational age (LGA) and small for gestational age (SGA) is influenced by maternal body mass index and glucose tolerance differently in male and female fetuses.

METHODS

A population study was conducted in 16 general hospitals from the Spanish National Health Service that included 9270 consecutive women with singleton pregnancies and without a former diagnosis of diabetes mellitus who delivered 4793 male and 4477 female newborns. Logistic regression analyses were performed to predict the effect of body mass index (BMI) category and glucose tolerance on macrosomia, large for gestational age newborns (LGA) and small for gestational age newborns (SGA) Separate analyses according to foetal sex were carried out for each outcome. The results were adjusted for maternal age, gestational age and pregnancy-induced hypertension.

RESULTS

There were significant differences between males and females in the percentage of infants who had macrosomia, LGA or SGA. Maternal BMI category was positively associated with the risk of macrosomia and LGA in both male and female newborns. In addition, there was a negative association between maternal BMI and SGA that only reached significance in males. In contrast, gestational diabetes was only a predictor of macrosomia exclusively in male fetuses (OR 1.67, 95% CI 1.12 to 2.49)

CONCLUSIONS

There is sexual dimorphism in the risk of abnormal birth weight attributed to maternal glucose tolerance status. A closer surveillance of foetal growth might be warranted in pregnant women with abnormal glucose tolerance carrying a male fetus.

T cell activation enhancement by endogenous pMHC acts for both weak and strong agonists but varies with differentiation state

T cells are extremely sensitive in their ability to find minute amounts of antigenic peptide in the midst of many endogenous peptides presented on an antigen-presenting cell. The role of endogenous peptides in the recognition of foreign peptide and hence in T cell activation has remained controversial for CD8(+) T cell activation. We showed previously that in a CD8(+) T cell hybridoma, nonstimulatory endogenous peptides enhance T cell sensitivity to antigen by increasing the coreceptor function of CD8. However, others were not able to detect such enhancement in naive and activated CD8(+) T cells. Here, we show that endogenous peptides substantially enhance the ability of T cells to detect antigen, an effect measurable by up-regulation of activation or maturation markers and by increased effector function. This enhancement is most pronounced in thymocytes, moderate in naive T cells, and mild in effector T cells. The importance of endogenous peptides is inversely proportional to the agonist activity of the stimulatory peptide presented. Unlike for CD4(+) T cells, the T cell receptor of CD8(+) T cells does not distinguish between endogenous peptides for their ability to enhance antigen recognition.

The role of non-stimulatory MHC-peptides in aiding antigen recognition by CD8+ T cells (87.49)

T cells are able to identify minute quantities of antigenic MHC-peptide (MHCp) complexes among a sea of endogenous MHCp presented on an antigen presenting cell. We previously showed that non-stimulatory endogenous peptides can enhance T cell sensitivity to limiting quantities of antigen. Here we extend these findings to different T cell populations, and show that non-stimulatory peptides are most important in antigen recognition by less differentiated cells, such that their ability to enhance antigen recognition is the best in thymocytes, moderate in naïve T cells, and mild in effector T cells. The increased sensitivity to antigen in the presence of non-stimulatory peptides can be seen in the level of effector functions such as cytokine production and killing of target cells, as well as by phenotypic maturation markers, such as CD25, CD69, CD44, CD5 and HSA. The importance of non-stimulatory peptides is inversely proportional to the agonist activity of the stimulatory peptide presented. Each of the endogenous non-stimulatory peptides tested showed similar ability to aid in antigen recognition. This may indicate that the limiting factor in the ability of non-stimulatory MHCp to aid recognition of a class I-restricted antigen is the CD8-MHC interaction, rather than the strength of the TCR-MHCp interaction, which seems to be paramount in class II-restricted systems.

Supported by NIH GM065230.

Altered Peptide Ligands Induce Delayed CD8-T Cell Receptor Interaction—a Role for CD8 in Distinguishing Antigen Quality

How T cells translate T cell receptor (TCR) recognition of almost identical pMHC ligands into distinct biological responses has remained enigmatic. Although differences in affinity or off rate are important, they offer at best an incomplete explanation. By using Förster resonance energy transfer (FRET), we have visualized the ligand-induced interaction between OT-I TCR and CD8. We found that both recruitment of TCR to the immunological synapse and the TCR-CD8 interaction induced by weak agonists (positive-selecting ligands) was delayed but not necessarily weaker than strong agonists (negative selectors). A delayed and perhaps longer lasting CD8-TCR interaction results in delayed phospho-ERK recruitment to the synapse. The kinetics of the TCR-CD8 interaction can reconcile previously anomalous data, where biological activity did not correlate with TCR-pMHC binding kinetics for certain ligands. Our findings indicate that the T cell translates antigen recognition into T cell responses by differential recruitment of CD8 to the TCR.

Body mass index has a greater impact on pregnancy outcomes than gestational hyperglycaemia

AIMS/HYPOTHESIS

We evaluated diabetes-related pregnancy outcomes in a cohort of Spanish women in relation to their glucose tolerance status, prepregnancy BMI and other predictive variables.

METHODS

The present paper is part of a prospective study to evaluate the impact of American Diabetes Association (2000) criteria in the Spanish population. A total of 9,270 pregnant women were studied and categorised as follows according to prepregnancy BMI quartiles and glucose tolerance status: (1) negative screenees; (2) false-positive screenees; (3) gestational diabetes mellitus (GDM) according to American Diabetes Association criteria only; and (4) GDM according to National Diabetes Data Group criteria (NDDG). We evaluated fetal macrosomia, Caesarean section and seven secondary outcomes as diabetes-related pregnancy outcomes. The population-attributable and population-prevented fractions of predictor variables were calculated after binary logistic regression analysis with multiple predictors.

RESULTS

Both prepregnancy BMI and abnormal glucose tolerance categories were independent predictors of pregnancy outcomes. The upper quartile of BMI accounted for 23% of macrosomia, 9.4% of Caesarean section, 50% of pregnancy-induced hypertension and 17.6% of large-for-gestational-age newborns. In contrast, NDDG GDM accounted for 3.8% of macrosomia, 9.1% of pregnancy-induced hypertension and 3.4% of preterm births.

CONCLUSIONS/INTERPRETATION

In terms of population impact, prepregnancy maternal BMI exhibits a much stronger influence than abnormal blood glucose tolerance on macrosomia, Caesarean section, pregnancy-induced hypertension and large-for-gestational-age newborns.

Nonstimulatory peptides contribute to antigen-induced CD8-T cell receptor interaction at the immunological synapse

It is unclear if the interaction between CD8 and the T cell receptor (TCR)-CD3 complex is constitutive or antigen induced. Here, fluorescence resonance energy transfer microscopy between fluorescent chimeras of CD3zeta and CD8beta showed that this interaction was induced by antigen recognition in the immunological synapse. Nonstimulatory endogenous or exogenous peptides presented simultaneously with antigenic peptides increased the CD8-TCR interaction. This finding indicates that the interaction between the intracellular regions of a TCR-CD3 complex recognizing its cognate peptide-major histocompatibility complex (MHC) antigen, and CD8 (plus the kinase Lck), is enhanced by a noncognate CD8-MHC interaction. Thus, the interaction of CD8 with a nonstimulatory peptide-MHC complex helps mediate T cell recognition of antigen, improving the coreceptor function of CD8.

Potential impact of American Diabetes Association (2000) criteria for diagnosis of gestational diabetes mellitus in Spain

AIMS/HYPOTHESIS

This study was carried out to determine the impact of American Diabetes Association (ADA) 2000 criteria for the diagnosis of gestational diabetes mellitus (GDM) in the Spanish population.

METHODS

Pregnant women were assigned to one of four categories: negative screenees, false-positive screenees, ADA-only-GDM (untreated) and GDM according to National Diabetes Data Group (NDDG) criteria (treated). Fetal macrosomia and Caesarean section were defined as primary outcomes, with seven additional secondary outcomes.

RESULTS

Of 9,270 pregnant women screened for GDM, 819 (8.8%) met NDDG criteria. If the threshold for defining GDM had been lowered to ADA criteria, an additional 2.8% of women would have been defined as having the condition (relative increase of 31.8%). Maternal characteristics of women with ADA-only-GDM were between those of false-positive screenees and women with NDDG-GDM. The risk of diabetes-associated complications was slightly elevated in the individuals who would have been classified as abnormal only after the adoption of ADA criteria. In addition, the ADA-only-GDM contribution to morbidity was lower than that of other variables, especially BMI.

CONCLUSIONS/INTERPRETATION

Use of the ADA criteria to identify GDM would result in a 31.8% increase in prevalence compared with NDDG criteria. However, as the contribution of these additionally diagnosed cases to adverse GDM outcomes is not substantial, a change in diagnostic criteria is not warranted in our setting.

Thymocyte stimulation by anti-TCR-beta, but not by anti-TCR-alpha, leads to induction of developmental transcription program

Anti-T cell receptor (aTCR) antibody (Ab) stimulation of T cells results in TCR down-modulation and T cell activation. Differences in the effect of anti-alpha-chain and beta-chain Ab have been reported on thymocytes. Anti-beta-chain Ab but not anti-alpha-chain reagents cause long-term TCR down-modulation. However, both types of Ab result in TCR cross-linking and activate early steps in signal transduction. In this study, we show that TCR internalization and calcium flux, hallmarks of T cell activation, are similar with aValpha and aVbeta treatment. Therefore, we have compared the gene expression profiles of preselection thymocytes stimulated with these reagents. We find that aValpha treatment does not cause any significant change in gene expression compared with control culture conditions. In contrast, aVbeta stimulation results in numerous changes in gene expression. The alterations of expression of genes known to be expressed in thymocytes are similar to changes caused by positive thymic selection, suggesting that the expression of some of the genes without known roles in thymocyte development and of novel genes whose expression is found to be altered may also be involved in this process.

Hodgkin's disease: internal mammary lymph nodes relapse diagnosed by gallium-67 scintigraphy

This article presents the case of a 62-year-old man with treated Hodgkin's disease who had internal mammary lymph nodes relapse after a complete initial response. These masses were gallium avid. These findings were explained by histologically documented Hodgkin's relapse, the first such case reported in that localization without chest wall involvement. The literature on mediastinal Hodgkin's disease and diagnostic procedures are reviewed.

Hodgkin’s Disease: Internal Mammary Lymph Nodes Relapse Diagnosed by Gallium-67 Scintigraphy

This article presents the case of a 62-year-old man with treated Hodgkin’s disease who had internal mammary lymph nodes relapse after a complete initial response. These masses were gallium avid. These findings were explained by histologically documented Hodgkin’s relapse, the first such case reported in that localization without chest wall involvement. The literature on mediastinal Hodgkin’s disease and diagnostic procedures are reviewed.

Prandial glycaemia after a carbohydrate-rich meal in type I diabetic patients: using the rapid acting insulin analogue [Lys(B28), Pro(B29)] human insulin

The time-action profile of the insulin analogue insulin lispro ([Lys(B28), Pro(B29)] human insulin) with its rapid onset and short duration of action might be more suitable to limit hyperglycaemic excursions after a meal rich in rapidly absorbable carbohydrates in comparison to regular human insulin. A randomized, double-blind study was performed in 10 Type I diabetic patients with good metabolic control (HbA1c 7.0 +/- 0.5%). After a baseline period of 3 h (blood glucose clamped at 6.7 mmol l-1, i.v. insulin infusion of 0.2 mU kg-1 min-1 throughout the study), the patients ate a pizza, drank a cola and had a carbohydrate-rich dessert (total carbohydrate content 140 g). Immediately before the meal 15.4 +/- 3.5 U of either insulin preparation were injected subcutaneously. Blood glucose concentrations were monitored continuously thereafter. Following the injection of insulin lispro the area under the blood glucose curve after the meal was 78% of that of regular insulin (1.76 +/- 0.34 vs 2.26 +/- 0.68 mol l-1 *240 min-1; p < 0.01). Maximal blood glucose excursions were higher and were reached later after regular insulin as compared to insulin lispro (11.9 +/- 2.8 vs 9.9 +/- 1.4 mmol l-1; p < 0.05; 66 +/- 37 vs 41 +/- 7 min; p < 0.05). Maximal individual differences in the blood glucose excursions (regular human insulin minus insulin lispro) were 4.8 +/- 2.2 mmol l-1 (p < 0.0001 against zero) after 110 +/- 37 min. In Type 1 diabetic patients prandial blood glucose excursions after a carbohydrate rich meal were reduced after preprandial injection of insulin lispro in comparison to human regular insulin.

Time-action profiles of the intermediate-acting insulin analogue des(64,65)-human proinsulin

Des(64,65)-proinsulin (DPRO) is one of several endogenous intermediates arising during the conversion of proinsulin to insulin. In pharmaceutic preparations it is a clear solution containing no other proteins. Animal experiments and preliminary human studies indicated that DPRO should have a protracted time-action profile similar to that of NPH-insulin. Accordingly, we compared the time-action profiles of these two preparations, using the euglycaemic glucose clamp-technique in 9 healthy male volunteers. Different doses of DPRO (0.1, 0.15, 0.2 U/kg) or equipotent doses of NPH ( 0.2, 0.3, 0.4 U/kg) were injected subcutaneously into the abdominal wall. The maximal metabolic effect (GIRmax) of DPRO was greater than that of NPH-insulin (p < 0.05). With increasing doses, GIRmax differed significantly for DPRO but not for NPH-insulin. The time to maximal metabolic effect (tmax) was similar for the three doses of either preparation. However, tmax was reached 30 min earlier with DPRO than with NPH-insulin (p < 0.01). the decline to half-maximal after maximal activity was significantly faster with DPRO than with NPH-insulin (p < 0.0001). Subcutaneous injection of DPRO thus produced a time-action profile between that of regular insulin and NPH-insulin.

Four week administration of an ACE inhibitor and a cardioselective beta-blocker in healthy volunteers: no influence on insulin sensitivity

In most, but not all, studies antihypertensive treatment with angiotensin converting enzyme inhibitors (ACE inhibitors) improves insulin sensitivity, whereas beta-blockers decrease insulin sensitivity. However, there was a significant increase in body weight with beta-blockers and changes in the body potassium homeostasis with ACE inhibitors. In order to compare the drug specific metabolic effects of an ACE inhibitor and a cardioselective beta-blocker controlling these factors, we measured insulin sensitivity in a randomized, double-blind cross-over study in 22 healthy volunteers (age 27 +/- 3 years; BMI 22.0 +/- 1.5 kg m-2 (mean +/- SD)) during euglycaemic glucose clamps before and after 4 weeks' administration of 5 mg Lisinopril or 5 mg Bisoprolol. Both drug phases were separated by 4 weeks of no drug administration. During the insulin sensitivity measurements potassium concentrations were clamped at basal levels by means of a variable i.v. potassium infusion. Body weight was monitored at weekly intervals and kept constant within +/- 1 kg of the subjects' baseline weight throughout the entire study period. Insulin sensitivity did not change significantly during either drug administration period. The insulin sensitivity index of the 22 volunteers after administration of the ACE inhibitor was 7.9 +/- 2.4 mL min-1 m2 microU-1 mL-1 (basal index 8.3 +/- 1.9 mL min-1 m2 microU-1 mL-1, and 7.5 +/- 2.1 mL min-1 m2 microU-1 mL-1 after administration of the beta-blocker (basal index 8.2 +/- 1.9 mL min-1 m2 microU-1 mL-1; NS).(ABSTRACT TRUNCATED AT 250 WORDS)

[Thyroid ophthalmopathy: clinical and tomographic study]

BACKGROUND

To evaluate exophthalmos by Hertel exophthalmometer (HE) compared to computed tomography (CT), and extraocular muscle width on CT and its relation with the clinical course in patients with thyroidal ophthalmopathy.

METHODS

On reviewed 118 orbits from 59 patients (50 women, mean age 40.6 y., range 12-84) who suffered a thyroidal ophthalmopathy (Graves' disease, n = 57; Hashimoto's thyroiditis, n = 2). Muscle width was evaluated using coronal and mid-axial scans in all cases. Medial rectus (MR) width was analysed by Hallin and Feldon technique.

RESULTS

Exophthalmos by HE was 22.5 +/- 2.5 and 23.2 +/- 3.2 mm (right-RE/left eye-LE), and CT 20.8 +/- 3.2 and 20.9 +/- 2.9 mm (p < 0.00001, r = 0.72 and 0.65, respectively). MR width on mid-axial scan was 4.1 +/- 1.6 and 4.2 +/- 1.5 mm (RE/LE). On coronal scans, MR was the muscle more often enlarged followed by superior, inferior and lateral rectus.

CONCLUSIONS

Exophthalmos measured by HE was greater than by CT-measured one, but with a good correlation. Muscle were not equally affected, being MR the most frequently enlarged. MR-width was not related to duration and severity of disease.

[Bartter's syndrome: variability and clinical course]

The clinical, hydroelectrolytical and hormonal features, as well as the treatment of 3 patients with Bartter's syndrome are analyzed. The patients consulted due to severe hypokalaemia with little clinical expression (paresthesiae, carpopedal spasms, polyuria, polydipsia and/or weakness). All had normal blood pressure, hypokalemia, hyperreninaemic hyperaldosteronism and a decrease in the fractional distal chloride reabsorption; hyperuricaemia was observed in two cases and hypomagnesemia in one. Treatment with oral potassium supplements and indomethacin managed to raise serum K to around the lower limit of the normal range. However, the tubular defect and hyperreninaemic hyperaldosteronism persisted. The urinary excretion of prostaglandin E2 was normal in both the patients in whom it was measured. Given the minimal clinical expression of hypokalemia despite the difficulty in correcting it, it is probable that this syndrome often remains unrecognized.