Preclinical Evidence for the Glucocorticoid-Sparing Potential of a Dual Toll-Like Receptor 7/8 Inhibitor in Autoimmune Diseases

Toll-like receptor 7 (TLR7) and TLR8 are single-stranded RNA-sensing endosomal pattern recognition receptors that evolved to defend against viral infections. However, aberrant TLR7/8 activation by endogenous ligands has been implicated in the pathogenesis of autoimmune diseases including systemic lupus erythematosus. TLR activation and type I interferon (IFN) were shown recently to impart resistance to glucocorticoids (GC), which are part of the standard of care for multiple autoimmune diseases. While GCs are effective, a plethora of undesirable effects limit their use. New treatment approaches that allow for the use of lower and safer doses of GCs would be highly beneficial. Herein, we report that a dual TLR7/8 inhibitor (TLR7/8i) increases the effectiveness of GCs in inflammatory settings. Human peripheral blood mononuclear cell studies revealed increased GC sensitivity in the presence of TLR7/8i for reducing inflammatory cytokine production, a synergistic effect that was most pronounced in myeloid cells, particularly monocytes. Gene expression analysis by NanoString and single-cell RNA sequencing revealed that myeloid cells were substantially impacted by combining low-dose TLR7/8i and GC, as evidenced by the effects on nuclear factor-kappa B-regulated cytokines and GC-response genes, although IFNs were affected to a smaller degree. Low dose of TLR7/8i plus GC was more efficacious then either agent alone in the MRL/lpr mouse model of lupus, with improved proteinuria and survival. Overall, our findings indicate a GC-sparing potential for TLR7/8i compounds, suggesting TLR7/8i may offer a new strategy for the treatment of autoimmune diseases. SIGNIFICANCE STATEMENT: Some features of autoimmune diseases may be resistant to glucocorticoids, mediated at least in part by toll-like receptor (TLR) activation, necessitating higher doses that are associated with considerable toxicities. We demonstrate that TLR7/8 inhibition and glucocorticoids work synergistically to reduce inflammation in a cell-type specific manner and suppress disease in a mouse model of lupus. TLR7/8 inhibition is a promising strategy for the treatment of autoimmune diseases and has glucocorticoid-sparing potential.

Analysis of transcriptomic features reveals molecular endotypes of SLE with clinical implications

BACKGROUND

Systemic lupus erythematosus (SLE) is known to be clinically heterogeneous. Previous efforts to characterize subsets of SLE patients based on gene expression analysis have not been reproduced because of small sample sizes or technical problems. The aim of this study was to develop a robust patient stratification system using gene expression profiling to characterize individual lupus patients.

METHODS

We employed gene set variation analysis (GSVA) of informative gene modules to identify molecular endotypes of SLE patients, machine learning (ML) to classify individual patients into molecular subsets, and logistic regression to develop a composite metric estimating the scope of immunologic perturbations. SHapley Additive ExPlanations (SHAP) revealed the impact of specific features on patient sub-setting.

RESULTS

Using five datasets comprising 2183 patients, eight SLE endotypes were identified. Expanded analysis of 3166 samples in 17 datasets revealed that each endotype had unique gene enrichment patterns, but not all endotypes were observed in all datasets. ML algorithms trained on 2183 patients and tested on 983 patients not used to develop the model demonstrated effective classification into one of eight endotypes. SHAP indicated a unique array of features influential in sorting individual samples into each of the endotypes. A composite molecular score was calculated for each patient and significantly correlated with standard laboratory measures. Significant differences in clinical characteristics were associated with different endotypes, with those with the least perturbed transcriptional profile manifesting lower disease severity. The more abnormal endotypes were significantly more likely to experience a severe flare over the subsequent 52 weeks while on standard-of-care medication and specific endotypes were more likely to be clinical responders to the investigational product tested in one clinical trial analyzed (tabalumab).

CONCLUSIONS

Transcriptomic profiling and ML reproducibly separated lupus patients into molecular endotypes with significant differences in clinical features, outcomes, and responsiveness to therapy. Our classification approach using a composite scoring system based on underlying molecular abnormalities has both staging and prognostic relevance.

Nucleic Acid-Sensing and Interferon-Inducible Pathways Show Differential Methylation in MZ Twins Discordant for Lupus and Overexpression in Independent Lupus Samples: Implications for Pathogenic Mechanism and Drug Targeting

Systemic lupus erythematosus (SLE) is a chronic, multisystem, autoimmune inflammatory disease with genomic and non-genomic contributions to risk. We hypothesize that epigenetic factors are a significant contributor to SLE risk and may be informative for identifying pathogenic mechanisms and therapeutic targets. To test this hypothesis while controlling for genetic background, we performed an epigenome-wide analysis of DNA methylation in genomic DNA from whole blood in three pairs of female monozygotic (MZ) twins of European ancestry, discordant for SLE. Results were replicated on the same array in four cell types from a set of four Danish female MZ twin pairs discordant for SLE. Genes implicated by the epigenetic analyses were then evaluated in 10 independent SLE gene expression datasets from the Gene Expression Omnibus (GEO). There were 59 differentially methylated loci between unaffected and affected MZ twins in whole blood, including 11 novel loci. All but two of these loci were hypomethylated in the SLE twins relative to the unaffected twins. The genes harboring these hypomethylated loci exhibited increased expression in multiple independent datasets of SLE patients. This pattern was largely consistent regardless of disease activity, cell type, or renal tissue type. The genes proximal to CpGs exhibiting differential methylation (DM) in the SLE-discordant MZ twins and exhibiting differential expression (DE) in independent SLE GEO cohorts (DM-DE genes) clustered into two pathways: the nucleic acid-sensing pathway and the type I interferon pathway. The DM-DE genes were also informatically queried for potential gene–drug interactions, yielding a list of 41 drugs including a known SLE therapy. The DM-DE genes delineate two important biologic pathways that are not only reflective of the heterogeneity of SLE but may also correlate with distinct IFN responses that depend on the source, type, and location of nucleic acid molecules and the activated receptors in individual patients. Cell- and tissue-specific analyses will be critical to the understanding of genetic factors dysregulating the nucleic acid-sensing and IFN pathways and whether these factors could be appropriate targets for therapeutic intervention.

Altered expression of genes controlling metabolism characterizes the tissue response to immune injury in lupus

To compare lupus pathogenesis in disparate tissues, we analyzed gene expression profiles of human discoid lupus erythematosus (DLE) and lupus nephritis (LN). We found common increases in myeloid cell-defining gene sets and decreases in genes controlling glucose and lipid metabolism in lupus-affected skin and kidney. Regression models in DLE indicated increased glycolysis was correlated with keratinocyte, endothelial, and inflammatory cell transcripts, and decreased tricarboxylic (TCA) cycle genes were correlated with the keratinocyte signature. In LN, regression models demonstrated decreased glycolysis and TCA cycle genes were correlated with increased endothelial or decreased kidney cell transcripts, respectively. Less severe glomerular LN exhibited similar alterations in metabolism and tissue cell transcripts before monocyte/myeloid cell infiltration in some patients. Additionally, changes to mitochondrial and peroxisomal transcripts were associated with specific cells rather than global signal changes. Examination of murine LN gene expression demonstrated metabolic changes were not driven by acute exposure to type I interferon and could be restored after immunosuppression. Finally, expression of HAVCR1, a tubule damage marker, was negatively correlated with the TCA cycle signature in LN models. These results indicate that altered metabolic dysfunction is a common, reversible change in lupus-affected tissues and appears to reflect damage downstream of immunologic processes.

Transcriptome and IgH Repertoire Analyses Show That CD11chi B Cells Are a Distinct Population With Similarity to B Cells Arising in Autoimmunity and Infection

A distinct B cell population marked by elevated CD11c expression is found in patients with systemic lupus erythematosus (SLE). Cells with a similar phenotype have been described during chronic infection, but variable gating strategies and nomenclature have led to uncertainty of their relationship to each other. We isolated CD11c^hi cells from peripheral blood and characterized them using transcriptome and IgH repertoire analyses. Gene expression data revealed the CD11c^hi IgD⁺ and IgD^- subsets were highly similar to each other, but distinct from naive, memory, and plasma cell subsets. Although CD11c^hi B cells were enriched in some germinal center (GC) transcripts and expressed numerous negative regulators of B cell receptor (BCR) activation, they were distinct from GC B cells. Gene expression patterns from SLE CD11c^hi B cells were shared with other human diseases, but not with mouse age-associated B cells. IgH V-gene sequencing analysis showed IgD⁺ and IgD^- CD11c^hi B cells had somatic hypermutation and were clonally related to each other and to conventional memory and plasma cells. However, the IgH repertoires expressed by the different subsets suggested that defects in negative selection during GC transit could contribute to autoimmunity. The results portray a pervasive B cell population that accumulates during autoimmunity and chronic infection and is refractory to BCR signaling.

Analysis of Trans-Ancestral SLE Risk Loci Identifies Unique Biologic Networks and Drug Targets in African and European Ancestries

Systemic lupus erythematosus (SLE) is a multi-organ autoimmune disorder with a prominent genetic component. Individuals of African ancestry (AA) experience the disease more severely and with an increased co-morbidity burden compared to European ancestry (EA) populations. We hypothesize that the disparities in disease prevalence, activity, and response to standard medications between AA and EA populations is partially conferred by genomic influences on biological pathways. To address this, we applied a comprehensive approach to identify all genes predicted from SNP-associated risk loci detected with the Immunochip. By combining genes predicted via eQTL analysis, as well as those predicted from base-pair changes in intergenic enhancer sites, coding-region variants, and SNP-gene proximity, we were able to identify 1,731 potential ancestry-specific and trans-ancestry genetic drivers of SLE. Gene associations were linked to upstream and downstream regulators using connectivity mapping, and predicted biological pathways were mined for candidate drug targets. Examination of trans-ancestral pathways reflect the well-defined role for interferons in SLE and revealed pathways associated with tissue repair and remodeling. EA-dominant genetic drivers were more often associated with innate immune and myeloid cell function pathways, whereas AA-dominant pathways mirror clinical findings in AA subjects, suggesting disease progression is driven by aberrant B cell activity accompanied by ER stress and metabolic dysfunction. Finally, potential ancestry-specific and non-specific drug candidates were identified. The integration of all SLE SNP-predicted genes into functional pathways revealed critical molecular pathways representative of each population, underscoring the influence of ancestry on disease mechanism and also providing key insight for therapeutic selection.

Patient ancestry significantly contributes to molecular heterogeneity of systemic lupus erythematosus

Gene expression signatures can stratify patients with heterogeneous diseases, such as systemic lupus erythematosus (SLE), yet understanding the contributions of ancestral background to this heterogeneity is not well understood. We hypothesized that ancestry would significantly influence gene expression signatures and measured 34 gene modules in 1566 SLE patients of African ancestry (AA), European ancestry (EA), or Native American ancestry (NAA). Healthy subject ancestry-specific gene expression provided the transcriptomic background upon which the SLE patient signatures were built. Although standard therapy affected every gene signature and significantly increased myeloid cell signatures, logistic regression analysis determined that ancestral background significantly changed 23 of 34 gene signatures. Additionally, the strongest association to gene expression changes was found with autoantibodies, and this also had etiology in ancestry: the AA predisposition to have both RNP and dsDNA autoantibodies compared with EA predisposition to have only anti-dsDNA. A machine learning approach was used to determine a gene signature characteristic to distinguish AA SLE and was most influenced by genes characteristic of the perturbed B cell axis in AA SLE patients.

Transcriptional profiling of lupus patients and healthy controls reveals ancestry-related differences and transcriptional heterogeneity among lupus patients.

Selective Histone Deacetylase 6 Inhibition Normalizes B Cell Activation and Germinal Center Formation in a Model of Systemic Lupus Erythematosus

Autoantibody production by plasma cells (PCs) plays a pivotal role in the pathogenesis of systemic lupus erythematosus (SLE). The molecular pathways by which B cells become pathogenic PC secreting autoantibodies in SLE are incompletely characterized. Histone deactylase 6 (HDAC6) is a unique cytoplasmic HDAC that modifies the interaction of a number of tubulin- associated proteins; inhibition of HDAC6 has been shown to be beneficial in murine models of SLE, but the downstream pathways accounting for the therapeutic benefit have not been clearly delineated. In the current study, we sought to determine whether selective HDAC6 inhibition would abrogate abnormal B cell activation in SLE. We treated NZB/W lupus mice with the selective HDAC6 inhibitor, ACY-738, for 4 weeks beginning at 20 weeks-of age. After only 4 weeks of treatment, manifestation of lupus nephritis (LN) were greatly reduced in these animals. We then used RNAseq to determine the genomic signatures of splenocytes from treated and untreated mice and applied computational cellular and pathway analysis to reveal multiple signaling events associated with B cell activation and differentiation in SLE that were modulated by HDAC6 inhibition. PC development was abrogated and germinal center (GC) formation was greatly reduced. When the HDAC6 inhibitor-treated lupus mouse gene signatures were compared to human lupus patient gene signatures, the results showed numerous immune, and inflammatory pathways increased in active human lupus were significantly decreased in the HDAC6 inhibitor treated animals. Pathway analysis suggested alterations in cellular metabolism might contribute to the normalization of lupus mouse spleen genomic signatures, and this was confirmed by direct measurement of the impact of the HDAC6 inhibitor on metabolic activities of murine spleen cells. Taken together, these studies show HDAC6 inhibition decreases B cell activation signaling pathways and reduces PC differentiation in SLE and suggest that a critical event might be modulation of cellular metabolism.

Identification and Characterization of Post-activated B Cells in Systemic Autoimmune Diseases

Autoimmune diseases (AID) such as systemic lupus erythematosus (SLE), primary Sjögren's syndrome (pSS), and rheumatoid arthritis (RA) are chronic inflammatory diseases in which abnormalities of B cell function play a central role. Although it is widely accepted that autoimmune B cells are hyperactive in vivo, a full understanding of their functional status in AID has not been delineated. Here, we present a detailed analysis of the functional capabilities of AID B cells and dissect the mechanisms underlying altered B cell function. Upon BCR activation, decreased spleen tyrosine kinase (Syk) and Bruton's tyrosine kinase (Btk) phosphorylation was noted in AID memory B cells combined with constitutive co-localization of CD22 and protein tyrosine phosphatase (PTP) non-receptor type 6 (SHP-1) along with hyporesponsiveness to TLR9 signaling, a Syk-dependent response. Similar BCR hyporesponsiveness was also noted specifically in SLE CD27⁻ B cells together with increased PTP activities and increased transcripts for PTPN2, PTPN11, PTPN22, PTPRC, and PTPRO in SLE B cells. Additional studies revealed that repetitive BCR stimulation of normal B cells can induce BCR hyporesponsiveness and that tissue-resident memory B cells from AID patients also exhibited decreased responsiveness immediately ex vivo, suggesting that the hyporesponsive status can be acquired by repeated exposure to autoantigen(s) in vivo. Functional studies to overcome B cell hyporesponsiveness revealed that CD40 co-stimulation increased BCR signaling, induced proliferation, and downregulated PTP expression (PTPN2, PTPN22, and receptor-type PTPs). The data support the conclusion that hyporesponsiveness of AID and especially SLE B cells results from chronic in vivo stimulation through the BCR without T cell help mediated by CD40–CD154 interaction and is manifested by decreased phosphorylation of BCR-related proximal signaling molecules and increased PTPs. The hyporesponsiveness of AID B cells is similar to a form of functional anergy.

Machine learning approaches to predict lupus disease activity from gene expression data

The integration of gene expression data to predict systemic lupus erythematosus (SLE) disease activity is a significant challenge because of the high degree of heterogeneity among patients and study cohorts, especially those collected on different microarray platforms. Here we deployed machine learning approaches to integrate gene expression data from three SLE data sets and used it to classify patients as having active or inactive disease as characterized by standard clinical composite outcome measures. Both raw whole blood gene expression data and informative gene modules generated by Weighted Gene Co-expression Network Analysis from purified leukocyte populations were employed with various classification algorithms. Classifiers were evaluated by 10-fold cross-validation across three combined data sets or by training and testing in independent data sets, the latter of which amplified the effects of technical variation. A random forest classifier achieved a peak classification accuracy of 83 percent under 10-fold cross-validation, but its performance could be severely affected by technical variation among data sets. The use of gene modules rather than raw gene expression was more robust, achieving classification accuracies of approximately 70 percent regardless of how the training and testing sets were formed. Fine-tuning the algorithms and parameter sets may generate sufficient accuracy to be informative as a standalone estimate of disease activity.

Genomic Identification of Low-Density Granulocytes and Analysis of Their Role in the Pathogenesis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the presence of low-density granulocytes (LDGs) with a heightened capacity for spontaneous NETosis, but the contribution of LDGs to SLE pathogenesis remains unclear. To characterize LDGs in human SLE, gene expression profiles derived from isolated LDGs were characterized by weighted gene coexpression network analysis, and a 92-gene module was identified. The LDG gene signature was enriched in genes related to neutrophil degranulation and cell cycle regulation. This signature was assessed in gene expression datasets from two large-scale SLE clinical trials to study associations between LDG enrichment, SLE manifestations, and treatment regimens. LDG enrichment in the blood was associated with corticosteroid treatment as well as anti-dsDNA, low serum complement, renal manifestations, and vasculitis, but the latter two of these associations were dependent on concomitant corticosteroid treatment. In addition, LDG enrichment was associated with enrichment of gene signatures induced by type I IFN and TNF irrespective of corticosteroid treatment. Notably, LDG enrichment was not found in numerous tissues affected by SLE. Comparison with relevant reference datasets indicated that LDG enrichment is likely reflective of increased granulopoiesis in the bone marrow and not peripheral neutrophil activation. The results have uncovered important determinants of the appearance of LDGs in SLE and have emphasized the likely role of LDGs in specific aspects of lupus pathogenesis.

Gene expression analysis delineates the potential roles of multiple interferons in systemic lupus erythematosus

A role for interferon (IFN) in systemic lupus erythematosus (SLE) pathogenesis is inferred from the prominent IFN gene signature (IGS), but the major IFN species and its relationship to disease activity are unknown. A bioinformatic approach employing individual IFN species gene signatures to interrogate SLE microarray datasets demonstrates a putative role for numerous IFN species, with prominent expression of IFNB1 and IFNW signatures. In contrast with other SLE-affected organs, the IGS is less prominent in lupus nephritis. SLE patients with active and inactive disease have readily detectable IGS and the IGS changes synchronously with a monocyte signature but not disease activity, and is significantly related to monocyte transcripts. Monocyte over-expression of three times as many IGS transcripts as T and B cells and IGS retention in monocytes, but not T and B cells from inactive SLE patients contribute to the lack of correlation between the IGS and SLE disease activity.

Identification of alterations in macrophage activation associated with disease activity in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by abnormalities in B cell and T cell function, but the role of disturbances in the activation status of macrophages (Mϕ) has not been well described in human patients. To address this, gene expression profiles from isolated lymphoid and myeloid populations were analyzed to identify differentially expressed (DE) genes between healthy controls and patients with either inactive or active SLE. While hundreds of DE genes were identified in B and T cells of active SLE patients, there were no DE genes found in B or T cells from patients with inactive SLE compared to healthy controls. In contrast, large numbers of DE genes were found in myeloid cells (MC) from both active and inactive SLE patients. Among the DE genes were several known to play roles in Mϕ activation and polarization, including the M1 genes STAT1 and SOCS3 and the M2 genes STAT3, STAT6, and CD163. M1-associated genes were far more frequent in data sets from active versus inactive SLE patients. To characterize the relationship between Mϕ activation and disease activity in greater detail, weighted gene co-expression network analysis (WGCNA) was used to identify modules of genes associated with clinical activity in SLE patients. Among these were disease activity-correlated modules containing activation signatures of predominantly M1-associated genes. No disease activity-correlated modules were enriched in M2-associated genes. Pathway and upstream regulator analysis of DE genes from both active and inactive SLE MC were cross-referenced with high-scoring hits from the drug discovery Library of Integrated Network-based Cellular Signatures (LINCS) to identify new strategies to treat both stages of SLE. A machine learning approach employing MC gene modules and a generalized linear model was able to predict the disease activity status in unrelated gene expression data sets. In summary, altered MC gene expression is characteristic of both active and inactive SLE. However, disease activity is associated with an alteration in the activation of MC, with a bias toward the M1 proinflammatory phenotype. These data suggest that while hyperactivity of B cells and T cells is associated with active SLE, MC potentially direct flare-ups and remission by altering their activation status toward the M1 state.

Novel targeted therapies for African-American and European-American SLE patients identified from E-Genes elucidated by transancestral SNP mapping

SLE is more prevalent and severe in African-American (AA) compared with European-American (EA) populations but standard-of-care drugs vary in effectiveness between these groups. To gain insight, drugs specific for E-gene containing pathways were investigated using the Immunochip transancestral SNP mapping and a curated database of SLE DE genes. SNPs proxy to SLE-associated SNPs were compared with known eQTLs contained in the GTEx database. Since GTEx contains genotype data as well as gene expression data from cell lines, tissues and whole blood from healthy individuals, an independent query of GTEx for expression of RNAs abnormally expressed in SLE patients compared to healthy individuals was carried out. The results of the eQTL and DE gene queries of GTEx were combined and eQTLs and associated E-Genes were pooled by ancestry. Drugs targeting E-genes/pathways shared by EA and AA include ibrutinib, ruxolitinib and ustekinumab. Predicted EA-specific drugs include antimalarials and cyclosporine, as well as drugs-in-development targeting CD40, CXCR1 and CXCR2; AA-specific drugs include retinoids and HDAC inhibitors. This analysis of the distinct genetic profiles of EA and AA populations indicates that unique sets of drugs may be particularly effective at treating lupus in each ancestral group.

Drug repositioning in SLE: crowd-sourcing, literature-mining and Big Data analysis

Lupus patients are in need of modern drugs to treat specific manifestations of their disease effectively and safely. In the past half century, only one new treatment has been approved by the US Food and Drug Administration (FDA) for systemic lupus erythematosus (SLE). In 2014–2015, the FDA approved 71 new drugs, only one of which targeted a rheumatic disease and none of which was approved for use in SLE. Repositioning/repurposing drugs approved for other diseases using multiple approaches is one possible means to find new treatment options for lupus patients. “Big Data” analysis approaches this challenge from an unbiased standpoint whereas literature mining and crowd sourcing for candidates assessed by the CoLTs (Combined Lupus Treatment Scoring) system provide a hypothesis-based approach to rank potential therapeutic candidates for possible clinical application. Both approaches mitigate risk since the candidates assessed have largely been extensively tested in clinical trials for other indications. The usefulness of a multi-pronged approach to drug repositioning in lupus is highlighted by orthogonal confirmation of hypothesis-based drug repositioning predictions by “Big Data” analysis of differentially expressed genes from lupus patient samples. The goal is to identify novel therapies that have the potential to affect disease processes specifically. Involvement of SLE patients and the scientists that study this disease in thinking about new drugs that may be effective in lupus though crowd-sourcing sites such as LRxL-STAT ( www.linkedin.com/in/lrxlstat ) is important in stimulating the momentum needed to test these novel drug targets for efficacy in lupus rapidly in small, proof-of-concept trials conducted by LuCIN, the Lupus Clinical Investigators Network ( www.linkedin.com/in/lucinstat ).

Role of Specific CD8+ T Cells in the Severity of a Fulminant Zoonotic Viral Hemorrhagic Fever, Hantavirus Pulmonary Syndrome

We report on the role of specific CD8(+) T cells in the pathogenesis of a highly lethal human viral disease, hantavirus pulmonary syndrome (HPS). HPS is a zoonotic disease caused by transmission of Sin Nombre virus (SNV) from chronically infected deer mice. In humans, this fulminant infection is characterized by lung capillary leakage, respiratory failure, and cardiogenic shock. Individuals with HLA-B*3501 have an increased risk of developing severe HPS, suggesting that CD8(+) T cell responses to SNV contribute to pathogenesis. We identified three CD8(+) T cell epitopes in SNV presented by HLA-B*3501 and quantitated circulating SNV-specific CD8(+) T cells in 11 acute HPS patients using HLA/peptide tetramers. We found significantly higher frequencies of SNV-specific T cells in patients with severe HPS requiring mechanical ventilation (up to 44.2% of CD8(+) T cells) than in moderately ill HPS patients hospitalized but not requiring mechanical ventilation (up to 9.8% of CD8(+) T cells). These results imply that virus-specific CD8(+) T cells contribute to HPS disease outcome. Intense CD8(+) T cell responses to SNV may be induced by the encounter of the unnatural human host to this zoonotic virus without coevolution. This may also be the immunopathologic basis of other life-threatening human virus infections.

Phenotypic and functional heterogeneity of EBV epitope-specific CD8+ T cells

High frequencies of EBV-specific CD8(+) T cells have been detected during acute EBV infection, yet persistent infection inevitably results. To address this issue, we characterized the phenotype and function of epitope-specific CD8(+) T cell populations from presentation with acute through latent infection. Considerable phenotypic and functional heterogeneity within, as well as between, two different epitope-specific populations was observed over time following acute infection. B7 EBV-encoded nuclear Ag (EBNA)-3A-specific CD8(+) T cells expressed only CD45RO from acute through latent EBV infection. A2 BMLF-1-specific CD8(+) T cells expressed CD45RO during acute infection and either CD45RA or CD45RO during latent EBV infection. This difference in CD45 isoform expression between the two epitope-specific populations did not translate into differences in perforin content, the ability to produce IFN-gamma, or the ability to proliferate in response to Ag in vitro. In individuals with latent EBV infection, the frequencies of A2 BMLF-1- or B7 EBNA-3A-specific CD8(+) T cells that expressed CD45RA, CD45RO, CD62 ligand, CCR7, and perforin were stable over time. However, the expression of CD62 ligand and CCR7 was significantly higher among EBNA-3A-specific CD8(+) T cells than among BMLF-1-specific CD8(+) T cells. Further work is necessary to understand how phenotypic and functional differences between EBV epitope-specific CD8(+) T cells are related to the biology of the virus and to the equilibrium between the virus and the host during persistent infection.

Infrequent detection of HIV-1-specific, but not cytomegalovirus-specific, CD8(+) T cell responses in young HIV-1-infected infants

Early potent combination antiretroviral therapies (ART) for HIV-1 infection can preserve or restore immune function, but control of viral replication early in infection may interfere with the development of HIV-1-specific immune responses. Using an IFN-gamma ELISPOT assay, we evaluated the breadth and intensity of HIV-1-specific CD8(+) T cell responses in 17 vertically infected infants who began ART at 1-23 mo of age. CMV-specific responses were also characterized in three infants coinfected with HIV-1 and CMV. Before ART, HIV-1-specific CD8(+) T cell responses were detected in two of 13 (15%) infants <6 mo of age. HIV-1-specific CD8(+) T cells became undetectable in these two infants after the control of viral replication. Intermittent HIV-1-specific responses were noted in six infants who did not experience durable control of viral replication. In contrast, HIV-1-specific responses were detected before ART in four of four infants >6 mo of age and became persistently undetectable in only one child. CMV-specific CD8(+) T cell responses were persistently detected in all HIV-1 and CMV coinfected infants. In conclusion, HIV-1-specific CD8(+) T cell responses were less commonly detected before therapy in young infants than in older infants. Suppression of viral replication appeared to interfere with the development and maintenance of HIV-1-specific CD8(+) T cell responses. The detection of CMV-specific responses in HIV-1 and CMV coinfected infants suggests a selective defect in the generation or maintenance of HIV-1-specific CD8(+) T cell responses. Therapeutic HIV-1 vaccine strategies in young infants may prolong the clinical benefit of ART by expanding the HIV-1-specific CD8(+) T cell pool.

Differential evolution and stability of epitope-specific CD8(+) T cell responses in EBV infection

Murine models of lymphocytic choriomeningitis virus infection suggest that the memory CD8(+) T cell repertoire is reflective of the CD8(+) T cell repertoire generated during acute infection. Less is known regarding the evolution of CD8(+) T cell repertoires during human viral infections. We therefore examined epitope-specific CD8(+) T cell responses in a large cohort of individuals with acute through latent Epstein-Barr virus infection. Using 16 of 20 published EBV epitopes restricted by HLA-A2, HLA-A3 or HLA-B7, we showed that lytic cycle-specific CD8(+) T cell responses predominated during acute EBV infection. However, whereas HLA-A2(+)-restricted BMLF-1-specific CD8(+) T cell responses were maintained through latency, HLA-A2(+)- and HLA-B7(+)-restricted BZLF-1, as well as HLA-A3(+)-restricted BRLF-1 CD8(+) T cell responses, were generated but not readily maintained. Analyses of CD8(+) T cell responses to EBV latent cycle Ags showed delayed detection and lower frequencies of latent epitope-specific CD8(+) T cell responses during acute EBV infection, with maintenance of these responses 1 yr post-EBV infection. Early BMLF-1 and EBNA-3A epitope-specific CD8(+) T cell frequencies did not correlate with their frequencies at 1 yr postinfection. Interestingly, populations of EBV-specific CD8(+) T cells were stable during 20 mo in our long term EBV-seropositive populations, suggesting homeostasis between virus and the host immune system. This study demonstrates that CD8(+) T cell repertoires generated during persistent viral infections are not simply reflective of the initial pool of CD8(+) T cells and provides evidence that the generation of CD8(+) T cell responses to a persistent infection is a dynamic process.

Normal hematopoiesis and inflammatory responses despite discrete signaling defects in Galpha15 knockout mice

Galpha15 activates phospholipase Cbeta in response to the greatest variety of agonist-stimulated heptahelical receptors among the four Gq class G-protein alpha subunits expressed in mammals. Galpha15 is primarily expressed in hematopoietic cells in fetal and adult mice. We disrupted the Galpha15 gene by homologous recombination in embryonic stem cells to identify its biological functions. Surprisingly, hematopoiesis was normal in Galpha15(-/-) mice, Galpha15(-/-) Galphaq(-/-) double-knockout mice (which express only Galpha11 in most hematopoietic cells), and Galpha11(-/-) mice, suggesting functional redundancy in Gq class signaling. Inflammatory challenges, including thioglycolate-induced peritonitis and infection with Trichinella spiralis, stimulated similar responses in Galpha15(-/-) adults and wild-type siblings. Agonist-stimulated Ca(2+) release from intracellular stores was assayed to identify signaling defects in primary cultures of thioglycolate-elicited macrophages isolated from Galpha15(-/-) mice. C5a-stimulated phosphoinositide accumulation and Ca(2+) release was significantly reduced in Galpha15(-/-) macrophages. Ca(2+) signaling was abolished only in mutant cells pretreated with pertussis toxin, suggesting that the C5a receptor couples to both Galpha15 and Galphai in vivo. Signaling evoked by other receptors coupled by Gq class alpha subunits appeared normal in Galpha15(-/-) macrophages. Despite discrete signaling defects, compensation by coexpressed Gq and/or Gi class alpha subunits may suppress abnormalities in Galpha15-deficient mice.

Selective requirements for leukocyte adhesion molecules in models of acute and chronic cutaneous inflammation: participation of E- and P- but not L-selectin

Adhesion molecules borne by both endothelial cells and circulating leukocytes are in large measure responsible for guiding the process of extravasation. The selectin family has been primarily associated with the early stages of adhesion involving initial contact and rolling. A significant body of evidence has accumulated indicating a fundamental role for the endothelial members of this family, E- and P-selectin, in a variety of inflammatory states and models. Although originally identified as the lymph node-specific lymphocyte homing receptor, L-selectin has also been suggested to play an important role in leukocyte recruitment to sites of inflammation. We have recently demonstrated, using L-selectin-deficient mice, that defects in contact hypersensitivity (CHS) responses are in essence due to the inability of T cells to home to and be sensitized within peripheral lymph nodes, whereas nonspecific effector cells are fully capable of entry into sites of cutaneous inflammation (Catalina et al, J Exp Med 184:2341, 1996). In the present study, we perform an analysis of adhesion molecule usage in two models of skin inflammation and show in both L-selectin-deficient as well as wild-type mice that a combination of P- and E-selectin is crucial for the development of both acute (croton oil) and chronic (contact hypersensitivity) inflammation at sites of the skin, whereas L-selectin does not appear to play a significant role. Moreover, alpha4 integrins are shown to be integral to a CHS but not an acute irritant response, whereas CD44 does not significantly contribute to either. These results provide a systematic examination in one study of major adhesion molecules that are critical in acute and chronic skin inflammation. They reinforce the essential role of the collaboration of E- and P-selectin in both specific and nonspecific skin inflammatory responses and the importance of alpha4 in the specific response only. In addition, they substantiate only a limited role, if any, for L-selectin in these cutaneous effector mechanisms and demonstrate the essential equivalence in this analysis of L-selectin-deficient mice compared with normal mice treated with blocking antibodies.

Circulating activated platelets reconstitute lymphocyte homing and immunity in L-selectin-deficient mice

Peripheral lymph nodes (PLN) are critical for immunologic memory formation in response to antigens that penetrate the skin. Blood-borne lymphocytes first encounter such antigens after they home to PLN through a multi-step adhesion process that is normally initiated by L-selectin (CD62L) in high endothelial venules (HEV). Since naive T cells can not enter PLN normally in L-selectin-deficient mice, a delayed type hypersensitivity response to cutaneously applied antigen cannot be mounted. In this study, we report that the administration of activated platelets into the systemic circulation of L-selectin knockout mice restores lymphocyte trafficking to PLN, and reconstitutes T cell-mediated immunity in response to a cutaneous antigen. These effects required platelet-expressed P-selectin that allows activated platelets to transiently form a bridge between lymphocytes and HEV, thereby enabling lymphocytes to undergo subsequent beta2 integrin-dependent firm adhesion. These profound effects of platelet-mediated cell-cell interactions on lymphocyte trafficking and formation of immunologic memory may impact on a variety of autoimmune and inflammatory conditions.

The route of antigen entry determines the requirement for L-selectin during immune responses

L-selectin, an adhesion molecule constitutively expressed on leukocytes, is important for primary adhesion and extravasation of lymphocytes at specialized high endothelial venules within lymph nodes and other leukocytes at sites of inflammation. We have generated L-selectin-deficient mice by targeted disruption, and have confirmed a previously reported phenotype which includes strikingly impaired contact hypersensitivity (CHS) responses to reactive haptens (Tedder, T.F., D.A. Steeber, and P. Pizcueta. 1995. J. Exp. Med. 181:2259-2264; Xu, J.C., I.S. Grewal, G.P. Geba, and R.A. Flavell. 1996. 183:589-598.). Since the mechanism of this impairment has not been clarified, we sought to define the stage(s) at which the CHS response is affected in L-selectin-deficient mice. We show that epidermal Langerhans cells in L-selectin-deficient mice are normal in number, migrate to peripheral lymph nodes appropriately, and are functional in presenting allogeneic and haptenic antigens. Moreover, T cells, as well as neutrophil and monocyte effector populations, are fully capable of entry into the inflamed skin sites in the absence of L-selectin. Thus, antigen presentation and effector mechanisms are intact in L-selectin deficient mice. In contrast, virtually no antigen-specific T cells can be found within draining peripheral nodes after a contact challenge, suggesting that the defect resides primarily in the inability of antigen-specific T cells to home to and be activated in these nodes. Indeed, L-selectin-deficient mice mount completely normal CHS responses when alternate routes of immunization are used. These studies pinpoint the lesion in CHS to a discrete stage of the afferent limb of the response, clarify the role of L-selectin on effector populations, and illustrate the critical importance of the route of antigen entry to the successful execution of an immune response.