The CD6 multiple sclerosis susceptibility allele is associated with alterations in CD4+ T cell proliferation

CD6 as a therapeutic target in autoimmune diseases: successes and challenges

The transmembrane surface glycoprotein CD6 was one of the first antigens identified on T lymphocytes. The recognition of its involvement in T-cell signaling processes heralds the potential of CD6 as a target for therapy in a number of pathologies associated with imbalances in T-cell function. Its tissue distribution, cellular expression, and overall molecular structure are well described, and the interaction with its physiological ligand CD166 has been determined to the amino-acid level. Nevertheless, the involvement of CD6 in signaling pathways remains poorly characterized and its biological function is controversial; still unresolved are whether CD6 is a co-stimulatory molecule in T-cell activation or, similar to the related CD5 antigen, a modulator of intracellular signaling. Here we revisit the earliest attempts of modulating immune function using CD6 monoclonal antibodies, and review the current thinking behind the recent developments in immunotherapy targeting CD6. Notwithstanding the promises and hopes brought by monoclonals already in clinical trials, the fact is that very little is known about the mechanism of action of these reagents, whether they enhance the physiological role of the receptor or whether they may induce a completely novel biochemical response that might, nevertheless, be beneficially used to treat human immune pathology.

Clinical relevance and functional consequences of the TNFRSF1A multiple sclerosis locus

OBJECTIVE

We set out to characterize the clinical impact and functional consequences of rs1800693(G), the multiple sclerosis (MS) susceptibility allele found in the TNFRSF1A locus.

METHODS

We analyzed prospectively collected data on patients with MS to assess the role of the TNFRSF1A locus on disease course and treatment response. Using archival serum samples and freshly isolated monocytes from patients with MS and healthy subjects, we evaluated the effects of rs1800693(G) and a second risk allele, R92Q, on immune function.

RESULTS

In 772 patients with MS, we see no evidence that rs1800693(G) strongly influences clinical or radiographic indices of disease course and treatment response; thus, rs1800693(G) appears to be primarily involved in the onset of MS. At the molecular level, this validated susceptibility allele generates an RNA isoform, TNFRSF1A Δ6, that lacks the transmembrane and cytoplasmic domains. While there was no measurable effect on serum levels of soluble TNFRSF1A, rs1800693(G) appears to alter the state of monocytes, which demonstrate a more robust transcriptional response of CXCL10 and other genes in response to tumor necrosis factor (TNF)-α. We also report that activation of the TNF-α pathway results in altered expression of 6 other MS susceptibility genes, including T-cell activation rho GTPase activating protein (TAGAP) and regulator of G-protein signaling 1 (RGS1), which are not previously known to be responsive to TNF-α.

CONCLUSIONS

The MS rs1800693(G) susceptibility allele affects the magnitude of monocyte responses to TNF-α stimulation, and the TNF pathway may be one network in which the effect of multiple MS genes becomes integrated.

Association of multiple sclerosis susceptibility variants and early attack location in the CNS

OBJECTIVE

The anatomic location of subsequent relapses in early multiple sclerosis (MS) appears to be predicted by the first attack location. We sought to determine if genetic polymorphisms associated with MS susceptibility are associated with attack location.

METHODS

17 genome-wide association study-identified MS susceptibility polymorphisms were genotyped in 503 white, non-Hispanic patients seen within a year of MS onset. Their association with the CNS location of the first two MS attacks was assessed in multivariate repeated measures analyses (generalized estimating equations with robust standard errors).

RESULTS

The IL12A polymorphism was independently associated with increased odds of attacks involving the spinal cord (OR = 1.52, 95% CI 1.11, 2.07, p = 0.009), as was the IRF8 polymorphism (OR = 2.40, 95% CI [1.04, 5.50], p = 0.040). The IL7R polymorphism was associated with reduced odds of attacks involving the brainstem/cerebellum (OR = 0.46, 95% CI 0.22, 0.97, p = 0.041), as were the TNFRSF1A and IL12A polymorphisms. The CD6 polymorphism conferred reduced odds of optic neuritis as an attack location (OR = 0.69, 95% CI [0.49, 0.97], p = 0.034). Several other genes showed trends for association with attack location.

CONCLUSIONS

Some of the MS susceptibility genes may be associated with MS attack location. The IL12A polymorphism is of particular interest given that interferon beta therapy appears to influence IL12 levels. These findings may lead to improved understanding of MS pathogenesis and treatment.

Multiple sclerosis susceptibility genes: associations with relapse severity and recovery

OBJECTIVE

Patients with early multiple sclerosis (MS) have stereotyped attack severity and recovery. We sought to determine if polymorphisms in MS susceptibility genes are associated with these attack features or with the risk of a second attack.

METHODS

503 white subjects evaluated within a year of MS onset were included in the study. The severity of and recovery from the first two attacks were determined based on published definitions. Seventeen MS susceptibility genes were genotyped at the UCSF MS Genetics laboratory. Each polymorphism was evaluated in multivariate ordinal models, adjusted for the other polymorphisms, for its association with attack severity and recovery. We also assessed if these polymorphisms were associated with increased risk of a second attack.

RESULTS

The MPHOSPH9 polymorphism was associated with greater attack severity (odds ratios [OR] = 1.47, 95% CI [1.11, 1.94], p = 0.008), while the RGS1 and TNFRSF1A polymorphisms tended to be associated with reduced attack severity. The CD6 polymorphism tended to be associated with increased odds of worse attack recovery (OR = 1.25, 95% CI [0.93, 1.68], p = 0.13). In those who were HLA-DRB1-negative, the EVI5 polymorphism was associated with attacks of less severity; in HLA-DRB1 positive patients, EVI5 was associated with attacks of greater severity and worse recovery. The IL7R, TNFRSF1A, and GPC5 polymorphisms tended to be associated with having a second event within a year.

CONCLUSIONS

Some MS susceptibility polymorphisms may be associated with attack severity, recovery, or frequency. Further characterization of these genes may lead to a better understanding of MS pathogenesis and to a more individualized treatment approach.

Combining genetic mapping with genome-wide expression in experimental autoimmune encephalomyelitis highlights a gene network enriched for T cell functions and candidate genes regulating autoimmunity

The experimental autoimmune encephalomyelitis (EAE) is an autoimmune disease of the central nervous system commonly used to study multiple sclerosis (MS). We combined clinical EAE phenotypes with genome-wide expression profiling in spleens from 150 backcross rats between susceptible DA and resistant PVG rat strains during the chronic EAE phase. This enabled correlation of transcripts with genotypes, other transcripts and clinical EAE phenotypes and implicated potential genetic causes and pathways in EAE. We detected 2285 expression quantitative trait loci (eQTLs). Sixty out of 599 cis-eQTLs overlapped well-known EAE QTLs and constitute positional candidate genes, including Ifit1 (Eae7), Atg7 (Eae20-22), Klrc3 (eEae22) and Mfsd4 (Eae17). A trans-eQTL that overlaps Eae23a regulated a large number of small RNAs and implicates a master regulator of transcription. We defined several disease-correlated networks enriched for pathways involved in cell-mediated immunity. They include C-type lectins, G protein coupled receptors, mitogen-activated protein kinases, transmembrane proteins, suppressors of transcription (Jundp2 and Nr1d1) and STAT transcription factors (Stat4) involved in interferon signaling. The most significant network was enriched for T cell functions, similar to genetic findings in MS, and revealed both established and novel gene interactions. Transcripts in the network have been associated with T cell proliferation and differentiation, the TCR signaling and regulation of regulatory T cells. A number of network genes and their family members have been associated with MS and/or other autoimmune diseases. Combining disease and genome-wide expression phenotypes provides a link between disease risk genes and distinct molecular pathways that are dysregulated during chronic autoimmune inflammation.

Progress in multiple sclerosis genetics

A genetic component in the susceptibility to multiple sclerosis (MS) has long been known, and the first and major genetic risk factor, the HLA region, was identified in the 1970’s. However, only with the advent of genome-wide association studies in the past five years did the list of risk factors for MS grow from 1 to over 50. In this review, we summarize the search for MS risk genes and the latest results. Comparison with data from other autoimmune and neurological diseases and from animal models indicates parallels and differences between diseases. We discuss how these translate into an improved understanding of disease mechanisms, and address current challenges such as genotype-phenotype correlations, functional mechanisms of risk variants and the missing heritability.

Fine mapping and functional analysis of the multiple sclerosis risk gene CD6

CD6 has recently been identified and validated as risk gene for multiple sclerosis (MS), based on the association of a single nucleotide polymorphism (SNP), rs17824933, located in intron 1. CD6 is a cell surface scavenger receptor involved in T-cell activation and proliferation, as well as in thymocyte differentiation. In this study, we performed a haptag SNP screen of the CD6 gene locus using a total of thirteen tagging SNPs, of which three were non-synonymous SNPs, and replicated the recently reported GWAS SNP rs650258 in a Spanish-Basque collection of 814 controls and 823 cases. Validation of the six most strongly associated SNPs was performed in an independent collection of 2265 MS patients and 2600 healthy controls. We identified association of haplotypes composed of two non-synonymous SNPs [rs11230563 (R225W) and rs2074225 (A257V)] in the 2^nd SRCR domain with susceptibility to MS (P_{max(T) permutation} = 1×10⁻⁴). The effect of these haplotypes on CD6 surface expression and cytokine secretion was also tested. The analysis showed significantly different CD6 expression patterns in the distinct cell subsets, i.e. – CD4⁺ naïve cells, P = 0.0001; CD8⁺ naïve cells, P<0.0001; CD4⁺ and CD8⁺ central memory cells, P = 0.01 and 0.05, respectively; and natural killer T (NKT) cells, P = 0.02; with the protective haplotype (RA) showing higher expression of CD6. However, no significant changes were observed in natural killer (NK) cells, effector memory and terminally differentiated effector memory T cells. Our findings reveal that this new MS-associated CD6 risk haplotype significantly modifies expression of CD6 on CD4⁺ and CD8⁺ T cells.

ALCAM--novel multiple sclerosis locus interfering with HLA-DRB1*1501

Activated leukocyte cell adhesion molecule (ALCAM) is a molecule involved in leukocyte migration across the blood-brain barrier which is a key stage in multiple sclerosis (MS) pathogenesis. The present study is the first to report evidence of the association of rs6437585 ALCAM polymorphism with risk and progression of MS. Our investigation revealed that rs6437585CT individuals had higher risk of MS (OR=2.34; 95%CI=1.22-4.51; P=0.011) and over 2 years earlier age of onset (95%CI=0.16-4.41, P=0.036). Moreover, we demonstrated that two ALCAM polymorphisms, rs11559013 and rs34926152, although not associated with MS itself, modify HLA-DRB1*1501 effect. Results obtained from logistic regression analysis showed five-fold lower risk for MS for both rs11559013GA/HLA-DRB1*1501+ and rs34926152GT/HLA-DRB1*1501+ individuals. This observations may suggest protective role against MS for both rs11559013GA and rs34926152GT genotypes in HLA-DRB1*1501 positive individuals.

The genetics of multiple sclerosis: an up-to-date review

Multiple sclerosis (MS) is a prevalent inflammatory disease of the central nervous system that often leads to disability in young adults. Treatment options are limited and often only partly effective. The disease is likely caused by a complex interaction between multiple genes and environmental factors, leading to inflammatory-mediated central nervous system deterioration. A series of genomic studies have confirmed a central role for the immune system in the development of MS, including genetic association studies that have now dramatically expanded the roster of MS susceptibility genes beyond the longstanding human leukocyte antigen (HLA) association in MS first identified nearly 40 years ago. Advances in technology together with novel models for collaboration across research groups have enabled the discovery of more than 50 non-HLA genetic risk factors associated with MS. However, with a large proportion of the disease heritability still unaccounted for, current studies are now geared towards identification of causal alleles, associated pathways, epigenetic mechanisms, and gene-environment interactions. This article reviews recent efforts in addressing the genetics of MS and the challenges posed by an ever increasing amount of analyzable data, which is spearheading development of novel statistical methods necessary to cope with such complexity.

Human genetics offers an emerging picture of common pathways and mechanisms in autoimmunity

In genetic studies of autoimmune and inflammatory diseases, one clear finding that has emerged from genome-wide association studies is that a substantial fraction of variation modifying risk in one disease also contributes mediate risk to multiple, additional autoimmune and inflammatory diseases. The unexpected magnitude of this overlap presents the unique opportunity to dissect the pathogenic mechanisms underlying multiple disease states in the expectation that this may lead to both more sensitive diagnostics and novel therapies. Here, we review the current evidence for this shared genetic architecture and, based on these data, outline models for shared pathways, the underlying hypotheses for them, how these models can be tested and validated.

The genetics of multiple sclerosis: an up-to-date review

Multiple sclerosis (MS) is a prevalent inflammatory disease of the central nervous system that often leads to disability in young adults. Treatment options are limited and often only partly effective. The disease is likely caused by a complex interaction between multiple genes and environmental factors, leading to inflammatory-mediated central nervous system deterioration. A series of genomic studies have confirmed a central role for the immune system in the development of MS, including genetic association studies that have now dramatically expanded the roster of MS susceptibility genes beyond the longstanding human leukocyte antigen (HLA) association in MS first identified nearly 40 years ago. Advances in technology together with novel models for collaboration across research groups have enabled the discovery of more than 50 non-HLA genetic risk factors associated with MS. However, with a large proportion of the disease heritability still unaccounted for, current studies are now geared towards identification of causal alleles, associated pathways, epigenetic mechanisms, and gene-environment interactions. This article reviews recent efforts in addressing the genetics of MS and the challenges posed by an ever increasing amount of analyzable data, which is spearheading development of novel statistical methods necessary to cope with such complexity.