Rheumatoid Arthritis, Psoriatic Arthritis and Autoimmunity: good genes, elegant mechanisms, bad results The meaning and significance of HLA associations Disclosures No relevant commercial relationships Robert Winchester Columbia University, College of Physicians and Surgeons References: Gregersen, P., J. Silver, and R. Winchester. 1987. The shared epitope hypothesis: An approach to understanding the molecular genetics of susceptibility to rheumatoid arthritis. Arthritis & Rheumatism. 30:1205-1213 Winchester, R., Minevich, G., Steshenko, V., Kirby, B., Kane, D., Greenberg, D.A., and FitzGerald, O. 2012. HLA Associations Reveal Genetic Heterogeneity in Psoriatic Arthritis and in the Psoriasis Phenotype. Arthritis & Rheumatism 64:1134-44 Rheumatoid Arthritis, Psoriatic Arthritis and Autoimmunity: good genes, elegant mechanisms, bad results Each disease is autoimmune in pathogenesis and certain alleles encoding particular major histocompatibility complex (MHC,HLA) molecules (allomorphs) are the most important determinants of susceptibility These molecules likely contribute importantly to specifying the type of adaptive immune response that underlies each disease The roles and significance of the MHC differ in these two diseases The potential for autoimmunity appears to be intrinsic to the way the adaptive immune system functions Clonotypes comprising the T cell repertoire are selected by recognition of self peptides in the context of the individual s MHC molecules Each T cell is distinguished by a specific clonotypic receptor (TCR) capable of recognizing amino acid sequences of nearly any peptide ~9-16 AA long bound to a MHC molecule TCR-p-MHC T cells selected to be in the individual s repertoire subsequently respond to pathogen peptides bound to the MHC by clonal expansion and differentiation to memory & effector stages TCR NEJM 6. A Report crd: where do we stand? Polymorphic residues of Major Histocompatibility Complex MHC 1
The task of the T cell clonotypic TCR of recognizing all the different pathogen peptides bound to MHC molecules is a daunting one Since there are 10 20 = ~10 13 different peptides, We need ~> 10 13 clonotypically distinct T cells with structurally different TCRs so each clonal progenitor can recognize a different peptide TCR-p-MHC This challenge of peptide recognition has two major consequences: Necessitates somatic generation and thymic selection of T cell repertoire on self-peptides bound to self-mhc MHC Class I Loci Class II 0 1 2 3 4m bp HLA-A HLA-B HLA-DR HLA-DP HLA-C HLA-DQ Number of alleles 2432 1445 2329 1476 51; 459 37; 193 (8,184,664,960) (246,733,575,444) MHC molecules need to bind and anchor each of the 10 13 different peptides with high affinity, this drives diversification of the MHC Human Leukocyte Antigens (HLA) Ch 6 This strategy of MHC diversification equips the species with a large number of alternative, polymorphic, MHC molecules that differ in their binding pockets and accordingly bind different selfpeptides Frequency dependent selection Heterozygote advantage Self-MHC molecules select an individuals personalized T cell repertoire Because the entire T cell portion of the adaptive immune system is built on self-recognition this leads to the potential risk that certain individuals will develop autoimmunity Likely because certain MHC molecules bind self peptides that are expressed on cells and tissues which become targets of the autoimmune adaptive immune response TCR-p-MHC 2
How did the shared epitope get that name? Pregnancy or transplant sera were the first HLA typing reagents: Apply HLA-DR-specific sera to examine autoimmune diseases 6. A Report crd: where do we stand? Gibofsky et al A&R 1978 Certain pregnancy sera, which were not good DR typing reagents because of their cross-reactivity, identified a high proportion of RA cases including those that lacked HLA-DR4 suggesting a shared epitope BUT in some populations studied the association of RA susceptibility with HLA-DR*04 could not be completely replicated Study location New York, London Jerusalem, Mumbai Rheumatoid arthritis associated with HLA-DRB1*04 HLA-DRB1*01 Strong No Weak Strong This suggested the possibility that Some varieties of HLA-DRB1*04 genes found in different ethnic groups were not associated with RA susceptibility Certain other HLA-DR genes such as HLA-DRB1*01 were associated with RA susceptibility Hypothesis: There was a shared structural feature, the shared epitope, encoded by some HLA-DRB1*01 and DRB1*04 alleles that certain pregnancy sera recognized This structure was absent from the type of DRB1*04 molecules in populations where DRB1*04 was not associated with RA What is the sequence of the shared epitope structure? Enter Peter Gregersen Sequence MHC alleles related to RA susceptibility to identify molecular basis of SE structure Mapping susceptibility to RA into a shared region of the DR b-chain The shared epitope hypothesis was developed to explain the pattern of association of RA susceptibility with HLA-DRB1*04 and HLA-DRB1*01 alleles But did it have any predictive value? Yakima Indians have a high frequency of rheumatoid arthritis The DR6 (Dw16) allele, DRB1*14:02, which contains the same shared epitope sequence motif, was found in 83% of Yakima Indian with rheumatoid arthritis and 60% of Yakima controls Wilkens et al. Association of HLA-Dw16 with rheumatoid arthritis in Yakima Indians. Further evidence for the "shared epitope" hypothesis. Arthritis & Rheumatism 1991 Alleles conferring susceptibility to RA have a shared sequence motif, the shared epitope Exploring the MHC type of RA cases positive for the serologic shared epitope resulted in identification of HLA-DRB1*10 as another RA susceptibility allele, as expected it had the shared epitope sequence motif Matsuyama et al. Identification of the DRw10 DRb 1 chain allele as encoding a polymorphic class II MHC epitope otherwise restricted to DRb 2 molecules of the DRw53 type. J. Immunology 1988 3
Major HLA-DR alleles encoding the SE sequence motif Crystallographic studies of DR molecules by Wylie and Strominger, et al. showed the location of the shared epitope structure DRB1*01:01 DRB1*01:02 DRB1*04:01 DRB1*04:04 DRB1*04:05 DRB1*04:08 DRB1*10:01 DRB1*14:02 What is the significance of the SE sequence? P4 pocket 74 71 70 Ala Arg/Lys Gln Amino acids comprising the shared epitope determines peptide binding properties of the P4 pocket Shared Epitope motif Peptide side chains bind to pockets in MHC class II molecules and TCR Preferential binding of peptide with negatively charged P4 AA (Glutamic acid) but not positively charged AA by P4 pocket in a DR molecule containing the shared epitope motif TCR 2 5 7 8 peptide 1 4 6 9 P1 P4 P6 P9 74 71 70 MHC class II Shared epitope region Amino acids comprising the shared epitope determine the predominant peptide binding properties of the P4 pocket Strong electrostatic bonds between HLA-DR 71 lysine and the peptide s P4 glutamic acid and P5 side chains Peptide binding properties of the pocket in SE negative alleles are markedly different Were the alleles associated with RA susceptibility identical to wild type alleles? The alleles in RA patients responsible for RA susceptibility were identical in sequence to the alleles in the healthy population, i.e. good genes and are not rare abnormal genes Merryman et al. Class II major histocompatibility complex gene sequences in rheumatoid arthritis: The third diversity regions of both DR b 1 genes in two DR1, DRw10-positive individuals specify the same inferred amino acid sequence as the DRb 1 and DRb 2 genes of a DR4 (Dw14) haplotype. Arthritis & Rheumatism. 1989 DR4 alleles that encode negative charged AA in P4 are not associated with RA susceptibility DRB1*0402 P4 pocket 71 70 Glu Asp Peptide with glutamic acid at P4 does not bind to a HLA-DR molecule with aspartic acid at position 70 or glutamic acid at position 71 4
Figure 2 10/28/2013 6. A Report crd: where do we stand? MHC allomorphs associated with disease susceptibility select a repertoire of T cells that recognize self-peptides as with MHC molecules not associated with a disease One potential explanation is that the T cell clonotypes selected by susceptibility MHC molecules are intrinsicaly more pathogenic i.e. a defect in central repertoire selection Another explanation is that the susceptibility MHC molecules are less adept at selecting T regs, so that the defect is in the regulation of the peripheral repertoire Non-MHC genes associated with susceptibility often confer enhanced immune responsiveness Once triggered by still-unknown processes, we presume T cells mediate the autoimmune disease by recognition of self-peptides in target cells and tissues Roudier et al Plos One 2013 Genotypic risk RA risk at the genotypic level is additive 2 SE alleles > 1 SE allele > no SE alleles SE alleles differ in risk conferred Among non-se alleles, none are associated with dominant protection, as is seen in T1DM, just the absence of susceptibility The risk for development of rheumatoid arthritis is defined by the number and type of HLA-DR alleles encoding shared epitope binding pockets versus other types of binding pockets Return to the question of what the P4 pocket does? DR1, DR10 and DR4 molecules each preferentially bind different peptides, however the common 4 th pocket in each formed by the SE sequence preferentially binds a peptide with a negativly charged amino acid at P4 An event associated with P4 pocket is critical to RA development The P4 side chain is primarily tethered to the MHC, and not recognized by the TCR Citrullination of peptides suggests a potential mechanism for breaking tolerance A SE-DR molecule could now bind and present a peptide with a P4 citrulline but not one with a P4 arginine A vimentin peptide does not bind to shared epitope bearing HLA-DR molecules because positively charged arginine prevents binding to P4 (shared epitope) pocket : SAVRARSSVPGVR Conversion of arginine to citrulline allows high affinity peptide interaction with HLA-DRB1 class II MHC molecules bearing the SE SE alleles Non SE alleles SAVRARSSVPGVR SAVRACitSSVPGVR Hill et al. J Imm 2003 Binding of a citrullinated peptide may allow certain TCR to be triggered by self-peptides to which the person is not tolerized 5
A problem with the citrulline hypothesis Is there a T cell repertoire to recognize self-peptides anchored by a P4 citrulline that has been positively selelcted in the thymus? Might such T cells be generated during physiologic apoptosis of embryogenesis? Might they be subsequently generated during intercurrent inflammation? Smoking? Of more concern, DRB1*0402 molecules can in principal bind citrullinated peptides 6. A Report crd: where do we stand? A different pattern of MHC gene effect in autoimmune disease The text book paradigm Psoriasis (Ps) Psoriatic arthritis (PsA) Contribution MHC genetics makes to psoriatic arthritis susceptibility and disease expression Oliver FitzGerald University College Dublin Peak onset age 15-30 yrs 10-20% ~15 years between Ps & PsA ~15% no prior psoriasis Study: Compare two cohorts in the homogeneous Irish population with Ps Psoriasis Psoriasis Cohort, without features of arthritis, spondylitis or enthesitis, n=214, presenting to a dermatologic clinic Psoriatic Arthritis Cohort, n=359, presenting to a rheumatology clinic Psoriatic Arthritis Goal: Is the genotype of psoriatic arthritis identical to that of psoriasis? Is the genotype of psoriatic arthritis homogeneous? Use CASPAR criteria and sequence-based HLA typing Psoriasis MHC genetics Telomere Principal psoriasis susceptibility HLA allele: HLA- C*06:02 (Psors 1) Frequency~ 60% in most series ascertained on psoriasis, ( 70% if eliminate late onset Ps) Psors 1 PSORS1C2 PSORS1C1 POU5F 1 LOG44219 9 CDSN TCF19 HCG27 HLA-C HLA-B MICA HCP5 TNF NFKB1L MICB BAT1 LTA 31,190 31,290 31,390 31,490 31,590 31,670kB *06:02 *13:01 *06:02 *37:01 *06:02 *57:01 Ps Susceptibility haplotypes Centromere 6
Findings in psoriatic arthritis cohort: Distribution of the HLA- C*06:02 and HLA- B*57:01 alleles Psoriasis w/o Arthritis Psoriatic Arthritis C*06:02 HLA-C 57.5% 28.7% B*57:01 31.3% 18.4 OR PsA vs Ps 0.26 (0.2-0.4) 0.30 (0.2-0.5) HLA-B MICA MICB Ps C*06:02 ~60% NFKB1L? PsA LTA TNF 6. A Report crd: where do we stand? 31,190 31,290 31,390 31,490 31,590 31,670kB Centromere Reject hypothesis of genetic homogeneity of psoriasispsoriatic arthritis p=9.94 x 10-12 Winchester A&R 2012 Distribution of the HLA-C*06:02 alleles 42.5% C*06:02 57.5% 71.3% 27.9% 83.0% C*06:02 17.0% p=9.9x10-12 OR 1.8 (1.3-2.5) Cohorts Psoriasis Psoriatic arthritis Ctrl Distribution of other HLA-B alleles in the Irish PsA and Ps Cohorts B*27:05 B*39:01 B*08:01 PsA 15.6% 2.6 (1.7-4.2) 6.4% 3.5 (1.6-7.6) 37.3% HLA-B*27:05 and HLA-B*39:01 are susceptibility alleles for PsA but are not high risk alleles for Ps in the absence of arthritis HLA-B*08:01 is associated with PsA susceptibility but appears protective for Ps Winchester et al. A&R 2012 Ps 4.7% 1.4% 24.8% 1.6 (1.2-2.0) 0.4 (0.3-0.8) Ctrl 5.5% 1.2% 30.1% HLA-B alleles in psoriatic arthritis cohort differ in frequency from those in the psoriasis cohort 15.6% C*06:02 57.5% Ps no A Psoriatic arthritis genetics Genetic Heterogeneity in MHC associations; no common HLA-C allele can be implicated by linkage disequilibrium HLA-C*02:02 HLA-B*27:05 HLA -C*01:01 HLA-B*27:05 B*27:05 15.6% B*08:01 37.3% 6.4% B*39:01 27.9% PsA 87.2% of all cases HLA -C*12:03 HLA-B*39:01 HLA -C*07:01 HLA-B*08:01 Susceptibility likely driven by other genes on haplotype, e.g. B alleles 5.5% 24.8% 1.8% 17.0% Ctrl PSORS1C2 PSORS1C1 POU5F1 LOG442199 CDSN TCF19 HCG27 HLA-C HLA-B MICA HCP5 NFKB1L TNF MICB BAT1 LTA 31,190 31,290 31,390 31,490 31,590 31,670kB Psors1 Telomere Centromere 7
New hypothesis Psoriasis is genetically heterogeneous with the musculoskeletal phenotype defined by several structurally unrelated HLA alleles / haplotypes Different genetic susceptibility genes imply different disease mechanisms, and possibly different clinical course and therapeutic responses Do the susceptibility genes also confer a phenotypic difference?? Psoriasis Psoriatic arthritis Susceptibility genes confer a phenotypic difference Arthritis develops much closer to the appearance of psoriasis in the HLA-B*27:05:02 or B*39:01:01 subset than in the HLA-C*06:02 subset of psoriatic arthritis cases PsA 11.28 3.84 years PsA p=0.0085 10-20% ~15 years between Ps & PsA Is this time interval a uniform property of PsA? ~15% no prior psoriasis HLA-C*06:02 HLA-B*27:05:02 or B*39:01:01 Time interval between Ps and PsA is a genetically determined quantitative trait Role of HLA-B alleles in influencing phenotype of symmetrical versus asymmetrical spine involvement in PsA Asymmetric Sacroiliitis more common in PsA (18.1%) than symmetric (6.3%) 1971 M. Haroon et al.concurrent abstract session #818 282 cases PsA phenotyped for sacroiliitis 69 (24.5%) in series have SI 18 (6.3%) have symmetrical sacroiliitis 16.7% are B*08 OR=0.32 (0.9-1.1) 61.1% are B*27 OR=10.63 (3.9-29.3) Male predominant (OR=11.91) 51 (18.1%) have asymmetrical sacroiliitis 62.7% are B*08 OR=3.8 (1.9-6.0) 9.8% AssymSI are B*27 0.52 (0.2-1.4) Hypothesis: Genotype Determines Disease Expression in PsA Principal patterns of MHC effect Alleles B*57:01; HLA-C*06:02 Highly penetrant early onset Psoriasis Late onset low penetrance musculoskeletal disease Alleles B*08:01:01; C*07:01:01 Highly penetrant skin and joint disease, milder skin disease Asymmetrical spinal involvement Alleles B*27:05:02; C*02:02:02; C*01:02:01 Early onset MSK disease more synchronous with skin disease Symmetrical spinal involvement M. Haroon poster session A #325 8
Conclusions: PsA is not a homogeneous disease Different MHC alleles and more importantly haplotypes implicated in determining PsA susceptibility were associated with different phenotypic characteristics (subphenotypes) of PsA These alleles and haplotypes are characteristics of different ethnic groups and populations B*27:05:02; C*02:02:02; C*01:02:01 and B*08:01:01- C*07:01:01 characterize Northern European populations Importance of performing similar studies in other human populations Potential influence on generality of classification criteria and on composition of those in clinical trials 6. A Report card: where do we stand? Different patterns of MHC gene effect found in PsA vs. RA In rheumatoid arthritis multiple susceptibiity MHC alleles, all have a common structural SE element and this diversity of susceptibility alleles does not appear to denote different phenotypes In psoriatic arthritis multiple susceptibiity MHC alleles do not exhibit a common structural feature Each specifies a distinguishable clinical phenotype and probably different underlying disease mechanisms likely based on binding and presentation of different peptides The TCR-p-MHC interaction that underlies the adaptive immune response is critical to the type of autoimmune disorder Where do we stand? 1. The general details of the MHC component are beginning to be identified These are good genes that are highly evolutionarily selected Genetic epidemiology is still incomplete SNP imputation may simplify the difficulties of HLA typing 2. The identity of the peptides that drive the autoimmune process are largely unknown 3. The identity and recognition properties of the T cell clonotypes that drive the autoimmune process are largely unknown Progress here will be based on powerful new technologies: Progress here will be based on: Microproteomics, etc. Like Prince Charming, the SE provides the equivalent of Cinderella s glass slipper to search for the peptide driving RA and T cell clonotypes Next generation sequencing and enhanced informatics Tetramers Personalized mice containing human imune systems generated from human stem cells reconstruction of patient s immune system prior to onset of clinical disease Kalscheuer et al. Science Translational Medicine 2012 9
One classification of autoimmune diseases is based on the class of MHC molecule implicated in susceptibility MHC Class I associated diseases Ankylosing spondylitis Psoriatic arthritis Psoriasis HLA-B*27 HLA-C*06, B*27, B*08 HLA-C*06 MHC Class II associated diseases Systemic lupus erythematosus Rheumatoid arthritis Multiple sclerosis Type I diabetes mellitus HLA-DR*02, DR*03 HLA-DR*04, DR*01, DR*10 (SE) HLA-DR*02 HLA-DR*03, DR*04 Focuses attention on the nature of driving peptide recognized by T cell Features of the subset of B*27 psoriatic arthritis cases are more analogous to those of ankylosing spondylitis Male predominance Symmetrical spine involvement 10