The Bruton tyrosine kinase inhibitor PCI-32765 blocks B-cell activation and is efficacious in models of autoimmune disease and B-cell malignancy.

Activation of the B-cell antigen receptor (BCR) signaling pathway contributes to the initiation and maintenance of B-cell malignancies and autoimmune diseases. The Bruton tyrosine kinase (Btk) is specifically required for BCR signaling as demonstrated by human and mouse mutations that disrupt Btk function and prevent B-cell maturation at steps that require a functional BCR pathway. Herein we describe a selective and irreversible Btk inhibitor, PCI-32765, that is currently under clinical development in patients with B-cell non-Hodgkin lymphoma. We have used this inhibitor to investigate the biologic effects of Btk inhibition on mature B-cell function and the progression of B cell-associated diseases in vivo. PCI-32765 blocked BCR signaling in human peripheral B cells at concentrations that did not affect T cell receptor signaling. In mice with collagen-induced arthritis, orally administered PCI-32765 reduced the level of circulating autoantibodies and completely suppressed disease. PCI-32765 also inhibited autoantibody production and the development of kidney disease in the MRL-Fas(lpr) lupus model. Occupancy of the Btk active site by PCI-32765 was monitored in vitro and in vivo using a fluorescent affinity probe for Btk. Active site occupancy of Btk was tightly correlated with the blockade of BCR signaling and in vivo efficacy. Finally, PCI-32765 induced objective clinical responses in dogs with spontaneous B-cell non-Hodgkin lymphoma. These findings support Btk inhibition as a therapeutic approach for the treatment of human diseases associated with activation of the BCR pathway.

The Role of the Complement Pathway in Clinical Progression of Geographic Atrophy: Analysis of the Phase III Chroma and Spectri Trials.

Purpose: To investigate the relationship between complement pathway activities and progression of geographic atrophy (GA) secondary to age-related macular degeneration in samples collected from patients enrolled in the Chroma and Spectri trials. Design: Chroma and Spectri were phase III, double-masked, and sham-controlled, 96-week trials. Participants: Aqueous humor (AH) samples collected at baseline and week 24 visits from 81 patients with bilateral GA across all 3 treatment groups (intravitreal lampalizumab 10 mg every 6 weeks, every 4 weeks, or corresponding sham procedures) were tested, along with patient-matched plasma samples collected at baseline. Methods: Antibody capture assays using the Simoa platform were used to measure the levels of complement factor B, the Bb fragment of complement factor B, intact complement component 3 (C3), processed C3, intact complement C4, and processed C4. Complement factor D levels were measured using enzyme-linked immunosorbent assay. Main Outcome Measures: Correlations of complement levels and activities (i.e., processed:intact ratio of complement component) in AH and plasma with baseline GA lesion size and growth rate. Results: In baseline AH, there were strong correlations (Spearman's rho ≥ 0.80) between intact complement proteins, between processed complement proteins, and between linked processed and intact complement proteins; weak correlations (rho ≤ 0.24) were found between complement pathway activities. There were no strong correlations between complement protein levels and activities measured in AH and plasma at baseline (rho ≤ 0.37). Baseline complement levels and activities in AH and plasma did not correlate with baseline GA lesion size or change from baseline in GA lesion area at week 48 (i.e., annualized growth rate). There were no strong correlations between changes in complement levels/activities in the AH from baseline to week 24 and annualized GA lesion growth rate. Genotype analysis did not reveal a meaningful correlation between complement-related, age-related macular degeneration risk single-nucleotide polymorphisms and complement levels and activities. Conclusions: Complement levels or activities in AH and plasma did not correlate with GA lesion size or growth rate. This suggests that local complement activation as measured in AH does not appear to be related to GA lesion progression. Financial Disclosures: Proprietary or commercial disclosure may be found after the references.

Alternative Complement Pathway Inhibition by Lampalizumab: Analysis of Data From Chroma and Spectri Phase III Clinical Trials.

Purpose: Lampalizumab, an antigen-binding fragment of a humanized monoclonal antibody directed against complement factor D (CFD), is designed to treat geographic atrophy (GA) secondary to age-related macular degeneration. Given the lack of clinical efficacy observed in patients with GA in the phase III Chroma/Spectri trials, we investigated the impact of lampalizumab on the complement system in vivo. We developed 6 novel assays to measure changes in complement pathway activities in aqueous humor samples collected from patients enrolled in these trials. Design: Chroma/Spectri were double-masked, sham-controlled, 96-week trials. Participants: Aqueous humor samples from 97 patients with bilateral GA across all groups (i.e., intravitreous lampalizumab 10 mg every 6 weeks, every 4 weeks, or corresponding sham procedures) were tested. Methods: Novel antibody capture assays were developed on the Simoa platform for complement factor B (CFB), the Bb fragment of CFB, intact complement component 3 (C3), processed C3, intact complement component 4 (C4), and processed C4. Main Outcome Measures: The ratio of processed vs. intact complement factors (i.e., complement activity) in aqueous humor were assessed. Results: Patients treated with either of the lampalizumab regimens demonstrated an increase in CFD level at week 24 compared with baseline, along with a corresponding median reduction in the Bb:CFB ratio of 41% to 43%. There were no strong correlations between lampalizumab concentrations in aqueous humor and change in CFD levels or Bb:CFB ratio over time. No change in downstream C3 processing was observed with lampalizumab treatment. Additionally, there was no change in C4 processing. Conclusions: The collection of aqueous humor samples from patients in Chroma and Spectri trials provided key insights on the effects of lampalizumab, a novel complement inhibitor, on local ocular complement activation. Lampalizumab inhibited the alternative complement pathway in the eyes of patients with GA; however, this did not translate into a measurable reduction in either classical or total complement activity, based on absence of changes in C4 and C3 processing, respectively. Financial Disclosures: Proprietary or commercial disclosure may be found after the references.

Evaluating the Safety and Efficacy of Crenezumab vs Placebo in Adults With Early Alzheimer Disease: Two Phase 3 Randomized Placebo-Controlled Trials.

Importance: Alzheimer disease (AD), a neurodegenerative disease characterized by ß-amyloid plaques and τ tangles in the brain, represents an unmet medical need with no fully approved therapeutics to modify disease progression. Objective: To investigate the safety and efficacy of crenezumab, a humanized monoclonal immunoglobulin G4 antibody targeting ß-amyloid oligomers, in participants with prodromal to mild (early) AD. Design, Setting, and Participants: Two phase 3 multicenter randomized double-blind placebo-controlled parallel-group efficacy and safety studies of crenezumab in participants with early AD, CREAD and CREAD2, were initiated in 2016 and 2017, respectively, and were designed to evaluate the efficacy and safety of crenezumab in participants with early AD. CREAD (194 sites in 30 countries) and CREAD2 (209 sites in 27 countries) were global multicenter studies. A total of 3736 and 3664 participants were screened in CREAD and CREAD2, respectively. A total of 3736 and 3664 participants were screened in CREAD and CREAD2, respectively. Both trials enrolled individuals aged 50 to 85 years with early AD. Participants with some comorbidities and evidence of cerebral infarction or more than 4 microbleeds or areas of leptomeningeal hemosiderosis on magnetic resonance imaging were excluded. After 2923 and 2858 were excluded, respectively, 813 participants in CREAD and 806 in CREAD2 were randomly assigned in a 1:1 ratio to either placebo or crenezumab. In the final analysis, there were 409 participants in the placebo group and 404 in the crenezumab group in CREAD and 399 in the placebo group and 407 in the crenezumab group in CREAD2. Data were analyzed up until January 2019 and August 2019, respectively. Interventions: Participants received placebo or 60 mg/kg crenezumab intravenously every 4 weeks for up to 100 weeks. Main Outcomes and Measures: The primary outcome was change from baseline to week 105 in Clinical Dementia Rating-Sum of Boxes (CDR-SB) score. Results: There were 813 participants in CREAD (mean [SD] age, 70.7 [8.2] years; 483 female and 330 male) and 806 in CREAD2 (mean [SD] age, 70.9 [7.7] years; 456 female and 350 male). Baseline characteristics were balanced between both groups. The between-group difference in mean change from baseline in CDR-SB score (placebo minus crenezumab) was -0.17 (95% CI, -0.86 to 0.53; P = .63) at week 105 in the CREAD study (88 placebo; 86 crenezumab). Compared with previous trials, no new safety signals were identified, and amyloid-related imaging abnormalities with edema were rare, mild, and transient. No meaningful changes in AD biomarkers were observed. Both studies were discontinued following a preplanned interim analysis indicating that CREAD was unlikely to meet the primary end point. Conclusions and Relevance: Crenezumab was well tolerated but did not reduce clinical decline in participants with early AD. Trial Registration: ClinicalTrials.gov Identifiers: CREAD, NCT02670083; CREAD2, NCT03114657.

Phase 1 Study of the Anti-HtrA1 Antibody-binding Fragment FHTR2163 in Geographic Atrophy Secondary to Age-related Macular Degeneration.

PURPOSE: FHTR2163 is a novel antigen-binding fragment (Fab) directed against high-temperature requirement protein A1 (HtrA1). HTRA1 inhibition may preserve retinal integrity and slow disease progression in geographic atrophy (GA) secondary to age-related macular degeneration (AMD). This study examined the safety, pharmacokinetics, immunogenicity, and changes in the HTRA1-specific substrate Dickkop-related protein 3 (DKK3) in patients with GA who received FHTR2163. DESIGN: Phase I, open-label, single ascending dose escalation and multiple-dose expansion study. METHODS: Adults aged ≥ 50 years with GA secondary to AMD with best corrected visual acuity ranging between Snellen 20/125 and 20/400 were enrolled. In the first stage, a single intravitreal injection of FHTR2163 was given in 5 dose-escalation cohorts ranging from 1 to 20 mg (n = 3 patients/cohort; n = 15 total patients). The second stage evaluated the maximum tested dose of 20 mg administered every 4 weeks for 3 doses (n = 13 patients). RESULTS: No dose limiting toxicities or ocular serious AEs were reported. The most frequently reported AEs in the study eye were conjunctival hemorrhage (n = 7), conjunctival hyperemia (n = 4), and eye pain (n = 2). No non-ocular or ocular AEs were assessed as drug related. There were no clinically significant changes in ocular exams. A sustained pharmacodynamic effect of anti-HtrA1 was observed in the aqueous humor, as measured by levels of cleaved DKK3. CONCLUSIONS: FHTR2163, a novel Fab directed against HtrA1, was well tolerated with no DLTs or significant ocular AEs. The molecule when injected intravitreally for 3 doses showed a sustained pharmacodynamic effect at the maximum tested dose of 20 mg.

Preanalytical approaches to improve recovery of amyloid-ß peptides from CSF as measured by immunological or mass spectrometry-based assays.

BACKGROUND: Amyloid-ß 1-42 (Aß1-42) peptide is a well-established cerebrospinal fluid (CSF) biomarker for Alzheimer's disease (AD). Reduced levels of Aß1-42 are indicative of AD, but significant variation in the absolute concentrations of this analyte has been described for both healthy and diseased populations. Preanalytical factors such as storage tube type are reported to impact Aß recovery and quantification accuracy. Using complementary immunological and mass spectrometry-based approaches, we identified and characterized preanalytical factors that influence measured concentrations of CSF Aß peptides in stored samples. METHODS: CSF from healthy control subjects and patients with AD was aliquoted into polypropylene tubes at volumes of 0.1 ml and 0.5 ml. CSF Aß1-42 concentrations were initially measured by immunoassay; subsequent determinations of CSF Aß1-42, Aß1-40, Aß1-38, Aß1-37, and Aß1-34 concentrations were made with an absolute quantitative mass spectrometry assay. In a second study, CSF from healthy control subjects and patients with dementia was denatured with guanidine hydrochloride (GuHCl) at different stages of the CSF collection and aliquoting process and then measured with the mass spectrometry assay. RESULTS: Two distinct immunoassays demonstrated that CSF Aß1-42 concentrations measured from 0.5-ml aliquots were higher than those from 0.1-ml aliquots. Tween-20 surfactant supplementation increased Aß1-42 recovery but did not effectively resolve measured concentration differences associated with aliquot size. A CSF Aß peptide mass spectrometry assay confirmed that Aß peptide recovery was linked to sample volume. Unlike the immunoassay experiments, measured differences were consistently eliminated when aliquots were denatured in the original sample tube. Recovery from a panel of low-retention polypropylene tubes was assessed, and 1.5-ml Eppendorf LoBind® tubes were determined to be the least absorptive for Aß1-42. A comparison of CSF collection and processing methods suggested that Aß peptide recovery was improved by denaturing CSF earlier in the collection/aliquoting process and that the Aß1-42/Aß1-40 ratio was a useful method to reduce variability. CONCLUSIONS: Analyte loss due to nonspecific sample tube adsorption is a significant preanalytical factor that can compromise the accuracy of CSF Aß1-42 measurements. Sample denaturation during aliquoting increases recovery of Aß peptides and improves measurement accuracy. The Aß1-42/Aß1-40 ratio can overcome some of the quantitative variability precipitated by preanalytical factors affecting recovery.

ABBY: A phase 2 randomized trial of crenezumab in mild to moderate Alzheimer disease.

OBJECTIVE: To evaluate the safety and efficacy of crenezumab in patients with mild to moderate Alzheimer disease (AD). METHODS: In this phase 2 trial, 431 patients with mild to moderate AD 50 to 80 years of age were randomized 2:1 (crenezumab:placebo). Patients received low-dose subcutaneous crenezumab 300 mg or placebo every 2 weeks (n = 184) or high-dose intravenous crenezumab 15 mg/kg or placebo every 4 weeks (n = 247) for 68 weeks. Primary outcome measures were change in Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog12) and Clinical Dementia Rating-Sum of Boxes scores from baseline to week 73. RESULTS: The primary and secondary endpoints were not met. In an exploratory post hoc analysis, a reduction in decline on the ADAS-Cog12 was observed in the high-dose group. Separation from the placebo group on the ADAS-Cog12 was greatest in the milder subsets of AD patients and reached statistical significance in the group with Mini-Mental State Examination scores of 22 to 26. In both groups, there was a significant increase in CSF ß-amyloid1-42 levels that correlated with crenezumab CSF levels. The overall rate of adverse events was balanced between groups. One case of amyloid-related imaging abnormalities indicative of vasogenic edema or effusions was reported. CONCLUSIONS: Although prespecified criteria for testing treatment effects were not met, these data suggest a potential treatment effect in patients with mild AD treated with high-dose crenezumab. Together with the safety profile for crenezumab, these data support the exploration of crenezumab treatment at even higher doses in patients with early AD. CLINICALTRIALSGOV IDENTIFIER: NCT 01343966. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that, for people with AD, crenezumab does not significantly improve cognition or function at 18 months. The study is rated Class II because <80% of enrolled patients completed the study.

Amyloid positron emission tomography and cerebrospinal fluid results from a crenezumab anti-amyloid-beta antibody double-blind, placebo-controlled, randomized phase II study in mild-to-moderate Alzheimer's disease (BLAZE).

BACKGROUND: We investigated the effect of crenezumab, a humanized anti-amyloid-beta (Aß) immunoglobulin (Ig)G4 monoclonal antibody, on biomarkers of amyloid pathology, neurodegeneration, and disease progression in patients with mild-to-moderate Alzheimer's disease (AD). METHODS: This double-blind, placebo-controlled, randomized phase II study enrolled patients with mild-to-moderate AD and a Mini-Mental State Examination (MMSE) score of 18-26. In part 1 of the study, patients were 2:1 randomized to receive low-dose subcutaneous (SC) 300 mg crenezumab every 2 weeks (q2w) or placebo for 68 weeks; in part 2, patients were 2:1 randomized to receive high-dose intravenous (IV) 15 mg/kg crenezumab every 4 weeks (q4w) or placebo for 68 weeks. The primary endpoint was change in amyloid burden from baseline to week 69 assessed by florbetapir positron emission tomography (PET) in the modified intent-to-treat population. Secondary endpoints were change from baseline to week 69 in cerebrospinal fluid (CSF) biomarkers and fluorodeoxyglucose PET, and change from baseline to week 73 in 12-point Alzheimer's Disease Assessment Scale cognitive subscale (ADAS-Cog12) and Clinical Dementia Rating Sum of Boxes (CDR-SB). Safety was assessed in patients who received at least one dose of study treatment. RESULTS: From August 2011 to September 2012, 91 patients were enrolled and randomized (low-dose SC cohort: crenezumab (n = 26) or placebo (n = 13); high-dose IV cohort: crenezumab (n = 36) or placebo (n = 16)). The primary endpoint was not met using a prespecified cerebellar reference region to calculate standard uptake value ratios (SUVRs) from florbetapir PET. Exploratory analyses using subcortical white matter reference regions showed nonsignificant trends toward slower accumulation of plaque amyloid in the high-dose IV cohort. In both cohorts, a significant mean increase from baseline in CSF Aß(1-42) levels versus placebo was observed. Nonsignificant trends toward ADAS-Cog12 and CDR-SB benefits were identified in a mild (MMSE 20-26) subset of the high-dose IV cohort. No amyloid-related imaging abnormalities due to edema/effusion were observed. CONCLUSION: The primary endpoint was not met. Exploratory findings suggest potential Aß target engagement with crenezumab and possible slower accumulation of plaque amyloid. Studies investigating the effects of higher doses of crenezumab on amyloid load and disease progression are ongoing. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01397578 . Registered on 18 July 2011.

Targeting factor D of the alternative complement pathway reduces geographic atrophy progression secondary to age-related macular degeneration.

Geographic atrophy is an advanced form of age-related macular degeneration (AMD) and a leading cause of vision loss for which there are no approved treatments. Genetic studies in AMD patients have implicated dysregulation of the alternative complement pathway in the pathogenesis of geographic atrophy. Lampalizumab is a potential therapeutic that targets complement factor D, a pivotal activator of the alternative complement pathway. The MAHALO phase 2 clinical trial was a multicenter, randomized, controlled study that evaluated lampalizumab administered by intravitreal injection monthly (n = 42) and every other month (n = 41) versus sham control (n = 40) in patients with geographic atrophy secondary to AMD. The primary endpoint was the mean change in lesion area from baseline to month 18 as measured by fundus autofluorescence. Specific AMD-associated genetic polymorphisms were also analyzed. The MAHALO study met its primary efficacy endpoint with an acceptable safety profile; monthly lampalizumab treatment demonstrated a 20% reduction in lesion area progression versus sham control [80% confidence interval (CI), 4 to 37%]. A more substantial monthly treatment benefit of 44% reduction in geographic atrophy area progression versus sham control (95% CI, 15 to 73%) was observed in a subgroup of complement factor I (CFI) risk-allele carriers (57% of the patients analyzed were CFI risk-allele carriers). The MAHALO study shows a potential treatment effect in patients with geographic atrophy and supports therapeutic targeting of the alternative complement pathway for treating AMD pathogenesis.

Development and evaluation of a multiplexed mass spectrometry based assay for measuring candidate peptide biomarkers in Alzheimer's Disease Neuroimaging Initiative (ADNI) CSF.

PURPOSE: We describe the outcome of the Biomarkers Consortium CSF Proteomics Project (where CSF is cerebral spinal fluid), a public-private partnership of government, academia, nonprofit, and industry. The goal of this study was to evaluate a multiplexed MS-based approach for the qualification of candidate Alzheimer's disease (AD) biomarkers using CSF samples from the AD Neuroimaging Initiative. EXPERIMENTAL DESIGN: Reproducibility of sample processing, analytic variability, and ability to detect a variety of analytes of interest were thoroughly investigated. Multiple approaches to statistical analyses assessed whether panel analytes were associated with baseline pathology (mild cognitive impairment (MCI), AD) versus healthy controls or associated with progression for MCI patients, and included (i) univariate association analyses, (ii) univariate prediction models, (iii) exploratory multivariate analyses, and (iv) supervised multivariate analysis. RESULTS: A robust targeted MS-based approach for the qualification of candidate AD biomarkers was developed. The results identified several peptides with potential diagnostic or predictive utility, with the most significant differences observed for the following peptides for differentiating (including peptides from hemoglobin A, hemoglobin B, and superoxide dismutase) or predicting (including peptides from neuronal pentraxin-2, neurosecretory protein VGF (VGF), and secretogranin-2) progression versus nonprogression from MCI to AD. CONCLUSIONS AND CLINICAL RELEVANCE: These data provide potential insights into the biology of CSF in AD and MCI progression and provide a novel tool for AD researchers and clinicians working to improve diagnostic accuracy, evaluation of treatment efficacy, and early diagnosis.

Identification of longitudinally dynamic biomarkers in Alzheimer's disease cerebrospinal fluid by targeted proteomics.

BACKGROUND: Alzheimer's disease (AD) is the leading cause of dementia affecting greater than 26 million people worldwide. Although cerebrospinal fluid (CSF) levels of Aß42, tau, and p-tau181 are well established as diagnostic biomarkers of AD, there is a need for additional CSF biomarkers of neuronal function that continue to change during disease progression and could be used as pharmacodynamic measures in clinical trials. Multiple proteomic discovery experiments have reported a range of CSF biomarkers that differ between AD and control subjects. These potential biomarkers represent multiple aspects of the disease pathology. The performance of these markers has not been compared with each other, and their performance has not been evaluated longitudinally. RESULTS: We developed a targeted-proteomic, multiple reaction monitoring (MRM) assay for the absolute quantitation of 39 peptides corresponding to 30 proteins. We evaluated the candidate biomarkers in longitudinal CSF samples collected from aged, cognitively-normal control (n = 10), MCI (n = 5), and AD (n = 45) individuals (age > 60 years). We evaluated each biomarker for diagnostic sensitivity, longitudinal consistency, and compared with CSF Aß42, tau, and p-tau181. Four of 28 quantifiable CSF proteins were significantly different between aged, cognitively-normal controls and AD subjects including chitinase-3-like protein 1, reproducing published results. Four CSF markers demonstrated significant longitudinal change in AD: Amyloid precursor protein, Neuronal pentraxin receptor, NrCAM and Chromogranin A. Robust correlations were observed within some subgroups of proteins including the potential disease progression markers. CONCLUSION: Using a targeted proteomics approach, we confirmed previous findings for a subset of markers, defined longitudinal performance of our panel of markers, and established a flexible proteomics method for robust multiplexed analyses.

Inhibition of IgE-mediated secretion from human basophils with a highly selective Bruton's tyrosine kinase, Btk, inhibitor.

The study of receptor-mediated signaling in human basophils is often limited by the availability of selective pharmacological agents. The early signaling reaction mediated by FcεRI aggregation is thought to require the activity of Bruton's tyrosine kinase (btk), an enzyme that has been identified as important in B cells signaling because mutations lead to X-linked agammaglobulinemia. This study uses the btk selective irreversible inhibitor, PCI-32765, to explore the role of btk in a variety of functions associated with the activation of human basophils. Nine endpoints of basophil activation were examined: induced cell surface expression of CD63, CD203c, CD11b; induced secretion of histamine, LTC4, IL-4 and IL-13; the cytosolic calcium response; and the induced loss of syk kinase. Four stimuli were examined; anti-IgE antibody, formyl-met-leu-phe (FMLP), C5a and IL-3. For stimulation with anti-IgE, PCI-32765 inhibited CD63, histamine, LTC4 and IL-4 secretion with an IC50 of 3-6 nM (with 100% inhibition at 50 nM) and it inhibited CD203c and CD11b and the cytosolic calcium response with and IC50 of 30-40 nM. Fifty percent occupancy of btk with PCI-32765 occurred at ~10nM. Consistent with btk functioning downstream or in parallel to syk activation, PCI-32765 did not inhibit the loss of syk induced by anti-IgE in overnight cultures. Finally, PCI-32765 did not significantly inhibit basophil activation by FMLP or C5a and did not inhibit IL-13 release induced by IL-3. These results suggest that btk is specifically required for IgE-mediated activation of human basophils.

Identification of substrates of human protein-tyrosine phosphatase PTPN22.

Stimulation of mature T cells activates a downstream signaling cascade involving temporally and spatially regulated phosphorylation and dephosphorylation events mediated by protein-tyrosine kinases and phosphatases, respectively. PTPN22 (Lyp), a non-receptor protein-tyrosine phosphatase, is expressed exclusively in cells of hematopoietic origin, notably in T cells where it represses signaling through the T cell receptor. We used substrate trapping coupled with mass spectrometry-based peptide identification in an unbiased approach to identify physiological substrates of PTPN22. Several potential substrates were identified in lysates from pervanadate-stimulated Jurkat cells using PTPN22-D195A/C227S, an optimized substrate trap mutant of PTPN22. These included three novel PTPN22 substrates (Vav, CD3epsilon, and valosin containing protein) and two known substrates of PEP, the mouse homolog of PTPN22 (Lck and Zap70). T cell antigen receptor (TCR) zeta was also identified as a potential substrate in Jurkat lysates by direct immunoblotting. In vitro experiments with purified recombinant proteins demonstrated that PTPN22-D195A/C227S interacted directly with activated Lck, Zap70, and TCRzeta, confirming the initial substrate trap results. Native PTPN22 dephosphorylated Lck and Zap70 at their activating tyrosine residues Tyr-394 and Tyr-493, respectively, but not at the regulatory tyrosines Tyr-505 (Lck) or Tyr-319 (Zap70). Native PTPN22 also dephosphorylated TCRzeta in vitro and in cells, and its substrate trap variant co-immunoprecipitated with TCRzeta when both were coexpressed in 293T cells, establishing TCRzeta as a direct substrate of PTPN22.

A missense single-nucleotide polymorphism in a gene encoding a protein tyrosine phosphatase (PTPN22) is associated with rheumatoid arthritis.

Rheumatoid arthritis (RA) is the most common systemic autoimmune disease, affecting approximately 1% of the adult population worldwide, with an estimated heritability of 60%. To identify genes involved in RA susceptibility, we investigated the association between putative functional single-nucleotide polymorphisms (SNPs) and RA among white individuals by use of a case-control study design; a second sample was tested for replication. Here we report the association of RA susceptibility with the minor allele of a missense SNP in PTPN22 (discovery-study allelic P=6.6 x 10(-4); replication-study allelic P=5.6 x 10(-8)), which encodes a hematopoietic-specific protein tyrosine phosphatase also known as "Lyp." We show that the risk allele, which is present in approximately 17% of white individuals from the general population and in approximately 28% of white individuals with RA, disrupts the P1 proline-rich motif that is important for interaction with Csk, potentially altering these proteins' normal function as negative regulators of T-cell activation. The minor allele of this SNP recently was implicated in type 1 diabetes, suggesting that the variant phosphatase may increase overall reactivity of the immune system and may heighten an individual carrier's risk for autoimmune disease.