The Impact of Autoantibodies on Outcomes in Patients with Idiopathic Pulmonary Fibrosis: Post-Hoc Analyses of the Phase III ASCEND Trial.

INTRODUCTION: Clinical practice guidelines recommend autoimmune serological testing in patients newly diagnosed with interstitial lung disease of apparently unknown cause who may have idiopathic pulmonary fibrosis (IPF), in order to exclude connective tissue disease (CTD). Autoantibody positivity has been associated with unique patient profiles and prognosis in patients with IPF who otherwise lack a CTD diagnosis. METHODS: This post-hoc analysis of patients with IPF from the Phase III ASCEND trial (NCT01366209) evaluated the association of antinuclear antibodies (ANA), rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) status with baseline disease characteristics, disease progression [percent predicted forced vital capacity (%FVC), forced vital capacity (FVC) volume and progression-free survival (PFS)], and treatment outcomes with pirfenidone and placebo (%FVC, FVC and PFS). RESULTS: Of 555 participants, 244/514 (47.5%) were ANA positive (ANA+), 83/514 (16.1%) had high ANA+ (ANA titre ≥ 1:160 or positive nucleolar- or centromere-staining patterns), 60/555 (10.8%) were RF positive (RF+) and/or anti-CCP positive (anti-CCP+) and 270/514 (52.5%) were autoantibody negative (AAb-). Baseline demographics and characteristics were generally comparable between autoantibody subgroups. Although not statistically significant, more placebo-treated participants with ANA+ or high ANA+ had a decline from baseline to Week 52 of ≥ 10% in %FVC or death (48.7% and 55.9%, respectively) or in FVC volume or death (48.7% and 47.1%, respectively) compared with the AAb- group (%FVC or death: 42.0%; FVC volume or death: 42.0%). The RF+ and/or anti-CCP+ group was similar to AAb-. No differences were observed in PFS. A treatment benefit for pirfenidone versus placebo was observed regardless of autoantibody status [PFS: ANA+ HR (95% CI): 0.56 (0.37 to 0.86), P = 0.007; AAb- HR (95% CI): 0.50 (0.32 to 0.78), P = 0.002]. CONCLUSION: IPF disease course did not differ by autoantibody status in ASCEND. Pirfenidone had a treatment benefit regardless of the presence of ANA. TRIAL REGISTRATION: ClinicalTrials.gov identifier, NCT01366209.

People with idiopathic pulmonary fibrosis sometimes have abnormal antibodies, called autoantibodies, in their blood. Uncommonly, autoantibodies may mistakenly target the person's own tissues, including the lungs. It is unknown whether these autoantibodies cause idiopathic pulmonary fibrosis or make it worse. This analysis looked at data from the ASCEND clinical trial in people with idiopathic pulmonary fibrosis, who were split randomly into two groups to receive tablets of either a medicine called pirfenidone or a placebo for 52 weeks. One goal was to see whether people with certain autoantibodies called antinuclear antibodies ('ANA' for short), rheumatoid factor ('RF') and anti-cyclic citrullinated peptide ('anti-CCP') had different traits from people without autoantibodies, such as age, race or smoking history. Other goals were to see if autoantibodies affected (1) how well people's lungs worked during the trial, (2) how quickly people's idiopathic pulmonary fibrosis got worse or they died and (3) how well pirfenidone worked. The analysis showed that most traits were similar in people with and without autoantibodies. In people who received placebo, the change in lung function during the trial was not different for people with ANA, RF or anti-CCP compared with people with no autoantibodies. People who received pirfenidone were less likely to have worsening lung function, or die, than people who received placebo, regardless of whether or not they had autoantibodies. Doctors evaluating patients with idiopathic pulmonary fibrosis should consider the impact of autoantibodies and feel confident that pirfenidone is effective regardless of whether or not autoantibodies are present.

High Interleukin-13 level is associated with disease stability in interstitial Lung disease.

Purpose: Cytokines can help predict prognosis in interstitial lung disease (ILD) and to differentiate between ILD subtypes. The objectives of our study were to evaluate association of baseline cytokine levels with time to ILD progression and to compare baseline cytokine levels between ILD subtypes. Methods: We quantified 27 cytokines using a multiplex assay in peripheral blood samples from 77 patients. Cox proportional hazards regression analysis was performed to evaluate cytokine impact on the time to progression in the total cohort and within each ILD type. We evaluated for significant differences in cytokine levels between ILD types using ANOVA, Wilcoxon signed-rank test and Tukey method. Results: Higher IL-13 level was associated with longer time to progression (hazard ratio 0.52 [0.33-0.81], p-value 0.004). FGF-ß, GM-CSF, and IL-17 levels differed significantly between fibrotic and inflammatory ILD subgroups. Conclusion: IL-13 may be a useful biomarker predicting ILD stability.

Biological Age, Chronological Age and Survival in Pulmonary Fibrosis: A Causal Mediation Analysis.

RATIONALE: Accelerated biological aging has been implicated in the development of interstitial lung disease (ILD) and other diseases of aging but remains poorly understood. OBJECTIVES: To identify plasma proteins that mediate the relationship between chronological age and survival association in patients with ILD. METHODS: Causal mediation analysis was performed to identify plasma proteins that mediated the chronological age-survival relationship in an idiopathic pulmonary fibrosis (IPF) discovery cohort. Proteins mediating this relationship after adjustment for false discovery were advanced for testing in an independent ILD validation cohort and explored in a chronic obstructive pulmonary disease (COPD) cohort. A proteomic-based measure of biological age was constructed and survival analysis performed assessing the impact of biological age and peripheral blood telomere length on the chronological age-survival relationship. RESULTS: Twenty-two proteins mediated the chronological age-survival relationship after adjustment for false discovery in the IPF discovery cohort (n=874), with nineteen remaining significant mediators of this relationship in the ILD validation cohort (n=983) and one mediating this relationship in the COPD cohort. Latent transforming growth factor beta binding protein 2 and ectodysplasin A2 receptor showed the strongest mediation across cohorts. A proteomic measure of biological age completely attenuated the chronological age-survival association and better discriminated survival than chronological age. Results were robust to adjustment for peripheral blood telomere length, which did not mediate the chronological age-survival relationship. CONCLUSIONS: Molecular measures of aging completely mediate the relationship between chronological age and survival, suggesting that chronological age has no direct effect on ILD survival.

Molecular Endotypes of Idiopathic Pulmonary Fibrosis: A Latent Class Analysis of Two Multicenter Observational Cohorts.

Rationale: Idiopathic pulmonary fibrosis (IPF) causes irreversible fibrosis of the lung parenchyma. Although antifibrotic therapy can slow IPF progression, treatment response is variable. There exists a critical need to develop a precision medicine approach to IPF. Objectives: To identify and validate biologically driven molecular endotypes of IPF. Methods: Latent class analysis (LCA) was independently performed in prospectively recruited discovery (n = 875) and validation (n = 347) cohorts. Twenty-five plasma biomarkers associated with fibrogenesis served as class-defining variables. The association between molecular endotype and 4-year transplant-free survival was tested using multivariable Cox regression adjusted for baseline confounders. Endotype-dependent differential treatment response to future antifibrotic exposure was then assessed in a pooled cohort of patients naive to antifibrotic therapy at the time of biomarker measurement (n = 555). Measurements and Main Results: LCA independently identified two latent classes in both cohorts (P < 0.0001). WFDC2 (WAP four-disulfide core domain protein 2) was the most important determinant of class membership across cohorts. Membership in class 2 was characterized by higher biomarker concentrations and a higher risk of death or transplant (discovery, hazard ratio [HR], 2.02; 95% confidence interval [CI], 1.64-2.48; P < 0.001; validation, HR, 1.95; 95% CI, 1.34-2.82; P < 0.001). In pooled analysis, significant heterogeneity in treatment effect was observed between endotypes (P = 0.030 for interaction), with a favorable antifibrotic response in class 2 (HR, 0.64; 95% CI, 0.45-0.93; P = 0.018) but not in class 1 (HR, 1.19; 95% CI, 0.77-1.84; P = 0.422). Conclusions: In this multicohort study, we identified two novel molecular endotypes of IPF with divergent clinical outcomes and responses to antifibrotic therapy. Pending further validation, these endotypes could enable a precision medicine approach for future IPF clinical trials.

Telomere length and immunosuppression in non-idiopathic pulmonary fibrosis interstitial lung disease.

BACKGROUND: Studies suggest a harmful pharmacogenomic interaction exists between short leukocyte telomere length (LTL) and immunosuppressants in idiopathic pulmonary fibrosis (IPF). It remains unknown if a similar interaction exists in non-IPF interstitial lung disease (ILD). METHODS: A retrospective, multicentre cohort analysis was performed in fibrotic hypersensitivity pneumonitis (fHP), unclassifiable ILD (uILD) and connective tissue disease (CTD)-ILD patients from five centres. LTL was measured by quantitative PCR for discovery and replication cohorts and expressed as age-adjusted percentiles of normal. Inverse probability of treatment weights based on propensity scores were used to assess the association between mycophenolate or azathioprine exposure and age-adjusted LTL on 2-year transplant-free survival using weighted Cox proportional hazards regression incorporating time-dependent immunosuppressant exposure. RESULTS: The discovery and replication cohorts included 613 and 325 patients, respectively. In total, 40% of patients were exposed to immunosuppression and 22% had LTL <10th percentile of normal. fHP and uILD patients with LTL <10th percentile experienced reduced survival when exposed to either mycophenolate or azathioprine in the discovery cohort (mortality hazard ratio (HR) 4.97, 95% CI 2.26-10.92; p<0.001) and replication cohort (mortality HR 4.90, 95% CI 1.74-13.77; p=0.003). Immunosuppressant exposure was not associated with differential survival in patients with LTL ≥10th percentile. There was a significant interaction between LTL <10th percentile and immunosuppressant exposure (discovery pinteraction=0.013; replication pinteraction=0.011). Low event rate and prevalence of LTL <10th percentile precluded subgroup analyses for CTD-ILD. CONCLUSION: Similar to IPF, fHP and uILD patients with age-adjusted LTL <10th percentile may experience reduced survival when exposed to immunosuppression.

Evaluation of Pulmonary Fibrosis Outcomes by Race and Ethnicity in US Adults.

Importance: Pulmonary fibrosis (PF) is characterized by progressive scarring of lung tissue and poor survival. Racial and ethnic minority populations face the greatest risk of morbidity and mortality from disparities impacting respiratory health, but the pattern of age at clinically relevant outcomes across diverse racial and ethnic populations with PF is unknown. Objective: To compare the age at PF-related outcomes and the heterogeneity in survival patterns among Hispanic, non-Hispanic Black, and non-Hispanic White participants. Design, Setting, and Participants: This cohort study included adult patients with a PF diagnosis and used data from prospective clinical registries: the Pulmonary Fibrosis Foundation Registry (PFFR) for the primary cohort and registries from 4 geographically distinct tertiary hospitals in the US for the external multicenter validation (EMV) cohort. Patients were followed between January 2003 and April 2021. Exposures: Race and ethnicity comparisons between Black, Hispanic, and White participants with PF. Main Outcomes and Measures: Age and sex distribution of participants were measured at the time of study enrollment. All-cause mortality and age at PF diagnosis, hospitalization, lung transplant, and death were assessed in participants over 14 389 person-years. Differences between racial and ethnic groups were compared using Wilcoxon rank sum tests, Bartlett 1-way analysis of variance, and χ2 tests, and crude mortality rates and rate ratios were assessed across racial and ethnic categories using Cox proportional hazards regression models. Results: In total, 4792 participants with PF were assessed (mean [SD] age, 66.1 [11.2] years; 2779 [58.0%] male; 488 [10.2%] Black, 319 [6.7%] Hispanic, and 3985 [83.2%] White); 1904 were in the PFFR and 2888 in the EMV cohort. Black patients with PF were consistently younger than White patients (mean [SD] age at baseline, 57.9 [12.0] vs 68.6 [9.6] years; P < .001). Hispanic and White patients were predominantly male (Hispanic: PFFR, 73 of 124 [58.9%] and EMV, 109 of 195 [55.9%]; and White: PFFR, 1090 of 1675 [65.1%] and EMV, 1373 of 2310 [59.4%]), while Black patients were less likely to be male (PFFR, 32 of 105 [30.5%] and EMV, 102 of 383 [26.6%]). Compared with White patients, Black patients had a lower crude mortality rate ratio (0.57 [95% CI, 0.31-0.97), but for Hispanic patients, the mortality rate ratio was similar to that of White patients (0.89; 95% CI, 0.57-1.35). Mean (SD) hospitalization events per person were highest among Black patients compared with Hispanic and White patients (Black: 3.6 [5.0]; Hispanic, 1.8 [1.4]; and White, 1.7 [1.3]; P < .001). Black patients were consistently younger than Hispanic and White patients at first hospitalization (mean [SD] age: Black, 59.4 [11.7] years; Hispanic, 67.5 [9.8] years; and White, 70.0 [9.3] years; P < .001), lung transplant (Black, 58.6 [8.6] years; Hispanic, 60.5 [6.1] years; and White, 66.9 [6.7] years; P < .001), and death (Black, 68.7 [8.4] years; Hispanic, 72.9 [7.6] years; and White, 73.5 [8.7] years; P < .001). These findings remained consistent in the replication cohort and in sensitivity analyses within prespecified deciles of age groups. Conclusions and Relevance: In this cohort study of participants with PF, racial and ethnic disparities, especially among Black patients, were found in PF-related outcomes, including earlier onset of death. Further research is essential to identify and mitigate the underlying responsible factors.

Telomere length associates with chronological age and mortality across racially diverse pulmonary fibrosis cohorts.

Pulmonary fibrosis (PF) is characterized by profound scarring and poor survival. We investigated the association of leukocyte telomere length (LTL) with chronological age and mortality across racially diverse PF cohorts. LTL measurements among participants with PF stratified by race/ethnicity were assessed in relation to age and all-cause mortality, and compared to controls. Generalized linear models were used to evaluate the age-LTL relationship, Cox proportional hazards models were used for hazard ratio estimation, and the Cochran-Armitage test was used to assess quartiles of LTL. Standardized LTL shortened with increasing chronological age; this association in controls was strengthened in PF (R = -0.28; P < 0.0001). In PF, age- and sex-adjusted LTL below the median consistently predicted worse mortality across all racial groups (White, HR = 2.21, 95% CI = 1.79-2.72; Black, HR = 2.22, 95% CI = 1.05-4.66; Hispanic, HR = 3.40, 95% CI = 1.88-6.14; and Asian, HR = 2.11, 95% CI = 0.55-8.23). LTL associates uniformly with chronological age and is a biomarker predictive of mortality in PF across racial groups.

Validation of Proposed Criteria for Progressive Pulmonary Fibrosis.

Rationale: Criteria for progressive pulmonary fibrosis (PPF) have been proposed, but their prognostic value beyond categorical decline in FVC remains unclear. Objectives: To determine whether proposed PPF criteria predict transplant-free survival (TFS) in patients with non-idiopathic pulmonary fibrosis (IPF) forms of interstitial lung disease (ILD). Methods: A retrospective, multicenter cohort analysis was performed. Patients with diagnoses of fibrotic connective tissue disease-associated ILD, fibrotic hypersensitivity pneumonitis, and non-IPF idiopathic interstitial pneumonia from three U.S. centers and one UK center constituted the test and validation cohorts, respectively. Cox proportional hazards regression was used to test the association between 5-year TFS and ⩾10% FVC decline, followed by 13 additional PPF criteria satisfied in the absence of ⩾10% FVC decline. Measurements and Main Results: One thousand three hundred forty-one patients met the inclusion criteria. A ⩾10% relative FVC decline was the strongest predictor of reduced TFS and showed consistent TFS association across cohorts, ILD subtypes, and treatment groups, resulting in a phenotype that closely resembled IPF. Ten additional PPF criteria satisfied in the absence of 10% relative FVC decline were also associated with reduced TFS in the U.S. test cohort, with 6 maintaining TFS associations in the UK validation cohort. Validated PPF criteria requiring a combination of physiologic, radiologic, and symptomatic worsening performed similarly to their stand-alone components but captured a smaller number of patients. Conclusions: An FVC decline of ⩾10% and six additional PPF criteria satisfied in the absence of such decline identify patients with non-IPF ILD at increased risk for death or lung transplantation.

Utility of whole genome sequencing in assessing risk and clinically relevant outcomes for pulmonary fibrosis.

BACKGROUND: Whole genome sequencing (WGS) can detect variants and estimate telomere length. The clinical utility of WGS in estimating risk, progression and survival of pulmonary fibrosis patients is unknown. METHODS: In this observational cohort study, we performed WGS on 949 patients with idiopathic pulmonary fibrosis or familial pulmonary fibrosis to determine rare and common variant genotypes, estimate telomere length and assess the association of genomic factors with clinical outcomes. RESULTS: WGS estimates of telomere length correlated with quantitative PCR (R=0.65) and Southern blot (R=0.71) measurements. Rare deleterious qualifying variants were found in 14% of the total cohort, with a five-fold increase in those with a family history of disease versus those without (25% versus 5%). Most rare qualifying variants (85%) were found in telomere-related genes and were associated with shorter telomere lengths. Rare qualifying variants had a greater effect on telomere length than a polygenic risk score calculated using 20 common variants previously associated with telomere length. The common variant polygenic risk score predicted telomere length only in sporadic disease. Reduced transplant-free survival was associated with rare qualifying variants, shorter quantitative PCR-measured telomere lengths and absence of the MUC5B promoter (rs35705950) single nucleotide polymorphism, but not with WGS-estimated telomere length or the common variant polygenic risk score. Disease progression was associated with both measures of telomere length (quantitative PCR measured and WGS estimated), rare qualifying variants and the common variant polygenic risk score. CONCLUSION: As a single test, WGS can inform pulmonary fibrosis genetic-mediated risk, evaluate the functional effect of telomere-related variants by estimating telomere length, and prognosticate clinically relevant disease outcomes.

Interstitial Pneumonia with Autoimmune Features: What the Rheumatologist Needs to Know.

PURPOSE OF REVIEW: This narrative review will focus on the role of the rheumatologist in evaluating patients with interstitial lung disease (ILD) without a defined rheumatic disease and will outline the current classification criteria for interstitial pneumonia with autoimmune features (IPAF) and describe what is known regarding IPAF pathobiology, natural history, prognosis, and treatment. Lastly, knowledge gaps and opportunities for future research will be discussed. RECENT FINDINGS: IPAF is a recently defined classification of ILD patients who have features suggesting an autoimmune-mediated process, but do not fulfill current rheumatic disease criteria. The goal of the IPAF criteria is to provide a uniform case definition for the study of autoimmune ILD patients who do not currently fit within standard ILD diagnostic categories, ultimately improving diagnosis and therapy. Many of these patients are referred for rheumatologic evaluation to aid the diagnostic process. The care of the IPAF patient is complex and is multidisciplinary with pulmonology, rheumatology, pathology, radiology, physical therapy, primary care, pulmonary transplant providers all serving vital roles. The rheumatologist has several roles which include classification, disease monitoring, and management.

Time-limited trials in the ICU: a mixed-methods sequential explanatory study of intensivists at two academic centres.

OBJECTIVE: To understand intensivist perceptions of the appropriateness of time-limited trials (TLTs)-a strategy to align life-sustaining care with patient goals and values in the midst of clinical uncertainty. DESIGN: We conducted a mixed-methods sequential explanatory study of intensive care unit (ICU) intensivists regarding appropriateness of utilising TLTs in three vignettes centred on invasive mechanical ventilation (IMV); continuous renal replacement therapy (CRRT); and heated high-flow nasal cannula (HHFNC). Semistructured interviews were conducted using the Tailored Implementation of Chronic Diseases framework. Data were analysed using thematic and matrix analysis. SETTING: Two academic medical centres in the USA participated in the randomised surveys and one centre participated in the semistructured interviews. PARTICIPANTS: Pulmonary and critical care intensivists and fellows. PRIMARY AND SECONDARY OUTCOMES: To understand intensivists perceptions of the appropriateness in using TLTs. RESULTS: Of 115 physicians surveyed, 71 initiated the survey and 44 completed the entire survey with a response rate of 38% (N=44/115) and a completion rate of 62% (N=44/71). While 35% (N=23/66) of intensivists had never heard of a TLT, of the intensivists who had heard of a TLT, 77% (N=33/43) had participated in one. In response to the vignettes, appropriateness of using a TLT varied (IMV: 74% (N=46/62); CRRT 78% (N=49/63); HHFNC 92% (N=56/61) as did the durations of the TLT. Semistructured interviews with 11 intensivists revealed having clarity about patient goals and clinical endpoints facilitated successful TLTs while lack of an evidenced-based framework was a barrier. CONCLUSION: More than half of the physicians who responded had conducted or participated in a TLT. To increase the use of TLTs in the ICU, clinicians desire a more robust, evidence-based framework on how to conduct TLTs.

Rare and Common Variants in KIF15 Contribute to Genetic Risk of Idiopathic Pulmonary Fibrosis.

Rationale: Genetic studies of idiopathic pulmonary fibrosis (IPF) have improved our understanding of this disease, but not all causal loci have been identified. Objectives: To identify genes enriched with rare deleterious variants in IPF and familial pulmonary fibrosis. Methods: We performed gene burden analysis of whole-exome data, tested single variants for disease association, conducted KIF15 (kinesin family member 15) functional studies, and examined human lung single-cell RNA sequencing data. Measurements and Main Results: Gene burden analysis of 1,725 cases and 23,509 control subjects identified heterozygous rare deleterious variants in KIF15, a kinesin involved in spindle separation during mitosis, and three telomere-related genes (TERT [telomerase reverse transcriptase], RTEL1 [regulator of telomere elongation helicase 1], and PARN [poly(A)-specific ribonuclease]). KIF15 was implicated in autosomal-dominant models of rare deleterious variants (odds ratio [OR], 4.9; 95% confidence interval [CI], 2.7-8.8; P = 2.55 × 10-7) and rare protein-truncating variants (OR, 7.6; 95% CI, 3.3-17.1; P = 8.12 × 10-7). Meta-analyses of the discovery and replication cohorts, including 2,966 cases and 29,817 control subjects, confirm the involvement of KIF15 plus the three telomere-related genes. A common variant within a KIF15 intron (rs74341405; OR, 1.6; 95% CI, 1.4-1.9; P = 5.63 × 10-10) is associated with IPF risk, confirming a prior report. Lymphoblastoid cells from individuals heterozygous for the common variant have decreased KIF15 and reduced rates of cell growth. Cell proliferation is dependent on KIF15 in the presence of an inhibitor of Eg5/KIF11, which has partially redundant function. KIF15 is expressed specifically in replicating human lung cells and shows diminished expression in replicating epithelial cells of patients with IPF. Conclusions: Both rare deleterious variants and common variants in KIF15 link a nontelomerase pathway of cell proliferation with IPF susceptibility.

The Role of Genetic Testing in Pulmonary Fibrosis: A Perspective From the Pulmonary Fibrosis Foundation Genetic Testing Work Group.

Patients with familial pulmonary fibrosis represent a subset of patients with pulmonary fibrosis in whom inherited gene variation predisposes them to disease development. In the appropriate setting, genetic testing allows for personalized assessment of disease, recognition of clinically relevant extrapulmonary manifestations, and assessing susceptibility in unaffected relatives. However currently, the use of genetic testing is inconsistent, partly because of the lack of guidance regarding high-yield scenarios in which the results of genetic testing can inform clinical decision-making. To address this, the Pulmonary Fibrosis Foundation commissioned a genetic testing work group comprising pulmonologists, geneticists, and genetic counselors from the United States to provide guidance on genetic testing in patients with pulmonary fibrosis. This CHEST special feature presents a concise review of these proceedings and reviews pulmonary fibrosis susceptibility, clinically available genetic testing methods, and clinical scenarios in which genetic testing should be considered.

Proteomic biomarkers of progressive fibrosing interstitial lung disease: a multicentre cohort analysis.

BACKGROUND: Progressive fibrosing interstitial lung disease (ILD) is characterised by parenchymal scar formation, leading to high morbidity and mortality. The ability to predict this phenotype remains elusive. We conducted a proteomic analysis to identify novel plasma biomarkers of progressive fibrosing ILD and developed a proteomic signature to predict this phenotype. METHODS: Relative plasma concentrations for 368 biomarkers were determined with use of a semi-quantitative, targeted proteomic platform in patients with connective tissue disease-associated ILD, chronic hypersensitivity pneumonitis, or unclassifiable ILD who provided research blood draws at the University of California (discovery cohort) and the University of Texas (validation cohort). Univariable logistic regression was used to identify individual biomarkers associated with 1-year ILD progression, defined as death, lung transplant, or 10% or greater relative forced vital capacity (FVC) decline. A proteomic signature of progressive fibrosing ILD was then derived with use of machine learning in the University of California cohort and validated in the University of Texas cohort. FINDINGS: The discovery cohort comprised 385 patients (mean age 63·6 years, 59% female) and the validation cohort comprised 204 patients (mean age 60·7 years, 61% female). 31 biomarkers were associated with progressive fibrosing ILD in the discovery cohort, with 17 maintaining an association in the validation cohort. Validated biomarkers showed a consistent association with progressive fibrosing ILD irrespective of ILD clinical diagnosis. A proteomic signature comprising 12 biomarkers was derived by machine learning and validated in the University of Texas cohort, in which it had a sensitivity of 0·90 and corresponding negative predictive value of 0·91, suggesting that approximately 10% of patients with a low-risk proteomic signature would experience ILD progression in the year after blood draw. Those with a low-risk proteomic signature experienced an FVC change of +85·7 mL (95% CI 6·9 to 164·4) and those with a high-risk signature experienced an FVC change of -227·1 mL (-286·7 to -167·5). A theoretical clinical trial restricted to patients with a high-risk proteomic signature would require 80% fewer patients than one designed without regard to proteomic signature. INTERPRETATION: 17 plasma biomarkers of progressive fibrosing ILD were identified and showed consistent associations across ILD subtypes. A proteomic signature of progressive fibrosing ILD could enrich clinical trial cohorts and avoid the need for antecedent progression when defining progressive fibrosing ILD for clinical trial enrolment. FUNDING: National Heart Lung and Blood Institute.