The Association of Class I and II Human Leukocyte Antigen Serotypes With End-Stage Kidney Disease Due to Membranoproliferative Glomerulonephritis and Dense Deposit Disease.

RATIONALE & OBJECTIVE: Membranoproliferative glomerulonephritis (MPGN), encompassing several distinct diseases, is a rare but significant cause of kidney failure in the United States. The potential etiologies of MPGN are unclear, but prior studies have suggested dysregulation of the alternative complement pathway and, recently, autoimmunity as potential mechanisms driving MPGN pathogenesis. In this study, we examined HLA associations with end-stage kidney disease (ESKD) due to MPGN and dense deposit disease (DDD) in a large racially and ethnically diverse US-based cohort. STUDY DESIGN: Case-control study. SETTING & PARTICIPANTS: Using US Renal Data System (USRDS) and United Network for Organ Sharing (UNOS) data, we identified 3,424 patients with kidney failure due to MPGN and 263 due to DDD. We matched patients to kidney donor controls on designated race and ethnicity in a 1:15 ratio. EXPOSURE: 58 class I and II HLA serotypes. OUTCOME: Case-control status. ANALYTICAL APPROACH: For each disease cohort, univariable and multivariable logistic regression analyses were used to investigate associations between the disease and 58 HLA serotypes. In subgroup analyses, we investigated HLA associations in White and Black patients. We also studied antiglomerular basement membrane (anti-GBM) nephritis as a positive-control outcome. We applied a Bonferroni correction to account for multiple comparisons. RESULTS: Eighteen serotypes were significantly associated with the odds of having MPGN in univariable analyses, with DR17 having the strongest association (odds ratio [OR], 1.55 [95% CI, 1.44-1.68], P=4.33e-28). No significant associations were found between any HLA serotype and DDD. Designated race-specific analyses showed comparable findings. We recapitulated known HLA associations in anti-GBM nephritis. LIMITATIONS: Reliance on HLA serotypes (rather than genotype), lack of biopsy-confirmed diagnoses. CONCLUSIONS: HLA-DR17 is associated with ESKD due to MPGN in a racially and ethnically diverse cohort. The strength of association was similar in White and Black patients, suggesting a role in the pathogenesis of MPGN. No HLA associations were observed in patients with DDD. PLAIN-LANGUAGE SUMMARY: Prior studies have suggested dysregulation of the alternative complement pathway as a potential etiology of membranoproliferative glomerulonephritis (MPGN), but recent evidence from a British White population has implicated an autoimmune mechanism in MPGN pathogenesis. We investigated HLA associations between MPGN and dense deposit disease (DDD) in a large racially and ethnically diverse cohort of patients. We found that HLA-DR17 is associated with end-stage kidney disease (ESKD) due to MPGN in both White and Black patients. By contrast, no significant HLA associations with ESKD due to DDD were identified. These results suggest a role for autoimmunity in some cases of MPGN and highlight differences in the disease etiology of MPGN compared with DDD.

Implementation, Evolution, and Laboratory Performance of Methods-Based Proficiency Testing for Next-Generation Sequencing Detection of Germline Sequence Variants.

CONTEXT.­: Next-generation sequencing (NGS)-based assays are used for diagnosis of diverse inherited disorders. Limited data are available pertaining to interlaboratory analytical performance of these assays. OBJECTIVE.­: To report on the College of American Pathologists (CAP) NGS Germline Program, which is methods based, and explore the evolution in laboratory testing practices. DESIGN.­: Results from the NGS Germline Program from 2016-2020 were analyzed for interlaboratory analytical performance. Self-reported laboratory testing practices were also evaluated. RESULTS.­: From 2016-2020, a total of 297 laboratories participated in at least 1 program mailing. Of the 289 laboratories that provided information on tests offered, 138 (47.8%) offered only panel testing throughout their enrollment, while 35 (12.1%) offered panels and exome testing, 30 (10.4%) offered only exomes, 9 (3.1%) offered only genomes, and 15 (5.2%) offered panels, exomes, and genomes. The remainder (62 laboratories, 21.4%) changed their test offerings during the 2016-2020 timeframe. Considering each genomic position/interval, the median detection percentage at variant positions across the 2016-2020 mailings ranged from 94.3% to 100%, while at reference positions (no variant detected), the median correct response percentage was 100% across all mailings. When considering performance of individual laboratories, 89.5% (136 of 152) to 98.0% (149 of 152) of laboratories successfully met the detection threshold (≥90% of the variants present), while 94.6% (87 of 92) to 100% (163 of 163) of laboratories met the 95% specificity threshold across mailings. CONCLUSIONS.­: Since the inception of this program, laboratories have consistently performed well. The median sensitivity and specificity of detection of sequence variants included in this program (eg, single nucleotide variants, insertions, and deletions) were 100.0%.

Minimal/Measurable Residual Disease Monitoring in Patients with Lymphoid Neoplasms by High-Throughput Sequencing of the T-Cell Receptor.

High-throughput sequencing of the T-cell receptor beta (TRB) and gamma (TRG) loci is increasingly utilized due to its high sensitivity, specificity, and versatility in the diagnosis of various T-cell malignancies. Application of these technologies for tracking disease burden can be valuable in detecting recurrence, determining response to therapy, guiding future management of patients, and establishing endpoints for clinical trials. In this study, the performance of the commercially available LymphoTrack high-throughput sequencing assay was assessed for determining residual disease burden in patients with various T-cell malignancies. A custom bioinformatics pipeline and database was also developed to facilitate minimal/measurable residual disease analysis and clinical reporting. This assay demonstrated excellent test performance characteristics, achieving a sensitivity of 1 of 100,000 T-cell equivalents for the DNA inputs evaluated and high concordance with orthogonal testing methods. This assay was further utilized to correlate disease burden in several patients, demonstrating its potential utility for monitoring patients with T-cell malignancies.

Primary Graft Dysfunction Is Associated With Development of Early Cardiac Allograft Vasculopathy, but Not Other Immune-mediated Complications, After Heart Transplantation.

BACKGROUND: We investigated associations between primary graft dysfunction (PGD) and development of acute cellular rejection (ACR), de novo donor-specific antibodies (DSAs), and cardiac allograft vasculopathy (CAV) after heart transplantation (HT). METHODS: A total of 381 consecutive adult HT patients from January 2015 to July 2020 at a single center were retrospectively analyzed. The primary outcome was incidence of treated ACR (International Society for Heart and Lung Transplantation grade 2R or 3R) and de novo DSA (mean fluorescence intensity >500) within 1 y post-HT. Secondary outcomes included median gene expression profiling score and donor-derived cell-free DNA level within 1 y and incidence of cardiac allograft vasculopathy (CAV) within 3 y post-HT. RESULTS: When adjusted for death as a competing risk, the estimated cumulative incidence of ACR (PGD 0.13 versus no PGD 0.21; P = 0.28), median gene expression profiling score (30 [interquartile range, 25-32] versus 30 [interquartile range, 25-33]; P = 0.34), and median donor-derived cell-free DNA levels was similar in patients with and without PGD. After adjusting for death as a competing risk, estimated cumulative incidence of de novo DSA within 1 y post-HT in patients with PGD was similar to those without PGD (0.29 versus 0.26; P = 0.10) with a similar DSA profile based on HLA loci. There was increased incidence of CAV in patients with PGD compared with patients without PGD (52.6% versus 24.8%; P = 0.01) within the first 3 y post-HT. CONCLUSIONS: During the first year after HT, patients with PGD had a similar incidence of ACR and development of de novo DSA, but a higher incidence of CAV when compared with patients without PGD.

The role of CD8+ T-cell clones in immune thrombocytopenia.

Immune thrombocytopenia (ITP) is traditionally considered an antibody-mediated disease. However, a number of features suggest alternative mechanisms of platelet destruction. In this study, we use a multidimensional approach to explore the role of cytotoxic CD8+ T cells in ITP. We characterized patients with ITP and compared them with age-matched controls using immunophenotyping, next-generation sequencing of T-cell receptor (TCR) genes, single-cell RNA sequencing, and functional T-cell and platelet assays. We found that adults with chronic ITP have increased polyfunctional, terminally differentiated effector memory CD8+ T cells (CD45RA+CD62L-) expressing intracellular interferon gamma, tumor necrosis factor α, and granzyme B, defining them as TEMRA cells. These TEMRA cells expand when the platelet count falls and show no evidence of physiological exhaustion. Deep sequencing of the TCR showed expanded T-cell clones in patients with ITP. T-cell clones persisted over many years, were more prominent in patients with refractory disease, and expanded when the platelet count was low. Combined single-cell RNA and TCR sequencing of CD8+ T cells confirmed that the expanded clones are TEMRA cells. Using in vitro model systems, we show that CD8+ T cells from patients with ITP form aggregates with autologous platelets, release interferon gamma, and trigger platelet activation and apoptosis via the TCR-mediated release of cytotoxic granules. These findings of clonally expanded CD8+ T cells causing platelet activation and apoptosis provide an antibody-independent mechanism of platelet destruction, indicating that targeting specific T-cell clones could be a novel therapeutic approach for patients with refractory ITP.

Longitudinal study of 2 patients with cyclic thrombocytopenia, STAT3 and MPL mutations.

Cyclic thrombocytopenia (CTP) is a rare disease of periodic platelet count oscillations. The pathogenesis of CTP remains elusive. To study the underlying pathophysiology and genetic and cellular associations with CTP, we applied systems biology approaches to 2 patients with stable platelet cycling and reciprocal thrombopoietin (TPO) cycling at multiple time points through 2 cycles. Blood transcriptome analysis revealed cycling of platelet-specific genes, which are in parallel with and precede platelet count oscillation, indicating that cyclical platelet production leads platelet count cycling in both patients. Additionally, neutrophil and erythrocyte-specific genes also showed fluctuations correlating with platelet count changes, consistent with TPO effects on hematopoietic progenitors. Moreover, we found novel genetic associations with CTP. One patient had a novel germline heterozygous loss-of-function (LOF) thrombopoietin receptor (MPL) c.1210G>A mutation, and both had pathogenic somatic gain-of-function (GOF) variants in signal transducer and activator of transcription 3 (STAT3). In addition, both patients had clonal T-cell populations that remained stable throughout platelet count cycles. These mutations and clonal T cells may potentially involve in the pathogenic baseline in these patients, rendering exaggerated persistent thrombopoiesis oscillations of their intrinsic rhythm upon homeostatic perturbations. This work provides new insights into the pathophysiology of CTP and possible therapies.

Complement-Binding Donor-Specific Anti-HLA Antibodies: Biomarker for Immunologic Risk Stratification in Pediatric Kidney Transplantation Recipients.

Antibody-mediated rejection is a common cause of early kidney allograft loss but the specifics of antibody measurement, therapies and endpoints have not been universally defined. In this retrospective study, we assessed the performance of risk stratification using systematic donor-specific antibody (DSA) monitoring. Included in the study were children who underwent kidney transplantation between January 1, 2010 and March 1, 2018 at Stanford, with at least 12-months follow-up. A total of 233 patients were included with a mean follow-up time of 45 (range, 9-108) months. Median age at transplant was 12.3 years, 46.8% were female, and 76% had a deceased donor transplant. Fifty-two (22%) formed C1q-binding de novo donor-specific antibodies (C1q-dnDSA). After a standardized augmented immunosuppressive protocol was implemented, C1q-dnDSA disappeared in 31 (58.5%). Graft failure occurred in 16 patients at a median of 54 (range, 5-83) months, of whom 14 formed dnDSA. The 14 patients who lost their graft due to rejection, all had persistent C1q-dnDSA. C1q-binding status improved the individual risk assessment, with persistent; C1q binding yielding the strongest independent association of graft failure (hazard ratio, 45.5; 95% confidence interval, 11.7-177.4). C1q-dnDSA is more useful than standard dnDSA as a noninvasive biomarker for identifying patients at the highest risk of graft failure.

Validation of a Next-Generation Sequencing-Based T-Cell Receptor Gamma Gene Rearrangement Diagnostic Assay: Transitioning from Capillary Electrophoresis to Next-Generation Sequencing.

Assessment of T-cell receptor γ gene (TRG) rearrangements is an importants consideration in the diagnostic workup of lymphoproliferative diseases. Although fragment analysis by PCR and capillary electrophoresis (CE) is the current standard of such assessment in clinical molecular diagnostic laboratories, it does not provide sequence information and is only semi-quantitative. Next-generation sequencing (NGS)-based assays are an attractive alternative to the conventional fragment size-based methods, given that they generate results with specific clonotype sequence information and allow for more accurate quantitation. The present study evaluated various test parameters and performance characteristics of a commercially available NGS-based TRG gene-rearrangement assay by testing 101 clinical samples previously characterized by fragment analysis. The NGS TRG assay showed an overall accuracy of 83% and an analytical specificity of 100%. The concordance rates were 88% to 95% in the Vγ1-8, Vγ10, and Vγ11 gene families, but lower in the Vγ9 gene family. This difference was mostly attributed to the incomplete polyclonal symmetry resulting from the two-tube CE assay versus the one-tube design of the NGS assay. The NGS assay also demonstrated strengths in distinguishing clonotypes of the same fragment size. This clinical validation demonstrated robust performance of the NGS-based TRG assay and identified potential pitfalls associated with CE assay design that are important for understanding the observed discrepancies with the CE-based assay.

An Overview of Characteristics of Clinical Next-Generation Sequencing-Based Testing for Hematologic Malignancies.

CONTEXT.­: With the increasing integration of molecular alterations into the evaluation of hematologic malignancies (HM), somatic mutation profiling by next-generation sequencing (NGS) has become a common clinical testing strategy. Limited data are available about the characteristics of these assays. OBJECTIVE.­: To describe assay characteristics, specimen requirements, and reporting practices for NGS-based HM testing using College of American Pathologists proficiency testing survey data. DESIGN.­: The College of American Pathologists NGS Hematologic Malignancies Survey (NGSHM) results from 78 laboratories were used to determine laboratory practices in NGS-based HM testing. RESULTS.­: The majority of laboratories performed tumor-only (88.5% [69 of 78]), targeted sequencing of cancer genes or mutation hotspots (98.7% [77 of 78]); greater than 90% performed testing on fresh bone marrow and peripheral blood. The majority of laboratories reported a 5% lower limit of detection for single-nucleotide variants (73.1% [57 of 78]) and small insertions and deletions (50.6% [39 of 77]). A majority of laboratories used benchtop sequencers and custom enrichment approaches. CONCLUSIONS.­: This manuscript summarizes the characteristics of clinical NGS-based testing for the detection of somatic variants in HM. These data may be broadly useful to inform laboratory practice and quality management systems, regulation, and oversight of NGS testing, and precision medicine efforts using a data-driven approach.

Specifications of the variant curation guidelines for ITGA2B/ITGB3: ClinGen Platelet Disorder Variant Curation Panel.

Accurate and consistent sequence variant interpretation is critical to the correct diagnosis and appropriate clinical management and counseling of patients with inherited genetic disorders. To minimize discrepancies in variant curation and classification among different clinical laboratories, the American College of Medical Genetics and Genomics (ACMG), along with the Association for Molecular Pathology (AMP), published standards and guidelines for the interpretation of sequence variants in 2015. Because the rules are not universally applicable to different genes or disorders, the Clinical Genome Resource (ClinGen) Platelet Disorder Expert Panel (PD-EP) has been tasked to make ACMG/AMP rule specifications for inherited platelet disorders. ITGA2B and ITGB3, the genes underlying autosomal recessive Glanzmann thrombasthenia (GT), were selected as the pilot genes for specification. Eight types of evidence covering clinical phenotype, functional data, and computational/population data were evaluated in the context of GT by the ClinGen PD-EP. The preliminary specifications were validated with 70 pilot ITGA2B/ITGB3 variants and further refined. In the final adapted criteria, gene- or disease-based specifications were made to 16 rules, including 7 with adjustable strength; no modification was made to 5 rules; and 7 rules were deemed not applicable to GT. Employing the GT-specific ACMG/AMP criteria to the pilot variants resulted in a reduction of variants classified with unknown significance from 29% to 20%. The overall concordance with the initial expert assertions was 71%. These adapted criteria will serve as guidelines for GT-related variant interpretation to increase specificity and consistency across laboratories and allow for better clinical integration of genetic knowledge into patient care.

Identification of a pathogenic TUBB1 variant in a Chinese family with congenital macrothrombocytopenia through whole genome sequencing.

Congenital macrothrombocytopenia is a genetically heterogeneous group of rare disorders. We herein report a large Chinese family presented with phenotypic variability involving thrombocytopenia and/or giant platelets. Whole genome sequencing (WGS) of the proband and one of his affected brothers identified a potentially pathogenic c.952 C > T heterozygous variant in the TUBB1 gene. This p.R318W ß1-tubulin variant was also identified in three additional siblings and five members of the next generation. These findings were consistent with an autosomal dominant inheritance with incomplete penetrance. Moreover, impaired platelet agglutination in response to ristocetin was detected in the patient's brother. Half of the family members harboring the p.R318W mutation displayed significantly decreased external release of p-selectin by stimulated platelets. The p.R318W ß1-tubulin mutation was identified for the first time in a Chinese family with congenital macrothrombocytopenia using WGS as an unbiased sequencing approach. Affected individuals within the family demonstrated impaired platelet aggregation and/or release functions.

Case series of MET exon 14 skipping mutation-positive non-small-cell lung cancers with response to crizotinib and cabozantinib.

The mesenchymal-to-epithelial transition (MET) gene is altered and becomes a driver mutation in up to 5% of non-small-cell lung cancer (NSCLC). We report our institutional experience treating patients with MET exon 14 skipping (METex14) mutations, including responses to the MET inhibitors crizotinib and cabozantinib. We identified cases of NSCLC with METex14 mutations using an institutionally developed or commercial next-generation sequencing assay. We assessed patient and disease characteristics by retrospective chart review. Some patients were treated off-label by the physician with crizotinib or cabozantinib, and tumor responses to these agents were assessed. A total of 15 patients with METex14-mutated NSCLC were identified, predominantly male (n=10) with a smoking history (60%) and a median age of 74.0 years. No other actionable somatic mutations were detected. Stage distribution included 26.7% stage I, 6.7% stage II, 6.7% stage III, and 60.0% stage IV. Among patients treated with crizotinib or cabozantinib (n=6), three patients showed partial response and one patient showed stable disease on the basis of RECIST criteria. Four patients experienced side effects requiring drug holiday, reduction, or cessation. Our findings highlight the diversity in presentation and histology of NSCLC with METex14 mutations, which were found in the absence of other actionable driver mutations. We observed evidence of tumor response to crizotinib and cabozantinib, supporting the previous reports that METex14 mutations in NSCLC are actionable driver events.

Methodologic Considerations in the Application of Next-Generation Sequencing of Human TRB Repertoires for Clinical Use.

Next-generation sequencing (NGS) of immune receptors has become a standard tool to assess minimal residual disease (MRD) in patients treated for lymphoid malignancy, and it is being used to study the T-cell repertoire in many clinical settings. To better understanding the potential clinical utility and limitations of this application outside of MRD, we developed a BIOMED-2 primer-based NGS method and characterized its performance in controls and patients with graft-versus-host disease (GVHD) after allogeneic hematopoietic transplant. For controls and patients with GVHD, replicate sequencing of the same T-cell receptor ß (TRB) libraries was highly reproducible. Higher variability was observed in sequencing of different TRB libraries made from the same DNA stock. Variability was increased in patients with GVHD compared with controls; patients with GVHD also had lower diversity than controls. In the T-cell repertoire of a healthy person, approximately 99.6% of the CDR3 clones were in low abundance, with frequency <10-3. A single library could identify >93% of the clones with frequency ≥10-3 in the repertoire. Sequencing in duplicate increased the average detection rate to >97%. This work demonstrates that NGS reliably and robustly characterizes TRB populations in healthy individuals and patients with GVHD with frequency ≥10-3 and provides a methodologic framework for applying NGS immune repertoire methods to clinical testing applications beyond MRD.