Complex Autoinflammatory Syndrome Unveils Fundamental Principles of JAK1 Kinase Transcriptional and Biochemical Function.

Autoinflammatory disease can result from monogenic errors of immunity. We describe a patient with early-onset multi-organ immune dysregulation resulting from a mosaic, gain-of-function mutation (S703I) in JAK1, encoding a kinase essential for signaling downstream of >25 cytokines. By custom single-cell RNA sequencing, we examine mosaicism with single-cell resolution. We find that JAK1 transcription was predominantly restricted to a single allele across different cells, introducing the concept of a mutational "transcriptotype" that differs from the genotype. Functionally, the mutation increases JAK1 activity and transactivates partnering JAKs, independent of its catalytic domain. S703I JAK1 is not only hypermorphic for cytokine signaling but also neomorphic, as it enables signaling cascades not canonically mediated by JAK1. Given these results, the patient was treated with tofacitinib, a JAK inhibitor, leading to the rapid resolution of clinical disease. These findings offer a platform for personalized medicine with the concurrent discovery of fundamental biological principles.

RASGRP1 deficiency causes immunodeficiency with impaired cytoskeletal dynamics.

RASGRP1 is an important guanine nucleotide exchange factor and activator of the RAS-MAPK pathway following T cell antigen receptor (TCR) signaling. The consequences of RASGRP1 mutations in humans are unknown. In a patient with recurrent bacterial and viral infections, born to healthy consanguineous parents, we used homozygosity mapping and exome sequencing to identify a biallelic stop-gain variant in RASGRP1. This variant segregated perfectly with the disease and has not been reported in genetic databases. RASGRP1 deficiency was associated in T cells and B cells with decreased phosphorylation of the extracellular-signal-regulated serine kinase ERK, which was restored following expression of wild-type RASGRP1. RASGRP1 deficiency also resulted in defective proliferation, activation and motility of T cells and B cells. RASGRP1-deficient natural killer (NK) cells exhibited impaired cytotoxicity with defective granule convergence and actin accumulation. Interaction proteomics identified the dynein light chain DYNLL1 as interacting with RASGRP1, which links RASGRP1 to cytoskeletal dynamics. RASGRP1-deficient cells showed decreased activation of the GTPase RhoA. Treatment with lenalidomide increased RhoA activity and reversed the migration and activation defects of RASGRP1-deficient lymphocytes.

ß-Actin G342D as a Cause of NK Cell Deficiency Impairing Lytic Synapse Termination.

NK cell deficiency (NKD) occurs when an individual's major clinical immunodeficiency derives from abnormal NK cells and is associated with several genetic etiologies. Three categories of ß-actin-related diseases with over 60 ACTB (ß-actin) variants have previously been identified, none with a distinct NK cell phenotype. An individual with mild developmental delay, macrothrombocytopenia, and susceptibility to infections, molluscum contagiosum virus, and EBV-associated lymphoma had functional NKD for over a decade. A de novo ACTB variant encoding G342D ß-actin was identified and was consistent with the individual's developmental and platelet phenotype. This novel variant also was found to have direct impact in NK cells because its expression in the human NK cell line YTS (YTS-NKD) caused increased cell spreading in lytic immune synapses created on activating surfaces. YTS-NKD cells were able to degranulate and perform cytotoxicity, but they demonstrated defective serial killing because of prolonged conjugation to the killed target cell and thus were effectively unable to terminate lytic synapses. G342D ß-actin results in a novel, to our knowledge, mechanism of functional NKD via increased synaptic spreading and defective lytic synapse termination with resulting impaired serial killing, leading to overall reductions in NK cell cytotoxicity.

Retraction Note: A homing system targets therapeutic T cells to brain cancer.

This Article has been retracted; see accompanying Retraction.

Validating inborn error of immunity prevalence and risk with nationally representative electronic health record data.

BACKGROUND: The 10 Warning Signs of Primary Immunodeficiency were created 30 years ago to advance recognition of inborn errors of immunity (IEI). However, no population-level assessment of their utility applied to electronic health record (EHR) data has been conducted. OBJECTIVE: We sought to quantify the value of having ≥2 warning signs (WS) toward diagnosing IEI using a highly representative real-world US cohort. A secondary goal was estimating the US prevalence of IEI. METHODS: In this cohort study, we accessed normalized and de-identified EHR data on 152 million US patients. An IEI cohort (n = 41,080), in which patients were defined by having at least 1 verifiable IEI diagnosis placed ≥2 times in their record, was compared with a matched set of controls (n = 250,262). WS were encoded along with relevant diagnoses, relative weights were calculated, and the proportion of IEI cases versus controls with ≥2 WS was compared. RESULTS: The proportion of IEI cases with ≥2 WS significantly differed from controls (0.33 vs 0.031; P < .0005, χ2 test). We also estimated a US IEI prevalence of 6 per 10,000 individuals (41,080/73,165,655; 0.056%). WS 9 (≥2 deep-seated infections), 7 (fungal infections), 5 (failure to thrive) and 4 (≥2 pneumonias in 1 year) were the most heavily weighted among the IEI cohort. CONCLUSIONS: This nationally representative US-based cohort study demonstrates that presence of WS and associated clinical diagnoses can facilitate identification of patients with IEI from EHR data. In addition, we estimate that 6 in 10,000, or approximately 150,000 to 200,000 individuals are affected by IEI across the United States.

Human PLCG2 haploinsufficiency results in a novel natural killer cell immunodeficiency.

BACKGROUND: Although most individuals effectively control herpesvirus infections, some suffer from severe and/or recurrent infections. A subset of these patients possess defects in natural killer (NK) cells, lymphocytes that recognize and lyse herpesvirus-infected cells; however, the genetic etiology is rarely diagnosed. PLCG2 encodes a signaling protein in NK-cell and B-cell signaling. Dominant-negative or gain-of-function variants in PLCG2 cause cold urticaria, antibody deficiency, and autoinflammation. However, loss-of-function variants and haploinsufficiency have not been reported to date. OBJECTIVES: The investigators aimed to identify the genetic cause of NK-cell immunodeficiency in 2 families and herein describe the functional consequences of 2 novel loss-of-function variants in PLCG2. METHODS: The investigators employed whole-exome sequencing in conjunction with mass cytometry, microscopy, functional assays, and a mouse model of PLCG2 haploinsufficiency to investigate 2 families with NK-cell immunodeficiency. RESULTS: The investigators identified novel heterozygous variants in PLCG2 in 2 families with severe and/or recurrent herpesvirus infections. In vitro studies demonstrated that these variants were loss of function due to haploinsufficiency with impaired NK-cell calcium flux and cytotoxicity. In contrast to previous PLCG2 variants, B-cell function remained intact. Plcg2+/- mice also displayed impaired NK-cell function with preserved B-cell function, phenocopying human disease. CONCLUSIONS: PLCG2 haploinsufficiency represents a distinct syndrome from previous variants characterized by NK-cell immunodeficiency with herpesvirus susceptibility, expanding the spectrum of PLCG2-related disease.

Treatment of Relapsing HPV Diseases by Restored Function of Natural Killer Cells.

Human papillomavirus (HPV) infections underlie a wide spectrum of both benign and malignant epithelial diseases. In this report, we describe the case of a young man who had encephalitis caused by herpes simplex virus during adolescence and currently presented with multiple recurrent skin and mucosal lesions caused by HPV. The patient was found to have a pathogenic germline mutation in the X-linked interleukin-2 receptor subunit gamma gene (IL2RG), which was somatically reverted in T cells but not in natural killer (NK) cells. Allogeneic hematopoietic-cell transplantation led to restoration of NK cytotoxicity, with normalization of the skin microbiome and persistent remission of all HPV-related diseases. NK cytotoxicity appears to play a role in containing HPV colonization and the ensuing HPV-related hyperplastic or dysplastic lesions. (Funded by the National Institutes of Health and the Herbert Irving Comprehensive Cancer Center Flow Cytometry Shared Resources.).

Degranulation enhances presynaptic membrane packing, which protects NK cells from perforin-mediated autolysis.

Natural killer (NK) cells kill a target cell by secreting perforin into the lytic immunological synapse, a specialized interface formed between the NK cell and its target. Perforin creates pores in target cell membranes allowing delivery of proapoptotic enzymes. Despite the fact that secreted perforin is in close range to both the NK and target cell membranes, the NK cell typically survives while the target cell does not. How NK cells preferentially avoid death during the secretion of perforin via the degranulation of their perforin-containing organelles (lytic granules) is perplexing. Here, we demonstrate that NK cells are protected from perforin-mediated autolysis by densely packed and highly ordered presynaptic lipid membranes, which increase packing upon synapse formation. When treated with 7-ketocholesterol, lipid packing is reduced in NK cells making them susceptible to perforin-mediated lysis after degranulation. Using high-resolution imaging and lipidomics, we identified lytic granules themselves as having endogenously densely packed lipid membranes. During degranulation, lytic granule-cell membrane fusion thereby further augments presynaptic membrane packing, enhancing membrane protection at the specific sites where NK cells would face maximum concentrations of secreted perforin. Additionally, we found that an aggressive breast cancer cell line is perforin resistant and evades NK cell-mediated killing owing to a densely packed postsynaptic membrane. By disrupting membrane packing, these cells were switched to an NK-susceptible state, which could suggest strategies for improving cytotoxic cell-based cancer therapies. Thus, lipid membranes serve an unexpected role in NK cell functionality protecting them from autolysis, while degranulation allows for the inherent lytic granule membrane properties to create local ordered lipid "shields" against self-destruction.

National Pediatrician-Scientist Collaborative Workgroup comment on new ACGME requirements' impact on pediatric physician-scientists.

BACKGROUND: The ACGME recently released its recommendation for updates to the program requirements for pediatrics. These updates proposed changes to allocation of resident clinical time and a greater emphasis on individualization. The potential impact of these changes on the training of physician-scientists is discussed. METHODS: Discussion of the proposed changes was held within the members of the National Pediatrician-Scientist Collaborative Workgroup, a group that represents scientists, trainees, program directors, chairs, and physician-scientist educators at nearly 30 residency programs from across the US with a focus on understanding and developing optimal approaches to physician-scientist training. Consideration was given to the both the personal and institutional impact of the proposal for physician-scientist development. RESULTS: Both threats and opportunities were identified. Key opportunities include the enhanced individualized training time that could be used to explore research. Threats include re-allocation of clinical training time that may strain institutions financially, expand clinical service requirements for other early career stage individuals, and alter exposure to a broad range of pediatric specialists and sub-specialists that impact career development. CONCLUSION: The NPSCW encourages consideration of the impact of changing program requirements on physician-scientist development to include ongoing discussion amongst mentors, programs, and trainees to understand and mitigate impact of new program requirements on the development of pediatrician-scientists.

A homing system targets therapeutic T cells to brain cancer.

Successful T cell immunotherapy for brain cancer requires that the T cells can access tumour tissues, but this has been difficult to achieve. Here we show that, in contrast to inflammatory brain diseases such as multiple sclerosis, where endothelial cells upregulate ICAM1 and VCAM1 to guide the extravasation of pro-inflammatory cells, cancer endothelium downregulates these molecules to evade immune recognition. By contrast, we found that cancer endothelium upregulates activated leukocyte cell adhesion molecule (ALCAM), which allowed us to overcome this immune-evasion mechanism by creating an ALCAM-restricted homing system (HS). We re-engineered the natural ligand of ALCAM, CD6, in a manner that triggers initial anchorage of T cells to ALCAM and conditionally mediates a secondary wave of adhesion by sensitizing T cells to low-level ICAM1 on the cancer endothelium, thereby creating the adhesion forces necessary to capture T cells from the bloodstream. Cytotoxic HS T cells robustly infiltrated brain cancers after intravenous injection and exhibited potent antitumour activity. We have therefore developed a molecule that targets the delivery of T cells to brain cancer.

A validated artificial intelligence-based pipeline for population-wide primary immunodeficiency screening.

BACKGROUND: Identification of patients with underlying inborn errors of immunity and inherent susceptibility to infection remains challenging. The ensuing protracted diagnostic odyssey for such patients often results in greater morbidity and suboptimal outcomes, underscoring a need to develop systematic methods for improving diagnostic rates. OBJECTIVE: The principal aim of this study is to build and validate a generalizable analytical pipeline for population-wide detection of infection susceptibility and risk of primary immunodeficiency. METHODS: This prospective, longitudinal cohort study coupled weighted rules with a machine learning classifier for risk stratification. Claims data were analyzed from a diverse population (n = 427,110) iteratively over 30 months. Cohort outcomes were enumerated for new diagnoses, hospitalizations, and acute care visits. This study followed TRIPOD (Transparent Reporting of a multivariable prediction model for Individual Prognosis Or Diagnosis) standards. RESULTS: Cohort members initially identified as high risk were proportionally more likely to receive a diagnosis of primary immunodeficiency compared to those at low-medium risk or those without claims of interest respectively (9% vs 1.5% vs 0.2%; P < .001, chi-square test). Subsequent machine learning stratification enabled an annualized individual snapshot of complexity for triaging referrals. This study's top-performing machine learning model for visit-level prediction used a single dense layer neural network architecture (area under the receiver-operator characteristic curve = 0.98; F1 score = 0.98). CONCLUSIONS: A 2-step analytical pipeline can facilitate identification of individuals with primary immunodeficiency and accurately quantify clinical risk.

Expanded Newborn Screening Using Genome Sequencing for Early Actionable Conditions.

Importance: The feasibility of implementing genome sequencing as an adjunct to traditional newborn screening (NBS) in newborns of different racial and ethnic groups is not well understood. Objective: To report interim results of acceptability, feasibility, and outcomes of an ongoing genomic NBS study in a diverse population in New York City within the context of the New York State Department of Health Newborn Screening Program. Design, Setting, and Participants: The Genomic Uniform-screening Against Rare Disease in All Newborns (GUARDIAN) study was a multisite, single-group, prospective, observational investigation of supplemental newborn genome screening with a planned enrollment of 100 000 participants. Parent-reported race and ethnicity were recorded at the time of recruitment. Results of the first 4000 newborns enrolled in 6 New York City hospitals between September 2022 and July 2023 are reported here as part of a prespecified interim analysis. Exposure: Sequencing of 156 early-onset genetic conditions with established interventions selected by the investigators were screened in all participants and 99 neurodevelopmental disorders associated with seizures were optional. Main Outcomes and Measures: The primary outcome was screen-positive rate. Additional outcomes included enrollment rate and successful completion of sequencing. Results: Over 11 months, 5555 families were approached and 4000 (72.0%) consented to participate. Enrolled participants reflected a diverse group by parent-reported race (American Indian or Alaska Native, 0.5%; Asian, 16.5%; Black, 25.1%; Native Hawaiian or Other Pacific Islander, 0.1%; White, 44.7%; 2 or more races, 13.0%) and ethnicity (Hispanic, 44.0%; not Hispanic, 56.0%). The majority of families consented to screening of both groups of conditions (both groups, 90.6%; disorders with established interventions only, 9.4%). Testing was successfully completed for 99.6% of cases. The screen-positive rate was 3.7%, including treatable conditions that are not currently included in NBS. Conclusions and Relevance: These interim findings demonstrate the feasibility of targeted interpretation of a predefined set of genes from genome sequencing in a population of different racial and ethnic groups. DNA sequencing offers an additional method to improve screening for conditions already included in NBS and to add those that cannot be readily screened because there is no biomarker currently detectable in dried blood spots. Additional studies are required to understand if these findings are generalizable to populations of different racial and ethnic groups and whether introduction of sequencing leads to changes in management and improved health outcomes. Trial Registration: ClinicalTrials.gov Identifier: NCT05990179.

Genetic errors of immunity distinguish pediatric nonmalignant lymphoproliferative disorders.

BACKGROUND: Pediatric nonmalignant lymphoproliferative disorders (PLPDs) are clinically and genetically heterogeneous. Long-standing immune dysregulation and lymphoproliferation in children may be life-threatening, and a paucity of data exists to guide evaluation and treatment of children with PLPD. OBJECTIVE: The primary objective of this study was to ascertain the spectrum of genomic immunologic defects in PLPD. Secondary objectives included characterization of clinical outcomes and associations between genetic diagnoses and those outcomes. METHODS: PLPD was defined by persistent lymphadenopathy, lymph organ involvement, or lymphocytic infiltration for more than 3 months, with or without chronic or significant Epstein-Barr virus (EBV) infection. Fifty-one subjects from 47 different families with PLPD were analyzed using whole exome sequencing. RESULTS: Whole exome sequencing identified likely genetic errors of immunity in 51% to 62% of families (53% to 65% of affected children). Presence of a genetic etiology was associated with younger age and hemophagocytic lymphohistiocytosis. Ten-year survival for the cohort was 72.4%, and patients with viable genetic diagnoses had a higher survival rate (82%) compared to children without a genetic explanation (48%, P = .03). Survival outcomes for individuals with EBV-associated disease and no genetic explanation were particularly worse than outcomes for subjects with EBV-associated disease and a genetic explanation (17% vs 90%; P = .002). Ascertainment of a molecular diagnosis provided targetable treatment options for up to 18 individuals and led to active management changes for 12 patients. CONCLUSIONS: PLPD defines children at high risk for mortality, and whole exome sequencing informs clinical risks and therapeutic opportunities for this diagnosis.

Emerging insights into human health and NK cell biology from the study of NK cell deficiencies.

Human NK cells are innate immune effectors that play a critical roles in the control of viral infection and malignancy. The importance of their homeostasis and function can be demonstrated by the study of patients with primary immunodeficiencies (PIDs), which are part of the family of diseases known as inborn defects of immunity. While NK cells are affected in many PIDs in ways that may contribute to a patient's clinical phenotype, a small number of PIDs have an NK cell abnormality as their major immunological defect. These PIDs can be collectively referred to as NK cell deficiency (NKD) disorders and include effects upon NK cell numbers, subsets, and/or functions. The clinical impact of NKD can be severe including fatal viral infection, with particular susceptibility to herpesviral infections, such as cytomegalovirus, varicella zoster virus, and Epstein-Barr virus. While NKD is rare, studies of these diseases are important for defining specific requirements for human NK cell development and homeostasis. New themes in NK cell biology are emerging through the study of both known and novel NKD, particularly those affecting cell cycle and DNA damage repair, as well as broader PIDs having substantive impact upon NK cells. In addition, the discovery of NKD that affects other innate lymphoid cell (ILC) subsets opens new doors for better understanding the relationship between conventional NK cells and other ILC subsets. Here, we describe the biology underlying human NKD, particularly in the context of new insights into innate immune cell function, including a discussion of recently described NKD with accompanying effects on ILC subsets. Given the impact of these disorders upon human immunity with a common focus upon NK cells, the unifying message of a critical role for NK cells in human host defense singularly emerges.

Bi-allelic Variants in TONSL Cause SPONASTRIME Dysplasia and a Spectrum of Skeletal Dysplasia Phenotypes.

SPONASTRIME dysplasia is an autosomal-recessive spondyloepimetaphyseal dysplasia characterized by spine (spondylar) abnormalities, midface hypoplasia with a depressed nasal bridge, metaphyseal striations, and disproportionate short stature. Scoliosis, coxa vara, childhood cataracts, short dental roots, and hypogammaglobulinemia have also been reported in this disorder. Although an autosomal-recessive inheritance pattern has been hypothesized, pathogenic variants in a specific gene have not been discovered in individuals with SPONASTRIME dysplasia. Here, we identified bi-allelic variants in TONSL, which encodes the Tonsoku-like DNA repair protein, in nine subjects (from eight families) with SPONASTRIME dysplasia, and four subjects (from three families) with short stature of varied severity and spondylometaphyseal dysplasia with or without immunologic and hematologic abnormalities, but no definitive metaphyseal striations at diagnosis. The finding of early embryonic lethality in a Tonsl-/- murine model and the discovery of reduced length, spinal abnormalities, reduced numbers of neutrophils, and early lethality in a tonsl-/- zebrafish model both support the hypomorphic nature of the identified TONSL variants. Moreover, functional studies revealed increased amounts of spontaneous replication fork stalling and chromosomal aberrations, as well as fewer camptothecin (CPT)-induced RAD51 foci in subject-derived cell lines. Importantly, these cellular defects were rescued upon re-expression of wild-type (WT) TONSL; this rescue is consistent with the hypothesis that hypomorphic TONSL variants are pathogenic. Overall, our studies in humans, mice, zebrafish, and subject-derived cell lines confirm that pathogenic variants in TONSL impair DNA replication and homologous recombination-dependent repair processes, and they lead to a spectrum of skeletal dysplasia phenotypes with numerous extra-skeletal manifestations.

A research-driven approach to the identification of novel natural killer cell deficiencies affecting cytotoxic function.

Natural killer cell deficiencies (NKDs) are an emerging phenotypic subtype of primary immune deficiency. NK cells provide a defense against virally infected cells using a variety of cytotoxic mechanisms, and patients who have defective NK cell development or function can present with atypical, recurrent, or severe herpesviral infections. The current pipeline for investigating NKDs involves the acquisition and clinical assessment of patients with a suspected NKD followed by subsequent in silico, in vitro, and in vivo laboratory research. Evaluation involves initially quantifying NK cells and measuring NK cell cytotoxicity and expression of certain NK cell receptors involved in NK cell development and function. Subsequent studies using genomic methods to identify the potential causative variant are conducted along with variant impact testing to make genotype-phenotype connections. Identification of novel genes contributing to the NKD phenotype can also be facilitated by applying the expanding knowledge of NK cell biology. In this review, we discuss how NKDs that affect NK cell cytotoxicity can be approached in the clinic and laboratory for the discovery of novel gene variants.

Lost in Translation: Lack of CD4 Expression due to a Novel Genetic Defect.

CD4 expression identifies a subset of mature T cells primarily assisting the germinal center reaction and contributing to CD8+ T-cell and B-cell activation, functions, and longevity. Herein, we present a family in which a novel variant disrupting the translation-initiation codon of the CD4 gene resulted in complete loss of membrane and plasma soluble CD4 in peripheral blood, lymph node, bone marrow, skin, and ileum of a homozygous proband. This inherited CD4 knockout disease illustrates the clinical and immunological features of a complete deficiency of any functional component of CD4 and its similarities and differences with other clinical models of primary or acquired loss of CD4+ T cells. The first inherited loss of any functional component of CD4, including soluble CD4, is clinically distinct from any other congenital or acquired CD4 T-cell defect and characterized by compensatory changes in T-cell subsets and functional impairment of B cells, monocytes, and natural killer cells.

Class Switch Recombination Defects: impact on B cell maturation and antibody responses.

To assess how B cell phenotype analysis correlates with antigen responses in patients with class switch recombination defects (CSRD) we quantified memory B cells by flow-cytometry and immunized CSRD patients with the neoantigen bacteriophage phiX174 (phage). CSRD patients showed uniformly absent or markedly reduced switched memory B cells (IgM-IgD-CD27+). CD40L patients had reduced CD27+ memory B cells (both non-switched and switched). In NEMO patients, results varied depending on the IKKγ gene variant. Three of four AID patients had normal percentages of CD27+ memory B cells while CD27+IgM-IgD- switched memory B cells were markedly reduced in all AID patients. Antibody response to phage was remarkably decreased with lack of memory amplification and class-switching in immunized CD40L, UNG deficient, and NEMO patients. Distinct B-cell phenotype pattern correlated with abnormal antibody responses to a T-cell dependent neoantigen, representing a powerful tool to identify CSRD patients.

Identifying Genes Whose Mutant Transcripts Cause Dominant Disease Traits by Potential Gain-of-Function Alleles.

Premature termination codon (PTC)-bearing transcripts are often degraded by nonsense-mediated decay (NMD) resulting in loss-of-function (LoF) alleles. However, not all PTCs result in LoF mutations, i.e., some such transcripts escape NMD and are translated to truncated peptide products that result in disease due to gain-of-function (GoF) effects. Since the location of the PTC is a major factor determining transcript fate, we hypothesized that depletion of protein-truncating variants (PTVs) within the gene region predicted to escape NMD in control databases could provide a rank for genic susceptibility for disease through GoF versus LoF. We developed an NMD escape intolerance score to rank genes based on the depletion of PTVs that would render them able to escape NMD using the Atherosclerosis Risk in Communities Study (ARIC) and the Exome Aggregation Consortium (ExAC) control databases, which was further used to screen the Baylor-Center for Mendelian Genomics disease database. This analysis revealed 1,996 genes significantly depleted for PTVs that are predicted to escape from NMD, i.e., PTVesc; further studies provided evidence that revealed a subset as candidate genes underlying Mendelian phenotypes. Importantly, these genes have characteristically low pLI scores, which can cause them to be overlooked as candidates for dominant diseases. Collectively, we demonstrate that this NMD escape intolerance score is an effective and efficient tool for gene discovery in Mendelian diseases due to production of truncated or altered proteins. More importantly, we provide a complementary analytical tool to aid identification of genes associated with dominant traits through a mechanism distinct from LoF.