Protective human monoclonal antibodies target conserved sites of vulnerability on the underside of influenza virus neuraminidase.

Continuously evolving influenza viruses cause seasonal epidemics and pose global pandemic threats. Although viral neuraminidase (NA) is an effective drug and vaccine target, our understanding of the NA antigenic landscape still remains incomplete. Here, we describe NA-specific human antibodies that target the underside of the NA globular head domain, inhibit viral propagation of a wide range of human H3N2, swine-origin variant H3N2, and H2N2 viruses, and confer both pre- and post-exposure protection against lethal H3N2 infection in mice. Cryo-EM structures of two such antibodies in complex with NA reveal non-overlapping epitopes covering the underside of the NA head. These sites are highly conserved among N2 NAs yet inaccessible unless the NA head tilts or dissociates. Our findings help guide the development of effective countermeasures against ever-changing influenza viruses by identifying hidden conserved sites of vulnerability on the NA underside.

Author Correction: Mosaic nanoparticle display of diverse influenza virus hemagglutinins elicits broad B cell responses.

In the version of this article initially published, the labels (50 Å) above the scale bars in Fig. 1b were incorrect. The correct size is 50 nm. The error has been corrected in the HTML and PDF versions of the article.

Mosaic nanoparticle display of diverse influenza virus hemagglutinins elicits broad B cell responses.

The present vaccine against influenza virus has the inevitable risk of antigenic discordance between the vaccine and the circulating strains, which diminishes vaccine efficacy. This necessitates new approaches that provide broader protection against influenza. Here we designed a vaccine using the hypervariable receptor-binding domain (RBD) of viral hemagglutinin displayed on a nanoparticle (np) able to elicit antibody responses that neutralize H1N1 influenza viruses spanning over 90 years. Co-display of RBDs from multiple strains across time, so that the adjacent RBDs are heterotypic, provides an avidity advantage to cross-reactive B cells. Immunization with the mosaic RBD-np elicited broader antibody responses than those induced by an admixture of nanoparticles encompassing the same set of RBDs as separate homotypic arrays. Furthermore, we identified a broadly neutralizing monoclonal antibody in a mouse immunized with mosaic RBD-np. The mosaic antigen array signifies a unique approach that subverts monotypic immunodominance and allows otherwise subdominant cross-reactive B cell responses to emerge.

Epstein-Barr virus gH/gL has multiple sites of vulnerability for virus neutralization and fusion inhibition.

Epstein-Barr virus (EBV) is nearly ubiquitous in adults. EBV causes infectious mononucleosis and is associated with B cell lymphomas, epithelial cell malignancies, and multiple sclerosis. The EBV gH/gL glycoprotein complex facilitates fusion of virus membrane with host cells and is a target of neutralizing antibodies. Here, we examined the sites of vulnerability for virus neutralization and fusion inhibition within EBV gH/gL. We developed a panel of human monoclonal antibodies (mAbs) that targeted five distinct antigenic sites on EBV gH/gL and prevented infection of epithelial and B cells. Structural analyses using X-ray crystallography and electron microscopy revealed multiple sites of vulnerability and defined the antigenic landscape of EBV gH/gL. One mAb provided near-complete protection against viremia and lymphoma in a humanized mouse EBV challenge model. Our findings provide structural and antigenic knowledge of the viral fusion machinery, yield a potential therapeutic antibody to prevent EBV disease, and emphasize gH/gL as a target for herpesvirus vaccines and therapeutics.

Co-immunization with hemagglutinin stem immunogens elicits cross-group neutralizing antibodies and broad protection against influenza A viruses.

Current influenza vaccines predominantly induce immunity to the hypervariable hemagglutinin (HA) head, requiring frequent vaccine reformulation. Conversely, the immunosubdominant yet conserved HA stem harbors a supersite that is targeted by broadly neutralizing antibodies (bnAbs), representing a prime target for universal vaccines. Here, we showed that the co-immunization of two HA stem immunogens derived from group 1 and 2 influenza A viruses elicits cross-group protective immunity and neutralizing antibody responses in mice, ferrets, and nonhuman primates (NHPs). Immunized mice were protected from multiple group 1 and 2 viruses, and all animal models showed broad serum-neutralizing activity. A bnAb isolated from an immunized NHP broadly neutralized and protected against diverse viruses, including H5N1 and H7N9. Genetic and structural analyses revealed strong homology between macaque and human bnAbs, illustrating common biophysical constraints for acquiring cross-group specificity. Vaccine elicitation of stem-directed cross-group-protective immunity represents a step toward the development of broadly protective influenza vaccines.

Prefusion stabilization of the Hendra and Langya virus F proteins.

Nipah virus (NiV) and Hendra virus (HeV) are pathogenic paramyxoviruses that cause mild-to-severe disease in humans. As members of the Henipavirus genus, NiV and HeV use an attachment (G) glycoprotein and a class I fusion (F) glycoprotein to invade host cells. The F protein rearranges from a metastable prefusion form to an extended postfusion form to facilitate host cell entry. Prefusion NiV F elicits higher neutralizing antibody titers than postfusion NiV F, indicating that stabilization of prefusion F may aid vaccine development. A combination of amino acid substitutions (L104C/I114C, L172F, and S191P) is known to stabilize NiV F in its prefusion conformation, although the extent to which substitutions transfer to other henipavirus F proteins is not known. Here, we perform biophysical and structural studies to investigate the mechanism of prefusion stabilization in F proteins from three henipaviruses: NiV, HeV, and Langya virus (LayV). Three known stabilizing substitutions from NiV F transfer to HeV F and exert similar structural and functional effects. One engineered disulfide bond, located near the fusion peptide, is sufficient to stabilize the prefusion conformations of both HeV F and LayV F. Although LayV F shares low overall sequence identity with NiV F and HeV F, the region around the fusion peptide exhibits high sequence conservation across all henipaviruses. Our findings indicate that substitutions targeting this site of conformational change might be applicable to prefusion stabilization of other henipavirus F proteins and support the use of NiV as a prototypical pathogen for henipavirus vaccine antigen design.IMPORTANCEPathogenic henipaviruses such as Nipah virus (NiV) and Hendra virus (HeV) cause respiratory symptoms, with severe cases resulting in encephalitis, seizures, and coma. The work described here shows that the NiV and HeV fusion (F) proteins share common structural features with the F protein from an emerging henipavirus, Langya virus (LayV). Sequence alignment alone was sufficient to predict which known prefusion-stabilizing amino acid substitutions from NiV F would stabilize the prefusion conformations of HeV F and LayV F. This work also reveals an unexpected oligomeric interface shared by prefusion HeV F and NiV F. Together, these advances lay a foundation for future antigen design targeting henipavirus F proteins. In this way, Nipah virus can serve as a prototypical pathogen for the development of protective vaccines and monoclonal antibodies to prepare for potential henipavirus outbreaks.

Global Inhibition with Specific Activation: How p53 and MYC Redistribute the Transcriptome in the DNA Double-Strand Break Response.

In response to stresses, cells often halt normal cellular processes, yet stress-specific pathways must bypass such inhibition to generate effective responses. We investigated how cells redistribute global transcriptional activity in response to DNA damage. We show that an oscillatory increase of p53 levels in response to double-strand breaks drives a counter-oscillatory decrease of MYC levels. Using RNA sequencing (RNA-seq) of newly synthesized transcripts, we found that p53-mediated reduction of MYC suppressed general transcription, with the most highly expressed transcripts reduced to a greater extent. In contrast, upregulation of p53 targets was relatively unaffected by MYC suppression. Reducing MYC during the DNA damage response was important for cell-fate regulation, as counteracting MYC repression reduced cell-cycle arrest and elevated apoptosis. Our study shows that global inhibition with specific activation of transcriptional pathways is important for the proper response to DNA damage; this mechanism may be a general principle used in many stress responses.

The Comparative Effectiveness of Perioperative Antibiotic Regimens to Prevent Surgical Site Infections in Pediatric Liver Transplant Recipients.

INTRODUCTION: Surgical site infections (SSIs) are a common complication in liver transplant(LT) recipients. Lack of pediatric prophylaxis guidelines results in variation in preventative antibiotic regimens. METHODS: We performed a retrospective observational study of LT recipients under 18 years using a merged dataset that included data from PHIS and UNOS between 2006 and 2017. The exposure was defined as the antibiotic(s) received within 24 hours of LT; with 6 categories, ranging from narrow (category 1: cefazolin), to broad). The primary outcome was presence or absence of SSI in the index admission. Mixed-effects logistic regression compared the effectiveness of each category relative to category 1 in preventing SSI. RESULTS: Of the 2586 LT, 284 (11%) met SSI criteria. SSI rate was higher (16.2%) in the younger sub-cohort compared to older (8.6%), necessitating a stratified analysis. Antibiotics from category 5 were most commonly used. In the younger sub-cohort, the adjusted risk was increased in all categories compared to the reference, most notably in category 3 (OR 2.58; 0.69-9.59) and category 6 (OR 2.76; 0.66-11.56). In the older sub-cohort, estimated ORs were also increased for each category, most notably in category 4 (2.49; 0.99-6.27). None of the ORs suggested benefit from broader-spectrum prophylaxis. Our E value assessment suggests it's unlikely there is unmeasured confounding by indication to the degree necessary to revert ORs to protective. CONCLUSION: There was wide variation in antibiotic prophylaxis. Adjusted analyses did not reveal a protective benefit of broader-spectrum prophylaxis in either sub-cohort, suggesting that narrower regimens may be adequate.

Association of the social disorganization index with time to first septic shock event in children with acute myeloid leukemia.

BACKGROUND: Pediatric acute myeloid leukemia (AML) chemotherapy increases the risk of life-threatening complications, including septic shock (SS). An area-based measure of social determinants of health, the social disorganization index (SDI), was hypothesized to be associated with SS and SS-associated death (SS-death). METHODS: Children treated for de novo AML on two Children's Oncology Group trials at institutions contributing to the Pediatric Health Information System (PHIS) database were included. The SDI was calculated via residential zip code data from the US Census Bureau. SS was identified via PHIS resource utilization codes. SS-death was defined as death within 2 weeks of an antecedent SS event. Patients were followed from 7 days after the start of chemotherapy until the first of end of front-line therapy, death, relapse, or removal from study. Multivariable-adjusted Cox regressions estimated hazard ratios (HRs) comparing time to first SS by SDI group. RESULTS: The assembled cohort included 700 patients, with 207 (29.6%) sustaining at least one SS event. There were 233 (33%) in the SDI-5 group (highest disorganization). Adjusted time to incident SS did not statistically significantly differ by SDI (reference, SDI-1; SDI-2: HR, 0.84 [95% confidence interval (CI), 0.51-1.41]; SDI-3: HR, 0.70 [95% CI, 0.42-1.16]; SDI-4: HR, 0.97 [95% CI, 0.61-1.53]; SDI-5: HR, 0.72 [95% CI, 0.45-1.14]). Nine patients (4.4%) with SS experienced SS-death; seven of these patients (78%) were in SDI-4 or SDI-5. CONCLUSIONS: In a large, nationally representative cohort of trial-enrolled pediatric patients with AML, there was no significant association between the SDI and time to SS.

Temperature and water availability drive insect seasonality across a temperate and a tropical region.

The more insects there are, the more food there is for insectivores and the higher the likelihood for insect-associated ecosystem services. Yet, we lack insights into the drivers of insect biomass over space and seasons, for both tropical and temperate zones. We used 245 Malaise traps, managed by 191 volunteers and park guards, to characterize year-round flying insect biomass in a temperate (Sweden) and a tropical (Madagascar) country. Surprisingly, we found that local insect biomass was similar across zones. In Sweden, local insect biomass increased with accumulated heat and varied across habitats, while biomass in Madagascar was unrelated to the environmental predictors measured. Drivers behind seasonality partly converged: In both countries, the seasonality of insect biomass differed between warmer and colder sites, and wetter and drier sites. In Sweden, short-term deviations from expected season-specific biomass were explained by week-to-week fluctuations in accumulated heat, rainfall and soil moisture, whereas in Madagascar, weeks with higher soil moisture had higher insect biomass. Overall, our study identifies key drivers of the seasonal distribution of flying insect biomass in a temperate and a tropical climate. This knowledge is key to understanding the spatial and seasonal availability of insects-as well as predicting future scenarios of insect biomass change.

Functional innovation promotes diversification of form in the evolution of an ultrafast trap-jaw mechanism in ants.

Evolutionary innovations underlie the rise of diversity and complexity-the 2 long-term trends in the history of life. How does natural selection redesign multiple interacting parts to achieve a new emergent function? We investigated the evolution of a biomechanical innovation, the latch-spring mechanism of trap-jaw ants, to address 2 outstanding evolutionary problems: how form and function change in a system during the evolution of new complex traits, and whether such innovations and the diversity they beget are repeatable in time and space. Using a new phylogenetic reconstruction of 470 species, and X-ray microtomography and high-speed videography of representative taxa, we found the trap-jaw mechanism evolved independently 7 to 10 times in a single ant genus (Strumigenys), resulting in the repeated evolution of diverse forms on different continents. The trap mechanism facilitates a 6 to 7 order of magnitude greater mandible acceleration relative to simpler ancestors, currently the fastest recorded acceleration of a resettable animal movement. We found that most morphological diversification occurred after evolution of latch-spring mechanisms, which evolved via minor realignments of mouthpart structures. This finding, whereby incremental changes in form lead to a change of function, followed by large morphological reorganization around the new function, provides a model for understanding the evolution of complex biomechanical traits, as well as insights into why such innovations often happen repeatedly.

Applying machine learning to identify pediatric patients with newly diagnosed acute lymphoblastic leukemia using administrative data.

Case identification in administrative databases is challenging as diagnosis codes alone are not adequate for case ascertainment. We utilized machine learning (ML) to efficiently identify pediatric patients with newly diagnosed acute lymphoblastic leukemia. We tested nine ML models and validated the best model internally and externally. The optimal model had 97% positive predictive value (PPV) and 99% sensitivity in internal validation; 94% PPV and 82% sensitivity in external validation. Our ML model identified a large cohort of 21,044 patients, demonstrating an efficient approach for cohort assembly and enhancing the usability of administrative data.

Clinical practice guideline-inconsistent management of fever and neutropenia in pediatric oncology: A Children's Oncology Group study.

BACKGROUND: The primary objective was to measure the proportion of episodes where care delivery was inconsistent with selected recommendations of a clinical practice guideline (CPG) on fever and neutropenia (FN) management. The influence of site size on CPG-inconsistent care delivery, and association between patient outcomes and CPG-inconsistent care were described. METHODS: This retrospective, multicenter study included patients less than 21 years old with cancer who were at high risk of poor FN outcomes and were previously enrolled to a Children's Oncology Group (COG) study at participating National Cancer Institute Community Oncology Research Program (NCORP) institutions from January 2014 through December 2015. Patients were randomly selected for chart review by participating sites from a COG-generated list. Care delivered in each episode was adjudicated (CPG-consistent or CPG-inconsistent) against each of five selected recommendations. RESULTS: A total of 107 patients from 22 sites, representing 157 FN episodes, were included. The most common CPG-inconsistent care delivered was omission of pulmonary computerized tomography in patients with persistent FN (60.3%). Of 74 episodes where assessment of four (episodes without persistent FN) or five (episodes with persistent FN) recommendations was possible, CPG-inconsistent care was delivered with respect to at least one recommendation in 63 (85%) episodes. Site size was not associated with CPG-inconsistent care delivery. No statistically significant association between CPG-inconsistent care and fever recurrence was observed. CONCLUSIONS: In this cohort of pediatric patients at high risk of poor FN outcomes, CPG-inconsistent care was common. Opportunities to optimize resource stewardship by boosting supportive care CPG implementation are highlighted.

Description of a national, multi-center registry of patients with sickle cell disease and SARS-CoV-2 infection: Data from the Pediatric COVID-19 United States Registry.

Children with sickle cell disease (SCD) are at risk of complications from viral infections, including SARS-CoV-2. We present the clinical characteristics and outcomes of pediatric patients with SCD from the Pediatric COVID-19 United States Registry who developed acute COVID-19 due to SARS-CoV-2 infection (n = 259) or multisystem inflammatory syndrome in children (MIS-C; n = 4). Nearly half of hospitalized children with SCD and SARS-CoV-2 infection required supplemental oxygen, though children with SCD had fewer intensive care (ICU) admissions compared to the general pediatric and immunocompromised populations. All registry patients with both SCD and MIS-C required ICU admission. Children with SCD are at risk of severe disease with SARS-CoV-2 infection, highlighting the importance of vaccination in this vulnerable population.

Effect of cytomegalovirus infection on post-transplant hospitalization days among children undergoing allogeneic hematopoietic cell transplantation: A marginal structural model approach.

BACKGROUND: Cytomegalovirus (CMV) commonly reactivates after allogeneic hematopoietic cell transplant (HCT), potentially leading to CMV disease and significant morbidity and mortality. To reduce morbidity and mortality, many centers conduct weekly CMV blood polymerase chain reaction (PCR) surveillance testing with subsequent initiation of antiviral therapy upon CMV DNAemia detection. However, the impact of CMV DNAemia on subsequent hospitalization risk has not been assessed using models accounting for the time-varying nature of the exposure, outcome, and confounders. METHODS: All allogeneic HCTs at the Children's Hospital of Philadelphia from January 2004-April 2017 were considered for inclusion. Patients were monitored with CMV surveillance via PCR testing for up to 105 days after HCT receipt. We estimated the association between CMV DNAemia and rate of hospitalization using marginal structural models (MSM). RESULTS: There were 343 allogeneic HCT episodes in 330 with CMV surveillance; median age was 9.0 (range: 0.1-26.2) and 46.5% were female. And 24.1% of HCT patients had at least one positive CMV blood PCR during the follow-up period. Median time to CMV DNAemia detection was 19 days (range: 4-97). The MSM estimated the incidence rate ratios for an association of CMV DNAemia with hospitalization to be 1.24, (95% confidence interval: 1.04-1.47). CONCLUSIONS: CMV DNAemia was associated with an increased hospitalization in the post-HCT period. The MSM accounted for time-varying nature of the outcome, exposure and confounders. The findings support prevention of CMV DNAemia in this population. We recommend further investigation into the effectiveness and safety of prophylaxis versus pre-emptive CMV prevention approaches.

Approach for defining human adenovirus infection and disease for central review adjudication in clinical studies.

BACKGROUND: Pediatric allogeneic hematopoietic cell transplant (allo-HCT) recipients are at risk for morbidity and mortality from human adenovirus (HAdV). HAdV can be detected in an asymptomatic state, referred to as infection or with signs or symptoms of illness, referred to as disease. Standardized case definitions are needed to distinguish infection from disease and allow for consistent reporting in both observational cohort studies and therapeutic clinical trials. METHODS: A working group of experts in virology, transplant infectious disease, and HCT was assembled to develop HAdV infection and disease definitions with the degree of certainty (i.e., possible, probable, and proven). Definitions were further refined through an iterative process and independently applied by two central review committees (CRCs) to 20 pediatric allo-HCT recipients with at least one HAdV-positive PCR. RESULTS: Initial HAdV infection and disease definitions were developed and updated through an iterative process after reviewing clinical and virological details for 81 subjects with at least one positive HAdV PCR detected in a clinical specimen. Independent application of final definitions to 20 HAdV positive allo-HCT recipients by two CRCs yielded similar number of HAdV infection or disease events but with variation of degree of certainty for some events. CONCLUSIONS: Application of definitions by a CRC for a study of HAdV infection and disease is feasible and can provide consistency in the assignment of outcomes. Definitions need further refinement to improve reproducibility and to provide guidance on determining clinical improvement or worsening after initial diagnosis of HAdV infection or disease.

Molecular Phylogeny Reveals the Past Transoceanic Voyages of Drywood Termites (Isoptera, Kalotermitidae).

Termites are major decomposers in terrestrial ecosystems and the second most diverse lineage of social insects. The Kalotermitidae form the second-largest termite family and are distributed across tropical and subtropical ecosystems, where they typically live in small colonies confined to single wood items inhabited by individuals with no foraging abilities. How the Kalotermitidae have acquired their global distribution patterns remains unresolved. Similarly, it is unclear whether foraging is ancestral to Kalotermitidae or was secondarily acquired in a few species. These questions can be addressed in a phylogenetic framework. We inferred time-calibrated phylogenetic trees of Kalotermitidae using mitochondrial genomes of ∼120 species, about 27% of kalotermitid diversity, including representatives of 21 of the 23 kalotermitid genera. Our mitochondrial genome phylogenetic trees were corroborated by phylogenies inferred from nuclear ultraconserved elements derived from a subset of 28 species. We found that extant kalotermitids shared a common ancestor 84 Ma (75-93 Ma 95% highest posterior density), indicating that a few disjunctions among early-diverging kalotermitid lineages may predate Gondwana breakup. However, most of the ∼40 disjunctions among biogeographic realms were dated at <50 Ma, indicating that transoceanic dispersals, and more recently human-mediated dispersals, have been the major drivers of the global distribution of Kalotermitidae. Our phylogeny also revealed that the capacity to forage is often found in early-diverging kalotermitid lineages, implying the ancestors of Kalotermitidae were able to forage among multiple wood pieces. Our phylogenetic estimates provide a platform for critical taxonomic revision and future comparative analyses of Kalotermitidae.

Evidence of cospeciation between termites and their gut bacteria on a geological time scale.

Termites host diverse communities of gut microbes, including many bacterial lineages only found in this habitat. The bacteria endemic to termite guts are transmitted via two routes: a vertical route from parent colonies to daughter colonies and a horizontal route between colonies sometimes belonging to different termite species. The relative importance of both transmission routes in shaping the gut microbiota of termites remains unknown. Using bacterial marker genes derived from the gut metagenomes of 197 termites and one Cryptocercus cockroach, we show that bacteria endemic to termite guts are mostly transferred vertically. We identified 18 lineages of gut bacteria showing cophylogenetic patterns with termites over tens of millions of years. Horizontal transfer rates estimated for 16 bacterial lineages were within the range of those estimated for 15 mitochondrial genes, suggesting that horizontal transfers are uncommon and vertical transfers are the dominant transmission route in these lineages. Some of these associations probably date back more than 150 million years and are an order of magnitude older than the cophylogenetic patterns between mammalian hosts and their gut bacteria. Our results suggest that termites have cospeciated with their gut bacteria since first appearing in the geological record.

"Extremely slow and capricious": A qualitative exploration of genetic researcher priorities in selecting shared data resources.

PURPOSE: Genetic researchers' selection of a database can have scientific, regulatory, and ethical implications. It is important to understand what is driving database selection such that database stewards can be responsive to user needs while balancing the interests of communities in equitably benefiting from advances. METHODS: We conducted 23 semistructured interviews with US academic genetic researchers working with private, government, and collaboratory data stewards to explore factors that they consider when selecting a genetic database. RESULTS: Interviewees used existing databases to avoid burdens of primary data collection, which was described as expensive and time-consuming. They highlighted ease of access as the most important selection factor, integrating concepts of familiarity and efficiency. Data features, such as size and available phenotype, were also important. Demographic diversity was not originally cited by any interviewee as a pivotal factor; when probed, most stated that the option to consider diversity in database selection was limited. Database features, including integrity, harmonization, and storage were also described as key components of efficient use. CONCLUSION: There is a growing market and competition between genetic data stewards. Data need to be accessible, harmonized, and administratively supported for their existence to be translated into use and, in turn, result in scientific advancements across diverse communities.

Using Nudges to Reduce Missed Appointments in Primary Care and Mental Health: a Pragmatic Trial.

BACKGROUND: Missed appointments ("no-shows") are a persistent and costly problem in healthcare. Appointment reminders are widely used but usually do not include messages specifically designed to nudge patients to attend appointments. OBJECTIVE: To determine the effect of incorporating nudges into appointment reminder letters on measures of appointment attendance. DESIGN: Cluster randomized controlled pragmatic trial. PATIENTS: There were 27,540 patients with 49,598 primary care appointments, and 9420 patients with 38,945 mental health appointments, between October 15, 2020, and October 14, 2021, at one VA medical center and its satellite clinics that were eligible for analysis. INTERVENTIONS: Primary care (n = 231) and mental health (n = 215) providers were randomized to one of five study arms (four nudge arms and usual care as a control) using equal allocation. The nudge arms included varying combinations of brief messages developed with veteran input and based on concepts in behavioral science, including social norms, specific behavioral instructions, and consequences of missing appointments. MAIN MEASURES: Primary and secondary outcomes were missed appointments and canceled appointments, respectively. STATISTICAL ANALYSIS: Results are based on logistic regression models adjusting for demographic and clinical characteristics, and clustering for clinics and patients. KEY RESULTS: Missed appointment rates in study arms ranged from 10.5 to 12.1% in primary care clinics and 18.0 to 21.9% in mental health clinics. There was no effect of nudges on missed appointment rate in primary care (OR = 1.14, 95%CI = 0.96-1.36, p = 0.15) or mental health (OR = 1.20, 95%CI = 0.90-1.60, p = 0.21) clinics, when comparing the nudge arms to the control arm. When comparing individual nudge arms, no differences in missed appointment rates nor cancellation rates were observed. CONCLUSIONS: Appointment reminder letters incorporating brief behavioral nudges were ineffective in improving appointment attendance in VA primary care or mental health clinics. More complex or intensive interventions may be necessary to significantly reduce missed appointments below their current rates. TRIAL NUMBER: ClinicalTrials.gov, Trial number NCT03850431.