Germinal center responses to SARS-CoV-2 mRNA vaccines in healthy and immunocompromised individuals.

Vaccine-mediated immunity often relies on the generation of protective antibodies and memory B cells, which commonly stem from germinal center (GC) reactions. An in-depth comparison of the GC responses elicited by SARS-CoV-2 mRNA vaccines in healthy and immunocompromised individuals has not yet been performed due to the challenge of directly probing human lymph nodes. Herein, through a fine-needle aspiration-based approach, we profiled the immune responses to SARS-CoV-2 mRNA vaccines in lymph nodes of healthy individuals and kidney transplant recipients (KTXs). We found that, unlike healthy subjects, KTXs presented deeply blunted SARS-CoV-2-specific GC B cell responses coupled with severely hindered T follicular helper cell, SARS-CoV-2 receptor binding domain-specific memory B cell, and neutralizing antibody responses. KTXs also displayed reduced SARS-CoV-2-specific CD4 and CD8 T cell frequencies. Broadly, these data indicate impaired GC-derived immunity in immunocompromised individuals and suggest a GC origin for certain humoral and memory B cell responses following mRNA vaccination.

Commensal Cryptosporidium colonization elicits a cDC1-dependent Th1 response that promotes intestinal homeostasis and limits other infections.

Cryptosporidium can cause severe diarrhea and morbidity, but many infections are asymptomatic. Here, we studied the immune response to a commensal strain of Cryptosporidium tyzzeri (Ct-STL) serendipitously discovered when conventional type 1 dendritic cell (cDC1)-deficient mice developed cryptosporidiosis. Ct-STL was vertically transmitted without negative health effects in wild-type mice. Yet, Ct-STL provoked profound changes in the intestinal immune system, including induction of an IFN-γ-producing Th1 response. TCR sequencing coupled with in vitro and in vivo analysis of common Th1 TCRs revealed that Ct-STL elicited a dominant antigen-specific Th1 response. In contrast, deficiency in cDC1s skewed the Ct-STL CD4 T cell response toward Th17 and regulatory T cells. Although Ct-STL predominantly colonized the small intestine, colon Th1 responses were enhanced and associated with protection against Citrobacter rodentium infection and exacerbation of dextran sodium sulfate and anti-IL10R-triggered colitis. Thus, Ct-STL represents a commensal pathobiont that elicits Th1-mediated intestinal homeostasis that may reflect asymptomatic human Cryptosporidium infection.

Mendelian segregation and high recombination rates facilitate genetic analyses in Cryptosporidium parvum.

Very little is known about the process of meiosis in the apicomplexan parasite Cryptosporidium despite the essentiality of sex in its life cycle. Most cell lines only support asexual growth of Cryptosporidium parvum (C. parvum), but stem cell derived intestinal epithelial cells grown under air-liquid interface (ALI) conditions support the sexual cycle. To examine chromosomal dynamics during meiosis in C. parvum, we generated two transgenic lines of parasites that were fluorescently tagged with mCherry or GFP on chromosomes 1 or 5, respectively. Infection of ALI cultures or Ifngr1-/- mice with mCherry and GFP parasites resulted in cross-fertilization and the formation of "yellow" oocysts, which contain 4 haploid sporozoites that are the product of meiosis. Recombinant oocysts from the F1 generation were purified and used to infect HCT-8 cultures, and phenotypes of the progeny were observed by microscopy. All possible phenotypes predicted by independent segregation were represented equally (~25%) in the population, indicating that C. parvum chromosomes exhibit a Mendelian inheritance pattern. The most common pattern observed from the outgrowth of single oocysts included all possible parental and recombinant phenotypes derived from a single meiotic event, suggesting a high rate of crossover. To estimate the frequency of crossover, additional loci on chromosomes 1 and 5 were tagged and used to monitor intrachromosomal crosses in Ifngr1-/- mice. Both chromosomes showed a high frequency of crossover compared to other apicomplexans with map distances (i.e., 1% recombination) of 3-12 kb. Overall, a high recombination rate may explain many unique characteristics observed in Cryptosporidium spp. such as high rates of speciation, wide variation in host range, and rapid evolution of host-specific virulence factors.

JAK2 is dispensable for maintenance of JAK2 mutant B-cell acute lymphoblastic leukemias.

Activating JAK2 point mutations are implicated in the pathogenesis of myeloid and lymphoid malignancies, including high-risk B-cell acute lymphoblastic leukemia (B-ALL). In preclinical studies, treatment of JAK2 mutant leukemias with type I JAK2 inhibitors (e.g., Food and Drug Administration [FDA]-approved ruxolitinib) provided limited single-agent responses, possibly due to paradoxical JAK2Y1007/1008 hyperphosphorylation induced by these agents. To determine the importance of mutant JAK2 in B-ALL initiation and maintenance, we developed unique genetically engineered mouse models of B-ALL driven by overexpressed Crlf2 and mutant Jak2, recapitulating the genetic aberrations found in human B-ALL. While expression of mutant Jak2 was necessary for leukemia induction, neither its continued expression nor enzymatic activity was required to maintain leukemia survival and rapid proliferation. CRLF2/JAK2 mutant B-ALLs with sustained depletion or pharmacological inhibition of JAK2 exhibited enhanced expression of c-Myc and prominent up-regulation of c-Myc target genes. Combined indirect targeting of c-Myc using the BET bromodomain inhibitor JQ1 and direct targeting of JAK2 with ruxolitinib potently killed JAK2 mutant B-ALLs.

Key subphenotypes of bipolar disorder are differentially associated with polygenic liabilities for bipolar disorder, schizophrenia, and major depressive disorder.

Bipolar disorder (BD) features heterogenous clinical presentation and course of illness. It remains unclear how subphenotypes associate with genetic loadings of BD and related psychiatric disorders. We investigated associations between the subphenotypes and polygenic risk scores (PRS) for BD, schizophrenia, and major depressive disorder (MDD) in two BD cohorts from Sweden (N = 5180) and the UK (N = 2577). Participants were assessed through interviews and medical records for inter-episode remission, psychotic features during mood episodes, global assessment of functioning (GAF, function and symptom burden dimensions), and comorbid anxiety disorders. Meta-analyses based on both cohorts showed that inter-episode remission and GAF-function were positively correlated with BD-PRS but negatively correlated with schizophrenia-PRS (SCZ-PRS) and MDD-PRS. Moreover, BD-PRS was negatively, and MDD-PRS positively, associated with the risk of comorbid anxiety disorders. Finally, SCZ-PRS was positively associated with psychotic symptoms during mood episodes. Assuming a higher PRS of certain psychiatric disorders in cases with a positive family history, we further tested the associations between subphenotypes in index BD people and occurrence of BD, schizophrenia, or MDD in their relatives using Swedish national registries. BD patients with a relative diagnosed with BD had: (1) higher GAF and lower risk of comorbid anxiety than those with a relative diagnosed with schizophrenia or MDD, (2) lower risk of psychotic symptoms than those with a relative diagnosed with schizophrenia. Our findings shed light on the genetic underpinnings of the heterogeneity in clinical manifestations and course of illness in BD, which ultimately provide insights for developing personalized approaches to the diagnosis and treatment.

Hydroxyl Radical Protein Footprinting: A Mass Spectrometry-Based Structural Method for Studying the Higher Order Structure of Proteins.

Hydroxyl radical protein footprinting (HRPF) coupled to mass spectrometry has been successfully used to investigate a plethora of protein-related questions. The method, which utilizes hydroxyl radicals to oxidatively modify solvent-accessible amino acids, can inform on protein interaction sites and regions of conformational change. Hydroxyl radical-based footprinting was originally developed to study nucleic acids, but coupling the method with mass spectrometry has enabled the study of proteins. The method has undergone several advancements since its inception that have increased its utility for more varied applications such as protein folding and the study of biotherapeutics. In addition, recent innovations have led to the study of increasingly complex systems including cell lysates and intact cells. Technological advances have also increased throughput and allowed for better control of experimental conditions. In this review, we provide a brief history of the field of HRPF and detail recent innovations and applications in the field.

Sentinel Surveillance System Implementation and Evaluation for SARS-CoV-2 Genomic Data, Washington, USA, 2020-2021.

Genomic data provides useful information for public health practice, particularly when combined with epidemiologic data. However, sampling bias is a concern because inferences from nonrandom data can be misleading. In March 2021, the Washington State Department of Health, USA, partnered with submitting and sequencing laboratories to establish sentinel surveillance for SARS-CoV-2 genomic data. We analyzed available genomic and epidemiologic data during presentinel and sentinel periods to assess representativeness and timeliness of availability. Genomic data during the presentinel period was largely unrepresentative of all COVID-19 cases. Data available during the sentinel period improved representativeness for age, death from COVID-19, outbreak association, long-term care facility-affiliated status, and geographic coverage; timeliness of data availability and captured viral diversity also improved. Hospitalized cases were underrepresented, indicating a need to increase inpatient sampling. Our analysis emphasizes the need to understand and quantify sampling bias in phylogenetic studies and continue evaluation and improvement of public health surveillance systems.

A Phase II Open-Label Trial of Binimetinib and Hydroxychloroquine in Patients With Advanced KRAS-Mutant Non-Small Cell Lung Cancer.

BACKGROUND: In RAS-mutant tumors, combined MEK and autophagy inhibition using chloroquine demonstrated synthetic lethality in preclinical studies. This phase II trial evaluated the safety and activity of the MEK inhibitor binimetinib combined with hydroxychloroquine (HCQ) in patients with advanced KRAS-mutant non-small cell lung cancer (NSCLC). METHODS: Eligibility criteria included KRAS-mutant NSCLC, progression after first-line therapy, ECOG PS 0-1, and adequate end-organ function. Binimetinib 45 mg was administered orally (p.o.) bid with HCQ 400 mg p.o. bid. The primary endpoint was objective response rate (ORR). A Simon's 2-stage phase II clinical trial design was used, with an α error of 5% and a power ß of 80%, anticipating an ORR of 30% to proceed to the 2-stage expansion. RESULTS: Between April 2021 and January 2022, 9 patients were enrolled to stage I: median age 64 years, 44.4% females, 78% smokers. The best response was stable disease in one patient (11.1%). The median progression free survival (PFS) was 1.9 months, and median overall survival (OS) was 5.3 months. Overall, 5 patients (55.6%) developed a grade 3 adverse event (AE). The most common grade 3 toxicity was rash (33%). Pre-specified criteria for stopping the trial early due to lack of efficacy were met. CONCLUSION: The combination of B + HCQ in second- or later-line treatment of patients with advanced KRAS-mutant NSCLC did not show significant antitumor activity. (ClinicalTrials.gov Identifier: NCT04735068).

Efficient Analysis of Proteome-Wide FPOP Data by FragPipe.

Monitoring protein structure before and after environmental alterations (e.g., different cell states) can give insights into the role and function of proteins. Fast photochemical oxidation of proteins (FPOP) coupled with mass spectrometry (MS) allows for monitoring of structural rearrangements by exposing proteins to OH radicals that oxidize solvent-accessible residues, indicating protein regions undergoing movement. Some of the benefits of FPOP include high throughput and a lack of scrambling due to label irreversibility. However, the challenges of processing FPOP data have thus far limited its proteome-scale uses. Here, we present a computational workflow for fast and sensitive analysis of FPOP data sets. Our workflow, implemented as part of the FragPipe computational platform, combines the speed of the MSFragger search with a unique hybrid search method to restrict the large search space of FPOP modifications. Together, these features enable more than 10-fold faster FPOP searches that identify 150% more modified peptide spectra than previous methods. We hope this new workflow will increase the accessibility of FPOP to enable more protein structure and function relationships to be explored.

Molecular characterization and clinical outcome of B-cell precursor acute lymphoblastic leukemia with IG-MYC rearrangement.

Rarely, immunophenotypically immature B-cell precursor acute lymphoblastic leukemia (BCP-ALL) carries an immunoglobulin- MYC rearrangement (IG-MYC-r). This can result in diagnostic confusion with Burkitt lymphoma/leukemia and use of individualized treatment schedules of unproven efficacy. Here we compare the molecular characteristics of these conditions and investigate historic clinical outcome data. We identified 90 cases registered in a national BCP-ALL clinical trial/registry. When present, diagnostic material underwent cytogenetic, exome, methylome and transcriptome analyses. The outcomes analyzed were 3-year event-free survival and overall survival. IG-MYC-r was identified in diverse cytogenetic backgrounds, co-existing with either established BCP-ALL-specific abnormalities (high hyperdiploidy, n=3; KMT2A-rearrangement, n=6; iAMP21, n=1; BCR-ABL1, n=1); BCL2/BCL6-rearrangements (n=15); or, most commonly, as the only defining feature (n=64). Within this final group, precursor-like V(D)J breakpoints predominated (8/9) and KRAS mutations were common (5/11). DNA methylation identified a cluster of V(D)J-rearranged cases, clearly distinct from Burkitt leukemia/lymphoma. Children with IG-MYC-r within that subgroup had a 3-year event-free survival of 47% and overall survival of 60%, representing a high-risk BCP-ALL. To develop effective management strategies this group of patients must be allowed access to contemporary, minimal residual disease-adapted, prospective clinical trial protocols.

Men and women experience different barriers to care seeking for fecal incontinence.

BACKGROUND: Despite effective treatments for fecal incontinence (FI), FI remains underdiagnosed and undertreated. This study sought to characterize and compare rates of, delays in, experiences with, and barriers to care seeking for FI among men and women. METHODS: This study was a secondary analysis of electronic survey data collected from adults with FI. The survey included the use of a validated instrument to assess FI severity and questions that now comprise a validated instrument for assessing barriers to care seeking for FI in women. Descriptive analyses characterized differences between men and women. χ2 testing for categorical variables and t-testing for normally distributed continuous variables compared statistical differences. RESULTS: The sample (N = 548) was predominately female (84%), non-Hispanic White (90%), and insured (96%), with a mean Vaizey score (13.4 ± 5.3) consistent with moderate or severe FI. Care seeking rates (p = 0.81) and symptom duration before care seeking (p = 0.23) did not differ between women and men, but women were more likely than men to be told that effective treatments exist; most male and female respondents who sought care were offered treatment. Very few respondents had been asked about FI by a healthcare provider. Whereas normative thinking, limited life impact, and believing that a healthcare provider could not help were more common barriers to care seeking among men, avoidance, fear, and discouragement were more common in women. CONCLUSIONS: Men and women with FI seek care at similar rates and after experiencing symptoms for a similar duration of time. Very few patients with FI have been screened for it by a healthcare provider. Barriers to FI care seeking are different for women and men, and men are less likely than women to be informed about effective treatments by a healthcare provider.

Prophage WO genes recapitulate and enhance Wolbachia-induced cytoplasmic incompatibility.

The genus Wolbachia is an archetype of maternally inherited intracellular bacteria that infect the germline of numerous invertebrate species worldwide. They can selfishly alter arthropod sex ratios and reproductive strategies to increase the proportion of the infected matriline in the population. The most common reproductive manipulation is cytoplasmic incompatibility, which results in embryonic lethality in crosses between infected males and uninfected females. Females infected with the same Wolbachia strain rescue this lethality. Despite more than 40 years of research and relevance to symbiont-induced speciation, as well as control of arbovirus vectors and agricultural pests, the bacterial genes underlying cytoplasmic incompatibility remain unknown. Here we use comparative and transgenic approaches to demonstrate that two differentially transcribed, co-diverging genes in the eukaryotic association module of prophage WO from Wolbachia strain wMel recapitulate and enhance cytoplasmic incompatibility. Dual expression in transgenic, uninfected males of Drosophila melanogaster crossed to uninfected females causes embryonic lethality. Each gene additively augments embryonic lethality in crosses between infected males and uninfected females. Lethality associates with embryonic defects that parallel those of wild-type cytoplasmic incompatibility and is notably rescued by wMel-infected embryos in all cases. The discovery of cytoplasmic incompatibility factor genes cifA and cifB pioneers genetic studies of prophage WO-induced reproductive manipulations and informs the continuing use of Wolbachia to control dengue and Zika virus transmission to humans.

The mental health of officials who regularly examine child sexual abuse material: strategies for harm mitigation.

BACKGROUND: The current study aims to better understand the mental health and subjective well-being of investigators and forensic examiners exposed to child sexual abuse material (CSAM) by examining which components of this work are associated with elevated mental health conditions and decreased well-being, as well as the intra-personal and organizational variables that may mitigate harm and improve well-being. METHODS: Police investigators, forensic examiners, and others connected with the criminal justice system from across the United States who were exposed to CSAM as part of their professions (N = 500) completed an anonymous online survey. Participants were recruited through connections with the National Criminal Justice Training Center. RESULTS: Duration, frequency, amount, and content of CSAM exposure was not related to poorer mental health with the exception of exposure to violent CSAM which was related to elevated post-traumatic stress symptoms. Several agency-level practices and policies, such as the availability of an Officer Wellness Program and more frequently knowing the final case resolution, were related to better mental health and well-being. Harm mitigation strategies, such as talking to other officers investigating the case and taking breaks from the material being viewed, were also related to better mental health. CONCLUSIONS: Findings indicate that police agencies have options for implementing agency-level procedures and practices that have the potential to reduce the negative impact of CSAM investigations. Additionally, many investigators use strategies that are correlated with greater well-being, suggesting opportunities for improving training programs.

Diffusion effects of a sexual violence prevention program leveraging youth-adult partnerships.

The purpose of the current study was to examine the diffusion effects of a youth-led sexual violence prevention program (i.e., Youth Voices in Prevention [Youth VIP]). Specifically, social network analysis was used to measure the extent to which Youth VIP changed behaviors for 1172 middle and high school youth who did not attend program events but were friends with Youth VIP participants and completed the first and final survey (approximately 2 years apart). Findings suggest that there was considerable interpersonal communication about Youth VIP among the students generated by program participation. Specifically, youth with friends who participated in Youth VIP were more likely to report hearing their friends talk about Youth VIP and reported talking to their friends about Youth VIP compared with those not connected to Youth VIP participants. However, there were no diffusion effects found for behavioral outcomes (i.e., bystander intervention behavior, violence victimization, and perpetration). Given the mixed findings, further research is needed to determine the extent to which youth-led sexual violence prevention initiatives lead to changes in broader community-wide changes in youths' behaviors.

Internal Standard Triggered-Parallel Reaction Monitoring Mass Spectrometry Enables Multiplexed Quantification of Candidate Biomarkers in Plasma.

Despite advances in proteomic technologies, clinical translation of plasma biomarkers remains low, partly due to a major bottleneck between the discovery of candidate biomarkers and costly clinical validation studies. Due to a dearth of multiplexable assays, generally only a few candidate biomarkers are tested, and the validation success rate is accordingly low. Previously, mass spectrometry-based approaches have been used to fill this gap but feature poor quantitative performance and were generally limited to hundreds of proteins. Here, we demonstrate the capability of an internal standard triggered-parallel reaction monitoring (IS-PRM) assay to greatly expand the numbers of candidates that can be tested with improved quantitative performance. The assay couples immunodepletion and fractionation with IS-PRM and was developed and implemented in human plasma to quantify 5176 peptides representing 1314 breast cancer biomarker candidates. Characterization of the IS-PRM assay demonstrated the precision (median % CV of 7.7%), linearity (median R2 > 0.999 over 4 orders of magnitude), and sensitivity (median LLOQ < 1 fmol, approximately) to enable rank-ordering of candidate biomarkers for validation studies. Using three plasma pools from breast cancer patients and three control pools, 893 proteins were quantified, of which 162 candidate biomarkers were verified in at least one of the cancer pools and 22 were verified in all three cancer pools. The assay greatly expands capabilities for quantification of large numbers of proteins and is well suited for prioritization of viable candidate biomarkers.

THE MAKING OF A FOOTPRINT IN PROTEIN FOOTPRINTING: A REVIEW IN HONOR OF MICHAEL L. GROSS.

Within the past decade protein footprinting in conjunction with mass spectrometry has become a powerful and versatile means to unravel the higher order structure of proteins. Footprinting-based approaches has demonstrated the capacity to inform on interaction sites and dynamic regions that participate in conformational changes. These findings when set in a biological perspective inform on protein folding/unfolding, protein-protein interactions, and protein-ligand interactions. In this review, we will look at the contribution of Dr. Michael L. Gross to protein footprinting approaches such as hydrogen deuterium exchange mass spectrometry and hydroxyl radical protein footprinting. This review details the development of novel footprinting methods as well as their applications to study higher order protein structure. © 2020 The Authors. Mass Spectrometry Reviews published by John Wiley & Sons Ltd. Mass Spec Rev.

Mental health prior to and during the COVID-19 pandemic in individuals with bipolar disorder: Insights from prospective longitudinal data.

OBJECTIVES: Many studies have examined the impact of COVID-19 on the mental health of the public, but few have focused on individuals with existing severe mental illness with longitudinal data before and during the pandemic. AIMS: To investigate the impact of the COVID-19 pandemic on the mental health of people with bipolar disorder (BD). METHODS: In an ongoing study of people with BD who used an online mood monitoring tool, True Colours, 356 participants provided weekly data on their mental health. Symptoms of depression, mania, insomnia, and suicidal thoughts were compared in 2019 and 2020. From May 2020, participants also provided weekly data on the effect of the COVID-19 pandemic on anxiety, coping strategies, access to care, and medications. RESULTS: On average, symptoms of depression, mania, insomnia, and suicidal thoughts did not significantly differ in 2020 compared to 2019, but there was evidence of heterogeneity. There were high rates of anxiety about the pandemic and its impact on coping strategies, which increased to over 70% of responders in January 2021. A significant proportion of participants reported difficulty accessing routine care (27%) and medications (21%). CONCLUSIONS: Although mood symptoms did not significantly increase during the pandemic overall, we observed heterogeneity among our BD sample and other impacted areas. Individuals' unique histories and psychosocial circumstances are key and should be explored in future qualitative studies. The significant impacts of the pandemic may take time to manifest, particularly among those who are socioeconomically disadvantaged, highlighting the need for further long-term prospective studies.

AhR controls redox homeostasis and shapes the tumor microenvironment in BRCA1-associated breast cancer.

Cancer cells have higher reactive oxygen species (ROS) than normal cells, due to genetic and metabolic alterations. An emerging scenario is that cancer cells increase ROS to activate protumorigenic signaling while activating antioxidant pathways to maintain redox homeostasis. Here we show that, in basal-like and BRCA1-related breast cancer (BC), ROS levels correlate with the expression and activity of the transcription factor aryl hydrocarbon receptor (AhR). Mechanistically, ROS triggers AhR nuclear accumulation and activation to promote the transcription of both antioxidant enzymes and the epidermal growth factor receptor (EGFR) ligand, amphiregulin (AREG). In a mouse model of BRCA1-related BC, cancer-associated AhR and AREG control tumor growth and production of chemokines to attract monocytes and activate proangiogenic function of macrophages in the tumor microenvironment. Interestingly, the expression of these chemokines as well as infiltration of monocyte-lineage cells (monocyte and macrophages) positively correlated with ROS levels in basal-like BC. These data support the existence of a coordinated link between cancer-intrinsic ROS regulation and the features of tumor microenvironment. Therapeutically, chemical inhibition of AhR activity sensitizes human BC models to Erlotinib, a selective EGFR tyrosine kinase inhibitor, suggesting a promising combinatorial anticancer effect of AhR and EGFR pathway inhibition. Thus, AhR represents an attractive target to inhibit redox homeostasis and modulate the tumor promoting microenvironment of basal-like and BRCA1-associated BC.

Voices of Youth and Emerging Adults on Suicide Prevention: Experiences and Expectations.

Self-directed violence (SDV) is a significant public health issue for adolescents and emerging adults, and yet youth exposure to prevention messaging and youth perspectives on SDV prevention needs are understudied. The current study sought to better understand the ways in which a national sample of youth and emerging adults were exposed to suicide prevention programs or conversations. A sample of 1031 young people ages 13-23 were recruited nationally through social media. Survey questions asked about SDV prevention exposure. Open-ended questions asked youth to suggest additional information they desired about SDV. A majority of participants (87%) reported that they had received prevention exposure from at least one source (i.e., family, online, attending a talk, or formal program) with few differences by demographic characteristics. However, sexual and gender minority (SGM) youth reported accessing more SDV prevention information online compared to other youth. Overall, youth had many ideas about what additional information they needed, including how to help someone at risk for SDV and how to access information about mental health. While the majority of youth are receiving some SDV prevention messages, there is variation in how they get this information, and survey participants still felt they were missing important information. Findings highlight the need to resource more comprehensive SDV prevention for youth and young adults.

Evaluating the Impact of a Youth-Led Sexual Violence Prevention Program: Youth Leadership Retreat Outcomes.

Involving youth in developing and implementing prevention programs to reduce sexual violence (SV) has the potential to improve prevention outcomes. However, there has been little focus on youth-led SV prevention programs, and limited evaluation research to help guide efforts. The current study examined the effectiveness of Youth Voices in Prevention (Youth VIP) leadership retreats on SV victimization and perpetration, forms of violence related to SV (e.g., bullying), SV bystander behaviors and readiness, and perceptions of norms related to SV prevention. Results identified mixed findings for program impact, with variations in outcomes that can help guide future youth-led prevention program initiatives. Youth attending a large "kick-off" leadership retreat (that was less youth-led that subsequent smaller retreats) later reported more bystander behaviors, but also reported increased perpetration and victimization, compared to non-attending youth. However, youth attending smaller, more focused leadership retreats held during the school year, reported reductions in sexual harassment perpetration and improved bystander behaviors and attitudes compared to non-attending youth. Evaluation of moderator variables suggests that program impact was generally stronger for younger participants, sexual minority youth, and non-White youth (which were largely Native American youth in this sample). Findings suggest promise for youth-led prevention work but also highlight the need for testing the impact of different training structures and modalities. Clinical trials number: NCT03207386.