Accurate prediction of peptide presentation by HLA molecules is important for generation of effective individualized cancer vaccines and immunotherapies. While presentation prediction algorithms for HLA class I have been successfully applied in the context of such therapies, improved prediction algorithms for class II are needed. EDGE-II is a novel algorithm based on a protein large language model that has a learned allele deconvolution network trained on existing and new immunopeptidomics data. It delivers state-of-the-art performance on prediction of peptide presentation by HLA class II and immunogenicity elicited by CD4+ T-cell epitopes. In a patient with a KRAS G12C positive tumor treated with a KRAS G12C targeting immunotherapy, EDGE-II identified KRAS G12C class II neoantigens that elicited clonally expanded CD4+ T cells with cytotoxic transcriptional profiles post-vaccination. EDGE-II could play an important role in the development of effective cancer immunotherapies by elucidating an enriched understanding of the immunopeptidome. ### Competing Interest Statement D.S, M.G.H., J. K., S. K., R. V., M. R., L. D. K.T., R.Z., L. K., A. C. G., J. A., A. M., B. A., C. D., A. R. F., M. L. J., M. J. D., M. L., C. D. P., K. J., and A. D. are stockholders and either current or previous employees at Gritstone bio, Inc. and may be listed as co-inventors on various pending patent applications related to the methods presented in this study. M.L.J.: financial interests, personal, advisory board: Astellas, Otsuka; financial interests, institutional, research grant: AbbVie, Acerta, Amgen, Apexigen, Arcus, Array, AstraZeneca, Atreca, Beigene, Birdie, Boehringer Ingelheim, Checkpoint Therapeutics, Guardant Health, Genocea, Hengrui, Immunocore, Incyte, Janseen, Jounce, Gritstone bio, Lycera, Merck, Mirati, Oncomed, Regeneron, Ribon, Sanofi, Shattuck Labs, Stem CentRx, Syndax, Takeda, Tarveda, TCR2 Therapeutics, University of Michigan and WindMIL.

Therapeutic vaccines that elicit cytotoxic T cell responses targeting tumor-specific neoantigens hold promise for providing long-term clinical benefit to patients with cancer. Here we evaluated safety and tolerability of a therapeutic vaccine encoding 20 shared neoantigens derived from selected common oncogenic driver mutations as primary endpoints in an ongoing phase 1/2 study in patients with advanced/metastatic solid tumors. Secondary endpoints included immunogenicity, overall response rate, progression-free survival and overall survival. Eligible patients were selected if their tumors expressed one of the human leukocyte antigen-matched tumor mutations included in the vaccine, with the majority of patients (18/19) harboring a mutation in KRAS. The vaccine regimen, consisting of a chimp adenovirus (ChAd68) and self-amplifying mRNA (samRNA) in combination with the immune checkpoint inhibitors ipilimumab and nivolumab, was shown to be well tolerated, with observed treatment-related adverse events consistent with acute inflammation expected with viral vector-based vaccines and immune checkpoint blockade, the majority grade 1/2. Two patients experienced grade 3/4 serious treatment-related adverse events that were also dose-limiting toxicities. The overall response rate was 0%, and median progression-free survival and overall survival were 1.9 months and 7.9 months, respectively. T cell responses were biased toward human leukocyte antigen-matched TP53 neoantigens encoded in the vaccine relative to KRAS neoantigens expressed by the patients’ tumors, indicating a previously unknown hierarchy of neoantigen immunodominance that may impact the therapeutic efficacy of multiepitope shared neoantigen vaccines. These data led to the development of an optimized vaccine exclusively targeting KRAS-derived neoantigens that is being evaluated in a subset of patients in phase 2 of the clinical study. ClinicalTrials.gov registration: NCT03953235 . In an interim analysis of a phase 1/2 trial, a heterologous prime boost vaccine comprised of a chimpanzee adenovirus and self-amplifying mRNA that encodes neoantigens derived from common oncogenic driver mutations in combination with immune checkpoint blockade was safe and elicited neoantigen-specific T cell responses in patients with advanced solid tumors.

Purpose: Circulating-tumor DNA (ctDNA) is an emerging, minimally invasive diagnostic and prognostic biomarker for patients receiving a variety of cancer therapies. Comprehensive and robust longitudinal monitoring of ctDNA can provide an understanding of tumor burden, heterogeneity, and response or resistance to treatment. Experimental Design: ctDNA of 28 metastatic cancer patients receiving an individualized neoantigen-directed immunotherapy was monitored longitudinally, up to two years, using a unique hybrid next generation sequencing assay targeting tumor-informed and tumor-naive variants. Patient-specific panels were designed targeting an average of 144 variants per patient. A tumor-naive universal panel was also designed for inclusion with patient-specific panels to monitor recurrently mutated tumor hotspots (e.g., KRAS and TP53 ) and genes implicated in immunotherapy resistance ( B2M , TAP1/2 ). Results: Analytical characterization of the assay established linearity with a mean variant allele frequency (VAF) ≥0.049%, and a variant-level limit of detection (LOD95) of 0.12%. Tumor-informed variants were detected in 26/28 patients, and de novo variants were observed in 25/28 patients. HLA LOH was also observed. Longitudinal ctDNA data provided key insights into patients' responses to vaccine treatment. Conclusions: The hybrid design of the ctDNA monitoring assay provides the sensitivity and specificity required for evaluating patient samples undergoing individualized therapy. It provides an improved capability to understand patient response to experimental therapies and further supports the utility of ctDNA as a cancer biomarker. ### Competing Interest Statement All authors are current or former employees and stockholders of Gritstone bio. They may be listed as co-inventors on pending patent applications relating to the ctDNA assay or therapeutic platform described in the study.

SARS-CoV-2 has resulted in high levels of morbidity and mortality world-wide, and severe complications can occur in older populations. Humoral immunity induced by authorized vaccines wanes within 6 months, and frequent boosts may only offer transient protection. GRT-R910 is an investigational self-amplifying mRNA (samRNA)-based SARS-CoV-2 vaccine delivering full-length Spike and selected conserved non-Spike T cell epitopes. This study reports interim analyses for a phase I open-label dose-escalation trial evaluating GRT-R910 in previously vaccinated healthy older adults (NCT05148962). Primary endpoints of safety and tolerability were assessed. Most solicited local and systemic adverse events (AEs) following GRT-R910 dosing were mild to moderate and transient, and no treatment-related serious AEs were observed. The secondary endpoint of immunogenicity was assessed via IgG binding assays, neutralization assays, interferon-gamma ELISpot, and intracellular cytokine staining. Neutralizing antibody titers against ancestral Spike and variants of concern were boosted or induced by GRT-R910 and, contrasting to authorized vaccines, persisted through at least 6 months after the booster dose. GRT-R910 increased and/or broadened functional Spike-specific T cell responses and primed functional T cell responses to conserved non-Spike epitopes. This study is limited due to small sample size, and additional data from ongoing studies will be required to corroborate these interim findings.

Background The belief that intermittent catheterization results in fewer infections than indwelling catheters is commonly expressed in the spinal cord injury literature. Some practice guidelines strongly recommend intermittent over indwelling catheterization due to concerns about infections and other complications. However, studies on this topic are of low quality. Guidelines from the Consortium for Spinal Cord Medicine suggest the data regarding infection risk are mixed, and they do not recommend one bladder management method over the other. Objectives To compare risk of bias in studies reporting higher rates of urinary tract infection (UTI) with indwelling catheters to studies that found equal rates of UTI between indwelling and intermittent catheterization, and to describe implications in clinical decision-making. Methods A systematic search of PubMed, CINAHL, Embase, and SCOPUS databases from January 1, 1980, to September 15, 2020, was conducted. Eligible studies compared symptomatic UTI rates between indwelling and intermittent catheterization. We used a risk of bias assessment tool to evaluate each study. Results Twenty-four studies were identified. Only three of these reported significantly higher UTI risk with indwelling catheters, and all three demonstrated a critical risk of bias. More than half of the studies reported differences in UTI risk of less than 20% between the two methods. Studies with larger (nonsignificant) differences favoring intermittent catheterization were more susceptible to bias from confounding. Conclusion The hypothesis that indwelling catheters cause more UTIs than intermittent catheterization is not supported by the scientific literature. Most studies failed to demonstrate a significant difference in UTI risk, and studies with nonsignificant trends favoring intermittent catheterization were more susceptible to bias from confounding. Perceived risk of infection should not influence a patient’s choice of catheter type.

Mutations in the KRAS gene are among the most common driver mutations in cancer. Targeting KRAS G12C mutations has shown some promise in clinical studies, though acquired resistance mutations pose a challenge for small molecule-based monotherapies. Vaccines targeting KRAS mutations remain highly desirable for durable tumor control and clinical benefit to patients with solid tumors. While cytotoxic CD8 T cells are critical to tumor control and clearance, CD4 T cell activation is a key component of a durable anti-tumor response. Cancer neoepitopes with homology to infectious diseases antigens (mimotopes) were associated with long-term clinical benefit following CTLA-4 blockade. In this study, we screened healthy donor PBMC samples via ex vivo interferon-gamma (IFNγ) ELISpot and identified KRAS G12C-specific T cell responses associated with cross-reactive TCRs recognizing a bacterial lipoprotein peptide sequence with homology to KRAS G12C. Healthy donors with T cell responses to both KRAS G12C and mimotope peptides shared common HLA-DR alleles, and KRAS G12C-specific T cell responses were CD4 dependent via depletion assays. KRAS G12C-reactive CD4 healthy donor T cells were polyfunctional as assessed by intracellular cytokine staining, and killing of class II target cells presenting G12C peptides assessed by Incucyte assay was CD4-dependent. We further identified vaccine-induced KRAS G12C specific CD4 T cell responses in a patient with KRAS G12C-positive non-small cell lung cancer (NSCLC) receiving a shared neoantigen-targeting cancer vaccine consisting of Chimpanzee adenovirus prime and self-amplifying mRNA (samRNA) boost vaccinations in combination with nivolumab 480 mg IV (NCT03953235). This patient had previously progressed on prior checkpoint inhibitor therapy and showed signs of clinical benefit with molecular response (e.g., ctDNA reduction) and tumor shrinkage following vaccination. Patient PBMCs were analyzed by ex vivo IFNγ ELISpot, and G12C-specific T cell responses were detectable at baseline and increased following vaccination. T cell receptor (TCR) and transcriptome single cell sequencing analyses showed a large clonal population of CD4 effector memory cells in the post-vaccination samples. Functional analyses of patient-derived TCR clonotypes from post-vaccination samples via recombinant TCR screening assays identified two functional clonotypes recognizing KRAS G12C epitopes in the context of HLA-DR on target cells. Studies to further elucidate KRAS G12C vaccine-induced TCR functionality in primary cells and transgenic mouse models are ongoing. This study provides important insight into both naturally occurring bacterial mimotope-based and vaccine-induced T cell responses against KRAS G12C neoepitopes that informs future therapeutic approaches targeting KRAS G12C tumors. Citation Format: Christine D. Palmer, Meghan G. Hart, Sonia Kounlavouth, Harshni Venkatraman, Lauren D. Kraemer, Martina Marrali, Calixto Dominguez, Fatema Z. Chowdhury, Jason R. Jaroslavsky, Lindsey Arcebuche, Lorenzo Hernandez, Bukola Adeoye, Severino Cuison, Amy R. Rappaport, Greg Boucher, Monica Lane, Melissa Rotunno, Kenneth Avocetien, Leiliane Sousa, Chris Puccia, Molly Likes, Rahul Vegesna, Rita Zhou, Alexis Mantilla, Matthew J. Davis, Ankur Dhanik, Melissa Johnson, Andrew R. Ferguson, Karin Jooss. HLA-DR-restricted CD4 T cell responses to KRAS G12C in healthy donors linked to bacterial mimotope: lessons for KRAS neoantigen vaccines in cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2267.

Background Individualized neoantigen cancer vaccines aim to benefit patients by generating strong, durable neoantigen-specific CD8 T cells. Previous data showed extended overall survival (OS) in patients with metastatic colorectal cancer (CRC) who achieved a molecular response (MR) versus those who did not after individualized neoantigen vaccination in combination with nivolumab and ipilimumab.1 We report updated OS and analysis of clinicopathologic features of patients achieving a MR. Methods Patients with metastatic CRC, non-small cell lung cancer, or gastroesophageal adenocarcinoma who had received routine chemotherapy were treated in a Phase 1/2 first-in-human study (NCT03639714). The vaccine regimen consisted of sequential administrations of chimpanzee adenovirus and self-amplifying mRNA (samRNA) vectors encoding 20 patient-specific neoantigens in combination with nivolumab (IV 480 mg Q4W) and ipilimumab (SC 30 mg). Results Thirteen of 29 patients treated had CRC. Six of these 13 had stable disease (SD) and 7 had progressive disease (PD) per RECIST v1.1. Six patients achieved a MR defined as ≥ -30% reduction in ctDNA. Patients with a MR had prolonged overall survival (OS) compared to patients without a MR (see Table 1). MR was not associated with primary tumor location, presence of liver metastases, or RAS mutations and patients with a MR were not enriched for higher tumor mutation burden (TMB), PD-L1, or T cell inflamed gene expression profiles (GEP), and had similar baseline ctDNA values based on variant allele frequency (VAF) (p-value=0.18) (table 1). Conclusions Patients who achieved MR had extended OS compared with those patients without MR. Patients with a MR were not enriched based on primary or metastatic tumor site or known correlates of response to checkpoint inhibitors. The lower baseline VAF observed in patients with a MR may be reflective of VAF in early metastatic disease. A subsequent, ongoing randomized study is evaluating individualized neoantigen vaccine in the 1L maintenance setting (NCT05141721). Acknowledgements We thank patients and their families for participating in this clinical study and Bristol-Myers Squibb for supply of nivolumab and ipilimumab. Trial Registration NCT03639714 Reference Catenacci et al. Clinical outcomes and immune responses in a phase I/II study of personalized, neoantigen-directed immunotherapy in patients with advanced MSS-CRC, GEA and NSCLC. European Society of Medical Oncology Annual Meeting 2021. https://doi.org/10.1016/j.annonc.2021.08.1345 Ethics Approval This study was reviewed and approved by institutional review boards at participating clinical sites and all patients gave informed consent before taking part in this clinical study.

Neoantigen directed immunotherapy holds promise to increase the likelihood of patients with solid tumor devoid of immune infiltration benefiting from immune checkpoint immunotherapy (CPI). A heterologous prime-boost vaccination approach consisting of Chimpanzee Adenovirus (ChAd) prime and multiple self-amplifying mRNA (SAM) boosts, delivering 20 neoantigens, has been evaluated in a Phase 1/2 clinical trial in late-stage solid tumor patients in combination with nivolumab and ipilimumab (NCT03639714). Neoantigen dynamics, tumor burden and genomic correlates of response were studied over time in 20 patients (8 GEA, 2 NSCLC, 10 MSS-CRC). Exome sequences from archival (sample used for neoantigen selection), baseline (start of immunization) and on-treatment biopsies were analyzed for 20, 16 and 10 patients respectively. Paired pre- and post-vaccine tumor transcriptomes were analyzed for 6 patients. Personalized capture baits were designed for all non-synonymous mutations detected in archival biopsies (mean 146; range: 67-402) for ctDNA monitoring. Longitudinal ctDNA samples were collected monthly on treatment (mean 7; range: 1-18). ctDNA duplex UMI libraries were captured and sequenced to a target mean raw depth >80,000x and reduced to 3x per strand consensus duplex reads. The majority of vaccine neoantigens were detected in ctDNA (87%; range 45%-100%) and mean neoantigen variant allele frequency (VAF) strongly correlated with all monitored mutations VAF (R2 = 0.90, p < 0.0001) through treatment. The percentage of vaccine neoantigens detected was higher than that for all monitored mutations in the same samples with a median of 80% (21%-98%) in ctDNA and 70% (44%-100%) in biopsies. Five of 9 MSS-CRC patients with measurable baseline ctDNA achieved molecular responses (MR, >50% reduction in ctDNA from baseline) that correlated with OS and PFS, and in some patients, was accompanied by radiologic tumor shrinkage. One MSS-CRC patient with MR for >7 months acquired novel biallelic loss-of-function mutations in TAP1 following 1 year of study treatment. Differential gene expression analysis from paired pre- and post-vaccine biopsies (including 2 MSS-CRC pairs with MR) demonstrated significant upregulation in gene signatures associated with immune-inflamed tumor microenvironments including interferon alpha and gamma responses. We demonstrate that tumor-informed neoantigen selection and vaccine manufacturing while patients receive chemotherapy is feasible, since the majority of neoantigens are retained in the tumor post-chemotherapy. Further, neoantigen-directed immunotherapy appears to drive clinical benefit in patients with advanced MSS-CRC tumors, where CPI alone has provided minimal benefit. Comprehensive ctDNA longitudinal monitoring enables real time assessment of clinical response and acquired resistance. Citation Format: Desiree Schenck, Rita Zhou, Alexis Mantilla, Oliver Spiro, Taylor Patch, Adrienne Johnson, Daniel Navarro Gomez, Brian S. Henick, Chih-Yi Liao, Sameek Roychowdhury, Steve Maron, Benjamin Solomon, Alexander I. Spira, Daniel V. Catenacci, Andrew R. Fergusson, Raphael F. Rousseau, Karin Jooss, Matthew J. Davis. Comprehensive ctDNA monitoring provides early signal of clinical benefit with a novel personalized neoantigen directed immunotherapy for late-stage cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1238.

Checkpoint inhibitor (CPI) therapies provide limited benefit to patients with tumors of low immune reactivity. T cell-inducing vaccines hold promise to exert long-lasting disease control in combination with CPI therapy. Safety, tolerability and recommended phase 2 dose (RP2D) of an individualized, heterologous chimpanzee adenovirus (ChAd68) and self-amplifying mRNA (samRNA)-based neoantigen vaccine in combination with nivolumab and ipilimumab were assessed as primary endpoints in an ongoing phase 1/2 study in patients with advanced metastatic solid tumors (NCT03639714). The individualized vaccine regimen was safe and well tolerated, with no dose-limiting toxicities. Treatment-related adverse events (TRAEs) >10% included pyrexia, fatigue, musculoskeletal and injection site pain and diarrhea. Serious TRAEs included one count each of pyrexia, duodenitis, increased transaminases and hyperthyroidism. The RP2D was 10 12 viral particles (VP) ChAd68 and 30 µg samRNA. Secondary endpoints included immunogenicity, feasibility of manufacturing and overall survival (OS). Vaccine manufacturing was feasible, with vaccination inducing long-lasting neoantigen-specific CD8 T cell responses. Several patients with microsatellite-stable colorectal cancer (MSS-CRC) had improved OS. Exploratory biomarker analyses showed decreased circulating tumor DNA (ctDNA) in patients with prolonged OS. Although small study size limits statistical and translational analyses, the increased OS observed in MSS-CRC warrants further exploration in larger randomized studies.

The use of multiple regression analysis (MRA) has been on the rise over the last few decades in part due to the realization that analysis of variance (ANOVA) statistics can be advantageously completed using MRA. Given the limitations of ANOVA strategies it is argued that MRA is the better analysis; however, in order to use ANOVA in MRA coding structures must be employed by the researcher which can be confusing to understand. The present paper attempts to simplify this discussion by providing a description of the most popular coding structures, with emphasis on their strengths, limitations, and uses. A visual analysis of each of these strategies is also included along with all necessary steps to create the contrasts. Finally, a decision tree is presented that can be used by researchers to determine which coding structure to utilize in their current research project.

I admire the commitment of researchers and clinicians at the Victorian Spinal Cord Service in their strong effort to improve bladder health among patients with spinal cord injuries (SCI). 1 May Goodwin D. Brock J. Dunlop S. et al. Optimal bladder management following spinal cord injury: evidence, practice and a cooperative approach driving future directions in Australia. Arch Phys Med Rehabil. 2018; 99: 2118-2121 Abstract Full Text Full Text PDF PubMed Scopus (5) Google Scholar During training, most of us learned that SCI patients suffer more urinary tract infections (UTIs) with indwelling urethral catheters (IUCs) than with intermittent catheterization (IC). Nonetheless, a review of the literature will show many studies that fail to demonstrate a difference in UTI risk between the 2 methods. Why do we see some studies demonstrating a large difference in UTI risk while others fail to detect any difference? The answer may lie in the field of SCI immunology. Reply to Letter re: “Optimal Bladder Management Following Spinal Cord Injury: Evidence, Practice and a Cooperative Approach Driving Future Directions in Australia”Archives of Physical Medicine and RehabilitationVol. 100Issue 9PreviewWe thank the author for raising the important issue of spinal cord injury (SCI) immune deficiency syndrome. Although outside the scope of our study, we agree that SCI immune deficiency syndrome is increasingly being recognized as a risk factor for urinary tract infection (UTI) and is critical for developing effective therapies for SCI.1 We are also cognizant of the paradox that the immune response after SCI, and in neurologic disease, has long been recognized as both detrimental and beneficial2 with identification of mechanisms, and therefore, development of treatments, requiring inclusion of both aspects. Full-Text PDF

On-orbit Robotic External Leak Locator (RELL) (i.e., mass spectrometer and ion gauge) measurements on the International Space Station (ISS) are presented to show the detection of recurring Environmental Control and Life Support System (ECLSS) vents at multiple ISS locations and RELL pointing directions. The path of ECLSS effluents to the RELL detectors is not entirely obvious at some locations, but the data indicates that diffuse gas-surface reflection or scattering resulting from plume interaction with vehicle surfaces is responsible. RELL was also able to confirm the ISS ECLSS constituents and distinguish them from the ammonia leak based on the ion mass spectra and known venting times during its operation to locate a leak in the ISS port-side External Active Thermal Control System (EATCS) coolant loop.

The Robotic External Leak Locator (RELL) was deployed to the International Space Station (ISS) with the goal of detecting and locating on-orbit leaks around the ISS. Three activities to characterize the background natural and induced environment of ISS were performed with RELL as part of the on-orbit validation and demonstration conducted in November – December 2016. The first demonstration activity pointed RELL directly in the ram (+X) and wake (-X) directions for one orbit each. The ram facing measurements showed high partial pressure for mass-to-charge ratio 16, corresponding to atomic oxygen (AO), as well as the presence of mass-to-charge ratio 17. RELL's view in the wake-facing direction included more ISS structure and several Environmental Control and Life Support System (ECLSS) on-orbit vents were detected, including the Carbon Dioxide Removal Assembly (CDRA), Russian segment ECLSS, and Sabatier vents. The second demonstration activity pointed RELL at three faces of the P1 Truss segment. Effluents from ECLSS and European Space Agency (ESA) Columbus module on-orbit vents were detected by RELL. The partial pressures of massto- charge ratios 17 and 18 remained consistent with the first on-orbit activity of characterizing the natural environment. The third demonstration activity involved RELL scanning an Active Thermal Control System (ATCS) radiator. Three locations along the radiator were scanned and the angular position of RELL with respect to the radiator was varied. Mass-to-charge ratios 16 and 17 both had upward shifts in partial pressure when pointing toward the Radiator Beam Valve Modules (RBVMs), likely corresponding to a known, small ammonia leak.

Neoantigens, which are expressed on tumor cells, are one of the main targets of an effective antitumor T-cell response. Cancer immunotherapies to target neoantigens are of growing interest and are in early human trials, but methods to identify neoantigens either require invasive or difficult-to-obtain clinical specimens, require the screening of hundreds to thousands of synthetic peptides or tandem minigenes, or are only relevant to specific human leukocyte antigen (HLA) alleles. We apply deep learning to a large (N = 74 patients) HLA peptide and genomic dataset from various human tumors to create a computational model of antigen presentation for neoantigen prediction. We show that our model, named EDGE, increases the positive predictive value of HLA antigen prediction by up to ninefold. We apply EDGE to enable identification of neoantigens and neoantigen-reactive T cells using routine clinical specimens and small numbers of synthetic peptides for most common HLA alleles. EDGE could enable an improved ability to develop neoantigen-targeted immunotherapies for cancer patients.

The Robotic External Leak Locator (RELL) was deployed to the International Space Station (ISS) with the objective of demonstrating the ability to detect and locate small leaks. On-orbit operations began in late November 2016 and following scanning activities to characterize the natural and induced environment of the ISS, RELL focused on the United States External Active Thermal Control System (EATCS). RELL successfully detected ammonia related to a known small ammonia leak in the port-side EATCS, with the highest pressure values around the inboard Radiator Beam Valve Module 1 (RBVM 1). An additional day of scanning was subsequently performed in December 2017 to focus on RBVM 1. RELL was approved for additional external operations in February 2017 with the goal of fine tuning the location of the leak. Using grid scanning patterns, RELL detected ammonia around RBVM 1 and located the approximate source of the leak. The potential leak site was inspected by a crew member during an Extravehicular Activity (EVA) in March 2017, and the suspected radiator-side lines were isolated from the port-side EATCS coolant loop in April 2017. Subsequent monitoring of the system pressures showed that the leak has stopped, indicating RELL accurately located the source of the EATCS leak. These activities verify that RELL enhances the ISS Program's ability to not only locate small leaks, but isolate the source with minimal impact to the entire ISS system.