TAV-in-TAV in patients with prosthesis embolization: Impact of commissural alignment and global outcomes.

BACKGROUND: Optimal strategies to manage embolization of transcatheter aortic valve implantation (TAVI) devices are unclear; valve-in-valve (ViV) is often used. We aimed to describe through one-single center experience its rate, causes, consequences, and management as well as the rate and relevance of commissural alignment (CA) in this context. METHODS: We identified across 1038 TAVI cases, those cases requiring ViV for the management of first device embolization. CA (absence or mild misalignment) after first and second device was assessed by CT or fluoroscopy. RESULTS: A total of 23 cases (2.2%) were identified, 52.3% embolized towards the aorta and 47.7% towards the ventricle. Suboptimal implant height (38%) and embolization at the time of post-dilation (23%) were the most frequent mechanisms together with greater rate of bicuspid valve (p < 0.001) and a trend to greater annular eccentricity. Procedural and 1-year death occurred in 13% and 34%, respectively (vs. 1.1% and 7.8% in the global cohort, p < 0.001). CA was present in 76.9% of the prostheses initially implanted but was only spontaneously achieved in 30.8% of the second ViV device. Adequate CA of both prostheses was identified in only two cases (8.7%). There were no cases of coronary obstruction. CONCLUSIONS: TAVI device embolization mechanisms can often be predicted and prevented. Mortality following bail-out ViV is higher than in regular TAVI procedures but 2/3 of these patients survived beyond 1-year follow-up. In them, valve degeneration or coronary re-access might be particularly challenging since CA was rarely achieved with both devices suggesting that greater efforts should be made in this regard.

Noncoding mutations drive persistence of a founder preleukemic clone which initiates late relapse in T-ALL.

ABSTRACT: T-ALL relapse usually occurs early but can occur much later, which has been suggested to represent a de novo leukemia. However, we conclusively demonstrate late relapse can evolve from a pre-leukemic subclone harbouring a non-coding mutation that evades initial chemotherapy.

Features and outcomes of bailout repeat transcatheter aortic valve implantation (TAVI): the Bailout Acute TAVI-in-TAVI to Lessen Events (BATTLE) international registry.

AIM: Transcatheter aortic valve implantation (TAVI) is a mainstay in the management of severe aortic stenosis in patients with intermediate to prohibitive surgical risk. When a single TAVI device fails and cannot be retrieved, TAVI-in-TAVI must be performed acutely, but outcomes of bailout TAVI-in-TAVI have been incompletely appraised. We aimed at analyzing patient, procedural and outcome features of patients undergoing bailout TAVI-in-TAVI in a multicenter registry. METHODS: Details of patients undergoing bailout TAVI-in-TAVI, performed acutely or within 24 h of index TAVI, in 6 international high-volume institutions, were collected. For every case provided, 2 same-week consecutive controls (prior TAVI, and subsequent TAVI) were provided. Outcomes of interest were procedural and long-term events, including death, myocardial infarction, stroke, access site complication, major bleeding, and reintervention, and their composite (i.e. major adverse events [MAE]). RESULTS: A total of 106 patients undergoing bailout TAVI-in-TAVI were included, as well as 212 controls, for a total of 318 individuals. Bailout TAVI-in-TAVI was less common in younger patients, those with higher body mass index, or treated with Portico/Navitor or Sapien devices (all p < 0.05). Bailout TAVI-in-TAVI was associated with higher in-hospital rates of death, emergency surgery, MAE, and permanent pacemaker implantation (all p < 0.05). Long-term follow-up showed that bailout TAVI-in-TAVI was associated with higher rates of death and MAE (both < 0.05). Similar findings were obtained at adjusted analyses (all p < 0.05). However, censoring early events, outlook was not significantly different when comparing the two groups (p = 0.897 for death, and p = 0.645 for MAE). CONCLUSIONS: Bail-out TAVI-in-TAVI is associated with significant early and long-term mortality and morbidity. Thus, meticulous preprocedural planning and sophisticated intraprocedural techniques are of paramount importance to avoid these emergency procedures.

Influenza A virus infection alters the resistance profile of gut microbiota to clinically relevant antibiotics.

IMPORTANCE: Influenza virus infection affects both lung and intestinal bacterial community composition. Most of the published analyses focus on the characterization of the microbiota composition changes. Here we assess functional alterations of gut microbiota such as nutrient and antibiotic resistance changes during an acute respiratory tract infection. Upon influenza A virus (IAV) infection, cecal microbiota drops accompanied by a decrease in the ability to metabolize some common nutrients under aerobic conditions. At the same time, the cecal community presents an increase in resistance against clinically relevant antibiotics, particularly cephalosporins. Functional characterization of complex communities presents an additional and necessary element of analysis that nowadays is mainly limited to taxonomic description. The consequences of these functional alterations could affect treatment strategies, especially in multimicrobial infections.

Diurnal source apportionment of organic and inorganic atmospheric particulate matter at a high-altitude mountain site under summer conditions (Sierra Nevada; Spain).

High-altitude mountain areas are sentinel ecosystems for global environmental changes such as anthropogenic pollution. In this study, we report a source apportionment of particulate material with an aerodynamic diameter smaller than 10 µm (PM10) in a high-altitude site in southern Europe (Sierra Nevada Station; SNS (2500 m a.s.l.)) during summer 2021. The emission sources and atmospheric secondary processes that determine the composition of aerosol particles in Sierra Nevada National Park (Spain) are identified from the concentrations of organic carbon (OC), elemental carbon (EC), 12 major inorganic compounds, 18 trace elements and 44 organic molecular tracer compounds in PM10 filter samples collected during day- and nighttime. The multivariate analysis of the joint dataset resolved five main PM10 sources: 1) Saharan dust, 2) advection from the urbanized valley, 3) local combustion, 4) smoke from a fire-event, and 5) aerosol from regional recirculation with high contribution of particles from secondary inorganic and organic aerosol formation processes. PM sources were clearly associated with synoptic meteorological conditions, and day- and nighttime circulation patterns typical of mountainous areas. Although a local pollution source was identified, the contribution of this source to PM10, OC and EC was small. Our results evidence the strong influence of middle- and long-range transport of aerosols, mainly from anthropogenic origin, on the aerosol chemical composition at this remote site.

Co-option of endogenous retroviruses through genetic escape from TRIM28 repression.

Endogenous retroviruses (ERVs) have rewired host gene networks. To explore the origins of co-option, we employed an active murine ERV, IAPEz, and an embryonic stem cell (ESC) to neural progenitor cell (NPC) differentiation model. Transcriptional silencing via TRIM28 maps to a 190 bp sequence encoding the intracisternal A-type particle (IAP) signal peptide, which confers retrotransposition activity. A subset of "escapee" IAPs (∼15%) exhibits significant genetic divergence from this sequence. Canonical repressed IAPs succumb to a previously undocumented demarcation by H3K9me3 and H3K27me3 in NPCs. Escapee IAPs, in contrast, evade repression in both cell types, resulting in their transcriptional derepression, particularly in NPCs. We validate the enhancer function of a 47 bp sequence within the U3 region of the long terminal repeat (LTR) and show that escapee IAPs convey an activating effect on nearby neural genes. In sum, co-opted ERVs stem from genetic escapees that have lost vital sequences required for both TRIM28 restriction and autonomous retrotransposition.

The Many Ways to Deal with STING.

The stimulator of interferon genes (STING) is an adaptor protein involved in the activation of IFN-ß and many other genes associated with the immune response activation in vertebrates. STING induction has gained attention from different angles such as the potential to trigger an early immune response against different signs of infection and cell damage, or to be used as an adjuvant in cancer immune treatments. Pharmacological control of aberrant STING activation can be used to mitigate the pathology of some autoimmune diseases. The STING structure has a well-defined ligand binding site that can harbor natural ligands such as specific purine cyclic di-nucleotides (CDN). In addition to a canonical stimulation by CDNs, other non-canonical stimuli have also been described, whose exact mechanism has not been well defined. Understanding the molecular insights underlying the activation of STING is important to realize the different angles that need to be considered when designing new STING-binding molecules as therapeutic drugs since STING acts as a versatile platform for immune modulators. This review analyzes the different determinants of STING regulation from the structural, molecular, and cell biology points of view.

The Clinicogenomic Landscape of Induction Failure in Childhood and Young Adult T-Cell Acute Lymphoblastic Leukemia.

PURPOSE: Failure to respond to induction chemotherapy portends a poor outcome in childhood acute lymphoblastic leukemia (ALL) and is more frequent in T-cell ALL (T-ALL) than B-cell ALL. We aimed to address the limited understanding of clinical and genetic factors that influence outcome in a cohort of patients with T-ALL induction failure (IF). METHODS: We studied all cases of T-ALL IF on two consecutive multinational randomized trials, UKALL2003 and UKALL2011, to define risk factors, treatment, and outcomes. We performed multiomic profiling to characterize the genomic landscape. RESULTS: IF occurred in 10.3% of cases and was significantly associated with increasing age, occurring in 20% of patients age 16 years and older. Five-year overall survival (OS) rates were 52.1% in IF and 90.2% in responsive patients (P < .001). Despite increased use of nelarabine-based chemotherapy consolidated by hematopoietic stem-cell transplant in UKALL2011, there was no improvement in outcome. Persistent end-of-consolidation molecular residual disease resulted in a significantly worse outcome (5-year OS, 14.3% v 68.5%; HR, 4.10; 95% CI, 1.35 to 12.45; P = .0071). Genomic profiling revealed a heterogeneous picture with 25 different initiating lesions converging on 10 subtype-defining genes. There was a remarkable abundance of TAL1 noncoding lesions, associated with a dismal outcome (5-year OS, 12.5%). Combining TAL1 lesions with mutations in the MYC and RAS pathways produces a genetic stratifier that identifies patients highly likely to fail conventional therapy (5-year OS, 23.1% v 86.4%; HR, 6.84; 95% CI, 2.78 to 16.78; P < .0001) and who should therefore be considered for experimental agents. CONCLUSION: The outcome of IF in T-ALL remains poor with current therapy. The lack of a unifying genetic driver suggests alternative approaches, particularly using immunotherapy, are urgently needed.

Determinants of poor clinical outcome in patients with influenza pneumonia: A systematic review and meta-analysis.

BACKGROUND: The clinical burden of influenza is increasing worldwide. Aging, immunosuppression, and underlying respiratory illness are determinants of poor clinical outcomes, including greater mortality. Bacterial infections seem to be the main reason. Updated information on the role of bacterial infection as the cause of complications would be of value in improving the prognosis of patients with influenza. METHODS: A systematic review and meta-analysis were performed by using the PubMed repository using keywords like: Influenza, H1N1, Streptococcus pneumoniae, bacterial coinfection, secondary coinfection, bacterial complications in pneumonia, and seasonal influenza. Only articles written in English were included in publications from 2010 to 2020. The analyses were conducted following the preferred reporting items for systematic review and meta-analyses guidelines. The results were independently validated using a TrinetX database cohort of roughly 4 million patients. RESULTS: We included 135 studies that contained data from 48,259 patients hospitalized with influenza of any age. Bacterial infections were diagnosed in 5391 (11.2%). Streptococcus pneumoniae (30.7%) and Staphylococcus aureus (30.4%) were the most frequent microorganisms, followed by Haemophilus influenzae (7.1%) and Pseudomonas aeruginosa (5.9%). The random-effects model of the meta-analysis indicated that bacterial infections posed a 3.4-fold increased risk of death compared with influenza infection alone. Unexpectedly, asthma was protective (odds ratio 0.8). CONCLUSION: Bacterial infections diagnosed in 11.2% of patients with influenza increase 3.4-fold the mortality risk. S. pneumoniae, S. aureus, H. influenzae, and P. aeruginosa account for nearly 75% of the cases. Earlier diagnosis and use of antibiotics should improve outcomes in this population.

Manejo laparoscópico de las hernias ventrales mediante abordaje totalmente extraperitoneal (eTEP): experiencia inicial y resultados a corto plazo / Laparoscopic Management of Ventral Hernias by Totally Extraperitoneal (eTEP) Approach: Initial Experience and Short-Term Results / Manejo laparoscópico de hérnias ventrais usando uma abordagem totalmente extraperitoneal (eTEP): experiência inicial e resultados em curto prazo

Introducción. El manejo de la hernia ventral sigue siendo un desafío para los cirujanos. Su reparación mediante técnicas mínimamente invasivas, como la totalmente extraperitoneal (eTEP) laparoscópica, permite una amplia disección del espacio a reparar, una recuperación postoperatoria más rápida, menor dolor postoperatorio y estancia hospitalaria. El abordaje eTEP es un enfoque novedoso que utiliza el espacio retromuscular para colocar material protésico y fortalecer la pared abdominal. El objetivo es describir los resultados a corto plazo de nuestra experiencia inicial con la técnica eTEP en el manejo de las hernias ventrales. Metodología. Estudio observacional, descriptivo, retrospectivo, donde se incluyen pacientes con el diagnóstico de hernia ventral, sometidos a cirugía laparoscópicaeTEP, entre julio-2021 y junio-2022. Resultados. De un total de 21 pacientes, el 61.9% fueron hombres. El 47.6% tenían sobrepeso y el 52.4% obesidad. Estancia hospitalaria media: 1.6 días. El 66.7% fueron hernias incisionales. Las técnicas quirúrgicas realizadas fueron: Rives-Stoppa (71.4%) asociándose liberación del músculo transverso en el 28.6%. El 19% de los pacientes presentaron complicaciones globales y solo uno fue grave, requiriendo reintervención quirúrgica. Se observó la presencia de seroma clínico en el 9.5% y ecográfico en 57.1%. No se evidenciaron hematomas, infección de herida quirúrgica ni casos de recidiva herniaria. Discusión y conclusiones. El abordaje laparoscópico eTEP Rives-Stoppa, asociado o no a separación posterior de componentes, en el manejo de las hernias ventrales ofrece buenos resultados asociando una baja incidencia de complicaciones postoperatorias, corta estancia hospitalaria, baja incidencia de recidivas herniarias, por lo que podría considerarse una técnica segura y efectiva en el tratamiento de las hernias ventrales.

Introduction. Managing ventral hernia remains a challenge for surgeons. Repairing it using minimally invasive techniques, such as laparoscopic totally extraperitoneal (eTEP), which allows for a wide dissection of the space to be repaired, faster postoperative recovery, less postoperative pain and shorter hospital stay. The eTEP approach is a novel technique that focus on the uses of the retromuscular space to place prosthetic material and strengthen the abdominal wall. The objective is to describe the short-term results of our initial experience with the eTEP technique in the management of ventral hernias. Methodology. Observational, descriptive, retrospective, study, which included patients with a diagnosis of ventral hernia, undergoing laparoscopic eTEP surgery, between July-2021 and June-2022. Results. Of a total of 21 patients, 61.9% were men. 47.6% were overweight and 52.4% were obese. Average hospital stay: 1.6 days. 66.7% were incisional hernias. The surgical techniques performed were: Rives-Stoppa (71.4%) with associated transversus abdominis muscle release in 28.6%. 19% of the patients presented global complications and only one was severe, requiring surgical reintervention. The presence of clinical seroma was observed in 9.5% and ultrasound in 57.1%. There was no evidence of hematomas, surgical wound infection or cases of hernia recurrence. Discussion and conclusions. The laparoscopic-eTEP Rives-Stoppa approach, associated or not with posterior separation of components, in the management of ventral hernias offers good results with a low incidence of postoperative complications, short hospital stay, low incidence of hernia recurrences, so it could be considered a safe and effective technique in the treatment of ventral hernias.

Introdução. O manejo da hérnia ventral continua sendo um desafio para os cirurgiões. Seu reparo por meio de técnicas minimamente invasivas, como a totalmente extraperitoneal (eTEP) laparoscópica, permite ampla dissecção do espaço a ser reparado, recuperação pós-operatória mais rápida, menor dor pós-operatória e menor tempo de internação. A abordagem eTEP é uma nova abordagem que usa o espaço retromuscular para colocar material protético e fortalecer a parede abdominal. O objetivo é descrever os resultados de curto prazo de nossa experiência inicial com a técnica eTEP no manejo de hérnias ventrais. Metodologia. Estudo observacional, descritivo, retrospectivo, longitudinal, que inclui pacientes com diagnóstico de hérnia ventral, submetidos a cirurgia laparoscópica-eTEP, entre julho-2021 e junho-2022. Resultados. De um total de 21 pacientes, 61.9% eram homens; 47.6% estavam com sobrepeso e 52.4% obesos. Tempo médio de internação: 1.6 dias; 66.7% eran hérnias incisionais. As técnicas cirúrgicas realizadas foram: Rives-Stoppa (71.4%) associada à liberação do músculo transverso em 28.6%. 19% dos pacientes apresentaram complicações globais e apenas um foi grave, necesitando de reintervenção cirúrgica. A presença de seroma clínico foi observada em 9.5% e ultrassonográfica em 57.1%. Não houve evidência de hematoma, infecção de ferida cirúrgica ou casos de recidiva de hérnia. Discussão e conclusões. A abordagem laparoscópica eTEP Rives-Stoppa, associada ou não à separação posterior dos componentes, no manejo das hérnias ventrais oferece bons resultados associando baixa incidência de complicações pós-operatórias, curto tempo de internação, baixa incidência de recidivas de hérnias, pelo que pode ser considerada uma técnica segura e eficaz no tratamento das hérnias ventrais.

Curative Pericardiectomy in Interpheron-Resistant Severe Pericardial Erdheim-Chester Disease.

Erdheim-Chester disease is a rare clonal non-Langerhans cell histiocytosis with multisystemic involvement. It affects bones, large vessels, and retroperitoneum. Cardiac involvement is one of the main mortality predictors.1 We present an unusual case that debuted with cardiac tamponade and pericardial constriction requiring pericardiectomy for definitive control. (Level of Difficulty: Intermediate.).

A satellite DNA array barcodes chromosome 7 and regulates totipotency via ZFP819.

Mammalian genomes are a battleground for genetic conflict between repetitive elements and KRAB-zinc finger proteins (KZFPs). We asked whether KZFPs can regulate cell fate by using ZFP819, which targets a satellite DNA array, ZP3AR. ZP3AR coats megabase regions of chromosome 7 encompassing genes encoding ZSCAN4, a master transcription factor of totipotency. Depleting ZFP819 in mouse embryonic stem cells (mESCs) causes them to transition to a 2-cell (2C)-like state, whereby the ZP3AR array switches from a poised to an active enhancer state. This is accompanied by a global erosion of heterochromatin roadblocks, which we link to decreased SETDB1 stability. These events result in transcription of active LINE-1 elements and impaired differentiation. In summary, ZFP819 and TRIM28 partner up to close chromatin across Zscan4, to promote exit from totipotency. We propose that satellite DNAs may control developmental fate transitions by barcoding and switching off master transcription factor genes.

Transcatheter Mitral Valve-in-Valve Implantation with the Balloon-Expandable Myval Device.

Background: The vast majority of transcatheter valve-in-valve (ViV) mitral procedures have been reported with the SAPIEN family. We aimed to report the preliminary experience with the Myval balloon-expandable device in this setting. Methods: Multicenter retrospective study of high-risk surgical patients with mitral bioprosthesis degeneration undergoing transcatheter ViV implantation with Myval device. Results: A total of 11 patients from five institutions were gathered between 2019 and 2022 (age 68 ± 7.8, 63% women). The peak and mean transvalvular gradients were 27 ± 5 mmHg and 14.7 ± 2.3 mmHg, respectively, and the predicted neo-left ventricular outflow tract (neo-LVOT) area was 183.4 ± 56 mm2 (range: 171 to 221 mm2). The procedures were performed via transfemoral access in all cases (through echocardiography-guided transeptal puncture (81.8% transesophageal, 11.2% intracardiac)). Technical success was achieved in all cases, with no significant residual mitral stenosis in any of them (peak 7.2 ± 2.7 and mean gradient 3.4 ± 1.7 mmHg) and no complications during the procedure. There were no data of LVOT obstruction, migration, or paravalvular leak in any case. Mean hospital stay was 3 days, with one major vascular complication and no stroke. At 6-month follow-up, there was one case with suboptimal anticoagulation presenting an increase in the transmitral gradients (mean 15 mmHg) that normalized after optimization of the anticoagulation, but no other relevant events. Conclusions: Transseptal ViV mitral implantation with the balloon-expandable Myval device was feasible and safe avoiding redo surgery in high-risk patients with bioprosthesis degeneration.

Aberrant paracrine signalling for bone remodelling underlies the mutant histone-driven giant cell tumour of bone.

Oncohistones represent compelling evidence for a causative role of epigenetic perturbations in cancer. Giant cell tumours of bone (GCTs) are characterised by a mutated histone H3.3 as the sole genetic driver present in bone-forming osteoprogenitor cells but absent from abnormally large bone-resorbing osteoclasts which represent the hallmark of these neoplasms. While these striking features imply a pathogenic interaction between mesenchymal and myelomonocytic lineages during GCT development, the underlying mechanisms remain unknown. We show that the changes in the transcriptome and epigenome in the mesenchymal cells caused by the H3.3-G34W mutation contribute to increase osteoclast recruitment in part via reduced expression of the TGFß-like soluble factor, SCUBE3. Transcriptional changes in SCUBE3 are associated with altered histone marks and H3.3G34W enrichment at its enhancer regions. In turn, osteoclasts secrete unregulated amounts of SEMA4D which enhances proliferation of mutated osteoprogenitors arresting their maturation. These findings provide a mechanism by which GCTs undergo differentiation in response to denosumab, a drug that depletes the tumour of osteoclasts. In contrast, hTERT alterations, commonly found in malignant GCT, result in the histone-mutated neoplastic cells being independent of osteoclasts for their proliferation, predicting unresponsiveness to denosumab. We provide a mechanism for the initiation of GCT, the basis of which is dysfunctional cross-talk between bone-forming and bone-resorbing cells. The findings highlight the role of tumour/microenvironment bidirectional interactions in tumorigenesis and how this is exploited in the treatment of GCT.

Adaptation of the Multidimensional Body Self Relations Questionnaire for Young People Between 9 and 16 Years old.

BACKGROUND: Young adolescents and pre-adolescents are the population most vulnerable to disorders derived from a distorted Body Image (BI). In this study, the Multidimensional Body Self Relations Questionnaire, MBSR®, was adapted and validated for young Spanish people between 9 and 16 years old. METHOD: 719 young people of both sexes participated. The internal structure, the invariance of the measure according to sex and age, and evidence of validity and reliability of the measure were examined. RESULTS: the dimensional model found in adults was not replicated in young people. The simplest, best-fitting BI construct in young people, examined from the perspective of the BI construct contained in the MBSRQ®, consisted of 20 items in 4 differentially correlated factors. The internal consistency of the factors contained in the MBSRQ-SA-a was shown to be satisfactory, as was the evidence of concurrent validity. Factor invariance was demonstrated as a function of gender and three age groups. CONCLUSIONS: the MBSRQ-SA-a is reliable and valid for the study of BI in young people aged 9-16 years to the extent permitted by the content of the 4 factors making it up.

Diverticulitis apendicular, como diagnóstico diferencial / Appendiceal diverticulitis as differential diagnosis

RESUMEN La diverticulitis apendicular (DA) es una patología poco frecuente, considerada clínicamente indistinguible de la apendicitis aguda, aunque podría presentar una sintomatología más leve. Este es el caso de un paciente masculino de 59 años, que concurre al Servicio de Urgencias presentando signos y síntomas sugestivos de una apendicitis aguda; una ecografía informa un asa tubular parcialmente compresible de 7,8 mm de diámetro y una fina banda de líquido laminar, compatible con proceso apendicular agudo. La apendicectomía se realizó de manera convencional evidenciándose un apéndice inflamado principalmente en su región distal. La histología reveló diverticulitis apendicular complicada con rotura. El paciente evolucionó favorablemente y se externó a las 24 horas. Existe una asociación de DA y neoplasia apendicular, por lo que se recomienda una colonoscopia y el seguimiento de este tipo de pacientes.

ABSTRACT Appendiceal diverticulitis (AD) is a rare condition considered clinically identical to acute appendicitis although it may present milder symptoms. We report the case of a 59-year-old male patient who visited the emergency department due to signs and symptoms suggestive of acute appendicitis. An abdominal ultrasound showed partially compressible tubular loop with a diameter of 7.8 mm and a thin band of laminar fluid, consistent with acute appendiceal process. During conventional appendectomy the appendix had signs of inflammation, mainly in the distal region. The histology revealed appendiceal diverticulitis complicated with rupture. The patient had favorable outcome and was discharged 24 hours later. As, there is a clear association between AD and appendiceal neoplasms, colonoscopy and patient monitoring is recommended.

Systematic Evaluation of the Immune Environment of Small Intestinal Neuroendocrine Tumors.

PURPOSE: The immune tumor microenvironment and the potential therapeutic opportunities for immunotherapy in small intestinal neuroendocrine tumors (siNET) have not been fully defined. EXPERIMENTAL DESIGN: Herein, we studied 40 patients with primary and synchronous metastatic siNETs, and matched blood and normal tissue obtained during surgery. We interrogated the immune checkpoint landscape using multi-parametric flow cytometry. In addition, matched FFPE tissue was obtained for multi-parametric IHC to determine the relative abundance and distribution of T-cell infiltrate. Tumor mutational burden (TMB) was also assessed and correlated with immune infiltration. RESULTS: Effector tumor-infiltrating lymphocytes (TIL) had a higher expression of PD-1 in the tumor microenvironment compared with the periphery. In addition, CD8+ TILs had a significantly higher co-expression of PD-1/ICOS and PD-1/CTLA-4 (cytotoxic T lymphocyte antigen-4) and higher levels of PD-1 expression compared with normal tissue. IHC revealed that the majority of cases have ≤10% intra-tumoral T cells but a higher number of peri-tumoral T cells, demonstrating an "exclusion" phenotype. Finally, we confirmed that siNETs have a low TMB compared with other tumor types in the TCGA database but did not find a correlation between TMB and CD8/Treg ratio. CONCLUSIONS: Taken together, these results suggest that a combination therapy approach will be required to enhance the immune response, using PD-1 as a checkpoint immunomodulator backbone in combination with other checkpoint targeting molecules (CTLA-4 or ICOS), or with drugs targeting other pathways to recruit "excluded" T cells into the tumor microenvironment to treat patients with siNETs.