Gastric outlet obstruction (GOO) is mainly due to advanced malignant disease. GOO can be treated by surgical gastroenterostomy (SGE), endoscopic enteral stenting (EES), or endoscopic ultrasound-guided gastroenterostomy (EUS-GE) to improve the quality of life. Between 2009 and 2022, patients undergoing SGE or EUS-GE for GOO were included at three centers. Technical and clinical success rates, post-procedure adverse events (AEs), length of hospital stay (LOS), 30-day all-cause mortality, and recurrence of GOO were retrospectively analyzed and compared between SGE and EUS-GE. Predictive factors for technical and clinical failure after SGE and EUS-GE were identified. Of the 97 patients included, 56 (57.7

Background: Due to the ongoing organ shortage, marginal grafts with steatosis are more frequently used in liver transplantation, leading to higher occurrences of graft dysfunction. A histological analysis is the gold standard for the quantification of liver steatosis (LS), but has its drawbacks: it is an invasive method that varies from one pathologist to another and is not available in every hospital at the time of organ procurement. This study aimed to compare non-invasive diagnostic tools to a histological analysis for the quantification of liver steatosis. Methods: Male C57BL6J mice were fed with a methioninecholine-deficient (MCD) diet for 14 days or 28 days to induce LS, and were compared to a control group of animals fed with a normal diet. The following non-invasive techniques were performed and compared to the histological quantification of liver steatosis: magnetic resonance spectroscopy (MRS), CARS microscopy, 99mTc MIBI SPECT imaging, and a new near-infrared spectrometer (NIR-SG1). Results: After 28 days on the MCD diet, an evaluation of LS showed ≥30% macrovesicular steatosis. High correlations were found between the NIR-SG1 and the blinded pathologist analysis (R2 = 0.945) (p = 0.001), and between the CARS microscopy (R2 = 0.801 (p < 0.001); MRS, R2 = 0.898 (p < 0.001)) and the blinded pathologist analysis. The ROC curve analysis showed that the area under the curve (AUC) was 1 for both the NIR-SG1 and MRS (p = 0.021 and p < 0.001, respectively), while the AUC = 0.910 for the Oil Red O stain (p < 0.001) and the AUC = 0.865 for the CARS microscopy (p < 0.001). The AUC for the 99mTc MIBI SPECT was 0.640 (p = 0.013), and this was a less discriminating technique for LS quantification. Conclusions: The best-performing non-invasive methods for LS quantification are MRS, CARS microscopy, and the NIR-SG1. The NIR-SG1 is particularly appropriate for clinical practice and needs to be validated by clinical studies on liver grafts.

Background: Hyperoxia is common during liver transplantation (LT), without being supported by any guidelines. Recent studies have shown the potential deleterious effect of hyperoxia in similar models of ischemia–reperfusion. Hyperoxia after graft reperfusion during orthotopic LT could increase lactate levels and worsen patient outcomes. Methods: We conducted a retrospective and monocentric pilot study. All adult patients who underwent LT from 26 July 2013 to 26 December 2017 were considered for inclusion. Patients were classified into two groups according to oxygen levels before graft reperfusion: the hyperoxic group (PaO2 > 200 mmHg) and the nonhyperoxic group (PaO2 < 200 mmHg). The primary endpoint was arterial lactatemia 15 min after graft revascularization. Secondary endpoints included postoperative clinical outcomes and laboratory data. Results: A total of 222 liver transplant recipients were included. Arterial lactatemia after graft revascularization was significantly higher in the hyperoxic group (6.03 ± 4 mmol/L) than in the nonhyperoxic group (4.81 ± 2 mmol/L), p < 0.01. The postoperative hepatic cytolysis peak, duration of mechanical ventilation and duration of ileus were significantly increased in the hyperoxic group. Conclusions: In the hyperoxic group, the arterial lactatemia, the hepatic cytolysis peak, the mechanical ventilation and the postoperative ileus were higher than in the nonhyperoxic group, suggesting that hyperoxia worsens short-term outcomes and could lead to increase ischemia–reperfusion injury after liver transplantation. A multicenter prospective study should be performed to confirm these results.

Natural killer (NK) cells are innate lymphoid cells (ILCs) involved in antimicrobial and antitumoral responses. Several NK cell subsets have been reported in humans and mice, but their heterogeneity across organs and species remains poorly characterized. We assessed the diversity of human and mouse NK cells by single-cell RNA sequencing on thousands of individual cells isolated from spleen and blood. Unbiased transcriptional clustering revealed two distinct signatures differentiating between splenic and blood NK cells. This analysis at single-cell resolution identified three subpopulations in mouse spleen and four in human spleen, and two subsets each in mouse and human blood. A comparison of transcriptomic profiles within and between species highlighted the similarity of the two major subsets, NK1 and NK2, across organs and species. This unbiased approach provides insight into the biology of NK cells and establishes a rationale for the translation of mouse studies to human physiology and disease.

It has recently been demonstrated that memory B cells can reenter and reengage germinal center (GC) reactions, opening the possibility that multi-hit lymphomagenesis gradually occurs throughout life during successive immunological challenges. Here, we investigated this scenario in follicular lymphoma (FL), an indolent GC-derived malignancy. We developed a mouse model that recapitulates the FL hallmark t(14;18) translocation, which results in constitutive activation of antiapoptotic protein B cell lymphoma 2 (BCL2) in a subset of B cells, and applied a combination of molecular and immunofluorescence approaches to track normal and t(14;18)(+) memory B cells in human and BCL2-overexpressing B cells in murine lymphoid tissues. BCL2-overexpressing B cells required multiple GC transits before acquiring FL-associated developmental arrest and presenting as GC B cells with constitutive activation-induced cytidine deaminase (AID) mutator activity. Moreover, multiple reentries into the GC were necessary for the progression to advanced precursor stages of FL. Together, our results demonstrate that protracted subversion of immune dynamics contributes to early dissemination and progression of t(14;18)(+) precursors and shapes the systemic presentation of FL patients.

Understanding Natural Killer (NK) cell anatomical distribution is key to dissect the role of these unconventional lymphocytes in physiological and disease conditions. In mouse, NK cells have been detected in various lymphoid and non-lymphoid organs, while in humans the current knowledge of NK cell distribution at steady state is mainly restricted to lymphoid tissues. The translation to humans of findings obtained in mice is facilitated by the identification of NK cell markers conserved between these two species. The Natural Cytotoxicity Receptor (NCR) NKp46 is a marker of the NK cell lineage evolutionary conserved in mammals. In mice, NKp46 is also present on rare T cell subsets and on a subset of gut Innate Lymphoid Cells (ILCs) expressing the retinoic acid receptor-related orphan receptor γt (RORγt) transcription factor. Here, we documented the distribution and the phenotype of human NKp46(+) cells in lymphoid and non-lymphoid tissues isolated from healthy donors. Human NKp46(+) cells were found in splenic red pulp, in lymph nodes, in lungs, and gut lamina propria, thus mirroring mouse NKp46(+) cell distribution. We also identified a novel cell subset of CD56(dim)NKp46(low) cells that includes RORγt(+) ILCs with a lineage(-)CD94(-)CD117(bright)CD127(bright) phenotype. The use of NKp46 thus contributes to establish the basis for analyzing quantitative and qualitative changes of NK cell and ILC subsets in human diseases.

Abstract Abstract 150 The recent demonstration that memory B-cells can re-enter germinal centers (GCs) and participate to new rounds of GC reactions has opened the possibility that multi-hit B-cell lymphomagenesis could be a much more dynamic process than initially anticipated, gradually progressing throughout the successive passages of memory B-cells in GCs during a lifetime of successive immunological challenges. Here, we provide evidence for this scenario in follicular lymphoma (FL), a GC derived B-cell malignancy initiated in the bone marrow by the hallmark t(14;18) BCL2/IGH translocation. To address this issue, we engineered an original sporadic BCL2tracer mouse model mimicking the rare occurrence of t(14;18) translocation in humans through V(D)J recombination errors (1 in a million B-cells) allowing to track the resultant BCL2-expressing clones; and underwent a molecular/immunofluorescent tracking of t(14;18)+ clones vs. normal memory B-cells in paired lymphoid tissue samples (spleen, lymph nodes, bone marrow) from healthy individuals. We first show that contrary to the current dogma, ectopic BCL2 expression is not sufficient to provoke the FL's characteristic differentiation arrest of activated B-cells as GC B-cells, thereby suggesting that differentiated BCL2+ memory B-cells must return to the GC to acquire additional oncogenic hits and “fix” in situ growth. Strikingly, we further find that in a small fraction of “healthy” humans, such differentiation arrest already operated, and that a clonally expanded population of t(14;18)+ cells with FL-like features have widely disseminated in blood and in multiple lymphoid organs (spleen, lymph nodes, bone marrow), with unprecedentedly reported frequencies (from 1/million to 1/500 cells in some individuals), shaping the systemic disease presentation observed in FL patients. Using molecular/immunofluorescent backtracking of such clones in various paired and remote lymphoid organs, we further demonstrate that t(14;18)+ clones systematically display an extensive history of AID (activation-induced cytidine deaminase)-mediated events compatible with iterative rounds of GC co-opting, in sharp contrast to single memory B-cell clones from the same individuals. We thus show that BCL2-expressing memory B-cells require multiple GC transits to acquire the distinctive FL-like maturation arrest as centrocyte/centroblasts and to progress to advanced FL precursor stages. Altogether, our data argue for a model of lymphomagenesis, in which progression from precursor stages to FL occurs asymptomatically over an extended period of time by subverting the dynamic and plastic attributes of memory B-cells. This understanding of the pre-clinical phases driving FL development in asymptomatic patients should help rationalize prospective approaches designed to identify biomarkers of risk, and innovative therapeutic targets present in early, potentially more curable phases of the disease. Disclosures: No relevant conflicts of interest to declare.

Abstract Abstract 466 Follicular Lymphoma (FL) is a frequent mature B-cell neoplasia resulting from the malignant transformation of germinal center (GC) B-cells in secondary lymphoid organs. The t(14;18) translocation constitute both a genetic hallmark and a critical early event in the natural history of FL. t(14;18) is however not sufficient for malignant transformation, and further synergistic oncogenic events are clearly required. In line with this, t(14;18)+ cells can be detected in the blood of most healthy individuals (HI). However, large differences in frequencies can be observed between individuals with yet uncertain significance. We recently demonstrated that in HI carrying high t(14;18) frequencies, such circulating translocated cells constitute an expanding population of atypical B-cells displaying the geno/phenotypic features of FL. In particular, we found that in such individuals, these cells are “frozen” at a GC B-cell stage of differentiation, where sustained AID expression leads to constitutive somatic hypermutation (SHM), class switch recombination (CSR) and genomic instability. As such processes are responsible for the progressive acquisition of secondary oncogenic alteration in B-cell lymphomagenesis, we proposed that t(14;18)+ cells could represent bona fide FL precursors released from established premalignant niches in lymphoid organs (Roulland et al. JEM 2006, Agopian et al. 2009). To address this possibility, we now performed a systemic characterization of FL precursors in normal human biopsies: 20 paired blood/spleen/lymph nodes (LN) issued from organ donors, 10 blood/BM samples from patients undergoing cardiac surgery and 7 hyperplastic tonsils. Using a sensitive fluctuation PCR assay, we found that while children tonsils were negative, t(14;18)+ cells were very frequent in adult tissues (75% of spleens, 59% of LN and 30% of BM samples). The frequencies were distributed over a wide frequency spectrum (>500-fold), among which t(14;18)+ frequencies in spleen (up to 1/1000 cells) were surprisingly high, far above levels generally found in blood (from 1/100,000 to 1/10 million). To test the possibility that lymphoid organs (and in particular the spleen) constitute sanctuaries of FL precursors, we characterized t(14;18) cells in tissues at the molecular level, and evaluated if paired circulating and resident t(14;18)+ cells are clonally related. Using detailed molecular analysis of BCL2/IGH amplicons obtained by LR-PCR on coupled tissue samples or isolated splenic B-cell subsets discriminating naïve and GC/post-GC B-cells, we demonstrate that t(14;18) clones issued from spleen, LN and BM are the resident counterparts of the circulating pre-FL cells (including a «frozen» GC phenotype maintaining AID activity, with the presence of highly mutated Sμ regions, intra-Sμ deletions and for the most advanced clones, unusual stigmata of AID-mediated genomic instability linked to malignant progression). Furthermore, intraclonal variation (ICV) analysis of the upstream Sμ flanking region revealed the presence of an intense trafficking of the t(14;18)+ FL-like clones between lymphoid organs and/or blood. Indeed, clones presenting identical BCL2/IGH signature could be found in different organs and blood, and yet displayed systematic ICV, indicative of ongoing SHM and further supporting the derivation of such cells from GC derived B-cells with sustained AID activity. Collectively, these data establish a direct clonal relationship between resident t(14;18)+ cells and their circulating counterparts, and the early potential of such pre-FL GC-B cells to invade other reactive GC, and to disseminate in BM. These findings strongly impact on the current understanding of disease progression, and on the proper handling of t(14;18) frequency in blood as a potential early biomarker for lymphoma. Disclosures: No relevant conflicts of interest to declare.

NKp46+CD3- natural killer lymphocytes isolated from blood, lymphoid organs, lung, liver and uterus can produce granule-dependent cytotoxicity and interferon-gamma. Here we identify in dermis, gut lamina propria and cryptopatches distinct populations of NKp46+CD3- cells with a diminished capacity to degranulate and produce interferon-gamma. In the gut, expression of the transcription factor RORgammat, which is involved in the development of lymphoid tissue-inducer cells, defined a previously unknown subset of NKp46+CD3- lymphocytes. Unlike RORgammat- lamina propria and dermis natural killer cells, gut RORgammat+NKp46+ cells produced interleukin 22. Our data show that lymphoid tissue-inducer cells and natural killer cells shared unanticipated similarities and emphasize the heterogeneity of NKp46+CD3- cells in innate immunity, lymphoid organization and local tissue repair.