Structures of the Hepaci-, Pegi-, and Pestiviruses envelope proteins suggest a novel membrane fusion mechanism

Enveloped viruses encode specialised glycoproteins that mediate fusion of viral and host membranes. Discovery and understanding of the molecular mechanisms of fusion have been achieved through structural analyses of glycoproteins from many different viruses, and yet the fusion mechanisms of some viral genera remain unknown. We have employed systematic genome annotation and AlphaFold modelling to predict the structures of the E1E2 glycoproteins from 60 viral species in the Hepacivirus, Pegivirus, and Pestivirus genera. While the predicted structure of E2 varied widely, E1 exhibited a very consistent fold across genera, despite little or no similarity at the sequence level. Critically, the structure of E1 is unlike any other known viral glycoprotein. This suggests that the Hepaci-, Pegi-, and Pestiviruses may possess a common and novel membrane fusion mechanism. Comparison of E1E2 models from various species reveals recurrent features that are likely to be mechanistically important and sheds light on the evolution of membrane fusion in these viral genera. These findings provide new fundamental understanding of viral membrane fusion and are relevant to structure-guided vaccinology.

A192 EFFICACY OF USTEKINUMAB IN SMALL BOWEL STRICTURES OF FIBROSTENOTIC CROHN'S DISEASE AS ASSESSED BY INTESTINAL ULTRASOUND

Background

Small bowel Crohn’s disease (CD) strictures can lead to debilitating obstructive symptoms and the deterioration of quality of life. Imaging modalities such as intestinal ultrasound (IUS) are invaluable in the diagnosis of strictures. The use of IUS in CD is rapidly growing, is cost-effective, easily repeatable, and similar in accuracy to magnetic resonance enterography. Evidence for medical management of fibrostenotic CD has been limited to anti-tumor necrosis factor biologics. Studies on the efficacy of other biologic therapies for strictures such as ustekinumab, a p40/interleukin 12 and 23 inhibitor, are lacking.

Purpose

The objective of this study was to evaluate the efficacy of ustekinumab in the treatment of small bowel strictures on IUS.

Method

This retrospective cohort study evaluated the IUS changes of terminal ileal (TI) CD strictures at baseline and 12 months following ustekinumab initiation from 2016 to 2020 at a single tertiary care center. Strictures identified were defined as 1) increased bowel wall thickness (BWT) > 3mm, 2) narrowed luminal apposition, and 3) presence of pre-stenotic dilation (PSD) or the inability to pass the colonoscope through the narrowed area. Changes in sonographic parameters (BWT, luminal size, PSD, length, hyperemia, inflammatory fat, dysfunctional peristalsis) were recorded at baseline prior to initiation of ustekinumab and compared 12 months after treatment. Differences from baseline to 12 months were paired within-person and statistical analysis was performed using paired T-tests for continuous variables and McNemar’s test for categorical variables.

Result(s)

Of the 18 patients identified, 55% (n = 10) were male, median age was 49 years (Q1-Q3: 33-63 years) at initial scan, with median CD duration of 10 years (Q1-Q3: 8-20 years). The majority of TI strictures were surgically naïve (67%, n = 12). Between pre- and 12-month post ustekinumab therapy scans, there was significant improvement in BWT [8.2 mm vs 7.2 mm, p = 0.048], however there was no significant difference in the presence of peri-enteric inflammatory fat (p = 0.10), mean stricture length (17.7 vs 21.7 cm, p = 0.18), and mean stricture lumen diameter (3.3 mm vs 2.7 mm, p = 0.44) (Table 1). There was also no significant difference in the presence of stricture-associated peri-enteric fat (89% vs 67%, p = 0.10), stricture-associated hyperemia (83% vs 89%, p = 0.65) or dysfunctional peristalsis (50% vs 61%, p = 0.41) (Table 1).

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Conclusion(s)

Our study is the first to report the efficacy of ustekinumab in small bowel CD strictures using IUS at baseline and 12 months. This study shows that although ustekinumab leads to improvement in overall sonographic appearance of bowel thickness, it does not improve luminal narrowing nor PSD, two hallmark criteria of fibrostenosis. More extensive studies with larger sample sizes evaluating ustekinumab, or combination therapies, are required to identify their role in stricturing CD.

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Disclosure of Interest

None Declared

Impact of omitting post-transplant minidose-methotrexate doses in allogeneic hematopoietic cell transplantation

Given prophylactic methotrexate (MTX) is often held in the setting of toxicity we investigated the impact of omitting minidose-MTX dose(s). Outcomes were compared between patients who had 1-3 doses omitted and those who received all four planned doses of minidose-MTX. Of 370 consecutive patients, 50 had MTX dose(s) omitted. When MTX was omitted, initial management was mycophenolate mofetil (MMF; 36/50 patients) with or without corticosteroids (14/50 patients). Rates of grade 3-4 acute GVHD were similar between groups. Omission of minidose-MTX resulted in an increased risk of chronic GVHD (cGVHD; HR 2.27; p = .024) and decreased overall survival (HR 1.61; p = .024). However, other transplant-related outcomes were comparable. In summary, omission of minidose-MTX doses was not associated with an increased risk of acute GVHD when an alternative was added (e.g. MMF ± corticosteroids). This did not abrogate the increased risk of cGVHD or decreased overall survival.

A173 INNOVATIVE CARE FOR INFLAMMATORY BOWEL DISEASE PATIENTS DURING THE COVID-19 PANDEMIC: USE OF BEDSIDE INTESTINAL ULTRASOUND TO OPTIMIZE MANAGEMENT

Background

The COVID-19 pandemic has led to significant alterations in the ability to deliver outpatient care to patients with inflammatory bowel disease (IBD) including endoscopic evaluation. This has highlighted the need for alternative, accurate, non-invasive strategies to safely assess disease activity.

Aims

The aim of this study is to describe the impact of point of care intestinal ultrasound (IUS) in a university-based tertiary care IBD urgent access clinic.

Methods

We prospectively evaluated a comprehensive care pathway which incorporated outpatient sigmoidoscopy and intestinal ultrasound with the purpose of directing further ambulatory clinical care and avoiding hospitalization or hospital-based investigations including endoscopy during the COVID pandemic for patients with established IBD with symptoms suggestive of a disease flare, or those at high risk of a new diagnosis of IBD. Non-invasive markers C Reactive Protein (CRP) and fecal calprotectin (fCal) were collected where available. Patients were pre-screened for influenza-like illness, as COVID-19 testing was not available for this population during the study period. Substantial management changes were defined as addition of any medications, biologic switch/ optimization, and or referral for surgical consultation.

Results

Between March 15^th and June 30^th 2020, a total of 72 patients were seen in the urgent access clinic. All patients were seen within 7 days of referral. The majority were female 57% (41/72) and/ or had Crohn’s disease 65.5% (47/72) (Table 1). Of these, 84.7% (61/72) underwent a substantial management change based on features of active inflammation detected by either IUS alone (53% 38/72) sigmoidoscopy alone (12.5% 9/72) or combination IUS with in-clinic sigmoidoscopy (32% 23/72) in addition to CRP and fCal. Three new diagnoses of IBD were made: one colonic Crohn’s and 2 with ulcerative colitis. One pregnant patient avoided all acute care utilization. Five patients were referred to colorectal surgery for urgent resection including two patients admitted directly for emergent operations. No patients required visits to the emergency department. Furthermore, there have been no unscheduled hospitalizations occurred in this cohort since inception March 23, 2020 til November 15^th 2020.

Conclusions

The implementation of IUS in a centralized, urgent access clinic pathway resulted in efficient and meaningful changes in IBD management while sparing the need for acute care services including ER visits, need for in-hospital endoscopy, and hospitalization. The pandemic highlights the utility of this patient-center tool and supports expansion of wider IUS adoption.

Funding Agencies

None

Degenerative Mitral Valve Repair Simplified: An Evolution to Universal Artificial Cordal Repair

BACKGROUND

Resectional and artificial cordal repair techniques are effective strategies for degenerative mitral valve (MV) repair. However, resectional repair requires a tailored approach using various techniques, whereas cordal repair offers a simpler, easily reproducible repair. The approach described in this study approach has evolved from resectional to cordal over time, and outcomes are compared between the eras.

METHODS

Clinical and echocardiographic outcomes of all patients undergoing MV repair for degenerative mitral regurgitation (MR) from January 2004 to September 2017 were reviewed. Patients were stratified by era: from January 2004 to June 2011 (era 1; n = 405), resectional techniques were used in 62% and artificial cordal techniques were used in 38%. From July 2011 to September 2017 (era 2; n = 438), artificial cordal repair was used in 98% of patients. The primary outcome was repair failure, defined as greater than moderate MR or MV reoperation.

RESULTS

Of 847 patients with degenerative MR, successful repair was achieved in 843 patients (99.5% repair rate). Leaflet prolapse was posterior in 66%, anterior in 8%, and bileaflet in 26%. Cardiopulmonary bypass time and cross-clamp times were shorter in era 2 (CPB: 109 [IQR, 92-128] minutes vs 97 [IQR, 76-121] minutes; P < .001; cross-clamp: 88 [IQR, 73-106] minutes vs. 79 [IQR, 61-99] minutes; P < .001). Predismissal echocardiography demonstrated no MR or trace MR in 95%, mild MR in 4.7%, and moderate MR in 0.3% of patients. Operative mortality was similar in the eras (0.5% vs 0.5%; P > .999). The rates of 5-year freedom from repair failure (95.1% vs 95.5%; P = .707), stroke (96.8% vs 95.3%; P = .538), and endocarditis (99.3% vs 99.7%; P = .604) were similar between the eras.

CONCLUSIONS

Artificial cordal repair for all patients with degenerative MR simplifies MV repair and yields equivalent, excellent outcomes compared with a tailored resectional approach.

Diffuse large B-cell lymphoma recurrence presenting as multiple, progressive cranial neuropathies

A 58-year-old man with a history of rheumatoid arthritis and stage IV diffuse large B-cell lymphoma, in complete remission with no evidence of residual disease on positron emission tomography/CT after completing six cycles of rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone chemotherapy, presented with acute onset of dysphagia to solids and liquids. On further evaluation, his dysphagia was attributed to a vagus nerve palsy, and later during his admission, he developed rapidly progressing left facial and vestibulocochlear nerve palsies. Imaging studies displayed pathological enhancement of bilateral seventh and eighth cranial nerves, concerning for leptomeningeal recurrence of lymphoma. Cerebrospinal fluid analysis and flow cytometry were confirmatory, revealing markedly atypical monotypic CD19 positive B cells.

Long term renal survival in patients undergoing T-Cell depleted versus conventional hematopoietic stem cell transplants

Calcineurin inhibitor-sparing T cell depleted (TCD) hematopoietic stem cell transplants HSCTs are presumed less nephrotoxic than conventional HSCTs. We evaluated incidence and risk factors for kidney failure and chronic kidney disease (CKD) in 231 TCD and 212 conventional HSCT recipients. Kidney failure required a median glomerular filtration rate (GFR) <60 mL/min/1.73 m² for ≥ 100 days anytime after 180 days post-HSCT. Two year cumulative incidence (CI) of kidney failure was 42% in the conventional vs. 31% in the TCD group (p=0.005). TCD, age, acute kidney injury and number of toxic CNI levels all impacted on kidney failure, which was associated with increased all-cause mortality (hazard ratio 2.86 (95% CI: 1.88–4.36), p <0.001). Renal recovery occurred in 28% of kidney failure patients, while the remaining patients were defined to have chronic kidney disease (CKD). In those with baseline GFR>60 mL/min/1.73 m² only exposure to nephrotoxic medications was associated with CKD (p=0.033). In the myeloablative conditioning subgroup only total body irradiation was associated with CKD (p=0.013). Of all patients, five (1.13%) required dialysis. These results confirm an impact of TCD on kidney failure but not CKD for which other risk factors such as radiation or nephrotoxic drug exposure may play a role.

Autologous transplant remains the preferred therapy for relapsed APL in CR2

Despite their favorable prognosis, 10-20% of acute promyelocytic leukemia (APL) patients relapse. Reinduction therapy is often followed by autologous hematopoietic cell transplantation (auto-HCT). Arsenic trioxide (ATO) has become part of standard reinduction and is often followed by auto-HCT. Data on patients in CR2 were collected from two large transplant registries (Center for International Blood and Marrow Transplant Research (CIBMTR) and European Group for Blood and Marrow Transplant (EBMT)) and two specialty referral centers. The outcome of patients in CR2 who received only ATO-based therapy as reinduction was retrospectively compared with those who got an auto-HCT, with or without ATO. Prognostic factors included age, disease risk, extramedullary disease and duration of CR1. Of 207 evaluable patients, the median age was 31.5 years, 15.3% had extramedullary disease and median WBC at diagnosis was 4.8 × 10(9)/L. Sixty-seven patients received ATO alone and 140 underwent auto-HCT. The groups were comparable for age, gender, extramedullary disease, risk group and duration of CR1. At 5 years, overall survival (OS) was 42% and 78% for the ATO-only and auto-HCT groups, respectively (P<0.001). In addition, OS was associated with longer duration of CR1 (P=0.002), but not with disease risk at diagnosis. These data suggest that auto-HCT for APL patients in CR2 results in better OS than ATO-based therapy alone.

Laparoscopic Subxiphoid Hernia Repair with Intracorporeal Suturing of Mesh to the Diaphragm as a Means to Decrease Recurrence

BACKGROUND

Subxiphoid hernias are a rare complication of median sternotomy with an incidence of 1%-4.2%. Repair of subxiphoid hernias is technically demanding with recurrence rates of 42% and 30% following open and laparoscopic repairs, respectively. We present a novel approach to the laparoscopic repair of subxiphoid hernias with improved overlap and fixation.

MATERIALS AND METHODS

A novel technique for repairing subxiphoid hernias is described. The falciform ligament is dissected superiorly toward the diaphragm to allow proper subfascial positioning of the mesh with adequate overlap. Multiple nonabsorbable intracorporeal sutures are used to anchor the mesh to the diaphragm above the costal margins. Transfascial nonabsorbable sutures and tacks are used to fix the mesh to the anterior abdominal wall below the costal margin.

RESULTS

We have used this method in 4 patients with a mean age of 60.5 years and a female to male ratio of 4:0. The average hernia defect size was 20.5 cm(2), and the average duration of operation was 93 minutes. There were no reported postoperative complications or evidence of recurrence at the 1-year follow-up.

CONCLUSIONS

Laparoscopic repair of subxiphoid hernias can be safely accomplished with mesh sutured to the diaphragm for improved overlap and fixation with the goal of reducing recurrence rates.

Upfront plerixafor plus G-CSF versus cyclophosphamide plus G-CSF for stem cell mobilization in multiple myeloma: efficacy and cost analysis study

Cyclophosphamide plus G-CSF (C+G-CSF) is one of the most widely used stem cell (SC) mobilization regimens for patients with multiple myeloma (MM). Plerixafor plus G-CSF (P+G-CSF) has demonstrated superior SC mobilization efficacy when compared with G-CSF alone and has been shown to rescue patients who fail mobilization with G-CSF or C+G-CSF. Despite the proven efficacy of P+G-CSF in upfront SC mobilization, its use has been limited, mostly due to concerns of high price of the drug. However, a comprehensive comparison of the efficacy and cost effectiveness of SC mobilization using C+G-CSF versus P+G-CSF is not available. In this study, we compared 111 patients receiving C+G-CSF to 112 patients receiving P+G-CSF. The use of P+G-CSF was associated with a higher success rate of SC collection defined as ⩾5 × 10(6) CD34+ cells/kg (94 versus 83%, P=0.013) and less toxicities. Thirteen patients in the C+G-CSF arm were hospitalized owing to complications while none in the P+G-CSF group. C+G-CSF was associated with higher financial burden as assessed using institutional-specific costs and charges (P<0.001) as well as using Medicare reimbursement rates (P=0.27). Higher rate of hospitalization, increased need for salvage mobilization, and increased G-CSF use account for these differences.

Network-based criterion for the success of cooperation in an evolutionary prisoner's dilemma

We consider an evolutionary prisoner's dilemma on a random network. We introduce a simple quantitative network-based parameter and show that it effectively predicts the success of cooperation in simulations on the network. The criterion is shown to be accurate on a variety of networks with degree distributions ranging from regular to Poisson to scale free. The parameter allows for comparisons of random networks regardless of their underlying topology. Finally, we draw analogies between the criterion for the success of cooperation introduced here and existing criteria in other contexts.

Cooperation in an evolutionary prisoner's dilemma on networks with degree-degree correlations

We study the effects of degree-degree correlations on the success of cooperation in an evolutionary prisoner's dilemma played on a random network. When degree-degree correlations are not present, the standardized variance of the network's degree distribution has been shown to be an accurate analytical measure of network heterogeneity that can be used to predict the success of cooperation. In this paper, we use a local-mechanism interpretation of standardized variance to give a generalization to graphs with degree-degree correlations. Two distinct mechanisms are shown to influence cooperation levels on these types of networks. The first is an intrinsic measurement of base-line heterogeneity coming from the network's degree distribution. The second is the increase in heterogeneity coming from the degree-degree correlations present in the network. A strong linear relationship is found between these two parameters and the average cooperation level in an evolutionary prisoner's dilemma on a network.

Evolution of cooperation through the heterogeneity of random networks

We use the standardized variance (nu_{st}) of the degree distribution of a random network as an analytic measure of its heterogeneity. We show that nu_{st} accurately predicts, quantitatively, the success of cooperators in an evolutionary prisoner's dilemma. Moreover, we show how the generating functional expression for nu_{st} suggests an intrinsic interpretation for the heterogeneity of the network that helps explain local mechanisms through which cooperators thrive in heterogeneous populations. Finally, we give a simple relationship between nu_{st} , the cooperation level, and the epidemic threshold of a random network that reveals an appealing connection between epidemic disease models and the evolutionary prisoner's dilemma.

Early post-transplant smooth muscle neoplasia of the colon presenting as diminutive polyps: a case complicating post-transplant lymphoproliferative disorder

A 44-year-old woman, 3 years post-transplant for pulmonary sarcoidosis, developed abdominal pain and diarrhea 13 months subsequent to an eradicated diffuse large B-cell-type, post-transplant lymphoproliferative disorder (PTLD) of the cecal region. Endoscopic examination identified multiple pale tan 5-to-9 mm rubbery nodules of the transverse and right colon in an otherwise unremarkable mucosa. Histology was characterized by bland smooth muscle proliferations, focally pushing into the mucosa. Immunohistochemistry (IHC), in situ hybridization (ISH), and polymerase chain reaction (PCR) of the sampled nodules confirmed Epstein-Barr virus (EBV) infection of neoplastic cells. To our knowledge, this is the first reported case of EBV-related post-transplant lymphoproliferative and smooth muscle neoplasms (PTSN) having distinct tropism for the colon. Endoscopic features of early PTSN, which in this case presented as diminutive polypoid lesions, have not been described previously.

Lipoprotein lipase prevents the hepatic lipase-induced reduction in particle size of high density lipoproteins during incubation of human plasma

Human plasma lipoproteins or human whole plasma have been incubated in vitro with canine hepatic lipase (HL) and bovine milk lipoprotein lipase (LPL) to determine the effects of lipases on the particle size distribution of HDL. Confirming previous reports, HL preferentially hydrolysed high density lipoprotein (HDL) triacylglycerol while LPL hydrolysed predominantly very low density lipoprotein (VLDL) triacylglycerol; however, neither lipase altered HDL particle size unless both VLDL and cholesteryl ester transfer protein (CETP) were present. Under these conditions HL promoted marked reduction in HDL particle size in a process dependent on the concentration of VLDL triacylglycerol while LPL was virtually without effect. When both LPL and HL were included in the same incubation, however, LPL prevented the effects of HL. These results are consistent with a proposition that HL has a direct effect on HDL particle size in a process which is dependent on concurrent lipid transfers between HDL and VLDL and that LPL reduces the effect of HL by reducing the concentration of VLDL triacylglycerol.