KRAS allelic imbalance drives tumour initiation yet suppresses metastasis in colorectal cancer in vivo.

Oncogenic KRAS mutations are well-described functionally and are known to drive tumorigenesis. Recent reports describe a significant prevalence of KRAS allelic imbalances or gene dosage changes in human cancers, including loss of the wild-type allele in KRAS mutant cancers. However, the role of wild-type KRAS in tumorigenesis and therapeutic response remains elusive. We report an in vivo murine model of colorectal cancer featuring deletion of wild-type Kras in the context of oncogenic Kras. Deletion of wild-type Kras exacerbates oncogenic KRAS signalling through MAPK and thus drives tumour initiation. Absence of wild-type Kras potentiates the oncogenic effect of KRASG12D, while incidentally inducing sensitivity to inhibition of MEK1/2. Importantly, loss of the wild-type allele in aggressive models of KRASG12D-driven CRC significantly alters tumour progression, and suppresses metastasis through modulation of the immune microenvironment. This study highlights the critical role for wild-type Kras upon tumour initiation, progression and therapeutic response in Kras mutant CRC.

Clinical outcomes of heart transplantation using hepatitis c-viremic donors: A systematic review with meta-analysis.

BACKGROUND: Heart transplantation (HTx) from hepatitis C virus (HCV)-viremic donors to nonviremic recipients decreases mortality and costs. Consequently, many transplant centers have reported their results using this strategy. Hence, there is a need for an outcome analysis. METHODS: We performed a systematic review with meta-analysis. In August 2020, we searched PubMed and EMBASE for publications containing data of nonviremic recipients who underwent HTx from HCV-viremic donors once direct-acting antiviral (DAA) therapy had become available (≥2014). RESULTS: We identified 398 publications, 13 of which met inclusion criteria, and analyzed the outcomes of 195 recipients. The HCV-transmission rate was >97% but, the cure rate was 100% with DAA therapy. The 6 and 12-month survival were 95.6% and 92.9%, respectively. Of 10 deaths reported, none were associated with HCV infection. The acute cellular rejection (ACR) rate was 31.1%. The overall DAA failure rate was 1.1%, defined as the need to alter the initial DAA therapy due to failure to cure HCV. However, the DAA failure rate was 0% when the DAA therapy was started within the first 2 weeks post-HTx. No statistically significant differences in HCV cure rates, survivals, ACR rates, and DAA failure rates were observed when outcomes were stratified by therapeutic approach type (i.e., a prophylactic approach in which DAA was given to the recipient before confirming HCV-transmission vs a reactive approach, in which DAA was given to the recipient only after an HCV-transmission was confirmed). CONCLUSIONS: Excellent clinical outcomes have been observed in nonviremic recipients of HTx from HCV-viremic donors since DAA had become available.

Efficacy of Bivalirudin for Therapeutic Anticoagulation in COVID-19 Patients Requiring ECMO Support.

OBJECTIVES: The Coronavirus Disease 2019 (COVID-19) pandemic has been associated with cases of refractory acute respiratory distress syndrome (ARDS) sometimes requiring support with extracorporeal membrane oxygenation (ECMO). Bivalirudin can be used for anticoagulation in patients on ECMO support, but its efficacy and safety in patients with COVID-19 is unknown. The authors set out to compare the pharmacologic characteristics and dosing requirements of bivalirudin in patients requiring ECMO support for ARDS due to COVID-19 versus ARDS from other etiologies. DESIGN AND SETTING: This retrospective case-control study was performed at Indiana University Health Methodist Hospital in Indianapolis, Indiana. PARTICIPANTS: Patients were included if they were on venovenous ECMO support between June 2019 and June 2020, and divided into two groups: ARDS secondary to COVID-19 and those with ARDS from another etiology (Non-COVID). INTERVENTIONS: Patient demographics, such as age, sex, weight, chronic comorbid conditions, baseline antiplatelet and anticoagulant use, antiplatelet use during ECMO, and need for renal replacement therapy were collected, and compared between groups. Time to activated partial thromboplastin time (aPTT) goal, percentage of time at aPTT goal, bivalirudin rates, total bivalirudin requirements, total duration on bivalirudin, total duration on ECMO, mortality, and complications associated with ECMO were collected and compared between groups. MEASUREMENTS AND MAIN RESULTS: A total of 42 patients met inclusion criteria (n = 19 COVID-19, n = 23 non-COVID). However, percentages of aPTTs at goal were maintained more consistently in patients with COVID-19 versus non-COVID (86% v 74%: p < 0.01). Higher median (IQR) daily rates (3.1 µg/kg/min [2.3-5.2] v 2.4 µg/kg/min [1.7-3.3]: p = 0.05) and higher median (IQR) maximum rates of bivalirudin (5 µg/kg/min [3.7-7.5] v 3.8 µg/kg/min [2.5-5]: p = 0.03) were required in the COVID-19 group versus the non-COVID group. Time to goal aPTT was similar between groups. There were no differences in complications associated with anticoagulation, as demonstrated by similar rates of bleeding and thrombosis between both groups. CONCLUSIONS: Patients on ECMO with ARDS from COVID-19 require more bivalirudin overall and higher rates of bivalirudin to maintain goal aPTTs compared with patients without COVID-19. However, COVID-19 patients more consistently maintain goal aPTT. Future randomized trials are needed to support efficacy and safety of bivalirudin for anticoagulation of COVID-19 patients on ECMO.

A Highly Conserved Shh Enhancer Coordinates Hypothalamic and Craniofacial Development.

Enhancers that are conserved deep in evolutionary time regulate characteristics held in common across taxonomic classes. Here, deletion of the highly conserved Shh enhancer SBE2 (Shh brain enhancer 2) in mouse markedly reduced Shh expression within the embryonic brain specifically in the rostral diencephalon; however, no abnormal anatomical phenotype was observed. Secondary enhancer activity was subsequently identified which likely mediates low levels of expression. In contrast, when crossing the SBE2 deletion with the Shh null allele, brain and craniofacial development were disrupted; thus, linking SBE2 regulated Shh expression to multiple defects and further enabling the study of the effects of differing levels of Shh on embryogenesis. Development of the hypothalamus, derived from the rostral diencephalon, was disrupted along both the anterior-posterior (AP) and the dorsal-ventral (DV) axes. Expression of DV patterning genes and subsequent neuronal population induction were particularly sensitive to Shh expression levels, demonstrating a novel morphogenic context for Shh. The role of SBE2, which is highlighted by DV gene expression, is to step-up expression of Shh above the minimal activity of the second enhancer, ensuring the necessary levels of Shh in a regional-specific manner. We also show that low Shh levels in the diencephalon disrupted neighbouring craniofacial development, including mediolateral patterning of the bones along the cranial floor and viscerocranium. Thus, SBE2 contributes to hypothalamic morphogenesis and ensures there is coordination with the formation of the adjacent midline cranial bones that subsequently protect the neural tissue.

Dynamic Cardiolipin Synthesis Is Required for CD8+ T Cell Immunity.

Mitochondria constantly adapt to the metabolic needs of a cell. This mitochondrial plasticity is critical to T cells, which modulate metabolism depending on antigen-driven signals and environment. We show here that de novo synthesis of the mitochondrial membrane-specific lipid cardiolipin maintains CD8+ T cell function. T cells deficient for the cardiolipin-synthesizing enzyme PTPMT1 had reduced cardiolipin and responded poorly to antigen because basal cardiolipin levels were required for activation. However, neither de novo cardiolipin synthesis, nor its Tafazzin-dependent remodeling, was needed for T cell activation. In contrast, PTPMT1-dependent cardiolipin synthesis was vital when mitochondrial fitness was required, most notably during memory T cell differentiation or nutrient stress. We also found CD8+ T cell defects in a small cohort of patients with Barth syndrome, where TAFAZZIN is mutated, and in a Tafazzin-deficient mouse model. Thus, the dynamic regulation of a single mitochondrial lipid is crucial for CD8+ T cell immunity.

Developmentally regulated Shh expression is robust to TAD perturbations.

Topologically associating domains (TADs) have been proposed to both guide and constrain enhancer activity. Shh is located within a TAD known to contain all its enhancers. To investigate the importance of chromatin conformation and TAD integrity on developmental gene regulation, we have manipulated the Shh TAD - creating internal deletions, deleting CTCF sites, and deleting and inverting sequences at TAD boundaries. Chromosome conformation capture and fluorescence in situ hybridisation assays were used to investigate the changes in chromatin conformation that result from these manipulations. Our data suggest that these substantial alterations in TAD structure have no readily detectable effect on Shh expression patterns or levels of Shh expression during development - except where enhancers are deleted - and result in no detectable phenotypes. Only in the case of a larger deletion at one TAD boundary could ectopic influence of the Shh limb enhancer be detected on a gene (Mnx1) in the neighbouring TAD. Our data suggests that, contrary to expectations, the developmental regulation of Shh expression is remarkably robust to TAD perturbations.

Intestinal Graft Failure: Should We Perform the Allograft Enterectomy Before or With Retransplantation?

BACKGROUND: Intestinal graft dysfunction is sometimes irreversible and requires allograft enterectomy with or without retransplantation. There is no comprehensive assessment of allograft enterectomy regarding indications and outcomes. The aim of this study was to evaluate management of patients with intestinal graft failure with special reference to indications and outcomes of allograft enterectomy and the procedure's validity as a bridge to retransplantation. METHODS: Graft and patient survivals, reason for graft failure, and rejection episodes were evaluated in 221 intestinal recipients (primary transplantation [n = 201], retransplantation [n = 20]). Indications, surgical factors, and outcomes of allograft enterectomy were investigated. RESULTS: Reasons for isolated enterectomy included systemic infection in 11, gastrointestinal bleeding in 1, and severe electrolyte imbalance in 1, all of which were associated with rejection. One isolated intestinal transplantation patient underwent isolated enterectomy due to cytomegalovirus enteritis. One multivisceral transplantation patient underwent isolated allograft enterectomy due to bowel necrosis. Of these 15 patients, 3 died from persistent infection postoperatively, whereas 8 underwent retransplantation with median interval of 74 days (42-252 days). Allosensitization occurred between isolated enterectomy and retransplantation in 2, one of whom lost the second graft due to rejection. Simultaneous allograft enterectomy and retransplantation was performed in 3 isolated intestinal transplantation and 9 multivisceral transplantation patients. Patient survival after retransplantation was similar between patients who underwent isolated allograft enterectomy and those who did simultaneous enterectomy with retransplantation (P = 0.82). CONCLUSIONS: In cases of irreversible intestinal graft dysfunction, isolated allograft enterectomy successfully provides recovery from comorbidities as a lifesaving procedure and does not compromise outcomes of retransplantation.

Rapid and strong de novo donor-specific antibody development in a lung transplant recipient: Short communication/case report.

A 66-yo female patient (typed B*39:01, 44:02) underwent first left single lung transplant (typed B*81:01, 15:17) on 02/07/2016 with negative for DSA in current and historical samples. On 02/17/2016 strong de novo DSA (MFI=15,200, C1q+) to B81 were detected. The recipient has two children typed B*07:02, 44:02 B*27:03, 39:01, and had received multiple vaccinations. Twinrix, Zostavax and MMR vaccines contain viruses grown on live human lung fibroblasts (MRC-5, typed B*07:02, 44:02, and WI-38, typed B*08:01, 58:01). Each dose of vaccine used for injection is known to contain protein components of fibroblasts including HLA. Most likely rapid de novo DSA development is due to booster effect produced by five exposures to mismatched B locus alleles which share the following epitopes: 70IAQ, 65QIA, 65QIA+76esn, 69aa+80n, and 163ew+73te. The later three consist of paired non-self and self eplets. Although likelihood of bystander effect produced by multiple vaccinations is low its impact cannot be ruled out.

Cytomegalovirus Infection After Intestinal/Multivisceral Transplantation: A Single-Center Experience With 210 Cases.

BACKGROUND: Cytomegalovirus (CMV) infection is the most prevalent infectious complication after solid organ transplantation, and recipients of isolated intestinal transplantation (IIT)/multivisceral transplantation (MVT) are among those at the highest risk. Limited clinical data exist regarding CMV infection after IIT/MVT. The aim of this study is to analyze risk factors for posttransplant CMV infection and to assess the efficacy and validity of our prophylaxis and treatment regimens in intestinal transplantation. METHODS: Medical records of 210 IIT/MVT patients were retrospectively reviewed. Posttransplant CMV prophylaxis regimen consisted of ganciclovir followed by 1 year of valganciclovir. The addition of CMV immunoglobulin (CMVIG) was decided according to donor/recipient CMV serostatus (D/R). All results of CMV PCR and/or pp65 antigenemia, and pathological reports were reviewed. Time to the incidence of CMV infection (viremia and/or tissue invasive disease) and risk factors for CMV infection were investigated. RESULTS: CMV infection was observed in 34 of 210 (16%) with a median onset of 347 days. Rejection was significantly associated with CMV infection (P = 0.01, odds ratio = 2.61). In the high-risk serostatus group (D+/R-), prophylactic CMVIG and induction with high-dose rabbit antithymocyte globulin (>10 mg/kg) were associated with a lower CMV infection rate on univariate analysis. The CMVIG remained to be an independent factor on multivariate analysis (P = 0.04, hazard ratio = 0.93/dose). Mortality associated with CMV infection occurred in 4, and CMV infection adversely affected patient survival (P = 0.001, hazard ratio = 2.71). CONCLUSIONS: Prophylaxis with CMVIG and appropriate induction with rabbit antithymocyte globulin may be important to reduce CMV infection in high-risk serostatus group (D+/R-).

Post-transplant persistent lymphopenia is a strong predictor of late survival in isolated intestine and multivisceral transplantation.

Absolute lymphocyte count (ALC) has been identified as a prognostic factor in liver transplantation. We hypothesized that a lower ALC may be linked to poor outcomes in isolated intestinal/multivisceral transplantation (IIT/MVT). The aim of this study was to investigate the prognostic impact of ALC in IIT/MVT. A total 141 IIT/MVT patients were eligible for the study. Post-transplant ALCs (at 3, 6, and 12 months) were evaluated, and prognostic impact of trend of ALC during the first year was investigated. Of these 141 patients, 108 patients survived in the first year (1-year survivors). One-year survivors were categorized according to post-transplant ALC at each time point. When ALC was decreased throughout the first year (post-transplant persistent lymphopenia: <500/µl at 3, 6, and 12 months), patient survival (P < 0.001, hazard ratio = 5.09) and graft survival (P < 0.001, hazard ratio = 5.15) after the first year was significantly worse, and this remained to be an independent risk factor. Negative impact of persistent lymphopenia on patient and graft survival was significant regardless of type of intestinal graft. Infection leading to mortality occurred more frequently in the persistent lymphopenia group (43% vs. 24%). Trend of post-transplant ALC may be a strong predictive marker for long-term outcome in 1-year survivors after IIT/MVT.

Mapping the Shh long-range regulatory domain.

Coordinated gene expression controlled by long-distance enhancers is orchestrated by DNA regulatory sequences involving transcription factors and layers of control mechanisms. The Shh gene and well-established regulators are an example of genomic composition in which enhancers reside in a large desert extending into neighbouring genes to control the spatiotemporal pattern of expression. Exploiting the local hopping activity of the Sleeping Beauty transposon, the lacZ reporter gene was dispersed throughout the Shh region to systematically map the genomic features responsible for expression activity. We found that enhancer activities are retained inside a genomic region that corresponds to the topological associated domain (TAD) defined by Hi-C. This domain of approximately 900 kb is in an open conformation over its length and is generally susceptible to all Shh enhancers. Similar to the distal enhancers, an enhancer residing within the Shh second intron activates the reporter gene located at distances of hundreds of kilobases away, suggesting that both proximal and distal enhancers have the capacity to survey the Shh topological domain to recognise potential promoters. The widely expressed Rnf32 gene lying within the Shh domain evades enhancer activities by a process that may be common among other housekeeping genes that reside in large regulatory domains. Finally, the boundaries of the Shh TAD do not represent the absolute expression limits of enhancer activity, as expression activity is lost stepwise at a number of genomic positions at the verges of these domains.

Long range regulation of the sonic hedgehog gene.

The regulatory architecture that controls developmental genes is often a collection of enhancers that, in combination, generate a complex spatial and temporal pattern of expression. These enhancers populate domains operating at long distances and, in the case of the sonic hedgehog (Shh) locus, this regulatory domain covers ∼900-1000kb. Within this context each embryonic tissue that expresses Shh has acquired its own regulatory apparatus which may require the activity from several distinct enhancers. Expression of Shh in the developing limb bud is driven by a single enhancer that interprets a myriad of genetic information to initiate expression in the posterior margin of the limb bud, inhibits expression along the anterior margin, defines the level of expression, and sets the tissue boundary of expression.

Miller (Genee-Wiedemann) syndrome represents a clinically and biochemically distinct subgroup of postaxial acrofacial dysostosis associated with partial deficiency of DHODH.

Biallelic mutations in the gene encoding DHOdehase [dihydroorotate dehydrogenase (DHODH)], an enzyme required for de novo pyrimidine biosynthesis, have been identified as the cause of Miller (Genée-Weidemann or postaxial acrofacial dysostosis) syndrome (MIM 263750). We report compound heterozygous DHODH mutations in four additional families with typical Miller syndrome. Complementation in auxotrophic yeast demonstrated reduced pyrimidine synthesis and in vitro enzymatic analysis confirmed reduced DHOdehase activity in 11 disease-associated missense mutations, with 7 alleles showing discrepant activity between the assays. These discrepancies are partly explained by the domain structure of DHODH and suggest both assays are useful for interpretation of individual alleles. However, in all affected individuals, the genotype predicts that there should be significant residual DHOdehase activity. Urine samples obtained from two mutation-positive cases showed elevated levels of orotic acid (OA) but not dihydroorotate (DHO), an unexpected finding since these represent the product and the substrate of DHODH enzymatic activity, respectively. Screening of four unrelated cases with overlapping but atypical clinical features showed no mutations in either DHODH or the other de novo pyrimidine biosynthesis genes (CAD, UMPS), with these cases also showing normal levels of urinary OA and DHO. In situ analysis of mouse embryos showed Dhodh, Cad and Umps to be strongly expressed in the pharyngeal arch and limb bud, supporting a site- and stage-specific requirement for de novo pyrimidine synthesis. The developmental sensitivity to reduced pyrimidine synthesis capacity may reflect the requirement for an exceptional mitogenic response to growth factor signalling in the affected tissues.

Human limb abnormalities caused by disruption of hedgehog signaling.

Human hands and feet contain bones of a particular size and shape arranged in a precise pattern. The secreted factor sonic hedgehog (SHH) acts through the conserved hedgehog (Hh) signaling pathway to regulate the digital pattern in the limbs of tetrapods (i.e. land-based vertebrates). Genetic analysis is now uncovering a remarkable set of pathogenetic mutations that alter the Hh pathway, thus compromising both digit number and identity. Several of these are regulatory mutations that have the surprising attribute of misdirecting expression of Hh ligands to ectopic sites in the developing limb buds. In addition, other mutations affect a fundamental structural property of the embryonic cell that is essential to Hh signaling. In this review, we focus on the role that the Hh pathway plays in limb development, and how the many human genetic defects in this pathway are providing clues to the mechanisms that regulate limb development.