Incidence, epidemiology, and outcomes of acute allograft rejection following liver transplantation in Australia.

Acute allograft rejection is a well-known complication of liver transplantation (LT). The incidence, epidemiology, and outcomes of acute rejection have not been well described in Australia. We retrospectively studied consecutive adults who underwent deceased donor LT at a single center between 2010 and 2020. Donor and recipient data at the time of LT and recipient outcomes were collected from a prospective LT database. Liver biopsy reports were reviewed, and only a graft's first instance of biopsy-proven acute rejection was analyzed. During the study period, 796 liver transplants were performed in 770 patients. Biopsy-proven rejection occurred in 34.9% of transplants. There were no significant changes in the incidence of rejection over time (linear trend p =0.11). The median time to the first episode of rejection was 71 days after LT: 2.2% hyperacute, 50.4% early (≤90 d), and 47.5% late rejection (>90 d). Independent risk factors for rejection were younger recipient age at transplant (aHR 0.98 per year increase, 95% CI: 0.97-1.00, p =0.01), and ABO-incompatible grafts (aHR 2.55 vs. ABO-compatible, 95% CI: 1.27-5.09, p <0.01) while simultaneous multiorgan transplants were protective (aHR 0.21 vs. LT only, 95% CI: 0.08-0.58, p <0.01). Development of acute rejection (both early and late) was independently associated with significantly reduced graft (aHR 3.13, 95% CI: 2.21-4.42, p <0.001) and patient survival (aHR 3.42, 95% CI: 2.35-4.98, p <0.001). In this 11-year Australian study, acute LT rejection occurred in 35%, with independent risk factors of younger recipient age and ABO-incompatible transplant, while having a simultaneous multiorgan transplant was protective. Acute rejection was independently associated with reduced graft and patient survival after adjustment for other factors.

Harnessing whole human liver ex situ normothermic perfusion for preclinical AAV vector evaluation.

Developing clinically predictive model systems for evaluating gene transfer and gene editing technologies has become increasingly important in the era of personalized medicine. Liver-directed gene therapies present a unique challenge due to the complexity of the human liver. In this work, we describe the application of whole human liver explants in an ex situ normothermic perfusion system to evaluate a set of fourteen natural and bioengineered adeno-associated viral (AAV) vectors directly in human liver, in the presence and absence of neutralizing human sera. Under non-neutralizing conditions, the recently developed AAV variants, AAV-SYD12 and AAV-LK03, emerged as the most functional variants in terms of cellular uptake and transgene expression. However, when assessed in the presence of human plasma containing anti-AAV neutralizing antibodies (NAbs), vectors of human origin, specifically those derived from AAV2/AAV3b, were extensively neutralized, whereas AAV8- derived variants performed efficiently. This study demonstrates the potential of using normothermic liver perfusion as a model for early-stage testing of liver-focused gene therapies. The results offer preliminary insights that could help inform the development of more effective translational strategies.

Novel miRNA-based drug CD5-2 reduces liver tumor growth in diethylnitrosamine-treated mice by normalizing tumor vasculature and altering immune infiltrate.

Introduction: Liver cancers exhibit abnormal (leaky) vasculature, hypoxia and an immunosuppressive microenvironment. Normalization of tumor vasculature is an emerging approach to treat many cancers. Blockmir CD5-2 is a novel oligonucleotide-based inhibitor of the miR-27a interaction with VE-Cadherin, the endothelial-specific cadherin. The combination of a vasoactive medication with inhibition of immune checkpoints such as programmed cell death protein 1 (PD1) has been shown to be effective in treating liver cancer in humans. We aimed to study the effect of CD5-2 combined with checkpoint inhibition (using an antibody against PD1) on liver tumor growth, vasculature and immune infiltrate in the diethylnitrosamine (DEN)-induced liver tumor mouse model. Methods: We first analyzed human miR-27a and VE-Cadherin expression data from The Cancer Genome Atlas for hepatocellular carcinoma. CD5-2 and/or anti-PD1 antibody were given to the DEN-treated mice from age 7-months until harvest at age 9-months. Tumor and non-tumor liver tissues were analyzed using histology, immunohistochemistry, immunofluorescence and scanning electron microscopy. Results: Human data showed high miR-27a and low VE-Cadherin were both significantly associated with poorer prognosis. Mice treated with CD5-2 plus anti-PD1 antibody had significantly smaller liver tumors (50% reduction) compared to mice treated with either agent alone, controls, or untreated mice. There was no difference in tumor number. Histologically, tumors in CD5-2-treated mice had less leaky vessels with higher VE-Cadherin expression and less tumor hypoxia compared to non-CD5-2-treated mice. Only tumors in the combination CD5-2 plus anti-PD1 antibody group exhibited a more favorable immune infiltrate (significantly higher CD3+ and CD8+ T cells and lower Ly6G+ neutrophils) compared to tumors from other groups. Discussion: CD5-2 normalized tumor vasculature and reduced hypoxia in DEN-induced liver tumors. CD5-2 plus anti-PD1 antibody reduced liver tumor size possibly by altering the immune infiltrate to a more immunosupportive one.

Vessels that encapsulate tumour clusters vascular pattern in hepatocellular carcinoma.

Vessels that encapsulate tumour clusters (VETC) is a distinct histologic vascular pattern associated with a novel mechanism of metastasis. First described in human cancers in 2004, its prevalence and prognostic significance in hepatocellular carcinoma (HCC) has only been appreciated in the past decade with a rapidly increasing body of literature. A robust biomarker of aggressive disease, the VETC pattern is easy to recognise but relies on histologic examination of tumour tissue for its diagnosis. Radiological recognition of the VETC pattern is an area of active research and is becoming increasingly accurate. As a prognostic marker, VETC has consistently proven to be an independent predictor of disease recurrence and overall survival in patients with HCC undergoing resection and liver transplantation. It can also guide treatment by predicting response to other therapies such as transarterial chemoembolisation and sorafenib. Without prospective randomised-controlled trials or routine evaluation of VETC in clinical practice, there are currently no firm treatment recommendations for VETC-positive tumours, although some perspectives are provided in this review based on the latest knowledge of their pathogenesis - a complex interplay between tumour angiogenesis and the immune microenvironment. Nevertheless, VETC has great potential as a future biomarker that could take us one step closer to precision medicine for HCC.

Association between vessels that encapsulate tumour clusters vascular pattern and hepatocellular carcinoma recurrence following liver transplantation.

Background: Vessels that encapsulate tumor clusters (VETC) is a novel vascular pattern seen on hepatocellular carcinoma (HCC) histology which has been shown to independently predict tumor recurrence and survival after liver resection. Its prognostic value in HCC patients receiving liver transplantation (LT) is unclear. Methods: We retrospectively studied consecutive adults who underwent deceased-donor LT with active HCC found on explant between 2010-2019. Tumor tissue was stained for CD34 and quantified for VETC. Primary and secondary endpoints were time to recurrence (TTR) and recurrence-free survival (RFS). Results: During the study period, 158 patients received LT where HCC was present on explant. VETC pattern was seen in 76.5% of explants. Patients with VETC-positive tumors spent longer on the waitlist (6.4 vs. 4.1 months, P=0.048), had higher median tumor numbers (2 vs. 1, P=0.001) and larger tumor sizes (20mm vs. 13mm, P<0.001) on explant pathology compared to those with VETC-negative tumors. Correspondingly, VETC-positive patients were more likely to be outside of accepted LT criteria for HCC. After 56.4 months median follow-up, 8.2% of patients developed HCC recurrence post-LT. On multivariable Cox regression, presence of VETC pattern did not predict TTR or RFS. However, the number of VETC-positive tumors on explant was an independent predictor of TTR (hazard ratio [HR] 1.411, P=0.001) and RFS (HR 1.267, P=0.014) after adjusting for other significant variables. Conclusion: VETC pattern is commonly observed in HCC patients undergoing LT. The number of VETC-positive tumors, but not its presence, is an independent risk factor for TTR and RFS post-LT.

Liver-specific deletion of miR-181ab1 reduces liver tumour progression via upregulation of CBX7.

MiR-181 expression levels increased in hepatocellular carcinoma (HCC) compared to non-cancerous tissues. MiR-181 has been widely reported as a possible driver of tumourigenesis but also acts as a tumour suppressor. In addition, the miR-181 family regulates the development and function of immune and vascular cells, which play vital roles in the progression of tumours. More complicatedly, many genes have been identified as miR-181 targets to mediate the effects of miR-181. However, the role of miR-181 in the development of primary tumours remains largely unexplored. We aimed to examine the function of miR-181 and its vital mediators in the progression of diethylnitrosamine-induced primary liver cancers in mice. The size of liver tumours was significantly reduced by 90% in global (GKO) or liver-specific (LKO) 181ab1 knockout mice but not in hematopoietic and endothelial lineage-specific knockout mice, compared to WT mice. In addition, the number of tumours was significantly reduced by 50% in GKO mice. Whole-genome RNA-seq analysis and immunohistochemistry showed that epithelial-mesenchymal transition was partially reversed in GKO tumours compared to WT tumours. The expression of CBX7, a confirmed miR-181 target, was up-regulated in GKO compared to WT tumours. Stable CBX7 expression was achieved with an AAV/Transposase Hybrid-Vector System and up-regulated CBX7 expression inhibited liver tumour progression in WT mice. Hepatic CBX7 deletion restored the progression of LKO liver tumours. MiR-181a expression was the lowest and CBX7 expression the highest in iClust2 and 3 subclasses of human HCC compared to iClust1. Gene expression profiles of GKO tumours overlapped with low-proliferative peri-portal-type HCCs. Liver-specific loss of miR-181ab1 inhibited primary liver tumour progression via up-regulating CBX7 expression, but tumour induction requires both hepatic and non-hepatic miR-181. Also, miR-181ab1-deficient liver tumours may resemble low-proliferative periportal-type human HCC. miR-181 was increased with liver tumour growth. More miR-181, darker colour and higher shape. CBX7 was very low in pericentral hepatocytes, increased in early liver tumours, but reduced in advanced liver tumours. Its levels were maintained in miR-181 KO liver tumours. In tumours (T), brown (darker is more) represents miR-181, the blue circle (thicker is more) represents CBX7.

The liver contains distinct interconnected networks of CX3CR1+ macrophages, XCR1+ type 1 and CD301a+ type 2 conventional dendritic cells embedded within portal tracts.

Portal tracts are key intrahepatic structures where leukocytes accumulate during immune responses. They contain the blood inflow, which includes portal blood from the gut, and lymphatic and biliary outflow of the liver, and as such represent a key interface for potential pathogen entry to the liver. Myeloid cells residing in the interstitium of the portal tract might play an important role in the surveillance or prevention of pathogen dissemination; however, the exact composition and localization of this population has not been explored fully. Our in-depth characterization of portal tract myeloid cells revealed that in addition to T lymphocytes, portal tracts contain a heterogeneous population of MHCIIhigh myeloid cells with potential antigen presenting cell (APC) function. These include a previously unreported subset of CSF1R-dependent CX3CR1+ macrophages that phenotypically and morphologically resemble liver capsular macrophages, as well as the two main dendritic cell subsets (cDC1 and cDC2). These cells are not randomly distributed, but each subset forms interconnected networks intertwined with specific components of the portal tract. The CX3CR1+ cells were preferentially detected along the outer border of the portal tracts, and also in the portal interstitium adjacent to the portal vein, bile duct, lymphatic vessels and hepatic artery. cDC1s abounded along the lymphatic vessels, while cDC2s mostly surrounded the biliary tree. The specific distributions of these discrete subsets predict that they may serve distinct functions in this compartment. Overall, our findings suggest that portal tracts and their embedded cellular networks of myeloid cells form a distinctive lymphoid compartment in the liver that has the potential to orchestrate immune responses in this organ.

Expansion of Liver Transplantation Criteria for Hepatocellular Carcinoma from Milan to UCSF in Australia and New Zealand and Justification for Metroticket 2.0.

Background: Expansion in liver transplantation (LT) criteria for HCC from Milan to UCSF has not adversely impacted overall survival, prompting further expansion towards Metroticket 2.0 (MT2). In this study, we compared patient survival post-transplant before and after 2007 and long-term outcomes for LT within Milan versus UCSF criteria (to determine the true benefit of the expansion of criteria) and retrospectively validated the MT2 criteria. Methods: Retrospective analysis of ANZLITR (including all patients transplanted for HCC since July 1997). The entire cohort was divided based on criteria used at the time of listing, namely, Milan era (1997−2006) and the UCSF era (2007−July 2015). Results: The overall 5- and 10-year cumulative survival rates for the entire cohort of 691 patients were 78% and 69%, respectively. Patients transplanted in UCSF era had significantly higher 5- and 10-year survival rates than in the Milan era (80% vs. 73% and 72% vs. 65%, respectively; p = 0.016). In the UCSF era, the 5-year survival rate for patients transplanted within Milan criteria was significantly better than those transplanted outside Milan but within UCSF criteria (83% vs. 73%; p < 0.024). Patients transplanted within the MT2 criteria had a significantly better 5- and 10-year survival rate as compared to those outside the criteria (81% vs. 64% and 73% vs. 50%, respectively; p = 0.001). Conclusion: Overall survival following LT for HCC has significantly improved over time despite expanding criteria from Milan to UCSF. Patients fulfilling the MT2 criteria have a survival comparable to the UCSF cohort. Thus, expansion of criteria to MT2 is justifiable.

Deletion of kif3a in CK19 positive cells leads to primary cilia loss, biliary cell proliferation and cystic liver lesions in TAA-treated mice.

BACKGROUND & AIMS: Loss of primary cilia in epithelial cells is known to cause cystic diseases of the liver and kidney. We have previously shown that during experimental and human cirrhosis that primary cilia were predominantly expressed on biliary cells in the ductular reaction. However, the role of primary cilia in the pathogenesis of the ductular reaction is not fully understood. METHODS: Primary cilia were specifically removed in biliary epithelial cells (BECs) by the administration of tamoxifen to Kif3af/f;CK19CreERT mice at week 2 of a 20-week course of TAA treatment. Biliary progenitor cells were isolated and grown as organoids from gallbladders. Cells and tissue were analysed using histology, immunohistochemistry and Western blot assays. RESULTS: At the end of 20 weeks TAA administration, primary cilia loss in liver BECs resulted in multiple microscopic cystic lesions within an unaltered ductular reaction. These were not seen in control mice who did not receive TAA. There was no effect of biliary primary cilia loss on the development of cirrhosis. Increased cellular proliferation was seen within the cystic structures associated with a decrease in hepatocyte lobular proliferation. Loss of primary cilia within biliary organoids was initially associated with reduced cell passage survival but this inhibitory effect was diminished in later passages. ERK but not WNT signalling was enhanced in primary cilia loss-induced cystic lesions in vivo and its inhibition reduced the expansion of primary cilia deficient biliary progenitor cells in vitro. CONCLUSIONS: TAA-treated kif3a BEC-specific knockout mice had an unaltered progression to cirrhosis, but developed cystic lesions that showed increased proliferation.

Dipeptidyl Peptidase Inhibition Enhances CD8 T Cell Recruitment and Activates Intrahepatic Inflammasome in a Murine Model of Hepatocellular Carcinoma.

The mRNA expression of the dipeptidyl peptidase 4 (DPP4) gene family is highly upregulated in human hepatocellular carcinoma (HCC) and is associated with poor survival in HCC patients. Compounds that inhibit the DPP4 enzyme family, such as talabostat and ARI-4175, can mediate tumour regression by immune-mediated mechanisms that are believed to include NLRP1 activation. This study investigated the expression and activity of the DPP4 family during the development of HCC and evaluated the efficacy of ARI-4175 in the treatment of early HCC in mice. This first report on this enzyme family in HCC-bearing mice showed DPP9 upregulation in HCC, whereas intrahepatic DPP8/9 and DPP4 enzyme activity levels decreased with age. We demonstrated that ARI-4175 significantly lowered the total number of macroscopic liver nodules in these mice. In addition, ARI-4175 increased intrahepatic inflammatory cell infiltration, including CD8+ T cell numbers, into the HCC-bearing livers. Furthermore, ARI-4175 activated a critical component of the inflammasome pathway, caspase-1, in these HCC-bearing livers. This is the first evidence of caspase-1 activation by a pan-DPP inhibitor in the liver. Our data suggest that targeting the DPP4 enzyme family may be a novel and effective approach to promote anti-tumour immunity in HCC via caspase-1 activation.

Drug-induced liver injury in Australia, 2009-2020: the increasing proportion of non-paracetamol cases linked with herbal and dietary supplements.

OBJECTIVE: To compare the characteristics and outcomes of drug-induced liver injury (DILI) caused by paracetamol and non-paracetamol medications, particularly herbal and dietary supplements. DESIGN: Retrospective electronic medical record data analysis. SETTING, PARTICIPANTS: Adults admitted with DILI to the Gastroenterology and Liver Centre at the Royal Prince Alfred Hospital, Sydney (a quaternary referral liver transplantation centre), 2009-2020. MAIN OUTCOME MEASURES: 90-day transplant-free survival; drugs implicated as causal agents in DILI. RESULTS: A total of 115 patients with paracetamol-related DILI and 69 with non-paracetamol DILI were admitted to our centre. The most frequently implicated non-paracetamol medications were antibiotics (19, 28%), herbal and dietary supplements (15, 22%), anti-tuberculosis medications (six, 9%), and anti-cancer medications (five, 7%). The number of non-paracetamol DILI admissions was similar across the study period, but the proportion linked with herbal and dietary supplements increased from 2 of 13 (15%) during 2009-11 to 9 of 19 (47%) during 2018-20 (linear trend: P = 0.011). Despite higher median baseline model for end-stage liver disease (MELD) scores, 90-day transplant-free survival for patients with paracetamol-related DILI was higher than for patients with non-paracetamol DILI (86%; 95% CI, 79-93% v 71%; 95% CI, 60-82%) and herbal and dietary supplement-related cases (59%; 95% CI, 34-85%). MELD score was an independent predictor of poorer 90-day transplant-free survival in both paracetamol-related (per point increase: adjusted hazard ratio [aHR], 1.19; 95% CI, 1.09-3.74) and non-paracetamol DILI (aHR, 1.24; 95% CI, 1.14-1.36). CONCLUSION: In our single centre study, the proportion of cases of people hospitalised with DILI linked with herbal and dietary supplements has increased since 2009. Ninety-day transplant-free survival for patients with non-paracetamol DILI, especially those with supplement-related DILI, is poorer than for those with paracetamol-related DILI.

DPP9: Comprehensive In Silico Analyses of Loss of Function Gene Variants and Associated Gene Expression Signatures in Human Hepatocellular Carcinoma.

Dipeptidyl peptidase (DPP) 9, DPP8, DPP4 and fibroblast activation protein (FAP) are the four enzymatically active members of the S9b protease family. Associations of DPP9 with human liver cancer, exonic single nucleotide polymorphisms (SNPs) in DPP9 and loss of function (LoF) variants have not been explored. Human genomic databases, including The Cancer Genome Atlas (TCGA), were interrogated to identify DPP9 LoF variants and associated cancers. Survival and gene signature analyses were performed on hepatocellular carcinoma (HCC) data. We found that DPP9 and DPP8 are intolerant to LoF variants. DPP9 exonic LoF variants were most often associated with uterine carcinoma and lung carcinoma. All four DPP4-like genes were overexpressed in liver tumors and their joint high expression was associated with poor survival in HCC. Increased DPP9 expression was associated with obesity in HCC patients. High expression of genes that positively correlated with overexpression of DPP4, DPP8, and DPP9 were associated with very poor survival in HCC. Enriched pathways analysis of these positively correlated genes featured Toll-like receptor and SUMOylation pathways. This comprehensive data mining suggests that DPP9 is important for survival and that the DPP4 protease family, particularly DPP9, is important in the pathogenesis of human HCC.

An improved production and purification protocol for recombinant soluble human fibroblast activation protein alpha.

Fibroblast activation protein alpha (FAP) is a cell-surface expressed type II glycoprotein that has a unique proteolytic activity. FAP has active soluble forms that retain the extracellular portion but lack the transmembrane domain and cytoplasmic tail. FAP expression is normally very low in adult tissue but is highly expressed by activated fibroblasts in sites of tissue remodelling. Thus, FAP is a potential biomarker and pharmacological target in liver fibrosis, atherosclerosis, cardiac fibrosis, arthritis and cancer. Understanding the biological significance of FAP by investigating protein structure, interactions and activities requires reliable methods for the production and purification of abundant pure and stable protein. We describe an improved production and purification protocol for His6-tagged recombinant soluble human FAP. A modified baculovirus expression construct was generated using the pFastBac1 vector and the gp67 secretion signal to produce abundant active soluble recombinant human FAP (residues 27-760) in insect cells. The FAP purification protocol employed ammonium sulphate precipitation, ion exchange chromatography, immobilised metal affinity chromatography and ultrafiltration. High purity was achieved, as judged by gel electrophoresis and specific activity. The purified 82 kDa FAP protein was specifically inhibited by a FAP selective inhibitor, ARI-3099, and was inhibited by zinc with an IC50 of 25 µM. Our approach could be adopted for producing the soluble portions of other type II transmembrane glycoproteins to study their structure and function.

A Novel Purification Procedure for Active Recombinant Human DPP4 and the Inability of DPP4 to Bind SARS-CoV-2.

Proteases catalyse irreversible posttranslational modifications that often alter a biological function of the substrate. The protease dipeptidyl peptidase 4 (DPP4) is a pharmacological target in type 2 diabetes therapy primarily because it inactivates glucagon-like protein-1. DPP4 also has roles in steatosis, insulin resistance, cancers and inflammatory and fibrotic diseases. In addition, DPP4 binds to the spike protein of the MERS virus, causing it to be the human cell surface receptor for that virus. DPP4 has been identified as a potential binding target of SARS-CoV-2 spike protein, so this question requires experimental investigation. Understanding protein structure and function requires reliable protocols for production and purification. We developed such strategies for baculovirus generated soluble recombinant human DPP4 (residues 29-766) produced in insect cells. Purification used differential ammonium sulphate precipitation, hydrophobic interaction chromatography, dye affinity chromatography in series with immobilised metal affinity chromatography, and ion-exchange chromatography. The binding affinities of DPP4 to the SARS-CoV-2 full-length spike protein and its receptor-binding domain (RBD) were measured using surface plasmon resonance and ELISA. This optimised DPP4 purification procedure yielded 1 to 1.8 mg of pure fully active soluble DPP4 protein per litre of insect cell culture with specific activity >30 U/mg, indicative of high purity. No specific binding between DPP4 and CoV-2 spike protein was detected by surface plasmon resonance or ELISA. In summary, a procedure for high purity high yield soluble human DPP4 was achieved and used to show that, unlike MERS, SARS-CoV-2 does not bind human DPP4.

Current perspectives on the tumor microenvironment in hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is a heterogeneous inflammation-driven malignancy, which, despite significant advances in management, continues to portend a poor prognosis. Recent advances in basic and translational research have increasingly defined the role of the tumor microenvironment in the development and progression of HCC and facilitated the development of novel molecular targets. The hepatoma microenvironment is characterised by an immunosuppressive milieu of immune cells and tumor vasculature that is both structurally and functionally abnormal. Normalising the tumor microenvironment by adopting a multipronged approach that targets both carcinogenic processes and the immunosuppressive milieu has been supported by pre-clinical and clinical data. In this review, we summarise the current understanding of the hepatoma microenvironment, its influences and dynamic interactions with tumor cells, the vasculature and the gut. Finally, we discuss how manipulating the tumor microenvironment continues to shape the evolving landscape of HCC therapy.

Efficacy and safety profile of calcineurin inhibitor salvage therapy in autoimmune hepatitis.

BACKGROUND: As data is limited on the outcomes of calcineurin inhibitors (CNI) in autoimmune hepatitis (AIH), we evaluated the efficacy and safety of CNI in AIH patients who failed prior treatment(s). METHODS: A retrospective study was performed of AIH patients who received cyclosporine A (CsA) and/or tacrolimus (TAC) after prior treatment(s) failure. Records were reviewed for baseline demographic and clinical characteristics, and treatment outcomes. The primary outcome was biochemical remission.Results: Thirty-three AIH patients received CNI across seven liver centers:17 received CsA, 21 TAC and 5 TAC after CsA failure/intolerance. 82% received CNI for an insufficient response to treatment(s). Overall, 48% of CNI treated patients achieved biochemical remission including 41% in prior non-responders and 83% in treatment intolerant patients. Remission rates with CNI as second-line and third-line therapy were 63% and 29% respectively. There were no baseline predictors of response to CNI on multivariate analysis. Eighteen (55%) patients developed significant side effects and 8 (24%) discontinued due to intolerance. Three patients required liver transplantation for decompensated cirrhosis and 6 patients died including one from malignancy possibly related to CNI. CONCLUSION: CNI salvage therapy is well tolerated and moderately effective achieving remission in around 50% of AIH who failed standard therapy.

Trp53 and Rb1 regulate autophagy and ligand-dependent Hedgehog signaling.

Ligand-dependent activation of Hedgehog (Hh) signaling in cancer occurs without mutations in canonical pathway genes. Consequently, the genetic basis of Hh pathway activation in adult solid tumors, such as small-cell lung cancer (SCLC), is unknown. Here we show that combined inactivation of Trp53 and Rb1, a defining genetic feature of SCLC, leads to hypersensitivity to Hh ligand in vitro, and during neural tube development in vivo. This response is associated with the aberrant formation of primary cilia, an organelle essential for canonical Hh signaling through smoothened, a transmembrane protein targeted by small-molecule Hh inhibitors. We further show that loss of both Trp53 and Rb1 disables transcription of genes in the autophagic machinery necessary for the degradation of primary cilia. In turn, we also demonstrate a requirement for Kif3a, a gene essential for the formation of primary cilia, in a mouse model of SCLC induced by conditional deletion of both Trp53 and Rb1 in the adult airway. Our results provide a mechanistic framework for therapeutic targeting of ligand-dependent Hh signaling in human cancers with somatic mutations in both TP53 and RB1.

COVID-19 and comorbidities: A role for dipeptidyl peptidase 4 (DPP4) in disease severity?

The coronavirus disease 2019 (COVID-19) pandemic is caused by a novel betacoronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), similar to SARS-CoV and Middle East respiratory syndrome (MERS-CoV), which cause acute respiratory distress syndrome and case fatalities. COVID-19 disease severity is worse in older obese patients with comorbidities such as diabetes, hypertension, cardiovascular disease, and chronic lung disease. Cell binding and entry of betacoronaviruses is via their surface spike glycoprotein; SARS-CoV binds to the metalloprotease angiotensin-converting enzyme 2 (ACE2), MERS-CoV utilizes dipeptidyl peptidase 4 (DPP4), and recent modeling of the structure of SARS-CoV-2 spike glycoprotein predicts that it can interact with human DPP4 in addition to ACE2. DPP4 is a ubiquitous membrane-bound aminopeptidase that circulates in plasma; it is multifunctional with roles in nutrition, metabolism, and immune and endocrine systems. DPP4 activity differentially regulates glucose homeostasis and inflammation via its enzymatic activity and nonenzymatic immunomodulatory effects. The importance of DPP4 for the medical community has been highlighted by the approval of DPP4 inhibitors, or gliptins, for the treatment of type 2 diabetes mellitus. This review discusses the dysregulation of DPP4 in COVID-19 comorbid conditions; DPP4 activity is higher in older individuals and increased plasma DPP4 is a predictor of the onset of metabolic syndrome. DPP4 upregulation may be a determinant of COVID-19 disease severity, which creates interest regarding the use of gliptins in management of COVID-19. Also, knowledge of the chemistry and biology of DPP4 could be utilized to develop novel therapies to block viral entry of some betacoronaviruses, potentially including SARS-CoV-2.