Is living donor liver transplantation justified in high model for end-stage liver disease candidates (35+)? Purpose of review Application of living donor liver transplantation (LDLT) in model for end-stage liver disease (MELD) 35+ patients has been regarded with skepticism. There is concern that a partial graft may not achieve favourable outcomes, and that a healthy donor is risked for a transplant which might turn out to be futile. Recent findings In practice, LDLT improves access to liver graft and allows timely transplantation. Long-term results from high-volume centres revealed that outcomes of LDLT in these patients have not been jeopardized by limited graft volumes. With unimpeded vascular outflow, a partial graft could provide sufficient function to overcome the stress of transplant operation. However, LDLT is a complex operation with immense technical demand. A steep learning curve is encountered before optimal outcomes could be produced. Meanwhile, donor safety remains the paramount concern. Donor should not be evaluated for futile candidates. MELD 35+ patients with refractory sepsis or cardiac event are unlikely to benefit from liver transplantation. Borderline donors, in terms of donor safety or graft quality, should not be accepted. As in recipient operation, accumulation of experience is crucial to reduce donor mortality and morbidity. Summary LDLT is justified for MELD 35+ in high-volume centres with vast experience. Satisfactory recipient outcomes can be produced with minimal donor morbidity. Correspondence to Albert C.Y. Chan, Division of Liver Transplantation, Department of Surgery, Queen Mary Hospital, The University of Hong Kong, Pokfulam, Hong Kong. Tel: +852 22553025; e-mail: acchan@hku.hk Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.

Adipogenesis for soft tissue reconstruction Purpose of review It has been increasingly common to use adipose tissue for regenerative and reconstructive purposes. Applications of autologous fat transfer and different stem cell therapies have significant limitations and adipose tissue engineering may have the potential to be an important strategy in the reconstruction of large tissue defects. A better understanding of adipogenesis will help to develop strategies to make adipose tissue more effective for repairing volumetric defects. Recent findings We provide an overview of the current applications of adipose tissue transfer and cellular therapy methods for soft tissue reconstruction, cellular physiology, and factors influencing adipogenesis, and adipose tissue engineering. Furthermore, we discuss mechanical properties and vascularization strategies of engineered adipose tissue, and its potential applications in the clinical settings. Summary Autologous fat tissue transfer is the standard of care technique for the majority of surgeons; however, high resorption rates, poor perfusion within a large volume fat graft and widely inconsistent graft survival are the main limitations. Adipose tissue engineering is a promising field to reach the first goal of producing adipose tissue which has more predictable survival and higher graft retention rates. Advancements of scaffold and vascularization strategies will contribute to metabolically and functionally more relevant adipose tissue engineering. Correspondence to Huseyin Karagoz, Department of Surgery, Institute for Regenerative Medicine, Wake Forest University School of Medicine, Room 318, Richard H. Dean Biomedical Building, 391 Technology Way NE, Winston Salem, NC 27101, USA. Tel: +1-336-716-5327; fax: +1 336 7137290; e-mail: hkaragoz@wakehealth.edu Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.

Auxiliary living donor liver transplantation combined with two-stage hepatectomy for unresectable colorectal liver metatstasis Purpose of review To review the role of liver transplantation for unresectable colorectal liver metastases (u-CRLM) and to describe the intial experience with auxiliary living donor liver transplantation combined with two-stage hepatectomy for u-CRLM (i.e. living donor RAPID). Recent findings Patients affected of u-CRLM have a poor prognosis with 5 years overall survival (OS) rate less than 10% under standard modern chemotherapy.There is an actual international consensus that liver transplantation for u-CRLM represents a viable option in highly selected patients with OS rate at 5 years up to 80% notwithstanding high recurrence rates. Due to the scarcity of whole liver graft from deceased donors, the RAPID procedure (i.e. resection and partial liver segment 2–3 transplantation from deceased donors with delayed total hepatectomy) has been introduced as possible alternative. The RAPID procedure represents the most actual and modern fusion of the two most challenging procedures of modern hepatobiliary and liver transplant surgery: that is Auxiliary Partial Orthotopic Liver Transplantation and Associating Liver Partition and Portal vein Ligation for Staged hepatectomy. Although the deceased donor-RAPID procedure may show promising results, the basic problem of scarcity of organs from deceased donors and mainly the lack of splittable organs still remains. Summary The living donor RAPID, based on transplantation of left lateral segments from living donor, may represent the way out to this problem. It is feasible and safe (for both donor and recipient), but characterized by a very challenging high-end transplantological procedure. Correspondence to Silvio Nadalin, MD, FEBS, Department of General, Visceral and Transplant Surgery, University Hospital Tuebingen, Hoppe-Seyler Str. 3, 72076 Tuebingen, Germany. Tel: +49 7071 2986600; fax: +49 7071 29 4934; e-mail: silvio.nadalin@med.uni-tuebingen.de Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.

The high-end range of biliary reconstruction in living donor liver transplant Purpose of review To summarize recent evidence in literature regarding incidence and risk factors for biliary complications in living donor liver transplantation (LDLT), and current concepts in evaluation of donor biliary anatomy, and surgical techniques of biliary reconstruction, to reduce the incidence of biliary complications. Recent findings Advances in biliary imaging in the donor, both before surgery, and during donor hepatectomy, as well as well tolerated hepatic duct isolation in the donor, have played a significant role in reducing biliary complications in both the donor and recipient. Duct-to-duct biliary anastomoses (DDA) is the preferred mode of biliary reconstruction currently, especially when there is a single bile duct orifice in the donor. The debate on stenting the anastomoses, especially a DDA, continues. Stenting a Roux en Y hepaticojejunostomy in children with small ductal orifices in the donor is preferred. With growing experience, and use of meticulous surgical technique and necessary modifications, the incidence of biliary complications in multiple donor bile ducts, and more than one biliary anastomoses can be reduced. Summary Biliary anastomosis continues to be the Achilles heel of LDLT. Apart from surgical technique, which includes correct choice of type of reconstruction technique and appropriate use of stents across ductal anastomoses, better imaging of the biliary tree, and safe isolation of the graft hepatic duct, could help reduce biliary complications in the recipient, and make donor hepatectomy well tolerated. Correspondence to Prashant Bhangui, MD, Senior Consultant, Hepatobiliary and Liver Transplant Surgeon, Medanta Institute of Liver Transplantation and Regenerative Medicine, Medanta-The Medicity, Gurugram, Delhi NCR, India. Tel: +91 9871299733; e-mail: pbhangui@gmail.com Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.

How far can we go with hepatocellular carcinoma in living donor liver transplantation? Purpose of review Living donor liver transplantation (LDLT) in the setting of hepatocellular carcinoma (HCC) has been adopted worldwide over the past decade. Many centers have implemented LDLT because of the limited supply of deceased organs, which has also provided an opportunity for centers to expand the indication for transplantation for patients with HCC. Recent findings Center-specific expanded HCC criteria have proven to be well tolerated in terms of overall and disease-free survival when compared with the standard, Milan criteria. There is a need to overcome size and number as the sole limiters. New technologies to better predict outcomes after liver transplantation for HCC, response to treatments and/or bridging therapies while waiting for a liver transplantation, along with determining tumour behaviour are being incorporated into criteria. Improved outcomes of LDLT for all causes has increased utilization of the procedure for HCC patients worldwide. Summary LDLT has become a great treatment option for HCC patients. Progressively better understanding of tumour behaviour and different surrogates of tumour biology assessments will allow better patient selection for LDLT. Correspondence to Gonzalo Sapisochin, MD, PhD, MSc, 585 University Avenue, Toronto, ON, Canada M5G 2N2. Tel: +1 416 340 5169; e-mail: gonzalo.sapisochin@uhn.ca Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.

Will cell therapies provide the solution for the shortage of transplantable organs? Purpose of review The potential to regenerate ischemically damaged kidneys while being perfused ex-vivo offers the best near-term solution to increasing kidney allografts for transplantation. Recent findings There are a number of stem-cell sources including: stromal mesenchymal cells (MSC), induced adult pluripotent stem cells, fetal stem cells from placenta, membranes, amniotic fluid and umbilical cord and hematopoietic cells. MSC are increasingly the stem cell of choice and studies are primarily focused on novel induction immunosuppression to prevent rejection. Stem-cell therapies applied in vivo may be of limited benefit because the nonintegrating cells do not remain in the kidney and are not detectable in the body after several days. MSC therapies for transplantation have demonstrated early safety and feasibility. However, efficacy has not been clearly established. A more feasible application of a stem-cell therapy in transplantation is the administration of MSC to treat damaged renal allografts directly while being perfused ex vivo. Initial feasibility has been established demonstrating MSC-treatment results in statistically significant reduction of inflammatory responses, increased ATP and growth factor synthesis and mitosis. Summary The ability to regenerate renal tissue ex-vivo sufficiently to result in immediate function could revolutionize transplantation by solving the chronic organ shortage. Correspondence to Lauren Brasile, PhD, BREONICS Inc., 44 Dalliba Avenue, Watervliet, NY 12189, USA. Tel: +1 518 459 2112; e-mail: lbrasile@citlink.net Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.

The ins and outs of engineering functional tissues and organs: evaluating the in-vitro and in-situ processes Purpose of review For many disorders that result in loss of organ function, the only curative treatment is organ transplantation. However, this approach is severely limited by the shortage of donor organs. Tissue engineering has emerged as an alternative solution to this issue. This review discusses the concept of tissue engineering from a technical viewpoint and summarizes the state of the art as well as the current shortcomings, with the aim of identifying the key lessons that we can learn to further advance the engineering of functional tissues and organs. Recent findings A plethora of tissue-engineering strategies have been recently developed. Notably, these strategies put different emphases on the in-vitro and in-situ processes (i.e. preimplantation and postimplantation) that take place during tissue formation. Biophysical and biomechanical interactions between the cells and the scaffold/biomaterial play a crucial role in all steps and have started to be exploited to steer tissue regeneration. Summary Recent works have demonstrated the need to better understand the in-vitro and in-situ processes during tissue formation, in order to regenerate complex, functional organs with desired cellular organization and tissue architecture. A concerted effort from both fundamental and tissue-specific research has the potential to accelerate progress in the field. Correspondence to Nicholas A. Kurniawan, PhD, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands. Tel: +31 40 247 2347; e-mail: kurniawan@tue.nl This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal. http://creativecommons.org/licenses/by-nc-nd/4.0 Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.

Infection in xenotransplantation: opportunities and challenges Purpose of review Posttransplantation infections are common. It is anticipated that infection will be no less common in xenotransplantation recipients. Prolonged xenograft survivals have resulted from advances in immunosuppressive strategies and development of swine that decrease host immune responses via genetic manipulation, notably CRISPR/cas9 manipulation. As prospects for clinical trials improve, consideration of the unique infectious risks posed by xenotransplantation reemerge. Recent findings Organisms likely to cause infection in human recipients of porcine xenografts are unknown in advance of clinical trials. Microbiological screening of swine intended as xenograft donors can be more intensive than is currently feasible for human allograft donors. Monitoring infection in recipients will also be more intensive. Key opportunities in infectious diseases of xenotransplantation include major technological advances in evaluation of the microbiome by unbiased metagenomic sequencing, assessments of some risks posed by porcine endogenous retroviruses (PERVs) including antiretroviral susceptibilities, availability of swine with deletion of genomic PERVs, and recognition of the rapidly changing epidemiology of infection in swine worldwide. Summary Unknown infectious risks in xenotransplantation requires application of advanced microbiological techniques to discern and prevent infection in graft recipients. Clinical trials will provide an opportunity to advance the safety of all of organ transplantation. Correspondence to Jay A. Fishman, MD, Transplantation Infectious Disease and Compromised Host Program, Infectious Disease Division and MGH Transplant Center, Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street, WH510A, Boston, MA 02114, USA. Tel: +1 617 643 4809; e-mail: Fishman.jay@mgh.harvard.edu Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.

The role of industry in advancing xenotransplantation Purpose of review Xenotransplantation offers the opportunity to alleviate the imbalance between the demand of patients with end stage organ failure and the supply of organs available for transplantation but remains aspirational. This review highlights how collaboration between academia and industry are essential for success. Recent findings The science of xenotransplantation has accelerated in recent years with key discoveries in genetic engineering, enabling disruption of genes facilitating rejection, and transgenic expression of desired human genes. Combined with similar progress directed toward induction of transplant tolerance, the stage has been set for meaningful progress. These advances are reviewed in detail elsewhere in this volume and argue that the breakthroughs needed to deliver substantial cross-species organ survival have largely been achieved, heralding a liminal stage of human xenotransplantation. However, xenotransplantation as a meaningful therapy for medically refractory end organ failure will not be realized through scientific innovation alone. The advent of broadly available, therapeutic xenogeneic tissues requires extensive development and regulatory expertise; the biotechnology/pharmaceutical industry can provide extensive resources and expertise in those essential areas. Summary Successful delivery of xenotransplantation as an available therapy for curing end stage organ failure is best accomplished through partnership and collaboration between academia and industry. Correspondence to Marc I. Lorber, MD, Sr. Vice President and Chief Medical Officer, Lung Biotechnology, PBC, United Therapeutics Corporation, 1040 Spring Street, Silver Spring, MD 20910, USA. Tel: +1 301 608 9292; e-mail: mlorber@lungbiotechnology.com Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.

The potential role of 3D-bioprinting in xenotransplantation Purpose of review To review the impact of a new technology, 3D-bioprinting, in xenotransplantation research. Recent findings Genetically engineered pigs, beginning with human (h) CD55-transgenic and Gal-knockout pigs, have improved the outcomes of xenotransplantation research. Today, there are more than 30 different genetically engineered pigs either expressing human gene(s) or lacking pig gene(s). CRIPSR/cas9 technology has facilitated the production of multigene pigs (up to nine genes in a single pig), which lack multiple pig xenoantigens, and express human transgenes, such as hCD46, hCD55, hThrombomodulin, hCD39, etc. Although recent studies in nonhuman primates (NHPs) have demonstrated prolonged survival after life-supporting pig kidney, heart, and islet xenotransplantation, researchers have difficulty determining the best genetic combination to test in NHPs because of a potential greater than 100 000 genetic combinations. 3D-bioprinting of genetically engineered pig cells: is superior to 2D in-vitro testing, enables organ-specific testing, helps to understand differences in immunogenicity between organs, and is faster and cheaper than testing in NHPs. Moreover, 3D-bioprinted cells can be continuously perfused in a bioreactor, controlling for all variables, except the studied variable. Summary 3D-bioprinting can help in the study of the impact of specific genes (human or pig) in xenotransplantation in a rapid, inexpensive, and reliable way. Correspondence to Burcin Ekser, MD, PhD, Division of Transplant Surgery, Department of Surgery, Indiana University School of Medicine, 550N University Blvd, UH 4601, Indianapolis, IN 46202, USA. Tel: +1 317 948 3835; fax: +1 317 968 1254; e-mail: bekser@iupui.edu Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.