title: Pre-clinical heterotopic intrathoracic heart xenotransplantation: a possibly useful clinical technique.
abstract: BACKGROUND
  As a step towards clinical cardiac xenotransplantation, our experimental heterotopic intrathoracic xenotransplantation model offers a beating and ejecting donor heart while retaining the recipient's native organ as a backup in case of graft failure. Clinically applicable immunosuppressive regimens (IS) were investigated first, then treatments known to be effective in hypersensitized patients or those with recalcitrant rejection reactions.
  
  
  METHODS
  Consecutive experiments were carried out between 2009 and 2013. Twenty-one genetically modified pigs (GGTA1-knockout/hCD46/± thrombomodulin, in one case HLA-E instead) were used as donors. In all experiments, two cycles of immunoabsorption reduced preformed antibodies. Recipient baboons were divided into two groups according to IS regimen: In group one (n = 10), pre-treatment started either one (anti-CD20) or four weeks (anti-CD20 plus the proteasome inhibitor bortezomib) prior to transplantation. The extended conventional (as for allotransplantation) immunosuppressive maintenance regimen included anti-thymocyte globuline, tacrolimus, mycophenolate mofetil, methylprednisolone and weekly anti-CD20. In group two (n = 11), myeloablative pre-treatment as in multiple myeloma patients (long and short regimens) was added to extended conventional IS; postoperative total thoracic and abdominal lymphoid irradiation (TLI; single dose of 600 cGY) was used to further reduce antibody-producing cells.
  
  
  RESULTS
  In the perioperative course, the surgical technique was safely applied: 19 baboons were weaned off extracorporeal circulation and 17 extubated. Nine animals were lost in the early postoperative course due to causes unrelated to surgical technique or IS regimen. Excluding these early failures, median graft survival times of group 1 and 2 were 18.5 (12-50) days and 16 (7-35) days. Necropsy examination of group 1 donor organs revealed hypertrophy of the left ventricular wall in the six longer-lasting grafts; myocardial histology confirmed pre-clinical suspicion of humoral rejection, which was not inhibited by the extended conventional IS including intensified treatments, and signs of thrombotic microangiopathy. Grafts of group 2 presented with only mild-to-moderate features of humoral rejection and thrombotic microangiopathy, except in one case of delayed rejection on day 17. The other experiments in this group were terminated because of untreatable pulmonary oedema, recurring ventricular fibrillation, Aspergillus sepsis, as well as a combination of a large donor organ and late toxic side effects due to TLI.
  
  
  CONCLUSIONS
  Longer-term results were difficult to achieve in this model due to the IS regimens used. However, we conclude that heterotopic intrathoracic heart transplantation may be an option for clinical xenotransplantation.
authors.affiliation: Department of Anaesthesiology, Ludwig-Maximilian University, Munich, Germany.|Transregio Collaborative Research Center 127, Walter Brendel Centre of Experimental Medicine, Ludwig Maximilian University, Munich, Germany.
authors.forename: Jan-Michael
authors.initials: JM
authors.lastname: Abicht
authors.affiliation: Department of Anaesthesiology, Ludwig-Maximilian University, Munich, Germany.|Transregio Collaborative Research Center 127, Walter Brendel Centre of Experimental Medicine, Ludwig Maximilian University, Munich, Germany.
authors.forename: Tanja
authors.initials: T
authors.lastname: Mayr
authors.affiliation: Transregio Collaborative Research Center 127, Walter Brendel Centre of Experimental Medicine, Ludwig Maximilian University, Munich, Germany.
authors.forename: Bruno
authors.initials: B
authors.lastname: Reichart
authors.affiliation: Department of Cardiovascular Surgery, Ludwig Maximilian University, Munich, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Buchholz
authors.affiliation: Department of Cardiovascular Surgery, Ludwig Maximilian University, Munich, Germany.
authors.forename: Fabian
authors.initials: F
authors.lastname: Werner
authors.affiliation: Department of Cardiovascular Surgery, Ludwig Maximilian University, Munich, Germany.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Lutzmann
authors.affiliation: Department of Cardiovascular Surgery, Ludwig Maximilian University, Munich, Germany.|Department of Cardiac Surgery, Asklepios Klinik St Georg, Hamburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Schmoeckel
authors.affiliation: Department of Anaesthesiology, Ludwig-Maximilian University, Munich, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Bauer
authors.affiliation: Department of Cardiovascular Surgery, Ludwig Maximilian University, Munich, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Thormann
authors.affiliation: Institute of Veterinary Pathology, Ludwig Maximilian University, Munich, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Langenmayer
authors.affiliation: Institute of Veterinary Pathology, Ludwig Maximilian University, Munich, Germany.
authors.forename: Nadja
authors.initials: N
authors.lastname: Herbach
authors.affiliation: Tumor Immunology Laboratory, LIFE Center, Ludwig Maximilian University, Munich, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Pohla
authors.affiliation: Transregio Collaborative Research Center 127, Walter Brendel Centre of Experimental Medicine, Ludwig Maximilian University, Munich, Germany.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Herzog
authors.affiliation: Mayo Clinic, Rochester, MN, USA.|University College London, London, UK.
authors.forename: Christopher G A
authors.initials: CG
authors.lastname: McGregor
authors.affiliation: Revivicor, Blacksburg, VA, USA.
authors.forename: David
authors.initials: D
authors.lastname: Ayares
authors.affiliation: Department of Molecular Animal Breeding and Biotechnology, Ludwig Maximilian University, Munich, Germany.
authors.forename: Eckhard
authors.initials: E
authors.lastname: Wolf
authors.affiliation: Department of Molecular Animal Breeding and Biotechnology, Ludwig Maximilian University, Munich, Germany.
authors.forename: Nikolai
authors.initials: N
authors.lastname: Klymiuk
authors.affiliation: Department of Molecular Animal Breeding and Biotechnology, Ludwig Maximilian University, Munich, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Baehr
authors.affiliation: Chair of Livestock Biotechnology, School of Life Sciences Weihenstephan, Technical University of Munich, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kind
authors.affiliation: Department of Cardiovascular Surgery, Ludwig Maximilian University, Munich, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Hagl
authors.affiliation: Department of Radiation Oncology, Ludwig Maximilian University, Munich, Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Ganswindt
authors.affiliation: Department of Radiation Oncology, Ludwig Maximilian University, Munich, Germany.
authors.forename: Claus
authors.initials: C
authors.lastname: Belka
authors.affiliation: Transregio Collaborative Research Center 127, Walter Brendel Centre of Experimental Medicine, Ludwig Maximilian University, Munich, Germany.|Department of Cardiovascular Surgery, Ludwig Maximilian University, Munich, Germany.
authors.forename: Sonja
authors.initials: S
authors.lastname: Guethoff
authors.affiliation: Transregio Collaborative Research Center 127, Walter Brendel Centre of Experimental Medicine, Ludwig Maximilian University, Munich, Germany.|Department of Cardiovascular Surgery, Ludwig Maximilian University, Munich, Germany.
authors.forename: Paolo
authors.initials: P
authors.lastname: Brenner
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D000906:Antibodies / Q000276:immunology / Q000494:pharmacology; D006084:Graft Rejection / Q000276:immunology*; D006085:Graft Survival / Q000276:immunology*; D016027:Heart Transplantation / Q000379:methods; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D013552:Swine; D014183:Transplantation, Heterologous / Q000379:methods
chemical_list: D000906:Antibodies; D007166:Immunosuppressive Agents
keywords: heart transplantation; heterotopic; intrathoracic; pre-clinical; total thoracic and abdominal lymphoid irradiation; xenotransplantation