Knock-out of N-glycolylneuraminic acid attenuates antibody-mediated rejection in xenogenically perfused porcine lungs.

BACKGROUND: Antibody-mediated rejection has long been known to be one of the major organ failure mechanisms in xenotransplantation. In addition to the porcine α1,3-galactose (α1,3Gal) epitope, N-Glycolylneuraminic acid (Neu5Gc), a sialic acid, has been identified as an important porcine antigen against which most humans have pre-formed antibodies. Here we evaluate GalTKO.hCD46 lungs with an additional cytidine monophospho-N-acetylneuraminic acid hydroxylase (CMAH) gene knock-out (Neu5GcKO) in a xenogeneic ex vivo perfusion model METHODS: Eleven GalTKO.hCD46.Neu5GcKO pig lungs were perfused for up to 6 h with fresh heparinized human blood. Six of them were treated with histamine (H) blocker famotidine and 1-thromboxane synthase inhibitor Benzylimidazole (BIA) and five were left untreated. GalTKO.hCD46 lungs without Neu5GcKO (n = 18: eight untreated and 10 BIA+H treated) served as a reference. Functional parameters, blood, and tissue samples were collected at pre-defined time points throughout the perfusion RESULTS: All but one Neu5GcKO organs maintained adequate blood oxygenation and "survived" until elective termination at 6 h whereas two reference lungs failed before elective termination at 4 h. Human anti-Neu5Gc antibody serum levels decreased during the perfusion of GalTKO.hCD46 lungs by flow cytometry (∼40% IgM, 60% IgG), whereas antibody levels in Neu5GcKO lung perfusions did not fall (IgM p = .007; IgG p < .001). Thromboxane elaboration, thrombin generation, and histamine levels were significantly reduced with Neu5GcKO lungs compared to reference in the untreated groups (p = .007, .005, and .037, respectively); treatment with BIA+H masked these changes. Activation of platelets, measured as CD62P expression on circulating platelets, was lower in Neu5GcKO experiments compared to reference lungs (p = .023), whereas complement activation (as C3a rise in plasma) was not altered. MCP-1 and lactotransferin level elevations were blunted in Neu5GcKO lung perfusions (p = .007 and .032, respectively). Pulmonary vascular resistance (PVR) rise was significantly attenuated and delayed in untreated GalTKO.hCD46.Neu5GcKO lungs in comparison to the untreated GalTKO.hCD46 lungs (p = .003) CONCLUSION: Additional Neu5GcKO in GalTKO.hCD46 lungs significantly reduces parameters associated with antibody-mediated inflammation and activation of the coagulation cascade. Knock-out of the Neu5Gc sialic acid should be beneficial to reduce innate immune antigenicity of porcine lungs in future human recipients.

Pig-to-baboon lung xenotransplantation: Extended survival with targeted genetic modifications and pharmacologic treatments.

Galactosyl transferase knock-out pig lungs fail rapidly in baboons. Based on previously identified lung xenograft injury mechanisms, additional expression of human complement and coagulation pathway regulatory proteins, anti-inflammatory enzymes and self-recognition receptors, and knock-down of the ß4Gal xenoantigen were tested in various combinations. Transient life-supporting GalTKO.hCD46 lung function was consistently observed in association with either hEPCR (n = 15), hTBM (n = 4), or hEPCR.hTFPI (n = 11), but the loss of vascular barrier function in the xenograft and systemic inflammation in the recipient typically occurred within 24 h. Co-expression of hEPCR and hTBM (n = 11) and additionally blocking multiple pro-inflammatory innate and adaptive immune mechanisms was more consistently associated with survival >1 day, with one recipient surviving for 31 days. Combining targeted genetic modifications to the lung xenograft with selective innate and adaptive immune suppression enables prolonged initial life-supporting lung function and extends lung xenograft recipient survival, and illustrates residual barriers and candidate treatment strategies that may enable the clinical application of other organ xenografts.

Postoperative small bowel obstruction secondary to single malformed staple following laparoscopic total abdominal colectomy.

Surgical staplers are ubiquitous in gastrointestinal surgery, especially laparoscopy. Intraperitoneal staples are designed to be inert and are generally regarded as benign; however, complications from primarily malformed staples can rarely occur. Here, we present a case of early mechanical postoperative small bowel obstruction due to a surgical staple following laparoscopic total abdominal colectomy and end ileostomy creation performed for medically refractory ulcerative colitis. Management consisted of diagnostic laparoscopy and careful extraction of a malformed surgical staple tethering a loop of small bowel to the rectal stump. Eight similar cases following gastrointestinal surgery have been identified in the literature, all occurring in the first 2 weeks following laparoscopic appendectomy. To our knowledge, this is the first case described following laparoscopic total abdominal colectomy, with high-grade small bowel obstruction at the level of the rectal stump staple line.

Pilot Study of Delayed ICOS/ICOS-L Blockade With αCD40 to Modulate Pathogenic Alloimmunity in a Primate Cardiac Allograft Model.

BACKGROUND: Inducible costimulator (ICOS) is rapidly upregulated with T-cell stimulation and may represent an escape pathway for T-cell costimulation in the setting of CD40/CD154 costimulation blockade. Induction treatment exhibited no efficacy in a primate renal allograft model, but rodent transplant models suggest that the addition of delayed ICOS/ICOS-L blockade may prolong allograft survival and prevent chronic rejection. Here, we ask whether ICOS-Ig treatment, timed to anticipate ICOS upregulation, prolongs NHP cardiac allograft survival or attenuates pathogenic alloimmunity. METHODS: Cynomolgus monkey heterotopic cardiac allograft recipients were treated with αCD40 (2C10R4, d0-90) either alone or with the addition of delayed ICOS-Ig (d63-110). RESULTS: Median allograft survival was similar between ICOS-Ig + αCD40 (120 days, 120-125 days) and αCD40 (124 days, 89-178 days) treated animals, and delayed ICOS-Ig treatment did not prevent allograft rejection in animals with complete CD40 receptor coverage. Although CD4+ TEM cells were decreased in peripheral blood (115 ± 24) and mLNs (49 ± 1.9%) during ICOS-Ig treatment compared with monotherapy (214 ± 27%, P = 0.01; 72 ± 9.9%, P = 0.01, respectively), acute and chronic rejection scores and kinetics of alloAb elaboration were similar between groups. CONCLUSIONS: Delayed ICOS-Ig treatment with the reagent tested is probably ineffective in modulating pathogenic primate alloimmunity in this model.

Selective CD28 Inhibition Modulates Alloimmunity and Cardiac Allograft Vasculopathy in Anti-CD154-Treated Monkeys.

BACKGROUND: Selective CD28 inhibition is actively pursued as an alternative to B7 blockade using cytotoxic T lymphocyte antigen 4 Ig based on the hypothesis that the checkpoint immune regulators cytotoxic T lymphocyte antigen 4 and programmed death ligand 1 will induce tolerogenic immune signals. We previously showed that blocking CD28 using a monovalent nonactivating reagent (single-chain anti-CD28 Fv fragment linked to alpha-1 antitrypsin [sc28AT]) synergizes with calcineurin inhibitors in nonhuman primate (NHP) kidney and heart transplantation. Here, we explored the efficacy of combining a 3-week "induction" sc28AT treatment with prolonged CD154 blockade. METHODS: Cynomolgus monkey heterotopic cardiac allograft recipients received sc28AT (10 mg/kg, d0-20, n = 3), hu5C8 (10-30 mg/kg, d0-84, n = 4), or combination (n = 6). Graft survival was monitored by telemetry. Protocol biopsies and graft explants were analyzed for International Society of Heart and Lung Transplantation acute rejection grade and cardiac allograft vasculopathy score. Alloantibody, T-cell phenotype and regulatory T cells were analyzed by flow cytometry. Immunochemistry and gene expression (NanoString) characterized intra-graft cellular infiltration. RESULTS: Relative to modest prolongation of median graft survival time with sc28AT alone (34 days), hu5C8 (133 days), and sc28AT + hu5C8 (141 days) prolonged survival to a similar extent. CD28 blockade at induction, added to hu5C8, significantly attenuated the severity of acute rejection and cardiac allograft vasculopathy during the first 3 months after transplantation relative to hu5C8 alone. These findings were associated with decreased proportions of circulating CD8 and CD3CD28 T cells, and modulation of inflammatory gene expression within allografts. CONCLUSIONS: Induction with sc28AT promotes early cardiac allograft protection in hu5C8-treated NHPs. These results support further investigation of prolonged selective CD28 inhibition with CD40/CD154 blockade in NHP transplants.

P- and E-selectin receptor antagonism prevents human leukocyte adhesion to activated porcine endothelial monolayers and attenuates porcine endothelial damage.

BACKGROUND: Alongside the need to develop more effective and less toxic immunosuppression, the shortage of human organs available for organ transplantation is one of the major hurdles facing the field. Research into xenotransplantation, as an alternative source of organs, has unveiled formidable challenges. Porcine lungs perfused with human blood rapidly sequester the majority of circulating neutrophils and platelets, which leads to inflammation and organ failure within hours, and is not significantly attenuated by genetic modifications to the pig targeted to diminish antibody binding and complement and coagulation cascade activation. METHODS: Here, we model the interaction of freshly isolated human leukocytes with xenotransplanted vasculature under physiologic flow conditions using microfluidic channels coated with porcine endothelial cells. Both isolated human neutrophils and whole human blood were perfused over transgenic pig aortic endothelial cells that had been activated with rhTNF-α or rhIL-4 using the BioFlux system. Novel compounds GMI-1271 and rPSGL1.Fc were tested as E- and P- selectin antagonists, respectively. Cellular adhesion and rolling events were tracked using FIJI (imageJ). RESULTS: Porcine endothelium activated with either rhTNF-α or rhIL-4 expressed high amounts of selectins, to which isolated human neutrophils readily rolled and tethered. Both E-and P-selectin antagonism significantly reduced the number of neutrophils rolling and rolling distance in a dose-dependent manner, with near total inhibition at higher doses (P < .001). Similarly, with whole human blood, selectin blocking compounds exhibited dose-dependent inhibition of prevalent leukocyte adhesion and severe endothelial injury (Untreated: 394 ± 97 PMNs/hpf, 57 ± 6% loss EC; GMI1271+rPSGL1.Fc: 23 ± 9 PMNs/hpf, 8 ± 6% loss EC P < .01). CONCLUSIONS: Selectin blockade may be useful as part of an integrated strategy to prevent neutrophil-mediated organ xenograft injury, especially during the early time points following reperfusion.

Harnessing the lymph node microenvironment.

PURPOSE OF REVIEW: To evaluate role of the lymph node in immune regulation and tolerance in transplantation and recent advances in the delivery of antigen and immune modulatory signals to the lymph node. RECENT FINDINGS: Lymph nodes are a primary site of immune cell priming, activation, and modulation, and changes within the lymph node microenvironment have the potential to induce specific regulation, suppression, and potentially tolerance. Antigen enters the lymph node either from tissues via lymphatics, from blood via high endothelial venules, or directly via injection. Here we review different techniques and materials to deliver antigen to the lymph node including microparticles or nanoparticles, ex-vivo antigen presenting cell manipulation, and use of receptor conjugation for specific intralymph node targeting locations. SUMMARY: The promising results point to powerful techniques to harness the lymph node microenvironment and direct systemic immune regulation. The materials, techniques, and approaches suggest that translational and clinical trials in nonhuman primate and patients may soon be possible.

Synthetic liver function is detectable in transgenic porcine livers perfused with human blood.

In addition to immune barriers, molecular incompatibilities between species are predicted to limit pig liver survival in primate xenotransplantation models. Assessment and measurement of synthetic function of genetically modified porcine livers after ex vivo perfusion with human blood have not previously been described. Eight porcine livers from α1,3-galactosyl transferase knockout and human membrane cofactor (GalTKO.hCD46), six livers from GalTKO.hCD46 and N-glycolylneuraminic acid knockout (GalTKO.hCD46.Neu5GcKO), and six livers from GalTKO.hCD46 with humanized decay-accelerating factor (hCD55), endothelial protein C receptor (hEPCR), tissue factor pathway inhibitor (hTFPI), and integrin-associated protein (hCD47) (GalTKO.hCD46.hCD55.hEPCR.hTFPI.hCD47) pigs were perfused with human blood under physiologic conditions. Timed blood samples were tested for liver enzymes and for pig-specific albumin production via Western blot. Porcine albumin levels increased with time in all experiments. By densitometry, GalTKO.hCD46.Neu5GcKO livers had the highest albumin levels, measured both as total produced, and when controlled for perfusion duration, compared to GalTKO.hCD46 (P = .068) and GalTKO.hCD46.hCD55.hEPCR.hTFPI.hCD47 livers (P = .04). Porcine livers perfused with human blood demonstrated the synthetic ability to produce albumin in all cases. GalTKO.hCD46.Neu5GcKO pig livers demonstrated the most robust albumin production. This suggests that the Neu5GcKO phenotype provides a protective effect on the graft due to decreased human antibody recognition and graft injury.

Transgenic expression of human leukocyte antigen-E attenuates GalKO.hCD46 porcine lung xenograft injury.

BACKGROUND: Lung xenografts remain susceptible to loss of vascular barrier function within hours in spite of significant incremental advances based on genetic engineering to remove the Gal 1,3-αGal antigen (GalTKO) and express human membrane cofactor protein (hCD46). Natural killer cells rapidly disappear from the blood during perfusion of GalTKO.hCD46 porcine lungs with human blood and presumably are sequestered within the lung vasculature. Here we asked whether porcine expression of the human NK cell inhibitory ligand HLA-E and ß2 microglobulin inhibits GalTKO.hCD46 pig cell injury or prolongs lung function in two preclinical perfusion models. METHODS: Lungs from pigs modified to express GalTKO.hCD46 (n=37) and GalTKO.hCD46.HLA-E (n=5) were harvested and perfused with human blood until failure or elective termination at 4 hours. Airway pressures and pulmonary artery hemodynamics were recorded in real time. Blood samples were also collected throughout the experiment for analysis. Porcine aortic endothelial cells (PAECs) from each genotype were cultured in monolayers in microfluidic channels and used in fluorescent cytotoxicity assays using human NK cells. RESULTS: HLA-E expression on GalTKO.hCD46 PAECs was associated with significantly decreased antibody-dependent and antibody-independent NK-mediated cytotoxicity under in vitro conditions simulating physiologic shear stress. Relative to GalTKO.hCD46 pig lungs perfused with human blood on an ex vivo platform, additional expression of HLA-E increased median lung survival (>4 hours, vs 162 minutes, P=.012), and was associated with attenuated rise in pulmonary vascular resistance, and decreased platelet activation and histamine elaboration. As expected, HLA-E expression was not associated with a significant difference in NK cell adhesion to endothelial cells in vitro, or NK cell and neutrophil sequestration during organ perfusion. CONCLUSIONS: We conclude human NK cell activation contributes significantly to GalTKO.hCD46 pig endothelial injury and lung inflammation and show that expression of HLA-E is associated with physiologically meaningful protection of GalTKO.hCD46 cells and organs exposed to human blood.

Vascularized Thymosternal Composite Tissue Allo- and Xenotransplantation in Nonhuman Primates: Initial Experience.

BACKGROUND: Vascularized composite allotransplantation is constrained by complications associated with standard immunosuppressive strategies. Vascularized thymus and bone marrow have been shown to promote prolonged graft survival in composite organ and soft-tissue vascularized composite allotransplantation models. We report development of a nonhuman primate vascularized thymosternal composite tissue transplant model as a platform to address donor-specific immune tolerance induction strategies. METHODS: Vascularized thymosternal allograft (skin, muscle, thymus, sternal bone) was transplanted between MHC-mismatched rhesus monkeys (feasibility studies) and baboons (long-term survival studies), with end-to-side anastomoses of the donor aorta and SVC to the recipient common femoral vessels. A male allograft was transplanted to a female's lower abdominal wall, and clinically applicable immunosuppression was given. Skin biopsies and immunological assays were completed at regular intervals, and chimerism was quantified using polymerase chain reaction specific for baboon Y chromosome. RESULTS: Four allo- and 2 xenotransplants were performed, demonstrating consistent technical feasibility. In 1 baboon thymosternal allograft recipient treated with anti-CD40-based immunosuppression, loss of peripheral blood microchimerism after day 5 was observed and anticipated graft rejection at 13 days. In the second allograft, when cutaneous erythema and ecchymosis with allograft swelling was treated with anti-thymocyte globulin starting on day 6, microchimerism persisted until immunosuppression was reduced after the first month, and the allograft survived to 87 days, 1 month after cessation of immunosuppression treatment. CONCLUSIONS: We established both allo- and xeno- composite vascularized thymosternal transplant preclinical models, which will be useful to investigate the role of primarily vascularized donor bone marrow and thymus.

The use of resuscitative endovascular balloon occlusion of the aorta to control hemorrhagic shock during video-assisted retroperitoneal debridement or infected necrotizing pancreatitis.

INTRODUCTION: Resuscitative endovascular balloon occlusion of the aorta (REBOA) is a technique that has been shown to provide central vascular control to support proximal aortic pressure and minimize hemorrhage in a wide variety of clinic settings, however the role of REBOA for emergency general surgery is less defined. CASE DESCRIPTION: This is a report of a 44 year old man who experienced hemorrhagic shock during video-assisted retroperitoneal debridement (VARD) for necrotizing pancreatitis where REBOA was used to prevent ongoing hemorrhage and death. DISCUSSION: This is the first documented report REBOA being used during pancreatic debridement in the literature and one of the first times it has been used in emergency general surgery. The use of REBOA is an option for those in hemorrhagic shock whom conventional aortic cross-clamping or supra-celiac aortic exposure is either not possible or exceedingly dangerous. CONCLUSION: REBOA allows for adequate resuscitation and can be used as a bridge to definitive therapy in a range of surgical subspecialties with minimal morbidity and complications. The risks associated with insertion of wires, sheaths, and catheters into the arterial system, as well as the risk of visceral and spinal cord ischemia due to aortic occlusion mandate that the use of this technique be utilized in only appropriate clinical scenarios.