Examining epitope mutagenesis as a strategy to reduce and eliminate human antibody binding to class II swine leukocyte antigens.

Xenotransplantation of pig organs into people may help alleviate the critical shortage of donors which faces organ transplantation. Unfortunately, human antibodies vigorously attack pig tissues preventing the clinical application of xenotransplantation. The swine leukocyte antigens (SLA), homologs of human HLA molecules, can be xenoantigens. SLA molecules, encoded by genes in the pig major histocompatibility complex, contribute to protective immune responses in pig. Therefore, simply inactivating them through genome engineering could reduce the ability of the human immune system to surveil transplanted pig organs for infectious disease or the development of neoplasms. A potential solution to this problem is to identify and modify epitopes in SLA proteins to eliminate their contribution to humoral xenoantigenicity while retaining their biosynthetic competence and ability to contribute to protective immunity. We previously showed that class II SLA proteins were recognized as xenoantigens and mutating arginine at position 55 to proline, in an SLA-DQ beta chain, could reduce human antibody binding. Here, we extend these observations by creating several additional point mutants at position 55. Using a panel of monoclonal antibodies specific for class II SLA proteins, we show that these mutants remain biosynthetically competent. Examining antibody binding to these variants shows that point mutagenesis can reduce, eliminate, or increase antibody binding to class II SLA proteins. Individual mutations can have opposite effects on antibody binding when comparing samples from different people. We also performed a preliminary analysis of creating point mutants near to position 55 to demonstrate that manipulating additional residues also affects antibody reactivity.

The desirable donor pig to eliminate all xenoreactive antigens.

The humoral barrier has been the limiting factor in moving xenotransplantation towards the clinic. Improvements in somatic cell nuclear transfer and genome editing, particularly CRISPR-Cas9, have made it possible to create pigs with multiple glycan xenoantigen deletions for the purposes of reducing xenoreactive antibody binding to the xenografted organ. Recent studies have also considered the aetiology and existence of antibodies directed at the swine leucocyte antigen (SLA) complex, and potential genetic engineering strategies to avoid these antibodies. Evaluation of xenoreactive antibody binding is very important for the advancement of xenotransplantation, because if patients do not have any detectable xenoreactive antibody, then it is reasonable to expect that cellular rejection and not antibody-mediated rejection (AMR) will be the next hurdle to clinical application.

Evaluation of human and non-human primate antibody binding to pig cells lacking GGTA1/CMAH/ß4GalNT2 genes.

BACKGROUND: Simultaneous inactivation of pig GGTA1 and CMAH genes eliminates carbohydrate xenoantigens recognized by human antibodies. The ß4GalNT2 glycosyltransferase may also synthesize xenoantigens. To further characterize glycan-based species incompatibilities, we examined human and non-human primate antibody binding to cells derived from genetically modified pigs lacking these carbohydrate-modifying genes. METHODS: The Cas9 endonuclease and gRNA were used to create pigs lacking GGTA1, GGTA1/CMAH, or GGTA1/CMAH/ß4GalNT2 genes. Peripheral blood mononuclear cells were isolated from these animals and examined for binding to IgM and IgG from humans, rhesus macaques, and baboons. RESULTS: Cells from GGTA1/CMAH/ß4GalNT2 deficient pigs exhibited reduced human IgM and IgG binding compared to cells lacking both GGTA1 and CMAH. Non-human primate antibody reactivity with cells from the various pigs exhibited a slightly different pattern of reactivity than that seen in humans. Simultaneous inactivation of the GGTA1 and CMAH genes increased non-human primate antibody binding compared to cells lacking either GGTA1 only or to those deficient in GGTA1/CMAH/ß4GalNT2. CONCLUSIONS: Inactivation of the ß4GalNT2 gene reduces human and non-human primate antibody binding resulting in diminished porcine xenoantigenicity. The increased humoral immunity of non-human primates toward GGTA1-/CMAH-deficient cells compared to pigs lacking either GGTA1 or GGTA1/CMAH/ß4GalNT2 highlights the complexities of carbohydrate xenoantigens and suggests potential limitations of the non-human primate model for examining some genetic modifications. The progressive reduction of swine xenoantigens recognized by human immunoglobulin through inactivation of pig GGTA1/CMAH/ß4GalNT2 genes demonstrates that the antibody barrier to xenotransplantation can be minimized by genetic engineering.

HLA Class I-sensitized Renal Transplant Patients Have Antibody Binding to SLA Class I Epitopes.

BACKGROUND: Highly sensitized patients are difficult to match with suitable renal allograft donors and may benefit from xenotransplant trials. We evaluate antibody binding from sensitized patients to pig cells and engineered single allele cells to identify anti-human leukocyte antigen (HLA) antibody cross-species reactivity with swine leukocyte antigen (SLA). These novel testing strategies assess HLA/SLA epitopes and antibody-binding patterns and introduce genetic engineering of SLA epitopes. METHODS: Sensitized patient sera were grouped by calculated panel reactive antibody and luminex single antigen reactivity profile and were tested with cloned GGTA1/CMAH/B4GalNT2 glycan knockout porcine cells. Pig reactivity was assessed by direct flow cytometric crossmatch and studied following elution from pig cells. To study the antigenicity of individual class I HLA and SLA alleles in cells, irrelevant sera binding to lymphoblastoid cells were minimized by CRISPR/Cas9 elimination of endogenous class I and class II HLA, B-cell receptor, and Fc receptor genes. Native HLA, SLA, and mutants of these proteins after mutating 144K to Q were assessed for antibody binding. RESULTS: Those with predominately anti-HLA-B&C antibodies, including Bw6 and Bw4 sensitization, frequently have low pig reactivity. Conversely, antibodies eluted from porcine cells are more commonly anti-HLA-A. Single HLA/SLA expressing engineered cells shows variable antigenicity and mutation of 144K to Q reduces antibody binding for some sensitized patients. CONCLUSIONS: Anti-HLA antibodies cross-react with SLA class I in predictable patterns, which can be identified with histocompatibility strategies, and SLA class I is a possible target of genetic engineering.

Induction immunosuppression with thymoglobulin and rituximab in intestinal and multivisceral transplantation.

BACKGROUND: Induction immunosuppression is now a common practice after intestinal and multivisceral transplantation. We report our experience in 27 adult recipients who received rituximab and rabbit antithymocyte globulin (rATG) in combination as induction agents. MATERIAL AND METHODS: Twenty-seven adult patients received 29 intestinal transplants between July 2004 and March 2007. All patients received induction immunosuppression therapy with rATG, rituximab, and steroids. Tacrolimums and a steroid taper were used for maintenance therapy. Patient and graft survival, episodes of rejection as well as posttransplant lymphoproliferative disease (PTLD) and graft-versus-host disease were analyzed. RESULTS: One-year patient and graft survival was 81% and 76%, respectively. Thirteen patients (48%) experienced 19 episodes of acute rejection (9 mild episodes, 2 moderate, and 8 severe). Patients with a multivisceral graft experienced less episodes of severe acute rejection (1 of 19, 5%) when compared with isolated intestinal transplants and modified multivisceral transplants (7 of 10, 70%). Two patients had episodes of skin graft-versus-host disease that responded to steroid boluses. PTLD was not seen in our series. Two patients developed cytomegalovirus enteritis. CONCLUSIONS: The combination of rATG and rituximab was an effective induction therapy in our preliminary data. The number and severity of rejection episodes increased when the liver was not included as part of the graft. An immunosuppression regimen including rATG, rituximab, and steroids may have a protective effect against PTLD and chronic rejection.

Initiation of an intestinal transplant program: the Indiana experience.

INTRODUCTION: Establishment of a new intestinal transplant (Itx) program in the United States entails significant programmatic costs and a steep learning curve. We report results of the first 4 years of the program at Indiana University. METHODS: Forty-six intestinal and multivisceral transplants (MVtx) were performed between 2003 and 2007. All organ procurements were performed by our team. Immunosuppression included an induction protocol combined with maintenance tacrolimus monotherapy. Scheduled rejection surveillance was with magnification endoscopy. RESULTS: Forty-three patients (13 children and 30 adults) received 10 Itx (22%), 5 modified MVtxs (11%), and 31 (MVtx, 67%). Recipient ages ranged from 3 months to 66 years, with median follow-up time of 15 months. Thirty-five patients are currently alive (81%). Patient and graft survival at 30 days was 85%/86% in pediatric and 93%/91% in adult; overall survival was 69%/64% in pediatric and 87%/75% in adult. Thirty patients (69%) experienced episodes of rejection. Multivisceral transplanted patients experienced less episodes of severe rejection (2/31, 6%) when compared with patients with isolated Itx and modified MVtxs. Retransplantation was performed in three patients with nonresponsive severe acute rejection. CONCLUSION: The Indiana University Intestinal and Multivisceral Transplant program experienced significant early graft loss and mortality among pediatric patients, but not among adults. This discrepancy resolved within 2 years of program initiation. After 4 years, adult and pediatric graft and patient survival statistics are similar to those at other programs.

Role of Stereotactic Body Radiation Therapy Before Orthotopic Liver Transplantation: Retrospective Evaluation of Pathologic Response and Outcomes.

PURPOSE: To analyze the results of stereotactic body radiation therapy (SBRT) in patients with early-stage, localized hepatocellular carcinoma who underwent definitive orthotopic liver transplantation (OLT). METHODS AND MATERIALS: The subjects of this retrospective report are 38 patients diagnosed with hepatocellular carcinoma who underwent SBRT per institutional phase 1 to 2 eligibility criteria, before definitive OLT. Pre-OLT radiographs were compared with pathologic gold standard. Analysis of treatment failures and deaths was undertaken. RESULTS: With median follow-up of 4.8 years from OLT, 9 of 38 patients (24%) recurred, whereas 10 of 38 patients (26%) died. Kaplan-Meier estimates of 3-year overall survival and disease-free survival are 77% and 74%, respectively. Sum longest dimension of tumors was significantly associated with disease-free survival (hazard ratio 1.93, P=.026). Pathologic response rate (complete plus partial response) was 68%. Radiographic scoring criteria performed poorly; modified Response Evaluation Criteria in Solid Tumors produced highest concordance (κ = 0.224). Explants revealed viable tumor in 74% of evaluable patients. Treatment failures had statistically larger sum longest dimension of tumors (4.0 cm vs 2.8 cm, P=.014) and non-statistically significant higher rates of lymphovascular space invasion (44% vs 17%), cT2 disease (44% vs 21%), ≥pT2 disease (67% vs 34%), multifocal tumors at time of SBRT (44% vs 21%), and less robust mean α-fetoprotein response (-25 IU/mL vs -162 IU/mL). CONCLUSIONS: Stereotactic body radiation therapy before to OLT is a well-tolerated treatment providing 68% pathologic response, though 74% of explants ultimately contained viable tumor. Radiographic response criteria poorly approximate pathology. Our data suggest further stratification of patients according to initial disease burden and treatment response.

Optimization of Perioperative Conditions to Prevent Ischemic Cholangiopathy in Donation After Circulatory Death Donor Liver Transplantation.

BACKGROUND: Donation after circulatory death (DCD) donor pool remains underutilized for liver transplantation (LT). We describe optimizing "modifiable risk factors," such as cold ischemia time (CIT) recipient warm ischemia time (WIT) and the use of thrombolytic flush at the time of procurement to minimize ischemic cholangiopathy (IC). METHODS: From July 2011 (era II), to improve outcomes after DCD LT, measures were taken to minimize CIT, operative time and recipient WIT along with the use of tissue plasminogen activator (tPA) flush during DCD procurements. Thirty consecutive DCD LTs were performed prospectively in era II. Outcomes were compared with 61 historic controls (era I). Reperfusion biopsies were evaluated for the presence of necrosis and biliary epithelial damage. RESULTS: Median CIT (4.9 [3.5-5.9] vs 6.4 [4.3-12]; P < 0.001), hepatectomy time (70 [42-120] vs 81 [58-207]; P = 0.02), and recipient WIT (16 [13-31] vs 24[15-40]; P < 0.001) were significantly shorter in era II. All patients in era II received tPA flushed liver grafts. None of the patients in era II developed IC (0% vs 18%; P = 0.013). There were fewer biliary complications in era II, and there was no increased risk of bleeding associated with the use of tPA. One-year graft survival was slightly better in era II (n = 24 patients with 1 year follow-up) (88% vs 80%; P = 0.14). CONCLUSIONS: Optimizing peritransplant conditions, such as shortening ischemic times with the use of thrombolytic donor flush, may prevent IC after DCD LT. With this approach, the DCD donor pool may be expanded.

Worse Long-term Patient Survival and Higher Cancer Rates in Liver Transplant Recipients With a History of Smoking.

BACKGROUND: This study is a retrospective review of liver transplant (LT) recipients to determine the impact of tobacco exposure on 10-year survival and de novo cancer (CA) incidence. METHODS: The records of 1275 consecutive LT patients were reviewed (2001 to 2011). Patients were categorized as current, previous, or never smokers (NS) at listing for LT. Additionally, smokers were stratified by pack-years of tobacco exposure. Events included patient death, cardiovascular events, and de novo cancers. Cox regression analysis was used to evaluate survival. A complete cause of death analysis is provided, as well as a detailed tumor registry. RESULTS: Current (n = 279) and previous smokers (n = 323) were more likely to have hepatocellular carcinoma (HCC) at transplant (25%, 29% vs 18% [NS], P < 0.001), and these 2 groups had higher HCC recurrence rates (21%, 14% vs 11% [NS], P = 0.18). De novo non-HCC CA was higher for current and previous smokers, compared to NS (18%, 16% vs 12% [NS], P = 0.05). Among those with de novo CA (n = 180), the 2 smoking groups were more likely to have non-skin CA (60%, 54% vs 27% [NS], P < 0.001). Patient survival at 10 years was worse for current smokers than the other study groups (55% vs 70%, P < 0.01). These results were largely mirrored with increased tobacco exposure. CONCLUSIONS: The LT outcomes are uniformly worse for patients with a history of smoking, and the risk of negative events increases with increasing tobacco use. Smokers have higher rates of HCC and recurrence, de novo cancer, and worse long-term survival. SUMMARY STATEMENT: This study summarizes the clinical outcomes for 1275 LT patients over 10 years, analyzing the impact of pre transplant recipient tobacco use. There are 47% of patients with a history of smoking. Because of demonstrated higher cancer rates and decreased survival, patients with a significant smoking history should be carefully scrutinized for liver transplantation.

Intestinal and multivisceral transplantation at Indiana University: 6 years' experience with 100 cases.

Intestinal transplantation has shown exceptional growth over the past 20 years with extraordinary progress. As with other solid organ transplants, intestinal transplantation has now transitioned from being experimental to being the standard of care for patients with intestinal failure. The currently reported 1-year graft and patient survival rate is 80%, which approaches that for other solid abdominal organs. Unfortunately, most of the gains in survival are seen in the first postoperative year, with long-term survival remaining basically unchanged since the early 1990s. Immunosuppressive regimens continue to evolve, with induction therapy being the major change in the past 10 years. No randomized trials compare intestinal transplantation to long-term PN to establish guidelines for timely referral for this treatment option, so late referral remains a crippling problem in the field of intestinal transplantation. Patients referred late often develop severe liver dysfunction and fibrosis, resulting in a great number of patients in need of simultaneous liver transplantation at the time of listing for intestinal transplantation.

Stem cells as a potential future treatment of pediatric intestinal disorders.

All surgical disciplines encounter planned and unplanned ischemic events that may ultimately lead to cellular dysfunction and death. Stem cell therapy has shown promise for the treatment of a variety of ischemic and inflammatory disorders where tissue damage has occurred. As stem cells have proven beneficial in many disease processes, important opportunities in the future treatment of gastrointestinal disorders may exist. Therefore, this article will serve to review the different types of stem cells that may be applicable to the treatment of gastrointestinal disorders, review the mechanisms suggesting that stem cells may work for these conditions, discuss current practices for harvesting and purifying stem cells, and provide a concise summary of a few of the pediatric intestinal disorders that could be treated with cellular therapy.