Pigs in Transplantation Research and Their Potential as Sources of Organs in Clinical Xenotransplantation

The pig has long been used as a research animal and has now gained importance as a potential source of organs for clinical xenotransplantation. When an organ from a wild-type (i. e., genetically unmodified) pig is transplanted into an immunosuppressed nonhuman primate, a vigorous host immune response causes hyperacute rejection (within minutes or hours). This response has been largely overcome by 1) extensive gene editing of the organ-source pig and 2) the administration to the recipient of novel immunosuppressive therapy based on blockade of the CD40/CD154 T cell costimulation pathway. Gene editing has consisted of 1) deletion of expression of the 3 known carbohydrate xenoantigens against which humans have natural (preformed) antibodies and 2) the introduction of human 'protective' genes. The combination of gene editing and novel immunosuppressive therapy has extended life-supporting pig kidney graft survival to greater than 1 y and of pig heart survival to up to 9 mo. This review briefly describes the techniques of gene editing, the potential risks of transfer of porcine endogenous retroviruses with the organ, and the need for breeding and housing of donor pigs under biosecure conditions.

Incidence of serum antibodies to xenoantigens on triple-knockout pig cells in different human groups

BACKGROUND

Xenoantigens other than Gal, Neu5Gc, and Sda may be playing a role in pig graft rejection. We investigated the incidence of antibodies to unknown pig xenoantigen in different human groups.

METHODS

We collected blood from TKO/hCD55 pigs (n = 3), and isolated PBMCs and RBCs. Serum samples were collected from (i) healthy human volunteers (n = 43), (ii) patients with end-stage renal disease (ESRD) (n = 87), (iii) the same patients after kidney allotransplantation (n = 50), and (iv) renal allotransplant recipients experiencing T cell-mediated rejection (allo-TCMR, n = 10). The sera were initially incubated with TKO/hCD55 pRBCs (1 × 108 cells) for 1 h to absorb anti-pig antibodies (except against SLA and possibly other antigens not expressed on pRBCs) and then the serum (absorbed or unabsorbed) was tested for antibody binding and complement-dependent cytotoxicity (CDC) to TKO/hCD55 pig PBMCs.

RESULTS

A significant reduction in IgM/IgG binding and CDC was observed in the absorbed sera. Serum obtained before and after renal allotransplantation showed no significant difference in IgM or IgG binding to, or in CDC of, TKO/hCD55 pig cells. IgM antibodies (but rarely IgG) against unknown xenoantigens expressed on TKO/hCD55 PBMCs, possibly against swine leukocyte antigens, were documented in healthy humans, patients with ESRD, and those with renal allografts undergoing acute T cell rejection. IgM (but not CDC) was higher in patients experiencing allo-TCMR.

CONCLUSION

Human sera contain IgM antibodies against unknown pig xenoantigens expressed on TKO/hCD55 pPBMCs. Although not confirmed in the present study, the targets for these antibodies may include swine leukocyte antigens.

In vitro and in vivo immune assessments of genetically-engineered pig skin grafts in New World (squirrel) monkeys

Half a million patients in the USA alone require treatment for burns annually. Following an extensive burn, it may not be possible to provide sufficient autografts in a single setting. Genetic manipulations (GM) of pigs offer the possibility of reducing primate humoral and cellular rejection of pig skin xenografts and thus extending graft survival. We compared the survival of skin grafts from pigs with 9-GM with that of autografts and allografts in squirrel monkeys. Monitoring for rejection was by (1) macroscopic examination, (2) histopathological examination of skin biopsies, and (3) measurement of anti-monkey and anti-pig IgM and IgG antibodies. Autografts (n = 5) survived throughout the 28 days of follow-up without histopathological features of rejection. Median survival of allografts (n = 6) was 14 days and of pig xenografts (n = 12) 21 days. Allotransplantation was associated with an increase in anti-monkey IgM, but the anticipated subsequent rise in IgG had not yet occurred at the time of euthanasia. Pig grafts were associated with increases in anti-pig IgM and IgG. In all cases, histopathologic features of rejection were similar. 9-GM pig skin xenografts survive at least as long as monkey skin allografts (and trended to survive longer), suggesting that they are a realistic clinical option for the temporary treatment of burns. Although monkeys with pig skin grafts developed anti-pig IgM and IgG antibodies, these did not cross-react with monkey antigens, indicating that a primary 9-GM pig skin graft would not be detrimental to a subsequent monkey skin allograft.

Future prospects for the clinical transfusion of pig red blood cells

Transfusion of allogeneic human red blood cell (hRBCs) is limited by supply and compatibility between individual donors and recipients. In situations where the blood supply is constrained or when no compatible RBCs are available, patients suffer. As a result, alternatives to hRBCs that complement existing RBC transfusion strategies are needed. Pig RBCs (pRBCs) could provide an alternative because of their abundant supply, and functional similarities to hRBCs. The ability to genetically modify pigs to limit pRBC immunogenicity and augment expression of human 'protective' proteins has provided major boosts to this research and opens up new therapeutic avenues. Although deletion of expression of xenoantigens has been achieved in genetically-engineered pigs, novel genetic methods are needed to introduce human 'protective' transgenes into pRBCs at the high levels required to prevent hemolysis and extend RBC survival in vivo. This review addresses recent progress and examines future prospects for clinical xenogeneic pRBC transfusion.

Antibody-mediated rejection in xenotransplantation: Can it be prevented or reversed?

Antibody-mediated rejection (AMR) is the commonest cause of failure of a pig graft after transplantation into an immunosuppressed nonhuman primate (NHP). The incidence of AMR compared to acute cellular rejection is much higher in xenotransplantation (46% vs. 7%) than in allotransplantation (3% vs. 63%) in NHPs. Although AMR in an allograft can often be reversed, to our knowledge there is no report of its successful reversal in a pig xenograft. As there is less experience in preventing or reversing AMR in models of xenotransplantation, the results of studies in patients with allografts provide more information. These include (i) depletion or neutralization of serum anti-donor antibodies, (ii) inhibition of complement activation, (iii) therapies targeting B or plasma cells, and (iv) anti-inflammatory therapy. Depletion or neutralization of anti-pig antibody, for example, by plasmapheresis, is effective in depleting antibodies, but they recover within days. IgG-degrading enzymes do not deplete IgM. Despite the expression of human complement-regulatory proteins on the pig graft, inhibition of systemic complement activation may be necessary, particularly if AMR is to be reversed. Potential therapies include (i) inhibition of complement activation (e.g., by IVIg, C1 INH, or an anti-C5 antibody), but some complement inhibitors are not effective in NHPs, for example, eculizumab. Possible B cell-targeted therapies include (i) B cell depletion, (ii) plasma cell depletion, (iii) modulation of B cell activation, and (iv) enhancing the generation of regulatory B and/or T cells. Among anti-inflammatory agents, anti-IL6R mAb and TNF blockers are increasingly being tested in xenotransplantation models, but with no definitive evidence that they reverse AMR. Increasing attention should be directed toward testing combinations of the above therapies. We suggest that treatment with a systemic complement inhibitor is likely to be most effective, possibly combined with anti-inflammatory agents (if these are not already being administered). Ultimately, it may require further genetic engineering of the organ-source pig to resolve the problem entirely, for example, knockout or knockdown of SLA, and/or expression of PD-L1, HLA E, and/or HLA-G.

What Have We Learned From In Vitro Studies About Pig-to-primate Organ Transplantation?

Natural preformed and de novo antibodies against pig antigens are a major cause of pig xenograft rejection in nonhuman primates (NHPs). In vivo studies in pig-to-NHP models are time consuming. In vitro assays, for example, antibody binding to pig cells, complement-dependent cytotoxicity assays, provide valuable information quickly and inexpensively. Using in vitro assays for several years, it has been documented that (1) during the first year of life, humans and NHPs develop anti-wild-type pig antibodies, but humans develop no or minimal antibody to triple-knockout (TKO) pig cells. (2) Some adult humans have no or minimal antibodies to TKO pig cells and are therefore unlikely to rapidly reject a TKO organ, particularly if the organ also expresses human "protective" proteins. (3) There is good correlation between immunoglobulin (Ig)M (but no t IgG) binding and complement injury. (4) All Old World NHPs develop antibodies to TKO pig cells and are not optimal recipients of TKO organs. (5) galactosyltransferase gene-knockout/β4GalNT2KO pigs are preferred for Old World NHPs. (6) Humans develop anti-pig IgE and IgA antibodies against pig cells, but their role remains uncertain. (7) In a small percentage of allosensitized humans, antibodies that cross-react with swine leukocyte antigens may be detrimental to a pig organ xenograft. (8) Prior sensitization to pig antigens is unlikely to be detrimental to a subsequent allograft. (9) Deletion of expression of Gal and Neu5Gc is associated with a reduction in the T-cell response to pig cells. All of these valuable observations have largely predicted the results of in vivo studies.

The case for the therapeutic use of mechanistic/mammalian target of rapamycin (mTOR) inhibitors in xenotransplantation

The mechanistic/mammalian target of rapamycin (mTOR) is one of the systems that are necessary to maintain cell homeostasis, such as survival, proliferation, and differentiation. mTOR inhibitors (mTOR-Is) are utilized as immunosuppressants and anti-cancer drugs. In organ allotransplantation, current regimens infrequently include an mTOR-I, which are positioned more commonly as alternative immunosuppressants. In clinical allotransplantation, long-term efficacy has been established, but there is a significant incidence of adverse events, for example, inhibition of wound healing, buccal ulceration, anemia, hyperglycemia, dyslipidemia, and thrombocytopenia, some of which are dose-dependent. mTOR-Is have properties that may be especially beneficial in xenotransplantation. These include suppression of T cell proliferation, increases in the number of T regulatory cells, inhibition of pig graft growth, and anti-inflammatory, anti-viral, and anti-cancer effects. We here review the potential benefits and risks of mTOR-Is in xenotransplantation and suggest that the benefits exceed the adverse effects.

Multicenter registry of the Watchman left atrial appendage closure device for patients with atrial fibrillation in Japan: The TERMINATOR registry

Funding Acknowledgements

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Boston Scientific Japan

Background

Transcatheter left atrial appendage closure (LAAC) provides an alternative to oral anticoagulation for thromboembolic risk reduction in patients with nonvalvular atrial fibrillation (AF). A meta-analysis of previous two randomized trials reported improved rates of hemorrhagic stroke, cardiovascular/unexplained death, and nonprocedural bleeding compared to warfarin (1). Recently, the next-generation LAAC device, the Watchman FLX system, became available, and showed a low incidence of adverse events and a high incidence of anatomic closure (2). This transcatheter stroke prevention has already been approved in Asian countries. However, there is little data of LAAC in Asian population.

Purpose

This study sought to assess efficacy and safety of LAAC for patients with nonvalvular AF in Asia.

Methods

The TERMINATOR (Transcatheter Modification of Left Atrial Appendage by Obliteration with Device) registry is a multicenter nonrandomized study in Japan. This enrolled patients who underwent LAAC in 23 Japanese institutions. The LAAC was indicated for patients with nonvalvular atrial fibrillation in whom oral anticoagulation is required, but who have a risk of bleeding (history of BARC type 3 bleeding or HAS-BLED score ≥3 points). Baseline patient and procedural characteristics and clinical outcomes were evaluated.

Results

A total of 729 patients were enrolled between September 2019 and November 2021. The mean age was 74.9±8.8 years and the mean CHA2DS2-VASc score was 4.7±1.5. The Watchman generation 2.5 and FLX system were used in 469 (64.3%) and 260 patients (35.7%), respectively. Procedural success was achieved in 722 patients (99.0%). In-hospital adverse events were as follows; 6 tamponades (0.8%), 3 pericardial effusion (0.4%), 2 device embolization (0.3%), no stroke (0%), and no death (0%). During follow-up, device-related thrombus and all-cause death were reported in 16 (2.2%) and 23 patients (3.2%), respectively.

Conclusions

LAAC with the Watchman system provides compatible efficacy and safety outcomes in Asian population.

The respective relevance of sensitization to alloantigens and xenoantigens in pig organ xenotransplantation

BACKGROUND

Antibody-mediated rejection is a major cause of graft injury and contributes to failure of pig xenografts in nonhuman primates (NHPs). Most 'natural' or elicited antibodies found in humans and NHPs are directed against pig glycan antigens, but antibodies binding to swine leukocyte antigens (SLA) have also been detected. Of clinical importance is (i) whether the presence of high levels of antibodies directed towards human leukocyte antigens (HLA) (i.e., high panel-reactive antibodies) would be detrimental to the outcome of a pig organ xenograft; and (ii) whether, in the event of sensitization to pig antigens, a subsequent allotransplant would be at increased risk of graft failure due to elicited anti-pig antibodies that cross-react with human HLA or other antigens.

SUMMARY

A literature review of pig-to-primate studies indicates that relatively few highly-HLA-sensitized humans have antibodies that cross-react with pigs, predicting that most would not be at increased risk of rejecting an organ xenograft. Furthermore, the existing evidence indicates that sensitization to pig antigens will probably not elicit increased alloantibody titers; if so, 'bridging' with a pig organ could be carried out without increased risk of subsequent antibody-mediated allograft failure.

KEY MESSAGE

These issues have important implications for the design and conduct of clinical xenotransplantation trials.

Observations on hydronephrosis after pig kidney transplantation in baboons

We have seen hydronephrosis (obstructive nephropathy) at necropsy in 3 of 11 (21%) genetically-engineered pig kidneys that functioned in baboons for >36 days, even when the clinical and histopathological features of rejection were minimal. We briefly report one such case and illustrate the macroscopic and microscopic appearances of such a kidney and ureter. The causes of the observed changes remain uncertain. In our small experience, there seems to be no correlation between the development of hydronephrosis and (i) the surgical technique, (ii) the genotype of the pig, (iii) the length of the pig ureter, or (iv) the immunosuppressive and anti-inflammatory therapy administered. We suggest that the distal ureteric thickening may be the result of an inflammatory response. In two cases, we resolved the problem by carrying out a secondary side-to-side anastomosis between the proximal pig ureter and the baboon bladder.

Ten years survival benefit of CABG or PCI based on individual prediction

Background

To compare the observed and individual predicted mortalities according to the SYNTAX score II 2020 (SSII-2020) in the all-comers SYNTAX population, and retrospectively assess the appropriateness of revascularization with percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG) in patients with three vessel disease (3VD) and/or left main disease (LMCAD).

Methods

Internal and external validation of the SSII-2020 to predict 10-year all-cause death was performed in the respective randomized and registry SYNTAX populations. Differences in individual predicted mortalities following CABG or PCI were ranked and displayed with the observed mortalities. The proportions of screened patients deriving a survival benefit from CABG or PCI were determined retrospectively.

Results

A total of 2602 participants (as-treated population) were included in the randomized and registry cohorts. In the randomized cohort, all-cause mortality at 10 years, as an average treatment effect, was 23.8% (199/865) with CABG and 28.6% (249/901) with PCI, with a differential survival benefit of 4.6% (95% CI: 0.58% to 8.7%, log-rank p value=0.023). In the CABG and PCI registries, mortalities were 27.8% (167/644) and 55.4% (99/192), respectively. Calibration and discrimination of the SSII-2020 was helpful in CABG and PCI patients in the randomized and registry cohorts. In the PCI registry, the SSII-2020 underestimated mortality since specific comorbidities that entail high mortality are not included in the formula (C-index: 0.72, intercept: 0.38, slope: 0.66), whilst in the CABG registry, it predicted mortality with a helpful calibration and discrimination (C-index: 0.70, intercept: 0.00, slope: 0.76). The proportions of patients with a predicted survival benefit following CABG and PCI were respectively 78.3% (1383/1766) and 21.7% (383/1766) in the randomized cohort, and 82.4% (2143/2602) and 17.7% (459/2602) in the whole SYNTAX trial population.

Conclusion

In the randomized and registry cohort of this all-comers population with 3VD and/or LMCAD, there was reasonable agreement between the individual predicted and observed mortalities after CABG or PCI, such that the predicted 10-year survival benefit might be helpful in determining the appropriateness of each modality of revascularization.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): The SYNTAX Extended Survival study was supported by the German Foundation of Heart Research (Frankfurt am Main, Germany). The SYNTAX trial, during 0-5 years follow-up, was funded by Boston Scientific Corporation (Marlborough, MA, USA). Both sponsors had no role in the study design, data collection, data analyses, and interpretation of the study data, nor were involved in the decision to publish the final manuscript. The principal investigators and authors had complete scientific freedom.

Will previous palliative surgery for congenital heart disease be detrimental to subsequent pig heart xenotransplantation?

INTRODUCTION

Pig heart xenotransplantation might act as a bridge in infants with complex congenital heart disease (CHD) until a deceased human donor heart becomes available. Infants develop antibodies to wild-type (WT, i.e., genetically-unmodified) pig cells, but rarely to cells in which expression of the 3 known carbohydrate xenoantigens has been deleted by genetic engineering (triple-knockout [TKO] pigs). Our objective was to test sera from children who had undergone palliative surgery for complex CHD (and who potentially might need a pig heart transplant) to determine whether they had serum cytotoxic antibodies against TKO pig cells.

METHODS

Sera were obtained from children with CHD undergoing Glenn or Fontan operation (n = 14) and healthy adults (n = 8, as controls). All of the children had complex CHD and had undergone some form of cardiac surgery. Seven had received human blood transfusions and 3 bovine pericardial patch grafts. IgM and IgG binding to WT and TKO pig red blood cells (RBCs) and peripheral blood mononuclear cells (PBMCs) were measured by flow cytometry, and killing of PBMCs by a complement-dependent cytotoxicity assay.

RESULTS

Almost all children and adults demonstrated relatively high IgM/IgG binding to WT RBCs, but minimal binding to TKO RBCs (p < 0.0001 vs WT), although IgG binding was greater in children than adults (p < 0.01). All sera showed IgM/IgG binding to WT PBMCs, but this was much lower to TKO PBMCs (p < 0.0001 vs WT) and was greater in children than in adults (p < 0.05). Binding to both WT and TKO PBMCs was greater than to RBCs. Mean serum cytotoxicity to WT PBMCs was 90% in both children and adults, whereas to TKO PBMCs it was only 20% and < 5%, respectively. The sera from 6/14 (43%) children were cytotoxic to TKO PBMCs, but no adult sera were cytotoxic.

CONCLUSIONS

Although no children had high levels of antibodies to TKO RBCs, 13/14 demonstrated antibodies to TKO PBMCs, in 6 of these showed mild cytotoxicity. As no adults had cytotoxic antibodies to TKO PBMCs, the higher incidence in children may possibly be associated with their exposure to previous cardiac surgery and biological products. However, the numbers were too small to determine the influence of such past exposures. Before considering pig heart xenotransplantation for children with CHD, testing for antibody binding may be warranted.

The potential of genetically engineered pig heart transplantation in infants with complex congenital heart disease

Despite advances in surgical and medical techniques, complex congenital heart disease in neonates and infants continues to be associated with significant mortality and morbidity. More than 500 infants in the USA are placed on the cardiac transplantation wait-list annually. However, there remains a critical shortage of deceased human donor organs for transplantation with a median wait-time of 4 months. Hence, infant mortality on the heart transplant wait-list in the USA is higher than for any other solid organ transplant group. Orthotopic transplantation of a pig heart as a bridge to allotransplantation might offer the best prospect of long-term survival of these patients. In recent years, there have been several advances in genetic engineering of pigs to mitigate the vigorous antibody-mediated rejection of a pig heart transplanted into a nonhuman primate. In this review, we briefly highlight (i) the history of clinical heart xenotransplantation, (ii) current advances and techniques of genetically engineering pigs, (iii) the current status of pig orthotopic cardiac graft survival in nonhuman primates, and (iv) progress toward pursuing clinical trials of cardiac xenotransplantation. Ultimately, we argue that pig heart xenotransplantation should initially be used as a bridge to cardiac allotransplantation in neonates and infants.

Cardiac and Pulmonary Histopathology in Baboons Following Genetically-Engineered Pig Orthotopic Heart Transplantation

BACKGROUND Although improving, survival after pig orthotopic heart transplantation (OHTx) in baboons has been mixed and largely poor. The causes for the high incidence of early failure remain uncertain. MATERIAL AND METHODS We have carried out pig OHTx in 4 baboons. Two died or were euthanized within hours, and 2 survived for 3 and 8 months, respectively. There was evidence of a significant 'cytokine storm' in the immediate post-OHTx period with the elevations in IL-6 correlating closely with the final outcome. RESULTS All 4 baboons demonstrated features suggestive of respiratory dysfunction, including increased airway resistance, hypoxia, and tachypnea. Histopathological observations of pulmonary infiltration by neutrophils and, notably, eosinophils within vessels and in the perivascular and peribronchiolar space, with minimal cardiac pathology, suggested a role for early lung acute inflammation. In one, features suggestive of transfusion-related acute lung injury were present. The 2 longer-term survivors died of (i) a cardiac dysrhythmia with cellular infiltration around the conducting tissue (at 3 months), and (ii) mixed cellular and antibody-mediated rejection (at 8 months). CONCLUSIONS These initial findings indicate a potential role of acute lung injury early after OHTx. If this response can be prevented, increased survival may result, providing an opportunity to evaluate the factors affecting long-term survival.

The first clinical pig heart transplant: Was IVIg or pig cytomegalovirus detrimental to the outcome?

The clinical course of the first patient to receive a gene-edited pig heart transplant was recently reported by the University of Maryland team. Although the pig heart functioned well for >40 days, serum anti-pig antibodies then increased, and the patient sadly died after 60 days. Because of his debilitated pre-transplant state, the patient never thrived despite excellent graft function for several weeks, and the cause of his demise continues to be uncertain. A few days before an increase in anti-pig antibodies was observed, the patient had received intravenous human immunoglobulin (IVIg), and whether this played a role in his cardiac deterioration has been discussed. Furthermore, mcfDNA testing indicated an increase in pig cytomegalovirus (CMV), and its possible role in the development of cardiac dysfunction has also been considered. On the basis of the limited data provided in the publication and on our previous investigations into whether IVIg contains anti-TKO pig antibodies and therefore might be deleterious to TKO pig organ xenografts, we suggest that the steady rise in anti-pig antibody titer was more consistent with the failure of the immunosuppressive regimen to prevent elicited anti-TKO pig antibody production, rather than from the passive transfusion of IVIg or the presence of pig CMV in the graft. Although the outcome of the Maryland experience was disappointing, valuable lessons were learned. Our attention was drawn to the potential risks of heart transplantation in a "deconditioned" patient, the administration of IVIg, the transmission of pig CMV, and of the difficulties in interpreting myocardial biopsy findings.

T and B lymphocyte dynamics after genetically-modified pig-to-baboon kidney xenotransplantation with an anti-CD40mAb-based immunosuppressive regimen

BACKGROUND

The aim was to monitor recovery of T/B lymphocytes in baboons after depletion by anti-thymocyte globulin (ATG) and anti-CD20mAb (Rituximab), followed by pig kidney transplantation and maintenance therapy with an anti-CD40mAb-based regimen.

METHODS

In baboons (n = 14), induction was with ATG and anti-CD20mAb, and maintenance with (i) anti-CD40mAb, (ii) rapamycin, and (iii) methylprednisolone. Follow-up was for 6 months, or until rejection or other complication developed. Baboon blood was collected at intervals to measure T/B cells and subsets by flow cytometry. In a separate study in baboons receiving the same immunosuppressive regimen (n = 10), the populations of T/B lymphocytes in PBMCs, lymph nodes, and spleen were examined.

RESULTS

After induction therapy, the total lymphocyte count and the absolute numbers of CD3⁺, CD4⁺, and CD8⁺T cells fell by >80%, and no CD22⁺B cells remained (all p < 0.001). T cell numbers began to recover early, but no CD22⁺B cells were present in the blood for 2 months. Recovery of both T and B cells remained at <30% of baseline (p < 0.001), even if rejection developed. At 6 months, effector memory CD8⁺T cells had increased more than other T cell subsets, but a greater percentage of B cells were naïve. In contrast to blood and spleen, T and B cells were not depleted in lymph nodes.

CONCLUSIONS

ATG and anti-CD20mAb effectively decreased T and B lymphocytes in the blood and, in the presence of anti-CD40mAb maintenance therapy, recovery of these cells was inhibited. The recovery of effector memory CD8⁺T cells may be detrimental to long-term graft survival.

Profound thrombocytopenia associated with administration of multiple anti-inflammatory agents in baboons

Congestion, granular platelet debris both within macrophage and extracellularly, and neutrophil infiltration in the spleen of a baboon that was euthanized with profound thrombocytopenia.

The Role of Interleukin-6 (IL-6) in the Systemic Inflammatory Response in Xenograft Recipients and in Pig Kidney Xenograft Failure

Background

In pig-to-baboon transplantation models, there is increasing evidence of systemic inflammation in xenograft recipients (SIXR) associated with pig xenograft failure. We evaluated the relationship between systemic inflammatory factors and pig kidney xenograft failure.

Methods

Baboons received kidney transplants from genetically engineered pigs (n=9), and received an anti-CD40mAb-based (n=4) or conventional (n=5) immunosuppressive regimen. The pig kidney grafts were monitored by measurements of serum creatinine, serum amyloid A (SAA), white blood cell (WBC) and platelet counts, plasma fibrinogen, and pro-inflammatory cytokines (baboon and pig IL-6, TNF-α, IL-1β).

Results

Six baboons were euthanized or died from rejection, and 3 were euthanized for infection. Changes in serum creatinine correlated with those of SAA (r=0.56, p<0.01). Serum baboon IL-6 was increased significantly on day 1 after transplantation and at euthanasia (both p<0.05) and correlated with serum creatinine and SAA (r=0.59, p<0.001, r=0.58, p<0.01; respectively). but no difference was observed between rejection and infection. Levels of serum pig IL-6, TNF-α, IL-1β were also significantly increased on day 1 and at euthanasia, and serum pig IL-6 and IL-1β correlated with serum creatinine and SAA. The level of serum baboon IL-6 correlated with the expression of IL-6 and amyloid A in the baboon liver (r=0.93, p<0.01, r=0.79, p<0.05; respectively).

Conclusion

Early upregulation of SAA and serum IL-6 may indicate the development of rejection or infection, and are associated with impaired kidney graft function. Detection and prevention of systemic inflammation may be required to prevent pig kidney xenograft failure after xenotransplantation.

Histopathology of pig kidney grafts with/without expression of the carbohydrate Neu5Gc in immunosuppressed baboons

INTRODUCTION

Pigs deficient in three glycosyltransferase enzymes (triple-knockout [TKO] pigs, that is, not expressing the three known carbohydrate xenoantigens) and expressing 'protective' human transgenes are considered a likely source of organs for transplantation into human recipients. Some human sera have no or minimal natural antibody binding to red blood cells (RBCs) and peripheral blood mononuclear cells (PBMCs) from TKO pigs. However, all Old World monkeys exhibit natural antibody binding to TKO pig cells. The xenoantigen targets of Old World monkey natural antibodies are postulated to be carbohydrate moieties exposed when the expression of the carbohydrate N-glycolylneuraminic acid (Neu5Gc) is deleted. The aim of this study was to compare the survival in baboons and histopathology of renal grafts from pigs that either (a) expressed Neu5Gc (GTKO pigs; Group 1) or (b) did not express Neu5Gc (GTKO/CMAHKO [DKO] or TKO pigs; Group 2).

METHODS

Life-supporting renal transplants were carried out using GTKO (n = 5) or DKO/TKO (n = 5) pig kidneys under an anti-CD40mAb-based immunosuppressive regimen.

RESULTS

Group 1 baboons survived longer than Group 2 baboons (median 237 vs. 35 days; mean 196 vs. 57 days; p < 0.07) and exhibited histopathological features of antibody-mediated rejection in only two kidneys. Group 2 exhibited histopathological features of antibody-mediated rejection in all five grafts, with IgM and IgG binding to renal interstitial arteries and peritubular capillaries. Rejection-free survival was significantly longer in Group 1 (p < 0.05).

CONCLUSIONS

The absence of expression of Neu5Gc on pig kidney grafts is associated with increased binding of baboon antibodies to pig endothelium and reduced graft survival.

Efficacy and safety of early aspirin withdrawal and continuation of ticagrelor monotherapy post PCI for STEMI. A post hoc analysis of the randomized global leaders trial

Background

Clinical presentation with STEMI is considered as a highly prothrombotic condition often associated with recurrent ischemic events. The role of aspirin as part of antiplatelet regimens in STEMI patients needs to be clarified especially in the context of new potent P2Y12 inhibitors

Aim

To assess the benefit and risk of 23-month ticagrelor monotherapy after one month of DAPT against the conventional 12-month DAPT with aspirin and ticagrelor followed by aspirin monotherapy among STEMI patients in the GLOBAL LEADERS trial.

Methods

We did a post hoc analysis of STEMI patients in the GLOBAL LEADERS trial (2092 patients). We compared the experimental ticagrelor monotherapy group (1062 patients) with the standard 12-month DAPT group (1030 patients) in rates of GLOBAL LEADERS predefined primary (composite of all-cause mortality or non-fatal, new Q-wave myocardial infarction (MI) and secondary end points (BARC 3 or 5 bleeding). NACE (Net Adverse Clinical Events) and POCE (Patient- Oriented Composite End points). We also compared GLOBAL LEADERS predefined end points in STEMI, UA, NSTEMI and CCS in both treatment arms.

Results

At two years, there were no significant differences in rates of GLOBAL LEADERS primary end points in patients who had or did not have STEMI. BARC bleeding in either treatment group didn't vary significantly among STEMI, NSTEMI and UA. Nevertheless, the experimental strategy had led to significant increase in BARC bleeding in CCS compared with STEMI at 1 and 2 years. There were similar rates of NACE and POCE in both the experimental and reference treatment groups at 1 and 2 years post PCI.

Conclusions and relevance

The incidence of GLOBAL LEADRER defined end points has not been impacted by STEMI presentation. Our findings suggest that an earlier cessation of DAPT at 1 month post primary PCI, with continuation of a potent P2Y12 antagonist monotherapy, could be safe and avoids additional bleeding risk in the STEMI setting. Given the post-hoc nature of the analysis, our findings should not necessitate changes in recommendations for practice by professional associations and regulatory agencies. However, all reported findings should rather be considered only as hypothesis-generating and need be replicated in dedicated large-scale randomized trials to further assess the role of Aspirin free antithrombotic strategies post PCI in STEMI.

Funding Acknowledgement

Type of funding sources: None.

Long-term prediction of mortality and comparative treatment benefit following percutaneous or surgical revascularization

Background

The SYNTAX score II 2020 (SSII-2020), which was derived and externally validated from randomized trials, was designed to predict death following percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG) in patients with three-vessel disease and/or left main disease. We aimed to investigate its value in identifying the safest modality of revascularization in a non-randomized setting.

Methods

Five-year mortality was assessed in 7362 patients with three-vessel disease and/or left main disease enrolled in a Japanese PCI/CABG registry. New-generation drug eluting stents and imaging guidance became the default PCI strategy during enrolment of the last cohort. The discriminative ability of the SSII-2020 for 5-year mortality was assessed using Harrell's C statistic (C-index). Agreement between observed and predicted rates of all-cause mortality following either PCI or CABG and treatment benefit (absolute risk difference) for this outcome were assessed by calibration plots.

Results

The SSII-2020 had helpful discrimination (C-index = 0.72) and good calibration (intercept = −0.11, slope = 0.92) for 5-year mortality. The absolute risk difference in mortality between CABG and PCI (treatment benefit) was well calibrated when the whole population was grouped into quarters according to the predicted absolute risk difference of 5-year mortality. The observed differences in survival in favor of CABG were 4.2% (0.1 to 8.2%, log-rank p=0.05) and 8.5% (3.8 to 13.2%, log-rank p&lt;0.01) in the respective third and fourth quarters. In contrast, the observed differences in survival were not significantly different in either the first (3.0% [−0.8 to 6.8%, log-rank p=0.12]) or the second quarter (1.3% [−2.4 to 5.1%, log-rank p=0.39]).

Conclusions

The SSII-2020 is well able to predict death at 5 years – and the mortality difference between PCI and CABG, and therefore has the potential to support decision making on revascularization in patients with three-vessel disease and/or left main coronary artery disease.

Funding Acknowledgement

Type of funding sources: None.

Initial experimental experience of triple-knockout pig red blood cells as potential sources for transfusion in alloimmunized patients with sickle cell disease

BACKGROUND

Blood transfusion remains important in the treatment of patients with sickle cell disease (SCD). However, alloimmunization after blood transfusion is associated with patient morbidity and mortality. Triple-knockout (TKO) pigs (i.e., pigs in which the three known xenoantigens to which humans have anti-pig antibodies have been deleted) may be an alternative source of RBCs for these patients because many humans have no preformed antibodies to TKO pig RBCs (pRBCs).

METHODS AND MATERIALS

In an in vitro study, plasma from alloimmunized (n = 12) or non-alloimmunized (n = 12) SCD patients was used to determine IgM/IgG binding to, and CDC of, TKO pRBCs. In an in vivo study, after an estimated 25% of blood volume was withdrawn from two capuchin monkeys, CFSE-labeled TKO pRBCs were transfused. Loss of TKO pRBCs was monitored by flow cytometry, and 7 weeks later, 25% of blood was withdrawn, and CFSE-labeled monkey RBCs were transfused.

RESULTS

The in vitro study demonstrated that plasma from neither alloimmunized nor non-alloimmunized SCD patients bound IgM/IgG to, or induced CDC of, TKO pRBCs. In the in vivo study, survival of TKO pRBCs in the two capuchin monkeys was of 5 and 7 days, respectively, whereas after allotransfusion, survival was >28 days.

CONCLUSIONS

In conclusion, (1) in the present limited study, no antibodies were detected that cross-reacted with TKO pRBCs, and (2) TKO pigs may possibly be an alternate source of RBCs in an emergency if no human RBCs are available.

"You cannot stay in the laboratory forever"*: Taking pig kidney xenotransplantation from the laboratory to the clinic

Progress in life-supporting kidney transplantation in the genetically-engineered pig-to-nonhuman primate model has been encouraging, with pig kidneys sometimes supporting life for > 1 year. What steps need to be taken by (i) the laboratory team, and (ii) the clinical team to prepare for the first clinical trial? The major topics include (i) what currently-available genetic modifications are optimal to reduce the possibility of graft rejection, (ii) what immunosuppressive therapeutic regimen is optimal, and (iii) what steps need to be taken to minimize the risk of transfer of an infectious microorganism with the graft. We suggest that patients who are unlikely to live long enough to receive a kidney from a deceased human donor would benefit from the opportunity of a period of dialysis-free support by a pig kidney, and the experience gained would enable xenotransplantation to progress much more rapidly than if we remain in the laboratory.

Aspects of histocompatibility testing in xenotransplantation

Xenotransplantation, using genetically-modified pigs for clinical organ transplantation, is a solution to the organ shortage. The biggest barrier to clinical implementation is the antigenicity of pig cells. Humans possess preformed antibody to pig cells that initiate antibody-mediated rejection of pig organs in primates. Advances in genetic engineering have led to the development of a pig lacking the three known glycan xenoantigens (triple-knockout [TKO] pigs). A significant number of human sera demonstrate no antibody binding to TKO pig cells. As a result of the TKO pig's low antigen expression, survival of life-supporting pig organs in immunosuppressed nonhuman primates has significantly increased, and hope has been renewed for clinical trials of xenotransplantation. It is important to understand the context in which xenotransplantation's predecessor, allotransplantation, has been successful, and the steps needed for the success of xenotransplantation. Successful allotransplantation has been based on two main immunological approaches - (i) adequate immunosuppressive therapy, and (ii) careful histocompatibility matching. In vivo studies suggest that the available immunosuppressive regimens are adequate to suppress the human anti-pig cellular response. Methods to evaluate and screen patients for the first clinical xenotransplantation trial are the next challenge. The goal of this review is to summarize the history of histocompatibility testing, and the available tools that can be utilized to determine xenograft histocompatibility.

What Therapeutic Regimen Will Be Optimal for Initial Clinical Trials of Pig Organ Transplantation?

We discuss what therapeutic regimen might be acceptable/successful in the first clinical trial of genetically engineered pig kidney or heart transplantation. As regimens based on a calcineurin inhibitor or CTLA4-Ig have proved unsuccessful, the regimen we administer to baboons is based on induction therapy with antithymocyte globulin, an anti-CD20 mAb (Rituximab), and cobra venom factor, with maintenance therapy based on blockade of the CD40/CD154 costimulation pathway (with an anti-CD40 mAb), with rapamycin, and a corticosteroid. An anti-inflammatory agent (etanercept) is administered for the first 2 wk, and adjuvant therapy includes prophylaxis against thrombotic complications, anemia, cytomegalovirus, and pneumocystis. Using this regimen, although antibody-mediated rejection certainly can occur, we have documented no definite evidence of an adaptive immune response to the pig xenograft. This regimen could also form the basis for the first clinical trial, except that cobra venom factor will be replaced by a clinically approved agent, for example, a C1-esterase inhibitor. However, none of the agents that block the CD40/CD154 pathway are yet approved for clinical use, and so this hurdle remains to be overcome. The role of anti-inflammatory agents remains unproven. The major difference between this suggested regimen and those used in allotransplantation is the replacement of a calcineurin inhibitor with a costimulation blockade agent, but this does not appear to increase the complications of the regimen.

Genetic engineering of porcine endothelial cell lines for evaluation of human-to-pig xenoreactive immune responses

Xenotransplantation (cross-species transplantation) using genetically-engineered pig organs offers a potential solution to address persistent organ shortage. Current evaluation of porcine genetic modifications is to monitor the nonhuman primate immune response and survival after pig organ xenotransplantation. This measure is an essential step before clinical xenotransplantation trials, but it is time-consuming, costly, and inefficient with many variables. We developed an efficient approach to quickly examine human-to-pig xeno-immune responses in vitro. A porcine endothelial cell was characterized and immortalized for genetic modification. Five genes including GGTA1, CMAH, β4galNT2, SLA-I α chain, and β2-microglobulin that are responsible for the production of major xenoantigens (αGal, Neu5Gc, Sda, and SLA-I) were sequentially disrupted in immortalized porcine endothelial cells using CRISPR/Cas9 technology. The elimination of αGal, Neu5Gc, Sda, and SLA-I dramatically reduced the antigenicity of the porcine cells, though the cells still retained their ability to provoke human natural killer cell activation. In summary, evaluation of human immune responses to genetically modified porcine cells in vitro provides an efficient method to identify ideal combinations of genetic modifications for improving pig-to-human compatibility, which should accelerate the application of xenotransplantation to humans.

The Genetically Engineered Heart as a Bridge to Allotransplantation in Infants Just Around the Corner?

BACKGROUND

Mortality for infants on the heart transplant wait list remains unacceptably high, and available mechanical circulatory support is suboptimal. Our goal is to demonstrate the feasibility of utilizing genetically engineered pig (GEP) heart as a bridge to allotransplantation by transplantation of a GEP heart in a baboon.

METHODS

Four baboons underwent orthotopic cardiac transplantation from GEP donors. All donor pigs had galactosyl-1,3-galactose knocked out. Two donor pigs had human complement regulatory CD55 transgene and the other 2 had human complement regulatory CD46 and thrombomodulin. Induction immunosuppression included thymoglobulin, and Anti-CD20. Maintenance immunosuppression was Rapamycin, AntiCD-40 and methylprednisolone. One donor heart was preserved with University of Wisconsin (UW) solution and the other three with del Nido solution.

RESULTS

All baboons weaned from cardiopulmonary bypass. B217 received a donor heart preserved with UW. Ventricular arrhythmias and depressed cardiac function resulted in early death. All recipients of del Nido preserved hearts easily weaned from cardiopulmonary bypass with minimal inotropic support. B15416 and B1917 survived for 90 days and 241 days respectively. Histopathology in B15416 revealed no significant myocardial rejection but cellular infiltrate around Purkinje fibers. Histopathology in B1917 was consistent with severe rejection. B37367 had uneventful transplant but developed significant respiratory distress with a cardiac arrest.

CONCLUSIONS

Survival of B15416 and B1917 demonstrates the feasibility of pursuing additional research to document the ability to bridge an infant to cardiac allotransplant with a GEP heart.

Stable expression of the human thrombomodulin transgene in pig endothelial cells is associated with a reduction in the inflammatory response

BACKGROUND

Xenotransplantation is associated with an inflammatory response. The proinflammatory cytokine, TNF-α, downregulates the expression of thrombomodulin (TBM), and induces coagulation dysfunction. Although human (h) TBM-transgenic pigs (p) have been developed to reduce coagulation dysfunction, the effect of TNF-α on the expression of hTBM and its functional activity has not been fully investigated. The aims of this study were to investigate (i) whether the expression of hTBM on pig (p) cells is down-regulated during TNF-α stimulation, and (ii) whether cells from hTBM pigs regulate the inflammatory response.

METHODS

TNF-α-producing T, B, and natural killer cells in blood from baboons with pig heart or kidney xenografts were investigated by flow cytometry. TNF-α staining in the grafts was detected by immunohistochemistry. Aortic endothelial cells (AECs) from GTKO/CD46 and GTKO/CD46/hTBM pigs were stimulated by hTNF-α, and the expression of the inflammatory/coagulation regulatory protein, TBM, was investigated.

RESULTS

After pig organ xenotransplantation, there was a trend to increases in TNF-α-producing T and natural killer cells in the blood of baboons. In vitro observations demonstrated that after hTNF-α stimulation, there was a significant reduction in the expression of endogenous pTBM on pAECs, and a significant increase in the expression of inflammatory molecules. Blocking of NF-κB signaling significantly up-regulated pTBM expression, and suppressed the inflammatory response induced by hTNF-α in pAECs. Whereas the expression of pTBM mRNA was significantly reduced by hTNF-α stimulation, hTBM expression on the GTKO/CD46/hTBM pAECs was not affected. Furthermore, after hTNF-α stimulation, there was significant suppression of expression of inflammatory molecules on GTKO/CD46/hTBM pAECs compared to GTKO/CD46 pAECs.

CONCLUSIONS

The stable expression of hTBM in pig cells may locally regulate the inflammatory response. This will help suppress the inflammatory response and prevent coagulation dysregulation after xenotransplantation.

Evidence that sensitization to triple-knockout pig cells will not be detrimental to subsequent allotransplantation

The current evidence is that sensitization to a pig xenograft does not result in the development of antibodies that cross-react with alloantigens, and therefore, sensitization to a pig xenograft would not be detrimental to the outcome of a subsequent allograft. This evidence relates almost entirely to the transplantation of cells or organs from wild-type or α1,3-galactosyltransferase gene-knockout (GTKO) pigs. However, it is not known whether recipients of triple-knockout (TKO) pig grafts who become sensitized to TKO pig antigens develop antibodies that cross-react with alloantigens and thus be detrimental to a subsequent organ allotransplant. We identified a single baboon (B1317) in which no (or minimal) serum anti-TKO pig antibodies could be measured-in our experience unique among baboons. We sensitized it by repeated subcutaneous injections of TKO pig peripheral blood mononuclear cells (PBMCs) in the absence of any immunosuppressive therapy. After TKO pig PBMC injection, there was a transient increase in anti-TKO pig IgM, followed by a sustained increase in IgG binding to TKO cells. In contrast, there was no serum IgM or IgG binding to PBMCs from any of a panel of baboon PBMCs (n = 8). We conclude that sensitization to TKO pig PBMCs in the baboon did not result in the development of antibodies that also bound to baboon cells, suggesting that there would be no detrimental effect of sensitization on a subsequent organ allotransplant.

Evidence suggesting that deletion of expression of N-glycolylneuraminic acid (Neu5Gc) in the organ-source pig is associated with increased antibody-mediated rejection of kidney transplants in baboons

Pigs deficient in three glycosyltransferase enzymes (triple-knockout [TKO] pigs) and expressing "protective" human transgenes are likely sources of organs for transplantation into human recipients. Testing of human sera against red blood cells (RBCs) and peripheral blood mononuclear cells (PBMCs) from TKO pigs has revealed minimal evidence of natural antibody binding. However, unlike humans, baboons exhibit natural antibody binding to TKO pig cells. The xenoantigen specificities of these natural antibodies are postulated to be one or more carbohydrate moieties exposed when N-glycolylneuraminic acid (Neu5Gc) is deleted. The aim of this study was to compare the survival of renal grafts in baboons from pigs that either expressed Neu5Gc (GTKO pigs; Group1, n = 5) or did not express Neu5Gc (GTKO/CMAHKO [DKO] or TKO pigs; Group2, n = 5). An anti-CD40mAb-based immunosuppressive regimen was administered in both groups. Group1 kidneys functioned for 90-260 days (median 237, mean 196 days), with histopathological features of antibody-mediated rejection in two kidneys. Group2 kidneys functioned for 0-183 days (median 35, mean 57), with all of the grafts exhibiting histologic features of antibody-mediated rejection. These findings suggest that the absence of expression of Neu5Gc on pig kidneys impacts graft survival in baboon recipients.

Immunological selection and monitoring of patients undergoing pig kidney transplantation

Pig kidney xenotransplantation has the potential to alleviate the current shortage of deceased and living human organs and provide patients with end-stage renal disease with a greater opportunity for long-term survival and a better quality of life. In recent decades, advances in the genetic engineering of pigs and in immunosuppressive therapy have permitted the resolution of many historical obstacles to the success of pig kidney transplantation in nonhuman primates. Pig kidney xenotransplantation may soon be translated to the clinic. Given the potential risks of kidney xenotransplantation, particularly of immunologic rejection of the graft, potential patients must be carefully screened for inclusion in the initial clinical trials and immunologically monitored diligently post-transplantation. We provide an overview of the immunological methods we believe should be used to (i) screen potential patients for the first clinical trials to exclude those with a higher risk of rejection, and (ii) monitor patients with a pig kidney graft to determine their immunological response to the graft.

Human Hemangioblast-Derived Mesenchymal Stem Cells Promote Islet Engraftment in a Minimal Islet Mass Transplantation Model in Mice

Islet transplantation can restore glycemic control in patients with type 1 diabetes. Using this procedure, the early stages of engraftment are often crucial to long-term islet function, and outcomes are not always successful. Numerous studies have shown that mesenchymal stem cells (MSCs) facilitate islet graft function. However, experimental data can be inconsistent due to variables associated with MSC generation (including donor characteristics and tissue source), thus, demonstrating the need for a well-characterized and uniform cell product before translation to the clinic. Unlike bone marrow- or adipose tissue-derived MSCs, human embryonic stem cell-derived-MSCs (hESC-MSCs) offer an unlimited source of stable and highly-characterized cells that are easily scalable. Here, we studied the effects of human hemangioblast-derived mesenchymal cells (HMCs), (i.e., MSCs differentiated from hESCs using a hemangioblast intermediate), on islet cell transplantation using a minimal islet mass model. The co-transplantation of the HMCs allowed a mass of islets that was insufficient to correct diabetes on its own to restore glycemic control in all recipients. Our in vitro studies help to elucidate the mechanisms including reduction of cytokine stress by which the HMCs support islet graft protection in vivo. Derivation, stability, and scalability of the HMC source may offer unique advantages for clinical applications, including fewer islets needed for successful islet transplantation.

A perspective on the potential detrimental role of inflammation in pig orthotopic heart xenotransplantation

There is a critical shortage of deceased human donor organs for transplantation. The need is perhaps most acute in neonates and infants with life-threatening congenital heart disease, in whom mechanical support devices are largely unsuccessful. If orthotopic (life-supporting) heart transplantation (OHTx) were consistently successful in the genetically engineered pig-to-nonhuman primate (NHP) model, a clinical trial of bridging with a pig heart in such patients might be justified. However, the results of pig OHTx in NHPs have been mixed and largely poor. We hypothesise that a factor is the detrimental effects of the inflammatory response that is known to develop (a) during any surgical procedure that requires cardiopulmonary bypass, and (b) immediately after an NHP recipient is exposed to a pig xenograft. We suggest that the combination of these two inflammatory responses has a direct detrimental effect on pig heart graft function, but also, and possibly of more importance, on recipient baboon pulmonary function, which further impacts survival of the pig heart graft. In addition, the inflammatory response almost certainly adversely impacts the immune response to the graft. If our hypothesis is correct, the potential steps that could be taken to reduce the inflammatory response or its effects (with varying degrees of efficacy) include (a) white blood cell filtration, (b) complement depletion or inactivation, (c) immunosuppressive therapy, (d) high-dose corticosteroid therapy, (e) cytokine/chemokine-targeted therapy, (f) ultrafiltration or CytoSorb hemoperfusion, (g) reduction in the levels of endogenous catecholamines, (h) triiodothyronine therapy and (i) genetic engineering of the organ-source pig. Prevention of the inflammatory response, or attenuation of its effects, by judicious anti-inflammatory therapy may contribute not only to early survival of the recipient of a genetically engineered pig OHTx, but also to improved long-term pig heart graft survival. This would open the possibility of initiating a clinical trial of genetically engineered pig OHTx as a bridge to allotransplantation.

Comparison of porcine corneal decellularization methods and importance of preserving corneal limbus through decellularization

Background

The aim of this study is to compare the three previously applied, conventional porcine corneal decellularization methods and to demonstrate the importance of preserving the corneal limbus through decellularization.

Methods

Fresh, wild-type (with or without) limbus porcine corneas were decellularized using three different methods, including (i) sodium dodecyl sulfate (SDS), (ii) hypertonic saline (HS), and (iii) N₂ gas (NG). Post-treatment evaluation was carried out using histological, residual nuclear material, and ultrastructural analyses. Glycerol was used to help reduce the adverse effects of decellularization. The corneas were preserved for two weeks in cornea storage medium.

Results

All three decellularization methods reduced the number of keratocytes at different rates in the stromal tissue. However, all methods, except SDS, resulted in the retention of large numbers of cells and cell fragments. The SDS method (0.1% SDS, 48h) resulted in almost 100% decellularization in corneas without limbus. Low decellularization capacity of the NG method (<50%) could make it unfavorable. Although HS method had a more balanced damage-decellularization ratio, its decellularization capacity was lower than SDS method. Preservation of the corneoscleral limbus could partially prevent structural damage and edema, but it would reduce the decellularization capacity.

Conclusion

Our results suggest that SDS is a very powerful decellularization method, but it damages the cornea irreversibly. Preserving the corneoscleral limbus reduces the efficiency of decellularization, but also reduces the damage.

Left atrial strain and outcome in heart failure with preserved ejection fraction

Funding Acknowledgements

Type of funding sources: None.

Background

Left atrial (LA) function is impaired in heart failure with preserved ejection fraction (HFpEF). However, the association between LA longitudinal strain and heart failure (HF) events in patients with HFpEF is still unknown. We evaluated whether LA strain measurements would be useful to predict hospitalizations for worsening HF in this study.

Methods

This study included 121 patients (Male 73, Female 48) with HFpEF who had echocardiogram at our institute (Age = 76 ± 14y, Left ventricular ejection fraction; LVEF = 63 ± 8%). Patients with atrial fibrillation were excluded. LA longitudinal strain was measured by speckle-tracking echocardiography, using TOMTEC imaging system. The endpoints were hospitalizations for worsening HF.

Results

During follow-up period of 319 ± 269 days, 33 patients (27%) experienced hospitalizations for worsening HF. LA strain was markedly lower in patients with HF events at 11.3 ± 5.6, whereas LA strain was higher at 20.3 ± 10.1 in patients without HF events. Kaplan-Meier analysis demonstrated a significant separation of survival curves stratified by median value of LA strain (Figure).

Conclusions

LA dysfunction in HFpEF is associated with a higher risk of HF hospitalization, and LA strain measurements would be useful to predict HF events.

Abstract Figure

Pulmonary arterial wave reflection as a novel estimate of pulmonary vascular resistance

Funding Acknowledgements

Type of funding sources: Public hospital(s). Main funding source(s): International Medical Research and Development Fund

Background

Measuring pulmonary vascular resistance (PVR) is essential for diagnosing pulmonary hypertension. PVR can be estimated from a simple ratio of tricuspid regurgitation velocity (TRV) to time-velocity integral of flow through right ventricular outflow tract (RVOT) (Abbas equation), but this relationship has been shown to be unreliable in patients with high PVR. Once PVR is elevated, there is an increased pressure wave reflected from the peripheral of pulmonary artery (PA). We tested the hypothesis that assessing PA wave reflection could be an alternative method for estimating PVR.

Methods

This study recruited 83 patients (69 ± 14 years old, 44 men), including 41 patients with left-sided heart disease, 23 patients with pulmonary arterial hypertension and 19 patients with chronic thromboembolic pulmonary hypertension. PA wave reflection was assessed by separating PA pressure waveform derived from a Doppler tracing of TRV into forward and backward pressure (Pf and Pb), using a velocity profile at RVOT. This separation was based on the concept of wave intensity. PVR was estimated using Abbas equation. Pb and PVR by Abbas equation were compared for the correlations with direct measurement of PVR by right heart catheterisation within 48 hours after echocardiography.

Results

Figure A illustrates Pb and Pf waveforms obtained from a patient with chronic thromboembolic pulmonary hypertension. Pb increased from mid systole and formed a late peak of PA pressure waveform. Pb correlated strongly with PVR by catheter (figure B), whereas PVR by Abbas equation underestimated PVR especially when PVR was high, resulting in a moderate correlation (figure C). Receiver-operator characteristic curves showed a higher accuracy of Pb for identifying PVR &gt; 3WU as well as 6WU, compared with PVR by Abbas equation (figure D and E).

Conclusions

This novel echocardiographic method for assessing PA wave reflection helps diagnose the severity of pulmonary hypertension.

Abstract Figure.

The Role of SLAs in Xenotransplantation

Advances in genetic engineering, particularly CRISPR/Cas9, have resulted in the development of a triple glycan-knockout (TKO) pig. There is minimal human antipig antibody binding to TKO pig cells. The TKO background has decreased antibody binding to a sufficiently low level that any additional xenoantigens expressed on the cells can now be more easily detected. One of these xenoantigens is the swine major histocompatibility complex, termed swine leukocyte antigens (SLA). SLA are the homolog to HLAs, a protein complex expressed on human tissue capable of stimulating the development of new antibodies in allotransplantation. These antibodies can result in graft failure through hyperacute, acute, or chronic rejection. Our knowledge of SLA, particularly in the last 5 years, has grown considerably. The presence, cause, and methods to detect anti-SLA antibodies will need to be carefully considered for the first clinical trial of xenotransplantation. The focus of this review is to summarize the role of SLA in xenotransplantation and consider whether it will prove to be a major barrier. Techniques are now available to mutate target SLA amino acids to ensure that cross-reactive anti-HLA antibodies no longer bind to SLA on the cells of the organ-source pigs. While deletion of SLA expression is possible, it would render the pig at risk for infectious complications. The ideal organ-source pig for HLA highly sensitized recipients may therefore be 1 with site-specific mutations to eliminate cross-reactive binding.