Humoral immune response to human aortic valve homografts

Physiological basis for xenotransplantation from genetically modified pigs to humans

The collective efforts of scientists over multiple decades have led to advancements in molecular and cellular biology-based technologies including genetic engineering and animal cloning that are now being harnessed to enhance the suitability of pig organs for xenotransplantation into humans. Using organs sourced from pigs with multiple gene deletions and human transgene insertions, investigators have overcome formidable immunological and physiological barriers in pig-to-nonhuman primate (NHP) xenotransplantation and achieved prolonged pig xenograft survival. These studies informed the design of Revivicor's (Revivicor Inc, Blacksburg, VA) genetically engineered pigs with 10 genetic modifications (10 GE) (including the inactivation of 4 endogenous porcine genes and insertion of 6 human transgenes), whose hearts and kidneys have now been studied in preclinical human xenotransplantation models with brain-dead recipients. Additionally, the first two clinical cases of pig-to-human heart xenotransplantation were recently performed with hearts from this 10 GE pig at the University of Maryland. Although this review focuses on xenotransplantation of hearts and kidneys, multiple organs, tissues, and cell types from genetically engineered pigs will provide much-needed therapeutic interventions in the future.

Preservation of human heart valves for replacement in children with heart valve disease: past, present and future

Valvular heart disease affects 30% of the new-borns with congenital heart disease. Valve replacement of semilunar valves by mechanical, bioprosthetic or donor allograft valves is the main treatment approach. However, none of the replacements provides a viable valve that can grow and/or adapt with the growth of the child leading to re-operation throughout life. In this study, we review the impact of donor valve preservation on moving towards a more viable valve alternative for valve replacements in children or young adults.

Immunogenicity of Homologous Heart Valves: Mechanisms and Future Considerations

Pediatric valvar heart disease continues to be a topic of interest due to the common and severe clinical manifestations. Problems with heart valve replacement, including lack of adaptive valve growth and accelerated structural valve degeneration, mandate morbid reoperations to serially replace valve implants. Homologous or homograft heart valves are a compelling option for valve replacement in the pediatric population but are susceptible to structural valve degeneration. The immunogenicity of homologous heart valves is not fully understood, and mechanisms explaining how implanted heart valves are attacked are unclear. It has been demonstrated that preservation methods determine homograft cell viability and there may be a direct correlation between increased cellular viability and a higher immune response. This consists of an early increase in human leukocyte antigen (HLA)-class I and II antibodies over days to months posthomograft implantation, followed by the sustained increase in HLA-class II antibodies for years after implantation. Cytotoxic T lymphocytes and T-helper lymphocytes specific to both HLA classes can infiltrate tissue almost immediately after implantation. Furthermore, increased HLA-class II mismatches result in an increased cell-mediated response and an accelerated rate of structural valve degeneration especially in younger patients. Further long-term clinical studies should be completed investigating the immunological mechanisms of heart valve rejection and their relation to structural valve degeneration as well as testing of immunosuppressant therapies to determine the needed immunosuppression for homologous heart valve implantation.

Early Outcome of Simplified Standardized Trileaflet Polytetrafluoroethylene Valved Conduit Placement

Background

Use of the expanded polytetrafluoroethylene (ePTFE) valved conduit in the pulmonary position during the correction of congenital heart defects has significantly increased in popularity over the last decade due to its promising conduit longevity. We describe the standardized process to create and implant a trileaflet ePTFE pulmonary conduit along with the early outcomes of such procedures at our institute.

Methods

Records of 100 consecutive patients who underwent ePTFE valved conduit placement using our technique from April 2018 through February 2022 were retrospectively analyzed. The function of the conduit was evaluated by transthoracic echocardiography.

Results

The mean age of the patients was 28 ± 13.2 years old at the time of the operation. The conduit diameters ranged from 16 to 24 mm (mean 23.0 ± 1.9 mm). Conduit placement was utilized for pulmonary valve replacement in 68 patients, conduit change in 25 patients, and as a part of total repair in 7 patients. There were 2 in-hospital conduit-unrelated deaths from multi-organ dysfunction and pulmonary hypertensive crisis. From the postoperative echocardiography, the average peak pressure gradient across the conduit was 18.6 ± 9.0 mm Hg, and the conduit regurgitation was graded as none or trace in 81 patients, mild in 17 patients, and moderate in 2 patients. At 589 days of median follow-up, there was no conduit reoperation. Follow-up imaging of 60 available patients at a median time of 511 days did not show a significant change in conduit function.

Conclusions

Our standardized ePTFE valved conduit creation and placement demonstrated satisfactory clinical and echocardiographic outcomes.

Long-term Persistence of Allosensitization After Islet Allograft Failure

BACKGROUND

Allosensitization has been reported after discontinuation of immunosuppression following graft failure in islet transplantation (ITx) recipients, though duration of its persistence is unknown.

METHODS

We evaluated 35 patients with type 1 diabetes who received ITx, including 17 who developed graft failure (ITx alone, n = 13; ITx plus bone marrow-derived hematopoietic stem cells, n = 4) and 18 with persistent graft function. Panel-reactive antibody (PRA) was measured yearly for the duration of graft function within 1 y after graft failure at enrollment and yearly thereafter.

RESULTS

In ITx alone graft failure patients, 61% (8/13) were PRA-positive at 6 y postgraft failure, and 46% (6/13) developed donor-specific anti-HLA antibodies (DSA to 2 ± 1 donors) during follow-up. The degree of sensitization was variable (cPRA ranging between 22% and 100% after graft failure). Allosensitization persisted for 7-15 y. Three subjects (3/13) were not allosensitized. In ITx plus bone marrow-derived hematopoietic stem cell recipients, cPRA-positivity (88%-98%) and DSA positivity persisted for 15 y in 75% (3/4) of subjects.

CONCLUSIONS

Allosensitization was minimal while subjects remained on immunosuppression, but after discontinuation of immunosuppressive therapy, the majority of subjects (77%) became allosensitized with persistence of PRA positivity for up to 15 y. Persistence of allosensitization in this patient population is of clinical importance as it may result in longer transplant waiting list times for identification of a suitable donor in the case of requiring a subsequent transplant.

Revisiting the guidelines and choice the ideal substitute for aortic valve endocarditis

Aortic valve replacement is the most commonly performed cardiac surgical operation worldwide for infective endocarditis (IE). Long-term durability and avoidance of infection relapse are the treatment goals. However, no detailed guidelines on prosthesis selection and surgical strategy are available. Management should be guided by a comprehensive evaluation of infection extension and its microbiological characteristics, the clinical profile of the patient and the risk of infection recurrence. We conducted a literature search of the PubMed database, EMBASE and Cochrane Library (through November 2019) for studies reporting to the use of biological substitutes in aortic valve endocarditis (AVE). Studies comparing long-term outcomes in the use of allogenic and autologous with conventional prostheses were investigated. Conventional mechanical or stented xenografts are the preferred choice for localized aortic infection. In cases of complex IE with the involvement of the root or the aorto-mitral continuity, the use of homografts are recommended, according to surgeon's and center experience. Homograft use needs to be balanced against the risk of structural degeneration. Prosthetic bioroot or prosthetic valved conduit with a mechanical or bioprosthetic valve are acceptable alternatives. The choice of aortic valves substitute and surgical strategy in IE is multifaceted. Principles guiding the selection of prosthesis and surgical approach rely on the long-term durability and the avoidance of infection relapse. A decisional algorithm considering the extension of the infection and its microbiological characteristics, the clinical profile of the patient and the risk of infection recurrence is provided. A multidisciplinary effort is required to achieve consistent outcomes.

Decellularized Cryopreserved Allografts as Off-the-Shelf Allogeneic Alternative for Heart Valve Replacement: In Vitro Assessment Before Clinical Translation

Cryopreserved allogeneic conduits are the elective biocompatible choice among currently available substitutes for surgical replacement in end-stage valvulopathy. However, degeneration occurs in 15 years in adults or faster in children, due to recipient's immunological reactions to donor's antigens. Here, human aortic valves were decellularized by TRICOL, based on Triton X-100 and sodium cholate, and submitted to standard cryopreservation (TRICOL-human aortic valves (hAVs)). Tissue samples were analyzed to study the effects of the combined procedure on original valve architecture and donor's cell removal. Residual amounts of nucleic acids, pathological microorganisms, and detergents were also investigated. TRICOL-hAVs proved to be efficaciously decellularized with removal of donor's cell components and preservation of valve scaffolding. Trivial traces of detergents, no cytotoxicity, and abrogated bioburden were documented. TRICOL-hAVs may represent off-the-shelf alternatives for both aortic and pulmonary valve replacements in pediatric and grown-up with congenital heart disease patients.

Homografts: a review

Since their introduction into clinical practice in 1965 homografts have become established in clinical routine. The storing and sterilization procedures have been improved over time. Long-term results showed that homografts had a superior durability compared to xenogenic biological prostheses. Approximately 40% were still in place 20 years after implantation in aortic position. Their low rate of thromboembolic events made a life-time anticoagulative therapy unnecessary and their hemodynamics were superior to all other heart valve prostheses. There exist two implantation techniques, subcoronary or mini-root, both technically more demanding compared with implantation of stented valve prostheses. When using the subcoronary technique, the valve is suspended into the aortic root leaving the coronary arteries untouched. The success of this technique, however, depends on the relation of the recipients aortic root and the implanted valve. The mini-root technique requires reimplantation of the coronary arteries but left the morphology of the valve and its root unchanged. Especially in patients with endocarditis, the mini-root technique offered the advantage of allowing for excision of all affected tissue with subsequent replacement by the homograft. The Ross-procedure uses the patient's own pulmonary valve as aortic valve substitute with implantation of a homograft in pulmonary position. This proved to be advantageous in children, since in these patients the degeneration of an aortic homograft was faster compared to an older population. This was explained by the recipient's immunologic response to the graft which was more pronounced in younger patients. The advantages of homografts with regards to hemodynamics and thromboembolic risk make them a good alternative to mechanical prostheses in younger, active patients. In very young patients, a Ross-procedure was shown to be superior to aortic homografts due to slower degeneration of the autograft. The decision to use a homograft must be made individually according to the patients demands.

Immune response to allograft implantation in children with congenital heart defects

Cryopreserved valved allografts are frequently used in the repair of congenital heart defects in children. Although the longevity of these grafts is generally good in most patients, there continue to be ongoing problems with allograft dysfunction and subsequent failure, particularly in infants and young children. The aim of this review is to discuss the immunogenicity of cryopreserved allograft tissue and measures that may minimize the deleterious effect of the immune system on allograft function and durability.

Long-term clinical outcomes after aortic valve replacement using cryopreserved aortic allograft

BACKGROUND

Although the frequency of biological valve use in treating aortic valve disease is increasing, the critical limiting factor, "structural deterioration," remains unresolved. Analysis of long-term outcomes after implantation of cryopreserved aortic allografts will yield further information related to the durability of the aortic allograft, possibly suggesting mechanisms underlying or strategies to prevent or treat the structural deterioration of biological valve substitutes.

METHODS

A total of 840 cryopreserved aortic allografts implanted in the last 35 years were reviewed with clinical follow-up completed in 99% of the consecutive series. By June 2010, 285 implanted allografts had been surgically explanted, 288 patients died before allograft removal, and 267 patients are under continued follow-up.

RESULTS

Cryopreserved aortic allografts were durable for more than 15 years in the middle-aged and older patient population. The estimated median time until structural deterioration was 20 years post-implantation, and 2 allografts have been functioning well for more than 30 years. Structural deterioration was independently related to the young age of the recipient, elderly age of the donor, severe obesity in the recipient, history of blood transfusion in the recipient, and full-root implantation technique. Infection of the implanted allograft necessitating reintervention rarely occurred. Reintervention for the allograft demonstrated 2% in-hospital mortality.

CONCLUSIONS

Cryopreserved aortic allografts were durable for more than 15 years. Structural deterioration of aortic allografts was related to multiple factors. The age of the recipient and the donor, obesity and blood transfusion history of the recipient, and implantation technique were identified as the most important factors contributing to allograft failure.

Persistence of anti-human leukocyte antibodies in congenital heart disease late after surgery using allografts and whole blood

BACKGROUND

Allografts are used for vascular reconstruction in many forms of congenital heart disease. Although allografts induce anti-human leukocyte antibody (HLA) formation, much about this response is unknown.

METHODS

Three groups of patients aged 8 to 18 years old underwent analysis for class I and II anti-HLA antibodies using Luminex. Groups were defined by timing of allograft exposure and diagnosis at Norwood for hypoplastic left heart syndrome (neonatal group), at Glenn for single-ventricle lesions not requiring arch reconstruction (infant group), and cardiac defects repaired during infancy without allografts (controls). Patients had significant anti-HLA (sensitization) if mean fluorescence intensity was ≥ 1500.

RESULTS

The study enrolled 29 patients (median age, 10.1 years). Significant class I anti-HLA antibodies were seen in 44% (8 of 18) of the neonatal group, 25% (1 of 4) of the infant group, and 14% (1 of 7) of controls; class II anti-HLA antibodies were seen in 44% (8 of 18) of the neonatal group, 25% (1 of 4) of the infant group, and 29% (2 of 7) of controls. All patients received fresh whole blood, but the neonatal group had greater exposure (p = 0.001). There was less sensitization with increasing time from last receipt of allograft(s) or blood transfusion (p = 0.05).

CONCLUSIONS

Exposure to allograft at the Norwood procedure is associated with long-term sensitization to anti-HLA antibodies in 56% of patients. Sensitization also occurs in those without prior exposure to allografts, may decrease over time, and appears related to whole blood. These findings have implications for those in whom heart transplant is considered late in the clinical course.

Immunologic considerations in heart transplantation for congenital heart disease

Children and adults with congenital heart disease (CHD) can require interventions that result in immunologic alterations that are different than those seen in patients with cardiomyopathies. Patients with CHD can be exposed to heart surgeries, blood products, valved and non-valved allograft tissue, and mechanical circulatory support, all of which can alter the immunologic status of these patients. This change in immunologic status is most commonly manifested as the development of anti-human leukocyte antigen (HLA) antibodies. This review will delineate a) the causes of anti-HLA anti-body production (often referred to as allosensitization); b) preventive strategies for anti-HLA antibody production before transplantation; c) treatment strategies for those patients who develop anti-HLA antibodies before transplantation; d) consequences of HLA allosensitization after transplantation; and e) treatment of HLA allosensitization and antibody-mediated rejection after transplantation.

Exploring the role of cyclosporine in reducing homograft degeneration post-Ross

The Ross procedure is safe and effective for children with aortic valve disease. Pulmonary homograft degeneration, proposed to be immune-mediated, is a major cause of reoperation. Cyclosporine increased homograft valve survival in animals, but has not been studied in humans. To investigate the efficacy of low-dose cyclosporine in preventing homograft degeneration and complications, a retrospective historical-controlled study was performed on data of all children who underwent Ross procedure and received cyclosporine. The primary endpoint was homograft function at the last follow-up; secondary endpoints were readmission, reoperation, death, and safety. Seventeen patients were matched with 16 controls. At the end of the follow-up period (cyclosporine, 6.7 years; controls, 8 years), homograft stenosis and/or regurgitation were present in half of all patients. Three (18%) patients in the cyclosporine group and 5 (29%) in the control group were readmitted. Surgical intervention due to homograft failure was needed in 1 (6%) cyclosporine patient and 3 (19%) of the controls. Although cyclosporine failed to show a significant difference in signs of homograft degeneration, it might decrease the need for reoperation following the Ross procedure. Larger prospective well-designed studies are required to confirm these findings.

Mid-Term Clinical Results Using a Tissue-Engineered Pulmonary Valve to Reconstruct the Right Ventricular Outflow Tract During the Ross Procedure

BACKGROUND

The Ross procedure is mainly limited by the durability of the valve prostheses used to reconstruct the right ventricular outflow tract. This study was performed to collect prospective safety and effectiveness data of the Ross procedure using a tissue-engineered heart valve to reconstruct the right ventricular outflow tract.

METHODS

Between May 2000 and February 2003, 23 patients received tissue-engineered heart valves. Two to four weeks before the Ross operation, a piece of forearm or saphenous vein was harvested to isolate, characterize, and expand endothelial cells. A pulmonary allograft (n = 11) or xenograft (n = 12) was decellularized, coated with fibronectin, and seeded with autologous vascular endothelial cells, using a specially developed bioreactor. Follow-up was performed by clinical evaluation, transthoracic echocardiography, magnetic resonance imaging, and multislice computed tomography.

RESULTS

The patient mean age was 44.0 +/- 13.7 years. Cell seeding density was 1.1 x 10(5) +/- 0.5 x 10(5) cells/cm2, with a viability of 90.2% +/- 8.9%. All patients survived the operation. One patient died during follow-up, and 1 patient required reoperation. All surviving patients are currently in New York Heart Association functional class I. Transthoracic echocardiographic evaluation of the tissue-engineered heart valve showed a mean flow velocity of 0.9 +/- 0.4 m/s at 5 years. Multislice computed tomography showed no calcification up to 5 years postoperatively.

CONCLUSIONS

Tissue-engineered heart valves showed excellent hemodynamic performance during mid-term follow-up. Decellularization of heart valves and seeding with autologous vascular endothelial cells may prevent tissue degeneration and improve valve durability.

Failure of prophylactic intravenous immunoglobulin to prevent sensitization to cryopreserved allograft tissue used in congenital cardiac surgery

OBJECTIVE

Cryopreserved allograft tissue used in the Norwood procedure for infants with hypoplastic left heart syndrome causes profound immunologic sensitization, which may complicate future transplantation. Intravenous immunoglobulin has been shown to reduce sensitization after it has developed, allowing successful transplantation. The purpose of this pilot trial was to determine whether intravenous immunoglobulin given before and after the procedure could prevent sensitization to cryopreserved allograft patches used in the initial repair of hypoplastic left heart syndrome.

METHODS

Intravenous immunoglobulin (2 g/kg) was given preoperatively, 3 weeks postoperatively, and 4 months postoperatively to 7 infants undergoing the Norwood procedure. Panel-reactive antibodies were measured with flow cytometry preoperatively and at 1, 4, 6, and 12 months postoperatively and compared with values from a contemporary cohort of 12 infants undergoing the Norwood procedure who did not receive intravenous immunoglobulin.

RESULTS

The groups were well matched for length and weight at time of surgery. Control infants were somewhat younger than the cohort receiving intravenous immunoglobulin (8 +/- 5 vs 17 +/- 14 days, P = .021). There were no differences in transfusion requirements. There was no difference in the degree of sensitization between control and intravenous immunoglobulin groups at 1 month (class I panel-reactive antibodies 20% +/- 30% vs 4% +/- 9%, P = .443, class II panel-reactive antibodies 17% +/- 27% vs 20% +/- 17%, P = .400), 4 months (class I panel-reactive antibodies 62% +/- 40% vs 73% +/- 41%, P = .813, class II panel-reactive antibodies 49% +/- 42% vs 54% +/- 41%, P = .706), and 12 months (class I panel-reactive antibodies 49% +/- 42% vs 58% +/- 39%, P = .686, class II panel-reactive antibodies 44% +/- 36% vs 49% +/- 42%, P = .651).

CONCLUSION

Despite studies showing intravenous immunoglobulin to reduce sensitization, we were unable to demonstrate that intravenous immunoglobulin prevented sensitization after exposure to allograft tissue in neonates undergoing congenital cardiac surgery.

Cryopreservation does not alter the allogenicity and development of vasculopathy in post-transplant rat aortas

BACKGROUND

Cryopreservation is a valuable technique for storing heart valve and vascular allografts. However, the biological ramifications of cryopreservation are still unclear; therefore, using animal experiments we assessed how 'cryopreservation' influences graft allogenicity and cell viability.

METHODS

Thoracic aortas of Lewis rats were prepared as fresh (F) or cryopreserved (CP) grafts, and implanted into the infrarenal aorta of Lewis or Brown Norway rats (BNs). The grafts and spleens were harvested at post-operative day 7 and 28 (POD7, POD28) for analyses.

RESULTS

First, the systemic immune response to transplantation was estimated by mixed lymphocyte reaction analyses using spleen cells from naïve or recipient BNs. The alloreactivity of the recipients increased to 1.5 times that of the naïve BNs at POD7 and POD28, when stimulated by mitomycin C-treated Lewis spleen cells. Second, local immune response was estimated by TNFalpha, IFNgamma, and iNOS mRNA expression in the grafts by quantitative PCR, which revealed 20- to 40-fold increases at POD28 after allotransplantation. Third, endothelial cell viability was estimated by endothelial NOS mRNA expression level: it was similar and highest in F and CP grafts before transplantation then significantly decreased after both syngeneic and allogeneic transplantation. Finally, intimal hyperplasia, expressed by I/M ratio, developed over time after allotransplantation, reaching 2.5 times the thickness of F grafts before transplantation. The results of these experiments revealed no difference between F and CP grafts before and after transplantation.

CONCLUSION

Cryopreservation did not modify the allogenicity of vascular allografts and had minimal adverse impacts on graft cell viability.

Factors influencing late allograft valve failure

Allograft valves are a valuable valve replacement substitute in the surgical management of heart valve disease. It remains the valve substitute of choice in the reconstruction of the right ventricular outflow tract in children with congenital heart disease and in the Ross procedure. However, its durability remains suboptimal, particularly in children. This article reviews the mechanisms and factors implicated in late allograft dysfunction, with a focus on the evidence for an immunological cause for allograft valve failure. Unravelling the mechanisms of allograft valve failure may allow modification of the allograft to improve its long-term durability.

Seeding of Human Endothelial Cells on Valve Containing Aortic Mini-Roots: Development of a Seeding Device and Procedure

PURPOSE

Complete covering of an artificial valvular scaffold with endothelial cells may prevent thromboembolic complications and lead to an excellent biocompatibility. For this purpose, we developed a seeding device for reproducible cell seeding on valve containing aortic roots.

DESCRIPTION

Human endothelial cells and fibroblasts were obtained from saphenous vein pieces. Cryopreserved aortic roots (n = 25) were put into an especially developed tube, set on a rotator, and incubated with the cell suspension. The device rotated in two axes (sagittal and axial), ensuring slight movements of the leaflets. The rotation alternated with resting periods, allowing cell attachment to the surface. Different resting periods were tested (groups 1, 2, and 3 were 30, 45, and 60 min, respectively; n = 5 each). Total incubation time was 24 hours followed by further culturing for 6 days. In two further groups (groups 4 and 5; n = 5 each), a modified inlay was used to allow the cell suspension to flow around the entire graft. In group 4 the grafts were again incubated with human endothelial cells; however, in group 5 pre-seeding with autologous fibroblasts was done in addition. Immunohistochemical staining with antibodies against factor VIII, CD31, laminin, collagen IV, and CD90 were done, and scanning electron microscopy was done after initial seeding and after 6 days in culture.

EVALUATION

Seeding resulted in homogenous cell layers on the luminal surface of the free walls in all groups. With resting periods of 45 minutes, these results were also obtained on the leaflets, whereas the other resting times resulted in defects of the endothelial cell layer on the cusps. After 6 days under culture conditions, the endothelial cell layers were confluent and viable, with the exception of the leaflets in group 1. With the modified inlay (groups 4 and 5), confluent cell layers were also achieved on the outer surface. In group 5 pre-seeding with autologous fibroblasts resulted in enhanced synthesis of extracellular matrix proteins, as was demonstrated with immunohistochemical staining for collagen IV and laminin.

CONCLUSIONS

With this newly developed seeding device, confluent cell layers on valve containing aortic roots were reproducibly achieved. The technique enables further experimental research and even clinical application.

Risk Factors, Dynamics, and Cutoff Values for Homograft Stenosis After the Ross Procedure

BACKGROUND

The purpose of this study was to find homograft-related factors that might be associated with the development of stenosis after the Ross procedure, as well as to identify the natural dynamics of stenosis and find echographic cutoff values after one year of follow-up that might predict such an outcome.

METHODS

We followed up 71 patients (mean age, 24.27 +/- 16.57 years) who had such a procedure prospectively by transthoracic echocardiography, between 1993 and 2002. Follow-up was 55.26 +/- 29.63 months and was 90.14% complete. Homografts were harvested from heart-beating donors or cardiac transplant recipients. Allograft stenosis was analyzed and risk factors were identified by univariate, multivariate, and survival analysis methods. Stenosis was defined as a mean gradient greater than or equal to 20 mm Hg.

RESULTS

There were two reoperations and 21 homografts were stenotic at the last follow-up, ten of which were already so at one year after the procedure. Cox regression analysis revealed a transhomograft gradient greater than 9 mm Hg at 1 year after the procedure (hazard ratio [HR] = 10.04) and homograft size (HR = 0.75) as independent predictors for stenosis. Stenosis-free survival was 85.94 +/- 4.35%, 75.51 +/- 5.55%, and 68.56 +/- 6.34 after 1, 3, and 5 years, respectively. A cutoff value of 9 mm Hg at 1 year of follow-up could predict different stenosis-free survival rates.

CONCLUSIONS

Homograft size is the most important homograft-related factor for stenosis. Most of the increase in transhomograft gradient occurs in the first 24 months. A gradient of 9 mm Hg or more after 1 year predicts the late occurrence of stenosis.

Panel-Reactive Antibodies Late After Allograft Implantation in Children

BACKGROUND

Circulating human leukocyte antigen (HLA) panel-reactive antibodies (PRA > 10%) have been independently associated with increased risk of rejection and mortality in patients who undergo cardiac transplantation. Cryopreserved allografts used to repair heart defects induce broadly reactive HLA antibodies in children that persist for an undetermined duration of time. The purpose of this study was to prospectively determine the level of HLA sensitization several years after implantation of cryopreserved allografts in children.

METHODS

We conducted late follow-up of 13 children previously screened for PRA before and after implantation of valved and nonvalved allografts who are alive and free from allograft replacement. Panel-reactive antibodies against HLA class I and II antigens were determined using flow cytometry and classified as high reactive (>50% PRA), low reactive (11% to 50%), or absent (0% to 10%). Follow-up PRA was compared with PRA obtained 3 months after initial allograft implantation.

RESULTS

Elevated HLA class I PRA persisted at late follow-up in 12 of 13 children, although it decreased significantly from high to low or from low to absent in 12 of 13 patients (p < 0.001). Elevated HLA class II PRA persisted at late follow-up in 6 of 13 children (46%) and had decreased significantly from prior levels (p = 0.011).

CONCLUSIONS

Circulating HLA antibodies induced by cryopreserved allograft tissue persist up to 8 years after implantation although they decrease with time. Therefore, children who have received cryopreserved allografts before cardiac transplantation may be at greater risk for transplant rejection.

Ovine panel reactive antibody assay of HLA responsivity to allograft bioengineered vascular scaffolds

BACKGROUND

Increasing evidence implicates immune response as a contributing factor in the failure of allograft valve transplants. Increases in panel reactive antibodies have been identified in human subjects. To correlate these responses with novel preimplantation processing methods to reduce cellularity, both a relevant panel reactive antibody assay and a chronic implantation animal model are necessary. We modified a human flow cytometric panel reactive antibody assay for ovine model use to detect antibody responses to residual antigen-loading decellularized scaffolds engineered from pulmonary artery tissue.

METHODS

A clinical panel reactive antibody assay was modified with anti-sheep antibodies. Dimethyl sulfoxide cryopreserved (n = 4) and decellularized scaffolds (n = 8) fashioned as patches from pulmonary arteries were implanted for study. Fresh (nonprocessed) tissue implants were used as positive controls (n = 2), and sham-treated animals were used as negative controls (n = 2). Baseline, 10-week, and 20-week blood samples were assayed for panel reactive antibody levels. Immunohistochemistry with anti-major histocompatibility complex antibodies were performed on preimplantation scaffolds.

RESULTS

Chronic implants of fresh tissue stimulated strong panel reactive antibody responses. Classically cryopreserved tissues provoked modest panel reactive antibody responses to major histocompatibility complex I antigen and no response to major histocompatibility complex II antigen. Decellularized tissue scaffolds provoked minimal to no panel reactive antibody responses to either major histocompatibility complex I or II antigen. Immunohistochemistry correlated with the panel reactive antibody results by identifying significant amounts of major histocompatibility complex I and II in fresh tissue, reduced antigen staining in cryopreserved control tissues, and minimal amounts in decellularized tissues.

CONCLUSIONS

These studies with an ovine modified panel reactive antibody assay confirmed minimal immune allosensitization to transplanted decellularized tissue patches. Qualifying criteria for putative tissue-engineered scaffolds should include minimal recipient panel reactive antibody response.

Early failure of a tricuspid valve replacement with a mitral valve homograft in a heart transplant recipient

A 24-year-old woman experienced severe tricuspid valve regurgitation 6 years after heart transplantation. Tricuspid valve replacement was performed using a cryopreserved mitral valve homograft. Severe tricuspid valve regurgitation recurred within 4 months, associated with an increase in the panel reactive antibody titers from zero to 72%. Tricuspid valve replacement was repeated with a porcine bioprosthesis with excellent recovery and function for >2 years. The mitral valve homograft displayed inflammatory features consistent with humoral immune-mediated destruction.

Six-year monitoring of the donor-specific immune response to cryopreserved aortic allograft valves: Implications with valve dysfunction

BACKGROUND

The immune rejection has been anticipated as one of the major causes of allograft aortic valve (AAV) degeneration. The purpose of this study was to prospectively serially measure the magnitude and evolution of the recipient anti-HLA class I antibody response up to 6 years from AAV implant and to correlate serologic data with valve performance by means of a concurrent echocardiographic survey.

METHODS

Cryopreserved AAVs were obtained from multiorgan HLA-typed donors. Nineteen patients younger than 50 years (mean age, 43.3 +/- 8 years) were prospectively studied. After successful surgery, all AAV recipient underwent at 3 and 6 months and each year postoperatively (mean follow-up, 71.9 months) concomitant serum sample collection and two-dimensional transthoracic echocardiography. The presence of anti-HLA antibodies was tested against a panel of lymphocytes obtained from 30 blood donors.

RESULTS

Progressive structural valve deterioration was seen in 6 patients (31.5%) of whom 4 (21%) were reoperated. All pretransplant recipients sera were panel-reactive antibody negative. Seventeen patients (89.4%) demonstrated significant panel-reactive antibody levels, which peaked at 6 months postoperatively, declined from 6 to 24 months, and slowly decreased afterward. In 14 of 19 cases (73.6%) donor-specific HLA antibodies were identified. A strong immunization (6-year persistence of panel-reactive antibody > 70% and peak panel-reactive antibody > 80%) was detected in 31.5% and 36.8% of recipients, respectively. Strong immunization was found to be significantly associated with progressive structural deterioration.

CONCLUSIONS

The immune reaction after cryopreserved AAV implantation is a peculiar long-lasting response occurring in the majority of recipients younger than 50 years of age. An association between a sustained and pronounced immunization and an aggressive AAV degeneration was observed.

Allograft Aortic Valve Replacement in the Adult: A Review

Aortic valve replacement using an allograft has been used continuously for over 40 years. Its advantages are excellent haemodynamic function, low thrombogenicity, resistance to infection and avoidance of the complications of anticoagulation. The main concern is its long-term durability, with the high hazard phase for failure between 10 and 20 years. We have only recently been able to judge the true long-term behaviour of the contemporary allograft with two recently published series of patients having reached follow-up beyond 20 years in significant numbers. This review of allograft aortic valve replacement in the adult covers the areas of history, benefits, techniques of sterilisation and preservation, operative methods and outcomes.

Human leukocyte antigen-DR and ABO mismatch are associated with accelerated homograft valve failure in children: implications for therapeutic interventions

OBJECTIVE

This study examines the incidence and factors associated with the failure of homograft valves and identifies those factors that are modifiable.

METHODS

From 1990 to 2001, 96 homograft valves were implanted in the right ventricular outflow tract of 83 children (mean age 5.1 +/- 5.6 years). Clinical and blinded serial echocardiographic follow-up was performed on all 90 valves in the 77 survivors.

RESULTS

Eighteen homograft valves were replaced as the result of pulmonary insufficiency (3), stenosis (9), or both (6). Freedom from reoperation was 71% at 9 years (95% confidence interval, 58%-84%). Forty-eight valves developed progressive pulmonary insufficiency of at least 2 grades, 26 valves developed transvalvular gradients of 50 mm Hg or greater, and 14 of these valves were also insufficient. The freedom from echocardiographic failure (progressive pulmonary insufficiency >or=2 grades or >or=50 mm Hg gradient) was only 27% at 5 years (95% confidence interval, 17%-37%). In a multivariate analysis (Cox regression), use of an aortic homograft (P =.001) and short antibiotic preservation time (P =.04) were associated with reoperation. Younger age (P =.01), ABO mismatch (P =.04), and diagnosis (P =.005) were associated with echocardiographic failure. In the subanalysis of patients with human leukocyte antigen typing, age (P =.002), aortic homograft (P =.04), and human leukocyte antigen-DR mismatch (P =.03) were associated with echocardiographic valve failure.

CONCLUSION

Many homografts rapidly become insufficient and require replacement. In our analysis of both reoperation and echocardiographic failure, several immunologic factors are consistently associated with homograft failure. Matching for human leukocyte antigen-DR, blood group, and avoiding short preservation times (thus minimizing antigenicity) offers the potential to extend the life of these valves.

Immunogenicity of decellularized cryopreserved allografts in pediatric cardiac surgery: comparison with standard cryopreserved allografts

BACKGROUND

Recognition of the immunogenicity of standard cryopreserved allografts has led to the development of new decellularized allografts (CryoValve SG; CryoLife, Inc, Kennesaw, Ga). This preliminary study examined the HLA antibody response to these decellularized allografts and compared it with the response to standard allograft material.

METHODS

We prospectively measured the frequency of panel-reactive HLA class I (HLA-A, HLA-B, and HLA-C) and class II (HLA-DR/DQ) alloantibodies in 14 children (age 8.5 +/- 7.9 years) receiving decellularized, cryopreserved allografts, including 6 undergoing allograft patch insertion and 8 with a valved pulmonary allograft. We compared them with 20 historical control subjects (age 1.7 +/- 2.4 years) undergoing implantation of standard cryopreserved allografts, 8 with valves and 12 with allograft patch. All patients had panel-reactive antibody levels measured before and at 1, 3, and 12 months after the operation. HLA class I and class II panel-reactive antibody levels were determined with a sensitive flow cytometry technique.

RESULTS

We found panel-reactive antibody levels in decellularized allografts to be elevated slightly from preoperative levels for both class I and class II antibodies at 1, 3, and 12 months (P >.05). The panel-reactive antibody level for both class I and class II antibodies were significantly lower for decellularized allografts as compared to standard allografts. Functionally, the allografts were similar with decellularized valved grafts showing a peak echo-determined systolic gradient of 13 +/- 15 mm Hg at 8 +/- 2.6 months postoperatively as compared to a gradient of 24 +/- 18 mm Hg measured 12 +/- 6 months postoperatively in standard allografts (P =.11).

CONCLUSIONS

Decellularized grafts elicited significantly lower levels of class I and class II HLA antibody formation at 1, 3, and 12 months after implantation than did standard cryopreserved allografts. Early hemodynamic function of decellularized grafts was similar to that of standard cryopreserved allograft valves. Further experience is necessary to determine whether the reduced immunogenicity of decellularized allografts will truly allow tissue ingrowth and improved long-term durability in patients.

Immunology and failure of valved allografts in children

Valved allografts are frequently used in the repair of congenital heart defects in children. Although the longevity of these grafts is generally very good, there continue to be ongoing problems with allograft stenosis, allograft valve insufficiency, and subsequent allograft failure, particularly in younger children. This review presents data on the immunologic and nonimmunologic risk factors implicated in valved allograft failure, in addition to ongoing investigation into the improvement of allograft function.

Pathological aspects of explanted homograft mitral valve

BACKGROUND

Homograft mitral valve replacement is an alternative therapeutic approach to prosthetic or bioprosthetic valve replacement. The present paper documents the pathological changes of explanted homograft mitral valve.

METHODS

We examined six explanted homograft mitral valves, which were taken out 6 weeks to 60 months following valve replacement procedure. Gross examination of the specimens was done, and representative sections were evaluated using haematoxylin-eosin, Masson's trichrome, Verhoeff's van Gieson and von Kossa stains.

RESULTS

On gross examination, the valves showed leaflet calcification and chordal rupture at the tip of the papillary muscles in three cases each. Microscopically, the valve leaflets appeared as aneucleated structures with loss of endocardial lining and lack of nuclear details. The collagenous skeleton was largely preserved. The papillary muscles underwent coagulative necrosis and lacked significant inflammatory infiltrate. One case had a few macrophages at the periphery of myonecrosis, while two cases revealed focal foreign body giant cell reaction. Foci of dystrophic calcification within the areas of myonecrosis were present in three cases.

CONCLUSION

Homograft mitral valve undergoes degenerative changes in the recipient, some of which can be attributed to ischaemia.

Histological and immunohistological study of cryopreserved aortic valve grafts: the possibility of a clinical application for cryopreserved aortic valve xenograft

The influence of preservation techniques on xenogeneic immune responses was examined to investigate the possibility of their clinical use. Mongrel dogs and pigs were used as allogeneic and discordant xenogeneic donors of aortic valve grafts, respectively. The allografts and xenografts were implanted in the abdominal aorta of mongrel dogs after cryopreservation or after fresh preservation. Allografts and xenografts were explanted at Days 7 and 42 for histological and immunohistochemical examination. In the fresh preserved allografts and the fresh preserved xenografts, the media of aortic wall grafts were significantly acellular at 7 days. Significant aortic medial destruction and neointimal proliferation with significant destruction of the valve leaflets was observed at 42 days. However, no differences were found among the preservation techniques in the xenogeneic grafts. To alleviate the lack of homografts, approaches such as the tissue-engineered graft may become an alternative in patients who are acceptable candidates.

The Ross procedure is the procedure of choice for congenital aortic valve disease

OBJECTIVES

The Ross procedure has emerged as an attractive option for aortic valve replacement in children and young adults. Our objective was to review our experience with the Ross procedure in young patients with congenital aortic valve disease. We also sought for evidence of growth in the autograft.

METHODS

From January 1990 to July 2000, 260 patients underwent the Ross procedure for various aortic valve diseases. There were 136 patients less than 18 years of age. Fifty-three (38%) of these patients had congenital aortic valve disease. Ages ranged from 3 months to 18 years (mean, 8 plus minus 5 years; median, 9 years). Ten patients were less than 2 years of age. Pure aortic stenosis was present in 18 patients, mixed stenosis and regurgitation in 32, and pure aortic regurgitation in 3. The aortic valve was bicuspid in 29 patients. Twenty-nine patients had previous procedures, mostly balloon dilation of the aortic valve (n = 8) or surgical aortic valvotomy (n = 12).

RESULTS

In all patients immediate results demonstrated a normally functioning neoaortic valve with not more than trivial aortic valve regurgitation. In the patients with stenosis, all levels of obstruction were relieved, and the gradient across the left ventricular outflow tract was completely abolished. Hospital mortality was 3 (5.6%) of 53 (overall Ross mortality was 34 of 260 [1.5%]). The patients were followed up for a mean of 4 years and up to 10 years. One patient died late of a noncardiac cause. Actuarial survival at 10 years was 94% plus minus 2%, and freedom from all events was 93% plus minus 5%. Only 1 patient needed autograft replacement for endocarditis. Intervention related to right ventricle-pulmonary artery conduit was required in 3 patients: balloon dilatation in 2, and reoperation in 1. At last follow-up, all patients but one were classified as being in New York Heart Association functional class I or II with normal or near-normal autograft valve function. Serial measurement of the left ventricular outflow tract and aortic root showed that as patients grew, the size of the outflow tract increased. When indexed to body surface area, this increase correlated with the patients' expected somatic growth.

CONCLUSIONS

The Ross procedure for congenital aortic valve disease in children and young adults offers excellent hemodynamics, with the added advantage of real potential for growth. It should be considered the treatment of choice in this age group.

Technical details with the use of cryopreserved arterial allografts for aortic infection: influence on early and midterm mortality

PURPOSE

In situ repair with cryopreserved vascular allografts improves the results in the surgical treatment of aortic infection. This study evaluated the technical pitfalls with the use of allografts that influence early and midterm mortality.

METHODS

Between 1990 and 1999, 49 patients, 21 (43%) with a mycotic aneurysm and 28 (57%) with a prosthetic graft infection of the thoracic and abdominal aorta including pelvic and groin vessels, underwent in situ repair with cryopreserved arterial allografts. Seventeen patients (35%) had aortobronchial, aortoesophageal, or aortoenteric fistulas.

RESULTS

Allograft-related technical problems occurred in eight patients (16%) in this series, and they included: intraoperative rupture caused by allograft friability; allograftenteric fistula from ligated allograft side branches rupturing 8, 18, and 48 months after implantation; anastomotic failure caused by inappropriate mechanical stress; anastomotic stricture after partial replacement of infected prosthetic grafts; allograft failure caused by inappropriate wound drainage; and recurrence of infection after inappropriate duration of antifungal treatment. Seven of the eight technical problems (87%) occurred in the first 10 patients (80%) in this series. There was one technical failure in the remaining 39 patients (2.6%; P =.0002) because of various technical adaptations, such as critical selection of allografts, use of allograft strips supporting large anastomoses, sealing with antibiotic-impregnated fibrin glue, and change in technique of allograft side-branch ligature. The 30-day mortality rate was 6% for the whole series; however, it was 2.6% for last 39 patients, with no recurrence of infection or allograft-related late death.

CONCLUSIONS

In situ repair with cryopreserved arterial allografts achieves excellent early and late results in the treatment of aortic infection. However, distinct allograft-related technical problems had to be overcome to improve the outcome of patients with major vascular infections.

Valve interstitial cells induce donor-specific T-cell anergy

OBJECTIVES

Valve allografts produce an immune response, which can influence their performance. The exact role of the interaction between recipient T cells and the different cellular components of the donor valve in stimulating an immune response is not known. Therefore the T-cell response to valve endothelial and interstitial cells was investigated in vitro.

METHODS

Valve endothelial and interstitial cells were characterized for cell-surface molecules before and after interferon gamma treatment by means of a panel of specific monoclonal antibodies and flow cytometry. The proliferative response of highly purified T lymphocytes was used to assess the immunogenicity of cultured valve endothelial and interstitial cells. This was further investigated by using a 2-step tolerance-induction protocol.

RESULTS

Valve endothelial and interstitial cells express similar levels of human leukocyte antigens and adhesion and costimulatory molecules, which are either induced or upregulated after interferon gamma treatment. T-cell responses to endothelial cells were detected after interferon gamma treatment, but responses to interferon gamma-treated interstitial cells were not detected. This lack of response resulted in the induction of T-cell anergy, which was reversed by the presence of the costimulatory molecule B7-1.

CONCLUSIONS

Although valve endothelial and interstitial cells express a similar range of cell-surface molecules, it is only the endothelial cells that are immunogenic. In addition, we have shown that these 2 cell types interact in a donor-specific manner to orchestrate the immune response and therefore may have clinical relevance in the allogeneic response of the heart valve recipients.

Decellularized human valve allografts

BACKGROUND

Variable performance of allograft tissues in children and some adults may be linked to an immune response and could be mitigated by reducing implant antigenicity.

METHODS

As endothelial and fibroblast cells are the likely source of valve antigenicity, human (CryoValve SG) and sheep pulmonary valves were decellularized using the SynerGraft treatment process. Treated valves were evaluated in vitro using histochemical, biomechanical, and hydrodynamic methods, and compared with standard cryopreserved valves. Four SynerGraft-treated and two cryopreserved sheep pulmonary valves were implanted as root replacements in the right ventricular outflow tract of growing sheep and monitored echocardiographically and histologically at 3 and 6 months. CryoValve SG human pulmonary valves were implanted in 36 patients.

RESULTS

SynerGraft treatment reduced tissue antigen expression but did not alter human valve biomechanics or strength. Decellularized sheep allograft valves were functional during the implantation period, and, they became progressively recellularized with recipient cells. In humans, CryoValve SG pulmonary valves did not provoke a panel reactive antibody response.

CONCLUSIONS

SynerGraft decellularization leaves the physical properties of valves unaltered and substantially diminishes antigen content. Reduction in implant cellularity enables host recellularization of the matrix, which should favorably impact long-term graft durability.

Growth of the pulmonary autograft after the Ross operation in childhood

OBJECTIVE

Excellent hemodynamic performance has been demonstrated after aortic valve replacement using the autologous pulmonary valve as described by D. Ross. However, in the pediatric population there is concern in regard to growth of the autograft and late dilatation in the systemic circulation.

METHODS

Since 1991, 30 children (mean age, 11.3+/-3.1 years) had aortic valve replacement with the pulmonary autograft as a root replacement. All children had yearly clinical and echocardiographic follow-up.

RESULTS

There were no perioperative deaths; one child died late in a car accident. At the last follow-up (mean follow-up, 4.3+/-2.6 years), all patients were in NYHA class I. There was one early reoperation, in which the autograft had to be reconstructed due to a leaflet perforation. There were no major valve related events. All children showed normal somatic growth. The annulus diameter increased significantly from 18+/-2 at surgery to 20+/-3.5 mm at the latest follow-up (P<0.004). The sinus also increased significantly in diameter from 29+/-4 at surgery to 34+/-2 mm at the last follow-up (P<0.001). This increase in autograft size, both for the annulus and the sinus, paralleled the increase in body surface area with no evidence for unproportional dilatation. Hemodynamic measurements demonstrated physiological peak gradients of 6.8+/-2.9 mmHg and no or trivial aortic insufficiency in 95% of this rapidly growing patient population.

CONCLUSION

These data demonstrate growth of the pulmonary autograft parallel to somatic growth without undue dilatation in the systemic circulation. The hemodynamics are excellent with regard to physiological gradients and no increase in aortic insufficiency.

Risk factors for late pulmonary homograft stenosis after the Ross procedure

BACKGROUND

We reviewed our experience with the Ross procedure to identify the prevalence and predictors of late pulmonary homograft stenosis.

METHODS

Between June 1992 and December 1997, 109 consecutive patients (age 34.5 +/- 8.6 years) underwent the Ross procedure, with reconstruction of the right ventricular outflow tract with a cryopreserved pulmonary homograft (22 to 30 mm diameter). There was one early and one late death. Echocardiographic follow-up was available in 105 of 108 patients (97%), with a follow-up of 39 +/- 20 months. Homograft donor and preservation measurements and patient variables were subjected to multivariable analyses to identify independent predictors of late homograft performance.

RESULTS

The major physiopathologic finding was homograft stenosis. Peak systolic gradients across the homograft were 20 mm Hg or more in 30 of 105 patients (28.5%) and 40 mm Hg or more in 4 of 105 patients (3.8%). One patient required two re-replacements of her homograft for severe stenosis. Moderate or severe homograft insufficiency was noted in 10 of 105 patients (9.5%). The independent predictors of late pulmonary homograft stenosis were younger donor age (p = 0.03), shorter duration of cryopreservation (p = 0.01), and smaller homograft size (p = 0.06). Beating heart donor status, short homograft ischemic time, and other factors that have been shown to be associated with increased graft viability were associated with graft stenosis but did not reach statistical significance. However, mean gradients across the homograft were significantly related (p = 0.002) to the number of these risk factors in each patient.

CONCLUSIONS

Stenosis of the pulmonary homograft can be a significant problem following the Ross procedure, and was predicted by younger donor age and shorter duration of cryopreservation. These factors may be related to increased cellular viability, which might actually predispose to late homograft stenosis in a subgroup of patients.

Activation of NF-kappa B in human endothelial cells induced by monoclonal and allospecific HLA antibodies

Chronic graft rejection, characterized by a gradual occlusion of grafted vessels, is the most serious complication following heart and kidney transplantation. Although often associated with chronic production of anti-HLA and anti-endothelial antibodies, the precise role of antibodies in chronic rejection remains uncertain. Here we have investigated whether HLA-specific antibodies, either monoclonal or derived from patients, cause endothelial cell activation. Thus we investigated tyrosine phosphorlyation, NF-kappaB activation and cell proliferation in human umbilical vein endothelial cells (HUVEC) or microvascular endothelial cells from adult human heart (CMEC). Ligation of monomorphic determinants of MHC class I molecules (using the mAb W6/32) on the surface of HUVEC caused an increase in tyrosine phosphorylation of proteins of mol. wt approximately 75-80 kDa. Similarly, ligation of monomorphic determinants on both CMEC and HUVEC resulted in increased NF-kappaB binding compared to controls (by 74.4 and 52.5%, P = 0.001) and this was enhanced by addition of secondary antibody. Two HLA-specific mAb resulted in a 277 and 170% increase in NF-kappaB-binding activity compared to controls. Four patient samples containing HLA antibodies were used against HLA-specific HUVEC and four samples were incubated with HUVEC bearing irrelevant antigens. Patient sera alone enhanced NF-kappaB binding by 27-186%, but only when added to HUVEC bearing relevant antigens. W6/32 and allospecific antibodies from patients significantly enhanced HUVEC proliferation, measured by uptake of [(3)H]thymidine. In conclusion, activation of NF-kappaB by human anti-HLA antibodies demonstrates their potential role in pathogenesis of chronic vascular occlusive disease following transplantation.

Class I and class II anti-HLA antibodies after implantation of cryopreserved allograft material in pediatric patients

OBJECTIVES

Very little is known regarding the immune response to cryopreserved allograft valves and patch material used in the surgical repair of congenital heart defects.

METHODS

We prospectively measured the frequency of panel reactive antibodies directed against HLA class I (HLA-A, B, and C) and class II (HLA-DR/DQ) alloantigens in 24 children receiving cryopreserved allografts. We compared them with results in 11 previously reported control patients. Sixteen of the study patients underwent placement of a valved conduit (11 pulmonic, 5 aortic) between the right ventricle and pulmonary arteries, 6 underwent patch angioplasty of stenotic vessels with cryopreserved pulmonary artery, and 2 underwent placement of a pulmonary monocusp patch. Study patients had panel reactive antibodies measured before, 1 month, 3 months, and 1 year after the operation.

RESULTS

With allograft implantation, panel reactive antibodies increased from 1.9% +/- 5% before the operation to 62% +/- 33% at 31 +/- 8 days after the operation, 92% +/- 15% at 3.3 +/- 0.6 months after the operation, and 85% +/- 18% at 1.1 +/- 0.2 years after the operation. The control group showed no change in panel reactive antibodies, with a level of 1.6% +/- 1% before the operation, 3.2% +/- 1% 28 +/- 5 days after the operation, and 1.7% +/- 1% 2.7 +/- 0.3 months after the operation. Class II antibodies (anti-HLA-DR/DQ) rose to 49% +/- 35% at 30 +/- 8 days and 70% +/- 26% at 3.3 +/- 0.6 months after the operation.

CONCLUSIONS

Cryopreserved allograft material induces a marked response that involves both class I and class II anti-HLA antibodies within 3 months after operation in children. This alloantibody response may represent a form of "rejection," may have implications for those who require subsequent cardiac transplantation, and may play a role in early allograft failure.

Immune response following fresh arterial homograft replacement for aortoiliac graft infection

INTRODUCTION

this prospective study defines the immune response to fresh arterial homograft replacement for graft infection.

MATERIALS AND METHODS

ten patients who underwent ABO-compatible homograft transplantation were studied for anti-HLA antibody production, and CD3-CD4-CD8-positive lymphocytes subset. Immunological studies were performed preoperatively, and at early (1, 3, 7 days) and late (1, 3, 6, 12, 18, 24 months) follow-up. All patients received immunosuppressive treatment with cyclosporine (1-3 mg/kg/day). Abdominal CT scans were performed postoperatively at the 1, 6, 12, 18, 24 months follow-up.

RESULTS

preoperatively, antibodies could not be detected. Postoperatively, as from 1st month post-transplant, a progressive increase in % PRA was observed in all patients, up to the 12th month of follow-up. Subsequently, at 18 and 36 months, a progressive decrease in % PRA was detected. Data showed that the recipient antibodies were directed against donor-specific antigens. During the immediate postoperative period (1, 3, 7 days) CD3- and CD4-positive T lymphocytes slightly increased, whereas CD8 simultaneously decreased. Later, CD3 and CD4 progressively decreased and CD8 increased. Clinically, all patients were cured of infection at late follow-up. CT scans showed thickening of the aortic wall (range: 2.5-4.5 mm), with no signs of aneurysmal degeneration.

CONCLUSIONS

fresh arterial homografts are immunogenic. Implanted homografts induce a strong anti-HLA antibody response, similar to chronic rejection, in spite of immunosuppressive treatment.