The influence of conventional and cross-reactive group HLA matching on cardiac transplant outcome: an analysis from the United Network of Organ Sharing Scientific Registry

Differential gene expression in non-adherent heart transplant survivors: Implications for regulatory T-cell expression

Survival despite prolonged non-adherence with immunosuppression is rare but has been reported in kidney, lung, and liver transplantation. Its occurrence in heart transplantation is quite rare. Our study was prompted by an index patient who survived despite prolonged medication non-adherence. Prospective consent and blood collection were conducted for seven additional patients who presented in a similar fashion. The blood of patients who were diagnosed with rejection, stable early post-transplant, and stable more than 5 years post-transplant were all compared with a custom gene array focusing on T-regulatory cell processes. The two genes that were differentially expressed in every comparison were TGF beta and RNASEN with very low expression in the rejector group. The prolonged non-adherent group had the maximum expression for TGF beta but average RNASEN expression as compared to the low expression for rejectors and high for post-5 years patients. The patients presented survived for varying lengths of time without immunosuppression. The gene array analysis showed intriguing differences between these rare patients and important patient cohorts. Further efforts should be directed to finding and studying more patients who survive despite lack of prescribed immunosuppression. The mechanisms underlying this phenomenon may inform future advances in transplant immunosuppression.

The impact of flow PRA on outcome in pediatric heart recipients in modern era: An analysis of the Pediatric Heart Transplant Study database

Data from patients in the Pediatric Heart Transplant Study (PHTS) registry transplanted between 2010 and 2014 were analyzed to determine the association between HLA antibody (PRA) determined by SPA using Luminex or flow cytometry with a positive retrospective cross-match and the post-transplant outcomes of acute rejection and graft survival. A total of 1459 of 1596 (91%) recipients had a PRA reported pretransplant; 26% had a PRA > 20%. Patients with a PRA > 20% were more likely to have CHD, prior cardiac surgery, ECMO support at listing, and waited longer for transplantation than patients with a PRA <20%. Patients with higher PRA% determined by SPA were predictive of a positive retrospective cross-match determined by flow cytometric method (P < .001). A PRA > 50% determined by SPA was independently associated with worse overall graft survival after first month of transplant in both unadjusted and adjusted for all other risk factors. In this large multicenter series of pediatric heart transplant recipients, an elevated PRA determined by SPA remains a significant risk factor in the modern era.

Association of the Number of HLA-DR Mismatches With Early Post-transplant Acute Cellular Rejection Among Heart Transplantation Recipients: A Cohort Study in Japanese Population

BACKGROUND

Although many risk factors are reported about graft rejection after heart transplantation (HTx), the effect of HLA mismatch (MM) still remains unknown, especially in the Japanese population. The aim of the present study was to investigate the influence of HLA MM on graft rejection among HTx recipients in Japan.

METHODS

We retrospectively investigated the association of the number of HLA MM including class I (A, B) and class II (DR) (for each locus MM: 0 to 2, total MM: 0 to 6) and the incidence of moderate to severe acute cellular rejection (ACR) confirmed by endomyocardial biopsy (International Society for Heart and Lung Transplantation grade ≥ 3A/2R) within 1 year after HTx.

RESULTS

Between 2007 and 2014, we had 49 HTx cases in our institute. After excluding those with insufficient data and positive donor-specific antigen, finally 35 patients were enrolled. Moderate to severe ACR was observed in 16 (45.7%) patients. The number of HLA-DR MM was significantly associated with the development of ACR (ACR+: 1.50 ± 0.63, ACR-: 1.11 ± 0.46, P = .029). From univariate analysis, DR MM = 2 was the only independent risk factor for ACR episodes (P = .017). The frequency of ACR within 1 year was significantly higher in those with DR MM = 2 (DR MM = 0 to 1: 0.3 ± 0.47, DR MM = 2: 1.17 ± 1.34 times, P = .007).

CONCLUSIONS

The number of HLA-DR MMs was associated with the development and recurrence of ACR episodes among HTx recipients within 1 year after transplantation in Japanese population.

Analysis of the Influence of HLA-A Matching Relative to HLA-B and -DR Matching on Heart Transplant Outcomes

Background

There are conflicting reports on the effect of donor-recipient HLA matching on outcomes in heart transplantation. The objective of this study was to investigate the effects of HLA-A matching relative to HLA-B and -DR matching on long-term survival in heart transplantation.

Methods

A total of 25 583 patients transplanted between 1988 and 2011 were identified from the International Society for Heart and Lung Transplantation registry. Transplants were divided into 2 donor-recipient matching groups: HLA-A–compatible (no HLA-A mismatches) and HLA-A–incompatible (1-2 HLA-A mismatches). Primary outcome was all-cause mortality. Secondary outcomes were graft failure-, cardiovascular-, infection-, or malignancy-related deaths.

Results

The risk of all-cause mortality 15 years after transplantation was higher for HLA-A–compatible (vs HLA-A–incompatible) grafts in patients who had HLA-B–, HLA-DR–, or HLA-B,DR–incompatible grafts (P = 0.027, P = 0.007, and P = 0.002, respectively) but not in HLA-B– and/or HLA-DR–compatible grafts. This was confirmed in multivariable Cox regression analysis where HLA-A compatibility (vs HLA-A incompatibility) was associated with higher mortality in transplants incompatible for HLA-DR or HLA-B and -DR (hazard ratio [HR], 1.59; 95% confidence interval [95% CI], 1.11-2.28; P = 0.012 and HR, 1.69; 95% CI, 1.17-2.43; P = 0.005, respectively). In multivariable analysis, the largest compromise in survival for HLA-A compatibility (vs HLA-incompatibility) was for chronic rejection in HLA-B– and -DR–incompatible grafts (HR, 1.91; 95% CI, 1.22-3.01; P = 0.005).

Conclusions

Decreased long-term survival in heart transplantation was associated with HLA-A compatibility in HLA-B,DR–incompatible grafts.

Human leukocyte antigens and alloimmunization in heart transplantation: an open debate

Considerable advances in heart transplantation outcome have been achieved through the improvement of donor-recipient selection, better organ preservation, lower rates of perioperative mortality and the use of innovative immunosuppressive protocols. Nevertheless, long-term survival is still influenced by late complications. We support the introduction of HLA matching as an additional criterion in the heart allocation. Indeed, allosensitization is an important factor affecting heart transplantation and the presence of anti-HLA antibodies causes an increased risk of antibody-mediated rejection and graft failure. On the other hand, the rate of heart-immunized patients awaiting transplantation is steadily increasing due to the limited availability of organs and an increased use of ventricular assist devices. Significant benefits may result from virtual crossmatch approach that prevents transplantation in the presence of unacceptable donor antigens. A combination of both virtual crossmatch and a tailored desensitization therapy could be a good compromise for a favorable outcome in highly sensitized patients. Here, we discuss the unresolved issue on the clinical immunology of heart transplantation.

The influence of human leukocyte antigen matching on outcomes in pediatric heart transplantation

Previous adult heart transplantation studies have demonstrated that donor-recipient human leukocyte antigen (HLA) matching results in reduced graft failure and improved patient survival. No study has examined these effects in children. This study investigated the effect of HLA matching on outcomes in pediatric heart transplantation. All pediatric heart transplantation data for patients 0-18 years of age available from the United Network for Organ Sharing Transplant Registry from 1987 to 2009 were analyzed retrospectively. Donor-recipient HLA matching at loci A, B, and DR (0-6) was compared with graft survival and recipient survival. For this study, 3,751 pediatric cardiac transplantation events with complete HLA matching data were identified and grouped as having 0 to 2 matches (3,416 events) or 3 to 6 matches (335 events). The 3- to 6-match group had less graft failure than the 0- to 2-match group (28.7% vs 34.4%; p = 0.035) and greater patient survival by 5 years (81% vs 72%; p = 0.045) and 10 years (66% vs 55%; p = 0.005) after transplantation. The HLA-DR matching alone resulted in less graft failure (p = 0.038) and improved patient survival (p = 0.017). A higher degree of HLA matching in pediatric heart transplantation is associated with decreased graft failure and improved patient survival. In this study, decreased graft failure rates and superior survival also were seen with DR matching alone.

Human leukocyte antigen matching in heart transplantation: systematic review and meta-analysis

Allocation of donors with regard to human leukocyte antigen (HLA) is controversial in heart transplantation. This paper is a systematic review and meta-analysis of the available evidence. PubMed, Embase, and the Cochrane Library were searched systematically for studies that addressed the effects of HLA matching on outcome after heart transplantation. Fifty-seven studies met the eligibility criteria. 34 studies had graft rejection as outcome, with 26 of the studies reporting a significant reduction in graft rejection with increasing degree of HLA matching. Thirteen of 18 articles that reported on graft failure found that it decreased significantly with increasing HLA match. Two multicenter studies and nine single-center studies provided sufficient data to provide summary estimates at 12 months. Pooled comparisons showed that graft survival increased with fewer HLA-DR mismatches [0-1 vs. 2 mismatches: risk ratio (RR) = 1.09 (95% confidence interval (CI): 1.01-1.19; P = 0.04)]. Having fewer HLA-DR mismatches (0-1 vs. 2) reduced the incidence of acute rejection [(RR = 0.81 (0.66-0.99; P = 0.04)]. Despite the considerable heterogeneity between studies, the short observation time, and older data, HLA matching improves graft survival in heart transplantation. Prospective HLA-DR matching is clinically feasible and should be considered as a major selection criterion.

Outcomes of cardiac transplantation in highly sensitized pediatric patients

Despite aggressive immunosuppressive therapy, pediatric orthotopic heart transplant (OHT) candidates with elevated pre-transplant panel reactive antibody (PRA) carry an increased risk of rejection and early graft failure following transplantation. This study has aimed to more specifically evaluate the outcomes of transplant candidates stratified by PRA values. Records of pediatric patients listed for OHT between April 2004 and July 2008 were reviewed (n = 101). Survival analysis was performed comparing patients with PRA < 25 to those with PRA > 25, as well as patients with PRA < 80 and PRA > 80. Patients with PRA > 25 had decreased survival compared with those with PRA < 25 after listing (P = 0.004). There was an even greater difference in survival between patients with PRA > 80 and those with PRA < 80 (P = 0.002). Similar analyses for the patients who underwent successful transplantation showed no significant difference in post-transplant survival between patients with a pre-transplant PRA > 25 and those with PRA < 25 (P = 0.23). A difference approaching significance was noted for patients with PRA > 80 compared with PRA < 80 (P = 0.066). Patients with significantly elevated pre-transplant PRAs at the time of listing have a significantly worse outcome compared to those with moderately increased PRA values or non-sensitized patients. Further study is necessary to guide physician and family treatment decisions at the time of listing.

Clinical predictors of immunotolerance in heart transplantation

BACKGROUND AND AIM

The drugs routinely administered to prevent rejection often cause lethal side effects. Tolerant patients, therefore, should be identified to minimize these problems. The aim of this analysis was to identify clinical variables that may be associated with tolerance.

METHODS

We recruited 522 heart transplants (HT), excluding combined procedures, retransplantations, pediatric recipients, and subjects who died in the first year to obtain a cohort of 375 patients. Two groups were distinguished by the presence of echocardiographic, clinical, or pathological evidence of rejection in the first year (15 echocardiograms and 10 protocol biopsies per patient); 99 tolerant patients were compared with 276 nontolerant patients. We analyzed clinical variables related to morbidity and mortality.

RESULTS

The univariate analysis showed few differences between the groups. The multivariate analysis showed that only major histocompatibility complex (MHC)-A and MHC-DR matched recipients were significantly associated with tolerance. Thus, the likelihood of tolerance was increased by 1.7- and 2.8-fold if 1 or 2 MHC-I matches were present and by 3.4- and 3.7-fold if 1 or 2 MHC-DR matches were present, respectively survival curves showed significant differences (P=.034). Most deaths in both groups were related to immunosuppressive drugs; among tolerant subjects, deaths were due to infection and neoplasms and among nontolerant patients, deaths were due to chronic rejection, neoplasms, and infection.

CONCLUSIONS

The only clinical parameter that can determined whether a HT recipient was tolerant was MHC-A and MHC-DR matching. If there is matching, a reduced immunosuppressive load should be prescribed to prevent drug toxicity.

Increased expression of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in rat cardiac allografts

This study was designed to investigate the role of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) during chronic cardiac allograft rejection. Wistar rats were used as donors, and SD rats as recipients heterotopic cardiac transplants. Recipients pretreated with inoculation of donor splenocytes (SPC) followed by cyclophosphamide (CP) were divided into 4 groups: (A) untreated group (n = 18) without immunosuppression; (B) SPC plus CP-treated group (n = 18) that were euthanized at 15-120 days posttransplantation; (C) CsA-treated group (n = 18) euthanized at 2-3 months posttransplantation; and (D) tolerance group (n = 18) treated with SPC plus CP and monitored for at least 1 year posttransplantation. Cardiac allografts were harvested at various times for immunohistochemical studies performed to evaluate the expression of ICAM-1 and VCAM-1. Pretreatment of animals with SPC and CP induced long-term cardiac allograft survival. Immunohistochemical staining demonstrated a low level of ICAM-1 and VCAM-1 expression in cardiac allograft muscle and coronary arteries among Groups B and D. In contrast, the expressions of ICAM-1 and VCAM-1 in cardiac allografts of Groups A and C were significantly higher than those in Groups B and D. Our results suggested that the expression of ICAM-1 and VCAM-1 plays an important role during the development of chronic cardiac allograft rejection.

Twenty-year survivors of heart transplantation at Stanford University

Human heart transplantation started 40 years ago. Medical records of all cardiac transplants performed at Stanford were reviewed. A total of 1446 heart transplantations have been performed between January 1968 and December 2007 with an increase of 1-year survival from 43.1% to 90.2%. Sixty patients who were transplanted between 1968 and 1987 were identified who survived at least 20 years. Twenty-year survivors had a mean age at transplant of 29.4 +/- 13.6 years. Rejection-free and infection-free 1-year survivals were 14.3% and 18.8%, respectively. At their last follow-up, 86.7% of long-term survivors were treated for hypertension, 28.3% showed chronic renal dysfunction, 6.7% required hemodialysis, 10% were status postkidney transplantation, 13.3% were treated for diabetes mellitus, 36.7% had a history of malignancy and 43.3% had evidence of allograft vasculopathy. The half-life conditional on survival to 20 years was 28.1 years. Eleven patients received a second heart transplant after 11.9 +/- 8.0 years. The most common causes of death were allograft vasculopathy (56.3%) and nonlymphoid malignancy (25.0%). Twenty-year survival was achieved in 12.5% of patients transplanted before 1988. Although still associated with considerable morbidity, long-term survival is expected to occur at much higher rates in the future due to major advances in the field over the past decade.

Association of device surface and biomaterials with immunologic sensitization after mechanical support

OBJECTIVE

Biomaterials and textured surfaces in early pulsatile left ventricular assist devices (HeartMate I; Thoratec Corporation, Pleasanton, Calif) may increase immunologic risk through allosensitization. We hypothesized that axial-flow devices without biologic membranes or textured surfaces (HeartMate II; Thoratec; and DeBakey; MicroMed Cardiovascular, Inc, Houston, Tex) would cause less allosensitization than devices with such membranes and surfaces.

METHODS

HeartMate II and DeBakey (n = 24) and HeartMate I (n = 36) devices were implanted from 1999 to 2006 in patients with severe heart failure cohort-matched for age, etiology, and support duration. Serum samples reacting with more than 10% of the HLA reference panel were considered positive for anti-HLA antibodies. Endomyocardial biopsy samples were collected after transplant.

RESULTS

There were no significant cohort differences in age, etiology, sex, blood transfusion, or support duration. Anti-HLA antibodies were not detected at implantation of either HeartMate II and DeBakey or HeartMate I devices; however, significant increases in anti-HLA antibodies were present within 1 and 3 months of support with HeartMate I but not HeartMate II and DeBakey devices. Overall, fewer patients with HeartMate II and DeBakey devices demonstrated positive anti-HLA antibodies during support (8% vs 28%, P = .02), and fewer episodes of acute rejection per patient were seen within the first 9 posttransplant months(0.31 vs 0.69, P = .052). Long-term posttransplant survival was not different between groups.

CONCLUSION

Hemodynamic support with HeartMate II and DeBakey devices produced less allosensitization than did HeartMate I devices. Device selection may improve clinical outcomes for high-risk patients.

Cardiac transplant outcomes in pediatric patients with pre-formed anti-human leukocyte antigen antibodies and/or positive retrospective crossmatch

BACKGROUND

Children undergoing heart transplantation who have preformed anti-human leucocyte antigen (HLA) panel reactive antibodies (PRA) or positive retrospective crossmatch (XM) may be at increased risk for rejection and graft failure. We assessed outcomes of transplant recipients with either positive PRA before transplant or positive retrospective XM.

METHODS

A review of 148 heart transplant patients between 1990 and 2006 was undertaken, identifying transplants in patients with pre-transplant PRA > 1% and/or a positive XM. Demographic information and detailed post-transplant outcomes including episodes of rejection, infection, and graft failure were recorded.

RESULTS

There were 11 PRA positive (PRA+) transplants, 135 PRA negative (PRA-) transplants, and no PRA data on 2. There were 14 XM+ transplants, 115 XM- transplants, and no XM data on 19. Kaplan-Meier graft survival was better in XM- than XM+ patients (p < 0.015), but not different between PRA+ and PRA- Groups. Timing of first rejection and number of rejection episodes were not different between XM+ and XM- Groups or between PRA+ and PRA- Groups. Infections were not different between PRA or XM Groups. Four patients were PRA+/XM- (all PRA, 1%-10%), 7 were PRA-/XM+, and 7 were PRA+/XM+ (6 of 7 PRA >10%).

CONCLUSIONS

Pediatric heart transplant patients whose retrospective XM is positive are at significantly increased risk for graft failure. Elevated pre-transplant PRA may not predict increased risk of graft failure, although markedly positive PRA (>10%) predicts a positive retrospective XM. Improved treatment for pediatric transplant patients with a positive retrospective XM is needed.

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.

Humoral Rejection in Pediatric Orthotopic Heart Transplantation

BACKGROUND

Pediatric heart transplant grafts may fail without evidence of cellular rejection or transplant coronary artery disease. The role of antibody-mediated humoral rejection (HR) in graft failure has not yet been described in the pediatric population.

METHODS

We reviewed the medical records of 103 pediatric heart transplantations performed at our institution from July 1997 to June 2004. Biopsy specimens were evaluated for HR histologically and by immunoperoxidase and immunofluorescence staining. Risk factors for HR were determined by statistical analysis. Graft survival curves were constructed and compared for patients testing negative or positive for HR.

RESULTS

A total of 358 endomyocardial biopsies (EMBs) from 103 pediatric heart transplant patients (age 3 weeks to 20 years; 52% males) were analyzed for HR. Thirty-six grafts (32%) showed evidence of HR. Grafts with a history of HR during the first year after transplant had a 47% failure rate over 3 years, compared with 29% of those hearts with no evidence of HR (p = 0.06). Although patients with congenital heart disease (CHD) appeared to be at greatest risk for developing HR (p = 0.01), patients with positive donor-specific crossmatch data showed a trend toward more significant risks for HR (p = 0.055). Hemodynamic data (including pulmonary capillary wedge pressure [PCWP] and cardiac index [CI]), left ventricular ejection fraction (LVEF), gender matching, recipient age, race of recipient vs donor and pre-transplant panel-reactive antibody (PRA) were not predictive of HR.

CONCLUSIONS

Patients with a pathologic diagnosis of HR have increased graft failure rates and overall mortality. Patients with congenital heart disease and positive cross-match results may be at increased risk for HR.

HLA mismatching within or outside of cross-reactive groups (CREGs) is associated with similar outcomes after unrelated hematopoietic stem cell transplantation

The National Marrow Donor Program maintains a registry of volunteer donors for patients in need of a hematopoietic stem cell transplantation. Strategies for selecting a partially HLA-mismatched donor vary when a full match cannot be identified. Some transplantation centers limit the selection of mismatched donors to those sharing mismatched antigens within HLA-A and HLA-B cross-reactive groups (CREGs). To assess whether an HLA mismatch within a CREG group ("minor") may result in better outcome than a mismatch outside CREG groups ("major"), we analyzed validated outcomes data from 2709 bone marrow and peripheral blood stem cell transplantations. Three-hundred and ninety-six pairs (15%) were HLA-DRB1 allele matched but had an antigen-level mismatch at HLA-A or HLA-B. Univariate and multivariate analyses of engraftment, graft-versus-host disease, and survival showed that outcome is not significantly different between minor and major mismatches (P = .47, from the log-rank test for Kaplan-Meier survival). However, HLA-A, HLA-B, and HLA-DRB1 allele-matched cases had significantly better outcome than mismatched cases (P < .001). For patients without an HLA match, the selection of a CREG-compatible donor as tested does not improve outcome.

Comparison of aortic valve allograft decellularization techniques in the rat

Rodent models have been essential to understanding the immune-mediated failure of aortic valve allografts (AVAs). Decellularization has been proposed to reduce the immunogenicity of AVAs. The objective of this study was to determine the most effective method to decellularize AVAs for use in a rat model. Three different decellularization techniques were compared in Lewis aortic valves. Detergent decellularization involved a series of hypotonic and hypertonic Tris buffers at 4 degrees C for 48 h/buffer containing 0.5% Triton X-100 followed by a 72 h washout in phosphate-buffered saline. Osmotic decellularization was performed in similar manner to the detergent-based technique except without the addition of Triton X-100. Enzymatic decellularization consisted of trypsin/EDTA at 37 degrees C for 48 h. Assessment was performed with light microscopy (H&E, Movat's pentachrome), immunohistochemistry for residual cellular elements, and hydroxyproline assays. Detergent-based methodology effected near-complete decellularization of both the leaflets and aortic wall in addition to preservation of the extracellular matrix (ECM). Osmotic lysis was associated with preservation of ECM and moderate decellularization. Enzymatic decellularization resulted in complete decellularization but extensive degeneration and fragmentation of the ECM. When implanted into the infrarenal aorta of allogeneic rats for 1 week, valves decellularized with detergent-based and osmotic methodology failed to stimulate an allogeneic immune response as evidenced by an absence of T cell infiltrates. Osmotic lysis protocols with low dose detergent appear to be most effective at both removing antigenic cellular elements and preserving ECM.

Low-Dose Prophylactic Intravenous Immunoglobulin Does Not Prevent HLA Sensitization in Left Ventricular Assist Device Recipients

BACKGROUND

The use of left ventricular assist devices is associated with human leukocyte antigen (HLA) allosensitization. We investigated whether prophylactic treatment with low-dose intravenous immunoglobulin (IVIG), analogous to the use of IgG anti-D (anti-Rh) in preventing Rh immunization, can abrogate HLA allosensitization after left ventricular assist device implantation.

METHODS

We retrospectively reviewed the data from 84 consecutive heart failure patients who underwent implantation of a left ventricular assist device as a bridge to transplantation. After implantation, panel reactive antibody (PRA) was measured biweekly to assess sensitization (defined by PRA > 10%). Patients who were sensitized before left ventricular assist device implantation were excluded from further analysis (n = 12). Patients who either did not require perioperatively transfusions of cellular blood products or received other immunomodifying regimens were also excluded from further analysis (n = 21). The rest of the patients were divided into two groups based on whether they received IVIG, 10 g daily for 3 days (IVIG group, n = 26; non-IVIG group, n = 25). The decision as to whether patients received IVIG was not randomized but was based on surgeon preference.

RESULTS

The sensitization rates (expressed as ratio of sensitized patients to total patients at risk) in the two groups were similar at consecutive time points (2, 4, 6, 8, 12, 20 weeks) after left ventricular assist device implantation. Also, mean PRA at the same time points did not differ between the two groups. Overall, 34.6% (9 of 26) of the IVIG group became sensitized during mechanical support, compared with 32% (8 of 25) of the non-IVIG group (p = 1.0). A PRA of 90% or greater (high-degree sensitization) occurred in 15.3% (4 of 26) of the IVIG group and 12.0% (3 of 25) of the non-IVIG group (p = 0.5).

CONCLUSIONS

The use of low-dose prophylactic IVIG after left ventricular assist device implantation affects neither the incidence nor the severity of HLA allosensitization.

The promise of protein-based and gene-based clinical markers in heart transplantation: from bench to bedside

Advances in immunosuppression, guided by invasive endomyocardial biopsy for the assessment of graft rejection, have ushered heart transplantation into the clinical arena by the demonstration of acceptable 1-year outcomes. Further decreases in the risk of malignancy and cardiac allograft vasculopathy that improve long-term outcomes, are, however, still desired. Attention has become directed towards the use of markers that can be detected noninvasively to provide insight into underlying molecular and cellular events associated with the immune response and graft function. Various candidate, protein-based markers have been identified: those of alloimmune activation; those of microvascular injury, such as cardiac-specific troponins; those of inflammation, including C-reactive protein; and surrogate markers of cardiac function, including natriuretic peptides such as brain natriuretic peptide. In the realm of genomics, it is becoming increasingly clear that a single molecular marker is unlikely to prove to be useful, but rather that multiple genes from a number of pathways are needed to capture biological complexity and overcome variability in the general population. Thus, the field of protein-based and gene-based biomarkers is advancing rapidly to define its place in clinical therapeutics and to guide immunosuppression according to molecular mechanisms of disease. We discuss here the main findings for the more-successful protein markers identified so far, and the genomic molecular approaches being used to improve heart transplant outcomes.

The virtual crossmatch--a screening tool for sensitized pediatric heart transplant recipients

Heart transplantation in the setting of human leukocyte antigen (HLA) sensitization is challenging, as a time-consuming prospective crossmatch (XM) may be required, severely limiting the number of potential donors. We evaluated a 'virtual XM', defining a positive virtual XM as the presence of recipient pre-formed anti-HLA antibodies to the prospective donor HLA type, and compared the virtual XM to a standard direct XM. Bead-based flow cytometric analysis was used to identify anti-HLA antibody (Ab) present in a child listed for heart transplantation. Using recipient serum, direct-flow cytometric T- and B-cell XM were run for potential donors against whose HLA type the recipient had specific antibodies (group 1, n = 7) and for potential donors with predicted compatible HLA types by virtual XM (group 2, n = 7). Results were expressed as median channel difference (MCD) between the control and recipient serum. A positive T-cell XM was defined as MCD > 50, whereas MCD > 100 constituted a positive B-cell result. The rate of T-cell reactivity was significantly less in group 2 than in group 1 (29% vs. 100%, p = 0.02); similarly, B-cell reactivity was also less for group 2 (14% vs. 100%, p = 0.005). The virtual XM was 100% sensitive in detecting positive flow cytometric XM results for T and B cells. Although only 72% specific in predicting a negative T-cell XM, and 86% specific for negative B-cell XM, the false negatives were weakly positive and would probably have been clinically acceptable. Currently, potentially suitable donor organs are often declined for lack of a prospective XM; these organs may ultimately be allocated to more distant recipients or perhaps not used at all. While further studies are needed, virtual XM has the potential to improve availability of organs for sensitized patients and improve the overall allocation process.

Disparities in outcome for black patients after pediatric heart transplantation

OBJECTIVE

To examine the relationship of black race to graft survival after heart transplantation in children.

STUDY DESIGN

United Network for Organ Sharing records of heart transplantation for subjects <18 years of age from 1987 to 2004 were reviewed. Analysis was performed using proportional hazards regression controlling for other potential risk factors.

RESULTS

Of the 4227 pediatric heart transplant recipients, 717 (17%) were black. The 1-year graft survival rate did not differ among groups; however, the 5-year graft survival rate was significantly lower for black recipients, 51% versus 69%, P < .001. The median graft survival for black recipients was 5.3 years as compared with 11.0 years for other recipients. Black recipients had a greater number of human leukocyte antigen mismatches, lower median household income, and a greater percentage with Medicaid as primary insurance, P < .001, P < .001, and P < .001. After adjusting for economic disparities, black race remained significantly associated with graft failure, odds ratio = 1.67 (95% CI 1.47 to 1.87), P < .001.

CONCLUSIONS

Median graft survival after pediatric heart transplantation for black recipients is less than half that of other racial groups. These differences do not appear to be related primarily to economic disparities.

The effect of HLA mismatches, shared cross-reactive antigen groups, and shared HLA-DR antigens on the outcome after pediatric liver transplantation

The aim of this study was to analyze the effect of human leukocyte antigen (HLA) class I and HLA-DR mismatching, sharing cross-reactive antigen groups (CREGs), and sharing HLA-DR antigens on the outcome after pediatric liver transplantation. Outcome parameters were graft survival, acute rejection, and portal fibrosis. A distinction was made between full-size (FSLTx) and technical-variant liver transplantation (TVLTx). A total of 136 primary transplants were analyzed. The effect of HLA on the outcome parameters was analyzed by adjusted multivariate logistic and Cox regression analysis. HLA mismatches, shared CREGs, and shared HLA-DR antigens affected neither overall graft survival nor survival after FSLTx. Survival after TVLTx was superior in case of 2 mismatches at the HLA-DR locus compared to 0 or 1 mismatch (P = 0.01) and in case of no shared HLA-DR antigen compared to 1 shared HLA-DR antigen (P = 0.004). The incidence of acute rejection was not influenced by HLA. The incidence of portal fibrosis could be analyzed in 62 1-yr biopsies and was higher after TVLTx than FSLTx (P = 0.04). The incidence of portal fibrosis after TVLTx with 0 or 1 mismatch at the HLA-DR locus was 100% compared to 43% with 2 mismatches (P = 0.004). After multivariate analysis, matching for HLA-DR and matching for TVLTx were independent risk factors for portal fibrosis. In conclusion, an overall beneficial effect of HLA matching, sharing CREGs, or sharing HLA-DR antigens was not observed. A negative effect was present for HLA-DR matching and sharing HLA-DR antigens on survival after TVLTx. HLA-DR matching might be associated with portal fibrosis in these grafts.

Decellularization reduces the immune response to aortic valve allografts in the rat

OBJECTIVES

Cryopreserved valve allografts used in congenital cardiac surgery are associated with a significant cellular and humoral immune response. This might be reduced by removal of antigenic cellular elements (decellularization). The aim of this study was to determine the immunologic effect of decellularization in a rat allograft valve model.

METHODS

Brown Norway and Lewis rat aortic valves were decellularized with a series of hypotonic and hypertonic buffers, protease inhibitors, gentle detergents (Triton X-100), and phosphate-buffered saline. Valves were implanted into Lewis rats in syngeneic and allogeneic combinations. Cellular (CD3 and CD8) infiltrates were assessed with morphometric analysis, and the humoral response was assessed with flow cytometry.

RESULTS

Morphometric analysis identified a significant reduction in CD3 + cell infiltrates (cells per square millimeter of leaflet tissue) in decellularized allografts compared with that seen in nondecellularized allografts at 1 (79 +/- 29 vs 3310 +/- 223, P < .001), 2 (26 +/- 11 vs 109 +/- 20, P = .004), and 4 weeks (283 +/- 122 vs 984 +/- 145, P < .001). Anti-CD8 staining confirmed the majority of infiltrates were cytotoxic T cells. Flow cytometric mean channel fluorescence intensity identified a negative shift (abrogated antibody formation) for decellularized allografts compared with nondecellularized allografts at 2 (19 +/- 1 vs 27 +/- 3, P = .033), 4 (35 +/- 2 vs 133 +/- 29, P = .001), and 16 weeks (28 +/- 2 vs 166 +/- 54, P = .017).

CONCLUSIONS

Decellularization significantly reduces the cellular and humoral immune response to allograft tissue. This could prolong the durability of valve allografts and might prevent immunologic sensitization of allograft recipients.

Utility of Post-Transplant Anti-HLA Antibody Measurements in Pediatric Cardiac Transplant Recipients

BACKGROUND

Studies have associated anti-HLA antibodies detected by panel-reactive antibody (PRA) with increased risk for rejection and transplant coronary artery disease (TCAD) in adults, but the role of PRAs in monitoring immunologic status after pediatric cardiac transplantation has not been described.

METHODS

We reviewed post-transplant PRAs in 96 pediatric heart recipients. PRAs were performed concurrently with endomyocardial biopsy and if rejection was suspected. The presence of anti-HLA IgG antibodies was defined as >10% reactivity. Pre-transplant variables, including age, race, gender, pre-transplant PRAs and presence of a mechanical assist device, were correlated with post-transplant PRAs. Outcome variables included rejection history, TCAD incidence and survival.

RESULTS

The mean age of patients was 9.0 +/- 6.8 years. A mean of 8.1 +/- 5.3 PRAs were measured over a follow-up period of 4.8 +/- 2.7 years. There was a mean of 0.55 +/- 0.71 rejection events per patient-year, and TCAD was detected in 19 (22%) patients. Nineteen patients (20%) had anti-HLA Class I antibodies and 37 (39%) had Class II antibodies detected after transplant. There was no association between Class I antibodies and survival, TCAD or rejection. Class II antibodies were associated with worse survival and a decreased time-free of TCAD. Class II antibodies were also associated with rejection at the time of measurement (sensitivity 17%, specificity 94%) and for the ensuing 3 months (sensitivity 12%, specificity 94%).

CONCLUSIONS

Class II anti-HLA antibodies correlate with worse patient outcomes and rejection episodes after pediatric cardiac transplant. A low sensitivity precludes use as a sole diagnostic tool, but post-transplant PRAs may be an important adjunct in a multi-faceted algorithm to assess immunologic status.

Management of Patients With Preformed Reactive Antibodies Who Are Awaiting Cardiac Transplantation

Patients with elevated levels of preformed reactive antibodies to HLA antigens have higher rates of organ rejection than do patients without such antibodies. Consequently, before proceeding with transplantation, many medical centers do prospective cross-matching, that is, mix lymphocytes from the organ donor with sera from the prospective organ recipient, to determine whether a higher rejection rate or an immediate episode of rejection will occur. The problem has been compounded by the increased frequency of preformed reactive antibodies in patients with ventricular assist devices who are awaiting cardiac transplantation. Performing a prospective cross-match can be time-consuming and often is impossible because of the unstable condition of the organ donor or travel logistics, leading to increased costs for transplantation and longer waiting times for recipients. A variety of treatments are used in cardiac transplantation programs in attempts to reduce the concentration of preformed reactive antibodies. Each of these treatments has accompanying complications and considerations for the transplant team. Each treatment must also be assessed for therapeutic response. Options for managing patients with preformed antibodies and a case report are presented.

Surrogate markers for late cardiac allograft survival

While no definite well-validated surrogate marker for late cardiac allograft outcome is available, the early detection of cardiac allograft vasculopathy represents the 'key' candidate as an effective surrogate. Intravascular ultrasound detected intimal thickening has been noted to possess prognostic capability despite the presence of a normal coronary angiogram. Several prospective investigations have pointed to accurate thresholds of intimal thickening that are prognostically relevant and predict not only future angiographic disease but also hard allograft related endpoints including ischemic cardiac events, allograft failure, and death. Because of the resolution of intravascular ultrasound, this technique accords reproducibility and the ability to standardize the degree of intimal thickening over time. Other candidates that may serve as surrogates once appropriately evaluated include measures of allograft pump function, intragraft histology, and peripheral markers including but not limited to structural proteins (cardiac specific troponins), inflammatory markers (CRP), fibrogenic markers (TGF-beta, fibroblast growth factor), and immune markers (anti-HLA Ab and indirect alloantibodies).

Orthotopic heart transplantation: highlights and limitations

A little more than three decades after the successful introduction of cardiac transplantation, this revolutionary concept of advanced heart failure treatment has gained tremendous momentum and is considered the gold standard therapy in selected patients. More specific modalities of immunosuppression continue to decrease the impact of acute and chronic rejection and immunosuppression-related side effects. The success of cardiac transplantation has led to a widespread initiation of transplant programs and a run on cardiac transplantation waiting lists. The increasing gap between waiting lists and donor organ supply has stimulated research to identify those patients who benefit most from cardiac transplantation, as well as research to develop alternative therapies for advanced heart failure. Furthermore, it serves as a stimulus to address paradigmatic issues that are fundamental to modern medicine and society.

Longer-term risks associated with 10-year survival after heart transplantation in the cyclosporine era

BACKGROUND

Long-term survival after heart transplantation is common in the cyclosporine era. However, there are few data documenting pre-transplant/peri-operative factors predictive of truly long-term survival (>10 years). The purpose of this study is to identify factors associated with 10-year survival after heart transplantation.

METHODS

Our study population included 197 adults who survived >6 months and died <10 years after heart transplant (medium-term group) and 140 adults who survived >10 years after heart transplant (long-term group) between December 1980 and May 2001. A comparison was done between the two groups and we used multivariate analysis to identify which factors predicted 10-year survival.

RESULTS

The long-term group had younger recipient and donor age, lower recipient body mass index at transplant, shorter waiting time and lower percentages of ischemic etiology/male recipient/non-white recipient. Kaplan-Meier plots of freedom from graft coronary artery disease and malignancy showed later onset patterns in the long-term group compared with the medium-term group. Multivariate analysis showed that white recipient, younger recipient and lower recipient body mass index at heart transplant were factors significantly associated with 10-year survival.

CONCLUSIONS

Several pre-transplant/peri-operative factors were associated with survival beyond 10 years after heart transplantation. Stratified/tailored strategies based on these factors may be helpful to attain longer-term survival of recipients with higher risks.

HLAmatchmaker: a molecularly based algorithm for histocompatibility determination. IV. An alternative strategy to increase the number of compatible donors for highly sensitized patients

BACKGROUND

HLAMatchmaker is a computer algorithm that determines human leukocyte antigen (HLA) compatibility at the level of polymorphic amino acid triplets in antibody-accessible sequence positions. Recent studies have shown that HLA-DR-matched kidney transplant recipients with zero to two triplet mismatches had almost identical graft survival rates as those with zero HLA-A,B,DR antigen mismatches. This report describes how HLAMatchmaker can be used to identify more compatible donors for highly sensitized patients.

METHODS

The HLAMatchmaker program was used to calculate the probability of finding a donor (PFD) with zero, one, or two triplet mismatches for 54 highly sensitized patients waiting for a kidney transplant and having panel reactive antibody (PRA) values greater than 85% and 50 randomly selected nonsensitized patients with PRA values less than 3%.

RESULTS

There was a wide variability for PFD values for the two patient cohorts. If only donors with zero HLA-A,B mismatches were deemed acceptable for recipients, the median PFD of a zero-antigen mismatch was 0.046% for nonsensitized patients and 0.009% for highly sensitized patients (P=0.007). Half of the highly sensitized patients had a PFD below 0.01%, or fewer than 1 in 10,000 donors would have zero antigen mismatches. Application of HLAMatchmaker identified additional HLA antigens with zero-triplet mismatches for 27 patients, resulting in a 1.8-fold increase in PFD. Considering additional antigens with one-triplet or two-triplet mismatches increased the PFD by an additional 3.8-fold and 13.7-fold, respectively. Acceptable antigen mismatches for 37 of the 54 highly sensitized patients were identified by consistently negative reactions in serum screens, and their addition resulted in a 12.7-fold increase of the PFD to a median of 0.141%. Applying these acceptable antigens to the HLAMatchmaker algorithm identified additional antigens with zero or acceptable triplet mismatches and their inclusion increased the PFD by 3.3-fold to 0.347%.

CONCLUSIONS

HLAMatchmaker offers a valuable strategy for identifying more suitably HLA-matched donors and has the potential for alleviating the problem of accumulation of highly sensitized patients on the transplant waiting list.

HLAmatchmaker: a molecularly based algorithm for histocompatibility determination. III. Effect of matching at the HLA-A,B amino acid triplet level on kidney transplant survival

BACKGROUND

HLAMatchmaker is a recently developed computer-based algorithm to determine donor-recipient HLA compatibility at the molecular level. Originally designed for highly alloimmunized patients, this algorithm is based on the concept that immunogenic epitopes are represented by amino acid triplets on exposed parts of protein sequences of HLA-A, -B, and -C chains accessible to alloantibodies. Donor HLA compatibility is determined by intralocus and interlocus comparisons of triplets in polymorphic sequence positions. For most patients, HLAMatchmaker can identify certain mismatched HLA antigens that are zero-triplet mismatches to the patient's HLA phenotype and should, therefore, be considered fully histocompatible. The present study was designed to determine how class I HLA matching at the triplet level affects kidney transplant outcome.

METHODS

We analyzed two multicenter databases of zero-HLA-DR-mismatched kidneys transplanted from 1987 to 1999. One database consisted of 31,879 primary allografts registered by U.S. transplant centers in the United Network for Organ Sharing database and the other consisted of 15,872 transplants in the Eurotransplant program.

RESULTS

HLA-A,B mismatched kidneys that were compatible at the triplet level exhibited almost identical graft survival rates as the zero-HLA-A,B antigen mismatches defined by conventional criteria. This beneficial effect of triplet matching was seen for both nonsensitized and sensitized patients and also for white and nonwhite patients.

CONCLUSIONS

These findings suggest that the application of HLAMatchmaker will increase the number of successful transplants, at least in the HLA-DR match combinations.

Allosensitization in heart transplantation: implications and management strategies

The detection of anti-human leukocyte antigen (HLA) donor-specific antibodies has been associated with a variety of clinical syndromes that determine short-term and long-term outcomes of cardiac transplant recipients, including an increased incidence of early and more severe allograft rejection and cardiac allograft vasculopathy. Recent surveys indicate marked heterogeneity in clinical protocols for detection and management of sensitization in heart transplantation. The commonly performed complement-dependent cytotoxicity assay is insensitive compared with newer methods such as flow cytometry for antibody screening. The imperative exists to create strategies that can decrease the level of sensitization and increase the likelihood for a negative crossmatch. In this effort, several strategies have been suggested, including administration of intravenous immunoglobulin, apheresis, and combination therapies using potent immunosuppression, particularly with cyclophosphamide. The future of managing allosensitization may be in induction of a chimeric state to allow graft tolerance.

Panel-reactive antibody screening practices prior to heart transplantation

BACKGROUND

Evaluation of humoral sensitization, commonly determined by the panel-reactive antibody (PRA) screen, is accepted as an important part of pre-transplant assessment. A variety of definitions and approaches to sensitization have been described in the literature but no analyses of actual practice have been reported.

METHODS

We sent surveys to 108 adult heart transplant program directors and 20 tissue-typing laboratories to obtain information about their approaches to PRA and crossmatch determination and management of sensitized patients.

RESULTS

Among 65 responding directors (60%), 63.1% were cardiologists and 36.9% surgeons. The most common threshold to consider PRA as positive is > or = 10%. Fifty-five of the respondents consider reactivity with T or B lymphocytes to be significant, whereas 34% consider only T-lymphocyte reactivity. Timing of PRA determination varies considerably among programs. Conversion to positive PRA results in more frequent PRA assessments and often therapy aimed to decrease the degree of sensitization. The most commonly utilized approaches are administration of immunoglobulin and plasmapheresis. The complement-dependent cytotoxicity (CDC) assay is the most commonly used method for PRA determination, but other techniques including flow cytometry and enzyme-linked immunosorbent assay (ELISA) are also used. Crossmatches are performed utilizing CDC and flow cytometry methods. Many laboratories employ more than one technique.

CONCLUSIONS

PRA screening, crossmatch determinations and management of sensitized patients vary considerably from center to center. Uncertainty exists about the importance of PRA values, threshold for treatment and clinical implications of sensitization. Important questions about the impact of sensitization on outcomes following heart transplantation may not be resolved until the measurement and management of sensitization becomes more uniform.

Recent advances in the immunology of chronic rejection

Chronic allograft rejection is a slowly progressive, insidious process in which the host immune system continues to mount an immunological attack on a transplanted organ, ultimately resulting in the failure of the graft. To varying degrees, all solid organ grafts are at risk for chronic rejection and undergo a stereotypic process of injury and inflammation, eventually leading to parenchymal fibrosis. The clinical consequences of chronic rejection are particularly apparent in thoracic transplantation, where both patient and graft survival decline steadily over time and the opportunities for re-transplantation or long-term extracorporeal support are limited. A variety of antigen-dependent and antigen-independent factors are known to modulate the propensity for an organ to undergo chronic rejection. Recent clinical and laboratory research has suggested that distinct immunologic mechanisms may underlie the process of chronic rejection. Ultimately, strategies to induce long-term tolerance to alloantigens will be necessary to prevent chronic rejection and to abrogate the deleterious sequelae of chronic immunosuppression.

ABO-incompatible heart transplantation in infants

BACKGROUND

Transplantation of hearts from ABO-incompatible donors is contraindicated because of the risk of hyperacute rejection mediated by preformed antibodies in the recipient to blood-group antigens of the donor. This contraindication may not apply to newborn infants, who do not yet produce antibodies to T-cell-independent antigens, including the major blood-group antigens.

METHODS

We studied 10 infants 4 hours to 14 months old (median, 2 months) who had congenital heart disease or cardiomyopathy and who received heart transplants from donors of incompatible blood type between 1996 and 2000. Serum isohemagglutinin titers were measured before and after transplantation. Plasma exchange was performed during cardiopulmonary bypass; no other procedures for the removal of antibodies were used. Standard immunosuppressive therapy was given, and rejection was monitored by means of endomyocardial biopsy. The results were compared with those in 10 infants who received heart transplants from ABO-compatible donors.

RESULTS

The overall survival rate among the 10 recipients with ABO-incompatible donors was 80 percent, with 2 early deaths due to causes presumed to be unrelated to ABO incompatibility. The duration of follow-up ranged from 11 months to 4.6 years. Two infants had serum antibodies to antigens of the donor's blood group before transplantation. No hyperacute rejection occurred; mild humoral rejection was noted at autopsy in one of the infants with antibodies. No morbidity attributable to ABO incompatibility has been observed. Despite the eventual development of antibodies to antigens of the donor's blood group in two infants, no damage to the graft has occurred. Because of the use of ABO-incompatible donors, the mortality rate among infants on the waiting list declined from 58 percent to 7 percent.

CONCLUSIONS

ABO-incompatible heart transplantation can be performed safely during infancy before the onset of isohemagglutinin production; this technique thus contributes to a marked reduction in mortality among infants on the waiting list.

Heart transplantation indicated only in the most severely ill patient: perspectives from the German heart transplant experience

The COCPIT study, performed in a complete national cohort of adult patients consecutively listed for cardiac transplantation in Germany in 1997, found a beneficial effect only in the group that was at high risk of dying from heart failure without transplantation. If these results can be reproduced in other countries, the discussion on the respective roles of pharmacological and organ-saving surgical therapies for advanced heart failure, medical urgency and waiting time as heart transplantation allocation criteria, and the feasibility of a randomized clinical trial testing the survival benefit of transplantation must be reopened.