Tuesday, July 29, 2014

HLA-haploidentical transplantation with regulatory and conventional T-cell adoptive immunotherapy prevents acute leukemia relapse

Posttransplant relapse is still the major cause of treatment failure in high-risk acute leukemia. Attempts to manipulate alloreactive T cells to spare normal cells while killing leukemic cells have been unsuccessful. In HLA-haploidentical transplantation, we reported that donor-derived T regulatory cells (Tregs), coinfused with conventional T cells (Tcons), protected recipients against graft-versus-host disease (GVHD). The present phase 2 study investigated whether Treg-Tcon adoptive immunotherapy prevents posttransplant leukemia relapse. Forty-three adults with high-risk acute leukemia (acute myeloid leukemia 33; acute lymphoblastic leukemia 10) were conditioned with a total body irradiation–based regimen. Grafts included CD34+ cells (mean 9.7 x 10^6/kg), Tregs (mean 2.5 x 10^6/kg), and Tcons (mean 1.1 x 10^6/kg). No posttransplant immunosuppression was given. Ninety-five percent of patients achieved full-donor type engraftment and 15% developed ≥grade 2 acute GVHD. The probability of disease-free survival was 0.56 at a median follow-up of 46 months. The very low cumulative incidence of relapse (0.05) was significantly better than in historical controls. These results demonstrate the immunosuppressive potential of Tregs can be used to suppress GVHD without loss of the benefits of graft-versus-leukemia (GVL) activity. Humanized murine models provided insights into the mechanisms underlying separation of GVL from GVHD, suggesting the GVL effect is due to largely unopposed Tcon alloantigen recognition in bone marrow (read more)

Monday, July 28, 2014

HLA Match Likelihoods for Hematopoietic Stem-Cell Grafts in the U.S. Registry

BACKGROUND : Hematopoietic stem-cell transplantation (HSCT) is a potentially lifesaving therapy for several blood cancers and other diseases. For patients without a suitable related HLA-matched donor, unrelated-donor registries of adult volunteers and banked umbilical cord–blood units, such as the Be the Match Registry operated by the National Marrow Donor Program (NMDP), provide potential sources of donors. Our goal in the present study was to measure the likelihood of finding a suitable donor in the U.S. registry.
METHODS : Using human HLA data from the NMDP donor and cord-blood-unit registry, we built population-based genetic models for 21 U.S. racial and ethnic groups to predict the likelihood of identifying a suitable donor (either an adult donor or a cord-blood unit) for patients in each group. The models incorporated the degree of HLA matching, adult-donor availability (i.e., ability to donate), and cord-blood-unit cell dose.
RESULTS : Our models indicated that most candidates for HSCT will have a suitable (HLA-matched or minimally mismatched) adult donor. However, many patients will not have an optimal adult donor — that is, a donor who is matched at high resolution at HLA-A, HLA-B, HLA-C, and HLA-DRB1. The likelihood of finding an optimal donor varies among racial and ethnic groups, with the highest probability among whites of European descent, at 75%, and the lowest probability among blacks of South or Central American descent, at 16%. Likelihoods for other groups are intermediate. Few patients will have an optimal cord-blood unit — that is, one matched at the antigen level at HLA-A and HLA-B and matched at high resolution at HLA-DRB1. However, cord-blood units mismatched at one or two HLA loci are available for almost all patients younger than 20 years of age and for more than 80% of patients 20 years of age or older, regardless of racial and ethnic background.
CONCLUSIONS : Most patients likely to benefit from HSCT will have a donor. Public investment in donor recruitment and cord-blood banks has expanded access to HSCT (read more)

Wednesday, July 16, 2014

Practical value of identifying antibodies to cryptic HLA epitopes in cardiac transplantation

Background: Identification of antibodies to human leukocyte antigens (HLA) by single antigen bead arrays has led to the common practice of virtual crossmatching. However, inappropriate assignment of anti-HLA specificities can lead to false-positive virtual crossmatching, resulting in the decline of potentially crossmatch-negative organ offers. In this study we describe identification of antibodies to cryptic HLA present on denatured forms of HLA on single antigen bead array and provide a reassessment of calculated panel-reactive antibody (CPRA) based on elimination of false-positive reactions due to antibodies to cryptic HLA epitopes.
Methods: Sera from 96 patients with positive HLA antibodies detected on a standard single antigen bead platform were tested under denaturing conditions and with a new single antigen bead product (iBeads; One Lambda, Inc., Canoga Park, CA) to identify antibodies to cryptic HLA vs native HLA. Flow cytometry crossmatching and complement-fixation assays were performed to assess clinical relevance.
Results: Antibodies to cryptic HLA were present in approximately 21% of patients on our waiting list for cardiac transplantation. These antibody responses were not associated with factors commonly thought to be associated with antibody responses to HLA such as age, gender, transfusions or presence of circulatory support.
Conclusions: Antibodies to cryptic HLA can be reliably identified by iBeads technology, and usually do not fix complement nor produce positive flow cytometry crossmatches. Identification and removal of antibodies to cryptic HLA from the panel of unacceptable antigens may have dramatic and meaningful effects on CPRA and virtual crossmatch strategies (read more)

Epitope Analysis of HLA-DQ Antigens: What Does the Antibody See?

Background : Human leukocyte antigen (HLA)-DQ has emerged as the alloantibody most frequently associated with the generation of de novo donor-specific antibody (DSA), antibody-mediated-rejection, and unfavorable transplantation outcome.
Methods : The generation of HLA-DQ de novo DSA was interrogated in 40 transplant recipients who were immunologically naive before their failed transplantation. Eplet and epitope analyses were performed using HLAMatchmaker and Cn3D software.
Results : Ten DQA and thirteen DQB eplets or eplet combinations were identified. All but one revealed an epitope footprint that includes both the DQα and DQβ chains. Four examples are illustrated in detail, representing a range of different epitope landscapes. A disparity between antigen density and mean fluorescence intensity values for some alleles within an eplet group was noted, with mean fluorescence intensity values of the lowest fluorescence bead being one tenth of the highest fluorescence bead, despite the fact that the amount of antigen on these beads were not significantly different.
Conclusion : Our data support the need for changing the manner in which HLA-DQ antigens and antibodies are evaluated for organ transplantation. The current nomenclature system does not reflect the true nature of HLA-DQ polymorphism. Moreover, epitope immunogenicity likely involves more than the mere presence of a specific eplet. Because our field contemplates the use of epitope matching as an approach to improve organ allocation and overall outcomes, it is imperative to have accurate characterization of the immunogenicity of each epitope. This will pave the way to identifying acceptable mismatches and will allow risk stratification for generating de novo HLA-DSA after transplantation (read more)

Monday, July 14, 2014

Haploidentical SCT: the mechanisms underlying the crossing of HLA barriers

Research on the different mechanisms for crossing HLA barriers has progressed over the past 10 years. General outlines have come into view for a solution to this issue and are often presented as ‘haploidentical SCT’ immunology. In this review, we discuss several mechanisms that have recently been described in ex vivo and in vivo settings that can either avoid GVHD or promote hematopoietic reconstitution in haploidentical settings. The host and donor T-cell responses to allogeneic HLA molecules are a fundamental obstacle to the successful application of haploidentical transplantation, which results in unacceptably high incidences of GVHD and graft rejection. Thus, the T-cell response is a central factor in the establishment of a novel haploidentical transplant protocol with superior outcomes (read more)

Saturday, July 12, 2014

Accelerated telomere reduction and hepatocyte senescence in tolerated human liver allografts

BACKGROUND: In living donor liver transplantation, the biological organ age of the donated allograft is unknown in young patients who receive grafts from older donors. Few studies have focused on the effects of aging on allografts in the state of tolerance. The purpose of this study was to assess the biological organ age of liver grafts.
METHODS: In 20 tolerated allografts over a 10-year post-transplant follow-up period, the relative telomere lengths were measured by multiplex quantitative polymerase chain reaction, and hepatocyte nuclear size and cell cycle phase markers were determined by immunohistochemistry. The results were compared with the same measurements that had been obtained prior to transplantation in the recipients' pre-implantation donor livers. Tolerance was defined strictly as a condition in which the allograft functioned normally and showed normal histology without any histological signs of rejection, fibrosis or inflammation in the absence of immunosuppression.
RESULTS: bFirst, telomere length correlated with chronological donor age (n=41). Accelerated telomere reduction was seen in tolerated grafts compared with the predicted telomere length of each allograft calculated from the regression line of donor livers. Tolerated grafts were associated with higher hepatocyte p21 expression and greater nuclear area than in the donor livers prior to transplantation.
CONCLUSIONS: These findings suggest that allografts age more rapidly than in the normal population, and that grafts may reach the limit of proliferative capacity even in the state of tolerance (read more)

Saturday, July 5, 2014

Risk of Pediatric Celiac Disease According to HLA Haplotype and Country

BACKGROUND : The presence of HLA haplotype DR3–DQ2 or DR4–DQ8 is associated with an increased risk of celiac disease. In addition, nearly all children with celiac disease have serum antibodies against tissue transglutaminase (tTG).
METHODS : We studied 6403 children with HLA haplotype DR3–DQ2 or DR4–DQ8 prospectively from birth in the United States, Finland, Germany, and Sweden. The primary end point was the development of celiac disease autoimmunity, which was defined as the presence of tTG antibodies on two consecutive tests at least 3 months apart. The secondary end point was the development of celiac disease, which was defined for the purpose of this study as either a diagnosis on biopsy or persistently high levels of tTG antibodies.
RESULTS : The median follow-up was 60 months (interquartile range, 46 to 77). Celiac disease autoimmunity developed in 786 children (12%). Of the 350 children who underwent biopsy, 291 had confirmed celiac disease; an additional 21 children who did not undergo biopsy had persistently high levels of tTG antibodies. The risks of celiac disease autoimmunity and celiac disease by the age of 5 years were 11% and 3%, respectively, among children with a single DR3–DQ2 haplotype, and 26% and 11%, respectively, among those with two copies (DR3–DQ2 homozygosity). In the adjusted model, the hazard ratios for celiac disease autoimmunity were 2.09 (95% confidence interval [CI], 1.70 to 2.56) among heterozygotes and 5.70 (95% CI, 4.66 to 6.97) among homozygotes, as compared with children who had the lowest-risk genotypes (DR4–DQ8 heterozygotes or homozygotes). Residence in Sweden was also independently associated with an increased risk of celiac disease autoimmunity (hazard ratio, 1.90; 95% CI, 1.61 to 2.25).
CONCLUSIONS : Children with the HLA haplotype DR3–DQ2, especially homozygotes, were found to be at high risk for celiac disease autoimmunity and celiac disease early in childhood. The higher risk in Sweden than in other countries highlights the importance of studying environmental factors associated with celiac disease (read more)

Thursday, July 3, 2014

Antibody-Mediated Rejection Despite Inhibition of Terminal Complement

Background : Terminal complement blockade has been shown to decrease the incidence of early acute antibody-mediated rejection (eAMR) in the first month after positive crossmatch kidney transplant recipients, yet some patients still develop eAMR.
Methods : The current study investigated possible mechanisms of eAMR despite eculizumab treatment. Of the 26 patients treated with eculizumab, 2 developed clinical eAMR and another patient developed histologic signs of eAMR without graft dysfunction (“subclinical eAMR”). Twenty three did not have histologic injury on early surveillance biopsies.
Results : All 26 patients had therapeutic levels of eculizumab and showed complete blockade of complement in hemolytic assays. High levels of donor-specific alloantibody (DSA) including total IgG, IgG3 and C1q+ DSA were present in patients with and without eAMR and none correlated well with eAMR. In contrast, IgM DSA was present in only 4 patients after transplantation: the 2 patients with clinical eAMR, 1 patient with subclinical AMR and 1 patient without eAMR (p=0.006 correlation with eAMR). Both clinical eAMR episodes were easily treated with plasma exchange which removed IgM more completely and rapidly than IgG, resulting in normalization of function and histology.
Conclusion : These data suggest a possible role of anti-donor IgM DSA in the pathogenesis of eAMR in patients treated with terminal complement blockade (read more)