In celebration of Ruggero Ceppellini: HLA in transplantation.

The availability of hematopoietic cell transplantation as curative therapy for blood disorders has been dramatically improved through a better understanding of the human leukocyte antigen (HLA) barrier. Although a fully compatible unrelated donor is preferable, transplantation from donors with a limited degree of HLA mismatching is associated with acceptable outcomes in many cases. Research on the limits of HLA mismatching, and the features that define permissible HLA mismatches will continue to enable transplantation to be more broadly available to patients in need.

16th IHIW: international histocompatibility working group in hematopoietic cell transplantation.

The International Histocompatibility Working Group is a collaborative international effort to understand the HLA and non-HLA genetics of the transplantation barrier. The Working Group is comprised of experts in the fields of histocompatibility and immunogenetics, hematopoietic cell transplantation and outcomes research. Data for 25 855 unrelated donor transplants were submitted in support of research studies for the 16th International Histocompatibility Workshop. Active investigation is in progress in seven key areas: the impact of HLA matching, role of race and ethnicity, identification of permissible HLA mismatches, haplotype-associated determinants, minor histocompatibility antigens, immune response genes and KIR genetics. New hypotheses for the 16th workshop were developed for immunogenetic studies in cord blood and haploidentical-related donor transplantation.

Comparison of matched unrelated and matched related donor myeloablative hematopoietic cell transplantation for adults with acute myeloid leukemia in first remission.

Hematopoietic cell transplantation (HCT) from a matched related donor (MRD) benefits many adults with acute myeloid leukemia (AML) in first complete remission (CR1). The majority of patients does not have such a donor and will require an alternative donor if HCT is to be undertaken. We retrospectively analyzed 226 adult AML CR1 patients undergoing myeloablative unrelated donor (URD) (10/10 match, n=62; 9/10, n=29) or MRD (n=135) HCT from 1996 to 2007. The 5-year estimates of overall survival, relapse and nonrelapse mortality (NRM) were 57.9, 29.7 and 16.0%, respectively. Failure for each of these outcomes was slightly higher for 10/10 URD than MRD HCT, although statistical significance was not reached for any end point. The adjusted hazard ratios (HRs) were 1.43 (0.89-2.30, P=0.14) for overall mortality, 1.17 (0.66-2.08, P=0.60) for relapse and 1.79 (0.86-3.74, P=0.12) for NRM, respectively, and the adjusted odds ratio for grades 2-4 acute graft-versus-host disease was 1.50 (0.70-3.24, P=0.30). Overall mortality among 9/10 and 10/10 URD recipients was similar (adjusted HR 1.16 (0.52-2.61), P=0.71). These data indicate that URD HCT can provide long-term survival for CR1 AML; outcomes for 10/10 URD HCT, and possibly 9/10 URD HCT, suggest that this modality should be considered in the absence of a suitable MRD.

The World Marrow Donor Association: 20 years of international collaboration for the support of unrelated donor and cord blood hematopoietic cell transplantation.

The transplantation of hematopoietic stem cells from unrelated volunteer donors and cord blood units is made possible through an international collaboration of registries and cord blood banks. The World Marrow Donor Association (WMDA) is a non-profit association based in Leiden, the Netherlands, whose mission is to assure that high-quality stem cell products are available for all patients in need, while maintaining the health and safety of the volunteer donors. This goal is accomplished through the work of six working groups and six board committees, in which issues of global significance to the clinical hematopoietic cell transplantation community are identified and guidelines are established. In this special issue of Bone Marrow Transplantation, the activities of the WMDA and a vision for future directions in the field are presented.

Genetic variation in CXCL12 and risk of cervical carcinoma: a population-based case-control study.

CXCL12 provides a chemotactic signal-directing leucocyte migration and regulates metastatic behaviour of tumour cells. We conducted a population-based case-control study to test the hypothesis that common genetic variation in CXCL12 individual single nucleotide polymorphism (SNP) alleles and haplotypes] is associated with the risk of cervical carcinoma. Cases (n = 917) were residents of western Washington State diagnosed with invasive squamous cell cervical carcinoma (SCC), invasive adenocarcinoma or adenosquamous carcinoma, or adenocarcinoma in situ of the cervix. Control participants (n = 849) were identified from the source population by random digit telephone dialling and frequency matched to cases on county and age. Nine CXCL12 tagSNPs chosen from the SeattleSNPs database were genotyped. The minor allele of intronic SNP rs266085 was inversely associated with cervical cancer under a recessive genetic effects model (OR = 0.74, 95% CI: 0.56-0.98). Among the ten common haplotypes inferred from the nine tagSNPs, one haplotype defined by minor alleles at 5'-flanking SNP rs17885289 and rs266085, and common alleles at the other seven SNPs occurred among 7.8% of cases and 10.6% of controls (dominant model OR = 0.72, 95% CI: 0.56-0.93; recessive model OR = 0.35, 95% CI: 0.12-0.97; and log-additive model OR = 0.72, 95% CI: 0.57-0.90). A stepwise procedure identified rs17885289, rs266085 and 3'-untranslated region (UTR) SNP rs266093 as the most parsimonious subset of SNPs necessary to define the haplotype inversely associated with cervical cancer risk in our study. A 3'-UTR SNP, rs1801157, previously found to be related to HIV pathogenesis, was not associated with cervical cancer risk. Further population-based studies are warranted to confirm these associations between genetic variation in CXCL12 and cervical cancer risk.

Clinical significance of donor-recipient HLA matching on survival after myeloablative hematopoietic cell transplantation from unrelated donors.

The application of unrelated donor hematopoietic cell transplantation can be expanded with the use of mismatched donors if human leukocyte antigen (HLA) disparity does not lead to increased morbidity and mortality. The rules that govern permissibility of HLA mismatches are not well defined. The International Histocompatibility Working Group in hematopoietic cell transplantation measured the risks associated with locus-specific disparity in 4796 patients transplanted for low, intermediate, or high-risk hematologic diseases. The permissibility of a given HLA mismatch is in part defined by the locus and by disease risk.

Effect of HLA-A2 allele disparity on clinical outcome in hematopoietic cell transplantation from unrelated donors.

Population-based differences in clinical outcome after unrelated donor hematopoietic cell transplantation suggest that the significance of human leukocyte antigen (HLA) mismatching may be related to locus-specific and allele-specific differences that distinguish ethnically diverse transplant donors and recipients. We studied the risks associated with HLA-A locus mismatching in two large transplant populations from the International Histocompatibility Working Group in hematopoietic cell transplantation data set to better understand permissible and nonpermissible HLA-A mismatches.

Clinical importance of HLA-DPB1 in haematopoietic cell transplantation.

There is increasing evidence for a significant effect of human leukocyte antigen (HLA)-DPB1 mismatching on complications following unrelated donor haematopoietic cell transplantation (HCT). In this analysis of 5930 patient/donor pairs, we found that a DPB1 mismatch predicted significantly for an increased risk of acute graft-vs-host disease [hazard ratio (HR): 1.33; P-value = <0.0001], while protecting against disease relapse (HR: 0.82, P-value = 0.01). These data support an immunogenic role for HLA-DPB1 in HCT and the need for pretransplant tissue typing at this locus.

Hematopoietic stem cell transplantation: killer immunoglobulin-like receptor component.

Recognition of recipient human leukocyte antigen (HLA) class I ligand by donor natural killer cell killer immunoglobulin-like receptors (KIR) has been proposed as the basis for donor allograft reactivity against malignancy leading to reduction in posttransplant relapse and higher survival for acute myelogenous leukemia. Analysis of KIR ligand effects in 1770 patients undergoing myeloablative T-replete hematopoietic cell transplantation (HCT) from HLA-matched or mismatched unrelated donors showed that lack of KIR ligand in patients for inhibitory KIR was associated with lower hazards of relapse in leukemia patients with in HLA-mismatched transplants [hazard ratio (HR): 0.061; 95% confidence interval (CI): 0.43-0.85; P-value = 0.004]. Absence of HLA-C group 2 or HLA-Bw4 KIR ligands were each associated with lower hazards of relapse (HR: 0.47; 95% CI: 0.28-0.79; P-value = 0.004; HR: 0.56; 95% CI: 0.33-0.97; P-value = 0.04, respectively). Based on these analyses, recipient homozygosity for HLA-B or -C epitopes that define KIR ligands is likely to be a predictive factor for leukemia relapse following myeloablative HCT from unrelated donors. KIR genotyping for unrelated donors and recipients will clarify the role of these receptors in transplant outcome.

MHC class I, II, and III microsatellite marker matching and survival in unrelated donor hematopoietic cell transplantation.

Microsatellites (Msats) are effective markers for disease association mapping. The International Histocompatibility Working Group in hematopoietic cell transplantation applied Msats to determine whether potential new transplantation determinants are encoded within the major histocompatibility complex. Retrospective analysis of human leukocyte antigen-identical unrelated donor transplants provided a homogeneous population to measure Msat-associated risks of mortality.

Immune response gene polymorphisms in unrelated donor hematopoietic cell transplantation.

Immune response genes (IRG) play an important role in inflammation and control of infection after allogeneic transplantation. The International Histocompatibility Working Group (IHWG) in hematopoietic cell transplantation took a candidate gene approach to define the risks associated with genetic variation for a panel of well-characterized IRG.

Tissue typing in support of unrelated hematopoietic cell transplantation.

The success of unrelated hematopoietic cell transplantation (HCT) for the treatment of hematologic malignancies has closely paralleled development of robust typing methods for comprehensive and precise donor-recipient matching. The application of molecular methods in clinical research has led to a more complete understanding of the immunogenetic barriers involving host-vs-graft (HVG) and graft-vs-host (GVH) reactions. Along with the development of less toxic transplant regimens, advances in the prevention and treatment of graft-vs-host disease (GVHD) and in the supportive care of the transplant recipient, improved HLA matching of potential unrelated donors has led to clinical results that begin to compare favorably with that of HLA-identical sibling transplants.

Busulfan concentration and graft rejection in pediatric patients undergoing hematopoietic stem cell transplantation.

We retrospectively analyzed the relationship between busulfan average steady-state plasma concentration (C(SS)) and graft rejection in 53 children receiving busulfan/cyclophosphamide (BU/CY) preparative regimens prior to hematopoietic stem cell transplantation (HSCT). Patients received a total oral busulfan dose of 11 to 28 mg/kg followed by a total cyclophosphamide dose of 120 to 335 mg/kg in preparation for allogeneic grafts (HLA-matched or HLA partially matched sibling, parent or unrelated donor). Graft rejection occurred in eight (15%) patients. Busulfan C(SS) (P = 0.0024) was the only statistically significant predictor of rejection on univariate logistic regression analysis, with the risk of rejection decreasing with an increase in busulfan C(SS). Severe (grade 3 or 4) regimen-related toxicity (RRT) occurred in four patients. Ten patients (19%) had a busulfan C(SS) higher than 900 ng/ml, one of whom had severe RRT. Higher and variable doses of cyclophosphamide may explain the lack of a relationship between busulfan C(SS) and RRT in children. It may be possible to improve the outcome of HSCT in pediatric patients receiving the BU/CY regimen through optimization of busulfan C(SS) and better definition of the contribution of activated cyclophosphamide metabolites to toxicity.

Major-histocompatibility-complex class I alleles and antigens in hematopoietic-cell transplantation.

BACKGROUND: Successful engraftment of hematopoietic stem cells from unrelated donors is influenced by disparities between the donor and recipient for HLA-A, B, and C alleles. Disparities between HLA sequence polymorphisms that are serologically detectable are termed antigen mismatches, whereas those that can be identified only by DNA-based typing methods are termed allele mismatches. Whether both kinds of polymorphisms are important in transplantation is not known. We tested the hypothesis that allele mismatches that are detectable only at the DNA level are less immunogenic than those that are serologically detectable and thereby are associated with a lower risk of graft failure after hematopoietic-cell transplantation METHODS: We used DNA sequencing to define the HLA-A, B, and C alleles in 471 patients who received bone marrow from unrelated donors for the treatment of chronic myeloid leukemia after myeloablative conditioning therapy. The odds ratios for graft failure were determined for recipients of transplants from donors with a single class I allele mismatch, a single class I antigen mismatch, or two or more class I mismatches, as compared with those with no mismatch RESULTS: A single HLA allele mismatch did not increase the risk of graft failure, whereas a single antigen mismatch significantly increased the risk. The risk was also increased if the recipient was HLA homozygous at the mismatched class I locus or if the donor had two or more class I mismatches CONCLUSIONS: HLA class I antigen mismatches that are serologically detectable confer an enhanced risk of graft failure after hematopoietic-cell transplantation. Transplants from donors with a single class I allele mismatch that is not serologically detectable may be used without an increased risk of graft failure.

Effect of HLA class II gene disparity on clinical outcome in unrelated donor hematopoietic cell transplantation for chronic myeloid leukemia: the US National Marrow Donor Program Experience.

The clinical importance of HLA class II gene disparity in unrelated stem cell transplantation is not entirely known. The impact was evaluated of matching donors and recipients for HLA-DR, HLA-DQ, and HLA-DP genes on clinical outcome after stem cell transplantation for chronic myeloid leukemia (CML) performed between 1988 and 1997. HLA-DRB1, -DQA1, -DQB1, -DPA1, and -DPB1 alleles were identified in 831 transplant pairs using a combination of sequence-specific oligonucleotide probes, sequence-specific priming, and sequencing methods. Among the 831 pairs, 696 (84%) were HLA-A and -B serologically matched; of these, 565 (81%) were also matched for HLA-DRB1. HLA-DRB1 matching correlated with significantly improved survival (relative risk [RR], 1.29 [95% confidence interval (CI), 1.02-1.64; P =.04]) independently of HLA-DQA1 or HLA-DQB1 (RR, 1.01 [95% CI, 0.81-1.26; P =.94]) and HLA-DPA1 or HLA-DPB1 (RR, 1.11 [95% CI, 0.84-1.48; P =.46]). Single-locus HLA-DQ or HLA-DP disparity was not associated with significantly poorer survival. For patients who underwent transplantation in the first chronic phase (CP) from HLA-A, B matched donors, the presence of DRB1 allele mismatching was independently associated with increased incidence of grades III-IV acute graft-versus-host disease (GVHD). No significant associations of class II allele mismatching with risk for delayed engraftment or chronic GVHD disease were detected. This study clearly demonstrates the importance of precise matching of HLA-DRB1 alleles for successful transplantation. Furthermore, a good-risk population of patients whose transplantations were performed in the first CP of disease from HLA-A, B, DRB1 matched unrelated donors can be shown to have superior survival.

Trends in transplantation of hematopoietic stem cells from unrelated donors.

Transplants of hematopoietic stem cells from unrelated donors have become feasible for patients with a growing variety of hematologic disorders. The probability of finding a suitable donor has increased because of the expansion of the network of registries containing more than seven million HLA-typed donors worldwide. The selection of compatible donors has become more effective, thanks to the discovery of new HLA alleles and the development of precise and efficient HLA typing methods using DNA technology. Improved methods for transplantation may provide the opportunity to further decrease treatment-related toxicity and improve survival.

Generation of HLA-C-specific cytotoxic T cells in association with marrow graft rejection: analysis of alloimmunity by T-cell cloning and testing of T-cell-receptor rearrangements.

Peripheral blood mononuclear cells from a patient who rejected a T-cell-depleted marrow graft showed spontaneous cytotoxic activity specific for HLA-Cw4 and HLA-B35 alloantigens of the donor. T-cell-receptor complementarity-determining region 3 length distributions in a blood sample obtained at the time of rejection generally showed distortions in only 1 or 2 peaks, indicating that recipient T cells with a broad repertoire of antigen receptors survived the pretransplantation conditioning regimen. An HLA-Cw4-specific, CD8 T-cell clone was recovered from a blood sample after rejection. The T-cell-receptor-B gene rearrangement expressed by this clone was not readily detectable in other blood samples drawn before or after the transplantation, indicating that this clone was only 1 of many recipient-derived T cells that recognized HLA alloantigens of the donor. These results demonstrate the role of the HLA-C locus in T-cell-mediated alloimmune responses and add to emerging evidence that indicates the need to evaluate HLA-C compatibility in selecting hematopoietic stem cell donors for patients who have an increased risk of rejection.

The biological significance of HLA-DP gene variation in haematopoietic cell transplantation.

Although it has been over 25 years since HLA-DP was mapped to the major histocompatibility complex (MHC), its biological functions remain ill-defined. We sought to test the hypothesis that HLA-DP functions in a manner similar to that of other class II genes by measuring the risk of clinically severe grades III-IV acute graft-vs.-host disease (GVHD) associated with recipient HLA-DP disparity after haematopoietic cell transplantation. HLA-DPB1 exon 2 was sequenced in 205 patients who underwent transplantation from HLA-A, -B, -C, -DRB1 and -DQB1 allele-matched unrelated donors. HLA-DPB1 mismatched recipients experienced a significantly increased risk of acute GVHD compared with HLA-DP-identical transplants. Patients who were mismatched for a single HLA-DPB1 allele had an odds ratio (OR) of 1.0 (0.5, 2.2; P = 0.99) and patients who were mismatched for two alleles had an OR of 2.2 (1.0, 4.9; P = 0.06) for developing acute GVHD. Compared with matched and single-allele mismatched transplants, patients who were mismatched for two DPB1 alleles had an OR of 2.2 (1.2, 4.1; P = 0.01). HLA-DP plays an important role in the alloimmune response. A threshold effect of multiple HLA-DP disparities is evident in determining the risk of acute GVHD after haematopoietic cell transplantation from unrelated donors.