The impact of HLA unidirectional mismatches on the outcome of myeloablative hematopoietic stem cell transplantation with unrelated donors

Permissible HLA mismatches in 9/10 unrelated donor pediatric stem cell transplants using HLA-EMMA: an EBMT Inborn Errors Working Party study

ABSTRACT

Allogeneic hematopoietic stem cell transplantation (HSCT) with mismatched unrelated donors (MMUD) is associated with inferior outcome compared with matched unrelated donors (MUDs). We aimed to identify permissible mismatches using HLA epitope mismatch algorithm, which determines permissibility by analyzing amino acid sequences, in a single-center cohort of 70 pediatric 9/10 MMUD HSCTs and 157 10/10 MUDs for comparison. Amino acid matching was evaluated for the whole HLA protein, the α-helices, and the β-sheets, in both host vs graft (HvG) and graft vs host (GvH) direction. Superior event-free survival (EFS) was found in 13 patients permissibly mismatched in the HvG direction (totalHvG, 92% vs 58% at 1 year; P = .009) and in 21 patients matched on the α-helices (αHvG, 90% vs 53%; P = .002). These rates were similar to EFS rates in patients with 10/10 MUDs (90% vs 80%; P = .60). EFS was not related to β-sheet amino acid matching, nor to matching in the GvH direction. Overall survival (OS) rates trended similarly to those of EFS for amino acid mismatches (totalHvG, 92% vs 74%; P = .075; αHvG, 90% vs 71%; P = .072). These findings were reproduced in an EBMT Registry inborn errors cohort of 271 pediatric 9/10 MMUD HSCTs and 929 10/10 MUD HSCTs, showing a significant effect of αHvG matching on both OS and EFS and similar OS and EFS between αHvG matched MMUDs and 10/10 MUDs. In summary, HvG amino acid matching on the α-helices identifies 9/10 MMUDs with permissible mismatches, which are correlated with favorable transplant outcomes similar to those of matched donors.

Allogeneic hematopoietic cell transplantation from alternative donors in acute myeloid leukemia

Allogeneic hematopoietic cell transplantation (HCT) potentially provides a cure for patients with acute myeloid leukemia (AML) who are unlikely to be cured with chemotherapy alone. Previously, human leukocyte antigen (HLA)-matched related donors were used exclusively, which made the procedure available for a limited proportion of patients. The introduction of high-resolution HLA-typing technology, innovations in immunosuppressive therapy, and improved supportive care measures have significantly changed the situation. Now, patients without a matched related donor have an ample opportunity to receive allogeneic HCT with the use of matched or mismatched unrelated donors, umbilical cord blood grafts, or haploidentical related donors. The outcomes of alternative donor transplantations have improved over the past decades, and the growth of unrelated donor registries as well as the donor diversification have enhanced the chance of finding a suitable donor. With multiple alternative donor choices available for most patients, the donor selection is becoming increasingly important. To discuss the optimal donor choice in case of unavailability of an HLA-matched related donor, this article reviews the existing literature of retrospective and prospective comparisons of different alternative donor transplantations in AML and discusses the current state-of-art modalities in allogeneic HCT using alternative donors.

Histocompatibility assessment in hematopoietic stem cell transplantation: recommendations from the Italian Society for Immunogenetics and Transplantation Biology (Associazione Italiana di Immunogenetica e Biologia dei Trapianti - AIBT)

The outcome of allogeneic hematopoietic stem cell transplantation (HSCT) is significantly influenced by the degree of HLA histocompatibility between donor and recipient. To provide shared indications for required histocompatibility testing and interpretation before HSCT, the Italian Society for Immunogenetics and Transplantation Biology (Associazione Italiana di Immunogenetica e Biologia dei Trapianti [AIBT]) gathered members and created a working group to discuss and develop recommendations for histocompatibility assessment in HSCT.After a review of the literature and multiple panel discussions, AIBT developed up-to-date recommendations for the resolution levels of HLA typing, histocompatibility definitions of patients and donors, importance of anti-HLA antibodies, and significance of NK alloreactivity, which are reported in this document. These recommendations have been shared with the Italian Group for Bone Marrow Transplantation (Gruppo Italiano per il Trapianto di Midollo Osseo, cellule staminali emopoietiche e terapia cellulare [GITMO]) and the Italian National Center for Transplantation (Centro Nazionale Trapianti [CNT]). Notably, the increased use of HLA-mismatched transplantation (i.e., mismatched unrelated, haploidentical) in recent years has made these indications even more relevant for the standardization and improvement of quality of care.This document represents a useful instrument for health care workers involved in the field of HSCT, enhancing synergy with transplant physicians and enabling greater optimization of the available resources.

[Unrelated donor selection for allogeneic hematopoietic stem cell transplantation: Guidelines from the Francophone Society of Bone Marrow Transplantation and Cellular Therapy (SFGM-TC)]

The selection of a donor is an essential element in allogeneic hematopoietic stem cell transplantation. In the absence of an HLA-matched related donor, the selection of an unrelated donor is considered, and is currently the most common type of allogenic donor used in practice. Many criteria are considered for the selection when multiple donors are available, particularly in case of partial match. The aim of this workshop is to assist in the selection of an unrelated donor, in keeping with recent data from the literature.

The use of prognostic models in allogeneic transplants: a perspective guide for clinicians and investigators

Allogeneic hematopoietic cell transplant (HCT) can cure many hematologic diseases, but it carries the potential risk of increased morbidity and mortality rates. Prognostic evaluation is a scientific entity at the core of care for potential recipients of HCT. It can improve the decision-making process of transplant vs no transplant, help choose the best transplant strategy and allows for future trials targeting patients' intolerances to transplant; hence, it ultimately improves transplant outcomes. Prognostic models are key for appropriate actuarial outcome estimates, which have frequently been shown to be better than physicians' subjective estimates. To make the most accurate prognostic evaluation for HCT, one should rely on >1 prognostic model. For relapse and relapse-related mortality risks, the refined disease risk index is currently the most informative model. It can be supplemented with disease-specific models that consider genetic mutations as predictors in addition to information on measurable residual disease. For nonrelapse mortality and HCT-related morbidity risks, the HCT-comorbidity index and Karnofsky performance status have proven to be the most reliable and most accepted by physicians. These can be supplemented with gait speed as a measure of frailty. Some other global prognostic models might add additional prognostic information. Physicians' educated perceptions can then put this information into context, taking into consideration conditioning regimen and donor choices. The future of transplant mandates (1) clinical investigators specifically trained in prognostication, (2) increased reliance on geriatric assessment, (3) the use of novel biomarkers such as genetic variants, and (4) the successful application of novel statistical methods such as machine learning.

Impact of the HLA Immunopeptidome on Survival of Leukemia Patients After Unrelated Donor Transplantation

PURPOSE

Immunopeptidome divergence between mismatched HLA-DP is a determinant of T-cell alloreactivity and clinical tolerability after fully HLA-A, -B, -C, -DRB1, -DQB1 matched unrelated donor hematopoietic cell transplantation (UD-HCT). Here, we tested this concept in HLA-A, -B, and -C disparities after single class I HLA-mismatched UD-HCT.

PATIENTS AND METHODS

We studied 2,391 single class I HLA-mismatched and 14,426 fully HLA-matched UD-HCT performed between 2008 and 2018 for acute leukemia or myelodysplastic syndromes. Hierarchical clustering of experimentally determined peptide-binding motifs (PBM) was used as a proxy for immunopeptidome divergence of HLA-A, -B, or -C disparities, allowing us to classify 1,629/2,391 (68.1%) of the HLA-mismatched UD-HCT as PBM-matched or PBM-mismatched. Risks associated with PBM-matching status were assessed by Cox proportional hazards models, with overall survival (OS) as the primary end point.

RESULTS

Relative to full matches, bidirectional or unidirectional PBM mismatches in graft-versus-host (GVH) direction (PBM-GVH mismatches, 60.7%) were associated with significantly lower OS (hazard ratio [HR], 1.48; P < .0001), while unidirectional PBM mismatches in host-versus-graft direction or PBM matches (PBM-GVH matches, 39.3%) were not (HR, 1.13; P = .1017). PBM-GVH mismatches also had significantly lower OS than PBM-GVH matches in direct comparison (HR, 1.32; P = .0036). The hazards for transplant-related mortality and acute and chronic graft-versus-host disease but not relapse increased stepwise from full HLA matches to single PBM-GVH matches, and single PBM-GVH mismatches. A webtool for PBM-matching of single class I HLA-mismatched donor-recipient pairs was developed.

CONCLUSION

PBM-GVH mismatches inform mortality risks after single class I HLA-mismatched UD-HCT, suggesting that prospective consideration of directional PBM-matching status might improve outcome. These findings highlight immunopeptidome divergence between mismatched HLA as a driver of clinical tolerability in UD-HCT.

Human Leucocyte Antigen System and Selection of Unrelated Hematopoietic Stem Cell Donors: Impact of Patient-Donor (Mis)matching and New Challenges with the Current Technologies

The selection of hematopoietic stem cell donors for allogeneic transplantation (allo-HSCT) is mainly driven by human leucocyte antigen (HLA) matching between patient and donor, with HLA-identical matched siblings being the preferred choice in most situations. Although other clinical and demographical variables matter, especially, donor age, which is unequivocally associated with better transplant outcomes, the histocompatibility criteria have a central role in the search for the best donor, particularly in the setting of unrelated allo-HSCT where HLA disparities between patient and donor are frequent. The present review is focused on the role of HLA incompatibilities on patient outcome according to the most recent literature, in an attempt to guide transplant physicians and search coordinators during the process of adult unrelated-donor selection. The technological progresses in HLA typing, i.e., with next-generation sequencing (NGS), now allow disclosing a growing number of HLA incompatibilities associated with a heterogeneous and sometimes unknown spectrum of clinical severity. Their immunogenic characteristics, i.e., their position inside or outside the antigen recognition domain (ARD), their permissiveness, their intronic or exonic nature and even the expected expression of the HLA loci where those mismatches occur, will be presented and discussed here, integrating the advances in the immunobiology of transplantation with survival and toxicity outcomes reported in the most relevant studies, within the perspective of improving donor selection in the current practice.

Hematology 2022-what is complete HLA match in 2022?

Allogeneic hematopoietic cell transplantation (alloHCT) often represents the only curative treatment for various malignant and nonmalignant disorders. Initially, the only suitable donors were considered human leukocyte antigen (HLA)-matched or partially matched relatives. The founding of international unrelated donor and umbilical cord blood registries expanded unrelated donor options and access for patients. In the absence of a matched sibling donor (MSD) with 13% to 51% availability, the current consensus recommends use of a matched unrelated donor (MUD) at HLA-A, B, C, and DRB1 with consideration of matching at HLA-DPB1 and -DQB1. MUD donor availability (donor willing and available to donate) ranges from 29% to 78% with African American patients on the lower end and white non-Hispanic patients with the highest likelihood of a match. Recent studies comparing donor to no-donor treatment options in malignant disease consistently point to substantially better outcomes following alloHCT. In the absence of an MSD or MUD, alternative donor choices turn to haploidentical related (Haplo), mismatched unrelated donor (MMUD), and umbilical cord blood (UCB). Novel strategies for alloHCT, including the use of posttransplant cyclophosphamide-based graft vs host disease prophylaxis, have expanded the safety and effectiveness of transplant procedures across HLA barriers using Haplo and MMUD. The less restrictive matching requirements for UCB transplant are well documented and allow for transplant across multiply mismatched HLA alleles. When all donor options are considered, nearly all patients have an available donor. Here we discuss the likelihood of donor availability, complete HLA match by available donor type, and current controversies warranting future research.

Current donor selection strategies for allogeneic hematopoietic cell transplantation

Since the first allogeneic hematopoietic stem cell transplantation (HCT) was performed by Dr. E. Donnall Thomas in 1957, the field has advanced with new stem cell sources, immune suppressive regimens, and transplant protocols. Stem cells may be collected from bone marrow, peripheral or cord blood from an identical twin, a sibling, or a related or unrelated donor, which can be human leukocyte antigen (HLA) matched, mismatched, or haploidentical. Although HLA matching is one of the most important criteria for successful allogeneic HCT (allo-HCT) to minimize graft vs host disease (GVHD), prevent relapse, and improve overall survival, the novel immunosuppressive protocols for GVHD prophylaxis offered improved outcomes in haploidentical HCT (haplo-HCT), expanding donor availability for the majority of HCT candidates. These immunosuppressive protocols are currently being tested with the HLA-matched and mismatched donors to improve HCT outcomes further. In addition, fine-tuning the DPB1 mismatching and discovering the B leader genotype and mismatching may offer further optimization of donor selection and transplant outcomes. While the decision about a donor type largely depends on the patient's characteristics, disease status, and the transplant protocols utilized by an individual transplant center, there are general approaches to donor selection dictated by donor-recipient histocompatibility and the urgency for HCT. This review highlights recent advances in understanding critical factors in donor selection strategies for allo-HCT. It uses clinical vignettes to demonstrate the importance of making timely decisions for HCT candidates.

HSCT with mismatched unrelated donors: Bone marrow versus peripheral blood stem cells sources in pediatric patients

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (HSCT) from an unrelated HLA-mismatched donor (MMUD) is one of the alternatives where an HLA-matched donor is not found. The aim of this study was to compare bone marrow (BM) versus peripheral blood stem cells (PBSC) as hematopoietic rescue following allogeneic unrelated mismatched stem cell transplantation (MMUD).

METHODS

The patients were divided into two groups: 43 pediatric patients were treated with BM and 17 pediatric patients with PBSC. The study was registered at ClinicalTrials.gov NCT04598789.

RESULTS

The 3-year Overall Survival (OS) was 74% versus 31% (p = .0011). Transplant related mortality (TRM) was 16% versus 33% (p = .025), and relapse incidence (RI) was 16% versus 35% (p = .005). The day-100 acute Graft-versus-host disease (GvHD) incidence grade II-IV and III-IV was 30% versus 28% (p = NS) and 17% versus 17% (p = NS). The 3-year chronic GvHD incidence was 22% versus 33% (p = NS).

CONCLUSION

Despite all the limits of this retrospective study we were able to show how the combination of BM and ATG is able to prevent GvHDs and guarantee a high OS. Future studies addressing the issue of a post-transplant cellular therapy approach may potentially reduce relapses when GvHD is absent.

HSCT with Mismatched Unrelated Donors (MMUD): A Comparison of Different Platforms for GvHD Prophylaxis

HSCT from an unrelated HLA-mismatched donor (MMUD) is one of the alternatives where an HLA-matched donor is not found. The aim of this study was to compare GvHD prophylaxis with anti-thymocyte globulin (ATG) vs. post-transplant cyclophosphamide (PT-Cy). Thirty-nine adult patients were uniformly treated with rabbit ATG-Cy-A-MTX and peripheral blood stem cell (PBSC) and 40 adult patients with PT-Cy-MMF-tacrolimus and PBSC. This retrospective study was registered at ClinicalTrials.gov NCT04598789. Three-year overall survival was 42% vs. 64% for ATG and PT-Cy (p < 0.0005), three-year treatment-related mortality (TRM) was 36% vs. 8% (p = 0.0033) and the three-year relapse incidence (RI) was 15% vs. 28% (p = NS), respectively. The incidences of day-100 GvHD graded II–IV and III–IV were 39% vs. 7% (p = 0.0006) and 11% vs. 0% (p = 0.04), respectively, whereas the three-year cGvHD incidences were 48% vs. 13% (p = 0.0005), respectively. We were able to show how PT-Cy can reduce the incidence of GvHDs and TRM in adults, but relapse remains an issue.

HLA-DRB3/4/5 Matching Improves Outcome of Unrelated Hematopoietic Stem Cell Transplantation

The HLA-DRB3/4/5 loci are closely linked to the HLA-DRB1 gene. Mismatches in these loci occur with a frequency of about 8%–12% in otherwise 10/10 HLA-matched transplant pairs. There is preliminary evidence that these disparities may associate with increased acute graft-versus-host disease (GvHD) rates. The aim of this study was to analyze a large cohort of German patients and their donors for HLA-DRB3/4/5 compatibility and to correlate the HLA-DRB3/4/5 matching status with the outcome of unrelated hematopoietic stem cell transplantation (uHSCT). To this end, 3,410 patients and their respective donors were HLA-DRB3/4/5 and HLA-DPB1 typed by amplicon-based next-generation sequencing (NGS). All patients included received their first allogeneic transplant for malignant hematologic diseases between 2000 and 2014. Mismatches in the antigen recognition domain (ARD) of HLA-DRB3/4/5 genes were correlated with clinical outcome. HLA-DRB3/4/5 incompatibility was seen in 12.5% (n = 296) and 17.8% (n = 185) of the 10/10 and 9/10 HLA-matched cases, respectively. HLA-DRB3/4/5 mismatches in the ARD associated with a worse overall survival (OS), as shown in univariate (5-year OS: 46.1% vs. 39.8%, log-rank p = 0.038) and multivariate analyses [hazard ratio (HR) 1.25, 95% CI 1.02–1.54, p = 0.034] in the otherwise 10/10 HLA-matched subgroup. The worse outcome was mainly driven by a significantly higher non-relapse mortality (HR 1.35, 95% CI 1.05–1.73, p = 0.017). In the 9/10 HLA-matched cases, the effect was not statistically significant. Our study results suggest that mismatches within the ARD of HLA-DRB3/4/5 genes significantly impact the outcome of otherwise fully matched uHSCT and support their consideration upon donor selection in the future.

BSHI guideline: HLA matching and donor selection for haematopoietic progenitor cell transplantation

A review of the British Society for Histocompatibility and Immunogenetics (BSHI) Guideline 'HLA matching and donor selection for haematopoietic progenitor cell transplantation' published in 2016 was undertaken by a BSHI appointed writing committee. Literature searches were performed and the data extracted were presented as recommendations according to the GRADE nomenclature.

Role of HLA-DP Expression in Graft-Versus-Host Disease After Unrelated Donor Transplantation

PURPOSE

The main aim of this study was to evaluate the significance of HLA-DPB1 expression in acute graft-versus-host disease (GVHD) after hematopoietic cell transplantation (HCT) from HLA-A, -B, -C, -DRB1, -DQB1-matched and -mismatched unrelated donors.

PATIENTS AND METHODS

Between January 1, 2017, and January 10, 2019, we assessed 19,136 patients who received HCT from an HLA-A, -B, -C, -DRB1, -DQB1-matched or -mismatched unrelated donor performed in Australia, the European Union, Japan, North America, and the United Kingdom between 1988 and 2016. Among transplant recipients with one HLA-DPB1 mismatch, the patient's mismatched HLA-DPB1 allotype was defined as low or high expression. Multivariable regression models were used to assess risks of GVHD associated with high expression relative to low expression HLA-DPB1 mismatches. The effect of increasing numbers of HLA-DPB1 mismatches on clinical outcome was assessed in HLA-mismatched transplant recipients.

RESULTS

In HLA-A, -B, -C, -DRB1,-DQB1-matched transplant recipients, donor mismatching against one high-expression patient HLA-DPB1 increased moderate (odds ratio [OR], 1.36; P = .001) and severe acute GVHD (OR, 1.32; P = .0016) relative to low-expression patient mismatches, regardless of the expression level of the donor's mismatched HLA-DPB1. Among transplant recipients with one HLA-A, -B, -C, -DRB1, or -DQB1 mismatch, the odds of acute GVHD increased with increasing numbers of HLA-DPB1 mismatches (OR, 1.23 for one; OR, 1.40 for two mismatches relative to zero mismatches for moderate GVHD; OR, 1.19 for one; OR, 1.40 for two mismatches relative to zero for severe GVHD), but not with the level of expression of the patient's mismatched HLA-DPB1 allotype.

CONCLUSION

The level of expression of patient HLA-DPB1 mismatches informs the risk of GVHD after HLA-A, -B, -C, -DRB1, -DQB1-matched unrelated HCT, and the total number of HLA-DPB1 mismatches informs the risk of GVHD after HLA-mismatched unrelated HCT. Prospective consideration of HLA-DPB1 may help to lower GVHD risks after transplantation.

Improved access to better HLA-matched hematopoietic cells for allogeneic transplant: analysis of donors and cord blood units selected for Canadian patients in 2018

BACKGROUND

Patients undergoing hematopoietic cell transplantation (HCT) often require use of an unrelated donor or cord blood unit (CBU). An understanding of evolving practices in graft selection is needed for optimization of donor recruitment and cord blood collection.

STUDY DESIGN AND METHODS

Each donor workup (WU) requested in 2018 involving a Canadian (CDN) patient and unique donor product or CBU was reviewed (n = 598). Degree of HLA match; product origin (domestic or international [INT]); and non-HLA factors including donor age, sex, cytomegalovirus (CMV), and ABO compatibility were analyzed for WUs that proceeded to transplant (n = 414). We also analyzed changes compared to a similar analysis performed in 2013.

RESULTS

The majority of transplants used matched unrelated donors (MUDs; n = 323; 78%) and were most often young (≤35 years), male, INT donors (n = 136). The proportion of transplants involving MUDs, as opposed to mismatched unrelated donors or CBUs, increased by 12.4% compared with 2013. When young, male, CDN MUDs were identified in patient search reports but not selected, CMV mismatching and ABO incompatibility were most likely to have influenced the decision to use an INT MUD. Consistent with global trends, CBU transplants decreased compared to 2013; however, the degree of HLA matching improved significantly, and 27% of transplanted CBUs were procured from the Canadian Blood Services Cord Blood Bank.

CONCLUSIONS

Access to MUDs and better HLA-matched CBUs by CDN patients has increased since 2013. Ongoing recruitment of young registrants and cord blood donors with diverse HLA haplotypes will support selection of donors with optimal non-HLA characteristics.

HLA Matching in Unrelated Stem Cell Transplantation up to Date

Unrelated hematopoietic stem cell transplantation (HSCT) has evolved from an experimental protocol to a potentially curative first-line treatment in certain disease instances. Factors enabling this transformation were the optimization of treatment protocols and supportive care as well as the availability of a large number of donors worldwide along with the higher quality and reliability of HLA typing. The main criterion for donor selection is HLA compatibility. In this review we discuss the current clinical evidence of HLA matching in unrelated HSCT. In this context, we address methodical aspects of transplantation immunobiology research and discuss the impact of locus and resolution of HLA differences. Furthermore, we address special constellations such as unidirectional mismatches or the presence of nonexpressed alleles as well as HLA alloimmunization and describe the perspective for HLA typing and matching strategies in the future, given the implementation of novel complete or near-complete gene typing approaches using next-generation sequencing short read technology, which are now entering the standard of clinical care.

Selection of unrelated donors and cord blood units for hematopoietic cell transplantation: guidelines from the NMDP/CIBMTR

Allogeneic hematopoietic cell transplantation involves consideration of both donor and recipient characteristics to guide the selection of a suitable graft. Sufficient high-resolution donor-recipient HLA match is of primary importance in transplantation with adult unrelated donors, using conventional graft-versus-host disease prophylaxis. In cord blood transplantation, optimal unit selection requires consideration of unit quality, cell dose and HLA-match. In this summary, the National Marrow Donor Program (NMDP) and the Center for International Blood and Marrow Transplant Research, jointly with the NMDP Histocompatibility Advisory Group, provide evidence-based guidelines for optimal selection of unrelated donors and cord blood units.

[Graft failure after allogeneic hematopoietic stem cell transplantation: Definition and risk factors]

Allogeneic hematopoietic stem cell transplantation is the only curative therapy for numerous malignant and non-malignant haematological diseases. A sustained engraftment of the donor stem cells is essential for transplant success and overall outcome. Graft failure is a rare but severe event after allogeneic hematopoietic stem cell transplantation. While different risk factors such as underlying disease, graft source or HLA matching have been found to be consistently associated with graft failure, other factors such as ABO mismatch graft-versus-host disease prophylaxis or infections, particularly viral reactivations, are more controversial. In this article, we review the different factors associated with graft failure.

Clinical implications of HLA locus mismatching in unrelated donor hematopoietic cell transplantation: a meta-analysis

It remains controversial that the impacts of individual HLA locus mismatches on clinical outcomes of patients receiving unrelated-donor hematopoietic cell transplantation (HCT), as compared to HLA allele matched controls. We conducted a meta-analysis to address these issues. Four databases (PubMed, Embase, Web of Science and the Cochrane Library) were searched to select eligible studies. All donor-recipient pairs were high-resolution typing for HLA-A, -B, -C, -DRB1, DQB1 and DPB1 loci. Multivariate-adjusted hazard ratios (HRs) were extracted and pooled using a random-effects model. A total of 36 studies were included, with 100,072 patients receiving HCT. Surprisingly, we found that HLA-DQB1 locus mismatches had no significantly increased risk of multiple outcomes including acute and chronic graft-versus-host disease (GVHD), overall mortality and disease relapse (HR, 1.07; P = .153; HR, 1.07; P = .271; HR, 1.09; P = .230; HR, 1.07; P = .142 and HR, 1.02; P = .806, respectively). Mismatched HLA-DPB1 was significantly associated with a reduced risk of disease relapse (HR, 0.74; P < .001) but not with increased risks of transplant-related mortality (TRM) and overall mortality (HR, 1.09; P = .591; I² = 74.2% and HR, 1.03; P = .460, respectively). In conclusion, HLA-DQB1 locus mismatches is a permissive mismatching. HLA-DPB1 locus mismatches significantly protect against leukemia relapse. Refining effects of individual HLA locus mismatches contributes to predicting prognosis of patients receiving unrelated donor HCT.

Directionality of non-permissive HLA-DPB1 T-cell epitope group mismatches does not improve clinical risk stratification in 8/8 matched unrelated donor hematopoietic cell transplantation

In 8/8 HLA-matched unrelated donor (UD) hematopoietic cell transplants (HCT), HLA-DPB1 mismatches between alleles from different T-cell epitope (TCE) groups (non-permissive mismatches) are associated with significantly higher risks of mortality compared with those between alleles from the same TCE group (permissive mismatches); however, the relevance of mismatch directionality, that is (host vs graft (uni-directional HvG), graft vs host (uni-directional GvH) or both (bi-directional) in the non-permissive setting is unknown. We show here significantly higher in vitro relative responses (RR) to bi-directional mismatches compared with uni-directional HvG or GvH mismatches in a total of 420 one-way mixed lymphocyte reactions between 10/10 matched pairs (RR 27.5 vs 7.5 vs 15.5, respectively, P<0.001). However, in 3281 8/8 matched UD HCT for leukemia or myelodysplastic syndrome, the hazards of transplant-related mortality (TRM) were similar for uni-directional HvG or GvH mismatches and bi-directional mismatches (hazard ratio (HR) 1.32, P=0.001 vs HR 1.28, P=0.005 and HR 1.34, P=0.046), compared with permissive mismatches. Similar results were observed for overall survival. No statistical differences between the uni- and the bi-directional non-permissive groups were detected in pairwise comparisons for any of the outcomes tested. We conclude that consideration of directionality does not improve risk stratification by non-permissive HLA-DPB1 TCE mismatches in UD searches.

Increased age-associated mortality risk in HLA-mismatched hematopoietic stem cell transplantation

We investigated a possible interaction between age-associated risk and HLA-mismatch associated risk on prognosis in different age categories of recipients of unrelated hematopoietic stem cell transplants (HSCT) (n=3019). Patients over 55 years of age transplanted with 8/10 donors showed a mortality risk of 2.27 (CI 1.70–3.03, P<0.001) and 3.48 (CI 2.49–4.86, P<0.001) when compared to 10/10 matched patients in the same age group and to 10/10 matched patients aged 18–35 years, respectively. Compared to 10/10 matched transplantations within each age category, the Hazards Ratio for 8/10 matched transplantation was 1.14, 1.40 and 2.27 in patients aged 18–35 years, 36–55 and above 55 years. Modeling age as continuous variable showed different levels of risk attributed to age at the time of transplantation [OS: 10/10: Hazards Ratio 1.015 (per life year); 9/10: Hazards Ratio: 1.019; 8/10: Hazards Ratio 1.026]. The interaction term was significant for 8/10 transplantations (P=0.009). Findings for disease-free survival and transplant-related mortality were similar. Statistical models were stratified for diagnosis and included clinically relevant predictors except cytomegalovirus status and Karnofsky performance status. The risk conferred by age at the time of transplantation varies according to the number of HLA-mismatches and leads to a disproportional increase in risk for elderly patients, particularly with double mismatched donors. Our findings highlight the importance of HLA-matching, especially in patients over 55 years of age, as HLA-mismatches are less well tolerated in these patients. The interaction between age-associated risk and HLA-mismatches should be considered in donor selection and in the risk assessment of elderly HSCT recipients.

Milestones of Hematopoietic Stem Cell Transplantation - From First Human Studies to Current Developments

Since the early beginnings, in the 1950s, hematopoietic stem cell transplantation (HSCT) has become an established curative treatment for an increasing number of patients with life-threatening hematological, oncological, hereditary, and immunological diseases. This has become possible due to worldwide efforts of preclinical and clinical research focusing on issues of transplant immunology, reduction of transplant-associated morbidity, and mortality and efficient malignant disease eradication. The latter has been accomplished by potent graft-versus-leukemia (GvL) effector cells contained in the stem cell graft. Exciting insights into the genetics of the human leukocyte antigen (HLA) system allowed improved donor selection, including HLA-identical related and unrelated donors. Besides bone marrow, other stem cell sources like granulocyte-colony stimulating-mobilized peripheral blood stem cells and cord blood stem cells have been established in clinical routine. Use of reduced-intensity or non-myeloablative conditioning regimens has been associated with a marked reduction of non-hematological toxicities and eventually, non-relapse mortality allowing older patients and individuals with comorbidities to undergo allogeneic HSCT and to benefit from GvL or antitumor effects. Whereas in the early years, malignant disease eradication by high-dose chemotherapy or radiotherapy was the ultimate goal; nowadays, allogeneic HSCT has been recognized as cellular immunotherapy relying prominently on immune mechanisms and to a lesser extent on non-specific direct cellular toxicity. This chapter will summarize the key milestones of HSCT and introduce current developments.

Matching for the MICA-129 polymorphism is beneficial in unrelated hematopoietic stem cell transplantation

Major histocompatibility complex class I polypeptide-related sequence A (MICA) is a highly polymorphic ligand of the activating NKG2D receptor on natural killer (NK) cells, γδ-T cells, and NKT cells. MICA incompatibilities have been associated with an increased graft-versus-host disease (GVHD) incidence, and the MICA-129 (met/val) dimorphism has been shown to influence NKG2D signaling in unrelated hematopoietic stem cell transplantation (uHSCT). We investigated the effect of MICA matching on survival after uHSCT. We sequenced 2172 patients and their respective donors for MICA. All patients and donors were high-resolution HLA-typed and matched for 10/10 (n = 1379), 9/10 (n = 636), or 8/10 (n = 157) HLA alleles. Within each HLA match group, cases matched and mismatched for MICA and MICA-129 were analyzed for the end points overall survival (OS), disease-free survival (DFS), nonrelapse mortality (NRM), relapse-incidence (RI), and GVHD. Mismatches at the MICA locus as well as MICA-129 increased with the number of HLA mismatches (MICA mismatched 10/10, 9.2% [n = 127]; 9/10, 22.3% [n = 142]; 8/10, 38.2% [n = 60]; MICA-129 mismatched 10/10, 3.9% [n = 54]; 9/10, 10.2% [n = 65]; 8/10, 17.2% [n = 27]). Adverse OS was observed in the 10/10 match group if MICA-129 was mismatched (10/10, hazard ratio [HR], 1.77; confidence interval [CI], 1.22-2.57; P = .003). MICA-129 mismatches correlated with a significantly worse outcome for DFS in the 10/10 HLA match group (HR, 1.77; CI, 1.26-2.50; P = .001). Higher rates of aGVHD were seen in MICA-129 mismatched cases. Our results indicate that MICA-129 matching is relevant in uHSCT. Prospective typing of patients and donors in unrelated donor search may identify mismatches for MICA-129, and compatible donor selection may improve outcome for this small but high-risk subgroup.

Mismatched unrelated donor transplantation

There are now more than 25 million volunteer donors registered worldwide for patients in need of a life-saving hematopoietic cell transplant to cure blood disorders. Although a human leukocyte antigen (HLA)-matched donor remains the preferred stem cell source for transplantation, the use of a donor with limited HLA mismatching may be considered. Significant advances in clinical and basic research have been instrumental in furthering the understanding of donor-recipient HLA mismatches that are better tolerated than other mismatches. An increased appreciation of the role of regulatory region variation that affects the level of HLA expression provides new approaches for the selection of HLA-mismatched donors.

HLA mismatching as a strategy to reduce relapse after alternative donor transplantation

Human leukocyte antigen (HLA) mismatches are targets of alloreactive T cells, mediators of graft-versus-leukemia (GvL) and graft-versus-host disease (GvHD) after alternative donor transplantation. Exploitation of HLA mismatching in order to reduce relapse is hampered by necessary interventions aimed at controlling GvHD on the one hand, and by the possibility of immune escape through selective loss of mismatched HLA in relapsing leukemia on the other. Retrospective studies reporting the impact of HLA mismatches on post-transplant relapse need to be interpreted with caution, due to many confounding factors, including disease and use of T-cell depletion, and to be constantly updated to the rapidly changing clinical protocols. Current evidence suggests similar relapse rates for 8/8, 7/8 HLA-matched unrelated, T-cell-replete haploidentical and umbilical cord blood transplantation; however, investigations of locus-specific effects are still scarce in the latter two settings. In unrelated transplantation, a specific role for mismatches at HLA-C and HLA-DPB1, and therein of permissive mismatches defined on the basis of T-cell alloreactivity and/or expression levels, in reducing relapse has been demonstrated in independent studies. This observation suggests new approaches to utilize HLA matching in unrelated donor searches, and the need for further research in the field.

HLA Mismatch Is Associated with Worse Outcomes after Unrelated Donor Reduced-Intensity Conditioning Hematopoietic Cell Transplantation: An Analysis from the Center for International Blood and Marrow Transplant Research

Over the past 2 decades, reduced-intensity conditioning allogeneic hematopoietic cell transplantation (RIC HCT) has increased substantially. Many patients do not have fully HLA-matched donors, and the impact of HLA mismatch on RIC HCT has not been examined in large cohorts. We analyzed 2588 recipients of 8/8 HLA-high resolution matched (n = 2025) or single-locus mismatched (n = 563) unrelated donor (URD) RIC HCT from 1999 to 2011. Overall survival (OS) was the primary outcome. Secondary endpoints included treatment-related mortality (TRM), relapse, disease-free survival (DFS), and acute/chronic graft-versus-host disease (GVHD). Adjusted 1- and 3-year OS was better in 8/8- versus 7/8-matched recipients (54.7% versus 48.8%, P = .01, and 37.4% versus 30.9%, P = .005, respectively). In multivariate models 7/8 URD RIC HCT recipients had more grades II to IV acute GVHD (RR = 1.29, P = .0034), higher TRM (RR = 1.52, P < .0001), and lower DFS (RR = 1.12, P = .0015) and OS (RR = 1.25, P = .0001), with no difference in relapse or chronic GVHD. In subgroup analysis, inferior transplant outcomes were noted regardless of the HLA allele mismatched. Previously reported permissive mismatches at HLA-C (C*03:03/C*03:04) and HLA-DP1 (based on T cell-epitope matching) were not associated with better outcomes. Although feasible, single-locus mismatch in RIC URD HCT is associated with inferior outcomes.

Recommendations for donor human leukocyte antigen assessment and matching for allogeneic stem cell transplantation: consensus opinion of the Blood and Marrow Transplant Clinical Trials Network (BMT CTN)

The Blood and Marrow Transplant Clinical Trials Network (BMT CTN) conducts large, multi-institutional clinical trials with the goal of improving the outcomes of hematopoietic cell transplantation (HCT) for patients with life-threatening disorders. Well-designed HCT trials benefit from standardized criteria for defining diagnoses, treatment plans, and graft source selection. In this perspective, we summarize evidence supporting criteria for the selection of related and unrelated adult volunteer progenitor cell donors or umbilical cord blood units. These standardized criteria for graft source selection have been adopted by the BMT CTN to enhance the interpretation of clinical findings within and among future clinical protocols.

A prognostic score for acute graft-versus-host disease based on biomarkers: a multicentre study

BACKGROUND

Graft-versus-host disease (GVHD) is the major cause of non-relapse mortality after allogeneic haemopoietic stem-cell transplantation (SCT). The severity of symptoms at the onset of GVHD does not accurately define risk, and thus most patients are treated alike with high dose systemic corticosteroids. We aimed to define clinically meaningful risk strata for patients with newly diagnosed acute GVHD using plasma biomarkers.

METHODS

Between April 13, 2000, and May 7, 2013, we prospectively collected plasma from 492 SCT patients with newly diagnosed acute GVHD and randomly assigned (2:1) using a random number generator, conditional on the final two datasets having the same median day of onset, into training (n=328) and test (n=164) sets. We used the concentrations of three recently validated biomarkers (TNFR1, ST2, and Reg3α) to create an algorithm that computed the probability of non-relapse mortality 6 months after GVHD onset for individual patients in the training set alone. We rank ordered the probabilities and identified thresholds that created three distinct non-relapse mortality scores. We evaluated the algorithm in the test set, and again in an independent validation set of an additional 300 patients who underwent stem cell transplant and were enrolled on multicentre clinical trials of primary therapy for acute GVHD.

FINDINGS

In all three datasets (training, test, and validation), the cumulative incidence of 6-month non-relapse mortality significantly increased as the Ann Arbor GVHD score increased. In the multicentre validation set, scores were 8% (95% CI 3-16) for score 1, 27% (20-34) for score 2, and 46% (33-58) for score 3 (p<0·0001). Conversely, the response to primary GVHD treatment within 28 days decreased as the GVHD score increased 86% for score 1, 67% for score 2, and 46% for score 3 in the multicentre validation set, p<0·0001).

INTERPRETATION

Biomarker-based scores can be used to guide risk-adapted therapy at the onset of acute GVHD. High risk patients with a score of 3 are candidates for intensive primary therapy, while low risk patients with a score of 1 are candidates for rapid tapers of systemic steroid therapy.

FUNDING

The National Cancer Institute, the National Heart, Lung, and Blood Institute, the National Institute of Allergy and Infectious Diseases, the Doris Duke Charitable Fund, the American Cancer Society, and the Judith Devries Fund.

Impact of HLA mismatch direction on the outcome of unrelated bone marrow transplantation: a retrospective analysis from the Japan Society for Hematopoietic Cell Transplantation

The relative desirability of an unrelated donor with a bidirectional 1-locus mismatch (1MM-Bi), a 1-locus mismatch only in the graft-versus-host direction (1MM-GVH), or a 1-locus mismatch only in the host-versus-graft direction (1MM-HVG) is not yet clear. We analyzed adult patients with leukemia or myelodysplastic syndrome who received a first allogeneic stem cell transplant from an HLA-A, -B, -C, and -DRB1 matched or 1-allele mismatched unrelated donor in Japan. The effects of 1MM-Bi (n = 1020), 1MM-GVH (n = 83), and 1MM-HVG (n = 83) compared with a zero mismatch (0MM) (n = 2570) were analyzed after adjusting for other significant variables. The risk of grades III to IV acute graft-versus-host disease (GVHD) was higher with marginal significance in the 1MM-GVH group than in the 0MM group (hazard ratio, 1.85; P = .014). However, there was no significant difference in overall or nonrelapse mortality between the 1MM-GVH and 0MM groups. There was no significant difference in acute GVHD or overall or nonrelapse mortality between the 1MM-HVG and 0MM groups. The risks of acute GVHD and overall mortality were significantly higher in the 1MM-Bi group than in the 0MM group. These findings indicate that unrelated donors with 1MM-GVH and 1MM-HVG are both good candidates for patients without an HLA-matched unrelated donor in a Japanese cohort.

High-resolution HLA matching in hematopoietic stem cell transplantation: a retrospective collaborative analysis

HLA mismatches at the allele and antigen level (possibly with the exception of HLA-DQB1) should be treated equally in donor selection. HLA mismatches at >1 locus (including HLA-DQB1) have additive detrimental effects.