Good engraftment after reduced intensity targeted busulfan-based conditioning and matched related donor hematopoietic cell transplantation in hemoglobinopathies.

BACKGROUND: Hematopoietic cell transplantation (HCT) is an established curative therapy for transfusion-dependent thalassemia (TDT) and sickle cell disease (SCD). The latest American Society of Hematology guidelines recommend myeloablative preparative regimen in patients under 18 years of age. PROCEDURE: The objective was to demonstrate safety and efficacy of a reduced intensity conditioning (RIC) regimen including high-dose fludarabine, anti-thymocyte globulin, and targeted busulfan as a single alkylator to sub-myeloablative exposures. RESULTS: Between 2012 and 2021, 11 patients with SCD and five patients with TDT and matched related donor (MRD) HCT were included. The median age at transplantation was 8.3 years (range: 3.7-18.8 years). The median administered busulfan AUC was 67.4 mg/L×h (range: 60.7-80 mg/L×h). Overall survival was 93.8% and event-free survival 87.5% with one engrafted SCD patient with pre-existing moyamoya disease succumbing after drainage of a subdural hematoma. One SCD patient developed a secondary graft failure and was treated with a second HCT. Myeloid chimerism was full in all other patients with a median follow-up time of 4.1 years (range: 2.0-11.1 years), whereas T-cell donor chimerism was frequently mixed. CONCLUSION: This RIC conditioning followed by MRD HCT is sufficiently myeloablative to cure pediatric patients with hemoglobinopathies without the need for additional total body irradiation or thiotepa.

Reducing Mortality and Morbidity in Children with Severe Combined Immunodeficiency in Switzerland: the Role of Newborn Screening.

Newborn screening (NBS) for severe combined immunodeficiency (SCID) has been introduced in various countries with the aim of reducing morbidity and mortality. However, studies analyzing outcomes before and after the implementation of NBS programs remain limited. This study sought to compare the outcomes of SCID patients identified through Switzerland's national SCID NBS program, introduced in January 2019, with those of a historical cohort diagnosed between 2007 and 2019. The study included seven patients (32%) identified through NBS, and 15 (68%) born before NBS implementation and diagnosed based on clinical signs. Children in the NBS group were younger at diagnosis (median age 9 days vs 9 months, P = .002) and at hematopoietic stem cell transplantation (HSCT, median age 5 months vs 11 months, P = .003) compared to the clinical group. The NBS group had a lower incidence of infections before HSCT (29% vs 93%, P = .004). Although not statistically significant, the overall survival rate on last follow-up was higher in the NBS group (86% vs 67%, P = .62). Importantly, patients with active infections undergoing HSCT had a significantly lower overall survival probability compared to those without (P = .01). In conclusion, the introduction of NBS in Switzerland has led to earlier and often asymptomatic diagnosis of affected children, enabling timely intervention, infection prevention, and prompt treatment. These factors have contributed to higher survival rates in the NBS group. These findings underscore the critical importance of NBS for SCID, offering potential life-saving benefits through early detection and intervention.

Hematopoietic cell transplantation and cellular therapies in Switzerland. Evolution over 25 years. A report from the stem cell transplantation and cellular therapies working groups of the SBST 1997-2021.

The Swiss Blood Stem Cell Transplantation and Cellular Therapy Group (SBST) leads a mandatory national registry for all hematopoietic stem cell transplants (HCT) and cellular therapies. After 25 years, information was available for 11,226 patients receiving an HCT (4031 allogeneic and 7195 autologous), including 925 pediatric patients. We compared patient characteristics and outcome by quinquennia 1997-2001, 2002-2006, 2007-2011, 2012-2016, and 2017-2021. There were numerous changes over time. Allogeneic transplant recipients became older (median age 33.7 vs. 54.3) and had more frequently unrelated donors and reduced intensity conditioning in later quinquennia. Similarly, age increased for recipients of autologous HCT (median 48.3 vs. 59.9). We did not see a significant drop in transplant activity during the SARS-CoV-2 pandemic. Analysis of outcome showed overall survival (relative risk (RR) of death 0.664 (0.529-0.832) and progression free survival (RR 0.708 (0.577-0.870) being improved over time comparing the latest to the first quinquennium adjusting for risk factors. Non-relapse mortality decreased in recipients of allogeneic HCT (RR: 0.371 (0.270-0.509)) over time but relapse risks did not. Outcome of autologous HCT improved as well across quinquennia, this improvement was mainly due to decreased relapse risks (RR 0.681 (0.597-0.777)), possibly related to maintenance treatment or rescue treatment for relapse mainly in myeloma patients. Cellular therapies other than allogeneic or autologous HCT, particularly chimeric antigen receptor T-cells (CAR-T) treatment have started to increase after 2019, year of approval of the first commercial CAR-T product in Switzerland. Data on chimeric antigen receptor T-cell treatment are too early for comparative analyses. Detailed analyses of changes over time are presented. This study includes all HCTs, and cellular therapies, data useful for quality assurance programs, health care cost estimation and benchmarking. Between 50% and 60% of patients are long-term survivors after both types of HCT, indicating growing populations of surviving patients requiring long-term care.

Low rate of nonrelapse mortality in under-4-year-olds with ALL given chemotherapeutic conditioning for HSCT: a phase 3 FORUM study.

ABSTRACT: Allogeneic hematopoietic stem cell transplantation (HSCT) is highly effective for treating pediatric high-risk or relapsed acute lymphoblastic leukemia (ALL). For young children, total body irradiation (TBI) is associated with severe late sequelae. In the FORUM study (NCT01949129), we assessed safety, event-free survival (EFS), and overall survival (OS) of 2 TBI-free conditioning regimens in children aged <4 years with ALL. Patients received fludarabine (Flu), thiotepa (Thio), and either busulfan (Bu) or treosulfan (Treo) before HSCT. From 2013 to 2021, 191 children received transplantation and were observed for ≥6 months (median follow-up: 3 years). The 3-year OS was 0.63 (95% confidence interval [95% CI], 0.52-0.72) and 0.76 (95% CI, 0.64-0.84) for Flu/Thio/Bu and Flu/Thio/Treo (P = .075), respectively. Three-year EFS was 0.52 (95% CI, 0.41-0.61) and 0.51 (95% CI, 0.39-0.62), respectively (P = .794). Cumulative incidence of nonrelapse mortality (NRM) and relapse at 3 years were 0.06 (95% CI, 0.02-0.12) vs 0.03 (95% CI: <0.01-0.09) (P = .406) and 0.42 (95% CI, 0.31-0.52) vs 0.45 (95% CI, 0.34-0.56) (P = .920), respectively. Grade >1 acute graft-versus-host disease (GVHD) occurred in 29% of patients receiving Flu/Thio/Bu and 17% of those receiving Flu/Thio/Treo (P = .049), whereas grade 3/4 occurred in 10% and 9%, respectively (P = .813). The 3-year incidence of chronic GVHD was 0.07 (95% CI, 0.03-0.13) vs 0.05 (95% CI, 0.02-0.11), respectively (P = .518). In conclusion, both chemotherapeutic conditioning regimens were well tolerated and NRM was low. However, relapse was the major cause of treatment failure. This trial was registered at www.clinicaltrials.gov as #NCT01949129.

Exposure-response analysis of alemtuzumab in pediatric allogeneic HSCT for nonmalignant diseases: the ARTIC study.

Alemtuzumab (anti-CD52 antibody) is frequently prescribed to children with nonmalignant diseases undergoing allogeneic hematopoietic stem cell transplantation (HSCT) to prevent graft failure (GF) and acute graft-versus-host disease (aGVHD). The aim of this multicenter study was the characterization of alemtuzumab population pharmacokinetics to perform a novel model-based exposure-response analysis in 53 children with nonmalignant immunological or hematological disease and a median age of 4.4 years (interquartile range [IQR], 0.8-8.7). The median cumulative alemtuzumab dose was 0.6 mg/kg (IQR, 0.6-1) administered over 2 to 7 days. A 2-compartment population pharmacokinetics model with parallel linear and nonlinear elimination including allometrically scaled bodyweight (median, 17.50 kg; IQR, 8.76-33.00) and lymphocyte count at baseline (mean, 2.24 × 109/L; standard deviation ± 1.87) as significant pharmacokinetic predictors was developed using nonlinear mixed effects modeling. Based on the model-estimated median concentration at day of HSCT (0.77 µg/mL; IQR, 0.33-1.82), patients were grouped into a low- (≤0.77 µg/mL) or high- (>0.77 µg/mL) exposure groups. High alemtuzumab exposure at day of HSCT correlated with delayed CD4+ and CD8+ T-cell reconstitution (P value < .0001) and increased risk of GF (P value = .043). In contrast, alemtuzumab exposure did not significantly influence the incidence of aGVHD grade ≥2, mortality, chimerism at 1 year, viral reactivations, and autoimmunity at a median follow-up of 3.3 years (IQR, 2.5-8.0). In conclusion, this novel population pharmacokinetics model is suitable for individualized intravenous precision dosing to predict alemtuzumab exposure in pediatric allogeneic HSCT for nonmalignant diseases, aiming at the achievement of early T-cell reconstitution and prevention of GF in future prospective studies.

Population Pharmacokinetic Modeling for Twice-Daily Intravenous Busulfan in a Large Cohort of Pediatric Patients Undergoing Hematopoietic Stem Cell Transplantation-A 10-Year Single-Center Experience.

Reaching target exposure of busulfan-based conditioning prior to hematopoietic stem cell transplantation is vital for favorable therapy outcomes. Yet, a wide inter-patient and inter-occasion variability in busulfan exposure has been reported, especially in children. We aimed to identify factors associated with the variability of busulfan pharmacokinetics in 124 consecutive patients transplanted at the University Children's Hospital Zurich between October 2010 and February 2020. Clinical data and busulfan plasma levels after twice-daily intravenous administration were analyzed retrospectively by population pharmacokinetic modeling. The volume of distribution correlated with total body water. The elimination rate constant followed an age-dependent maturation function, as previously suggested, and correlated with the levels of serum albumin. Acute lymphoblastic leukemia reduced busulfan clearance by 20%. Clearance significantly decreased by 17% on average from the start to the third day of busulfan administration, in agreement with other studies. An average reduction of 31% was found in patients with hemophagocytic lymphohistiocytosis and X-linked lymphoproliferative disease. In conclusion, we demonstrate that in addition to known factors, underlying disease and serum albumin significantly impact busulfan pharmacokinetics in pediatric patients; yet, substantial unexplained variability in some patients remained. Thus, we consider repeated pharmacokinetic assessment essential to achieve the desired target exposure in twice-daily busulfan administration.

Incidence of subsequent malignancies after total body irradiation-based allogeneic HSCT in children with ALL - long-term follow-up from the prospective ALL-SCT 2003 trial.

Total body irradiation (TBI)-based conditioning is associated with superior leukemia-free survival in children with ALL undergoing HSCT. However, the risk for subsequent malignant neoplasms (SMN) remains a significant concern. We analyzed 705 pediatric patients enrolled in the prospective ALL-SCT-BFM-2003 trial and its subsequent registry. Patients >2 years received conditioning with TBI 12 Gy/etoposide (n = 558) and children ≤2 years of age or with contraindications for TBI received busulfan/cyclophosphamide/etoposide (n = 110). The 5- and 10-year cumulative incidence of SMN was 0.02 ± 0.01 and 0.13 ± 0.03, respectively. In total, 39 SMN (34 solid tumors, 5 MDS/AML) were diagnosed in 33 patients at a median of 5.8 years (1.7-13.4), exclusively in the TBI group. Of 33 affected patients, 21 (64%) are alive at a median follow-up of 5.1 years (0-9.9) after diagnosis of their first SMN. In univariate analysis, neither age at HSCT, donor type, acute GVHD, chronic GVHD, nor CMV constituted a significant risk factor for SMN. The only significant risk factor was TBI versus non-TBI based conditioning. This analysis confirms and quantifies the increased risk of SMN in children with ALL after conditioning with TBI. Future strategies to avoid TBI will need careful tailoring within prospective, controlled studies to prevent unfavorable outcomes.

Hematopoietic stem cell transplantation for adolescents and adults with inborn errors of immunity: an EBMT IEWP study.

Allogeneic hematopoietic stem cell transplantation (HSCT) is the gold standard curative therapy for infants and children with many inborn errors of immunity (IEI), but adolescents and adults with IEI are rarely referred for transplant. Lack of published HSCT outcome data outside small, single-center studies and perceived high risk of transplant-related mortality have delayed the adoption of HSCT for IEI patients presenting or developing significant organ damage later in life. This large retrospective, multicenter HSCT outcome study reports on 329 IEI patients (age range, 15-62.5 years at HSCT). Patients underwent first HSCT between 2000 and 2019. Primary endpoints were overall survival (OS) and event-free survival (EFS). We also evaluated the influence of IEI-subgroup and IEI-specific risk factors at HSCT, including infections, bronchiectasis, colitis, malignancy, inflammatory lung disease, splenectomy, hepatic dysfunction, and systemic immunosuppression. At a median follow-up of 44.3 months, the estimated OS at 1 and 5 years post-HSCT for all patients was 78% and 71%, and EFS was 65% and 62%, respectively, with low rates of severe acute (8%) or extensive chronic (7%) graft-versus-host disease. On univariate analysis, OS and EFS were inferior in patients with primary antibody deficiency, bronchiectasis, prior splenectomy, hepatic comorbidity, and higher hematopoietic cell transplant comorbidity index scores. On multivariable analysis, EFS was inferior in those with a higher number of IEI-associated complications. Neither age nor donor had a significant effect on OS or EFS. We have identified age-independent risk factors for adverse outcome, providing much needed evidence to identify which patients are most likely to benefit from HSCT.

Successful Induction of Specific Immunological Tolerance by Combined Kidney and Hematopoietic Stem Cell Transplantation in HLA-Identical Siblings.

Induction of immunological tolerance has been the holy grail of transplantation immunology for decades. The only successful approach to achieve it in patients has been a combined kidney and hematopoietic stem cell transplantation from an HLA-matched or -mismatched living donor. Here, we report the first three patients in Europe included in a clinical trial aiming at the induction of tolerance by mixed lymphohematopoietic chimerism after kidney transplantation. Two female and one male patient were transplanted with a kidney and peripherally mobilized hematopoietic stem cells from their HLA-identical sibling donor. The protocol followed previous studies at Stanford University: kidney transplantation was performed on day 0 including induction with anti-thymocyte globulin followed by conditioning with 10x 1.2 Gy total lymphoid irradiation and the transfusion of CD34+ cells together with a body weight-adjusted dose of donor T cells on day 11. Immunosuppression consisted of cyclosporine A and steroids for 10 days, cyclosporine A and mycophenolate mofetil for 1 month, and then cyclosporine A monotherapy with tapering over 9-20 months. The 3 patients have been off immunosuppression for 4 years, 19 months and 8 months, respectively. No rejection or graft-versus-host disease occurred. Hematological donor chimerism was stable in the first, but slowly declining in the other two patients. A molecular microscope analysis in patient 2 revealed the genetic profile of a normal kidney. No relevant infections were observed, and the quality of life in all three patients is excellent. During the SARS-CoV-2 pandemic, all three patients were vaccinated with the mRNA vaccine BNT162b2 (Comirnaty®), and they showed excellent humoral and in 2 out 3 patients also cellular SARS-CoV-2-specific immunity. Thus, combined kidney and hematopoietic stem cell transplantation is a feasible and successful approach to induce specific immunological tolerance in the setting of HLA-matched sibling living kidney donation while maintaining immune responsiveness to an mRNA vaccine (ClinicalTrials.gov: NCT00365846).

Dynamics of recent thymic emigrants in pediatric recipients of allogeneic hematopoetic stem cell transplantation.

After allogeneic hematopoietic stem cell transplantation (allo-HSCT), the recurrence of recent thymic emigrants (RTE) and self-tolerant T cells indicate normalized thymic function. From 2008 to 2019, we retrospectively analyzed the RTE-reconstitution rate and the minimal time to reach normal age-specific first percentiles for CD31+CD45RA+CD4+T cells in 199 pediatric patients after allo-HSCT for various malignant and non-malignant diseases. The impact of clinically significant graft-versus-host disease (GvHD), age at transplantation, underlying disease and cumulative area under the curve of busulfan on RTE-reemergence was assessed in multivariable longitudinal analysis. RTE-reconstitution (coefficient -0.24, 95% CI -0.33 to -0.14, p < 0.001) was slowed down by GvHD and the time to reach P1 was significantly longer (Event Time Ratio 1.49, 95% CI 1.25 to 1.78, p < 0.001). Older age at transplantation was also associated with a slower RTE-reconstitution (coefficient -0.028, 95% CI -0.04 to -0.02, p < 0.001) and time to reach P1 was significantly longer (Event Time Ratio 1.03, 95% CI 1.02 to 1.05, p < 0.001). RTE-reconstitution velocity was not influenced by underlying disease or cumulative busulfan exposure. In summary, duration until thymic reactivation was independent of both conditioning intensity and underlying disease and was negatively influenced by older age and GvHD.

Hematopoietic stem cell transplantation for Wiskott-Aldrich syndrome: an EBMT Inborn Errors Working Party analysis.

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative treatment for patients affected by Wiskott-Aldrich syndrome (WAS). Reported HSCT outcomes have improved over time with respect to overall survival, but some studies have identified older age and HSCT from alternative donors as risk factors predicting poorer outcome. We analyzed 197 patients undergoing transplant at European Society for Blood and Marrow Transplantation centers between 2006 and 2017 who received conditioning as recommended by the Inborn Errors Working Party (IEWP): either busulfan (n = 103) or treosulfan (n = 94) combined with fludarabine ± thiotepa. After a median follow-up post-HSCT of 44.9 months, 176 patients were alive, resulting in a 3-year overall survival of 88.7% and chronic graft-versus-host disease (GVHD)-free survival (events include death, graft failure, and severe chronic GVHD) of 81.7%. Overall survival and chronic GVHD-free survival were not significantly affected by conditioning regimen (busulfan- vs treosulfan-based), donor type (matched sibling donor/matched family donor vs matched unrelated donor/mismatched unrelated donor vs mismatched family donor), or period of HSCT (2006-2013 vs 2014-2017). Patients aged <5 years at HSCT had a significantly better overall survival. The overall cumulative incidences of grade III to IV acute GVHD and extensive/moderate/severe chronic GVHD were 6.6% and 2.1%, respectively. Patients receiving treosulfan-based conditioning had a higher incidence of graft failure and mixed donor chimerism and more frequently underwent secondary procedures (second HSCT, unconditioned stem cell boost, donor lymphocyte infusion, or splenectomy). In summary, HSCT for WAS with conditioning regimens currently recommended by IEWP results in excellent survival and low rates of GVHD, regardless of donor or stem cell source, but age ≥5 years remains a risk factor for overall survival.

Association Between the Magnitude of Intravenous Busulfan Exposure and Development of Hepatic Veno-Occlusive Disease in Children and Young Adults Undergoing Myeloablative Allogeneic Hematopoietic Cell Transplantation.

Intravenous busulfan is widely used as part of myeloablative conditioning regimens in children and young adults undergoing allogeneic hematopoietic cell transplantation (HCT). Hepatic veno-occlusive disease/sinusoidal obstruction syndrome (VOD/SOS) is a serious clinical problem observed with busulfan-based conditioning HCT. The development of VOD/SOS may be associated with busulfan exposure. Getting more insight into the association between busulfan exposure and the development of VOD/SOS enables further optimization of dosing and treatment strategies. The objective of this study was to assess the association between the magnitude of busulfan exposure and the occurrence of VOD/SOS in children and young adults undergoing myeloablative conditioning with a busulfan-containing regimen before allogeneic HCT. In this observational study we included all patients who underwent allogeneic HCT with intravenous busulfan as part of the conditioning regimen at 15 pediatric transplantation centers between 2000 and 2015. The endpoint was the development of VOD/SOS. The magnitude of busulfan exposure was estimated using nonlinear mixed effect modeling and expressed as the maximal concentration (Cmax; day 1 and day 1 to 4 Cmax), cumulative area under the curve (AUC; day 1, highest 1-day AUC in 4 days, and 4-day cumulative AUC), cumulative time above a concentration of 300 µg/L, and clearance on day 1. A total of 88 out of 697 patients (12.6%) developed VOD/SOS. The number of alkylators in the conditioning regimen was a strong effect modifier; therefore we stratified the regression analysis for the number of alkylators. For patients receiving only busulfan as one alkylator (36.3%, n = 253), cumulative busulfan exposure (>78 mg × h/L) was associated with increased VOD/SOS risk (12.6% versus 4.7%; odds ratio [OR] = 2.95, 95% confidence interval [CI] 1.13 to 7.66). For individuals receiving busulfan with one or two additional alkylators (63.7%, n = 444), cumulative busulfan exposure (≤78 and >78 mg × h/L) did not further increase the risk of VOD/SOS (15.4% versus 15.2%; OR = 1.03, 95% CI 0.61 to 1.75). The effect of the magnitude of busulfan exposure on VOD/SOS risk in children and young adults undergoing HCT is dependent on the number of alkylators. In patients receiving busulfan as the only alkylator, higher cumulative busulfan exposure increased the risk of VOD/SOS, whereas in those receiving multiple alkylators, the magnitude of busulfan exposure did not further increase this risk.

Longitudinal lung function in childhood cancer survivors after hematopoietic stem cell transplantation.

Longitudinal data on pulmonary function after pediatric allogeneic or autologous hematopoietic stem cell transplantation (HSCT) are rare. We examined pulmonary function and associated risk factors in 5-year childhood cancer survivors (CCSs) longitudinally. We included 74 CCSs diagnosed between 1976 and 2010, treated with HSCT, and with at least two pulmonary function tests performed during follow-up. Median follow-up was 9 years (range 6-13). We described pulmonary function as z-scores for lung volumes (forced vital capacity [FVC], residual volume [RV], total lung capacity [TLC]), flows (forced expiratory volume in 1 s [FEV1], maximal mid-expiratory flow [MMEF]), and diffusion capacity for carbon monoxide (DLCO) and assessed associations with potential risk factors using multivariable regression analysis. The median z-scores for FEV1, FVC, and TLC were below the expected throughout the follow-up period. This was not the case for RV, MMEF and DLCO. Female gender, radiotherapy to the chest, and relapse were associated with lower z-scores of FEV1, FVC, MMEF, RV or DLCO. Childhood cancer survivors after HSCT are at risk of pulmonary dysfunction. The complex and multifactorial etiology of pulmonary dysfunction emphasizes the need for longitudinal prospective studies to better characterize the course and causes of pulmonary function impairment in CCSs.

Hematopoietic cell transplantation in severe combined immunodeficiency: The SCETIDE 2006-2014 European cohort.

BACKGROUND: Hematopoietic stem cell transplantation (HSCT) represents a curative treatment for patients with severe combined immunodeficiency (SCID), a group of monogenic immune disorders with an otherwise fatal outcome. OBJECTIVE: We performed a comprehensive multicenter analysis of genotype-specific HSCT outcome, including detailed analysis of immune reconstitution (IR) and the predictive value for clinical outcome. METHODS: HSCT outcome was studied in 338 patients with genetically confirmed SCID who underwent transplantation in 2006-2014 and who were registered in the SCETIDE registry. In a representative subgroup of 152 patients, data on IR and long-term clinical outcome were analyzed. RESULTS: Two-year OS was similar with matched family and unrelated donors and better than mismatched donor HSCT (P < .001). The 2-year event-free survival (EFS) was similar in matched and mismatched unrelated donor and less favorable in mismatched related donor (MMRD) HSCT (P < .001). Genetic subgroups did not differ in 2-year OS (P = .1) and EFS (P = .073). In multivariate analysis, pretransplantation infections and use of MMRDs were associated with less favorable OS and EFS. With a median follow-up of 6.2 years (range, 2.0-11.8 years), 73 of 152 patients in the IR cohort were alive and well without Ig dependency. IL-2 receptor gamma chain/Janus kinase 3/IL-7 receptor-deficient SCID, myeloablative conditioning, matched donor HSCT, and naive CD4 T lymphocytes >0.5 × 10e3/µL at +1 year were identified as independent predictors of favorable clinical and immunologic outcome. CONCLUSION: Recent advances in HSCT in SCID patients have resulted in improved OS and EFS in all genotypes and donor types. To achieve a favorable long-term outcome, treatment strategies should aim for optimal naive CD4 T lymphocyte regeneration.

Analysis of biological models to predict clinical outcomes based on HLA-DPB1 disparities in unrelated transplantation.

HLA compatibility is a key factor for survival after unrelated hematopoietic stem cell transplantation (HSCT). HLA-A, -B, -C, -DRB1, and -DQB1 are usually matched between donor and recipient. By contrast, HLA-DPB1 mismatches are frequent, although it is feasible to optimize donor selection and DPB1 matching with prospective typing. Because classical DPB1 allele mismatches are often unavoidable, however, several biological models have been developed to predict the optimal DPB1 mismatch combination for less graft-versus-host disease (GVHD) and better overall survival. In 909 recipient/donor pairs, we analyzed the role of 3 biological models: T-cell epitopes (TCEs) based on the immunogenicity of DPB1, cell surface expression of DPB1 molecules based on a single-nucleotide polymorphism located in the 3' untranslated region, and the Predicted Indirectly ReCognizable HLA Epitopes (PIRCHE) model based on the presentation of allogeneic peptides derived from mismatched HLA, compared with the classical allele mismatch. Matching for both DPB1 alleles remains the best option to prevent acute GVHD. In the situation of one DPB1 allele mismatch, the donor associated with the lowest acute GVHD risks is mismatched for an allele with a low expression profile in the recipient, followed by a permissive TCE3/4 mismatch and/or the absence of PIRCHE II potential against the recipient. In the context of 2 DPB1 mismatches, the same considerations apply for a permissive TCE3/4 mismatch and no PIRCHE II. By combining the biological models, the most favorable DPB1 constellation can be defined. This approach will help optimize donor selection and improve post-HSCT complications and patient prognosis.