Optimal Donor Selection Across Multiple Outcomes For Hematopoietic Stem Cell Transplantation By Bayesian Nonparametric Machine Learning.

Allogeneic hematopoietic cell transplantation (HCT) is one of the only curative treatment options for patients suffering from life-threatening hematologic malignancies; yet, the possible adverse complications can be serious even fatal. Matching between donor and recipient for 4 of the HLA genes is widely accepted and supported by the literature. However, among 8/8 allele matched unrelated donors, there is less agreement among centers and transplant physicians about how to prioritize donor characteristics like additional HLA loci (DPB1 and DQB1), donor sex/parity, CMV status, and age to optimize transplant outcomes. This leads to varying donor selection practice from patient to patient or via center protocols. Furthermore, different donor characteristics may impact different post transplant outcomes beyond mortality, including disease relapse, graft failure/rejection, and chronic graft-versus-host disease (components of event-free survival, EFS). We develop a general methodology to identify optimal treatment decisions by considering the trade-offs on multiple outcomes modeled using Bayesian nonparametric machine learning. We apply the proposed approach to the problem of donor selection to optimize overall survival and event-free survival, using a large outcomes registry of HCT recipients and their actual and potential donors from the Center for International Blood and Marrow Transplant Research (CIBMTR). Our approach leads to a donor selection strategy that favors the youngest male donor, except when there is a female donor that is substantially younger.

Measurable Residual FLT3 Internal Tandem Duplication Before Allogeneic Transplant for Acute Myeloid Leukemia.

Importance: Persistence of FLT3 internal tandem duplication (ITD) in adults with acute myeloid leukemia (AML) in first complete remission (CR) prior to allogeneic hematopoietic cell transplant (HCT) is associated with increased relapse and death after transplant, but the association between the level of measurable residual disease (MRD) detected and clinical outcome is unknown. Objective: To examine the association between pre-allogeneic HCT MRD level with relapse and death posttransplant in adults with AML in first CR. Design, Setting, and Participants: In this cohort study, DNA sequencing was performed on first CR blood from patients with FLT3-ITD AML transplanted from March 2013 to February 2019. Clinical follow-up was through May 2022. Data were analyzed from October 2022 to December 2023. Exposure: Centralized DNA sequencing for FLT3-ITD in pre-allogeneic HCT first CR blood using a commercially available kit. Main Outcomes and Measures: The primary outcomes were overall survival and cumulative incidence of relapse, with non-relapse-associated mortality as a competing risk post-allogeneic HCT. Kaplan-Meier estimations (log-rank tests), Cox proportional hazards models, and Fine-Gray models were used to estimate the end points. Results: Of 537 included patients with FLT3-ITD AML from the Pre-MEASURE study, 296 (55.1%) were female, and the median (IQR) age was 55.6 (42.9-64.1) years. Using the variant allele fraction (VAF) threshold of 0.01% or greater for MRD positivity, the results closely aligned with those previously reported. With no VAF threshold applied (VAF greater than 0%), 263 FLT3-ITD variants (median [range] VAF, 0.005% [0.0002%-44%]), and 177 patients (33.0%) with positive findings were identified. Multivariable analyses showed that residual FLT3-ITD was the variable most associated with relapse and overall survival, with a dose-dependent correlation. Patients receiving reduced-intensity conditioning without melphalan or nonmyeloablative conditioning had increased risk of relapse and death at any given level of MRD compared with those receiving reduced-intensity conditioning with melphalan or myeloablative conditioning. Conclusions and Relevance: This study provides generalizable and clinically applicable evidence that the detection of residual FLT3-ITD in the blood of adults in first CR from AML prior to allogeneic HCT is associated with an increased risk of relapse and death, particularly for those with a VAF of 0.01% or greater. While transplant conditioning intensification, an intervention not available to all, may help mitigate some of this risk, alternative approaches will be necessary for this high-risk population of patients who are underserved by the current standard of care.

Donor KIR genotype based outcome prediction after allogeneic stem cell transplantation: no land in sight.

Optimizing natural killer (NK) cell alloreactivity could further improve outcome after allogeneic hematopoietic cell transplantation (alloHCT). The donor's Killer-cell Immunoglobulin-like Receptor (KIR) genotype may provide important information in this regard. In the past decade, different models have been proposed aiming at maximizing NK cell activation by activating KIR-ligand interactions or minimizing inhibitory KIR-ligand interactions. Alternative classifications intended predicting outcome after alloHCT by donor KIR-haplotypes. In the present study, we aimed at validating proposed models and exploring more classification approaches. To this end, we analyzed samples stored at the Collaborative Biobank from HLA-compatible unrelated stem cell donors who had donated for patients with acute myeloid leukemia (AML) or myelodysplastic neoplasm (MDS) and whose outcome data had been reported to EBMT or CIBMTR. The donor KIR genotype was determined by high resolution amplicon-based next generation sequencing. We analyzed data from 5,017 transplants. The median patient age at alloHCT was 56 years. Patients were transplanted for AML between 2013 and 2018. Donor-recipient pairs were matched for HLA-A, -B, -C, -DRB1, and -DQB1 (79%) or had single HLA mismatches. Myeloablative conditioning was given to 56% of patients. Fifty-two percent of patients received anti-thymocyte-globulin-based graft-versus-host disease prophylaxis, 32% calcineurin-inhibitor-based prophylaxis, and 7% post-transplant cyclophosphamide-based prophylaxis. We tested several previously reported classifications in multivariable regression analyses but could not confirm outcome associations. Exploratory analyses in 1,939 patients (39%) who were transplanted from donors with homozygous centromeric (cen) or telomeric (tel) A or B motifs, showed that the donor cen B/B-tel A/A diplotype was associated with a trend to better event-free survival (HR 0.84, p=.08) and reduced risk of non-relapse mortality (NRM) (HR 0.65, p=.01). When we further dissected the contribution of B subtypes, we found that only the cen B01/B01-telA/A diplotype was associated with a reduced risk of relapse (HR 0.40, p=.04) while all subtype combinations contributed to a reduced risk of NRM. This exploratory finding has to be validated in an independent data set. In summary, the existing body of evidence is not (yet) consistent enough to recommend use of donor KIR genotype information for donor selection in routine clinical practice.

Donor whole blood DNA methylation is not a strong predictor of acute graft versus host disease in unrelated donor allogeneic haematopoietic cell transplantation.

Allogeneic hematopoietic cell transplantation (HCT) is used to treat many blood-based disorders and malignancies, however it can also result in serious adverse events, such as the development of acute graft-versus-host disease (aGVHD). This study aimed to develop a donor-specific epigenetic classifier to reduce incidence of aGVHD by improving donor selection. Genome-wide DNA methylation was assessed in a discovery cohort of 288 HCT donors selected based on recipient aGVHD outcome; this cohort consisted of 144 cases with aGVHD grades III-IV and 144 controls with no aGVHD. We applied a machine learning algorithm to identify CpG sites predictive of aGVHD. Receiver operating characteristic (ROC) curve analysis of these sites resulted in a classifier with an encouraging area under the ROC curve (AUC) of 0.91. To test this classifier, we used an independent validation cohort (n = 288) selected using the same criteria as the discovery cohort. Attempts to validate the classifier failed with the AUC falling to 0.51. These results indicate that donor DNA methylation may not be a suitable predictor of aGVHD in an HCT setting involving unrelated donors, despite the initial promising results in the discovery cohort. Our work highlights the importance of independent validation of machine learning classifiers, particularly when developing classifiers intended for clinical use.

Combined effect of unrelated donor age and HLA peptide-binding motif match status on HCT outcomes.

ABSTRACT: An HLA-mismatched unrelated donor who is class I peptide-binding motif (PBM)-matched is preferred over a PBM-mismatched donor. We hypothesized that using a younger donor (aged ≤35 years vs >35 years) could compensate for the inferior overall survival (OS) associated with PBM mismatches. We compared 6 groups: HLA-matched/younger donor (n = 10 531), HLA-matched/older donor (n = 3572), PBM-matched/younger donor (n = 357), PBM-matched/older donor (n = 257), PBM-mismatched/younger donor (n = 616), and PBM-mismatched/older donor (n = 339) in patients undergoing transplantation with conventional graft-versus-host disease prophylaxis. In multivariate analysis, HLA-matched/younger donors were associated with superior OS relative to any other group. Pairwise comparisons showed that donor age significantly impacted OS in both HLA-matched and HLA-mismatched groups. Moreover, younger donors appeared to negate the detrimental effect of PBM mismatching: the PBM-matched/younger donor group had similar OS as the HLA-matched/older donor group and the PBM-mismatched/younger donor group had similar OS as the PBM-matched/older donor group. Our study suggests that older unrelated donor age and PBM mismatching confer similarly adverse effects on OS and the impacts are additive, a finding which may widen the "acceptable" donor pool. The best OS is observed with HLA-matched/younger donors and the worst with PBM-mismatched/older donors. These findings should be validated with other data sets and with posttransplantation cyclophosphamide-based prophylaxis.

Donor germ-line variants associate with outcomes of allogeneic hematopoietic stem cell transplantation in patients with myelodysplastic syndromes.

Overall survival probability for MDS patients who underwent allo-HCT and were matched to donors that are wild-type (red) and heterozygous (blue) for the rs111224634 SNP.

HLA Haplotypes and Relapse After Hematopoietic Cell Transplantation.

PURPOSE: Recurrence of blood malignancy is the major cause of hematopoietic cell transplant failure. HLA class II molecules play a fundamental role in antitumor responses but the role of class II haplotypes is not known. METHODS: HLA-DR, -DQ, -DM, and -DO allele variation was determined in 1,629 related haploidentical transplants to study the clinical significance of individual molecules and haplotypes. RESULTS: Outcome correlated with patient and donor variation for HLA-DRß residue 86 (Gly/Val), HLA-DQ (G1/G2) heterodimers, and donor HLA-DM (DM11,11/nonDM11,11) molecules, and depended on patient-donor mismatching. Risks of relapse were lower for DRß-86 GlyGly patients when the donor was GlyVal (hazard ratio [HR], 0.46 [95% CI, 0.30 to 0.68]; P < .001); GlyVal patients benefited from HLA-DRB1-matched donors, whereas no donor was superior to another for ValVal patients. G1G2 patients with G1G2-mismatched donors had lower relapse. Transplantation from donors with DMα residue 184 ArgHis was associated with higher risk of relapse (HR, 1.60 [95% CI, 1.09 to 2.36]; P = .02) relative to ArgArg. Relapse and mortality risks differed across HLA-DR-DQ-DM haplotypes. CONCLUSION: HLA class II haplotypes may be functional constituents of the transplantation barrier, and their consideration in patients and donors may improve the success of transplantation.

Systematic evaluation of donor-KIR/recipient-HLA interactions in HLA-matched hematopoietic cell transplantation for AML.

ABSTRACT: In acute myeloid leukemia (AML), donor natural killer cell killer immunoglobulin-like receptors (KIR) and recipient HLA interactions may contribute to the graft-versus-leukemia effect of allogeneic hematopoietic cell transplantation (HCT). Analyses of individual KIR/HLA interactions, however, have yielded conflicting findings, and their importance in the HLA-matched unrelated donor (MUD) setting remains controversial. We systematically studied outcomes of individual donor-KIR/recipient-HLA interactions for HCT outcomes and empirically evaluated prevalent KIR genotypes for clinical benefit. Adult patients with AML (n = 2025) who received HCT with MUD grafts in complete remission reported to the Center for International Blood and Marrow Transplantation were evaluated. Only the donor-2DL2+/recipient-HLA-C1+ pair was associated with reduced relapse (hazard ratio [HR], 0.79; 95% confidence interval [CI], 0.67-0.93; P = .006) compared with donor-2DL2-/recipient-HLA-C1+ pair. However, no association was found when comparing HLA-C groups among KIR-2DL2+-graft recipients. We identified 9 prevalent donor KIR genotypes in our cohort and screened them for association with relapse risk. Genotype 5 (G5) in all recipients and G3 in Bw4+ recipients were associated with decreased relapse risk (HR, 0.52; 95% CI, 0.35-0.78; P = .002; and HR, 0.32; 95% CI, 0.14-0.72; P = .006; respectively) and G2 (HR 1.63, 95% CI, 1.15-2.29; P = .005) with increased relapse risk in C1-homozygous recipients, compared with other patients with the same ligand. However, we could not validate these findings in an external data set of 796 AML transplants from the German transplantation registry. Neither a systematic evaluation of known HLA-KIR interactions nor an empiric assessment of prevalent KIR genotypes demonstrated clinically actionable associations; therefore, these data do not support these KIR-driven strategies for MUD selection in AML.

Severity of Chronic Graft-versus-Host Disease and Late Effects Following Allogeneic Hematopoietic Cell Transplantation for Adults with Hematologic Malignancy.

The study aimed to determine the association of chronic graft-versus-host disease (cGVHD) diagnosis and severity with the development of subsequent neoplasms (SN) and nonmalignant late effects (NM-LE) in 2-year disease-free adult survivors following hematopoietic cell transplantation (HCT) for a hematologic malignancy. To do so, we conducted a retrospective analysis of 3884 survivors of HCT for hematologic malignancy in the Center of International Blood and Marrow Transplant Research database. We conducted a landmark analysis at the 2-year post-transplantation date, comparing first SN and NM-LE in survivors with and without cGVHD. The cumulative incidence (CuI) of SN and NM-LE were estimated through 10 years post-HCT in both groups, with death or disease relapse as a competing risk. Cox proportional hazards models were used to evaluate the associations of cGVHD and its related characteristics with the development of SN and NM-LE. The estimated 10-year CuI of SN in patients with GVHD (n = 2669) and patients without cGVHD (n = 1215) was 15% (95% confidence interval [CI], 14% to 17%) versus 9% (7.2% to 11%) (P < .001). cGVHD by 2 years post-HCT was independently associated with SN (hazard ratio [HR], 1.94; 95% CI, 1.53 to 2.46; P < .0001) with a standardized incidence ratio of 3.2 (95% CI, 2.9 to 3.5; P < .0001). Increasing severity of cGVHD was associated with an increased risk of SN. The estimated 10-year CuI of first NM-LE in patients with and without cGVHD was 28 (95% CI, 26% to 30%) versus 13% (95% CI, 11% to 15%) (P < .001). cGVHD by 2 years post-HCT was independently associated with NM-LE (HR, 2.23; 95% CI, 1.81 to 2.76; P < .0001). Multivariate analysis of cGVHD-related factors showed that increasing severity of cGVHD, extensive grade, having both mucocutaneous and visceral involvement, and receiving cGVHD treatment for >12 months were associated with the greatest magnitude of risk for NM-LE. cGVHD was closely associated with both SN and NM-LE in adult survivors of HCT for hematologic malignancy. Patients identified as having more severe involvement and both mucocutaneous and visceral organ involvement may warrant enhanced monitoring and screening for SNs and NM-LEs. However, caution is warranted when interpreting these results, as patients with cGVHD may have more vigilant post-transplantation health care and surveillance for late effects.

Comparison of Vital Status, Cause of Death, and Follow-Up after Hematopoietic Cell Transplantation in Linked Center for International Blood and Marrow Transplant Research and California Cancer Registry Data, 1991 to 2018.

Assessing outcomes following hematopoietic cell transplantation (HCT) poses challenges due to the necessity for systematic and often prolonged patient follow-up. Linking the HCT database of the Center for International Blood and Marrow Transplant Research (CIBMTR) with cancer registry data may improve long-term outcome ascertainment, but the reliability of mortality data in death certificates from cancer registries among HCT recipients remains unknown. We compared the classification of vital status and primary cause of death (COD), as well as the length of follow-up between the CIBMTR and California Cancer Registry (CCR) to assess the possibility of supplementing the CIBMTR with cancer registry data. This retrospective study leveraged a linked CIBMTR-CCR dataset. We included patients who were California residents at the time of HCT and received a first allogeneic (allo) or autologous (auto) HCT for a hematologic malignancy diagnosed during 1991-2016. Follow-up was through 2018. We analyzed 18,450 patients (alloHCT, n = 8232; autoHCT, n = 10,218). The Vital status agreement was 97.7% for alloHCT and 97.2% for autoHCT. Unknown COD was higher in CIBMTR (12.9%) than in CCR (1.6%). After excluding patients with unknown COD information, the overall agreement of primary COD (cancer versus noncancer) was 53.7% for alloHCT and 83.2% for autoHCT. This agreement was lower within the first 100 days post-HCT (alloHCT, 31.0%; autoHCT, 54.6%). Compared with CIBMTR, deaths due to cancer were higher in CCR (alloHCT, 90.0%; autoHCT, 90.1% versus alloHCT, 47.3%; autoHCT, 82.5% in CIBMTR). CIBMTR reports more frequently noncancer-related deaths, including graft-versus-host disease and infections. The cumulative incidence of cancer-specific mortality at 20 years differed, particularly for alloHCT (CCR, 53.7%; CIBMTR, 27.6%). The median follow-up among alive patients was longer in CCR (alloHCT, 6.0 years; autoHCT, 4.7 years) than in CIBMTR (alloHCT, 5.0 years; autoHCT, 3.8 years). Our findings highlight the completeness of vital status data in CIBMTR but reveal substantial disagreement in primary COD. Consequently, caution is required when interpreting HCT studies that use only death certificates to estimate cause-specific mortality outcomes. Improving the accuracy of COD registration and follow-up completeness by developing communication pathways between cancer registries and hospital-based cohorts may enhance our understanding of late effects and long-term outcomes among HCT survivors.

Expanding donor options: haploidentical transplant recipients are also highly likely to have a 7/8-matched unrelated donor.

ABSTRACT: The use of haploidentical related donor (HRD) hematopoietic cell transplants (HCTs) in the United States grew by more than fourfold in the last decade, driven mainly by use of posttransplant cyclophosphamide (PTCy)-based graft-versus-host-disease prophylaxis. However, not all patients have a suitable HRD available. In this study, we explored the existence of unrelated donors (URDs) on the National Marrow Donor Program (NMDP) registry at the 8/8- or 7/8-match level for patients receiving HRD HCT in the United States and reporting to the Center for International Blood and Marrow Transplant Research between 2013 and 2020. The data consist of 9696 HRD HCT recipients. The NMDP search prognosis score and a search simulation were used to estimate counts of URD matches on the registry. NMDP search prognosis varied by patient ancestry, with 27.5% non-Hispanic White having a good score compared with 4.6% of African American HRD HCT recipients. Overall, 34% of recipients had ≥1 8/8-matched URDs and 84% had ≥1 7/8 URDs. Recipients of older HRDs (≥35 years) had a likelihood of between 20%- 65% of having ≥5 existing 7/8-matched URDs who were aged ≤35 years. Donor-selection practices varied among the 10 highest-volume HRD centers: 6 had >20% chance of an existing 8/8-matched URD for their HRD recipients, whereas 4 centers had low likelihood of identifying an 8/8-matched URD. In conclusion, although most US patients undergoing HRD HCT do not have an existing 8/8 URD, the majority have an existing 7/8-matched URD. Studies comparing outcomes in patients receiving either HRD or 7/8-matched URD HCT and PTCy-based graft-versus-host disease prophylaxis may be warranted.

JAK2 V617F mutation and associated chromosomal alterations in primary and secondary myelofibrosis and post-HCT outcomes.

JAK2 V617F is the most common driver mutation in primary or secondary myelofibrosis for which allogeneic hematopoietic cell transplantation (HCT) is the only curative treatment. Knowledge of the prognostic utility of JAK2 alterations in the HCT setting is limited. We identified all patients with MF who received HCT between 2000 and 2016 and had a pre-HCT blood sample (N = 973) available at the Center of International Blood and Marrow Transplant Research biorepository. PacBio sequencing and single nucleotide polymorphism-array genotyping were used to identify JAK2V617F mutation and associated mosaic chromosomal alterations (mCAs), respectively. Cox proportional hazard models were used for HCT outcome analyses. Genomic testing was complete for 924 patients with MF (634 primary MF [PMF], 135 postpolycythemia vera [PPV-MF], and 155 postessential thrombocytopenia [PET-MF]). JAK2V617F affected 562 patients (57.6% of PMF, 97% of PPV-MF, and 42.6% of PET-MF). Almost all patients with mCAs involving the JAK2 region (97.9%) were JAK2V617-positive. In PMF, JAK2V617F mutation status, allele burden, or identified mCAs were not associated with disease progression/relapse, nonrelapse mortality (NRM), or overall survival. Almost all PPV-MF were JAK2V617F-positive (97%), with no association between HCT outcomes and mutation allele burden or mCAs. In PET-MF, JAK2V617F high mutation allele burden (≥60%) was associated with excess risk of NRM, restricted to transplants received in the era of JAK inhibitors (2013-2016; hazard ratio = 7.65; 95% confidence interval = 2.10-27.82; P = .002). However, allele burden was not associated with post-HCT disease progression/relapse or survival. Our findings support the concept that HCT can mitigate the known negative effect of JAK2V617F in patients with MF, particularly for PMF and PPV-MF.

Measurable Residual IDH1 before Allogeneic Transplant for Acute Myeloid Leukemia.

Measurable residual disease (MRD) in adults with acute myeloid leukemia (AML) in complete remission is an important prognostic marker, but detection methodology requires optimization. The persistence of mutated NPM1 or FLT3-ITD in the blood of adult patients with AML in first complete remission (CR1) prior to allogeneic hematopoetic cell transplant (alloHCT) has been established as associated with increased relapse and death after transplant. The prognostic implications of persistence of other common AML-associated mutations, such as IDH1, at this treatment landmark however remains incompletely defined. We performed testing for residual IDH1 variants (IDH1m) in pre-transplant CR1 blood of 148 adult patients undergoing alloHCT for IDH1-mutated AML at a CIBMTR site between 2013-2019. No post-transplant differences were observed between those testing IDH1m positive (n=53, 36%) and negative pre-transplant (overall survival: p = 0.4; relapse: p = 0.5). For patients with IDH1 mutated AML co-mutated with NPM1 and/or FLT3-ITD, only detection of persistent mutated NPM1 and/or FLT3-ITD was associated with significantly higher rates of relapse (p = 0.01). These data, from the largest study to date, do not support the detection of IDH1 mutation in CR1 blood prior to alloHCT as evidence of AML MRD or increased post-transplant relapse risk.

Existence of HLA-Mismatched Unrelated Donors Closes the Gap in Donor Availability Regardless of Recipient Ancestry.

In patients without a matched sibling donor (MSD) or well-matched unrelated donor (MUD), hematopoietic cell transplantation (HCT) can still be successful when using an HLA-mismatched unrelated donor (MMUD) in combination with post-transplantation cyclophosphamide (PTCy), abatacept, or other novel approaches. This may allow clinicians to choose a suitable donor from a wide range of donor options while optimizing other donor selection characteristics, including donor age. We hypothesized that allowing for a 5/8 HLA match level considering high-resolution matching at HLA-A, -B, -C and -DRB1, there is a potential to close the donor availability gap for all patients regardless of their race/ethnicity. In this work, we estimate the likelihood of matching for all racial/ethnic groups at different HLA match thresholds. Our study aimed to assess the potential for identifying an available MUD or MMUD in the National Marrow Donor Program (NMDP)/Be The Match (BTM) donor registry for 21 detailed and 5 broad racial/ethnic groups, using high-resolution HLA matching for HLA-A, -B, -C, and -DRB1 at various levels (8/8, 7/8, 6/8, and 5/8). We used donor registry population data from the NMDP/BTM in 2020 and redistributed the donor registry data according to existing population ratios, accounting for demonstrated donor availability. Finally, we used a genetic model at the population level to estimate the match likelihood for detailed and broad racial/ethnic groups. Likelihood of 8/8 HLA match ranging from 16% to 74% were obtained for various detailed racial/ethnic groups with available donors age ≤35 years. When considering more mismatches in the HLA loci, registry coverage became >99% with a 5/8 HLA match level for donors of all ages or those age ≤35 years, with HLA-DPB1 T cell epitope permissive matching, or when searching for donors outside of their racial/ethnic group. Our registry models demonstrate the potential for using MMUDs at various HLA match levels to study whether this will expand access to HCT across racial/ethnic groups. Expanded donor options may erase the donor availability gap for all patients while allowing for selection of MMUDs with favorable characteristics, such as younger age.

Pilot Study of Donor-Engrafted Clonal Hematopoiesis Evolution and Clinical Outcomes in Allogeneic Hematopoietic Cell Transplantation Recipients Using a National Registry.

Improved treatment options, such as reduced-intensity conditioning (RIC), enable older patients to receive potentially curative allogeneic hematopoietic cell transplantation (HCT). This progress has led to increased use of older HLA-matched sibling donors. An unintended potential risk associated with older donors is transplantation of donor cells with clonal hematopoiesis (CH) into patients. We aimed to determine the prevalence of CH in older HLA-matched sibling donors pretransplantation and to assess the clinical impact of donor-engrafted CH on HCT outcomes. This was an observational study using donor peripheral blood samples from the Center for International Blood and Marrow Transplant Research repository, linked with corresponding recipient outcomes. To explore engraftment efficiency and evolution of CH mutations following HCT, recipient follow-up samples available through the Bone Marrow Transplant Clinical Trials Network (Protocol 1202) were included. Older donors and patients (both ≥55 years) receiving first RIC HCT for myeloid malignancies were eligible. DNA from archived donor blood samples was used for targeted deep sequencing to identify CH. The associations between donor CH status and recipient outcomes, including acute graft-versus-host disease (aGVHD), chronic GVHD (cGVHD), overall survival, relapse, nonrelapse mortality, disease-free survival, composite GVHD-free and relapse-free survival, and cGVHD-free and relapse-free survival, were analyzed. A total of 299 donors were successfully sequenced to detect CH. At a variant allele frequency (VAF) ≥2%, there were 44 CH mutations in 13.7% (41 of 299) of HLA-matched sibling donors. CH mostly involved DNMT3A (n = 27; 61.4%) and TET2 (n= 9; 20.5%). Post-HCT samples from 13 recipients were also sequenced, of whom 7 had CH+ donors. All of the donor CH mutations (n = 7/7; 100%) were detected in recipients at day 56 or day 90 post-HCT. Overall, mutation VAFs remained relatively constant up to day 90 post-HCT (median change, .005; range, -.008 to .024). Doubling time analysis of recipient day 56 and day 90 data showed that donor-engrafted CH mutations initially expand then decrease to a stable VAF; germline mutations had longer doubling times than CH mutations. The cumulative incidence of grade II-IV aGVHD at day 100 was higher in HCT recipients with CH+ donors (37.5% versus 25.1%); however, the risk for aGVHD by donor CH status did not reach statistical significance (hazard ratio, 1.35; 95% confidence interval, .61 to 3.01; P = .47). There were no statistically significant differences in the cumulative incidence of cGVHD or any secondary outcomes by donor CH status. In subset analysis, the incidence of cGVHD was lower in recipients of grafts from DNMT3A CH+ donors versus donors without DNMT3A CH (34.4% versus 57%; P = .035). Donor cell leukemia was not reported in any donor-recipient pairs. CH in older HLA-matched sibling donors is relatively common and successfully engrafts and persists in recipients. In a homogenous population (myeloid malignancies, older donors and recipients, RICr, non-cyclophosphamide-containing GVHD prophylaxis), we did not detect a difference in cGVHD risk or other secondary outcomes by donor CH status. Subgroup analyses suggest potential differential effects by clinical characteristics and CH mutations. Larger prospective studies are needed to robustly determine which subsets of patients and CH mutations elicit meaningful impacts on clinical outcomes.

A common allele of HLA is associated with asymptomatic SARS-CoV-2 infection.

Studies have demonstrated that at least 20% of individuals infected with SARS-CoV-2 remain asymptomatic1-4. Although most global efforts have focused on severe illness in COVID-19, examining asymptomatic infection provides a unique opportunity to consider early immunological features that promote rapid viral clearance. Here, postulating that variation in the human leukocyte antigen (HLA) loci may underly processes mediating asymptomatic infection, we enrolled 29,947 individuals, for whom high-resolution HLA genotyping data were available, in a smartphone-based study designed to track COVID-19 symptoms and outcomes. Our discovery cohort (n = 1,428) comprised unvaccinated individuals who reported a positive test result for SARS-CoV-2. We tested for association of five HLA loci with disease course and identified a strong association between HLA-B*15:01 and asymptomatic infection, observed in two independent cohorts. Suggesting that this genetic association is due to pre-existing T cell immunity, we show that T cells from pre-pandemic samples from individuals carrying HLA-B*15:01 were reactive to the immunodominant SARS-CoV-2 S-derived peptide NQKLIANQF. The majority of the reactive T cells displayed a memory phenotype, were highly polyfunctional and were cross-reactive to a peptide derived from seasonal coronaviruses. The crystal structure of HLA-B*15:01-peptide complexes demonstrates that the peptides NQKLIANQF and NQKLIANAF (from OC43-CoV and HKU1-CoV) share a similar ability to be stabilized and presented by HLA-B*15:01. Finally, we show that the structural similarity of the peptides underpins T cell cross-reactivity of high-affinity public T cell receptors, providing the molecular basis for HLA-B*15:01-mediated pre-existing immunity.

Genotype List String 1.1: Extending the Genotype List String grammar for describing HLA and Killer-cell Immunoglobulin-like Receptor genotypes.

The Genotype List (GL) String grammar for reporting HLA and Killer-cell Immunoglobulin-like Receptor (KIR) genotypes in a text string was described in 2013. Since this initial description, GL Strings have been used to describe HLA and KIR genotypes for more than 40 million subjects, allowing these data to be recorded, stored and transmitted in an easily parsed, text-based format. After a decade of working with HLA and KIR data in GL String format, with advances in HLA and KIR genotyping technologies that have fostered the generation of full-gene sequence data, the need for an extension of the GL String system has become clear. Here, we introduce the new GL String delimiter "?," which addresses the need to describe ambiguity in assigning a gene sequence to gene paralogs. GL Strings that do not include a "?" delimiter continue to be interpreted as originally described. This extension represents version 1.1 of the GL String grammar.

Worldwide sources of data in haematology: Importance of clinician-biostatistician collaboration.

The field of haematology has benefitted greatly from registry-based observational research. Medical and technical advances, changes in regulations and events such as the global pandemic is changing the landscape for registries. This review describes features of high-quality registries, statistical approaches and study design needed, an overview of worldwide hematologic registries, and how registries are evolving and expanding. The importance of collaborations between biostatisticians and haematologists in designing and conducting registry-related research is highlighted.

The distribution and accumulation of the shortest telomeres in telomere biology disorders.

Individuals with telomere biology disorders (TBDs) have very short telomeres, high risk of bone marrow failure (BMF), and reduced survival. Using data from TBD patients, a mean leukocyte Southern blot telomere length (TL) of 5 kilobases (kb) was estimated as the 'telomere brink' at which human survival is markedly reduced. However, the shortest telomere, not the mean TL, signals replicative senescence. We used the Telomere Shortest Length Assay (TeSLA) to tally TL of all 46 chromosomes in blood-derived DNA and examined its relationship with TBDs. Patients (n = 18) had much shorter mean TL (TeSmTL) (2.54 ± 0.41 kb vs. 4.48 ± 0.52 kb, p < 0.0001) and more telomeres <3 kb than controls (n = 22) (70.43 ± 8.76% vs. 33.05 ± 6.93%, p < 0.0001). The proportion of ultrashort telomeres (<1.6 kb) was also higher in patients than controls (39.29 ± 10.69% vs. 10.40 ± 4.09%, p < 0.0001). TeS <1.6 kb was associated with severe (n = 11) compared with non-severe (n = 7) BMF (p = 0.027). Patients with multi-organ manifestations (n = 10) had more telomeres <1.6 kb than those with one affected organ system (n = 8) (p = 0.029). Findings suggest that TBD clinical manifestations are associated with a disproportionately higher number of haematopoietic cell telomeres reaching a telomere brink, whose length at the single telomere level is yet to be determined.

Clinical impact of cryopreservation of allogeneic hematopoietic cell grafts during the onset of the COVID-19 pandemic.

At the onset of the COVID-19 pandemic, the National Marrow Donor Program mandated the cryopreservation of hematopoietic cell grafts from volunteer unrelated donors because of numerous patient and donor safety concerns and logistical hurdles. Using the Center for International Blood and Marrow Transplant Research outcomes database, we report the impact of cryopreservation on overall survival (OS) and other outcomes within 1 year after hematopoietic cell transplantation (HCT). We analyzed 1543 recipients of cryopreserved allografts receiving HCT at US centers during the first 6 months of the pandemic and compared them with 2499 recipients of fresh allografts during a 6-month period in 2019. On multivariable regression analysis, we observed no difference in the OS (P = .09), nonrelapse mortality (P = .89), graft-versus-host disease (GVHD), or GVHD- and relapse-free survival (P = .58) in recipients of cryopreserved vs fresh allografts. Disease-free survival (DFS) was lower in the cryopreserved allograft recipients (P = .006) because of a higher risk of relapse (P = .01) compared with the fresh allograft recipients. Primary graft failure was higher (P = .01), and the risk of chronic GVHD was lower (P = .001) with cryopreservation compared with fresh grafts. In conclusion, although there was no negative impact of cryopreservation on OS, relapse was higher, and DFS was lower than that with no cryopreservation. Fresh grafts are recommended as the pandemic-related logistical hurdles resolve. Cryopreservation should be considered an option for patients when fresh grafts are not feasible.