Acute Leukemia Research Articles

USP22 regulates APL differentiation via PML-RARα stabilization and IFN repression

Ubiquitin-specific peptidase 22 (USP22) is a deubiquitinating enzyme (DUB) that underlies tumorigenicity, proliferation, cell death and differentiation through deubiquitination of histone and non-histone targets. Ubiquitination determines stability, localization and functions of cell fate proteins and controls cell-protective signaling pathways to surveil cell cycle progression. In a variety of carcinomas, lymphomas and leukemias, ubiquitination regulates the tumor-suppressive functions of the promyelocytic leukemia protein (PML), but PML-specific DUBs, DUB-controlled PML ubiquitin sites and the functional consequences of PML (de)ubiquitination remain unclear. Here, we identify USP22 as regulator of PML and the oncogenic acute promyelocytic leukemia (APL) fusion PML-RARα protein stability and identify a destabilizing role of PML residue K394. Additionally, loss of USP22 upregulates interferon (IFN) and IFN-stimulated gene (ISG) expression in APL and induces PML-RARα stabilization and a potentiation of the cell-autonomous sensitivity towards all-trans retinoic acid (ATRA)-mediated differentiation. Our findings imply USP22-dependent surveillance of PML-RARα stability and IFN signaling as important regulator of APL pathogenesis, with implications for viral mimicry, differentiation and cell fate regulation in other leukemia subtypes.

[Retracted] Tanshinone IIA enhances the inhibitory effect of imatinib on proliferation and motility of acute leukemia cell line TIB‑152 invivo and invitro by inhibiting the PI3K/AKT/mTOR signaling pathway.

Following the publication of the above article, a concerned reader drew to the Editor's attention that the Transwell cell invasion assay data featured in Figs.2D and 4E, certain of the tumor images in Fig.5A and the TUNEL assay data in Fig.5C were strikingly similar to data appearing in different form in other articles written by different authors at different research institutes that had either already been published elsewhere prior to the submission of this paper to OncologyReports, or which under consideration for publication at around the same time (some papers of which have been retracted). In view of the fact that certain of these data had already apparently been published prior to the submission of this article for publication, the Editor of OncologyReports has decided that this paper should be retracted from the Journal. The authors were asked for an explanation to account for these concerns, but the Editorial Office did not receive a reply. The Editor apologizes to the readership for any inconvenience caused. [Oncology Reports 43: 503‑515, 2020; DOI: 10.3892/or.2019.7453].

The human health effects of unconventional oil and gas development (UOGD): A scoping review of epidemiologic studies.

Unconventional oil and gas development (UOGD, sometimes termed "fracking" or "hydraulic fracturing") is an industrial process to extract methane gas and/or oil deposits. Many chemicals used in UOGD have known adverse human health effects. Canada is a major producer of UOGD-derived gas with wells frequently located in and around rural and Indigenous communities. Our objective was to conduct a scoping review to identify the extent of research evidence assessing UOGD exposure-related health impacts, with an additional focus on Canadian studies. We included English- or French-language peer-reviewed epidemiologic studies (January 2000-December 2022) which measured exposure to UOGD chemicals directly or by proxy, and where health outcomes were plausibly caused by UOGD-related chemical exposure. Results synthesis was descriptive with results ordered by outcome and hierarchy of methodological approach. We identified 52 studies from nine jurisdictions. Only two were set in Canada. A majority (n = 27) used retrospective cohort and case-control designs. Almost half (n = 24) focused on birth outcomes, with a majority (n = 22) reporting one or more significant adverse associations of UOGD exposure with: low birthweight; small for gestational age; preterm birth; and one or more birth defects. Other studies identified adverse impacts including asthma (n = 7), respiratory (n = 13), cardiovascular (n = 6), childhood acute lymphocytic leukemia (n = 2), and all-cause mortality (n = 4). There is a growing body of research, across different jurisdictions, reporting associations of UOGD with adverse health outcomes. Despite the rapid growthof UOGD, which is often located in remote, rural, and Indigenous communities, Canadian research on its effects on human health is remarkably sparse. There is a pressing need for additional evidence.

Validation of a Stenotrophomonas maltophilia bloodstream infection prediction score in the hematologic malignancy population

Stenotrophomonas maltophilia (SM) bloodstream infections (BSIs) contribute to significant mortality in hematologic malignancy (HM) and hematopoietic stem cell transplantation (HSCT) patients. A risk score to predict SM BSI could reduce time to appropriate antimicrobial therapy (TTAT) and improve patient outcomes. A single center cohort study of hospitalized adults with HM/HSCT was conducted. Patients had ≥ 1 blood culture with a Gram-negative (GN) organism. A StenoSCORE was calculated for each patient. The StenoSCORE2 was developed using risk factors for SM BSI identified via logistic regression. Receiver operating characteristic (ROC) curves were plotted. Sensitivity and specificity for the StenoSCORE and StenoSCORE2 were calculated. Thirty-six SM patients and 534 non-SM patients were assessed. A StenoSCORE ≥ 33 points was 80% sensitive, 68% specific, and accurately classified 69% of GN BSIs. StenoSCORE2 variables included acute leukemia, prolonged neutropenia, mucositis, ICU admission, recent meropenem and/or cefepime exposure. The StenoSCORE2 performed better than the StenoSCORE (ROC AUC 0.84 vs. 0.77). A StenoSCORE2 ≥ 4 points was 86% sensitive, 76% specific, and accurately classified 77% of GN BSIs. TTAT was significantly longer for patients with SM BSI compared with non-SM BSI (45.16 h vs. 0.57 h; p < 0.0001). In-hospital and 28-day mortality were significantly higher for patients with SM BSI compared to non-SM BSI (58.3% vs. 18.5% and 66.7% vs. 26.4%; p-value < 0.0001). The StenoSCORE and StenoSCORE2 performed well in predicting SM BSIs in patients with HM/HSCT and GN BSI. Clinical studies evaluating whether StenoSCORE and/or StenoSCORE2 implementation improves TTAT and clinical outcomes are warranted.

Study of the intestinal microbiota composition and the effect of treatment with intensive chemotherapy in patients recovered from acute leukemia

A dataset comprising metagenomes of outpatients (n = 28) with acute leukemia (AL) and healthy controls (n = 14) was analysed to investigate the associations between gut microbiota composition and metabolic activity and AL. According to the results obtained, no significant differences in the microbial diversity between AL outpatients and healthy controls were found. However, significant differences in the abundance of specific microbial clades of healthy controls and AL outpatients were found. We found some differences at taxa level. The relative abundance of Enterobacteriaceae, Prevotellaceae and Rikenellaceae was increased in AL outpatients, while Bacteirodaceae, Bifidobacteriaceae and Lachnospiraceae was decreased. Interestingly, the abundances of several taxa including Bacteroides and Faecalibacterium species showed variations based on recovery time from the last cycle of chemotherapy. Functional annotation of metagenome-assembled genomes (MAGs) revealed the presence of functional domains corresponding to therapeutic enzymes including l-asparaginase in a wide range of genera including Prevotella, Ruminococcus, Faecalibacterium, Alistipes, Akkermansia. Metabolic network modelling revealed potential symbiotic relationships between Veillonella parvula and Levyella massiliensis and several species found in the microbiota of AL outpatients. These results may contribute to develop strategies for the recovery of microbiota composition profiles in the treatment of patients with AL.

Incidence and outcome of central nervous system relapse after hematopoietic stem cell transplantation in patients suffering from acute myeloid leukemia and acute lymphoblastic leukemia: a study from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation.

Not available.

Therapeutic Targeting of TIM-4-L with Engineered T Cells for Acute Myeloid Leukemia.

Disruption of lipid bilayer asymmetry is a common feature observed in cancer cells and offers novel routes for therapeutic targeting. We used the natural immune receptor TIM-4 to interrogate for loss of plasma membrane phospholipid polarity in primary acute myelogenous leukemia (AML) samples and evaluated the anti-leukemic activity of TIM-4-L-directed T-cell therapy in preclinical AML models. We performed FACS analysis on 33 primary AML bone marrow specimens and correlated TIM-4-L expression frequency and intensity with molecular disease characteristics. Using Kasumi-1 and MV-4-11 AML cell lines, we further tested the anti-leukemic effects of TIM-4-L-directed engineered T cells in vitro and in vivo. We found that 86% of untreated AML blasts displayed upregulation of cell surface TIM-4-L. These observations were agnostic to AML genetic classification, as samples with mutations in TP53, ASXL1, and RUNX1 displayed TIM-4-L upregulation similar to that seen in favorable and intermediate subtypes. TIM-4-L dysregulation was also stably present in AML cell lines. To evaluate the potential of targeting upregulated TIM-4-L with adoptive T-cell therapy, we constructed TIM-4-L-directed engineered T cells, which demonstrated potent anti-leukemic effects, effectively eliminating AML cell lines with a range of endogenous TIM-4-L expression levels both in vitro and in vivo. These results highlight TIM-4-L as a highly prevalent target on AML across a range of genetic classifications and novel target for T-cell-based therapy in AML. Further investigations into the role of TIM-4-L in AML pathogenesis and its potential as an anti-leukemic target for clinical development are warranted.

Chronic disseminated candidiasis in a patient with acute leukemia - an illustrative case and brief review for clinicians

Chronic disseminated candidiasis (CDC) is a severe but rarely seen fungal infection presenting in patients with hematologic malignancies after a prolonged duration of neutropenia. A high index of suspicion is required to diagnose CDC as standard culture workup is often negative. While tissue biopsy is the gold standard of diagnosis, it is frequently avoided in patients with profound cytopenias and increased bleeding risks. A presumptive diagnosis can be made in patients with recent neutropenia, persistent fevers unresponsive to antibiotics, imaging findings of hypoechoic, non-rim enhancing target-like lesions in the spleen and liver, and mycologic evidence. Here, we describe the case of an 18-year-old woman with relapsed B-cell acute lymphoblastic leukemia treated with re-induction chemotherapy who subsequently developed CDC with multi-organ involvement. The diagnosis was made based on clinical and radiologic features with positive tissue culture from a skin nodule and hepatic lesion. The patient was treated for a total course of 11 months with anti-fungal therapy, most notably amphotericin B and micafungin, and splenectomy. After initial diagnosis, the patient was monitored with monthly CT abdomen imaging that showed disease control after 5 months of anti-fungal therapy and splenectomy. The diagnosis, treatment, and common challenges of CDC are outlined here to assist with better understanding, diagnosis, and treatment of this rare condition.

Acute erythroid leukemia leading to the diagnosis of Schwachman-Diamond syndrome

Acute erythroid leukemia leading to the diagnosis of Schwachman-Diamond syndrome

Unpredicted transformation of acute myeloid leukemia with translocation (16;16) (p13; q22): a case report and review of the literature

IntroductionThe transformation of acute myeloid leukemia with translocation (16;16) (p13; q22) from AML M2 to acute monocytic leukemia (AML M5) during therapy is a rare clinical occurrence, and this is the first time it has been reported.Clinical complainA 19-year-old male patient was admitted for severe fatigue with anemic manifestation and weight loss, for more than 1 month, with exacerbation of the condition in the last 2 days.DiagnosisA primary diagnosis was made for AML M2 with t (16;16) (p13; q22) established on bone marrow (BM) morphology. A consequential detection of FLT-3 ITD mutation was done. At day 28 follow-up after induction and maintenance therapy, the diagnosis of AML M2 was maintained with a high bone marrow (BM) blast count, prompting the initiation of a more aggressive treatment protocol. After 1 month of implementing the recent protocol, the patient remains morphologically resistant with a notable transformation of bone marrow infiltration by an abnormal monocytic population (monoblasts and promonocytes). The final diagnosis of transforming FLT3-mutated AML with t (16;16) (p13; q22) was established.InterventionAfter the initial diagnosis of AML M2 with t (16;16) (p13; q22), the patient received the 3 + 7 induction protocol. The 2nd induction protocol initiated after the second evaluation and morphological resistance was the FLAG Adrian protocol. The 3rd protocol after transformation to AML M5 was 1 cycle of the MEC protocol. Anti-FLT3 treatment was considered.OutcomesThe patient was maintained on the 3rd protocol of chemotherapy. Unfortunately, he was admitted to the ICU unit complaining of neutropenic fever and severe sepsis where he died before final re-evaluation and the anti-FLT3 treatment initiation.ConclusionAML with t (16;16) (p13; q22) characterized by favorable outcome. However, identifying additional chromosome abnormality or genetic aberration, especially FLT3 gene mutation, is recognized as an important factor influencing final disease outcome. Therefore, early detection of FLT3 mutations will allow comprehensive disease course prediction and targeted therapy that might achieve longer and more durable remissions.

Incidence of QT interval prolongation during arsenic trioxide-based therapy in a sample of Iraqi adult patients with acute promyelocytic leukemia (a single-center experience)

Abstract: BACKGROUND: Arsenic trioxide (ATO) regimen is now the standard of care for acute promyelocytic leukemia (APL). The complete remission and possible cure are reported to be 50%–80% of APL patients. Prolongation of the QT interval has been consistently observed in clinical trials with ATO, which is known to have a direct effect on cardiac repolarization with the recommendations for management include electrocardiogram (ECG) monitoring, discontinuation of drugs that prolong the QT interval, and careful repletion of serum potassium and magnesium. OBJECTIVES: To study the incidence and clinical consequences of QT prolongation in a sample of Iraqi APL patients treated with ATO. PATIENTS AND METHODS: A prospective, cross-sectional study was conducted on 24 adult patients with newly diagnosed APL at Baghdad Teaching Hospital. ECG was performed at baseline and twice weekly till the end of induction treatment course. Corrected QT interval was calculated based on Bazett and Fridericia formulas (QTc interval of more than 500 ms is considered dangerous): Serum potassium, calcium, and magnesium levels were also measured simultaneously. RESULTS: The mean QT at baseline was 424 ± 18 ms and 402 ± 15 ms by Bazett and Fridericia, respectively, and at the end of induction, the mean QT was 436 ± 20 ms and 418 ± 20 ms by Bazett and Fridericia, respectively. The rate of developing prolonged QT was 62.5% by Bazet, in which 15 patients developed prolonged QT (at any time point). The comparison between prolonged and dangerous QT groups by Bazet showed significant difference, in which QT-related complications were associated with dangerous QT (&gt;500 ms) prolongation significantly, while Fridrica method did not label these patients as having dangerous QT prolongation. The change in QT started as early as 1 week after treatment, the comparison between baseline QT and QT at week 1 showed that there was significant increase in QT. The electrolytes analysis and comparison with baseline results for potassium, magnesium, and calcium showed that there were no significant differences over time for tested electrolytes. CONCLUSION: Bazett formula is useful to monitor Iraqi patients with APL who are treated with ATO for the detection of dangerous prolongation of QT.

Increased donor inhibitory KIR are associated with reduced GVHD and improved survival following HLA-matched unrelated donor HCT in paediatric acute leukaemia.

Killer immunoglobulin-like receptor (KIR) and KIR-ligand (KIRL) interactions play an important role in natural killer cell-mediated effects after haematopoietic stem cell transplantation (HCT). Previous work has shown that accounting for known KIR-KIRL interactions may identify donors with optimal NK cell-mediated alloreactivity in the adult transplant setting. Paediatric acute leukaemia patients were retrospectively analysed, and KIR-KIRL combinations and maximal inhibitory KIR ligand (IM-KIR) scores were determined. Clinical outcomes were examined using a series of graphs depicting clinical events and endpoints. The graph methodology demonstrated that prognostic variables significant in the occurrence of specific clinical endpoints remained significant for relevant downstream events. KIR-KIRL combinations were significantly predictive for reduced grade 3-4 aGVHD likelihood, in patients transplanted with increased inhibitory KIR gene content and IM-KIR = 5 scores. Improvements were also observed in associated outcomes for both ALL and AML patients, including relapse-free survival, GRFS and overall survival. This study demonstrates that NK cell KIR HLA interactions may be relevant to the paediatric acute leukaemia transplant setting. Reduction in aGVHD suggests KIR effects may extend beyond NK cells. Moving forward clinical trials utilizing donors with a higher iKIR should be considered for URD HCT in paediatric recipients with acute leukaemia to optimize clinical outcomes.

The Association between Single Nucleotide Polymorphisms rs1042522 and rs1642785 in the TP53 gene and Acute Myeloid leukemia in a sample of the Baghdad/ Iraq population

يمثل سرطان الدم النخاعي الحاد (AML) أكثر أنواع سرطان الدم الحاد انتشارًا بين البالغين تصل نسبته 80% من جميع الحالات. الجين المثبط للورم TP53  هو جين تمت دراسته بشكل متكرر في مرض السرطان  .والطفرات في هذا الجين تسبب ما يقارب 50% من الامراض السرطانية. هدفت هذه الدراسة إلى تقييم العلاقة بين اثنين من تعدد أشكال النوكليوتيدات المفردة في جين TP53: rs1042522 ، rs1642785  ومجموعة من المرضى العراقيين الذين يعانون من التشخيص الاولي لسرطان الدم النخاعي الحاد. جمعت عينات الدم من ستين مريضاً 26 ذكور و 34 أناث وستين عينة سيطرة 26 ذكور و 34 أناث متوافقين في الجنس والعمر والعرق. تم استخلاص الحمض النووي الجيني من عينات الدم المجمدة بالكامل باستخدامEasy Pure® Blood Genomic Kit . ثم تم قياس النقاوة والتركيز باستخدام مقياس الطيف الضوئي Nano drop NAS-99. حيث تراوحت قراءات التركيز بين (7-55 نانوغرام / ميكرولتر) وتراوحت النقاوة بين 1.78 - 1.9 تم استخدام تقنيةreal time PCR  (High resolution melt (HRM للكشف عن تعدد اشكال النيوكليوتيدات المفردة و كانت تكرارات النمط الجيني لجين TP53 متوافقة مع توازن هاردي-واينبرغ مع وجود فروق معنوية ذات دلالة إحصائية  p≤0.05  بين الأنماط الجينية لمجموعة السيطرة والمرضى. كان تكرار النمط الجيني rs1042522 مختلفًا بشكل كبير بين المرضى وافراد السيطرة p = 0.0001، وكان المشاركون الذين لديهم النمط الوراثي GA أكثر عرضة للإصابة بسرطان الدم النخاعي الحاد OR=7.8, 95% CI 3.2–18.4, p = 0.0001. بالإضافة الى تكرار النمط الجيني rs1642785 مختلفًا بشكل كبير بين المرضى و افراد السيطرة p=0.002 والذين يحملون النمط الجيني GA أكثر عرضة للإصابة بسرطان الدم النخاعي الحاد OR=3.5, 95% CI 1.5–8.12, p=0.002.

Disseminated Intravascular Coagulation in Acute Promyelocytic Leukemia Patients: A Retrospective Analysis of Outcomes and Healthcare Burden in US Hospitals

Acute promyelocytic leukemia (APL) is associated with an elevated risk of developing disseminated intravascular coagulation (DIC). The purpose of this study was to assess the outcomes of hospitalizations related to DIC in APL and their impact on healthcare. This study entailed a cross-sectional and retrospective analysis of the US National Inpatient Sample database. We identified adults with APL and categorized them into groups of patients with and without DIC. Our focus areas included in-hospital mortality, length of stay, charges, and complications associated with DIC. Unadjusted odds ratios/coefficients were computed in univariate analysis, followed by adjusted odds ratios (aOR)/coefficients from multivariate analysis that accounted for confounding factors. Our analysis revealed that APL patients with DIC had a substantially higher aOR for mortality (aOR: 6.68, 95% confidence interval [CI]: 4.76-9.37, p<0.001) and a prolonged length of stay (coefficient: 10.28 days, 95% CI: 8.48-12.09, p<0.001) accompanied by notably elevated total hospital charges (coefficient: $215,512 [95% CI: 177,368-253,656], p<0.001), thereby emphasizing the reality of extended medical care and economic burden. The presence of DIC was associated with increased odds of sepsis, vasopressor support, pneumonia, acute respiratory failure, intubation/mechanical ventilation, and acute kidney injury, reflecting heightened vulnerability to these complications. Patients with DIC demonstrated significantly higher odds ratios for major bleeding, intracranial hemorrhage, gastrointestinal bleeding, red blood cell transfusion, platelet transfusion, fresh frozen plasma transfusion, and cryoprecipitate transfusion, highlighting the pronounced hematological risks posed by DIC. This study has revealed the significant associations between DIC in APL and various outcomes, underscoring the clinical and economic implications of these conditions. The hematological risks further increase patients’ vulnerability to bleeding events and the need for transfusions.

Abstract B012: Transcriptomic insights reveal role of BCL2 proteins in replication checkpoint inhibitor response

Abstract B012: Transcriptomic insights reveal role of BCL2 proteins in replication checkpoint inhibitor response

Calycosin Induces Ferroptosis by SLC7A11 Through the PI3K/Akt Pathway in Acute Myelocytic Leukemia

Calycosin Induces Ferroptosis by SLC7A11 Through the PI3K/Akt Pathway in Acute Myelocytic Leukemia

Real-Life Data on the Efficacy and Safety of Letermovir for Primary Prophylaxis of Cytomegalovirus in Allogeneic Hematopoietic Stem Cell Recipients: A Single-Center Analysis

Cytomegalovirus (CMV) reactivation is a life-threatening complication after allogeneic hematopoietic stem cell transplantation (HSCT). Introduction of letermovir (LMV) seems to improve post-transplant outcomes, but delayed-onset CMV reactivation still remains a challenge. In this study, we report on our first experience with LMV prophylaxis in 93 CMV-seropositive adult patients receiving HSCT in our center. We retrospectively analyzed the data of 93 adult CMV-seropositive recipients receiving LMV as CMV prophylaxis after HSCT for hematological malignancies between 2019 and 2023. The starting LMV dose was 480 mg daily, reduced to 240 mg daily for those receiving cyclosporin A co-administration. CMV DNA in the blood was measured by real-time polymerase chain reaction weekly for the first 2 months after transplantation, then every other week until the end of immunosuppressive treatment. LMV was continued to day +100 or to CMV reactivation. The median recipient age at the time of transplant was 51 (range: 20-71) years. All patients received grafts from peripheral blood, mostly for acute myeloid leukemia (60%). The median time from transplantation to LMV initiation was 3 (range: 0-24) days. While 55% of patients were transplanted from matched related donors, 32% had unrelated donors and 13% underwent haploidentical HSCT. Four patients (4%) had CMV “blips” while on LMV, but the drug was continued and repeated assays were negative. Only 2 patients (2%) experienced CMV reactivation while on LMV, on days 48 and 34 after HSCT, respectively. Seven patients (7%) developed late-onset CMV reactivation after a median of 124 days after HSCT (range: 118-152 days) and they were successfully treated with ganciclovir. CMV disease was not observed. Grade III-IV acute graft-versus-host disease occurred in 6 patients (6%) during LMV treatment. LMV treatment was free of side effects. LMV prophylaxis was effective in preventing CMV reactivation with a favorable safety profile. CMV reactivation occurred mostly after LMV discontinuation; thus, extending the duration of prophylaxis beyond 100 days could be beneficial.

Abstract P25: Identification of biological components and novel clinical subsets of NPM1-mutated AML using an integrated, multi-omics approach

Abstract P25: Identification of biological components and novel clinical subsets of <i>NPM1</i>-mutated AML using an integrated, multi-omics approach

Haploidentical stem cell donor choice for patients with acute myeloid leukemia: a study from the ALWP of the EBMT

AbstractThere is a paucity of information to guide the selection of the most suitable donor in haploidentical (Haplo) hematopoietic stem cell transplantation (HSCT). For this reason, from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation, we conducted a retrospective analysis to evaluate the impact of Haplo donor characteristics on outcomes in patients with acute myeloid leukemia (AML) who received graft-versus-host disease prophylaxis with posttransplant cyclophosphamide (PTCy). The primary end point was graft-versus-host disease (GVHD)-free and relapse-free survival (GRFS). Overall, 2200 patients were included. The median age of donors was 37 years (range, 8-71); 820 (37%) were females, including 458 (21%) who were used for male recipients. In addition, 1631 donors (74%) donated peripheral blood (PB). Multivariable analysis identified certain donor-related risk factors with a detrimental impact on transplant outcomes. The use of PB, older donors’ ages (>37 years), and female donors to male recipients negatively affected GRFS. Donor’s age and female donor-to-male recipient combination also affected nonrelapse mortality, leukemia-free survival, and overall survival. In conclusion, donor-related variables significantly influence outcomes in patients with AML after Haplo-HSCT with PTCy. When possible, younger donors and male donors for male recipients should be prioritized. The use of bone marrow can additionally prevent GVHD.

Racial/ethnic disparities in availability of volunteer unrelated donors for allogeneic transplantation

AbstractDespite the global unrelated donor (URD) registry size, the degree to which URD availability is a transplant barrier is not established. We evaluated the availability of 3843 URDs requested for 455 diverse adult patients (predominantly with acute leukemia). URDs for non-Europeans were more likely to be domestic and had markedly lower Donor Readiness scores. Of URDs requested for confirmatory HLA-typing (CT) alone (ie, without simultaneous workup), 1894 of 3529 (54%) were available. Availability of domestic URDs was 45%. Donor Readiness score was highly predictive of CT availability. More non-European patients (n = 120) than Europeans (n = 335) had >10 URDs requested and <5 available. Of workup requests (after CT or CT-workup), <70% (604/889 [68%]) were available. More non-Europeans had <2 URDs available. URD availability for CT was markedly worse for non-Europeans, with availabilities for African, non-Black Hispanic, and Asian patients being 150 of 458 (33%), 120 of 258 (47%), and 119 of 270 (44%), respectively, with further decrements in URD workup availability. Our data suggest the functional size of the URD pool is much smaller than appreciated, mandating major operational changes for transplant centers and donor registries. Likelihood of donor availability should have a high priority in donor selection. Considering patient ancestry and URD Donor Readiness scores, centers should pursue, and registries permit, simultaneous pursuit of many URDs and abandon futile searches. Patients should be informed about their likelihood of donor availability and alternative options. Finally, although registries should address high URD attrition and speed procurement, use of all HLA-disparate graft types is needed to facilitate timely transplant for all.