Clinical characteristics and overall survival among acute myeloid leukemia patients with TP53 gene mutation or chromosome 17p deletion.

Approximately 5% to 15% of acute myeloid leukemia (AML) patients have TP53 gene mutations (TP53m), which are associated with very poor outcomes. Adults (≥18 years) with a new AML diagnosis were included from a nationwide, de-identified, real-world database. Patients receiving first-line therapy were divided into three cohorts: venetoclax (VEN) + hypomethylating agents (HMAs; Cohort A), intensive chemotherapy (Cohort B), or HMA without VEN (Cohort C). A total of 370 newly diagnosed AML patients with TP53m (n = 124), chromosome 17p deletion (n = 166), or both (n = 80) were included. The median age was 72 years (range, 24-84); most were male (59%) and White (69%). Baseline bone marrow (BM) blasts were ≤30%, 31%-50%, and >50% in 41%, 24%, and 29% of patients in Cohorts A, B, and C, respectively. BM remission (<5% blasts) with first-line therapy was reported in 54% of patients (115/215) overall, and 67% (38/57), 62% (68/110), and 19% (9/48) for respective cohorts (median BM remission duration: 6.3, 6.9, and 5.4 months). Median overall survival (95% CI) was 7.4 months (6.0-8.8) for Cohort A, 9.4 months (7.2-10.4) for Cohort B, and 5.9 months (4.3-7.5) for Cohort C. There were no differences in survival by treatment type after adjusting for the effects of relevant covariates (Cohort A vs. C adjusted hazard ratio [aHR] = 0.9; 95% CI, 0.7-1.3; Cohort A vs. B aHR = 1.0; 95% CI, 0.7-1.5; and Cohort C vs. B aHR = 1.1; 95% CI, 0.8-1.6). Patients with TP53m AML have dismal outcomes with current therapies, demonstrating the high unmet need for improved treatments.

Role of TP53 mutations in the origin and evolution of therapy-related acute myeloid leukaemia.

Therapy-related acute myeloid leukaemia (t-AML) and therapy-related myelodysplastic syndrome (t-MDS) are well-recognized complications of cytotoxic chemotherapy and/or radiotherapy. There are several features that distinguish t-AML from de novo AML, including a higher incidence of TP53 mutations, abnormalities of chromosomes 5 or 7, complex cytogenetics and a reduced response to chemotherapy. However, it is not clear how prior exposure to cytotoxic therapy influences leukaemogenesis. In particular, the mechanism by which TP53 mutations are selectively enriched in t-AML/t-MDS is unknown. Here, by sequencing the genomes of 22 patients with t-AML, we show that the total number of somatic single-nucleotide variants and the percentage of chemotherapy-related transversions are similar in t-AML and de novo AML, indicating that previous chemotherapy does not induce genome-wide DNA damage. We identified four cases of t-AML/t-MDS in which the exact TP53 mutation found at diagnosis was also present at low frequencies (0.003-0.7%) in mobilized blood leukocytes or bone marrow 3-6 years before the development of t-AML/t-MDS, including two cases in which the relevant TP53 mutation was detected before any chemotherapy. Moreover, functional TP53 mutations were identified in small populations of peripheral blood cells of healthy chemotherapy-naive elderly individuals. Finally, in mouse bone marrow chimaeras containing both wild-type and Tp53(+/-) haematopoietic stem/progenitor cells (HSPCs), the Tp53(+/-) HSPCs preferentially expanded after exposure to chemotherapy. These data suggest that cytotoxic therapy does not directly induce TP53 mutations. Rather, they support a model in which rare HSPCs carrying age-related TP53 mutations are resistant to chemotherapy and expand preferentially after treatment. The early acquisition of TP53 mutations in the founding HSPC clone probably contributes to the frequent cytogenetic abnormalities and poor responses to chemotherapy that are typical of patients with t-AML/t-MDS.

Fresh or Cryopreserved CD34+-Selected Mobilized Peripheral Blood Stem and Progenitor Cells for the Treatment of Poor Graft Function after Allogeneic Hematopoietic Cell Transplantation.

CD34+-selected stem cell boost (SCB) without conditioning has recently been utilized for poor graft function (PGF) after allogeneic hematopoietic stem cell transplantation with promising results. Unfortunately, many patients have been unable to receive the boost infusion as their donors were unwilling or unable to undergo an additional stem cell collection. Therefore, we conducted this study utilizing either fresh or cryopreserved peripheral blood stem cell products to create CD34+-selected boost infusions for the treatment of PGF. Additionally, to explore relationship of CD34+ dose and response, we included a cohort of donors mobilized with plerixafor in addition to the standard granulocyte colony-stimulating factor (G-CSF). Twenty-six patients with PGF were included in this study. Seventeen donor-recipient pairs were enrolled onto the prospective study; an additional 9 patients treated off protocol were reviewed retrospectively. Three different donor products were used for CD34+ selection: (1) fresh mobilized product using G-CSF only, (2) fresh mobilized products using G-CSF and plerixafor, and (3) cryopreserved cells mobilized with G-CSF. CD34+ cell selection was performed using a CliniMACS. The infusion was not preceded by administration of any chemotherapy or conditioning regimen. The primary objective was hematologic response rate and secondary objectives included CD34+ yields, incidence and severity of acute and chronic graft-versus-host disease (GVHD), overall survival (OS), and relapse-free survival (RFS). The median post-selection CD34+ counts per kilogram of recipient weight were 3.1 × 106, 10.9 × 106, and 1 × 106 for G-CSF only, G-CSF plus plerixafor, and cryopreserved products, respectively. The median CD34+ yields (defined as the number of CD34+ cells after selection/CD34+ cells before CD34+ selection) were 69%, 66%, and 28% for G-CSF only, G-CSF plus plerixafor, and cryopreserved products, respectively. After SCB, 16 of the 26 recipients (62%) had a complete response, including 5 of 8 (63%) who received cryopreserved products. Five had a partial response (19%), resulting in an overall response rate of 81%. One-year RFS and OS were 50% and 65%, respectively. There was no treatment-related toxicity reported other than GVHD: 6 (23%) developed acute GVHD (2 grade I and 4 grade II) and 8 (31%) developed chronic GVHD (2 limited and 6 extensive). Cryopreserved products are viable alternatives to create SCB for the treatment of PGF. When collecting fresh products is an option, the addition of plerixafor increases CD34+ yield over G-CSF alone; however, it is currently unclear if the CD34+ cell dose impacts the efficacy of the SCB.

The presence of Philadelphia chromosome does not confer poor prognosis in adult pre-B acute lymphoblastic leukaemia in the tyrosine kinase inhibitor era - a surveillance, epidemiology, and end results database analysis.

The BCR-ABL1 fusion gene is caused by a translocation between chromosomes 9 and 22, resulting in an abnormal chromosome 22 (Philadelphia chromosome; Ph). Prior to the introduction of tyrosine kinase inhibitors (TKI), the presence of BCR-ABL1 conferred a poor prognosis in patients with acute lymphoblastic leukaemia (ALL). We compared the survival of Ph+ and Ph-ALL during the period when TKIs were universally available in the US for Ph+ALL, using a Surveillance, Epidemiology, and End Results (SEER) Database analysis. A total of 2694 patients with pre-B ALL (206 Ph+ALL; 2488 Ph-ALL) aged ≥18 years, who were diagnosed between 2010 and 2014, were identified in SEER registries. The median overall survival (OS) was 32 months in Ph+ALL (95% confidence interval [CI] 18 months-not reached) and 27 months (95% CI 24-30 months) in Ph-ALL (Log-rank test P-value 0·34). Older age was associated with worse prognosis in both Ph+ALL and Ph-ALL. Age-adjusted OS was inferior in Hispanics and African-Americans compared to non-Hispanic whites. Survival of pre-B ALL shows continued improvement with time. Philadelphia chromosome status does not confer poor prognosis in pre-B ALL in the TKI era: prognostic factors in pre-B ALL should be re-evaluated in the light of this finding.

Acquired copy number alterations of miRNA genes in acute myeloid leukemia are uncommon.

Altered microRNA (miRNA) expression is frequently observed in acute myelogenous leukemia (AML) and has been implicated in leukemic transformation. Whether somatic copy number alterations (CNAs) are a frequent cause of altered miRNA gene expression is largely unknown. Herein, we used comparative genomic hybridization with a custom high-resolution miRNA-centric array and/or whole-genome sequence data to identify somatic CNAs involving miRNA genes in 113 cases of AML, including 50 cases of de novo AML, 18 cases of relapsed AML, 15 cases of secondary AML following myelodysplastic syndrome, and 30 cases of therapy-related AML. We identified a total of 48 somatic miRNA gene-containing CNAs that were not identified by routine cytogenetics in 20 patients (18%). All these CNAs also included one or more protein coding genes. We identified a single case with a hemizygous deletion of MIR223, resulting in the complete loss of miR-223 expression. Three other cases of AML were identified with very low to absent miR-223 expression, an miRNA gene known to play a key role in myelopoiesis. However, in these cases, no somatic genetic alteration of MIR223 was identified, suggesting epigenetic silencing. These data show that somatic CNAs specifically targeting miRNA genes are uncommon in AML.

Next-generation sequencing identifies the natural killer cell microRNA transcriptome.

Natural killer (NK) cells are innate lymphocytes important for early host defense against infectious pathogens and surveillance against malignant transformation. Resting murine NK cells regulate the translation of effector molecule mRNAs (e.g., granzyme B, GzmB) through unclear molecular mechanisms. MicroRNAs (miRNAs) are small noncoding RNAs that post-transcriptionally regulate the translation of their mRNA targets, and are therefore candidates for mediating this control process. While the expression and importance of miRNAs in T and B lymphocytes have been established, little is known about miRNAs in NK cells. Here, we used two next-generation sequencing (NGS) platforms to define the miRNA transcriptomes of resting and cytokine-activated primary murine NK cells, with confirmation by quantitative real-time PCR (qRT-PCR) and microarrays. We delineate a bioinformatics analysis pipeline that identified 302 known and 21 novel mature miRNAs from sequences obtained from NK cell small RNA libraries. These miRNAs are expressed over a broad range and exhibit isomiR complexity, and a subset is differentially expressed following cytokine activation. Using these miRNA NGS data, miR-223 was identified as a mature miRNA present in resting NK cells with decreased expression following cytokine activation. Furthermore, we demonstrate that miR-223 specifically targets the 3' untranslated region of murine GzmB in vitro, indicating that this miRNA may contribute to control of GzmB translation in resting NK cells. Thus, the sequenced NK cell miRNA transcriptome provides a valuable framework for further elucidation of miRNA expression and function in NK cell biology.

Treatment outcomes for newly diagnosed, treatment-naïve TP53-mutated acute myeloid leukemia: a systematic review and meta-analysis.

BACKGROUND: TP53 mutations, which are present in 5% to 10% of patients with acute myeloid leukemia (AML), are associated with treatment resistance and poor outcomes. First-line therapies for TP53-mutated (TP53m) AML consist of intensive chemotherapy (IC), hypomethylating agents (HMA), or venetoclax combined with HMA (VEN + HMA). METHODS: We conducted a systematic review and meta-analysis to describe and compare treatment outcomes in newly diagnosed treatment-naïve patients with TP53m AML. Randomized controlled trials, single-arm trials, prospective observational studies, and retrospective studies were included that reported on complete remission (CR), CR with incomplete hematologic recovery (CRi), overall survival (OS), event-free survival (EFS), duration of response (DoR), and overall response rate (ORR) among patients with TP53m AML receiving first-line treatment with IC, HMA, or VEN + HMA. RESULTS: Searches of EMBASE and MEDLINE identified 3006 abstracts, and 17 publications describing 12 studies met the inclusion criteria. Random-effects models were used to pool response rates, and time-related outcomes were analyzed with the median of medians method. IC was associated with the greatest CR rate of 43%, and CR rates were 33% for VEN + HMA and 13% for HMA. Rates of CR/CRi were comparable for IC (46%) and VEN + HMA (49%) but were lower for HMA (13%). Median OS was uniformly poor across treatments: IC, 6.5 months; VEN + HMA, 6.2 months; and HMA, 6.1 months. For IC, the EFS estimate was 3.7 months; EFS was not reported for VEN + HMA or HMA. The ORR was 41% for IC, 65% for VEN + HMA, and 47% for HMA. DoR was 3.5 months for IC, 5.0 months for VEN + HMA, and was not reported for HMA. CONCLUSIONS: Despite improved responses seen with IC and VEN + HMA compared to HMA, survival was uniformly poor, and clinical benefits were limited across all treatments for patients with newly diagnosed, treatment-naïve TP53m AML, demonstrating a significant need for improved treatment for this difficult-to-treat population.

Magrolimab in Combination With Azacitidine in Patients With Higher-Risk Myelodysplastic Syndromes: Final Results of a Phase Ib Study.

PURPOSE: Magrolimab is a monoclonal antibody that blocks cluster of differentiation 47, a don't-eat-me signal overexpressed on cancer cells. Cluster of differentiation 47 blockade by magrolimab promotes macrophage-mediated phagocytosis of tumor cells and is synergistic with azacitidine, which increases expression of eat-me signals. We report final phase Ib data in patients with untreated higher-risk myelodysplastic syndromes (MDS) treated with magrolimab and azacitidine (ClinicalTrials.gov identifier: NCT03248479). PATIENTS AND METHODS: Patients with previously untreated Revised International Prognostic Scoring System intermediate-/high-/very high-risk MDS received magrolimab intravenously as a priming dose (1 mg/kg) followed by ramp-up to a 30 mg/kg once-weekly or once-every-2-week maintenance dose. Azacitidine 75 mg/m2 was administered intravenously/subcutaneously once daily on days 1-7 of each 28-day cycle. Primary end points were safety/tolerability and complete remission (CR) rate. RESULTS: Ninety-five patients were treated. Revised International Prognostic Scoring System risk was intermediate/high/very high in 27%, 52%, and 21%, respectively. Fifty-nine (62%) had poor-risk cytogenetics and 25 (26%) had TP53 mutation. The most common treatment-emergent adverse effects included constipation (68%), thrombocytopenia (55%), and anemia (52%). Median hemoglobin change from baseline to first postdose assessment was -0.7 g/dL (range, -3.1 to +2.4). CR rate and overall response rate were 33% and 75%, respectively. Median time to response, duration of CR, duration of overall response, and progression-free survival were 1.9, 11.1, 9.8, and 11.6 months, respectively. Median overall survival (OS) was not reached with 17.1-month follow-up. In TP53-mutant patients, 40% achieved CR with median OS of 16.3 months. Thirty-four patients (36%) had allogeneic stem-cell transplant with 77% 2-year OS. CONCLUSION: Magrolimab + azacitidine was well tolerated with promising efficacy in patients with untreated higher-risk MDS, including those with TP53 mutations. A phase III trial of magrolimab/placebo + azacitidine is ongoing (ClinicalTrials.gov identifier: NCT04313881 [ENHANCE]).

Tolerability and Efficacy of the Anticluster of Differentiation 47 Antibody Magrolimab Combined With Azacitidine in Patients With Previously Untreated AML: Phase Ib Results.

PURPOSE: Magrolimab is a first-in-class humanized monoclonal antibody against cluster of differentiation 47, an antiphagocytic signal used by cancer cells to evade phagocytosis. Azacitidine upregulates prophagocytic signals on AML cells, further increasing phagocytosis when combined with magrolimab. We report final phase Ib data for magrolimab with azacitidine in patients with untreated AML ineligible for intensive chemotherapy (ClinicalTrials.gov identifier: NCT03248479). PATIENTS AND METHODS: Patients with previously untreated AML, including TP53-mutant AML, received magrolimab intravenously as an initial dose (1 mg/kg, days 1 and 4), followed by 15 mg/kg once on day 8 and 30 mg/kg once weekly or every 2 weeks as maintenance. Azacitidine 75 mg/m2 was administered intravenously/subcutaneously once daily on days 1-7 of each 28-day cycle. Primary end points were safety/tolerability and proportion with complete remission (CR). RESULTS: Eighty-seven patients were enrolled and treated; 72 (82.8%) had TP53 mutations with a median variant allele frequency of 61% (range, 9.8-98.7). Fifty-seven (79.2%) of TP53-mutant patients had European LeukemiaNet 2017 adverse-risk cytogenetics. Patients received a median of 4 (range, 1-39) cycles of treatment. The most common treatment-emergent adverse events included constipation (49.4%), nausea (49.4%), and diarrhea (48.3%). Thirty (34.5%) experienced anemia, and the median hemoglobin change from baseline to first postdose assessment was -0.9 g/dL (range, -3.6 to 2.5 g/dL). Twenty-eight (32.2%) patients achieved CR, including 23 (31.9%) patients with TP53 mutations. The median overall survival in TP53-mutant and wild-type patients were 9.8 months and 18.9 months, respectively. CONCLUSION: Magrolimab with azacitidine was relatively well tolerated with promising efficacy in patients with AML ineligible for intensive induction chemotherapy, including those with TP53 mutations, warranting further evaluation of magrolimab with azacitidine in AML. The phase III randomized ENHANCE-2 (ClinicalTrials.gov identifier: NCT04778397) and ENHANCE-3 (ClinicalTrials.gov identifier: NCT05079230) studies are recruiting frontline patients with AML.

Complete characterization of the microRNAome in a patient with acute myeloid leukemia.

MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression and have been implicated in the pathogenesis of cancer. In this study, we applied next generation sequencing techniques to comprehensively assess miRNA expression, identify genetic variants of miRNA genes, and screen for alterations in miRNA binding sites in a patient with acute myeloid leukemia. RNA sequencing of leukemic myeloblasts or CD34(+) cells pooled from healthy donors showed that 472 miRNAs were expressed, including 7 novel miRNAs, some of which displayed differential expression. Sequencing of all known miRNA genes revealed several novel germline polymorphisms but no acquired mutations in the leukemia genome. Analysis of the sequence of the 3'-untranslated regions (UTRs) of all coding genes identified a single somatic mutation in the 3'-UTR of TNFAIP2, a known target of the PML-RARα oncogene. This mutation resulted in translational repression of a reporter gene in a Dicer-dependent fashion. This study represents the first complete characterization of the "miRNAome" in a primary human cancer and suggests that generation of miRNA binding sites in the UTR regions of genes is another potential mechanism by which somatic mutations can affect gene expression.

Publisher Correction: The molecular landscape of pediatric acute myeloid leukemia reveals recurrent structural alterations and age-specific mutational interactions.

In the version of this article originally published, the color key in Fig. 1a was wrong. In the Cytogenetics key, the box over t(8;21) originally was green. It should have been red, matching the color of the sections of the pie graphs below the key that were labeled with 15% and 19%.

Transposable Element Expression in Acute Myeloid Leukemia Transcriptome and Prognosis.

Over half of the human genome is comprised of transposable elements (TE). Despite large-scale studies of the transcriptome in cancer, a comprehensive look at TE expression and its relationship to various mutations or prognosis has not been performed. We characterized the expression of TE in 178 adult acute myeloid leukemia (AML) patients using transcriptome data from The Cancer Genome Atlas. We characterized mutation specific dysregulation of TE expression using a multivariate linear model. We identified distinct patterns of TE expression associated with specific mutations and transcriptional networks. Genes regulating methylation was not associated with significant change in TE expression. Using an unpenalized cox regression analysis we identified a TE expression signature that predicted prognosis in AML. We identified 14 candidate prognostic TE transcripts (TEP) that classified AML as high/low-risk and this was independent of mutation-based and coding-gene expression based risk-stratification. TEP was able to predict prognosis in independent cohorts of 284 pediatric AML patients and 19 relapsed adult AML patients. This first comprehensive study of TE expression in AML demonstrates that TE expression can serve as a biomarker for prognosis in AML, and provides novel insights into the biology of AML. Studies characterizing its role in other cancers are warranted.

Senescence induction universally activates transposable element expression.

Senescent cells constitutively secrete inflammatory cytokines, known as the senescence-associated secretory phenotype (SASP). Previous work has implicated SASP in immune-mediated clearance of senescent cells; however, its regulation remains unknown. Our recent transcriptome profiling study has shown that human senescent human stem and progenitors (s-HSPCs) robustly express genomic transposable elements (TEs) and pathways of inflammation. Furthermore, hypomethylating agents have been previously shown to induce expression of TEs and activate the dsRNA recognition pathway and downstream interferon-stimulated genes, leading to immune mediated cell death. Therefore, to examine whether activation of TEs occurred universally, independent of their modality of senescence induction, we performed transcriptomic analysis in artificially-induced senescent cell-lines and observed a robust activation of TEs. Hence we propose that the expression of TEs might play a role in immune mediated clearance of senescent cells.

Methylome of human senescent hematopoietic progenitors.

Senescence, a state of permanent cell cycle arrest, can be induced by DNA damage. This process, which was initially described in fibroblasts, is now recognized to occur in stem cells. It has been well characterized in cell lines, but there is currently very limited data available on human senescence in vivo. We recently reported that the expression of transposable elements (TE), including endogenous retroviruses, was up-regulated along with inflammatory genes in human senescent hematopoietic stem and progenitor cells (HSPCs) in vivo. The mechanism of regulation of TE expression is not completely understood, but changes in DNA methylation and chromatin modifications are known to alter their expression. In order to elucidate the molecular mechanisms for TE up-regulation after senescence of HSPCs, we employed whole-genome bisulfite sequencing in paired senescent and active human HSPCs in vivo from healthy subjects. We found that the senescent HSPCs exhibited hypomethylated regions in the genome, which were enriched for TEs. This is the first report characterizing the methylome of senescent human HSPCs.

The role of FLT3 inhibitors as maintenance therapy following hematopoietic stem cell transplant.

Activating mutations in FLT3 in acute myeloid leukemia (AML) portend a poor prognosis, and targeting FLT3 with a tyrosine kinase inhibitor has been an area of intense research recently. Most FLT3 mutated AML patients undergo hematopoietic stem cell transplantation (HSCT) as standard of care but a significant proportion of patients relapse. Although the use of FLT3 inhibitors in the pre-HSCT perspective is more clearly defined, its use in the post-HSCT scenario, when most relapses occur, remains unclear. In this review, we comprehensively present the data on the recent and ongoing studies evaluating the role of various FLT3 inhibitors in AML with a particular focus in the post-HSCT setting.

Understanding metabolic changes in aging bone marrow.

BACKGROUND: Aging is associated with complex molecular alterations at the cellular level. Bone marrow exhibits distinct phenotypic, genetic and epigenetic alterations with aging. Metabolic changes in the bone marrow related to aging have not been studied. METHODS: In this study, we characterized the metabolome and transcriptome of aging murine bone marrow and compared it with bone marrow from young healthy mice and chemotherapy treated mice; chemotherapy treatment is known to induce age-related changes in hematopoiesis. RESULTS: The metabolome of the aging bone marrow exhibited a signature of suppressed fatty-acid oxidation: accumulation of free fatty acids, reduced acyl-carnitines and low ß-hydroxy butyric acid. The aged bone marrow also exhibited a significant reduction in amino acid and nucleic acid pool. The transcriptome of the aging bone marrow revealed a signature of oxidative stress, known to be associated with mitochondrial dysfunction. Lastly, the metabolic and transcriptomic profiles of the bone marrow of chemotherapy treated mice did not show broad age-related changes but rather mostly resembled young healthy mice, suggestive of a lack of 'metabolic aging' with chemotherapy exposure. CONCLUSION: Our results revealed broad changes in lipids, amino acids, and nucleotides in aging marrow tissue. Together, these data provide a rich resource for the study of metabolic changes associated with aging in bone marrow.

A Case of Recurrent Pregnancy-Induced Adult Onset Familial Hemophagocytic Lymphohistiocytosis.

Hemophagocytic lymphohistiocytosis (HLH) is a rare and potentially fatal disease primarily of children, characterized by a severe hyperinflammatory state. We describe a case of adult onset familial HLH with a novel exon 19, c.1607G>T (p.Arg536Leu) heterozygous mutation of the UNC13D gene in a 40-year-old woman who developed HLH during her first and second pregnancies, both episodes occurring during the first trimester. Our patient was treated successfully both times with HLH-94 protocol following spontaneous abortions and is currently in the process of getting a bone marrow transplant. We also discuss pregnancy as a potential trigger for late onset familial HLH.

Author Correction: Suppression of Transposable Elements in Leukemic Stem Cells.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Unrelated HLA mismatched microtransplantation in a patient with refractory secondary acute myeloid leukemia.

Microtransplantation (MST), a type of HLA-mismatched allogeneic cellular therapy, is a promising, cellular therapy for acute myeloid leukemia (AML). MST transfuses granulocyte colony-stimulating factor (G-CSF)-mobilized, HLA-mismatched donor peripheral blood stem cells into patients undergoing conventional chemotherapy. MST, using haploidentical donors, has been shown to yield clinical benefit without any permanent marrow engraftment in AML. Consequently, graft-versus-host disease concerns are rendered irrelevant with no need for immunosuppression. We describe the first reported patient with refractory AML who underwent salvage MST from an unrelated, complete HLA-mismatched donor. The patient achieved remission without complication, warranting further study of unrelated HLA-mismatched donor MST in AML.