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TP53, which encodes the tumor suppressor p53, is the most frequently mutated gene in human cancer. The selective pressures shaping its mutational spectrum, dominated by missense mutations, are enigmatic, and neomorphic gain-of-function (GOF) activities have been implicated. We used CRISPR-Cas9 to generate isogenic human leukemia cell lines of the most common TP53 missense mutations. Functional, DNA-binding, and transcriptional analyses revealed loss of function but no GOF effects. Comprehensive mutational scanning of p53 single–amino acid variants demonstrated that missense variants in the DNA-binding domain exert a dominant-negative effect (DNE). In mice, the DNE of p53 missense variants confers a selective advantage to hematopoietic cells on DNA damage. Analysis of clinical outcomes in patients with acute myeloid leukemia showed no evidence of GOF for TP53 missense mutations. Thus, a DNE is the primary unit of selection for TP53 missense mutations in myeloid malignancies.

About 10% of people older than 70 years of age carry one or more mutations in their hematopoietic cells, and these persons have a higher relative risk of a hematologic cancer (by a factor of 11) and of death from cardiovascular disease (by a factor of 2.0 to 2.6). Cancer is thought to arise through the stepwise acquisition of genetic or epigenetic changes that transform a normal cell. 1 Hence, the existence of a premalignant state bearing only the initiating lesions may be detectable in some persons who have no other signs of disease. For example, multiple myeloma is frequently preceded by monoclonal gammopathy of unknown significance, 2 and chronic lymphocytic leukemia is commonly preceded by monoclonal B-cell lymphocytosis. 3 Several lines of evidence have suggested that clonal hematopoiesis resulting from an expansion of cells that harbor an initiating driver mutation might be an aspect of the aging hematopoietic system. Clonal hematopoiesis . . .

Prognostic systems for myelodysplasia rely on clinical factors, but particular genetic lesions can influence relapse rate, overall survival, and nonrelapse-related mortality as well as the choice of conditioning regimen for hematopoietic stem-cell transplantation. The myelodysplastic syndrome (MDS) is clinically and biologically heterogeneous. In children and young adults, MDS can arise in the context of congenital mutations that cause bone marrow failure syndromes or inherited predisposition to myeloid cancers. 1 Therapy-related MDS develops as a late complication in patients with previous exposure to chemotherapy, radiation therapy, or both. 2 In most patients, however, primary MDS arises in the absence of an identified exposure, prodromal bone marrow failure syndrome, or inherited predisposition. Although allogeneic hematopoietic stem-cell transplantation is the only curative therapy for MDS, mortality after transplantation is high, with deaths attributable to relapsed disease and to . . .

Greater than 90% of cases of systemic mastocytosis (SM) harbor pathogenic KIT mutations, particularly KIT D816V . Prognostically-significant pathogenic KIT mutations also occur in 30–40% of core binding factor-associated acute myeloid leukemia (CBF-AML), but are uncommonly associated with concurrent SM. By comparison, the occurrence of SM in other myeloid neoplasms bearing pathogenic KIT mutations, particularly those with a chronic course, is poorly understood. Review of clinical next-generation sequencing (NGS) performed at our institutions in patients with known or suspected hematologic malignancies over an 8-year period revealed 64 patients with both a pathogenic KIT mutation detected at one or more timepoints and available bone marrow biopsy materials. Patients with KIT D816V -mutated myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), or overlap MDS/MPN ( n  = 22) accounted for approximately one-third of our cohort (34%). Comprehensive morphologic and immunophenotypic characterization revealed that nearly all cases ( n  = 20, 91%) exhibited concurrent SM. In contrast, of the 18 patients (28%) with AML and KIT D816V , only eight (44%) showed evidence of SM at any point in their disease course ( p  = 0.0021); of these eight, the AML component was characterized as AML with myelodysplasia-related changes (AML-MRC) in all but one instance ( n  = 7, 87%). Twelve patients (19%) had pathogenic KIT mutations other than p.D816V, all in the setting of AML (CFB-AML, n  = 7; AML, not otherwise specified, n  = 2; AML-MRC, n  = 1; acute promyelocytic leukemia, n  = 1); only two of these patients (17%), both with CBF-AML, exhibited concurrent SM. The remaining 12 patients (19%) had SM without evidence of an associated hematological neoplasm (AHN). For nearly one-third of the 30 SM-AHN patients in our cohort ( n  = 9, 30%), the SM component of their disease was not initially clinicopathologically recognized. We propose that identification of the KIT D816V mutation in patients diagnosed with MDS, MPN, MDS/MPN, or AML-MRC should trigger reflex testing for SM.

B and T lymphocyte attenuator (BTLA) provides an inhibitory signal to B and T cells. Previously, indirect observations suggested that B7x was a ligand for BTLA. Here we show that BTLA does not bind B7x; instead, we identify herpesvirus entry mediator (HVEM) as the unique BTLA ligand. BTLA bound the most membrane-distal cysteine-rich domain of HVEM, distinct from regions where the ligands LIGHT and lymphotoxin-α bound HVEM. HVEM induced BTLA tyrosine phosphorylation and association of the tyrosine phosphatase SHP-2 and repressed antigen-driven T cell proliferation, providing an example of reverse signaling to a non–tumor necrosis factor family ligand. The conservation of the BTLA-HVEM interaction between mouse and human suggests that this system is an important pathway regulating lymphocyte activation and/or homeostasis in the immune response.

Upfront resistance to chemotherapy and relapse following remission are critical problems in leukemia that are generally attributed to subpopulations of chemoresistant tumor cells. There are, however, limited means for prospectively identifying these subpopulations, which hinders an understanding of therapeutic resistance. BH3 profiling is a functional single-cell analysis using synthetic BCL-2 BH3 domain-like peptides that measures mitochondrial apoptotic sensitivity or \"priming.\" Here, we observed that the extent of apoptotic priming is heterogeneous within multiple cancer cell lines and is not the result of experimental noise. Apoptotic priming was also heterogeneous in treatment-naive primary human acute myeloid leukemia (AML) myeloblasts, and this heterogeneity decreased in chemotherapy-treated AML patients. The priming of the most apoptosis-resistant tumor cells, rather than the median priming of the population, best predicted patient response to induction chemotherapy. For several patients, these poorly primed subpopulations of AML tumor cells were enriched for antiapoptotic proteins. Developing techniques to identify and understand these apoptosis-insensitive subpopulations of tumor cells may yield insights into clinical chemoresistance and potentially improve therapeutic outcomes in AML.

To understand the mechanisms that mediate germline genetic leukemia predisposition, we studied the inherited ribosomopathy Shwachman-Diamond syndrome (SDS), a bone marrow failure disorder with high risk of myeloid malignancies at an early age. To define the mechanistic basis of clonal hematopoiesis in SDS, we investigate somatic mutations acquired by patients with SDS followed longitudinally. Here we report that multiple independent somatic hematopoietic clones arise early in life, most commonly harboring heterozygous mutations in EIF6 or TP53 . We show that germline SBDS deficiency establishes a fitness constraint that drives selection of somatic clones via two distinct mechanisms with different clinical consequences. EIF6 inactivation mediates a compensatory pathway with limited leukemic potential by ameliorating the underlying SDS ribosome defect and enhancing clone fitness. TP53 mutations define a maladaptive pathway with enhanced leukemic potential by inactivating tumor suppressor checkpoints without correcting the ribosome defect. Subsequent development of leukemia was associated with acquisition of biallelic TP53 alterations. These results mechanistically link leukemia predisposition to germline genetic constraints on cellular fitness, and provide a rational framework for clinical surveillance strategies. Understanding the molecular basis of leukaemia predisposition is essential for intervention. The authors here investigate germline genetic leukaemia predisposition by studying Shwachman-Diamond syndrome and report compensatory inactivating mutations in EIF6 and transforming biallelic TP53 alterations.

In a mouse model of the 5q- subtype of myelodysplastic syndrome, haploinsufficiency of the ribosomal protein gene Rps14 leads to anemia through a mechanism involving innate immune signaling and the Tlr4 ligand S100A8, which induces a p53-dependent block to erythroid differentiation. Impaired erythropoiesis in the deletion 5q (del(5q)) subtype of myelodysplastic syndrome (MDS) has been linked to heterozygous deletion of RPS14 , which encodes the ribosomal protein small subunit 14. We generated mice with conditional inactivation of Rps14 and demonstrated an erythroid differentiation defect that is dependent on the tumor suppressor protein p53 (encoded by Trp53 in mice) and is characterized by apoptosis at the transition from polychromatic to orthochromatic erythroblasts. This defect resulted in age-dependent progressive anemia, megakaryocyte dysplasia and loss of hematopoietic stem cell (HSC) quiescence. As assessed by quantitative proteomics, mutant erythroblasts expressed higher levels of proteins involved in innate immune signaling, notably the heterodimeric S100 calcium-binding proteins S100a8 and S100a9. S100a8—whose expression was increased in mutant erythroblasts, monocytes and macrophages—is functionally involved in the erythroid defect caused by the Rps14 deletion, as addition of recombinant S100a8 was sufficient to induce a differentiation defect in wild-type erythroid cells, and genetic inactivation of S100a8 expression rescued the erythroid differentiation defect of Rps14 -haploinsufficient HSCs. Our data link Rps14 haploinsufficiency in del(5q) MDS to activation of the innate immune system and induction of S100A8-S100A9 expression, leading to a p53-dependent erythroid differentiation defect.

Akiko Shimamura and colleagues report the identification of dominant-negative germline variants in ETV6 that cause thrombocytopenia and hematologic malignancies in the affected members of three families. All three mutations alter conserved amino acids in the transcriptional repressor encoded by ETV6 and affect its DNA binding. We report germline missense mutations in ETV6 segregating with the dominant transmission of thrombocytopenia and hematologic malignancy in three unrelated kindreds, defining a new hereditary syndrome featuring thrombocytopenia with susceptibility to diverse hematologic neoplasms. Two variants, p.Arg369Gln and p.Arg399Cys, reside in the highly conserved ETS DNA-binding domain. The third variant, p.Pro214Leu, lies within the internal linker domain, which regulates DNA binding. These three amino acid sites correspond to hotspots for recurrent somatic mutation in malignancies. Functional studies show that the mutations abrogate DNA binding, alter subcellular localization, decrease transcriptional repression in a dominant-negative fashion and impair hematopoiesis. These familial genetic studies identify a central role for ETV6 in hematopoiesis and malignant transformation. The identification of germline predisposition to cytopenias and cancer informs the diagnosis and medical management of at-risk individuals.

The clinical impact of molecular ontogeny in acute myeloid leukemia (AML) was defined in patients treated with intensive chemotherapy. In a cohort of 314 newly diagnosed AML patients, we evaluated whether molecular ontogeny subgroups have differential benefit of venetoclax (VEN) added to hypomethylating agents (HMA). In secondary ontogeny ( n  = 115), median overall survival (OS)(14.1 vs . 6.9 months, P  = 0.0054), composite complete remission (cCR 61% vs . 18%, P  < 0.001) and allogeneic hematopoietic stem cell transplant (alloHCT) (24% vs . 6%, P  = 0.02) rates were better in patients treated with HMA + VEN vs . HMA. In contrast, in TP53 AML( n  = 111) median OS (5.7 vs . 6.1, P  = 0.93), cCR (33% vs. 37%, P  = 0.82) and alloHCT rates (15% vs . 8%, P  = 0.38) did not differ between HMA + VEN vs. HMA. The benefit of VEN addition in the secondary group was preserved after adjustment for significant clinicopathologic variables (HR 0.59 [95% CI 0.38–0.94], P  = 0.025). The OS benefit of HMA + VEN in secondary ontogeny was similar in those with vs . without splicing mutations ( P  = 0.92). Secondary ontogeny AML highlights a group of patients whose disease is selectively responsive to VEN added to HMA and that the addition of VEN has no clinical benefit in TP53 -mutated AML.