Monocytic leukemia with CALM/AF10 rearrangement showing mediastinal emphysema

CXCR4 Mediates Enhanced Cell Migration in CALM-AF10 Leukemia

Leukemia transformed by the CALM-AF10 chromosomal translocation is characterized by a high incidence of extramedullary disease, central nervous system (CNS) relapse, and a poor prognosis. Invasion of the extramedullary compartment and CNS requires leukemia cell migration out of the marrow and adherence to the cells of the local tissue. Cell adhesion and migration are increasingly recognized as contributors to leukemia development and therapeutic response. These processes are mediated by a variety of cytokines, chemokines, and their receptors, forming networks of both secreted and cell surface factors. The cytokines and cytokine receptors that play key roles in CALM-AF10 driven leukemia are unknown. We find high cell surface expression of the cytokine receptor CXCR4 on leukemia cells expressing the CALM-AF10 oncogenic protein, contributing to the migratory nature of this leukemia. Our discovery of altered cytokine receptor expression and function provides valuable insight into the propagation and persistence of CALM-AF10 driven leukemia.

The target cell of transformation is distinct from the leukemia stem cell in murine CALM/AF10 leukemia models

The CALM/AF10 fusion gene is found in various hematological malignancies including acute myeloid leukemia (AML), T-cell acute lymphoblastic leukemia and malignant lymphoma. We have previously identified the leukemia stem cell (LSC) in a CALM/AF10-driven murine bone marrow transplant AML model as B220+ lymphoid cells with B-cell characteristics. To identify the target cell for leukemic transformation or 'cell of origin of leukemia' (COL) in non-disturbed steady-state hematopoiesis, we inserted the CALM/AF10 fusion gene preceded by a loxP-flanked transcriptional stop cassette into the Rosa26 locus. Vav-Cre-induced panhematopoietic expression of the CALM/AF10 fusion gene led to acute leukemia with a median latency of 12 months. Mice expressing CALM/AF10 in the B-lymphoid compartment using Mb1-Cre or CD19-Cre inducer lines did not develop leukemia. Leukemias had a predominantly myeloid phenotype but showed coexpression of the B-cell marker B220, and had clonal B-cell receptor rearrangements. Using whole-exome sequencing, we identified an average of two to three additional mutations per leukemia, including activating mutations in known oncogenes such as FLT3 and PTPN11. Our results show that the COL for CALM/AF10 leukemia is a stem or early progenitor cell and not a cell of B-cell lineage with a phenotype similar to that of the LSC in CALM/AF10+ leukemia.

Pneumomediastinum, pneumorachis, subcutaneous emphysema: An unusual complication of leukemia in a child

Pneumorrhachis (PR), or epidural emphysema, denotes the presence of air in the spinal epidural space. It can be associated with a variety of etiologies, including trauma; recent iatrogenic manipulations during surgical, anesthesiological and diagnostic interventions; malignancy and its associated therapy. It usually represents an asymptomatic epiphenomenon but also can be symptomatic by itself, as well as by its underlying pathology, and rarely can be fatal. The pathogenesis and etiology of PR are varied and can sometimes be a diagnostic challenge. As such, there are no standard guidelines for the management of symptomatic PR and its treatment is often individualized. Here, we present a case of a 14-year-old boy treated for leukemia who developed this complication and whether chemotherapy related or not, it proved to be fatal for him. To our knowledge, this is the first case in the literature of this complication with acute lymphoblastic leukemia.

New recurrent balanced translocations in acute myeloid leukemia and myelodysplastic syndromes: cancer and leukemia group B 8461

Acquired chromosome abnormalities in patients with acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) are among the most valuable determinants of diagnosis and prognosis. In search of new recurrent balanced translocations, we reviewed the Cancer and Leukemia Group B (CALGB) cytogenetics database containing pretreatment and relapse karyotypes of 4,701 adults with AML and 565 with MDS who were treated on CALGB trials. We identified all cases with balanced structural rearrangements occurring as a sole abnormality or in addition to one other abnormality, excluded abnormalities known to be recurrent, and then reviewed the literature to determine whether any of what we considered unique, previously unknown abnormalities had been reported. As a result, we identified seven new recurrent balanced translocations in AML or MDS: t(7;11)(q22;p15.5), t(10;11)(q23;p15), t(2;12)(p13;p13), t(12;17)(p13;q12), t(2;3)(p21;p21), t(5;21)(q31;q22), and t(8;14)(q24.1;q32.2), and additionally, t(10;12)(p11;q15), a new translocation in AML previously reported in a case of acute lymphoblastic leukemia. Herein, we report hematologic and clinical characteristics and treatment outcomes of patients with these newly recognized recurrent translocations. We also report 52 unique balanced translocations, together with the clinical data of patients harboring them, which to our knowledge have not been previously published. We hope that once the awareness of their existence is increased, some of these translocations may become recognized as novel recurring abnormalities. Identification of additional cases with both the new recurrent and the unique balanced translocations will enable determination of their prognostic significance and help to provide insights into the mechanisms of disease pathogenesis in patients with these rare abnormalities.

Design and feasibility of a novel, rapid, and simple fluorescence 26-plex rt-PCR assay for simultaneous detection of 24 fusion transcripts in adult acute myeloid leukemia

Identification of chromosomal abnormalities is mandatory for classification of acute myeloid leukemia (AML), and the abnormalities have to be determined quickly, to allow patient enrollment in multicenter protocols and/or for selecting therapeutic strategies. Rapid AML molecular diagnosis is often difficult to achieve, however, because it is based on numerous different RT-PCR protocols. We developed a new RT-PCR method, one that does not require a nested step, to simultaneously detect all AML fusion transcripts from six major recurrent translocations found in adults: t(15;17)(q22;q12), inv(16)(p13.1q22) [t(16;16)(p13.1;q22)], t(8;21)(q22;q22), t(6;9)(p23;q34), t(9;22)(q34;q11), and t(10;11)(p13;q14). Specific primers for RT-PCR detection of the 24 fusion transcripts, along with two transcripts for controls, were designed for this 26-plex RT-PCR. Each PCR product had a different size and was separated by capillary electrophoresis. We also designed a multiplex positive control with 24 chimeric RNAs, corresponding to all chimeric RNAs tested. Compared with classical molecular biology protocols and cytogenetic analyses used as reference standards, results of the 26-plex RT-PCR method were concordant in all 204 (100%) cases of adult AML tested. Results were obtained in less than 24 hours. Because of the multiplex positive control, interpretation of the peaks was very easy, without any ambiguity. The tumor cell detection threshold was 1.5%.

Clathrin assembly lymphoid myeloid leukemia-AF10-positive acute leukemias: a report of 2 cases with a review of the literature

The translocation t(10;11)(p13;q14q21) has been found to be recurrent in acute lymphoblastic and myeloid leukemias, and results in the fusion of the clathrin assembly lymphoid myeloid leukemia (CALM) gene with the AF10 gene; these genes are present on chromosomes 11 and 10, respectively. Because the CALM-AF10 rearrangement is a rare chromosomal abnormality, it is not included in routine molecular tests for acute leukemia. Here, we describe the cases of 2 patients with the CALM-AF10 fusion gene. The first patient (case 1) was diagnosed with T-cell ALL, and the second patient (case 2) was diagnosed with AML. Both patient samples showed expression of the homeobox A gene cluster and the histone methyltransferase hDOT1L, which suggests that they mediate leukemic transformation in CALM-AF10-positive and mixed-lineage leukemia-AF10-positive leukemias. Both patients achieved complete remission after induction chemotherapy. The first patient (case 1) relapsed after double-unit cord blood transplantation; there was no evidence of relapse in the second patient (case 2) after allogenic peripheral blood stem cell transplantation. Since CALM-AF10- positive leukemias have been shown to have poor prognosis with conventional therapy, molecular tests for CALM-AF10 rearrangement would be necessary to detect minimal residual disease during follow-up.

The role of CALM-AF10 gene fusion in acute leukemia

Chromosomal translocations are important genetic perturbations frequently associated with hematologic malignancies; characterization of these events has been a rich source of insights into the mechanisms that lead to malignant transformation. The t(10;11)(p13;q14-21) results in a recently identified rare but recurring chromosomal translocation seen in patients with ALL as well as AML, and results in the production of a CALM-AF10 fusion gene. Although the details by which the CALM-AF10 fusion protein exerts its leukemogenic effect remain unclear, emerging data suggests that the CALM-AF10 fusion impairs differentiation of hematopoietic cells, at least in part via an upregulation of HOXA cluster genes. This review discusses the normal structure and function of CALM and AF10, describes the spectrum of clinical findings seen in patients with CALM-AF10 fusions, summarizes recently published CALM-AF10 mouse models and highlights the role of HOXA cluster gene activation in CALM-AF10 leukemia.

The novel CALM interactor CATS influences the subcellular localization of the leukemogenic fusion protein CALM/AF10

The Clathrin Assembly Lymphoid Myeloid leukemia gene (CALM or PICALM) was first identified as the fusion partner of AF10 in the t(10;11)(p13;q14) translocation, which is observed in acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL) and malignant lymphoma. The CALM/AF10 fusion protein plays a crucial role in t(10;11)(p13;q14) associated leukemogenesis. Using the N-terminal half of CALM as a bait in a yeast two-hybrid screen, a novel protein named CATS (CALM interacting protein expressed in thymus and spleen) was identified. Multiple tissue Northern blot analysis showed predominant expression of CATS in thymus, spleen and colon. CATS codes for two protein isoforms of 238 and 248 amino acids (aa). The interaction between CALM and CATS could be confirmed using pull down assays, co-immunoprecipitation and colocalization experiments. The CATS interaction domain of CALM was mapped to aa 221-335 of CALM. This domain is contained in the CALM/AF10 fusion protein. CATS localizes to the nucleus and shows a preference for nucleoli. Expression of CATS was able to markedly increase the nuclear localization of CALM and of the leukemogenic fusion protein CALM/AF10. The possible implications of these findings for CALM/AF10-mediated leukemogenesis are discussed.