Ashish R. Kumar

Malignant Transformation Initiated by Mll-AF9: Gene Dosage and Critical Target Cells

The pathways by which oncogenes, such as MLL-AF9, initiate transformation and leukemia in humans and mice are incompletely defined. In a study of target cells and oncogene dosage, we found that Mll-AF9, when under endogenous regulatory control, efficiently transformed LSK (Lin(-)Sca1(+)c-kit(+)) stem cells, while committed granulocyte-monocyte progenitors (GMPs) were transformation resistant and did not cause leukemia. Mll-AF9 was expressed at higher levels in hematopoietic stem (HSC) than GMP cells. Mll-AF9 gene dosage effects were directly shown in experiments where GMPs were efficiently transformed by the high dosage of Mll-AF9 resulting from retroviral transduction. Mll-AF9 upregulated expression of 192 genes in both LSK and progenitor cells, but to higher levels in LSKs than in committed myeloid progenitors.

EVI1 is critical for the pathogenesis of a subset of MLL-AF9–rearranged AMLs

The proto-oncogene EVI1 (ecotropic viral integration site-1), located on chromosome band 3q26, is aberrantly expressed in human acute myeloid leukemia (AML) with 3q26 rearrangements. In the current study, we showed, in a large AML cohort carrying 11q23 translocations, that ∼ 43% of all mixed lineage leukemia (MLL)-rearranged leukemias are EVI1(pos). High EVI1 expression occurs in AMLs expressing the MLL-AF6, -AF9, -AF10, -ENL, or -ELL fusion genes. In addition, we present evidence that EVI1(pos) MLL-rearranged AMLs differ molecularly, morphologically, and immunophenotypically from EVI1(neg) MLL-rearranged leukemias. In mouse bone marrow cells transduced with MLL-AF9, we show that MLL-AF9 fusion protein maintains Evi1 expression on transformation of Evi1(pos) HSCs. MLL-AF9 does not activate Evi1 expression in MLL-AF9-transformed granulocyte macrophage progenitors (GMPs) that were initially Evi1(neg). Moreover, shRNA-mediated knockdown of Evi1 in an Evi1(pos) MLL-AF9 mouse model inhibits leukemia growth both in vitro and in vivo, suggesting that Evi1 provides a growth-promoting signal. Using the Evi1(pos) MLL-AF9 mouse leukemia model, we demonstrate increased sensitivity to chemotherapeutic agents on reduction of Evi1 expression. We conclude that EVI1 is a critical player in tumor growth in a subset of MLL-rearranged AMLs.

Allogeneic hematopoietic cell transplantation (allogeneic HCT) for treatment of pediatric Philadelphia chromosome-positive acute lymphoblastic leukemia (ALL)†

Allogeneic hematopoietic cell transplant (HCT) with best available donor for children with Philadelphia positive (Ph+) acute lymphoblastic leukemia (ALL) has previously been considered standard practice. Since the introduction of imatinib into the treatment of this disease, the role of allogeneic HCT is more uncertain.

t(4;11) leukemias display addiction to MLL-AF4 but not to AF4-MLL

The most frequent MLL-gene rearrangement found in leukemia is a reciprocal translocation with AF4 on chromosome 4 resulting in the formation of the MLL-AF4 and the AF4-MLL fusion genes. The oncogenic role of MLL-AF4 is documented but the significance of the reciprocal product - AF4-MLL in leukemia is less clear. In the human leukemia cell lines - RS4;11 and SEMK2-M1, both of which express MLL-AF4 and AF4-MLL, we knocked down the expression of AF4-MLL using siRNA. Loss of AF4-MLL had no effect on the growth of either RS4;11 or SEMK2-M1 cells. Furthermore, in SEMK2-M1 cells there were no changes in cell cycle or apoptosis with loss of AF4-MLL. In contrast, knockdown of MLL-AF4 significantly inhibited growth of both RS4;11 and SEMK2-M1. Additionally, in SEMK2-M1 cells, loss of MLL-AF4 led to G2/M cell cycle arrest and increased apoptosis. Overall, these results demonstrate that in t(4;11) leukemia, the MLL-AF4 fusion protein is critical for leukemia cell proliferation and survival while the AF4-MLL fusion product is dispensable.

Familial hemophagocytic lymphohistiocytosis in two brothers with X-linked agammaglobulinemia†

Hemophagocytic lymphohistiocytosis (HLH) is often familial and is associated with high mortality. Primary (familial) HLH is known to occur in children with mutations in perforin, Munc13‐4, or syntaxin 11. We describe a case series of two brothers who developed HLH in the setting of X‐linked agammaglobulinemia (XLA, Brutons disease) and adenovirus infection. Further studies revealed absence of Brutons tyrosine kinase (BTK) protein expression and a novel BTK mutation. Pediatr Blood Cancer 2008;51:293–295.

Fatal hemorrhage from androgen-related hepatic adenoma after hematopoietic cell transplantation.

Fanconi anemia is a rare genetic disorder that leads to bone marrow failure. Hematopoietic cell transplantation (HCT) is currently the only treatment option with curative potential. When a suitable HLA-matched sibling donor is not available, patients are often treated with androgenic steroids before considering HCT. Such androgen treatments can lead to the development of hepatic adenomas, which usually regress upon stopping androgen therapy. A patient with Fanconi anemia is described who underwent an unrelated umbilical cord blood transplant with a history of a hepatic adenoma related to androgen therapy. No adenomas were detected on an ultrasound examination prior to HCT. Soon after HCT, he died due to sudden rupture and hemorrhage of a hepatic adenoma. This case illustrates the need for extra vigilance in the detection and management of hepatic adenomas in patients treated with androgens, especially prior to HCT.