Search

IL-15 may have a role in the development of T cell large granular lymphocyte (T-LGL) or NKT leukemias. However, the mechanisms of action and the identity of the cell subset that undergoes leukemic transformation remain elusive. Here we show that in both mice and humans, NKp46 expression marks a minute population of WT NKT cells with higher activity and potency to become leukemic. Virtually 100% of T-LGL leukemias in IL-15 transgenic mice expressed NKp46, as did a majority of human T-LGL leukemias. The minute [NKp46.sup.+] NKT population, but not the NKp46 NKT population, was selectively expanded by overexpression of endogenous IL-15. Importantly, IL-15 transgenic NKp46 NKT cells did not become [NKp46.sup.+] in vivo, suggesting that [NKp46.sup.+] T-LGL leukemia cells were the malignant counterpart of the minute WT [NKp46.sup.+] NKT population. Mechanistically, [NKp46.sup.+] NKT cells possessed higher responsiveness to IL-15 in vitro and in vivo compared with that of their NKp46 NKT counterparts. Furthermore, interruption of IL-15 signaling using a neutralizing antibody could prevent LGL leukemia in IL-15 transgenic mice. Collectively, our data demonstrate that NKp46 identifies a functionally distinct NKT subset in mice and humans that appears to be directly susceptible to leukemic transformation when IL-15 is overexpressed. Thus, IL-15 signaling and NKp46 maybe useful targets in the treatment of patients with T-LGL or NKT leukemia., Introduction NKT cells are defined as a subset of T cells that share some characteristics with NK cells, particularly expression of the NK1.1 or DX5 antigen in mice and CD56 [...]

Blast crisis chronic myelogenous leukemia (CML-BC) and Philadelphia chromosome-positive (Ph1-positive) acute lymphocytic leukemia (ALL) are 2 fatal BCR/ABL-driven leukemias against which Abl kinase inhibitors fail to induce a long-term response. [...]

Human NK cells are characterized by their ability to initiate an immediate and direct cytolytic response to virally infected or malignantly transformed cells. Within human peripheral blood, the more mature CD56dim NK cell efficiently kills malignant targets at rest, whereas the less mature CD56bright NK cells cannot. In this study, we show that resting CD56bright NK cells express significantly more phosphatase and tensin homolog deleted on chromosome 10 (PTEN) protein when compared with CD56dimT1 NK cells. Consistent with this, forced overexpression of PTEN in NK cells resulted in decreased cytolytic activity, and loss of PTEN in CD56bright NK cells resulted in elevated cytolytic activity. Comparable studies in mice showed PTEN overexpression did not alter NK cell development or NK cell-activating and inhibitory receptor expression yet, as in humans, did decrease expression of downstream NK activation targets MAPK and AKT during early cytolysis of tumor target cells. Confocal microscopy revealed that PTEN overexpression disrupts the NK cell's ability to organize immunological synapse components including decreases in actin accumulation, polarization of the microtubule organizing center, and the convergence of cytolytic granules. In summary, our data suggest that PTEN normally works to limit the NK cell's PI3K/AKT and MAPK pathway activation and the consequent mobilization of cytolytic mediators toward the target cell and suggest that PTEN is among the active regulatory components prior to human NK cells transitioning from the noncytolytic CD56bright NK cell to the cytolytic CD56dim NK cells. [ABSTRACT FROM AUTHOR]

Accumulating evidence indicates that human natural killer (NK) cells develop in secondary lymphoid tissue (SLT) through a so-called "stage 3" developmental intermediate minimally characterized by a CD34-CD117+CD94- immunophenotype that lacks mature NK cell function. This stage 3 population is heterogeneous, potentially composed of functionally distinct innate lymphoid cell (ILC) types that include interleukin-1 receptor (IL-1R1)-positive, IL-22-producing ILC3s. Whether human ILC3s are developmentally related to NK cells is a subject of ongoing investigation. Here, we show that antagonism of the aryl hydrocarbon receptor (AHR) or silencing of AHR gene expression promotes the differentiation of tonsillar IL-22-producing IL-1R1hi human ILC3s to CD56brightCD94+ interferon (IFN)-γ-producing cytolytic mature NK cells expressing eomesodermin (EOMES) and T-Box Protein 21 (TBX21 or TBET). Hence, we demonstrate the lineage plasticity of human ILCs by identifying AHR as a transcription factor that prevents IL-1R1hi ILC3s from differentiating into NK cells. [ABSTRACT FROM AUTHOR]

Activation of the fibromyalgia syndrome-like tyrosine kinase 3 ( FLT3) by its ligand, FLT3 ligand ( FL), strongly augments the development of natural killer ( NK) cells from human CD34+ hematopoietic progenitor cells ( HPCs) in the presence of IL-15, compared with NK-cell development in the presence of IL-15 alone. In this study, we observed that blocking the receptor tyrosine kinase Axl/ Gas6 pathway with a soluble Axl-IgG1 Fc fusion protein ( Axl- Fc) in the presence of FL significantly diminished the absolute number of CD3− CD56+ NK cells derived from human CD34+ HPCs. Axl- Fc reduced the expression levels of the IL-2/15 receptor β chain ( CD122) and γ chain ( CD132) induced by activation of FLT3 and consequently reduced the frequency of NK precursor cells responding to IL-15. Furthermore, Axl- Fc diminished FL-induced FLT3 phosphorylation and impeded the physical interaction between Axl and FLT3 in CD34+ HPCs. Collectively, our data suggest that the Axl/ Gas6 pathway contributes to normal human NK-cell development at least in part via its positive regulatory effect on FLT3 signaling in CD34+ HPCs. [ABSTRACT FROM AUTHOR]

Abstract: Molecular characterization of human natural killer (NK) cells will require targeted gene delivery to inhibit and activate specific signaling pathways, yet to our knowledge, an effective means to deliver such products for long-term gene expression without disrupting normal cellular processes has not been described. In this study, we have developed a retroviral strategy to effectively express gene products in the NK cell, whereby its effector functions of cytotoxicity and cytokine production remain intact. Using an EBV/retroviral hybrid vector, we demonstrate infection of human peripheral blood NK cells with simultaneous expression of a marker for infection–the enhanced green fluorescent protein (EGFP)–along with various genes of interest. This technique results in successful infection of the CD56dim NK population that predominates among human peripheral blood NK and is the effector of antibody-dependent cellular cytotoxicity and natural killing. In addition, we demonstrate infection of the CD56bright NK subset as well as the NK-92 cell line. In summary, we have devised an efficient and reproducible methodology for the targeted delivery of gene products to human NK cells that should now provide opportunities to dissect the molecular processes critical to normal NK cell physiology. [Copyright &y& Elsevier]

The arrest of differentiation is a feature of both chronic myelogenous leukemia cells in myeloid blast crisis and myeloid precursors that ectopically express the p210[sup BCR-ABL] oncoprotein; however, its underlying mechanisms remain poorly understood. Here we show that expression of BCR-ABL in myeloid precursor cells leads to transcriptional suppression of the granulocyte colony-stimulating factor receptor G-CSF-R (encoded by CSF3R), possibly through down-modulation of C/EBPα—the principal regulator of granulocytic differentiation. Expression of C/EBPα protein is barely detectable in primary marrow cells taken from individuals affected with chronic myeloid leukemia in blast crisis. In contrast, CEBPA RNA is clearly present. Ectopic expression of C/EBPα induces granulocytic differentiation of myeloid precursor cells expressing BCR-ABL. Expression of C/EBPα is suppressed at the translational level by interaction of the poly(rC)-binding protein hnRNP E2 with CEBPA mRNA, and ectopic expression of hnRNP E2 in myeloid precursor cells down-regulates both C/EBPα and G-CSF-R and leads to rapid cell death on treatment with G-CSF (encoded by CSF3). Our results indicate that BCR-ABL regulates the expression of C/EBPα by inducing hnRNP E2—which inhibits the translation of CEBPA mRNA. [ABSTRACT FROM AUTHOR]

The BCR/ABL oncogenic tyrosine kinase activates phosphatidylinositol 3-kinase (PI-3k) by a mechanism that requires binding of BCR/ABL to p85, the regulatory subunit of PI-3k, and an intact BCR/ABL SH2 domain. SH2 domain BCR/ABL mutants deficient in PI-3k activation failed to stimulate Akt kinase, a recently identified PI-3k downstream effector with oncogenic potential, but did activate p21 RAS and p70 S6 kinase. The PI-3k/Akt pathway is essential for BCR/ABL leukemogenesis as indicated by experiments demonstrating that wortmannin, a PI-3k specific inhibitor at low concentrations, suppressed BCR/ABL-dependent colony formation of murine marrow cells, and that a kinase-deficient Akt mutant with dominant-negative activity inhibited BCR/ABL-dependent transformation of murine bone marrow cells in vitro and suppressed leukemia development in SCID mice. In complementation assays using mouse marrow progenitor cells, the ability of transformation-defective SH2 domain BCR/ABL mutants to induce growth factor-independent colony formation and leukemia in SCID mice was markedly enhanced by expression of constitutively active Akt. In retrovirally infected mouse marrow cells, the BCR/ABL mutant lacking the SH2 domain was unable to upregulate the expression of c-Myc and Bcl-2; in contrast, expression of a constitutively active Akt mutant induced Bcl-2 and c-Myc expression, and stimulated the transcription activation function of c-Myc. Together, these data demonstrate the requirement for the BCR/ABL SH2 domain in PI-3k activation and document the essential role of the PI-3k/Akt pathway in BCR/ABL leukemogenesis. [ABSTRACT FROM AUTHOR]

The leukemogenic potential of BCR/ABL oncoproteins depends on their tyrosine kinase activity and involves the activation of several downstream effectors, some of which are essential for cell transformation. Using electrophoretic mobility shift assays and Southwestern blot analyses with a double-stranded oligonucleotide containing a zinc finger consensus sequence, we identified a 68 kDa DNA-binding protein specifically induced by BCR/ABL. The peptide sequence of the affinity-purified protein was identical to that of the RNA- binding protein FUS (also called TLS). Binding activity of FUS required a functional BCR/ABL tyrosine kinase necessary to induce PKCβII-dependent FUS phosphorylation. Moreover, suppression of PKCβII activity in BCR/ABL-expressing cells by treatment with the PKCβII inhibitor CGP53353, or by expression of a dominant-negative PKCβII, markedly impaired the ability of FUS to bind DNA. Suppression of FUS expression in myeloid precursor 32Dcl3 cells transfected with a FUS antisense construct was associated with upregulation of the granulocyte-colony stimulating factor receptor (G-CSFR) and downregulation of interleukin-3 receptor (IL-3R) β-chain expression, and accelerated G-CSF-stimulated differentiation. Down-regulation of FUS expression in BCR/ABL-expressing 32Dcl3 cells was associated with suppression of growth factor-independent colony formation, restoration of G-CSF-induced granulocytic differentiation and reduced tumorigenic potential in vivo. Together, these results suggest that FUS might function as a regulator of BCR/ABL leukemogenesis, promoting growth factor independence and preventing differentiation via modulation of cytokine receptor expression. [ABSTRACT FROM AUTHOR]

CD20 is a widely validated, B cell-specific target for therapy in B cell malignancies. Rituximab is an anti-CD20 Ab that prolongs survival of chronic lymphocytic leukemia (CLL) patients when combined with chemotherapy. Ofatumumab and GA101 (obinutuzumab) are CD20-directed Abs currently being developed as alternative agents to rituximab in CLL based upon different properties of enhanced direct cell death, NK cell-mediated Ab-dependent cellular cytotoxicity, or complement-dependent cytotoxicity. Despite widespread study, ofatumumab and GA101 have not been compared with each other, nor studied for their interactions with monocytes and macrophages which are critical for the efficacy of anti-CD20 Abs in murine models. In CLL cells, we show that direct cell death and complement-dependent cytotoxicity are greatest with GA101 and ofatumumab, respectively. GA101 promotes enhanced NK cell activation and Ab-dependent cellular cytotoxicity at high Ab concentrations. Ofatumumab elicits superior Ab-dependent cellular phagocytosis with monocyte-derived macrophages. GA101 demonstrated reduced activation of monocytes with diminished pERK, TNF-α release, and FcγRIIa recruitment to lipid rafts. These data demonstrate that GA101 and ofatumumab are both superior to rituximab against CLL cells via different mechanisms of potential tumor elimination. These findings bear relevance to potential combination strategies with each of these anti-CD20 Abs in the treatment of CLL. [ABSTRACT FROM AUTHOR]

IL-15 may have a role in the development of T cell large granular lymphocyte (T-LGL) or NKT leukemias. However, the mechanisms of action and the identity of the cell subset that undergoes leukemic transformation remain elusive. Here we show that in both mice and humans, NKp46 expression marks a minute population of WT NKT cells with higher activity and potency to become leukemic. Virtually 100% of T-LGL leukemias in IL-15 transgenic mice expressed NKp46, as did a majority of human T-LGL leukemias. The minute NKp46- NKT population, but not the NKp46 NKT population, was selectively expanded by overexpression of endogenous IL-15. Importantly, IL-15 transgenic NKp46 NKT cells did not become NKp46+ in vivo, suggesting that NKp46+ T-LGL leukemia cells were the malignant counterpart of the minute WT NKp4+ NKT population. Mechanistically, NKp46+ NKT cells possessed higher responsiveness to IL-is in vitro and in vivo compared with that of their NKp46- NKT counterparts. Furthermore, interruption of IL-15 signaling using a neutralizing antibody could prevent LGL leukemia in IL-15 transgenic mice. Collectively, our data demonstrate that NKp46 identifies a functionally distinct NKT subset in mice and humans that appears to be directly susceptible to leukemic transformation when IL-15 is overexpressed. Thus, IL-15 signaling and NKp46 may be useful targets in the treatment of patients with T-LGL or NKT leukemia. [ABSTRACT FROM AUTHOR]