BCR-ABL1 mediated miR-150 downregulation through MYC contributed to myeloid differentiation block and drug resistance in chronic myeloid leukemia.

The fusion oncoprotein BCR-ABL1 exhibits aberrant tyrosine kinase activity and it has been proposed that it deregulates signaling networks involving both transcription factors and non-coding microRNAs that result in chronic myeloid leukemia (CML). Previously, microRNA expression profiling showed deregulated expression of miR-150 and miR-155 in CML. In this study, we placed these findings into the broader context of the MYC/miR-150/MYB/miR-155/PU.1 oncogenic network. We propose that up-regulated MYC and miR-155 in CD34+ leukemic stem and progenitor cells, in concert with BCR-ABL1, impair the molecular mechanisms of myeloid differentiation associated with low miR-150 and PU.1 levels. We revealed that MYC directly occupied the -11.7 kb and -0.35 kb regulatory regions in the MIR150 gene. MYC occupancy was markedly increased through BCR-ABL1 activity, causing inhibition of MIR150 gene expression in CML CD34+ and CD34- cells. Furthermore, we found an association between reduced miR-150 levels in CML blast cells and their resistance to tyrosine kinase inhibitors (TKIs). Although TKIs successfully disrupted BCR-ABL1 kinase activity in proliferating CML cells, this treatment did not efficiently target quiescent leukemic stem cells. The study presents new evidence regarding the MYC/miR-150/MYB/miR-155/PU.1 leukemic network established by aberrant BCR-ABL1 activity. The key connecting nodes of this network may serve as potential druggable targets to overcome resistance of CML stem and progenitor cells.

PTEN is a negative regulator of NK cell cytolytic function.

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 CD56(dim) NK cell efficiently kills malignant targets at rest, whereas the less mature CD56(bright) NK cells cannot. In this study, we show that resting CD56(bright) NK cells express significantly more phosphatase and tensin homolog deleted on chromosome 10 (PTEN) protein when compared with CD56(dim) NK cells. Consistent with this, forced overexpression of PTEN in NK cells resulted in decreased cytolytic activity, and loss of PTEN in CD56(bright) 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 CD56(bright) NK cell to the cytolytic CD56(dim) NK cells.

Overexpression of miR-155 causes expansion, arrest in terminal differentiation and functional activation of mouse natural killer cells.

It is known that microRNAs (miRs) are involved in lymphocyte development, homeostasis, activation, and occasionally malignant transformation. In this study, a miR-155 transgene (tg) was driven to be overexpressed off of the lck promoter in order to assess its effects on natural killer (NK) cell biology in vivo. miR-155 tg mice have an increase in NK-cell number with an excess of the CD11b(low)CD27(high) NK subset, indicative of a halt in terminal NK-cell differentiation that proved to be intrinsic to the cell itself. The increase in NK cells results, in part, from improved survival in medium alone and enhanced expansion with endogenous or exogenous interleukin 15. Phenotypic and functional data from miR-155 tg NK cells showed constitutive activation and enhanced target cell conjugation, resulting in more potent antitumor activity in vitro and improved survival of lymphoma-bearing mice in vivo when compared with wild type NK cells. The enhanced NK-cell survival, expansion, activation, and tumor control that result from overexpression of miR-155 in NK cells could be explained, in part, via diminished expression of the inositol phosphatase SHIP1 and increased activation of ERK and AKT kinases. Thus, the regulation of miR-155 is important for NK-cell development, homeostasis, and activation.

Comparative assessment of clinically utilized CD20-directed antibodies in chronic lymphocytic leukemia cells reveals divergent NK cell, monocyte, and macrophage properties.

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.

Axl/Gas6 pathway positively regulates FLT3 activation in human natural killer cell development.

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 ß 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.

miR-155 regulates IFN-γ production in natural killer cells.

MicroRNAs (miRs) are small, noncoding RNA molecules with important regulatory functions whose role in regulating natural killer (NK) cell biology is not well defined. Here, we show that miR-155 is synergistically induced in primary human NK cells after costimulation with IL-12 and IL-18, or with IL-12 and CD16 clustering. Over-expression of miR-155 enhanced induction of IFN-γ by IL-12 and IL-18 or CD16 stimulation, whereas knockdown of miR-155 or its disruption suppressed IFN-γ induction in monokine and/or CD16-stimulated NK cells. These effects on the regulation of NK cell IFN-γ expression were found to be mediated at least in part via miR-155's direct effects on the inositol phosphatase SHIP1. Consistent with this, we observed that modulation of miR-155 overrides IL-12 and IL-18-mediated regulation of SHIP1 expression in NK cells. Collectively, our data indicate that miR-155 expression is regulated by stimuli that strongly induce IFN-γ in NK cells such as IL-12, IL-18, and CD16 activation, and that miR-155 functions as a positive regulator of IFN-γ production in human NK cells, at least in part via down-regulating SHIP1. These findings may have clinical relevance for targeting miR-155 in neoplastic disease.

The PP2A inhibitor SET regulates natural killer cell IFN-gamma production.

Monokines (i.e., interleukin [IL]-12, -18, and -15) induce natural killer (NK) cells to produce interferon-gamma (IFN-gamma), which is a critical factor for immune surveillance of cancer and monocyte clearance of infection. We show that SET, which is a potent inhibitor of protein phosphatase type 2A (PP2A) activity, is highly expressed in human CD56bright NK cells, which produce more IFN-gamma than CD56dim NK cells. SET was up-regulated upon monokine stimulation of primary human NK cells. Furthermore, ectopic overexpression of SET significantly enhanced IFN-gamma gene expression in monokine-stimulated NK cells. In contrast, RNAi-mediated suppression of SET expression renders NK cells inefficient in producing high levels of IFN-gamma in response to monokine costimulation. Mechanistically, suppression of PP2A activity by SET is important for IFN-gamma gene expression in NK cells. In fact, treatment of primary human NK cells with the PP2A activator 1,9-dideoxy-forskolin, as well as administration of the drug to C57BL/6 mice, significantly reduced NK-dependent IFN-gamma production in response to monokine treatment. Further, SET knockdown or pharmacologic activation of PP2A diminished extracellular signal-regulated kinase 1/2, p65RelA, signal transducer and activator of transduction 4 (STAT4), and STAT5 activity in monokine-stimulated NK cells, potentially contributing to the reduction in IFN-gamma gene expression. Thus, SET expression is essential for suppressing PP2A phosphatase activity that would otherwise limit NK cell antitumoral and/or antiinflammatory functions by impairing NK cell production of IFN-gamma.

The PP2A inhibitor SET regulates granzyme B expression in human natural killer cells.

The ability of natural killer (NK) cells to kill malignant or infected cells depends on the integration of signals from different families of cell surface receptors, including cytokine receptors. How such signals then regulate NK-cell cytotoxicity is incompletely understood. Here we analyzed an endogenous inhibitor of protein phosphatase 2A (PP2A) activity called SET, and its role in regulating human NK-cell cytotoxicity and its mechanism of action in human NK cells. RNAi-mediated suppression of SET down-modulates NK-cell cytotoxicity, whereas ectopic overexpression of SET enhances cytotoxicity. SET knockdown inhibits both mRNA and protein granzyme B expression, as well as perforin expression, whereas SET overexpression enhances granzyme B expression. Treatment of NK cells with the PP2A activator 1,9-dideoxy-forskolin also inhibits both granzyme B expression and cytotoxicity. In addition, pretreatment with the PP2A inhibitor okadaic acid rescues declining granzyme B mRNA levels in SET knockdown cells. Down-modulation of SET expression or activation of PP2A also decreases human NK-cell antibody-dependent cellular cytotoxicity. Finally, the induction of granzyme B gene expression by interleukin-2 and interleukin-15 is inhibited by SET knockdown. These data provide evidence that granzyme B gene expression and therefore human NK-cell cytotoxicity can be regulated by the PP2A-SET interplay.

The tumor suppressor PP2A is functionally inactivated in blast crisis CML through the inhibitory activity of the BCR/ABL-regulated SET protein.

The oncogenic BCR/ABL kinase activity induces and maintains chronic myelogenous leukemia (CML). We show here that, in BCR/ABL-transformed cells and CML blast crisis (CML-BC) progenitors, the phosphatase activity of the tumor suppressor PP2A is inhibited by the BCR/ABL-induced expression of the PP2A inhibitor SET. In imatinib-sensitive and -resistant (T315I included) BCR/ABL+ cell lines and CML-BC progenitors, molecular and/or pharmacological activation of PP2A promotes dephosphorylation of key regulators of cell proliferation and survival, suppresses BCR/ABL activity, and induces BCR/ABL degradation. Furthermore, PP2A activation results in growth suppression, enhanced apoptosis, restored differentiation, impaired clonogenic potential, and decreased in vivo leukemogenesis of imatinib-sensitive and -resistant BCR/ABL+ cells. Thus, functional inactivation of PP2A is essential for BCR/ABL leukemogenesis and, perhaps, required for blastic transformation.

BCR-ABL suppresses C/EBPalpha expression through inhibitory action of hnRNP E2.

The arrest of differentiation is a feature of both chronic myelogenous leukemia cells in myeloid blast crisis and myeloid precursors that ectopically express the p210BCR-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/EBPalpha-the principal regulator of granulocytic differentiation. Expression of C/EBPalpha 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/EBPalpha induces granulocytic differentiation of myeloid precursor cells expressing BCR-ABL. Expression of C/EBPalpha 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/EBPalpha 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/EBPalpha by inducing hnRNP E2-which inhibits the translation of CEBPA mRNA.

A phase I study of the combination of palbociclib and dexamethasone for the treatment of relapsed or refractory B-cell acute lymphoblastic leukemia.

PURPOSE: Despite advances in the treatment of B-cell acute lymphoblastic leukemia (B-ALL), outcomes for relapsed/refractory (R/R) disease remain poor. Preclinical studies suggest that the combination of the CDK4/6 inhibitor palbociclib and dexamethasone may be effective in targeting leukemic cell growth. We conducted a phase I study of escalating doses of palbociclib in combination with dexamethasone in adults with R/R B-ALL. METHODS: Cycle 1 consisted of single agent palbociclib given for 7 days and continued for 28 additional days in combination with dexamethasone 20 mg daily. Palbociclib dosing began at 100 mg daily. Patients with a response were eligible for maintenance consisting of 1 week of palbociclib plus dexamethasone (20 mg daily × 2 days, 16 mg daily × 2 days, 12 mg daily × 2 days, 6 mg daily × 1 day), followed by 3 weeks of palbociclib alone. Safety, efficacy, and the expression of phospho-RB and c-MYB/BCL-2 were measured. CONCLUSIONS: Seven patients were treated on study before it was closed early due to slow accrual. No dose limiting toxicities were identified. One patient had a complete response with incomplete hematologic recovery, suggesting possible efficacy of the treatment. Reduction in CD34+ cells, p-RB, c-MYB, and BCL-2 expression also suggested on-target therapy effects.

CD94 surface density identifies a functional intermediary between the CD56bright and CD56dim human NK-cell subsets.

Human CD56(bright) natural killer (NK) cells possess little or no killer immunoglobulin-like receptors (KIRs), high interferon-gamma (IFN-gamma) production, but little cytotoxicity. CD56(dim) NK cells have high KIR expression, produce little IFN-gamma, yet display high cytotoxicity. We hypothesized that, if human NK maturation progresses from a CD56(bright) to a CD56(dim) phenotype, an intermediary NK cell must exist, which demonstrates more functional overlap than these 2 subsets, and we used CD94 expression to test our hypothesis. CD94(high)CD56(dim) NK cells express CD62L, CD2, and KIR at levels between CD56(bright) and CD94(low)CD56(dim) NK cells. CD94(high)CD56(dim) NK cells produce less monokine-induced IFN-gamma than CD56(bright) NK cells but much more than CD94(low)CD56(dim) NK cells because of differential interleukin-12-mediated STAT4 phosphorylation. CD94(high)CD56(dim) NK cells possess a higher level of granzyme B and perforin expression and CD94-mediated redirected killing than CD56(bright) NK cells but lower than CD94(low)CD56(dim) NK cells. Collectively, our data suggest that the density of CD94 surface expression on CD56(dim) NK cells identifies a functional and likely developmental intermediary between CD56(bright) and CD94(low)CD56(dim) NK cells. This supports the notion that, in vivo, human CD56(bright) NK cells progress through a continuum of differentiation that ends with a CD94(low)CD56(dim) phenotype.

CD19 targeting of chronic lymphocytic leukemia with a novel Fc-domain-engineered monoclonal antibody.

CD19 is a B cell-specific antigen expressed on chronic lymphocytic leukemia (CLL) cells but to date has not been effectively targeted with therapeutic monoclonal antibodies. XmAb5574 is a novel engineered anti-CD19 monoclonal antibody with a modified constant fragment (Fc)-domain designed to enhance binding of FcgammaRIIIa. Herein, we demonstrate that XmAb5574 mediates potent antibody-dependent cellular cytotoxicity (ADCC), modest direct cytotoxicity, and antibody-dependent cellular phagocytosis but not complement-mediated cytotoxicity against CLL cells. Interestingly, XmAb5574 mediates significantly higher ADCC compared with both the humanized anti-CD19 nonengineered antibody it is derived from and also rituximab, a therapeutic antibody widely used in the treatment of CLL. The XmAb5574-dependent ADCC is mediated by natural killer (NK) cells through a granzyme B-dependent mechanism. The NK cell-mediated cytolytic and secretory function with XmAb5574 compared with the nonengineered antibody is associated with enhanced NK-cell activation, interferon production, extracellular signal-regulated kinase phosphorylation downstream of Fcgamma receptor, and no increased NK-cell apoptosis. Notably, enhanced NK cell-mediated ADCC with XmAb5574 was enhanced further by lenalidomide. These findings provide strong support for further clinical development of XmAb5574 as both a monotherapy and in combination with lenalidomide for the therapy of CLL and related CD19(+) B-cell malignancies.

BCR/ABL activates mdm2 mRNA translation via the La antigen.

In a BCR/ABL-expressing myeloid precursor cell line, p53 levels were markedly downmodulated. Expression of MDM2, the negative regulator of p53, was upregulated in a tyrosine kinase-dependent manner in growth factor-independent BCR/ABL-expressing cells, and in accelerated phase and blast crisis CML samples. Increased MDM2 expression was associated with enhanced mdm2 mRNA translation, which required the interaction of the La antigen with mdm2 5' UTR. Expression of MDM2 correlated with that of La and was suppressed by La siRNAs and by a dominant negative La mutant, which also enhanced the susceptibility to drug-induced apoptosis of BCR/ABL-transformed cells. By contrast, La overexpression led to increased MDM2 levels and enhanced resistance to apoptosis. Thus, La-dependent activation of mdm2 translation might represent an important molecular mechanism involved in BCR/ABL leukemogenesis.

Altered sialidase expression in human myeloid cells undergoing apoptosis and differentiation.

To gain insight into sialic acid biology and sialidase/neuraminidase (NEU) expression in mature human neutrophil (PMN)s, we studied NEU activity and expression in PMNs and the HL60 promyelocytic leukemic cell line, and changes that might occur in PMNs undergoing apoptosis and HL60 cells during their differentiation into PMN-like cells. Mature human PMNs contained NEU activity and expressed NEU2, but not NEU1, the NEU1 chaperone, protective protein/cathepsin A(PPCA), NEU3, and NEU4 proteins. In proapoptotic PMNs, NEU2 protein expression increased > 30.0-fold. Granulocyte colony-stimulating factor protected against NEU2 protein upregulation, PMN surface desialylation and apoptosis. In response to 3 distinct differentiating agents, dimethylformamide, dimethylsulfoxide, and retinoic acid, total NEU activity in differentiated HL60 (dHL60) cells was dramatically reduced compared to that of nondifferentiated cells. With differentiation, NEU1 protein levels decreased > 85%, PPCA and NEU2 proteins increased > 12.0-fold, and 3.0-fold, respectively, NEU3 remained unchanged, and NEU4 increased 1.7-fold by day 3, and then returned to baseline. In dHL60 cells, lectin blotting revealed decreased α2,3-linked and increased α2,6-linked sialylation. dHL60 cells displayed increased adhesion to and migration across human bone marrow-derived endothelium and increased bacterial phagocytosis. Therefore, myeloid apoptosis and differentiation provoke changes in NEU catalytic activity and protein expression, surface sialylation, and functional responsiveness.

The Axl/Gas6 pathway is required for optimal cytokine signaling during human natural killer cell development.

Interleukin-15 (IL-15) is essential for natural killer (NK) cell differentiation. In this study, we assessed whether the receptor tyrosine kinase Axl and its ligand, Gas6, are involved in IL-15-mediated human NK differentiation from CD34(+) hematopoietic progenitor cells (HPCs). Blocking the Axl-Gas6 interaction with a soluble Axl fusion protein (Axl-Fc) or the vitamin K inhibitor warfarin significantly diminished the absolute number and percentage of CD3(-)CD56(+) NK cells derived from human CD34(+) HPCs cultured in the presence of IL-15, probably resulting in part from reduced phosphorylation of STAT5. In addition, CD3(-)CD56(+) NK cells derived from culture of CD34(+) HPCs with IL-15 and Axl-Fc had a significantly diminished capacity to express interferon-gamma or its master regulator, T-BET. Culture of CD34(+) HPCs in the presence of c-Kit ligand and Axl-Fc resulted in a significant decrease in the frequency of NK precursor cells responding to IL-15, probably the result of reduced c-Kit phosphorylation. Collectively, our data suggest that the Axl/Gas6 pathway contributes to normal human NK-cell development, at least in part via its regulatory effects on both the IL-15 and c-Kit signaling pathways in CD34(+) HPCs, and to functional NK-cell maturation via an effect on the master regulatory transcription factor T-BET.

Stem cell factor and interleukin-2/15 combine to enhance MAPK-mediated proliferation of human natural killer cells.

Stem cell factor (SCF) promotes synergistic cellular proliferation in combination with several growth factors, and appears important for normal natural killer (NK)-cell development. CD34(+) hematopoietic precursor cells (HPCs) require interleukin-15 (IL-15) for differentiation into human NK cells, and this effect can be mimicked by IL-2. Culture of CD34(+) HPCs or some primary human NK cells in IL-2/15 and SCF results in enhanced growth compared with either cytokine alone. The molecular mechanisms responsible for this are unknown and were investigated in the present work. Activation of NK cells by IL-2/15 increases expression of c-kit whose kinase activity is required for synergy with IL-2/15 signaling. Mitogen-activated protein kinase (MAPK) signaling intermediaries that are activated both by SCF and IL-2/15 are enhanced in combination to facilitate earlier cell-cycle entry. The effect results at least in part via enhanced MAPK-mediated modulation of p27 and CDK4. Collectively the data reveal a novel mechanism by which SCF enhances cellular proliferation in combination with IL-2/15 in primary human NK cells.

Src homology 2 domain-containing inositol-5-phosphatase and CCAAT enhancer-binding protein beta are targeted by miR-155 in B cells of Emicro-MiR-155 transgenic mice.

We showed that Emicro-MiR-155 transgenic mice develop acute lymphoblastic leukemia/high-grade lymphoma. Most of these leukemias start at approximately 9 months irrespective of the mouse strain. They are preceded by a polyclonal pre-B-cell proliferation, have variable clinical presentation, are transplantable, and develop oligo/monoclonal expansion. In this study, we show that in these transgenic mice the B-cell precursors have the highest MiR-155 transgene expression and are at the origin of the leukemias. We determine that Src homology 2 domain-containing inositol-5-phosphatase (SHIP) and CCAAT enhancer-binding protein beta (C/EBPbeta), 2 important regulators of the interleukin-6 signaling pathway, are direct targets of MiR-155 and become gradually more down-regulated in the leukemic than in the preleukemic mice. We hypothesize that miR-155, by down-modulating Ship and C/EBPbeta, initiates a chain of events that leads to the accumulation of large pre-B cells and acute lymphoblastic leukemia/high-grade lymphoma.

TSC-22 contributes to hematopoietic precursor cell proliferation and repopulation and is epigenetically silenced in large granular lymphocyte leukemia.

Aberrant methylation of tumor suppressor genes can lead to their silencing in many cancers. TSC-22 is a gene silenced in several solid tumors, but its function and the mechanism(s) responsible for its silencing are largely unknown. Here we demonstrate that the TSC-22 promoter is methylated in primary mouse T or natural killer (NK) large granular lymphocyte (LGL) leukemia and this is associated with down-regulation or silencing of TSC-22 expression. The TSC-22 deregulation was reversed in vivo by a 5-aza-2'-deoxycytidine therapy of T or NK LGL leukemia, which significantly increased survival of the mice bearing this disease. Ectopic expression of TSC-22 in mouse leukemia or lymphoma cell lines resulted in delayed in vivo tumor formation. Targeted disruption of TSC-22 in wild-type mice enhanced proliferation and in vivo repopulation efficiency of hematopoietic precursor cells (HPCs). Collectively, our data suggest that TSC-22 normally contributes to the regulation of HPC function and is a putative tumor suppressor gene that is hypermethylated and silenced in T or NK LGL leukemia.

CD94 defines phenotypically and functionally distinct mouse NK cell subsets.

Understanding of heterogeneous NK subsets is important for the study of NK cell biology and development, and for the application of NK cell-based therapies in the treatment of disease. Here we demonstrate that the surface expression of CD94 can distinctively divide mouse NK cells into two approximately even CD94(low) and CD94(high) subsets in all tested organs and tissues. The CD94(high) NK subset has significantly greater capacity to proliferate, produce IFN-gamma, and lyse target cells than does the CD94(low) subset. The CD94(high) subset has exclusive expression of NKG2A/C/E, higher expression of CD117 and CD69, and lower expression of Ly49D (activating) and Ly49G2 (inhibitory). In vivo, purified mouse CD94(low) NK cells become CD94(high) NK cells, but not vice versa. Collectively, our data suggest that CD94 is an Ag that can be used to identify functionally distinct NK cell subsets in mice and could also be relevant to late-stage mouse NK cell development.