ALBERT

Description: The region of southern Africa (SA) has a fragile food economy and is vulnerable to frequent droughts. Interventions to mitigate food insecurity impacts require early warning of droughts – preferably as early as possible before the harvest season (typically starting in April) and lean season (typically starting in November). Hydrologic monitoring and forecasting systems provide a unique opportunity to support early warning efforts, since they can provide regular updates on available root-zone soil moisture (RZSM), a critical variable for crop yield, and provide forecasts of RZSM by combining the estimates of antecedent soil moisture conditions with climate forecasts. For SA, this study documents the predictive capabilities of RZSM products from the recently developed NASA Hydrological Forecasting and Analysis System (NHyFAS). Results show that the NHyFAS products would have identified the regional severe drought event – which peaked during December–February of 2015–2016 – at least as early as 1 November 2015. Next, it is shown that during 1982–2016, February RZSM (Feb-RZSM) forecasts (monitoring product) available in early November (early March) have a correlation of 0.49 (0.79) with the detrended regional crop yield. It is also found that when the February RZSM forecast (monitoring product) available in early November (early March) is indicated to be in the lowest tercile, the detrended regional crop yield is below normal about two-thirds of the time (always), at least over the sample years considered. Additionally, it is shown that the February RZSM forecast (monitoring product) can provide “out-of-sample” crop yield forecasts with comparable (substantially better with 40 % reduction in mean error) skill to December–February ENSO. These results indicate that the NHyFAS products can effectively support food insecurity early warning in the SA region. Finally, since a framework similar to NHyFAS can be used to provide RZSM monitoring and forecasting products over other regions of the globe, this case study also demonstrates potential for supporting food insecurity early warning globally.

Description: Juvenile and chronic myelomonocytic leukemias (JMML and CMML) are aggressive myeloid malignancies categorized as myelodysplastic syndromes/myeloproliferative neoplasms (MDS/MPN). Chemotherapy has little benefit for MDS/MPN patients, and new therapies are needed. We have used mouse models investigate the potential of signal transduction inhibitors in MDS/MPN, as JMML and CMML are associated with mutations in NRAS, KRAS, PTPN11, CBL, or NF1 that activate Ras signaling. Conditional Mx1-Cre, KrasLSL-D12 (designated KrasD12) mice develop an aggressive and fully penetrant MDS/MPN characterized by leukocytosis, splenomegaly, anemia, and death by 10-16 weeks of age. Mx1-Cre, Nf1flox/- mice (hereafter Nf1Δ/-) undergo conditional loss of Nf1. These mice also develop MDS/MPN, but the disease is more indolent. We and others have investigated inhibition of effector networks downstream of Ras, such as the Raf/MEK/ERK (MAPK) and phosphotidylinositol-3 kinase (PI3K)/Akt pathways. We previously showed that the MEK inhibitor PD0325901 induced sustained hematologic improvement in both KrasD12 and Nf1Δ/- mice. We also have reported that the class I PI3K inhibitor GDC-0941 improves hematologic function and prolongs survival in KrasD12 mice. However, GDC-0941 and other PI3K inhibitors attenuate both PI3K/Akt and Raf/MEK/ERK pathways due to effects of PI3K upstream of Ras. Therefore, the benefit from GDC-0941 could have been due to its modulation of Raf/MEK/ERK signaling. Here, we specifically test the importance of Akt signaling in MDS/MPN in KrasD12 and Nf1 mouse models using the allosteric inhibitor MK-2206. This compound binds to the interface of the PH and kinase domains of Akt1, Akt2, and Akt3, and does not inhibit any of 250 other kinases at 1 µM. MK-2206 induced substantial improvement in both KrasD12 and Nf1Δ/- mice. Mice treated with MK-2206 had pronounced reduction in leukocytosis, reticulocytosis and splenomegaly, increased hemoglobin concentration, and prolonged survival. MK-2206 had no hematologic effects in control WT mice, indicating some selectivity against aberrant hematopoiesis. Importantly, MK-2206 inhibited Akt but not Raf/MEK/ERK or Jak/STAT signaling. This demonstrates that canonical PI3K/Akt signaling plays an important role in Ras-driven MDS/MPN. Furthermore, combined inhibition of MEK and Akt with PD0325901+MK-2206 yielded a greater improvement in splenomegaly than either agent alone in both KrasD12 and Nf1Δ/- models. Akt has multiple effectors relevant to hematopoiesis and leukemia. Of these, mTOR is of particular interest for targeted cancer therapy. Therefore, we tested the response of KrasD12 mice to rapamycin, a partial inhibitor of mTOR with preferential activity against the mTORC1 complex. KrasD12 mice demonstrated variable responses to rapamycin, with approximately half undergoing a complete and durable hematologic response and the remainder having no response. Together, these studies further implicate PI3K/Akt signaling as a pathogenic effector downstream of Ras in MDS/MPN and support the idea that inhibitors targeting this pathway may have a role in treatment of JMML or CMML. Disclosures No relevant conflicts of interest to declare.

Description: Introduction Recombinant FXIII (rFXIII) represents a new treatment opportunity for patients with congenital FXIII A-subunit deficiency. Monthly prophylaxis with 35 IU/kg rFXIII was shown to effectively control bleeding with an annualized bleeding rate (ABR) of 0.138 bleeds requiring treatment per patient per year and an excellent safety profile (Inbal A, et al. Blood 2012;119:5111-7). PK analysis revealed first-order elimination of rFXIII with a geometric mean half-life of 13.6 days. All patients had a mean FXIII trough activity level of 〉0.1 IU/mL (Kerlin B, et al.JTH 2013;11:235). The PK profile was independent of age, supporting that monthly dosing with a fixed 35 IU/Kg rFXIII regimen for all patients with FXIII A-subunit deficiency (regardless of age) was adequate for prophylaxis (Brand-Staufer B, et al. Blood 2013;122:3613. Williams M, et al. Haemophilia 2014;20:99–105). Due to the novel nature of this recombinant molecule, a phase 3b safety extension program was offered to bridge to product availability, the extensive interim results of which are analyzed here. Methods The mentorTM2 trial is an ongoing safety extension trial to the pivotal mentorTM1 trial (Figure). All patients were dosed with 35 IU/kg rFXIII every 4th week. Figure. The Novo Nordisk clinical trial program for recombinant Factor 13 Figure. The Novo Nordisk clinical trial program for recombinant Factor 13 A planned interim analysis for mentorTM2 trial was performed (data cut-off: 31-DEC-2013). The Berichrom® FXIII activity assay was used for measurement of FXIII activity. Results Sixty patients have been enrolled into mentorTM2; baseline patient demographics are presented in the Table. Of these 60, 34 patients were enrolled from the mentorTM1 trial, and 26 new patients were enrolled. Table. Age, median (range) 26 (7-77) Age, mean (range) 31 (7-77) Male sex, n (%) 38 (63) Race, n (%) Black or African American American Indian or Alaska Native White Asian* Other Unknown** 6 (10)1 (2)34 (57)9 (15)6 (10)4 (7) Body Mass Index, median (range) 23.7 (12.8-36.9) Height in cm, median (range) 167.0 (131.0-187.5) Weight in kg, median (range) 67.5 (22.0-119.4) * Including 5 Japanese ** French patients are marked as unknown as per the French authorities guideline In mentorTM2, 60 patients had 2,157 exposures (monthly dosing), corresponding to a total of 168 patient years. The ABR was 0.042 bleeds/patient/year overall, 0.012 bleeds/patient/year for spontaneous bleeds, and 0.030 bleeds/patient/year for traumatic bleeds. In total 6 patients experienced 7 bleeds requiring FXIII treatment (5 trauma-induced and 2 spontaneous). Of these 7 bleeds, 1 trauma-induced muscular bleed was treated with rFXIII with excellent hemostatic response. No intracranial, internal organ or severe gastrointestinal bleeds occurred during the trial period. Mean FXIII trough levels were greater than 0.10 IU/mL in all patients. No thromboembolic events, fatal adverse events or adverse events leading to withdrawal were reported. Serious adverse events were few (16 events in 10 patients) and were evaluated by the investigators as unlikely related to trial drug. No anti-rFXIII antibodies were detected. Discussion Prophylaxis of bleeding of patients with congenital FXIII A-subunit deficiency with rFXIII in the mentor™ trials program has demonstrated very effective bleed control, with an excellent safety profile. The ABR in the ongoing mentorTM2 safety extension trial was 0.042, which is lower than the rate of 0.138 seen in the mentor™1 pivotal study. A bleeding rate of 0.042 corresponds to an average patient having 1 bleed approximately every 24 years. One patient who had a traumatic breakthrough bleed was treated with rFXIII with excellent outcome. These efficacy data, combined with comprehensive PK- and safety data, represent the largest data collection in congenital FXIII A-subunit deficiency in the world, and provide extensive evidence for the safety and efficacy of monthly prophylaxis with 35 IU/kg rFXIII. Disclosures Fukutake: Novo Nordisk: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Baxter: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bayer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Biogen Idec: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Kaketsuken: Consultancy, Honoraria, Research Funding, Speakers Bureau; CSL Behring: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; SRL, Inc: Consultancy; LSI Medience Corporation: Consultancy, Honoraria, Speakers Bureau; Chugai Pharm: Honoraria, Membership on an entity's Board of Directors or advisory committees; TORII PHARMACEUTICAL CO., LTD.: Honoraria; Sekisui Medical CO., LTD: Honoraria, Research Funding, Speakers Bureau. Carcao:Baxter, Bayer, Biogen, Novo Nordisk, Pfizer, CSL Behring, Octapaharma : Honoraria, Research Funding, Speakers Bureau. Kerlin:Bayer HealthCare US: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novo Nordisk: Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees. Oldenburg:Baxter: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bayer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Biogen Idec: Honoraria, Membership on an entity's Board of Directors or advisory committees; Biotest: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; CSL Behring: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Grifols: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novo Nordisk: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Octapharma: Honoraria, Membership on an entity's Board of Directors or advisory committees; Swedish Orphan Biovitrum: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Rosholm:Novo Nordisk: Employment, Equity Ownership. Garly:Novo Nordisk: Employment, Equity Ownership. Nugent:Novo Nordisk: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Description: CD74 is an integral membrane protein that was thought to function mainly as an MHC class II chaperone. However, CD74 was recently shown to have a role as an accessory-signaling molecule. Our studies demonstrated that CD74 regulates B-cell differentiation by inducing a pathway leading to the activation of transcription mediated by the NF-κB p65/RelA homodimer and its coactivator, TAFII105. Here, we show that CD74 stimulation with anti-CD74 antibody leads to an induction of a signaling cascade resulting in NF-κB activation, entry of the stimulated cells into the S phase, elevation of DNA synthesis, cell division, and augmented expression of BCL-XL. These studies therefore demonstrate that surface CD74 functions as a survival receptor.

Description: Several recent studies evaluated a possible effect of the prothrombotic polymorphisms such as 5,10 methylenetetrahydrofolate reductase (MTHFR) nt 677C → T, factor V (F V) nt 1691G → A (F V Leiden), and factor II (F II) nt 20210 G → A on the risk of myocardial infarction. In the present study, we analyzed the effect of these prothrombotic polymorphisms, as well as apolipoprotein (Apo) E4, smoking, hypertension, diabetes mellitus, and hypercholesterolemia, on the risk of myocardial infarction in young males. We conducted a case-control study of 112 young males with first acute myocardial infarction (AMI) before the age of 52 and 187 healthy controls of similar age. The prevalences of heterozygotes for F V G1691A and F II G20210A were not significantly different between cases and controls (6.3% v 6.4% and 5.9% v 3.4% among cases and controls, respectively). In contrast, the prevalence of MTHFR 677T homozygosity and the allele frequency of Apo E4 were significantly higher among patients (24.1% v 10.7% and 9.4% v5.3% among cases and controls, respectively). Concomitant presence of hypertension, hypercholesterolemia, or diabetes and one or more of the four examined polymorphisms increased the risk by almost ninefold (odds ratio [OR] = 8.66; 95% confidence interval [CI], 3.49 to 21.5) and concomitant smoking by almost 18-fold (OR = 17.6; 95% CI, 6.30 to 48.9). When all atherogenic risk factors were analyzed simultaneously by a logistic model, the combination of prothrombotic and Apo E4 polymorphisms with current smoking increased the risk 25-fold (OR = 24.7; 95% CI, 7.17 to 84.9).The presented data suggest a synergistic effect between atherogenic and thrombogenic risk factors in the pathogenesis of AMI, as was recently found in a similar cohort of women.

Description: High dose chemotherapy of Ph+ ALL is rarely curative and clinical responses to protein kinase inhibitors have been transient. Although new regimens combining chemotherapy with Bcr-Abl kinase inhibitors improve survival, the long-term prognosis of patients with Ph+ ALL remains guarded. Thus, novel therapeutic strategies are needed. Hsp90 is a ubiquitous molecular chaperone protein required for the folding, activation and assembly of mediators of signal transduction, cell cycle control, and transcription regulation. The Hsp90 inhibitor EC141 (Biogen Idec, Inc.) blocks the chaperone activity of Hsp90 and induces proteasomal degradation of it’s client proteins. Because Hsp90 is a chaperone of Bcr-Abl we investigated the activity of EC141 against the Ph+ ALL B-cell lines Z-119, Z-181 and Z-33 (Estrov et al. J Cell Physiol166: 618, 1996; Leukemia10:1534, 1996). First we studied the effect of EC141 on Hsp levels in Ph+ ALL cells. EC141 (50 nM) down-regulated the protein levels of Hsp90 and upregulated those of Hsp70. Then, the effect of EC141 on the proliferation of Ph+ ALL cells was evaluated using the MTT assay. EC141 inhibited the growth and metabolic activity of Z-119, Z-181 and Z-33 Ph+ ALL cells in a dose-dependent manner at concentrations ranging from 1 to 100 nM. Similar results were obtained with primary bone marrow cells from patients with Ph+ ALL. Using the ALL blast colony culture assay we found that EC141 inhibited the proliferation of marrow-derived ALL colony-forming cells in a dose-dependent fashion. To explore the mechanism of action Z-181 were incubated cells with increasing concentrations of EC141; immunoprecipitation and Western immunoblotting were used to detect changes in cellular protein levels. EC141 degraded the Bcr-Abl p190 protein and inhibited the phosphorylation of CrkL in a dose-dependent manner. Furthermore, exposure of Z-181 cells to EC141 resulted in a time- and dose-dependent activation of procaspase 3, cleavage of poly (adenosine diphosphate-ribose) polymerase and apoptotic cell death as assessed by Annexin V. Taken together, our data suggest that EC141 degrades the Bcr-Abl p190 protein, inhibits proliferation, and induces apoptosis of Ph+ ALL cells. Additional studies aimed at investigating the in vivo activity of EC141 in Ph+ ALL are warranted.

Description: B-cell chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the Western hemisphere. Although several chromosomal and molecular abnormalities have been identified in CLL cells in recent years, the pathogenesis of CLL is still poorly understood. Signal transducer and activator of transcription 3 (STAT3) plays a major role in cellular physiology. Upon exposure to cytokines or growth factors, STAT3 is tyrosine-phosphorylated, migrates to the nucleus, and binds to DNA. Constitutive phosphorylation of STAT3 on tyrosine 705 residues has been found in several solid tumors and hematologic malignancies. Remarkably, CLL is the only disease in which STAT3 is constitutively phosphorylated (p) on serine rather than tyrosine residues (Frank et al. JCI100:3149, 1997). We have recently discovered that serine pSTAT3 translocates to the nucleus, binds to DNA, activates transcription, and plays a major role in the pathogenensis of CLL. Little is known about the transport mechanisms utilized by STAT molecules in fresh leukemia cells, and no data are available on the transport mechanism of serine pSTAT3. Therefore, we sought to identify the nucleocytoplasmic transport system of serine pSTAT3 in CLL cells. In other cellular systems, importin-α3 or -α6 binds to the nuclear localization signal in STAT3, the N terminus of importin-α is directly recognized by importin-β1, and the complex consisting of STAT3, importin-α3 and improtin-β1 transits through the nuclear pore complexes (NPC). To identify which nucleocytoplasmic transport mechanism of serine pSTAT3 is operative in CLL cells, we performed a series of immunoprecipitation experiments with antibodies to STAT3 and importin-β1. We found that STAT3 co-immunoprecipitated with importin-β1 in whole cell, cytoplasmic, and nuclear extracts. We could not determine which member of the importin-α family binds serine pSTAT3 to form a complex with importin-β1 because none of the investigated α-importins (importin-α1, -α3, -α5, -α6, and -α7) co-immunoprecipitated with STAT3. Similar results were obtained when importin-β1 was immunoprecipitated. Unlike the studied α-importins, serine pSTAT3 and STAT3 co-immunoprecipitated with importin-β1. Thus, either an α-importin binds serine pSTAT3 but failed to co-immunoprecipitate, or an unidentified transporter binds serine pSTAT3. After establishing that importin-β1 translocates serine pSTAT3 to the nucleus, we sought to identify the nuclear export mechanism. The established nuclear export mechanism of STAT3 consists of CRM1 that binds to the nuclear export signal on STAT3 and exports STAT3 through the NPC. Using an identical experimental design, we immunoprecipitated whole cell, cytoplasmic, and nuclear extracts with anti-CRM1 antibodies and found that STAT3 and serine pSTAT3 co-immunoprecipitated with CRM1. Then, we immunoprecipitated the cell extracts with anti-STAT3 antibodies. In these experiments, CRM1 co-immunoprecipitated with STAT3. To further elucidate the role of CRM1 in the STAT3 nuclear export system, we incubated CLL cells with increasing concentrations of the CRM1 inhibitor leptomycin B and assessed STAT3 protein levels in nuclear extracts by Western immunoblotting. We found that leptomycin B increased the accumulation of STAT3 in the nucleus in a dose dependent manner, further confirming that CRM1 exports STAT3 from the nucleus to the cytoplasm. Taken together, our data demonstrate for the first time that in CLL cells STAT3 and serine pSTAT3 are transported into the nucleus by importin-β1 and exported by CRM1. Targeting this nuclear trafficking system might provide a new therapeutic strategy for the treatment of CLL.

Description: Activated protein C resistance (APCR) in the absence of alterations in the factor V gene has been observed during pregnancy, in patients on oral contraceptives, in the presence of antiphospholipid antibodies, and in patients with ischemic stroke. We report a 49-year-old woman with recurrent major venous and arterial thromboses who displayed pronounced APCR, yet no changes in the activated protein C (APC) cleavage sites of factor V. The APCR values determined by four different assays were similar to those obtained in plasma from a homozygote for factor V Q506. Addition of IgG isolated from the patient’s serum to normal plasma lowered the APCR ratio from 2.4 to 1.6. Incubation of patient’s IgG with normal APC resulted in a profound change in the mobility of APC in crossed immunoelectrophoresis. APC was also shown to bind to patient’s IgG immobilized on a protein A agarose column. Factor Va inactivation by APC was inhibited by patient’s IgG, but not by control IgG in the presence or absence of either phospholipids or protein S. These results provide evidence for the existence of an acquired antibody against APC in the patient’s plasma, which gave rise to the APCR phenotype and was probably responsible for the major thrombotic events. We suggest that acquired APCR due to anti-APC antibodies be considered a potential cause for severe venous and arterial thromboses.

Description: CTLA-4 and PD-1 are receptors that negatively regulate T cell activation. Ligation of both CTLA-4 and PD-1 blocked CD3/CD28 mediated upregulation of glucose metabolism and Akt activity, but each accomplished this regulation using separate mechanisms. CTLA-4 mediated inhibition of Akt phosphorylation is sensitive to okadaic acid, providing direct evidence that PP2A plays a prominent role in mediating CTLA-4 suppression of T cell activation. In contrast, PD-1 signaling inhibits Akt phosphorylation by preventing CD28 mediated activation of phosphatidylinositol 3-kinase (PI3K). The ability of PD-1 to suppress PI3K/Atk activation was dependent upon the ITSM located in its cytoplasmic tail. Lastly, PD-1 ligation is more effective in suppressing CD3/28 induced changes in the T cell transcriptional profile, suggesting that differential regulation of PI3K activation by PD-1 and CTLA-4 ligation results in distinct cellular phenotypes. Together, these data suggest that CTLA-4 and PD-1 inhibit T cell activation through distinct and potentially synergistic mechanisms.

Description: Signal transducer and activator of transcription 3 (STAT3) plays a pivotal role in cellular physiology and organ development. Tyrosine phosphorylation of STAT3 provides cells with survival advantage and induces proliferation, whereas deletion of STAT3 results in embryonic lethality. As might be expected, STAT3 is commonly activated in neoplastic cells. Constitutive phosphorylation of STAT3 on tyrosine 705 residues has been found in a number of solid tumors and hematologic malignancies. A decade ago, Frank et al. (JCI100:3149, 1997) reported that unlike other neoplasms in B-cell chronic lymphocytic leukemia (CLL), STAT3 is constitutively phosphorylated (p) on serine 727 but not on tyrosine residues. This observation prompted us to investigate the role of STAT3 in CLL. We studied peripheral blood (PB) cells from ~100 patients with CLL using Western immunoblotting and found that in all patients, regardless of PB count, disease stage, or treatment status, STAT3 is constitutively phosphorylated on serine 727 but not on tyrosine residues. Serine pSTAT3 was detected in CD19+ but not in CD19− CLL PB-derived cells or in normal PB-derived B-lymphocytes isolated by immunomagnetic beads. Unlike constitutive serine pSTAT3, tyrosine pSTAT3 could be induced by incubating CLL cells with cytokines, such as interleukin (IL)-6, or anti-IgM antibodies. However, expression of cytokine-induced tyrosine pSTAT3 was transient and was no longer detected shortly (2 hours) after removal of the stimulating agent. In contrast, serine pSTAT3 levels remained stable in vitro for up to 72 hours, confirming that serine phosphorylation of STAT3 is constitutive in CLL cells. Because CLL is the only disease in which STAT3 is constitutively phosphorylated exclusively on serine residues and since tyrosine phosphorylation is thought to be required for STAT3 activation, we sought to determine whether serine pSTAST3 is biologically active. First, we isolated cytoplasmic and nuclear extracts and used Western immunoblotting to demonstrate that pSTAT3 is present both in the cytoplasm and the nucleus. Then, we confirmed these findings using confocal microscopy. After confirming that serine pSTAT3 translocates to the nucleus, we asked whether serine pSTAT3 binds to DNA. Using the electrophoretic mobility shift assay we demonstrated that nuclear STAT3 binds to a STAT3-specific DNA probe and that STAT3-DNA binding was eliminated by both anti-STAT3 and anti-serine pSTAT3 antibodies. Furthermore, although induction of tyrosine pSTAT3 by exogenous IL-6 slightly increased STAT3-DNA binding, complete dephosphorylation of tyrosine pSTAT3 by T-cell tyrosine phosphatase did not affect STAT3-DNA binding, suggesting that STAT3-DNA binding does not require tyrosine phosphorylation. Finally, pull-down of STAT3 with biotin-labeled DNA further confirmed that serine pSTAT3 binds to DNA in CLL cells. We then asked whether serine pSTAT3 initiates transcription. To answer this question we infected CLL cells with a lentiviral GFP-STAT3-shRNA and, as control, with GFP-empty vector and calculated changes in RNA levels by relative real-time PCR. In several CLL samples, infection with GFP-STAT3-shRNA induced a ~4-fold time-dependent reduction in the STAT3-regulated genes Bcl2, Pim1, Bcl-xL, Cyclin D1, p21 Waf1, and c-Myc, implying that serine pSTAT3 initiates transcription. Taken together, our data suggest that constitutive phosphorylation of STAT3 on serine 727 residues is a hallmark of CLL and induces activation of proliferation and survival genes. Therefore, STAT3 should be considered a therapeutic target in this disease.