ALBERT

Description: T-cell prolymphocytic leukemia (T-PLL) is a poor-prognostic neoplasm. Differentiation stage and immune-effector functions of the underlying tumor cell are insufficiently characterized. Constitutive activation of the T-cell-leukemia-1A (TCL1A) oncogene distinguishes the (pre)leukemic cell from regular post-thymic T-cells. We assessed here activation-response patterns of the T-PLL lymphocyte and interrogated the modulatory impact by TCL1A. Immunophenotypic and gene expression profiles revealed a unique spectrum of memory-type differentiation of T-PLL with predominant central-memory stages and frequent non-canonical patterns. Virtually all T-PLL expressed a T-cell receptor (TCR) and/or CD28-coreceptor without overrepresentation of specific TCR-clonotypes. The highly activated leukemic cells also revealed losses of negative-regulatory TCR-coreceptors (e.g. CTLA4). TCR-stimulation of T-PLL cells evoked higher-than-normal cell-cycle transition and profiles of cytokine release that resembled those of normal memory T-cells. More activated phenotypes and higher TCL1A correlated with inferior clinical outcomes. TCL1A was linked to T-PLL's marked resistance to activation- and FAS-induced cell death. Enforced TCL1A enhanced phosho-activation of TCR-kinases, second-messenger generation, and JAK/STAT or NFAT transcriptional responses. This reduced the input thresholds for IL-2 secretion in a sensitizer-like fashion. Mice of TCL1A-initiated protracted T-PLL development resembled such features. When equipped with epitope-defined TCRs or CARs, these Lckpr-hTCL1Atg T-cells gained a leukemogenic growth advantage in scenarios of receptor stimulation. Overall, we propose a model of T-PLL pathogenesis in which TCL1A enhances TCR-signals and drives accumulation of death-resistant memory-type cells that utilize amplified low-level stimulatory input and whose loss of negative coregulators additionally maintains their activated state. Treatment rationales are provided by combined interception in TCR- and survival signaling.

Description: Introduction CLL remains an incurable disease and represents a significant health problem in the western world. Increasing evidence highlights that the impact of marrow stromal cells is a key component influencing CLL B-cell survival. We have utilized an in vitro bone marrow stromal cell (BMSC) model system and found unique alterations in CLL B-cells with BMSC co-culture that point to previously unidentified biologic changes in the CLL B-cells that may influence CLL B-cell signaling and drug resistance. Methods Purified primary CLL B-cells (n= 39) from previously untreated CLL patients were cultured alone or co-cultured with primary BMSCs from either normal individuals (n=26) or CLL patients (n=17) at a 50:1 ratio in AIMV medium. After 48 hours, separated CLL B-cells or BMSCs were examined by immunoprecipitation/Western blot analyses and where needed real time PCR was done to assess the presence of intracellular proteins. In separate experiments to assess CLL B-cell killing, purified CLL B-cells were treated with TP-0903, fludarabine, chlorambucil and ibrutinib as single agents with or without BMSC co-culture. Results We observed significant increases in expression of Axl for both mRNA and protein levels in CLL B-cells co-cultured with BMSCs compared to CLL B-cells cultured alone. We also detected significantly increased expression of β-catenin at the protein level in CLL B-cells co-cultured with BMSC. But, we did not see any significant change in β-catenin or Axl protein expression in BMSCs co-cultured with CLL B-cells. Co-culturing of CLL B-cells with BMSCs using transwells confirmed that the upregulation of both Axl and β-catenin is dependent on the direct contact of CLL B-cells with BMSCs. The CLL B-cells from co-culture also had upregulation in phosphorylated (P)-ERK-1/2 but no change in P-AKT(Ser473). High nuclear β-catenin and P-ERK-1/2 levels were also detected in co-cultured CLL B-cells. ERK associates with and inactivates GSK-3β resulting in the up-regulation of β-catenin. We next checked for P-GSK-3β (Ser9) in co-cultured CLL B-cells. Upregulation in P-GSK-3β (Ser9) detected in co-cultured CLL B-cells suggests inactivation of GSK-3β and increasing β-catenin accumulation in co-cultured CLL B-cells. Moreover, inhibition of P-ERK-1/2 with inhibitor PD98059 in CLL B-cells cultured with BMSCs inhibited β-catenin as well as Axl expression levels. We also determined the phosphorylation status of Axl in CLL B-cells in co-culture with BMSC but found no change either at Y702 (Axl kinase domain) or total tyrosine phosphorylation levels for Axl in CLL B-cells. Thus, we assume that the role of Axl in co-cultured leukemic B-cells is independent of its kinase activity. Next we determined the effect of the highly specific Axl inhibitor TP-0903 on CLL B-cell status of Axl and b-catenin while in BMSC co-culture. Interestingly, both Axl and β-catenin protein expression levels were found to be further upregulated in CLL B-cells exposed to sub-lethal doses of TP-0903 in co-culture with BMSC. Treatment with chemotherapeutic or targeted therapy drugs, (i.e. fludarabine, chlorambucil or ibrutinib) also led to increase in expression levels of both β-catenin and Axl CLL B-cells co-cultured with BMSC. Of interest CLL B-cells were less sensitive to the chemotherapy drugs in presence of BMSCs, suggesting a role for both Axl and β-catenin in stromal mediated CLL B-cell drug resistance to these agents. This was not true for the Axl inhibitor as TP-0903 was able to induce robust cell death by targeting P-Axl and overcome BMSC mediated protection even in the presence of increased Axl and b-catenin. We also found that TP-0903 decreased P-Axl as well as the Axl downstream mediator, P-Akt(S473) and reduced Mcl-1 expression in CLL B-cells in BMSC co-culture. Conclusions Here we show that marrow stromal cell mediated increased expression in both β-catenin and Axl in CLL B-cells is associated with leukemic B cell survival and drug resistance. The mechanism for this may in part be via activated ERK levels that also occur when CLL B-cells contact BMSC. The BMSC resistance appears to be more profound for chemotherapeutic agents since Axl inhibitor can still induce CLL B-cell killing with BMSC co-culture. These studies suggest that a further understanding of the roles of Axl and β-catenin in the resistance status of CLL B-cells mediated by contact with BMSC are warranted. Disclosures Warner: Tolero Pharmaceuticals: Employment. Bearss:Tolero Pharmaceuticals, Inc: Employment. Kay:Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Cytomx Therapeutics: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Infinity Pharm: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Acerta: Research Funding; Tolero Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Agios Pharm: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees.

Description: 1. Whole blood histamine content was measured in 80 patients with myeloproliferative disease. Increased levels were found in 60 per cent of patients with uncontrolled polycythemia vera, in 7 per cent of patients with polycythemia vera being controlled by myelosuppressive therapy, and in 71 per cent of a group with "spent" polycythemia, myeloid metaplasia and myelofibrosis. 2. The excretion of histamine in the urine was measured in 60 patients, 30 with elevated blood histamine and 30 with normal blood histamine. The urine findings paralleled the blood findings in 90 per cent of the cases. 3. Measurements of cell-poor and cell-rich fractions of blood showed that the histamine is contained in the white cell fraction. Elevated basophil counts were present in 50 per cent of the patients and occurred with the greatest frequency in the groups with elevated blood and urine histamine. A rough correlation between the basophil count and the histamine content of blood and white cell fractions was observed in normal subjects and most cases with myeloproliferative disease. Data obtained in some cases of myeloproliferative disease suggest that the histamine content of the basophil may be abnormal and that other granulocytes may contribute to the total leukocyte histamine. 4. Myelosuppressive agents produced a reduction in histamine (expressed per 109 myeloid cells) and a decrease in urine histamine as control of the myeloproliferative process was achieved. Treatment with phlebotomy alone produced no change in histamine levels. 5. The incidence of pruritus, upper gastrointestinal distress and urticarial manifestations was increased 7-fold, 4-fold and 12-fold, respectively, in patients with elevated histamine levels as compared with those who had normal histamine levels. 6. Cyproheptadine, a potent antihistaminic, successfully controlled pruritus, relieved pyrosis and suppressed urticarial eruptions in patients with elevated histamine levels. Suppression of the reaction to subcutaneously administered codeine (a histamine-releaser) afforded objective evidence that cyproheptadine blocked the effects of histamine release in vivo. 7. The metabolism of histamine and the role of elevated histamine levels in the clinical manifestations and pathophysiology of myeloproliferative disease are discussed.

Description: We have previously reported that the addition of monocytes results in enhanced modulation of the T65 antigen when normal or leukemic lymphoid cells were cultured in vitro with the T101 monoclonal antibody. In the present investigation, we extend these findings to demonstrate that monocyte-enhanced modulation is a phenomenon that occurs with a variety of T and B lymphoid antigens identified by murine monoclonal antibodies. Two patterns of monocyte-enhanced modulation were observed: (1) augmentation by monocytes of existing antigen modulation by the T101 and anti-Leu-4 antibodies, and (2) induction by monocytes of previously unrecognized modulation with the anti-Leu-2 and anti-Leu-9 antibodies. Enhancement of modulation by monocytes was also detected with antibodies to surface IgM and HLA-DR antigens. Antigen modulation on lymphoid cell lines appeared to be more variable than on fresh cells, with or without monocytes. Monocyte-enhanced antigen modulation was not demonstrated with two monoclonal antibodies against solid tumors. Monocyte-enhanced modulation was shown to be dependent upon the Fc portion of the antibody, but independent of proteolytic or oxidative compounds released by monocytes. These findings indicate that the results obtained during in vitro studies of antigen modulation may vary with the source of cells and the extent to which monocytic cells are present. In addition, these findings suggest an enhanced role for Fc receptor-bearing cells of monocytic origin in antigen modulation following in vivo administration of monoclonal antibodies.

Description: Introduction: Ublituximab (UTX) is a novel chimeric mAb targeting a unique epitope on the CD20 antigen, glycoengineered to enhance affinity to FcγRIIIa receptors, thereby demonstrating significantly greater ADCC than rituximab. UTX monotherapy in patients (pts) with rituximab relapsed/refractory NHL and CLL has reported a 43% ORR (ASCO 2014). TGR-1202 is a next generation, once daily, oral PI3Kδ inhibitor which notably lacks the hepatotoxicity associated with other PI3Kδ inhibitors, and is active in pts with relapsed and refractory hematologic malignancies (EHA 2014). UTX and TGR-1202 have shown synergistic activity in-vitroin various lymphoid cell lines (Lugano 2013). This Phase 1 trial evaluates safety and efficacy of the combination of a glycoengineered anti-CD20 (UTX) and a PI3Kδ inhibitor (TGR-1202) in pts with heavily pre-treated relapsed or refractory CLL and NHL. Methods: Eligible pts have relapsed/refractory CLL or NHL with an ECOG PS ≤ 2. A 3+3 design evaluates cohorts of CLL and NHL pts independently with UTX dosed on Days 1, 8, 15 of Cycles 1 & 2 followed by maintenance therapy. UTX starts at 600 mg in Cohort 1 and increases to 900 mg for pts with CLL and is fixed at 900 mg for pts with NHL. TGR-1202 starts at 800 mg QD in Cohort 1 and is increased in subsequent cohorts. An amendment in July 2014 was introduced to include an improved micronized formulation of TGR-1202, starting at 400 mg once daily and increasing in subsequent cohorts. There are no limits on prior therapy, and patients with Richter’s Transformation or who are refractory to prior PI3Kδ inhibitors or BTK inhibitors are eligible. Primary endpoints: Safety and Dose Limiting Toxicities (DLT). Secondary endpoints: Efficacy (ORR, CR rate). Results: As of August 2014, 21 pts have been enrolled: 8 CLL/SLL, 7 DLBCL, 5 Follicular Lymphoma, and 1 patient with Richter’s Transformation. Median age is 64 years (range 35-82); 12 male/9 female. Median prior Tx = 3 (range 1-9); median ECOG PS = 1. All pts are evaluable for safety. Adverse events have been manageable with no safety concerns noted. Day 1 infusion related reactions (IRR) were the most common treatment related adverse event (48%), with all but one event Grade 1 or 2 in severity, followed by neutropenia (38%), diarrhea (29%), and nausea (29%). Notably, no events of TGR-1202 related hepatotoxicity have been reported to date. All IRR and neutropenia events have been manageable with dose delays. One neutropenia related dose delay in a CLL patient at UTX 600 mg + TGR 800 mg met the criteria for a DLT, necessitating enrollment of additional pts into this cohort. No other DLTs have been reported, including at higher dose levels. Fifteen pts were evaluable for efficacy with 6 pts too early for response assessment. Among evaluable pts, 80% displayed a reduction in tumor burden at first efficacy assessment, despite pts exhibiting a number of high-risk characteristics, including 3/5 CLL pts having 17p/11q deletion and a median of 6 prior lines of therapy amongst pts with FL. Objective responses are summarized below: Table TypePts (n)PRn (%)ORRn (%)PD(n)% pts ≥ SD for 12 wksMedian Prior Rx CLL/SLL54 (80%)4 (80%)-5 (100%)2 (1 – 3) Richter’s1---1 (100%)1 FL4---4 (100%)6 (3 – 8) DLBCL52 (40%)2 (40%)14 (80%)3 (1 – 6) Total156 (40%)6 (40%)114 (93%)3 (1 – 8) Amongst pts with CLL, 2/2 pts with normal cytogenetics achieved a PR including a patient with prior treatment with a BTK inhibitor, while 2/3 pts with presence of 17p/11q deletion achieved a PR, with the remaining patient having SD with a 44% nodal reduction at first assessment. Conclusions: Preliminary data suggests the combination of UTX + TGR-1202 is well tolerated with early signs of clinical activity in heavily pre-treated and high-risk patient subsets. Enrollment is ongoing with at least 30 patients anticipated. Disclosures Lunning: Onyx: Consultancy; Alexion: Consultancy; Gilead: Consultancy; Spectrum Pharmaceuticals: Consultancy. Schreeder:TG Therapeutics, Inc.: Research Funding. Pauli:TG Therapeutics, Inc.: Consultancy. Miskin:TG Therapeutics, Inc.: Employment, Equity Ownership. Sportelli:TG Therapeutics: Employment, Equity Ownership. Weiss:TG Therapeutics, Inc.: Employment, Equity Ownership. Vakkalanka:Rhizen: Employment, Equity Ownership. Viswanadha:Incozen: Employment. O'Brien:Amgen, Celgene, GSK: Consultancy; CLL Global Research Foundation: Membership on an entity's Board of Directors or advisory committees; Emergent, Genentech, Gilead, Infinity, Pharmacyclics, Spectrum: Consultancy, Research Funding; MorphoSys, Acerta, TG Therapeutics: Research Funding.

Description: von Willebrand factor (vWF), as secreted by endothelial cells (ECs), is a highly thrombogenic, ultra-large multimeric protein which promotes platelet adhesion and clot formation. This ultra-large vWF would lead to platelet aggregation even without vascular injury if not for the activity of a plasma vWF-cleaving protease, ADAMTS-13, which cleaves the ultra-large vWF multimers upon secretion into the more moderately-sized, less thrombogenic multimers commonly found circulating in normal plasma. The production of ADAMTS-13 was first described in hepatic stellate cells, but has since been found to be produced in a variety of tissues and cell types including ECs. Production of ADAMTS-13 by ECs is of interest as the newly secreted ultra-large vWF is immediately cleaved on the surface of ECs by ADAMTS-13. Quiescent ECs normally exist as a confluent non-thrombogenic monolayer lining the lumen of the vasculature. Damage to the EC monolayer results in cell activation, stimulating not only thrombosis but proliferation as the ECs attempt to prevent blood loss and repair vascular wall damage. To assess the production of ADAMTS-13 by human umbilical vein ECs, as measured by a commercially-available ELISA (American Diagnostica Inc., Stamford, CT), cellular supernatants were collected and cellular proteins extracted from either confluent ECs (EC monolayers), damaged confluent ECs (EC monolayers which had narrow strips of cells removed with a sterile pipette tip), or subconfluent ECs (50% confluence). After four hours, supernatants from subconfluent ECs contained 2.5X as much ADAMTS-13 (161.5±29.1 pg/ml/μg cellular protein; p

Description: Aminoglycoside antibiotics exhibit their bactericidal effect by interfering with normal ribosomal activity. In this pilot study, we have evaluated the effect of the aminoglycoside antibiotic gentamicin on the factor VIII (FVIII) and IX levels of severe hemophiliacs with known nonsense mutations. Five patients were enrolled and each patient was given 3 consecutive days of gentamicin at a dose of 7 mg/kg intravenously every 24 hours. Two patients (patient no. 1: hemophilia A, Ser1395Stop; and patient no. 5: hemophilia B, Arg333Stop) showed a decrease in their activated partial thromboplastin time (aPTT), an increase in their FVIII (0.016 IU/mL, 1.6%) or FIX (0.02 IU/mL, 2%) levels, and an increase in thrombin generation. The remaining 3 patients (patient no. 2: hemophilia B, Arg252Stop; patient no. 3: hemophilia A, Arg2116Stop; and patient no. 4: hemophilia A, Arg427Stop) showed no response in the aPTTs or factor levels, but one (patient no. 2: hemophilia B, Arg252Stop) showed an increase in the factor IX antigen level (2%-5.5%) that persisted throughout the period of the study and was concordant with an increase in thrombin generation. Gentamicin is unlikely to be an effective treatment for severe hemophilia due to its potential toxicities and the minimal response documented in this report. This study, however, does provide a proof of principle, suggesting that ribosomal interference with a less toxic agent may be a potential therapeutic mechanism for severe hemophilia patients with nonsense mutations.

Description: Discovery of somatic mutation of JAK-2 (G1849T that produces JAK-2V617F) in the hematopoietic cells of patients with Philadelphia chromosome negative myeloproliferative disorders (Ph−MPDs) was a watershed event that not only provided new insights into the pathobiology of polycythemia vera, essential thrombocytosis and primary myelofibrosis but also identified a potential target for therapy. Herein we report the results of preclinical studies designed to characterize the activity of a novel inhibitor of JAK-2. The compound, SGI-1252, developed by SuperGen (Dublin, CA) incorporates with high affinity into the ATP-binding site of JAK-2. SGI-1252 was tested against a panel of 75 kinases and was found to have significant activity against only FLT-3, TYK-2 and the SRC family members, ABL, LCK, YES, in addition to JAK-2 and JAK-1. SGI-1252 has an IC50 for JAK-2 of 5.4 nM with an IC50 for JAK-2V617F of 19.7 nM. The inhibitor also effectively blocks the activity of JAK-1 (IC50 14.8 nM) but has little JAK-3 inhibitory activity (IC50 1,700 nM). SGI-1252 is a potent inhibitor of STAT-5 phosphorylation (EC50 76.2 nM) and was also found to block the JAK-2 dependent expression of the anti-apoptotic protein, BCL-XL (EC50 778 nM). Drug treatment of a murine cell line (FDCP) transfected with either human wild-type JAK-2 or JAK-2G1849Tgenerated IC50 values of 83 nM and 108 nM, respectively, and SGI-1252 treatment of human cell lines, HEL, UKE-1 and SET-2, that express mutant JAK2 in different copy numbers, gave IC50 values of 472 nM, 83 nM and 63 nM, repectively. When tested in ex-vivo expanded native human erythroid progenitor cells from 17 patients with Ph−MPDs (10 PV and 7 MF), SGI-1252 showed an IC50 of ~100 nM, regardless of the JAK-2V617F allele burden. Using a flow cytometric assay, SGI-1252 was shown to induce apoptotic cell death in a concentration dependent manner. Luminex technology allows for concurrent quantitative analysis of multiple proteins from the same tissue source, and this technology was used to investigate simultaneously the effects of SGI-1252 on total and phospho ERK1/2, total and phospho STAT3, phospho STAT5, caspase 3, cleaved PARP and GAPDH (control) in untreated and drug treated cells at IC50 and IC80 concentrations. Significant in vivo efficacy of SGI-1252 was also observed using HEL and MV-4-11 xenograft models when compared to treatment with vehicle or daunorubicin. Using a murine model, we found that SGI-1252 has high oral bioavailability and is well tolerated with a five-day repeat maximum dose of at least 900 mg/kg. Together, these studies demonstrate that SGI-1252 is a potent inhibitor of JAK-2 dependent proliferation in both JAK-2V617F positive cell lines and in ex vivo expanded erythroid progenitors derived from patients with JAK-2V617F positive Ph−MPDs. Moreover, our studies show that the effects of SGI-1252 are mediated by blocking both JAK-2 dependent anti-apoptoic pathways and JAK-2 dependent proliferative pathways. Using the orally available form of the compound, pharmacokinetic, pharmacodynamic and toxicity studies in mice suggest that serum concentration of the drug well above the predicted therapeutic range can be achieved without significant hematological toxicity. Based on these preclinical experiments, SGI-1252 appears to be an excellent candidate for phase I/II studies in patients with Ph−MPDs.

Description: Retinoid X receptors (RXRs) are important transcriptional nuclear hormone receptors, acting as either homodimers or the binding partner for at least one fourth of all the known human nuclear receptors. Functional nongenomic effects of nuclear receptors are poorly understood; however, recently peroxisome proliferator-activated receptor (PPAR) #947;, PPAR#946;, and the glucocorticoid receptor have all been found active in human platelets. Human platelets express RXR#945; and RXR#946;. RXR ligands inhibit platelet aggregation and TXA2 release to ADP and the TXA2 receptors, but only weakly to collagen. ADP and TXA2 both signal via the G protein, Gq. RXR rapidly binds Gq but not Gi/z/o/t/gust in a ligand-dependent manner and inhibits Gq-induced Rac activation and intracellular calcium release. We propose that RXR ligands may have beneficial clinical actions through inhibition of platelet activation. Furthermore, our results demonstrate a novel nongenomic mode for nuclear receptor action and a functional cross-talk between G-protein and nuclear receptor signaling families.

Description: Our goal is to test mesenchymal stem cell therapy in a mouse model of Hutchinson-Gilford Progeria Syndrome (HGPS), a lethal childhood disorder for which no definitive therapy is available. HGPS patients have failure to thrive, lipodystrophy, skeletal dysplasia, sclerotic skin, alopecia, and occlusive vascular disease that results in premature death from myocardial infarction or stroke in early teens. In HGPS, the accumulation of incompletely processed nuclear architectural protein lamin A (a farnesylated version of prelamin A, termed progerin) results in dysfunction of multiple organ systems, particularly those of mesenchymal origin. Consistent with this, progerin has been shown to interfere with the proliferation and differentiation of mesenchymal stem cells (MSCs). Furthermore, MSC depletion is thought to account for the specific segmental nature of human progeria. The identification of HGPS-specific MSC dysfunction, and emerging evidence about the plasticity and paracrine effects of MSCs have prompted us to test the hypothesis that MSCs might be coaxed into becoming cells able to correct widespread pathology in HGPS. To determine whether MSCs can be used to rescue progeria phenotype, MSCs from wild-type donors were tested. First, donor MSCs (0.5 × 106 per recipient) were stably transfected to express the red fluoroform DsRed2, which permitted donor cell tracking in tissues post mortem. Next, to achieve wide biodistribution DsRed2+ MSCs were injected intra-arterially into 2-week-old ZMPSTE24−/− mutant mice. Like HGPS cells, ZMPSTE24−/− mutant mice accumulate progerin and the mice exhibit many progeria-like signs, including alopecia, micrognathia, dental abnormalities, osteolytic lesions in bones, osteoporosis, retarded growth, muscle weakness, and shortened lifespan. Therefore, survival, growth (measured by weight gain), and muscle weakness (measured by grip strength) were analyzed. MSC-treated (n = 13) versus untreated (n = 23) ZMPSTE24−/− mice had significantly increased survival (65% versus 100%), weight gain after 6 weeks of life, and grip strength (judged by the ability to hang onto an upside–down grid). These data are consistent with the hypothesis that the transfer of wild-type MSCs reduces the severity of the lamin A defect. To investigate whether the benefits associated with MSC infusion were attributable to persistent tissue engraftment or to a transient paracrine effect of donor MSCs, all mice were electively harvested at 20 weeks of age. Because dermal lipodystrophy, cardiac arteriosclerosis, and skeletal myopathy are prominent pathological findings in both human and murine progeria, post-mortem analyses focused on donor cell engraftment and progerin expression in corresponding organs of pathology (skin, liver, and skeletal muscle). Donor cells were identified in skin, liver, and skeletal muscle specimens with a frequency of 1%–5%, indicating that donor MSCs can repopulate tissue niches presumed to be dysfunctional in progeria. Experiments are ongoing to evaluate tissue levels of prelamin A and mature lamin A, abnormalities in nuclear shape, and pertubations in intracellular signaling pathway genes known to be dysregulated in human progeria. Collectively, these data demonstrate the proof of principle of MSC transfer for phenotypic reversion of lamin A defect in murine progeria. This may offer a valuable approach for treatment of human HGPS with human MSCs, which are already in clinical use.