Treatment optimization and genomic outcomes in refractory severe aplastic anemia treated with eltrombopag.

Eltrombopag (EPAG) received approval from the US Food and Drug Administration for the treatment of refractory severe aplastic anemia (rSAA) based on treatment of 43 patients with doses escalating from 50 to 150 mg daily for 12 weeks. Response kinetics suggested that more prolonged administration of EPAG at a dose of 150 mg could speed and improve response rates. We enrolled 40 patients with rSAA in a study of EPAG 150 mg daily, with a primary end point of response at 24 weeks. Twenty (50%) of 40 patients responded at 24 weeks; 5 (25%) of 20 would have been deemed nonresponders at 12 weeks, the end point of the previous study. Fifteen of the 19 responding patients continuing on EPAG had drug discontinued for robust response; 5 of the 15 required EPAG re-initiation for relapse, with all recovering response. To analyze risk of clonal progression, we combined long-term data from the 83 patients with rSAA enrolled in both studies. Evolution to an abnormal karyotype occurred in 16 (19%), most within 6 months of EPAG initiation. Targeted deep sequencing/whole-exome sequencing was performed pre-EPAG and at primary response end point and/or time of clonal evolution or longest follow-up. Cytogenetic evolution did not correlate with mutational status, and overall mutated allele fractions of myeloid cancer genes did not increase on EPAG. In summary, extended administration of EPAG at a dose of 150 mg for 24 weeks rescued responses in some patients with rSAA not responding at 12 weeks. The temporal relationship between clonal evolution and drug exposure suggests that EPAG may promote expansion of dormant preexisting clones with an aberrant karyotype. The studies were registered at www.clinicaltrials.gov as #NCT00922883 and #NCT01891994.

Eltrombopag Added to Standard Immunosuppression for Aplastic Anemia.

BACKGROUND: Acquired aplastic anemia results from immune-mediated destruction of bone marrow. Immunosuppressive therapies are effective, but reduced numbers of residual stem cells may limit their efficacy. In patients with aplastic anemia that was refractory to immunosuppression, eltrombopag, a synthetic thrombopoietin-receptor agonist, led to clinically significant increases in blood counts in almost half the patients. We combined standard immunosuppressive therapy with eltrombopag in previously untreated patients with severe aplastic anemia. METHODS: We enrolled 92 consecutive patients in a prospective phase 1-2 study of immunosuppressive therapy plus eltrombopag. The three consecutively enrolled cohorts differed with regard to the timing of initiation and the duration of the eltrombopag regimen (cohort 1 received eltrombopag from day 14 to 6 months, cohort 2 from day 14 to 3 months, and cohort 3 from day 1 to 6 months). The cohorts were analyzed separately. The primary outcome was complete hematologic response at 6 months. Secondary end points included overall response, survival, relapse, and clonal evolution to myeloid cancer. RESULTS: The rate of complete response at 6 months was 33% in cohort 1, 26% in cohort 2, and 58% in cohort 3. The overall response rates at 6 months were 80%, 87%, and 94%, respectively. The complete and overall response rates in the combined cohorts were higher than in our historical cohort, in which the rate of complete response was 10% and the overall response rate was 66%. At a median follow-up of 2 years, the survival rate was 97%; one patient died during the study from a nonhematologic cause. Marked increases in bone marrow cellularity, CD34+ cell number, and frequency of early hematopoietic progenitors were noted. Rates of relapse and clonal evolution were similar to our historical experience. Severe rashes occurred in two patients, resulting in the early discontinuation of eltrombopag. CONCLUSIONS: The addition of eltrombopag to immunosuppressive therapy was associated with markedly higher rates of hematologic response among patients with severe aplastic anemia than in a historical cohort. (Funded by the National Heart, Lung, and Blood Institute; ClinicalTrials.gov number, NCT01623167 .).

Telomerase enzyme deficiency promotes metabolic dysfunction in murine hepatocytes upon dietary stress.

BACKGROUND & AIMS: Short telomeres and genetic telomerase defects are risk factors for some human liver diseases, ranging from non-alcoholic fatty liver disease and non-alcoholic steatohepatitis to cirrhosis. In murine models, telomere dysfunction has been shown to metabolically compromise hematopoietic cells, liver and heart via the activation of the p53-PGC axis. METHODS: Tert- and Terc-deficient mice were challenged with liquid high-fat diet. Liver metabolic contents were analysed by CE-TOFMS and liver fat content was confirmed by confocal and electronic microscopy. RESULTS: Tert-deficient but not Terc-deficient mice develop hepatocyte injury and frank steatosis when challenged with liquid high-fat diet. Upon high-fat diet, Tert-/- hepatocytes fail to engage the citric acid cycle (TCA), with an imbalance of NADPH/NADP+ and NADH/NAD+ ratios and depletion of intermediates of TCA cycle, such as cis-aconitic acid. Telomerase deficiency caused an intrinsic metabolic defect unresponsive to environmental challenge. Chemical inhibition of telomerase by zidovudine recapitulated the abnormal Tert-/- metabolic phenotype in Terc-/- hepatocytes. CONCLUSIONS: Our findings indicate that in telomeropathies short telomeres are not the only molecular trigger and telomerase enzyme deficiency provokes hepatocyte metabolic dysfunction, abrogates response to environmental challenge, and causes cellular injury and steatosis, providing a mechanism for liver damage in telomere diseases.

IFN-γ-mediated hematopoietic cell destruction in murine models of immune-mediated bone marrow failure.

Interferon gamma (IFN-γ) has been reported to have both negative and positive activity on hematopoietic cells, adding complexity to the interpretation of its pleiotropic functions. We examined the effects of IFN-γ on murine hematopoietic stem cells (HSCs) and progenitors in vitro and in vivo by using mouse models. IFN-γ treatment expanded bone marrow (BM) c-Kit(+)Sca1(+)Lin(-) (KSL) cell number but reduced BM KLCD150(+) and KLCD150(+)CD48(-) cells. IFN-γ-expanded KSL cells engrafted poorly when tested by competitive repopulation in vivo. KSL, KLCD150(+), and KLCD150(+)CD48(-) cells from IFN-γ-treated animals all showed significant upregulation in Fas expression. When cocultured with activated T cells in vitro, KSL and KLCD150(+) cells from IFN-γ-treated donors showed increased apoptosis relative to those from untreated animals, and infusion of activated CD8 T cells into IFN-γ-injected animals in vivo led to partial elimination of KSL cells. Exposure of BM cells or KSL cells to IFN-γ increased expression of Fas, caspases, and related proapoptotic genes and decreased expression of Ets-1 and other hematopoietic genes. In mouse models of BM failure, mice genetically deficient in IFN-γ receptor expression showed attenuation of immune-mediated marrow destruction, whereas effector lymphocytes from IFN-γ-deficient donors were much less potent in initiating BM damage. We conclude that the activity of IFN-γ on murine hematopoiesis is context dependent. IFN-γ-augmented apoptotic gene expression facilitates destruction of HSCs and progenitors in the presence of activated cytotoxic T cells, as occurs in human BM failure.

Rapamycin is highly effective in murine models of immune-mediated bone marrow failure.

Acquired aplastic anemia, the prototypical bone marrow failure disease, is characterized by pancytopenia and marrow hypoplasia. Most aplastic anemia patients respond to immunosuppressive therapy, usually with anti-thymocyte globulin and cyclosporine, but some relapse on cyclosporine withdrawal or require long-term administration of cyclosporine to maintain blood counts. In this study, we tested efficacy of rapamycin as a new or alternative treatment in mouse models of immune-mediated bone marrow failure. Rapamycin ameliorated pancytopenia, improved bone marrow cellularity, and extended animal survival in a manner comparable to the standard dose of cyclosporine. Rapamycin effectively reduced Th1 inflammatory cytokines interferon-γ and tumor necrosis factor-α, increased the Th2 cytokine interleukin-10, stimulated expansion of functional regulatory T cells, eliminated effector CD8+ T cells (notably T cells specific to target cells bearing minor histocompatibility antigen H60), and preserved hematopoietic stem and progenitor cells. Rapamycin, but not cyclosporine, reduced the proportion of memory and effector T cells and maintained a pool of naïve T cells. Cyclosporine increased cytoplasmic nuclear factor of activated T-cells-1 following T-cell receptor stimulation, whereas rapamycin suppressed phosphorylation of two key signaling molecules in the mammalian target of rapamycin pathway, S6 kinase and protein kinase B. In summary, rapamycin was an effective therapy in mouse models of immune-mediated bone marrow failure, acting through different mechanisms to cyclosporine. Its specific expansion of regulatory T cells and elimination of clonogenic CD8+ effectors support its potential clinical utility in the treatment of aplastic anemia.

A plasma microRNA signature as a biomarker for acquired aplastic anemia.

Aplastic anemia is an acquired bone marrow failure characterized by marrow hypoplasia, a paucity of hematopoietic stem and progenitor cells, and pancytopenia of the peripheral blood, due to immune attack on the bone marrow. In aplastic anemia, a major challenge is to develop immune biomarkers to monitor the disease. We measured circulating microRNAs in plasma samples of aplastic anemia patients in order to identify disease-specific microRNAs. A total of 179 microRNAs were analyzed in 35 plasma samples from 13 aplastic anemia patients, 11 myelodysplastic syndrome patients, and 11 healthy controls using the Serum/Plasma Focus microRNA Polymerase Chain Reaction Panel. Subsequently, 19 microRNAs from the discovery set were investigated in the 108 plasma samples from 41 aplastic anemia patients, 24 myelodysplastic syndrome patients, and 43 healthy controls for validation, confirming that 3 microRNAs could be validated as dysregulated (>1.5-fold change) in aplastic anemia, compared to healthy controls. MiR-150-5p (induction of T-cell differentiation) and miR-146b-5p (involvement in the feedback regulation of innate immune response) were elevated in aplastic anemia plasma, whereas miR-1 was decreased in aplastic anemia. By receiver operating characteristic curve analysis, we developed a logistic model with these 3 microRNAs that enabled us to predict the probability of a diagnosis of aplastic anemia with an area under the curve of 0.86. Dysregulated expression levels of the microRNAs became normal after immunosuppressive therapy at 6 months. Specifically, miR-150-5p expression was significantly reduced after successful immunosuppressive therapy, but did not change in non-responders. We propose 3 novel plasma biomarkers in aplastic anemia, in which miR-150-5p, miR-146b-5p, and miR-1 can serve for diagnosis and miR-150-5p for disease monitoring. Clinicaltrials.gov identifiers:00260689, 00217594, 00961064.

PPARγ antagonist attenuates mouse immune-mediated bone marrow failure by inhibition of T cell function.

Acquired aplastic anemia is an immune-mediated disease, in which T cells target hematopoietic cells; at presentation, the bone marrow is replaced by fat. It was reported that bone marrow adipocytes were negative regulators of hematopoietic microenvironment. To examine the role of adipocytes in bone marrow failure, we investigated peroxisomal proliferator-activated receptor gamma, a key transcription factor in adipogenesis, utilizing an antagonist of this factor called bisphenol-A-diglycidyl-ether. While bisphenol-A-diglycidyl-ether inhibited adipogenesis as expected, it also suppressed T cell infiltration of bone marrow, reduced plasma inflammatory cytokines, decreased expression of multiple inflammasome genes, and ameliorated marrow failure. In vitro, bisphenol-A-diglycidyl-ether suppressed activation and proliferation, and reduced phospholipase C gamma 1 and nuclear factor of activated T-cells 1 expression, as well as inhibiting calcium flux in T cells. The in vivo effect of bisphenol-A-diglycidyl-ether on T cells was confirmed in a second immune-mediated bone marrow failure model, using different strains and non-major histocompatibility antigen mismatched: bisphenol-A-diglycidyl-ether ameliorated marrow failure by inhibition of T cell infiltration of bone marrow. Our data indicate that peroxisomal proliferator-activated receptor gamma antagonists may attenuate murine immune-mediated bone marrow failure, at least in part, by suppression of T cell activation, which might hold implications in the application of peroxisomal proliferator-activated receptor gamma antagonists in immune-mediated pathophysiologies, both in the laboratory and in the clinic. Genetically "fatless" mice developed bone marrow failure with accumulation of marrow adipocytes in our model, even in the absence of body fat, suggesting different mechanisms of systematic and marrow adipogenesis and physiologic versus pathophysiologic fat accumulation.

Peromyscus leucopus mice: a potential animal model for haematological studies.

Peromyscus leucopus mice share physical similarities with laboratory mice Mus musculus (MM) but have higher agility and longer lifespan. We compared domesticated P. leucopus linville (PLL) and M. musculus C57BL/6 (MMB6) mice for cellular composition of peripheral blood (PB), bone marrow (BM) and spleen. PLL mice had significantly fewer platelets and significantly more monocytes in the blood, and notably fewer megakaryocytes in the BM. Spleens of PLL mice were significantly smaller, with 50% fewer cells and reduced 'red pulp'. There was no obvious haematological change in PLL mice between 2-8 and 16-26 months of age, except for a significant increase in blood monocytes. Cellular reactive oxygen species (ROS) content showed no change with age but differed significantly between different cell types. Treating two to eight month-old PLL mice with antioxidant N-acetylcysteine in drinking water for three months did not affect cellular ROS content, but increased blood leucocytes especially the concentration of monocytes. The low platelets, low megakaryocytes, high monocytes and low splenic erythropoiesis in PLL mice resemble human measurements better than the values seen in MMB6.

Cell-type specific molecular signatures of aging revealed in a brain-wide transcriptomic cell-type atlas.

Biological aging can be defined as a gradual loss of homeostasis across various aspects of molecular and cellular function. Aging is a complex and dynamic process which influences distinct cell types in a myriad of ways. The cellular architecture of the mammalian brain is heterogeneous and diverse, making it challenging to identify precise areas and cell types of the brain that are more susceptible to aging than others. Here, we present a high-resolution single-cell RNA sequencing dataset containing ~1.2 million high-quality single-cell transcriptomic profiles of brain cells from young adult and aged mice across both sexes, including areas spanning the forebrain, midbrain, and hindbrain. We find age-associated gene expression signatures across nearly all 130+ neuronal and non-neuronal cell subclasses we identified. We detect the greatest gene expression changes in non-neuronal cell types, suggesting that different cell types in the brain vary in their susceptibility to aging. We identify specific, age-enriched clusters within specific glial, vascular, and immune cell types from both cortical and subcortical regions of the brain, and specific gene expression changes associated with cell senescence, inflammation, decrease in new myelination, and decreased vasculature integrity. We also identify genes with expression changes across multiple cell subclasses, pointing to certain mechanisms of aging that may occur across wide regions or broad cell types of the brain. Finally, we discover the greatest gene expression changes in cell types localized to the third ventricle of the hypothalamus, including tanycytes, ependymal cells, and Tbx3+ neurons found in the arcuate nucleus that are part of the neuronal circuits regulating food intake and energy homeostasis. These findings suggest that the area surrounding the third ventricle in the hypothalamus may be a hub for aging in the mouse brain. Overall, we reveal a dynamic landscape of cell-type-specific transcriptomic changes in the brain associated with normal aging that will serve as a foundation for the investigation of functional changes in the aging process and the interaction of aging and diseases.

The role of the Th1 transcription factor T-bet in a mouse model of immune-mediated bone-marrow failure.

The transcription factor T-bet is a key regulator of type 1 immune responses. We examined the role of T-bet in an animal model of immune-mediated bone marrow (BM) failure using mice carrying a germline T-bet gene deletion (T-bet(-/-)). In comparison with normal C57BL6 (B6) control mice, T-bet(-/-) mice had normal cellular composition in lymphohematopoietic tissues, but T-bet(-/-) lymphocytes were functionally defective. Infusion of 5 x 10(6) T-bet(-/-) lymph node (LN) cells into sublethally irradiated, major histocompatibility complex-mismatched CByB6F1 (F1) recipients failed to induce the severe marrow hypoplasia and fatal pancytopenia that is produced by injection of similar numbers of B6 LN cells. Increasing T-bet(-/-) LN-cell dose to 10 to 23 x 10(6) per recipient led to only mild hematopoietic deficiency. Recipients of T-bet(-/-) LN cells had no expansion in T cells or interferon-gamma-producing T cells but showed a significant increase in Lin(-)Sca1(+)CD117(+)CD34(-) BM cells. Plasma transforming growth factor-beta and interleukin-17 concentrations were increased in T-bet(-/-) LN-cell recipients, possibly a compensatory up-regulation of the Th17 immune response. Continuous infusion of interferon-gamma resulted in hematopoietic suppression but did not cause T-bet(-/-) LN-cell expansion or BM destruction. Our data provided fresh evidence demonstrating a critical role of T-bet in immune-mediated BM failure.

Th17 immune responses contribute to the pathophysiology of aplastic anemia.

T helper type 17 (Th17) cells have been characterized based on production of interleukin-17 (IL-17) and association with autoimmune diseases. We studied the role of Th17 cells in aplastic anemia (AA) by isolating Th17 cells from patients blood (n = 41) and bone marrow (BM) mononuclear cells (n = 7). The frequency and total number of CD3(+)CD4(+)IL-17-producing T cells were increased in AA patients at presentation compared with healthy controls (P = .0007 and .02, respectively) and correlated with disease activity. There was an inverse relationship between the numbers of Th17 cells and CD4(+)CD25(high)FoxP3(+) regulatory T cells (Tregs) in the blood of AA patients. Concomitant with the classical Th1 response, we detected the presence of CD4(+) and CD8(+) IL-17-producing T cells in a mouse model of lymph node infusion-induced BM failure. Although anti-IL-17 treatment did not abrogate BM failure, early treatment with the anti-IL-17 antibody reduced the severity of BM failure with significantly higher platelet (P < .01) and total BM cell (P < .05) counts at day 10. Recipients that received anti-IL-17 treatment had significantly fewer Th1 cells (P < .01) and more Treg cells (P < .05) at day 10 after lymph node infusion. Th17 immune responses contribute to AA pathophysiology, especially at the early stage during disease progression.

Lymphocytes with aberrant expression of Fas or Fas ligand attenuate immune bone marrow failure in a mouse model.

Bone marrow (BM) and lymphocyte samples from aplastic anemia patients show up-regulated Fas and Fas-ligand (FasL) expression, respectively, supporting a relationship between immune-mediated BM destruction and the Fas apoptotic pathway. Mice with spontaneous lymphoproliferation (lpr) and generalized lymphoproliferative disease (gld) mutations exhibit abnormal expression of Fas and FasL, serving as potential models to elucidate underlying mechanisms of BM failure. We examined cellular and functional characteristics of lpr and gld mutants on the C57BL/6 (B6) background. Lymph node (LN) cells from lpr and gld mice produced less apoptosis when coincubated with C.B10-H2(b)/LilMcd (C.B10) BM cells in vitro. This functional difference was confirmed by infusing lpr, gld, and B6 LN cells into sublethally irradiated CB10 mice. All donor LN cells showed significant T cell expansion and activation, but only B6 LN cells caused severe BM destruction. Mice infused with gld LN cells developed mild to moderate BM failure despite receiving FasL-deficient effectors, thus suggesting the existence of alternative pathways or incomplete penetrance of the mutation. Paradoxically, mice that received Fas-deficient lpr LN cells also had reduced BM failure, likely due to down-regulation of proapoptotic genes, an effect that can be overcome by higher doses of lpr LN cells. Our model demonstrates that abnormal Fas or FasL expression interferes with the development of pancytopenia and marrow hypoplasia, validating a major role for the Fas/FasL cytotoxic pathway in immune-mediated BM failure, although disruption of this pathway does not completely abolish marrow destruction.

Phenotypic and functional characterization of a mouse model of targeted Pig-a deletion in hematopoietic cells.

BACKGROUND: Somatic mutation in the X-linked phosphatidylinositol glycan class A gene (PIG-A) causes glycosyl phosphatidylinositol anchor deficiency in human patients with paroxysmal nocturnal hemoglobinuria. DESIGN AND METHODS: We produced an animal model of paroxysmal nocturnal hemoglobinuria by conditional Pig-a gene inactivation (Pig-a(-/-)) in hematopoietic cells; mice carrying two lox sites flanking exon 6 of the Pig-a gene were bred with mice carrying the transgene Cre-recombinase under the human c-fes promoter. We characterized the phenotypic and functional properties of glycosyl phosphatidylinositol-deficient and glycosyl phosphatidylinositol-normal hematopoietic cells from these Pig-a(-/-) mice using gene expression microarray, flow cytometry, bone marrow transplantation, spectratyping, and immunoblotting. RESULTS: In comparison to glycosyl phosphatidylinositol-normal bone marrow cells, glycosyl phosphatidylinositol-deficient bone marrow cells from the same Pig-a(-/-) animals showed up-regulation of the expression of immune function genes and contained a significantly higher proportion of CD8 T cells. Both characteristics were maintained when glycosyl phosphatidylinositol-deficient cells were transplanted into lethally-irradiated recipients. Glycosyl phosphatidylinositol-deficient T cells were inactive, showed pronounced Vbeta5.1/5.2 skewing, had fewer gamma-interferon-producing cells after lectin stimulation, and contained fewer CD4(+)CD25(+)FoxP3(+) regulatory T cells. However, the levels of T-cell receptor signaling proteins from glycosyl phosphatidylinositol-deficient cells were normal relative to glycosyl phosphatidylinositol-normal cells from wild type animals, and cells were capable of inducing target cell apoptosis in vitro. CONCLUSIONS: Deletion of the Pig-a gene in hematopoietic cells does not cause frank marrow failure but leads to the appearance of clonally-restricted, inactive yet functionally competent CD8 T cells.

Enrichment of hematopoietic stem cells with SLAM and LSK markers for the detection of hematopoietic stem cell function in normal and Trp53 null mice.

OBJECTIVE: To test function of hematopoietic stem cells (HSCs) in vivo in C57BL/6 (B6) and Trp53-deficient (Trp53 null) mice by using two HSC enrichment schemes. MATERIALS AND METHODS: Bone marrow (BM) Lin-CD41-CD48-CD150+ (signaling lymphocyte activation molecules [SLAM]), Lin-CD41-CD48-CD150- (SLAM-) and Lin-Sca1+CD117+ (LSK) cells were defined by fluorescence-activated cell staining (FACS). Cellular reactive oxygen species (ROS) level was also analyzed by FACS. Sorted SLAM, SLAM-, and LSK cells were tested in vivo in the competitive repopulation (CR) and serial transplantation assays. RESULTS: SLAM cell fraction was 0.0078%+/-0.0010% and 0.0135%+/-0.0010% of total BM cells in B6 and Trp53 null mice, and was highly correlated (R2=0.7116) with LSK cells. CD150+ BM cells also contained more ROSlow cells than did CD150- cells. B6 SLAM cells repopulated recipients much better than B6 SLAM- cells, showing high HSC enrichment. B6 SLAM cells also engrafted recipients better than Trp53 null SLAM cells in the CR and the follow-up serial transplantation assays. Similarly, LSK cells from B6 donors also had higher repopulating ability than those from Trp53 null donors. However, whole BM cells from the same B6 and Trp53 null donors showed the opposite functional trend in recipient engraftment. CONCLUSION: Both SLAM and LSK marker sets can enrich HSCs from B6 and Trp53 mice. Deficiency of Trp53 upregulates HSC self-renewal but causes no gain of HSC function.

Hematopoietic lineage skewing and intestinal epithelia degeneration in aged mice with telomerase RNA component deletion.

A deletion of a telomerase RNA component (Terc(-/-)) in C57BL/6 (B6) mice resulted in hematopoietic lineage skewing with increased neutrophils and CD11b(+) myeloid cells and decreased red blood cells and CD45R(+) B lymphocytes when animals reach ages older than 12 months. There was no decline in bone marrow (BM) c-Kit(+)Sca-1(+)Lin(-) (KSL) cells in old Terc(-/-) mice, and the lineage skewing phenomenon was not transferred when BM cells from old Terc(-/-) donors were transplanted into young B6 recipients. Necropsy and histological examinations found minimal to no change in the lung, spleen and liver but detected severe epithelia degeneration, ulceration and infection in small and large intestines, leading to enteritis, typhlitis and colitis in old Terc(-/-) mice. In a mouse model of dextran-sulfate-sodium-induced typhlitis and colitis, development of intestinal pathology was associated with increases in neutrophils and CD11b(+) myeloid cells and a decrease in CD45R(+) B cells, similar to those observed in old Terc(-/-) mice. Treatment of 11-13 month old Terc(-/-) mice with antibiotic trimethoprim-sulfa water reduced neutrophils and myeloid cells and increased B lymphocytes in the blood, indicating that mitigation of intestinal infection and inflammation could alleviate hematological abnormalities in old Terc(-/-) animals.

Immune-mediated bone marrow failure in C57BL/6 mice.

We established a model of immune-mediated bone marrow (BM) failure in C57BL/6 (B6) mice with 6.5 G total-body irradiation followed by the infusion of 4-10 × 10(6) lymph node (LN) cells/recipient from Friend leukemia virus B/N (FVB) donors. Forty-three percent of animals succumbed, with surviving animals showing marked declines in blood neutrophils, red blood cells, platelets and total BM cells at 8 to 14 days following LN cell infusion. Lowering the total-body irradiation dose to 5 G or altering the LN source from FVB to BALB/cBy donors failed to produce BM destruction. Affected animals showed significant expansion and activation of CD8 T lymphocytes in both the blood and BM; cytotoxic T cells had elevated Fas ligand expression and were oligoclonal, mainly displaying Vß7 and Vß17 T cell receptors. There were significant increases in blood plasma interferon γ and tissue necrosis factor α in affected animals. Chemokine ligands CCL3, CCL4, CCL5, CCL20, CXCL2, and CXCL5 and hematopoietic growth factors G-CSF, M-CSF, GM-CSF, VEGF were also elevated. In B6 mice carrying a Fas gene mutation, BM failure was attenuated when they were infused with FVB LN cells. Our model establishes a useful platform to define the roles of individual genes and their products in immune-mediated BM failure.

Cloning and molecular characterization of telomerase reverse transcriptase (TERT) and telomere length analysis of Peromyscus leucopus.

Telomerase reverse transcriptase (TERT) is the catalytic subunit of telomerase complex that regulates telomerase activity to maintain telomere length for all animals with linear chromosomes. As the Mus musculus (MM) laboratory mouse has very long telomeres compared to humans, a potential alternative animal model for telomere research is the Peromyscus leucopus (PL) mouse that has telomere lengths close to the human range and has the wild counterparts for comparison. We report the full TERT coding sequence (pTERT) from PL mice to use in the telomere research. Comparative analysis with eight other mammalian TERTs revealed a pTERT protein considerably homologous to other TERTs and preserved all TERT specific-sequence signatures, yet with some distinctive features. pTERT displayed the highest nucleotide and amino acid sequence homology with hamster TERT. Unlike human but similar to MM mice, pTERT expression was detected in various adult somatic tissues of PL mice, with the highest expression in testes. Four different captive stocks of PL mice and wild-captured PL mice each displayed group-specific average telomere lengths, with the longest and shortest telomeres in inbred and outbred stock mice, respectively. pTERT showed considerable numbers of synonymous and nonsynonymous mutations. A pTERT proximal promoter region cloned was homologous among PL and MM mice and rat, but with species-specific features. From PL mice, we further cloned and characterized ribosomal protein, large, P0 (pRPLP0) to use as an internal control for various assays. Peromyscus mice have been extensively used for various studies, including human diseases, for which pTERT and pRPLP0 would be useful tools.

MHC class II upregulation and colocalization with Fas in experimental models of immune-mediated bone marrow failure.

OBJECTIVE: To test the hypothesis that γ-interferon (IFN-γ) promotes major histocompatibility complex (MHC) class II expression on bone marrow (BM) cell targets that facilitate T-cell-mediated BM destruction in immune-mediated BM failure. MATERIALS AND METHODS: Allogeneic lymph node (LN) cells were infused into MHC- or minor histocompatibility antigen-mismatched hosts to induce BM failure. MHC class II and Fas expression and cell apoptosis were analyzed by flow cytometry. MHC class II-Fas colocalization was detected by ImageStream Imaging Flow Cytometry and other cell-to-cell associations were visualized by confocal microscopy. T-cell-mediated BM cell apoptosis and effects of IFN-γ on MHC class II-Fas colocalization on normal BM cells were studied using cell culture in vitro followed by conventional and imaging flow cytometry. RESULTS: BM failure animals had significantly upregulated MHC class II expression on CD4(-)CD8(-)CD11b(-)CD45R(-) residual BM cells and significantly increased MHC class II-Fas colocalization on BM CD150(+) and CD34(+) hematopoietic cells. MHC class II(+)Fas(+) BM cells were closely associated with CD4(+) T cells in the BM of affected animals, and they were significantly more responsive to T-cell-mediated cell apoptosis relative to MHC class II(-)Fas(-) BM cells. Infusion of IFN-γ-deficient LN cells into minor histocompatibility antigen-mismatched recipients resulted in no MHC class II-Fas upregulation and no clinically overt BM failure. Treatment with recombinant IFN-γ significantly increased both MHC class II-Fas coexpression and colocalization on normal BM cells. CONCLUSIONS: Elevation of the inflammatory cytokine IFN-γ-stimulated MHC class II expression and MHC class II-Fas colocalization, which may facilitate T-cell-mediated cell destruction.

Role of perforin-mediated cell apoptosis in murine models of infusion-induced bone marrow failure.

OBJECTIVE: To investigate the role of perforin-mediated cell apoptosis in murine models of immune-mediated bone marrow (BM) failure. MATERIALS AND METHODS: We compared C57BL/6J (B6) mice carrying a perforin gene deletion (Prf(-/-)) with wild-type (WT) controls for cellular composition in lymphohematopoietic tissues. Lymph node (LN) cells from Prf(-/-) mice were coincubated with BM cells from B10-H2(b)/LilMcdJ (C.B10) mice in an apoptosis assay in vitro. We then infused Prf(-/-) and WT B6 LN cells into sublethally irradiated C.B10 and CByB6F1 recipients with mismatches at the minor and major histocompatibility loci, respectively, in order to induce BM failure. Cellular composition was analyzed by flow cytometry. RESULTS: Prf(-/-) mice showed normal lymphoid cell composition, but Prf(-/-) LN cells had reduced ability to induce C.B10 BM cell apoptosis in vitro. Infusion of 5 to 10 x 10(6) Prf(-/-) LN cells produced obvious BM failure in C.B10 and CByB6F1 recipients; pancytopenia and BM hypocellularity were only slightly less severe than those caused by infusion of 5 x 10(6) WT B6 LN cells. Infused Prf(-/-) LN cells showed less T-cell expansion, normal T-cell activation, and higher proportions of T cells expressing gamma-interferon, tissue necrosis factor-alpha, and Fas ligand CD178, in comparison to infused WT B6 LN cells. Fas expression was equally high in residual BM cells in recipient of both Prf(-/-) and B6 LN cells. CONCLUSION: Perforin deficiency alters T-cell expansion but upregulates T-cell Fas ligand expression. Perforin-mediated cell death appears to play a minor role in mouse models of immune-mediated BM failure.