Operando analysis of a solid oxide fuel cell by environmental transmission electron microscopy.

Correlating the microstructure of an energy conversion device to its performance is often a complex exercise, notably in solid oxide fuel cell research. Solid oxide fuel cells combine multiple materials and interfaces that evolve in time due to high operating temperatures and reactive atmospheres. We demonstrate here that operando environmental transmission electron microscopy can identify structure-property links in such devices. By contacting a cathode-electrolyte-anode cell to a heating and biasing microelectromechanical system in a single-chamber configuration, a direct correlation is found between the environmental conditions (oxygen and hydrogen partial pressures, temperature), the cell open circuit voltage, and the microstructural evolution of the fuel cell, down to the atomic scale. The results shed important insights into the impact of the anode oxidation state and its morphology on the cell electrical properties.

Grain trapping by filamentous cyanobacterial and algal mats: implications for stromatolite microfabrics through time.

Archean and Proterozoic stromatolites are sparry or fine-grained and finely laminated; coarse-grained stromatolites, such as many found in modern marine systems, do not appear until quite late in the fossil record. The cause of this textural change and its relevance to understanding the evolutionary history of stromatolites is unclear. Cyanobacteria are typically considered the dominant stromatolite builders through time, but studies demonstrating the trapping and binding abilities of cyanobacterial mats are limited. With this in mind, we conducted experiments to test the grain trapping and binding capabilities of filamentous cyanobacterial mats and trapping in larger filamentous algal mats in order to better understand grain size trends in stromatolites. Mats were cut into squares, inclined in saltwater tanks at angles from 0 to 75° (approximating the angle of lamina in typical stromatolites), and grains of various sizes (fine sand, coarse sand, and fine pebbles) were delivered to their surface. Trapping of grains by the cyanobacterial mats depended strongly on (i) how far filaments protruded from the sediment surface, (ii) grain size, and (iii) the mat's incline angle. The cyanobacterial mats were much more effective at trapping fine grains beyond the abiotic slide angle than larger grains. In addition, the cyanobacterial mats actively bound grains of all sizes over time. In contrast, the much larger algal mats trapped medium and coarse grains at all angles. Our experiments suggest that (i) the presence of detrital grains beyond the abiotic slide angle can be considered a biosignature in ancient stromatolites where biogenicity is in question, and, (ii) where coarse grains are present within stromatolite laminae at angles beyond the abiotic angle of slide (e.g., most modern marine stromatolites), typical cyanobacterial-type mats are probably not solely responsible for the construction, giving insight into the evolution of stromatolite microfabrics through time.

Stabilization mechanism of electrodeposited silicon thin films.

Amorphous composite silicon thin films electrodeposited in tetrahydrofuran, containing up to 80 at% of Si and exhibiting an homogeneous dispersions of O, C and Cl in the amorphous Si matrix, have been successfully stabilized against oxidation using a post-annealing step in inert atmosphere. In order to understand the impact of the annealing step on their stabilization against oxidation, their composition and structure have been investigated upon heat treatments. It has been shown that the presence of impurities such as O, C and Cl does not have any impact on the stabilization process, which is rather linked to the presence of hydrogen in the Si composites. This conclusion has been drawn after a detailed analysis of the bonding structure of films annealed at different temperatures and dwell times by the mean of Raman spectroscopy. It has been shown that annealing the as-deposited films at 350 °C for a couple of hours or at higher temperatures induced a hydrogen evolution, characterized by the breaking of Si-H bonds and the formation of Si-Si bonds, which stabilized the silicon network. The understanding and the reproducibility of this stabilization process of silicon thin film electrodeposited in organic solvent paves the way for their use for many applications.

Investigation of mechanism of drug-induced cardiac injury and torsades de pointes in cynomolgus monkeys.

BACKGROUND AND PURPOSE: Drug candidates must be thoroughly investigated for their potential cardiac side effects. During the course of routine toxicological assessment, the compound RO5657, a CCR5 antagonist, was discovered to have the rare liability of inducing torsades de pointes (polymorphic ventricular arrhythmia) in normal, healthy animals. Studies were conducted to determine the molecular mechanism of this arrhythmia. EXPERIMENTAL APPROACH: Toxicological effects of repeat dosing were assessed in naïve monkeys. Cardiovascular effects were determined in conscious telemetry-implanted monkeys (repeat dosing) and anaesthetized instrumented dogs (single doses). Mechanistic studies were performed in guinea-pig isolated hearts and in cells recombinantly expressing human cardiac channels. KEY RESULTS: In cynomolgus monkeys, RO5657 caused a low incidence of myocardial degeneration and a greater incidence of ECG abnormalities including prolonged QT/QTc intervals, QRS complex widening and supraventricular tachycardia. In telemetry-implanted monkeys, RO5657 induced arrhythmias, including torsades de pointes and in one instance, degeneration to fatal ventricular fibrillation. RO5657 also depressed both heart rate (HR) and blood pressure (BP), with no histological evidence of myocardial degeneration. In the anaesthetized dog and guinea-pig isolated heart studies, RO5657 induced similar cardiovascular effects. RO5657 also inhibited Kv11.1 and sodium channel currents. CONCLUSIONS AND IMPLICATIONS: The molecular mechanism of RO5657 is hypothesized to be due to inhibition of cardiac sodium and Kv11.1 potassium channels. These results indicate that RO5657 is arrhythymogenic due to decreased haemodynamic function (HR/BP), decreased conduction and inhibition of multiple cardiac channels, which precede and are probably the causative factors in the observed myocardial degeneration.

Restoration of shp1 expression by 5-AZA-2'-deoxycytidine is associated with downregulation of JAK3/STAT3 signaling in ALK-positive anaplastic large cell lymphoma.

Anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALK+ ALCL) is characterized by constitutive activation of the Janus kinase (JAK)3/signal transducers and activators of transcription 3 (STAT3) signaling pathway. SHP1, a tyrosine phosphatase that negatively regulates JAK/STAT, is frequently absent in ALK+ ALCL owing to gene methylation. To test the hypothesis that loss of SHP1 contributes to JAK3/STAT3 activation in ALK+ ALCL cells, we induced SHP1 expression using 5-aza-2'-deoxycytidine (5-AZA), an inhibitor of DNA methyltransferase, in ALK+ ALCL cell lines, and correlated with changes in the JAK3/STAT3 pathway. 5-AZA gradually restored SHP1 expression in Karpas 299 and SU-DHL-1 cells over 5 days. The initially low level of SHP1 expression did not result in significant changes to the expression or tyrosine phosphorylation of JAK3 and STAT3. However, higher levels of SHP1 seen subsequently correlated with substantial decreases in JAK3 and pJAK3, followed by pSTAT3 (but not STAT3). Importantly, the decrease in JAK3 was abrogated by MG132, a proteasome inhibitor. 5-AZA induced no significant increase in apoptosis but it sensitized ALCL cells to doxorubicin-induced apoptosis. Our findings support the concept that loss of SHP1 contributes to the constitutive activation of JAK3/STAT3 in ALK+ ALCL cells. SHP1 appears to downregulate JAK3 by two mechanisms: tyrosine dephosphorylation and increased degradation via the proteasome pathway.

Characterization and mechanisms of chromosomal alterations induced by benzene in mice and humans.

Elevated frequencies of chromosomal aberrations have been observed in the lymphocytes of benzene-exposed workers. Similar changes occurring in the bone marrow may play an important role in the development of leukemia. The objective of this research has been to characterize chromosomal alterations induced by benzene in mice and humans and to investigate the potential role of inhibition of topoisomerase II in the myelotoxic effects of benzene. The research is presented in three sections corresponding to the specific aims of the project: genotoxicity studies in the mouse, topoisomerase II studies, and initial studies using a new fluorescence in situ hybridization (FISH) approach to detect chromosome alterations in benzene-exposed workers. The results of the mouse experiments indicate that both chromosome breakage and aneuploidy are induced in the bone marrow of B6C3F1 mice following benzene administration. Chromosome breakage is the predominant effect, and this occurs primarily in the mouse euchromatin. Significant breakage within the mouse heterochromatin was also observed, as was aneuploidy. Breakage in the mouse bone marrow erythrocytes increased as a function of both dose and duration of benzene administration. The aneuploidy resulting from benzene exposure in mice was a relatively infrequent event, with increases of both chromosome loss and hyperdiploidy being observed. In the topoisomerase studies, benzene or its metabolites were shown to inhibit topoisomerase II enzyme activity in an isolated enzyme system, in a human bone marrow-derived leukemia cell line, and in vivo in the bone marrow of treated mice. The decreased activity was probably due to the rapid degradation of the topoisomerase II protein in the treated cells. In the human biomonitoring studies, the feasibility of using FISH with tandem DNA probes to detect chromosome alterations in interphase granulocytes and lymphocytes of benzene-exposed workers was demonstrated. The results from the two worker studies were somewhat inconsistent, however. In the study of Estonian workers, characterized by lower exposures and a smaller sample size, the benzene-exposed workers exhibited elevated frequencies of breakage in the lq12 region as compared with those seen in controls. A suggestive trend toward increased hyperdiploidy was also seen, although the frequencies in the exposed workers were low and within the range of our laboratory's historical control frequencies. In the larger study of more highly exposed Chinese workers, no increase in breakage affecting the 1q12 region was seen among the exposed workers. A trend toward increased hyperdiploidy of chromosome 1 was seen in the exposed workers when the concentration of urinary benzene metabolites was used in conjunction with the frequency of hyperdiploidy observed in the lymphocytes of the individual workers. The results of these studies indicate that benzene exposure is characterized by chromosome breakage, primarily within the euchromatin, and modest increases in aneuploidy. These findings also provide the first direct evidence that benzene is capable of inhibiting the enzymatic activity of topoisomerase II in vivo, providing additional support for the hypothesis that inhibition of topoisomerase II contributes to benzene-induced toxicity and leukemogenesis.

Inhibition of N-myc expression and induction of apoptosis by iron chelation in human neuroblastoma cells.

Neuroblastoma is the second most common solid malignancy of childhood. Enhanced expression of the amplified N-myc gene in the tumor cells may be associated with poor patient prognosis and may contribute to tumor development and progression. The use of deferoxamine mesylate (DFO), an iron chelator, to treat neuroblastoma is being investigated in national clinical studies. We show here by TUNEL assay and DNA laddering that DFO induces apoptosis in cultured human neuroblastoma cells, which is preceded by a decrease in the expression of N-myc and the altered expression of some other oncogenes (up-regulating c-fos and down-regulating c-myb) but not housekeeping genes. The decrease in N-myc expression is iron-specific but does not result from inhibition of ribonucleotide reductase, because specific inhibition of this iron-containing enzyme by hydroxyurea does not affect N-myc protein levels. Nuclear run-on and transient reporter gene expression experiments show that the decrease in N-myc expression occurs at the level of initiation of transcription and by inhibiting N-myc promoter activity. Comparison across neuroblastoma cell lines of the amount of residual cellular N-myc protein with the extent of apoptosis measured as pan-caspase activity after 48 h of iron chelation reveals no correlation, suggesting that the decrease in N-myc expression is unlikely to mediate apoptosis. In conclusion, chelation of cellular iron by DFO may alter the expression of multiple genes affecting the malignant phenotype by multiple pathways. Given the clinical importance of N-myc overexpression in neuroblastoma malignancy, decreasing N-myc expression by DFO might be useful as an adjunct to current

Characterization of trans-splicing in Euglenoids.

We have looked for trans-splicing of nuclear mRNAs in several Euglenoid species. In Cyclidiopsis acus, Phacus curvicauda, Rhabdomonas costata and Menoidium pellucidum we showed that several premRNAs chosen at random are matured by a transsplicing process: we identified SL-RNA genes whose 5' ends (SLs for spliced leader-sequences) were transferred to the 5' extremities of mRNAs. The SL-RNA genes are located on repeated DNA fragments which also encode 5S rRNA in P. curvicauda and C. acus. The potential secondary structures of SL-RNAs are compared to those previously characterized in two other Euglenoids: Euglena gracilis and Entosiphon sulcatum. In another Euglenoid species, Distigma proteus, since none of the mRNAs examined were trans-spliced, it is possible that trans-splicing does not occur. Phylogeny based on 5S rRNA sequences suggests that the species which have, or have had, chloroplasts (E. gracilis, P. curvicauda, C. acus) diverged early from the others.

Phosphoinositide 3-hydroxide kinase blockade enhances apoptosis in the Ewing's sarcoma family of tumors.

Ewing's sarcoma family of tumors (ESFTs) affects patients between the ages of 3 and 40 years, with most cases occurring in the second decade of life. These tumors contain a characteristic translocation, t(11;22), that produces a unique fusion protein, EWS/FLI-1. EWS/FLI-1 transforms mouse fibroblasts; this transformation requires intact EWS and FLI-1 domains as well as the insulin-like growth factor-I receptor (IGF-IR). The IGF-IR is a well-described transmembrane tyrosine kinase receptor that modulates transformation, cell growth, and survival. IGF-IR survival signaling is mediated through the downstream activation of phosphoinositide 3-OH kinase (PI 3-K) and Akt. Apoptosis, programmed cell death, progresses from a central death signal to a caspase cascade, including activation of caspase-3. Because the IGF-IR has been shown to play a role in the transformation and growth of ESFTs, we wanted to determine the role of downstream molecules in the cellular response to doxorubicin treatment. Doxorubicin increased caspase-3 activity in two ESFT cell lines, TC-32 and TC-71. Concomitant treatment of the doxorubicin-treated cells with IGF-I reduced caspase-3 activity 8-fold in TC-32 and 4-fold in TC-71. To determine whether PI 3-K has a role in IGF-I-mediated survival in ESFTs, PI 3-K was then inhibited with wortmannin and LY294002. Doxorubicin treatment reduced cell number and enhanced apoptosis in PI 3-K inhibited cells compared with noninhibited cells. Akt, a serine/threonine kinase activated downstream of PI 3-K, was investigated to determine whether its constitutive activation would render ESFT cells more resistant to doxorubicin. A constitutively activated Akt was stably transfected into ESFT and those cells with high levels of expression demonstrated increased resistance to doxorubicin-induced caspase-3 activation. These results indicate that ESFT cell lines use an IGF-IR initiated signaling pathway through PI 3-K and Akt for survival when treated with doxorubicin.

Trans-splicing and cis-splicing in the colourless Euglenoid, Entosiphon sulcatum.

The colourless Euglenoid Entosiphon sulcatum is thought to have diverged before the symbiotic event which gave rise to the photosynthetic Euglenoid species as Euglena gracilis. We have isolated genes encoding spliced leader-sequence RNA (SL-RNA) and we show that pre-mRNAs are matured via a trans-splicing reaction in E. sulcatum, as in the case of E. gracilis. The 2.5-kb repeated DNA fragment which encodes the SL-RNA gene also encodes a 5S rRNA gene as well as the genes for the small nuclear (sn) RNAs U1, U2 and U5. The presence of snRNA U1 indicates that the classical cis-splicing mechanism also exists in E. sulcatum. In addition, we show that the E. sulcatum beta-tubulin gene has the intron borders GU-AG, typical of spliceosome-matured introns which have not yet been found in E. gracilis. The probable origins of trans- and cis-mechanisms in Euglenoids are discussed.

Human herpesvirus-8 (HHV-8) associated with small non-cleaved cell lymphoma in a child with AIDS.

The association of human herpesvirus-8 (HHV-8) with a small non-cleaved cell lymphoma is described in a child with the acquired immunodeficiency syndrome (AIDS) who developed a malignant pleural effusion and radiologic evidence of multiple solid tumors. HHV-8 DNA and Epstein-Barr virus DNA were identified in pleural fluid cells by polymerase chain reaction (PCR) amplification. The serum antibody titer against lytic HHV-8 proteins was 1:640; antibodies to latent HHV-8 proteins were not detected. Cytogenetic analysis of malignant cells revealed three abnormal karyotypes sharing the common finding of a t(8;14) translocation. Rearrangement of c-myc was demonstrated by PCR analysis. Oligoclonal JH immunoglobulin bands were found. Insufficient pleural fluid cells were available to permit localization of HHV-8 to malignant cells by in situ hybridization. This malignancy contrasts with HHV-8-associated lymphomas reported in adult patients with AIDS with respect to cell morphology, c-myc translocation, and oligoclonal immunoglobulin gene rearrangement. HHV-8 is associated with a wider spectrum of malignancies than recognized previously.

Induction of heat shock protein 27 by hydroxyurea and its relationship to experimental metastasis.

Treatment of tumor cells with hydroxyurea (HU) has been shown to increase the experimental metastatic potential of these cells. We have previously described the induction of stress proteins (antioxidants) by HU in B16 murine melanoma cells and their relationship to the metastatic process. We have now investigated the induction by HU of another set of stress proteins, the heat shock proteins, and their role in experimental metastasis. HU markedly increased the cellular content of heat shock protein (hsp) 27 but not of hsp 90, 72/73, or 60 as measured by immunoblotting. The induction of hsp27 protein was preceded by a specific increase in hsp27 mRNA. Furthermore, HU-treated cells were more thermotolerant. To investigate the functional role of hsp27, human hsp27 cDNA was constitutively overexpressed in B16 cells at levels seen in HU-treated cells. In separate experiments, we induced a global increase in hsps by heat shock. Neither the hsp27 transfectants nor the heat-shocked cells demonstrated an increase in their experimental metastatic capacity. We conclude that hsp27 protein is increased by HU by the specific induction of hsp27 mRNA in B16 melanoma cells but increased hsp27 protein is not responsible for the increase in experimental metastasis. Since high levels of hsp27 are associated with metastatic disease in breast and ovarian cancers, but not in our experimental system, the functional role of hsp27 in metastasis requires further study.

Isochromosome 7q: the primary cytogenetic abnormality in hepatosplenic gammadelta T cell lymphoma.

Malignant lymphomas often have complex, nonrandom chromosomal abnormalities. Hepatosplenic gammadelta T cell lymphoma (gammadelta TCL) is an unusual post-thymic T cell lymphoma that primarily involves liver and spleen, often in young adult males. Few cases have had cytogenetic analysis. We report a consistent isochromosome 7q [i(7q)] abnormality in three cases of hepatosplenic gammadelta TCL, one with i(7q) as the sole abnormality at presentation. Three patients, 15-, 37- and 65-year-old males, presented with hepatosplenomegaly and fevers. Histopathologic, immunophenotypic, and molecular genetic studies supported the diagnosis. Spleen, liver, and bone marrow contained sinusoidal infiltrates of atypical lymphoid cells of T cell immunophenotype. PCR performed on two cases demonstrated clonal T cell receptor gamma gene rearrangements. Cytogenetic analysis of bone marrow showed i(7q) as the sole abnormality at presentation in one case. The second case showed i(7q) in addition to two normal chromosomes 7, and other structural and numerical abnormalities. The third case showed i(7q) and a deletion in the long arm of chromosome 11. These findings support the proposal that i(7q) represents the primary nonrandom cytogenetic abnormality in hepatosplenic gammadelta TCL, and plays a role in its pathogenesis.

MeIQx-DNA adduct formation in rodent and human tissues at low doses.

Heterocyclic amines, such as 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), are mutagenic/carcinogenic compounds formed during the cooking of protein-rich foods. Human exposure to MeIQx has been estimated to range from ng/person/day to a few microgram/person/day. In contrast, animal studies have been conducted at doses in excess of 10 mg/kg/day. In order to determine the relevance of high-dose animal data for human exposure, the dose-response curves for [14C]-MeIQx have been determined in rodents at low doses under both single-dose and chronic dosing regimens using the high sensitivity of accelerator mass spectrometry (AMS). To make a direct species comparison, rodent and human colonic MeIQx-DNA adduct levels have been compared following oral administration of [14C]-MeIQx. The results of these studies show: (1) total MeIQx levels are highest in the liver > kidney > pancreas > intestine > blood; (2) MeIQx levels in the liver plateau after 7 days of chronic feeding; (3) hepatic MeIQx-DNA adducts begin to plateau after 2-4 weeks and reach steady-state levels between 4 and 12 weeks on chronic exposures; (4) hepatic DNA adducts generally increase as a linear function of administered dose for a single-dose exposure and as a power function for chronic feeding over a dose range spanning 4 orders of magnitude; (5) human colon DNA adduct levels are approximately 10 times greater than in rodents at the same dose and time point following exposure; and (6) > or = 90% of the MeIQx-DNA adduct in both rodent and human colon appears to be the dG-C8-MeIQx adduct. These studies show that MeIQx is readily available to the tissues for both humans and rodents and that adduct levels are generally linear with administered dose except at high chronic doses where adduct levels begin to plateau slightly. This plateau indicates that linear extrapolation from high-dose studies probably underestimates the amount of DNA damage present in the tissues following low dose. Further, if adducts represent the biologically effective dose, these data show that human colon may be as sensitive to the genotoxic effects of MeIQx as rat liver. The significance of these endpoints to tumor response remains to be determined.

Bimolane: in vitro inhibitor of human topoisomerase II.

Bimolane is a member of the bis(2,6-dioxopiperazine) class of drugs and has been widely used in China as an anti-neoplastic agent and for the treatment of psoriasis. Recent case reports indicate that bimolane is leukemogenic and is thought to exert its effects through the inhibition of topoisomerase II. However, there are no data showing the inhibition of topoisomerase II by this agent. In this report bimolane was shown to inhibit the activity of human topoisomerase II in vitro at concentrations of 100 microM and higher when pBR322 was used as the DNA substrate, whereas inhibition was seen at 1.5 mM when using kDNA as a substrate. The results of enzyme and DNA titration assays indicate that inhibition of topoisomerase II by bimolane occurred through interactions with DNA, similar to the mechanism seen with the epipodophyllotoxin-type inhibitors. These results provide evidence that bimolane is an inhibitor of topoisomerase II in vitro.

Allelic imbalance on chromosome 5q predicts long-term survival in neuroblastoma.

Neuroblastoma is the most common extracranial solid tumour of childhood. Amplification of the proto-oncogene, N-myc, confers a poor prognosis in neuroblastoma, while hyperdiploidy is associated with a favourable outcome. Little is known about the contribution of tumour-suppressor genes to the development or progression of neuroblastoma. We examined allelic imbalance at the locus of the tumour-suppressor gene, APC (adenomatous polyposis coli), on chromosome 5q using a polymerase chain reaction (PCR)-based assay. Nine of 24 (37.5%) informative neuroblastoma tumours showed allelic imbalance (AI) at this locus. Clinical data concerning N-myc amplification and DNA content were correlated with these results in the same patients. Allelic imbalance was found only in tumours containing a single copy of the N-myc gene and exhibiting hyperdiploidy. All nine patients with AI of chromosome 5q were alive after a median follow-up period of 46 months, while 7 of 15 (47%) of those lacking AI at this locus had died (P = 0.018). Allelic imbalance at three additional loci on chromosome 5 was demonstrated in tumours that exhibited AI at the APC locus, suggesting that endoreduplication of chromosome 5 had occurred. Fluorescent in situ hybridisation (FISH) analysis of tumour tissue from one patient exhibiting AI demonstrated two, three, four or six copies of the APC gene per cell, consistent with this hypothesis. These data suggest that allelic imbalance of chromosome 5 is involved in at least a subset of neuroblastomas and influences survival in patients with neuroblastoma.

Hepatosplenic T-cell lymphoma: a distinct clinicopathologic entity of cytotoxic gamma delta T-cell origin.

We identified eight cases of T-cell lymphoma with evidence of a gamma delta phenotype over a 13-year period. Seven of these cases conformed to a distinct clinicopathologic entity of hepatosplenic gamma delta T-cell lymphoma. Nearly all of these patients were young adult males (five of seven), with a median age at presentation of 20 years. They presented with marked hepatosplenomegaly, without lymphadenopathy or significant peripheral blood lymphocytosis. Thrombocytopenia was seen in all patients, and five of seven were mildly anemic. The clinical course was aggressive, and despite multiagent chemotherapy, the median survival duration was less than 1 year. The morphologic findings were uniform; a monomorphic population of medium-sized lymphoid cells with moderately clumped chromatin and a rim of pale cytoplasm infiltrated the sinusoids of the spleen, liver, and bone marrow. The cells had a characteristic immunophenotype: CD2+, CD3+, CD4-, CD5-, CD7+, CD16+, CD57-, CD25-, T-cell receptor (TCR)delta +, beta F1-. CD8 was positive in four of seven cases tested, and CD56 was positive in five of six. All cases expressed the cytotoxic granule-associated protein, TIA1, but perforin was detected in only one case. All cases with assessable DNA had a TCR gamma gene rearrangement, and lacked Epstein-Barr virus sequences. Isochromosome 7q was identified in two cases with cytogenetic information. The one case of cutaneous gamma delta T-cell lymphoma differed in its clinical manifestations, histologic appearance, and immunophenotype. We conclude that hepatosplenic gamma delta T-cell lymphoma is a distinct clinicopathologic entity derived from cytotoxic gamma delta T cells, and should be distinguished from other lymphomas of T-cell and natural-killer cell (NK)-like T-cell derivation.