Issue published July 15, 1998

G lucocorticoid-induced bone disease is characterized by decreased bone formation and in situ death of isolated segments of bone (osteonecrosis) suggesting that glucocorticoid excess, the third most common cause of osteoporosis, may affect the birth or death rate of bone cells, thus reducing their numbers. To test this hypothesis, we administered prednisolone to 7-mo-old mice for 27 d and found decreased bone density, serum osteocalcin, and cancellous bone area along with trabecular narrowing. These changes were accompanied by diminished bone formation and turnover, as determined by histomorphometric analysis of tetracycline-labeled vertebrae, and impaired osteoblastogenesis and osteoclastogenesis, as determined by ex vivo bone marrow cell cultures. In addition, the mice exhibited a threefold increase in osteoblast apoptosis in vertebrae and showed apoptosis in 28% of the osteocytes in metaphyseal cortical bone. As in mice, an increase in osteoblast and osteocyte apoptosis was documented in patients with glucocorticoid-induced osteoporosis. Decreased production of osteoclasts explains the reduction in bone turnover, whereas decreased production and apoptosis of osteoblasts would account for the decline in bone formation and trabecular width. Furthermore, accumulation of apoptotic osteocytes may contribute to osteonecrosis. These findings provide evidence that glucocorticoid-induced bone disease arises from changes in the numbers of bone cells.

T hyroglobulin is the major secretory protein of thyroid epithelial cells. Part of thyroglobulin reaches the circulation of vertebrates by transcytosis across the epithelial wall of thyroid follicles. Clearance of thyroglobulin from the circulation occurs within the liver via internalization of thyroglobulin by macrophages. Here we have analyzed the interaction of thyroglobulin with the cell surface of J774 macrophages with the aim to identify the possible thyroglobulin-binding sites on macrophages. Binding of thyroglobulin to J774 cells was saturated at approximately 100 nM thyroglobulin with a Kd of 50 nM, and it was competed by the ligand itself. Preincubation of J774 cells with thyroglobulin resulted in downregulation of thyroglobulin-binding sites, indicating internalization of thyroglobulin and its binding proteins. By affinity chromatography, two proteins from J774 cells were identified as thyroglobulin-binding proteins with an apparent molecular mass of approximately 33 kD. Unexpectedly, both proteins were identified as histone H1 by protein sequencing. The occurrence of histone H1 at the plasma membrane was further proven by biotinylation or immunolabeling of J774 cells. The in vitro interaction between histone H1 and thyroglobulin was analyzed by surface plasmon resonance that revealed a Kd at 46 nM. In situ, histone H1 was colocalized to FITC-Tg-containing endocytic compartments of Kupffer cells, i.e., liver macrophages. We conclude that histone H1 is detectable at the cell surface of macrophages where it serves as a thyroglobulin-binding protein and mediates thyroglobulin endocytosis.

A ctivin, a member of the TGF-beta superfamily, regulates the growth and differentiation of a variety of cell types. Based on the expression of activin in pancreatic rudiments of rat embryos and stimulation of insulin secretion from adult rat pancreatic islets by activin, activin is implicated in the development and function of islets. To examine the significance of activin signaling in the fetal and postnatal development of islets, transgenic mice expressing a dominant negative form of activin receptor (dn-ActR) or a constitutively active form of activin receptor (ActR-T206D) in islets were generated together with the transgenic mice expressing intact activin receptor (intact ActR) as a negative control. Transgenic mice with both dn-ActR and ActR-T206D showed lower survival rates, smaller islet area, and lower insulin content in the whole pancreas with impaired glucose tolerance when compared with transgenic mice with intact ActR or littermates, but they showed the same alpha cell/beta cell ratios as their littermates. In addition to islet hypoplasia, the insulin response to glucose was severely impaired in dn-ActR transgenic mice. It is suggested that a precisely regulated intensity of activin signaling is necessary for the normal development of islets at the stage before differentiation into alpha and beta cells, and that activin plays a role in the postnatal functional maturation of islet beta cells.

H eat shock proteins (hsp) have been repeatedly implicated to participate in the pathogenesis of rheumatoid arthritis (RA). Herein, we investigated the regulation of synovial hsp70 expression by analyzing the DNA-binding activity of heat shock transcription factor 1 (HSF1) as well as inducible hsp70 expression. Experiments were performed both on synovial tissue and on synovial fibroblast-like cells (SFC). Gel mobility shift analysis revealed increased HSF1 activation, and Western blotting and immunohistochemistry revealed increased hsp70 expression in RA synovial tissue, but not in synovial tissue derived from patients with osteoarthritis. Proinflammatory cytokines (TNF-alpha, IL-1alpha, IL-6), but not IFN-gamma or TGF-beta, induced activation of HSF1-DNA binding and hsp70 expression in cultivated SFC. Activation of HSF1 in SFC was accompanied by hyperphosphorylation and nuclear translocation of HSF1. Furthermore, shear stress also induced a complete heat shock response in cultivated synovial cells. In contrast, nonsteroidal antiinflammatory drugs triggered only an incomplete heat shock response, with HSF1 activation but not hsp70 induction, whereas steroids and immunosuppressive drugs did not affect the heat shock response at all. In summary, these data suggest that induction of hsp70 expression in rheumatoid synovial tissue is based on transcriptional activation of HSF1 due to the presence of proinflammatory cytokines (and possibly also shear stress).

O menn's syndrome is an inherited human combined immunodeficiency condition characterized by the presence of a large population of activated and tissue-infiltrating T cells. Analysis of the TCRB repertoire revealed a highly restricted TCRBV usage in three patients. More strikingly, T cell clones from the three patients expressed TCRB chains with VDJ junction similarities, suggesting a common antigenic specificity. Analysis of the TCRA repertoire in one patient also revealed a restricted TCRAV usage. Finally, analysis of the TCRBV repertoire of tissue-infiltrating T cells in one patient suggested nonrandom tissue migration. These results suggest that the oligoclonal expansion of T cells observed in Omenn's syndrome could be the consequence of autoimmune proliferation generated by a profound defect in lymphocyte development.

T he folate antagonist methotrexate (MTX) is extensively used in graft-versus-host disease, rheumatoid arthritis, and other chronic inflammatory disorders. In addition to its antiinflammatory activity associated with increased release of adenosine, MTX exerts antiproliferative properties by inhibition of dihydrofolate reductase and other folate-dependent enzymes. However, the mechanisms of immunosuppressive properties associated with low-dose MTX treatments are still elusive. We report here that MTX (0.1-10 microM) induces apoptosis of in vitro activated T cells from human peripheral blood. PBL exposed to MTX for 8 h, then activated in drug-free medium, underwent apoptosis, which was completely abrogated by addition of folinic acid or thymidine. Apoptosis of activated T cells did not require interaction between CD95 (Fas, APO-1) and its ligand, and adenosine release accounted for only a small part of this MTX activity. Apoptosis required progression of activated T cells to the S phase of the cell cycle, as it was prevented by drugs or antibodies that interfere with IL-2 synthesis or signaling pathways. MTX achieved clonal deletion of activated T cells in mixed lymphocyte reactions. Finally, in vitro activation of PBL taken from rheumatoid arthritis patients after MTX injection resulted in apoptosis. Altogether, the data demonstrate that MTX can selectively delete activated peripheral blood T cells by a CD95-independent pathway. This property could be used as a new pharmacological end point to optimize dosage and timing of MTX administration. It may account for the immunosuppressive effects of low-dose MTX treatments.

B oth p53 and ceramide have been implicated in the regulation of growth suppression. p53 has been proposed as the "guardian of the genome" and ceramide has been suggested as a "tumor suppressor lipid. " Both molecules appear to regulate cell cycle arrest, senescence, and apoptosis. In this study, we investigated the relationship between p53 and ceramide. We found that treatment of Molt-4 cells with low concentrations of actinomycin D or gamma-irradiation, which activate p53-dependent apoptosis, induces apoptosis only in cells expressing normal levels of p53. In these cells, p53 activation was followed by a dose- and time-dependent increase in endogenous ceramide levels which was not seen in cells lacking functional p53 and treated similarly. Similar results were seen in irradiated L929 cells whereby the p53-deficient clone was significantly more resistant to irradiation and exhibited no ceramide response. However, in p53-independent systems, such as growth suppression induced by TNF-alpha or serum deprivation, ceramide accumulated irrespective of the upregulation of p53, indicating that p53 regulates ceramide accumulation in only a subset of growth-suppressive pathways. Finally, ceramide did not increase p53 levels when used at growth-suppressive concentrations. Also, when cells lacking functional p53, either due to mutation or the expression of the E6 protein of human papilloma virus, were treated with exogenous ceramide, there was equal growth suppression, cell cycle arrest, and apoptosis as compared with cells expressing normal p53. These results indicate that p53 is unlikely to function "downstream" of ceramide. Instead, they suggest that, in situations where p53 performs a critical regulatory role, such as the response to genotoxic stress, it functions "upstream" of ceramide. These studies begin to define a relationship between these two pathways of growth inhibition.

I nsulin-deficient diabetic rats are markedly hyperphagic when fed a high-carbohydrate (HC) diet, but normophagic when fed a high-fat (HF) diet. When maintained on a HC diet, diabetic rats also exhibit increased gene expression of the orexigenic peptide neuropeptide Y (NPY) in the hypothalamic arcuate nucleus, and reduced expression of the anorectic peptide corticotropin-releasing hormone (CRH) in the paraventricular nucleus, and these changes are hypothesized to contribute to diabetic hyperphagia. In this experiment we assessed whether the normophagia displayed by HF-fed diabetic rats is associated with the opposite profile of NPY and CRH expression. Our results show that relative to diabetic rats on the HC diet, the diabetic rats on the HF diet exhibited significantly reduced caloric intake (-40%), NPY expression in the arcuate nucleus (-27%), and elevated CRH expression in the paraventricular nucleus (+37%). Insulin and corticosterone, which are known to affect hypothalamic NPY and CRH expression, were not different between these two groups, making it unlikely that they can account for the differences in either feeding behavior or hypothalamic peptide expression. There was a small but significant increase in plasma leptin levels in the diabetic animals maintained on the HF, and large differences in parameters associated with elevated fat oxidation. These observations support the hypothesis that the normalization of food intake observed in diabetic rats consuming a HF diet may in part be mediated by reductions in NPY expression and elevations in CRH expression.

A lthough Streptococcus pneumoniae is a major cause of meningitis in humans, the mechanisms underlying its traversal from the circulation across the blood-brain barrier (BBB) into the subarachnoid space are poorly understood. One mechanism might involve transcytosis through microvascular endothelial cells. In this study we investigated the ability of pneumococci to invade and transmigrate through monolayers of rat and human brain microvascular endothelial cells (BMEC). Significant variability was found in the invasive capacity of clinical isolates. Phase variation to the transparent phenotype increased invasion as much as 6-fold and loss of capsule approximately 200-fold. Invasion of transparent pneumococci required choline in the pneumococcal cell wall, and invasion was partially inhibited by antagonists of the platelet-activating factor (PAF) receptor on the BMEC. Pneumococci that gained access to an intracellular vesicle from the apical side of the monolayer subsequently were subject to three fates. Most opaque variants were killed. In contrast, the transparent phase variants were able to transcytose to the basal surface of rat and human BMEC in a manner dependent on the PAF receptor and the presence of pneumococcal choline-binding protein A. The remaining transparent bacteria entering the cell underwent a previously unrecognized recycling to the apical surface. Transcytosis eventually becomes a dominating process accounting for up to 80% of intracellular bacteria. Our data suggest that interaction of pneumococci with the PAF receptor results in sorting so as to transcytose bacteria across the cell while non-PAF receptor entry shunts bacteria for exit and reentry on the apical surface in a novel recycling pathway.

M utations in a newly described lysosomal enzyme, palmitoyl-protein thioesterase (PPT), were recently shown to be responsible for an autosomal recessive neurological disorder prevalent in Finland, infantile neuronal ceroid lipofuscinosis. The disease results in blindness, motor and cognitive deterioration, and seizures. Characteristic inclusion bodies (granular osmiophilic deposits [GROD]) are found in the brain and other tissues. The vast majority of Finnish cases are homozygous for a missense mutation (R122W) that severely affects PPT enzyme activity, and the clinical course in Finnish children is uniformly rapidly progressive and fatal. To define the clinical, biochemical, and molecular genetic characteristics of subjects with PPT deficiency in a broader population, we collected blood samples from U.S. and Canadian subjects representing 32 unrelated families with neuronal ceroid lipofuscinosis who had GROD documented morphologically. We measured PPT activity and screened the coding region of the PPT gene for mutations. In 29 of the families, PPT deficiency was found to be responsible for the neurodegenerative disorder, and mutations were identified in 57 out of 58 PPT alleles. One nonsense mutation (R151X) accounted for 40% of the alleles and was associated with severe disease in the homozygous state. A second mutation (T75P) accounted for 13% of the alleles and was associated with a late onset and protracted clinical course. A total of 19 different mutations were found, resulting in a broader spectrum of clinical presentations than previously seen in the Finnish population. Symptoms first appeared at ages ranging from 3 mo to 9 yr, and about half of the subjects have survived into the second or even third decades of life.

A lthough angiotensin-converting enzyme (ACE) has been studied primarily in the context of its role in blood pressure regulation, this widely distributed enzyme has many other physiological functions. The ACE gene encodes two isozymes. The somatic isozyme is expressed in many tissues, including vascular endothelial cells, renal epithelial cells, and testicular Leydig cells, whereas the testicular or germinal angiotensin-converting enzyme is expressed only in sperm. The ACE gene knockout mice lack both isozymes and they exhibit low blood pressure, kidney dysfunctions, and male infertility. Here, we report the use of a sperm-specific promoter and interbreeding of transgenic and gene knockout mice for generating a mouse strain that expressed ACE only in sperm. The experimental mice maintained the kidney defects of ACE-/- mice, but unlike the knockout strain, the males were fertile. Thus, we established that the role of ACE in male fertility is completely dependent on its exclusive expression in sperm. Our study clearly demonstrated how transgenic and knockout techniques can be combined for ascribing a specific physiological function to the expression of a multifunctional protein in a given tissue.

H DL metabolism and atherosclerosis were studied in apo E knockout (KO) mice overexpressing human apo AI, a des- (190-243)-apo AI carboxyl-terminal deletion mutant of human apo AI or an apo AI-(1-189)-apo AII-(12-77) chimera in which the carboxyl-terminal domain of apo AI was substituted with the pair of helices of apo AII. HDL cholesterol levels ranked: apo AI/apo E KO approximately apo AI-(1-189)-apo AII- (12-77)/apo E KO > > des-(190-243)-apo AI/apo E KO > apo E KO mice. Progression of atherosclerosis ranked: apo E KO > des-(190-243)-apo AI/apo E KO > > apo AI-(1-189)- apo AII-(12-77)/apo E KO approximately apo AI/apo E KO mice. Whereas the total capacity to induce cholesterol efflux from lipid-loaded THP-1 macrophages was higher for HDL of mice overexpressing human apo AI or the apo AI/apo AII chimera, the fractional cholesterol efflux rate, expressed in percent cholesterol efflux/microg apolipoprotein/h, for HDL of these mice was similar to that for HDL of mice overexpressing the deletion mutant and for HDL of apo E KO mice. This study demonstrates that the tertiary structure of apo AI, e.g., the number and organization of its helices, and not its amino sequence is essential for protection against atherosclerosis because it determines HDL cholesterol levels and not cholesterol efflux. Amino acid sequences of apo AII, which is considered to be less antiatherogenic, can be used to restore the structure of apo AI and thereby its antiatherogenicity.

A po E is a key molecule in the lipoprotein metabolism; thus, genetic manipulation of apo E may prove useful in the treatment of hypercholesterolemia. To test the feasibility of this idea, we have generated low density lipoprotein receptor (LDLR) knockout mice that overexpress the rat apo E transgene (ETg+/+:LDLRKO), and compared their plasma lipoprotein profiles with those of nonexpressing LDLR knockout mice (ETg-/-:LDLRKO). On a normal chow diet, the mean plasma cholesterol level of ETg+/+:LDLRKO mice was significantly lower than that of ETg-/-:LDLRKO mice (189 versus 240 mg/dl, P < 0. 01). The LDL fraction was selectively reduced in the ETg+/+:LDLRKO mice. Despite the challenge with an atherogenic diet, cholesterol lowering was persistently observed and fatty streak lesions in the aortic sinus were significantly suppressed in the mice overexpressing apo E. These results imply that stimulation of hepatic production of apo E may be used as a promising adjunctive therapy for homozygous familial hypercholesterolemia.

C yclic ADP-ribose (cADPR) has been shown to be a mediator for intracellular Ca2+ mobilization for insulin secretion by glucose in pancreatic beta cells, and CD38 shows both ADP-ribosyl cyclase to synthesize cADPR from NAD+ and cADPR hydrolase to hydrolyze cADPR to ADP-ribose. We show here that 13.8% of Japanese non-insulin-dependent diabetes (NIDDM) patients examined have autoantibodies against CD38 and that the sera containing anti-CD38 autoantibodies inhibit the ADP-ribosyl cyclase activity of CD38 (P </= 0.05). Insulin secretion from pancreatic islets by glucose is significantly inhibited by the addition of the NIDDM sera with anti-CD38 antibodies (P </= 0.04-0.0001), and the inhibition of insulin secretion is abolished by the addition of recombinant CD38 (P </= 0.02). The increase of cADPR levels in pancreatic islets by glucose was also inhibited by the addition of the sera (P </= 0.05). These results strongly suggest that the presence of anti-CD38 autoantibodies in NIDDM patients can be one of the major causes of impaired glucose-induced insulin secretion in NIDDM.

T NF-alpha may play a role in mediating insulin resistance associated with obesity. This concept is based on studies of obese rodents and humans, and cell culture models. TNF elicits cellular responses via two receptors called p55 and p75. Our purpose was to test the involvement of TNF in glucose homeostasis using mice lacking one or both TNF receptors. C57BL/6 mice lacking p55 (p55(-)/-), p75, (p75(-)/-), or both receptors (p55(-)/-p75(-)/-) were fed a high-fat diet to induce obesity. Marked fasting hyperinsulinemia was seen for p55(-)/-p75(-)/- males between 12 and 16 wk of feeding the high-fat diet. Insulin levels were four times greater than wild-type mice. In contrast, p55(-)/- and p75(-)/- mice exhibited insulin levels that were similar or reduced, respectively, as compared with wild-type mice. In addition, high-fat diet-fed p75(-)/- mice had the lowest body weights and leptin levels, and improved insulin sensitivity. Obese (db/db) mice, which are not responsive to leptin, were used to study the role of p55 in severe obesity. Male p55(-)/-db/db mice exhibited threefold higher insulin levels and twofold lower glucose levels at 20 wk of age than control db/db expressing p55. All db/db mice remained severely insulin resistant based on fasting plasma glucose and insulin levels, and glucose and insulin tolerance tests. Our data do not support the concept that TNF, acting via its receptors, is a major contributor to obesity-associated insulin resistance. In fact, data suggest that the two TNF receptors work in concert to protect against diabetes.

T he mRNA levels for the mitochondrial uncoupling protein (UCP1) in fat tissues of A/J and C57BL/6J inbred strains of mice varied in a regional-specific manner after stimulation of adrenergic signaling by cold exposure or treatment with a beta3-adrenergic agonist. While the differences between strains were minimal in interscapular brown fat, large differences occurred in white fat tissues, particularly in retroperitoneal fat. Among the AXB recombinant inbred strains, the Ucp1 mRNA levels varied up to 130-fold. This large induction at the mRNA level was accompanied by a corresponding increase in brown adipocytes as revealed by immunohistology with anti-UCP1 antibodies. A high capacity to induce brown fat in areas of traditional white fat had no impact on the ability to gain weight in response to high fat and sucrose diets, but did correlate with the loss of weight in response to treatment with a beta3-adrenergic agonist (CL 316,243). This genetic variation in mice provides an experimental approach to identify genes controlling the induction of brown adipocytes in white fat tissues.

S evere combined immune deficiency (SCID) is a heterogeneous disorder characterized by profound defects in cellular and humoral immunity. We report here an infant with clinical and laboratory features of SCID and selective CD4 lymphopenia and lack of CD28 expression on CD8(+) T cells. T cells from this patient showed poor blastogenic responses to various mitogens and IL-2. Other T cell antigen receptor- induced responses, including upregulation of CD69, were similarly inhibited. However, more proximal T cell antigen receptor signaling events, such as anti-CD3 induced protein tyrosine phosphorylation, phosphorylation of mitogen-associated protein kinase, and calcium mobilization were intact. Although p59fyn and ZAP-70 protein tyrosine kinases were expressed at normal levels, a marked decrease in the level of p56lck was noted. Furthermore, this decrease was associated with the presence of an alternatively spliced lck transcript lacking the exon 7 kinase encoding domain. These data suggest that a deficiency in p56lck expression can produce a SCID phenotype in humans.

V ascular beds are known to differ in structure and metabolic function, but less is known about their molecular diversity. We have studied organ-specific molecular differences of the endothelium in various tissues by using in vivo screening of peptide libraries expressed on the surface of a bacteriophage. We report here that targeting of a large number of tissues with this method yielded, in each case, phage that homed selectively to the targeted organ. Different peptide motifs were recovered from each of these tissues. The enrichment in homing to the target organs relative to an unselected phage was 3-35-fold. Peptide sequences that conferred selective phage homing to the vasculature of lung, skin, and pancreas were characterized in detail. Immunohistochemistry showed that the phage localized in the blood vessels of their target organ. When tested, the phage homing was blocked in the presence of the cognate peptide. By targeting several tissues and by showing that specific homing could be achieved in each case, we provide evidence that organ- and tissue-specific molecular heterogeneity of the vasculature is a general, perhaps even universal, phenomenon. Our results also show that these molecular differences can serve as molecular addresses.

T his report evaluates the efficacy of DNA encoding TGF-beta administered mucosally to suppress immunity and modulate the immunoinflammatory response to herpes simplex virus (HSV) infection. A single intranasal administration of an eukaryotic expression vector encoding TGF-beta1 led to expression in the lung and lymphoid tissue. T cell-mediated immune responses to HSV infection were suppressed with this effect persisting as measured by the delayed-type hypersensitivity reaction for at least 7 wk. Treated animals were more susceptible to systemic infection with HSV. Multiple prophylactic mucosal administrations of TGF-beta DNA also suppressed the severity of ocular lesions caused by HSV infection, although no effects on this immunoinflammatory response were evident after therapeutic treatment with TGF-beta DNA. Our results demonstrate that the direct mucosal gene transfer of immunomodulatory cytokines provides a convenient means of modulating immunity and influencing the expression of inflammatory disorders.

T o determine whether asbestos inhalation induces the formation of reactive nitrogen species, three groups of rats were exposed intermittently over 2 wk to either filtered room air (sham-exposed) or to chrysotile or crocidolite asbestos fibers. The rats were killed at 1 or 6 wk after exposure. At 1 wk, significantly greater numbers of alveolar and pleural macrophages from asbestos-exposed rats than from sham-exposed rats demonstrated inducible nitric oxide synthase protein immunoreactivity. Alveolar macrophages from asbestos-exposed rats also generated significantly greater nitrite formation than did macrophages from sham-exposed rats. Strong immunoreactivity for nitrotyrosine, a marker of peroxynitrite formation, was evident in lungs from chrysotile- and crocidolite-exposed rats at 1 and 6 wk. Staining was most evident at alveolar duct bifurcations and within bronchiolar epithelium, alveolar macrophages, and the visceral and parietal pleural mesothelium. Lungs from sham-exposed rats demonstrated minimal immunoreactivity for nitrotyrosine. Significantly greater quantities of nitrotyrosine were detected by ELISA in lung extracts from asbestos-exposed rats than from sham-exposed rats. These findings suggest that asbestos inhalation can induce inducible nitric oxide synthase activation and peroxynitrite formation in vivo, and provide evidence of a possible alternative mechanism of asbestos-induced injury to that thought to be induced by Fenton reactions.

C ytotoxic T lymphocytes (CTL) are potent effector cells that could provide long term antitumor immunity if induced by appropriate vaccines. CTL recognize 8-14 amino acid-long peptides processed intracellularly and presented by MHC class I molecules. A well-characterized example of a potential tumor antigen in childhood pre-B Acute Lymphoblastic Leukemia (ALL) results from the chromosomal translocation 12;21 leading to the fusion of the ETV6 and AML1 genes. This translocation is observed in > 25% of ALL-patients. In this study, we have examined whether the chimeric ETV6-AML1 protein could serve as a tumor specific antigen for CTL in HLA-A2.1 individuals. We have identified a nonapeptide (RIAECILGM), encoded by the fusion region of the ETV6-AML1 protein, that binds to HLA-A2.1 molecules and induces specific primary CTL in peripheral blood lymphocytes from healthy donors. These CTL specifically lysed HLA-A2.1 tumor cells endogeneously expressing the ETV6-AML fusion protein. CTL with similar functional capacities were found with high frequencies and cloned from one patient's bone marrow indicating that ETV6-AML1-specific anti-ALL CTL are, at least in some patients, spontaneously stimulated and might participate to host antileukemia defense.