Streptococcal superantigen-induced expansion of human tonsil T cells leads to altered T follicular helper cell phenotype, B cell death and reduced immunoglobulin release.

Streptococcal pyrogenic exotoxin (Spe) A expression is epidemiologically linked to streptococcal tonsillo-pharyngitis and outbreaks of scarlet fever, although the mechanisms by which superantigens confer advantage to Streptococcus pyogenes are unclear. S. pyogenes is an exclusively human pathogen. As the leucocyte profile of tonsil is unique, the impact of SpeA production on human tonsil cell function was investigated. Human tonsil cells from routine tonsillectomy were co-incubated with purified streptococcal superantigens or culture supernatants from isogenic streptococcal isolates, differing only in superantigen production. Tonsil cell proliferation was quantified by tritiated thymidine incorporation, and cell surface characteristics assessed by flow cytometry. Soluble mediators including immunoglobulin were measured using enzyme-linked immunosorbent assay. Tonsil T cells proliferated in response to SpeA and demonstrated typical release of proinflammatory cytokines. When cultured in the absence of superantigen, tonsil preparations released large quantities of immunoglobulin over 7 days. In contrast, marked B cell apoptosis and abrogation of total immunoglobulin (Ig)A, IgM, and IgG production occurred in the presence of SpeA and other superantigens. In SpeA-stimulated cultures, T follicular helper (Tfh) cells showed a reduction in C-X-C chemokine receptor (CXCR)5 (CD185) expression, but up-regulation of OX40 (CD134) and inducible T cell co-stimulator (ICOS) (CD278) expression. The phenotypical change in the Tfh population was associated with impaired chemotactic response to CXCL13. SpeA and other superantigens cause dysregulated tonsil immune function, driving T cells from Tfh to a proliferating phenotype, with resultant loss of B cells and immunoglobulin production, providing superantigen-producing bacteria with a probable survival advantage.

Toxicological profile and safety pharmacology of a single dose of fibroblast activation protein-α-based doxorubicin prodrug: in-vitro and in-vivo evaluation.

Fibroblast activation protein-α (FAPα) is a promising tumor-associated target expressed by reactive stromal fibroblasts in tumor tissue. FAPα has a postprolyl peptidase activity and can specifically cleave N-terminal benzyloxycarbonyl (Z)-blocked peptides, such as the substrate Z-Gly-Pro-AMC. Doxorubicin (DOX) is an effective antitumor drug, but its application is greatly limited by toxic adverse effects owing to poor tumor selectivity. Based on these facts, we previously designed a FAPα-targeting prodrug of doxorubicin (FTPD) which can be selectively hydrolyzed by FAPα. FTPD can retain potent antitumor efficacy and has favorable tumor targeting. The present study aimed to further evaluate the toxicological profile and the safety pharmacological property of FTPD in vitro and in vivo. The cytotoxicity assay showed that FTPD displayed markedly lower cytotoxicity to 3T3 cells and HEK-293 cells compared with DOX. In the short-term toxicity study, mice treated with 25 mg/kg of FTPD showed no obvious change in the appearance and general behavior, and no case of mortality was observed within 14 days. Unlike DOX, FTPD exhibited reduced toxicity to heart, liver, kidney, spleen as well as peripheral white blood cells in mice. Moreover, open file test and general pharmacology study were also conducted correspondingly in mice and beagle dogs. It was found that FTPD may not produce significant pharmacological effects on spontaneous locomotor activity and cardiovascular-respiratory system except for a transient decreasing in systolic blood pressure. Taken together, the results of this work suggest that FTPD has more favorable toxicological profile and better drug safety compared with its parent drug DOX.

Towards designing a synthetic antituberculosis vaccine: The Rv3587c peptide inhibits mycobacterial entry to host cells.

Mycobacterium tuberculosis is considered one of the most successful pathogens in the history of mankind, having caused 1.7 million deaths in 2016. The amount of resistant and extensively resistant strains has increased; BCG has been the only vaccine to be produced in more than 100 years though it is still unable to prevent the disease's most disseminated form in adults; pulmonary tuberculosis. The search is thus still on-going for candidate antigens for an antituberculosis vaccine. This paper reports the use of a logical and rational methodology for finding such antigens, this time as peptides derived from the Rv3587c membrane protein. Bioinformatics tools were used for predicting mycobacterial surface location and Rv3587c protein structure whilst circular dichroism was used for determining its peptides' secondary structure. Receptor-ligand assays identified 4 high activity binding peptides (HABPs) binding specifically to A549 alveolar epithelial cells and U937 monocyte-derived macrophages, covering the region between amino acids 116 and 193. Their capability for inhibiting Mtb H37Rv invasion was evaluated. The recognition of antibodies from individuals suffering active and latent tuberculosis and from healthy individuals was observed in HABPs capable of avoiding mycobacterial entry to host cells. The results showed that 8 HABPs inhibited such invasion, two of them being common for both cell lines: 39265 (155VLAAYVYSLDNKRLWSNLDT173) and 39266 (174APSNETLVKTFSPGEQVTTY192). Peptide 39265 was the least recognised by antibodies from the individuals' sera evaluated in each group. According to the model proposed by FIDIC regarding synthetic vaccine development, peptide 39265 has become a candidate antigen for an antituberculosis vaccine.

The cellular prion protein mediates neurotoxic signalling of ß-sheet-rich conformers independent of prion replication.

Formation of aberrant protein conformers is a common pathological denominator of different neurodegenerative disorders, such as Alzheimer's disease or prion diseases. Moreover, increasing evidence indicates that soluble oligomers are associated with early pathological alterations and that oligomeric assemblies of different disease-associated proteins may share common structural features. Previous studies revealed that toxic effects of the scrapie prion protein (PrP(Sc)), a ß-sheet-rich isoform of the cellular PrP (PrP(C)), are dependent on neuronal expression of PrP(C). In this study, we demonstrate that PrP(C) has a more general effect in mediating neurotoxic signalling by sensitizing cells to toxic effects of various ß-sheet-rich (ß) conformers of completely different origins, formed by (i) heterologous PrP, (ii) amyloid ß-peptide, (iii) yeast prion proteins or (iv) designed ß-peptides. Toxic signalling via PrP(C) requires the intrinsically disordered N-terminal domain (N-PrP) and the GPI anchor of PrP. We found that the N-terminal domain is important for mediating the interaction of PrP(C) with ß-conformers. Interestingly, a secreted version of N-PrP associated with ß-conformers and antagonized their toxic signalling via PrP(C). Moreover, PrP(C)-mediated toxic signalling could be blocked by an NMDA receptor antagonist or an oligomer-specific antibody. Our study indicates that PrP(C) can mediate toxic signalling of various ß-sheet-rich conformers independent of infectious prion propagation, suggesting a pathophysiological role of the prion protein beyond of prion diseases.

Alzheimer's disease: insights from Drosophila melanogaster models.

The power of fruit fly genetics is being deployed against some of the most intractable and economically significant problems in modern medicine, the neurodegenerative diseases. Fly models of Alzheimer's disease can be exposed to the rich diversity of biological techniques that are available to the community and are providing new insights into disease mechanisms, and assisting in the identification of novel targets for therapy. Similar approaches might also help us to interpret the results of genome-wide association studies of human neurodegenerative diseases by allowing us to triage gene "hits" according to whether a candidate risk factor gene has a modifying effect on the disease phenotypes in fly model systems.

Calsyntenin-3 C-terminal fragment accumulates in dystrophic neurites surrounding aß plaques in tg2576 mouse and Alzheimer disease brains: its neurotoxic role in mediating dystrophic neurite formation.

Dystrophic neurites surrounding ß-amyloid (Aß) plaques precede neuronal death in Alzheimer disease. These neuritic alterations may be one of the initial stages for synaptic loss and dysfunction. However, intracellular pathways that cause local disruption of neuronal processes by Aß remain to be fully elucidated. The identification of Aß-induced genes that mediate neuritic pathology would provide considerable insight into the mechanisms of Alzheimer's disease. Previously, we reported that selective up-regulation of calsyntenin-3 (Cst-3) by Aß and accumulation of neurotoxic Cst-3 in dystrophic neurites surrounding Aß plaques may lead to local disruption of these neurites. Like amyloid precursor protein, Cst-3 undergoes two-step proteolytic processing: the primary cleavage with α-secretase generates an N-terminal ectodomain and a C-terminal fragment (CTF). The CTF is subsequently cleaved into p3 peptide and an intracellular domain via γ-secretase. It would be interesting to know whether accumulated Cst-3 in dystrophic neurites surrounding Aß plaques is the full-length version or a CTF. Herein, we show that the CTF but not full-length Cst-3 accumulated in dystrophic neurites surrounding Aß plaques in Tg2576 mouse and Alzheimer disease brains. In vitro experiments with Cst-3 fragments have revealed that only the CTF resulted in acceleration of neuronal death. These results indicate that accumulation of the neurotoxic CTF in neurites surrounding Aß plaques may lead to local disruption of neuronal processes and development of dystrophic neurites.

The interconversion between a flexible ß-sheet and a fibril ß-arrangement constitutes the main conformational event during misfolding of PSD95-PDZ3 domain.

The temperature-induced misfolding pathway of PDZ3, the third PDZ domain of the PSD95 neuronal protein, is populated by a trimeric ß-sheet-rich intermediate state that leads to a stepwise and reversible formation of supramacromolecular structures. Using FTIR, we have found that misfolding of this pathway is not due to different ensembles of a variety of precursors, but comes mainly from the interconversion of a flexible ß-sheet of the domain to wormlike fibrils. The appearance of the wormlike fibril FTIR component is also accompanied by a slight decrease of the band that corresponds to loops in the native state, whereas the rest of the regular elements of secondary structure are fairly well maintained upon misfolding. Transmission electron microscope micrographs have confirmed the presence of wormlike fibrils upon heating at 60°C, where the trimeric intermediate is maximally populated. Toxicity assays in the human neuroblastoma cell line SH-SY5Y show that cytotoxicity increases as the aggregation pathway proceeds. NMR analysis of chemical shifts as a function of temperature has revealed, as one of the main conformational aspects of such an interconversion at the residue level, that the ß-sheet arrangement around strand ß3 promotes the change that drives misfolding of the PDZ3 domain.

Membrane-bound Fas ligand requires RIP1 for efficient activation of caspase-8 within the death-inducing signaling complex.

The serine-threonine kinase RIP1 was originally identified through its ability to bind to the death domain of Fas (CD95). RIP1 has been shown to be recruited to the Fas death-inducing signaling complex (DISC) and is required for the induction of necrotic cell death. In this study, we show that in Jurkat T lymphocytes, RIP1 is also necessary for the most efficient activation of downstream caspases by Fas when treated with membrane-bound Fas ligand, but not with agonistic Abs or cross-linked soluble Fas ligand. RIP1 participates in the Fas-associated death domain protein-mediated recruitment of caspase-8 to the Fas receptor complex in a manner that promotes caspase-8 activation. Cross-linking Abs, such as CH11, bypass the requirement for RIP1 in caspase activation by initiating larger, though less efficient, DISC complexes, while membrane-bound Fas ligand initiates a smaller but more efficient DISC that functions, in part, by effectively incorporating more RIP1 into the complex. Consequently, RIP1 is likely a more integral part of physiological signaling through the Fas/CD95 receptor complex than previously recognized; at least when the signal is mediated by full-length membrane-bound FasL. Cross-linked soluble FasL, which also occurs physiologically, behaves similarly to the CH11 Ab, and may therefore be more likely to initiate nonapoptotic Fas signaling due to less RIP1 in the receptor complex. Thus, agonists that bind the same Fas receptor initiate mechanistically distinct pathways resulting in differential cytotoxicity.

Calpain activator dibucaine induces platelet apoptosis.

Calcium-dependent calpains are a family of cysteine proteases that have been demonstrated to play key roles in both platelet glycoprotein Ibα shedding and platelet activation and altered calpain activity is associated with thrombotic thrombocytopenic purpura. Calpain activators induce apoptosis in several types of nucleated cells. However, it is not clear whether calpain activators induce platelet apoptosis. Here we show that the calpain activator dibucaine induced several platelet apoptotic events including depolarization of the mitochondrial inner transmembrane potential, up-regulation of Bax and Bak, down-regulation of Bcl-2 and Bcl-X(L), caspase-3 activation and phosphatidylserine exposure. Platelet apoptosis elicited by dibucaine was not affected by the broad spectrum metalloproteinase inhibitor GM6001. Furthermore, dibucaine did not induce platelet activation as detected by P-selectin expression and PAC-1 binding. However, platelet aggregation induced by ristocetin or α-thrombin, platelet adhesion and spreading on von Willebrand factor were significantly inhibited in platelets treated with dibucaine. Taken together, these data indicate that dibucaine induces platelet apoptosis and platelet dysfunction.

Digestion and Transport across the Intestinal Epithelium Affects the Allergenicity of Ara h 1 and 3 but Not of Ara h 2 and 6.

SCOPE: No accepted and validated methods are currently available which can accurately predict protein allergenicity. In this study, the role of digestion and transport on protein allergenicity is investigated. METHODS AND RESULTS: Peanut allergens (Ara h 1, 2, 3, and 6) and a milk allergen (ß-lactoglobulin) are transported across pig intestinal epithelium using the InTESTine model and afterward basophil activation is measured to assess the (remaining) functional properties. Additionally, allergens are digested by pepsin prior to epithelial transport and their allergenicity is assessed in a human mast cell activation assay. Remarkably, transported Ara h 1 and 3 are not able to activate basophils, in contrast to Ara h 2 and 6. Digestion prior to transport results in a significant increase in mast cell activation of Ara h 1 and 3 dependent on the length of digestion time. Activation of mast cells by Ara h 2 and 6 is unaffected by digestion prior to transport. CONCLUSIONS: Digestion and transport influences the allergenicity of Ara h 1 and 3, but not of Ara h 2 and 6. The influence of digestion and transport on protein allergenicity may explain why current in vitro assays are not predictive for allergenicity.

N-methyl-D-aspartate receptor subunit- and neuronal-type dependence of excitotoxic signaling through post-synaptic density 95.

NMDA receptors (NMDARs) mediate excitatory synaptic transmission during repetitive or prolonged glutamate release, playing a critical role in synaptic plasticity or cell death, respectively. Evidence indicates that a major pathway of NMDAR signaling to cell death in cortical and hippocampal neurons requires the scaffolding protein post-synaptic density 95 (PSD-95) and activation of neuronal nitric oxide synthase. However, it is not known if this PSD-95-dependent pathway contributes to excitotoxicity in other brain regions. It is also unclear whether the neuroprotective effects of Tat-NR2B9c, a membrane-permeant peptide that disrupts PSD-95/NMDAR binding, correlate with uncoupling NR2B- and/or NR2A-type NMDARs from PSD-95. In this study, we used cultured hippocampal and striatal neurons to test the potency of Tat-NR2B9c on uncoupling NR2 subunits from PSD-95 and protecting against NMDA-induced excitotoxicity. We found that the concentration of Tat-NR2B9c required to dissociate 50% of PSD-95 was fourfold lower for NR2B than NR2A in cultured hippocampal and striatal neurons, and that this concentration correlated tightly with protection against NMDA-induced toxicity in hippocampal neurons without altering NMDAR current. In contrast, NMDAR signaling to cell death in cultured striatal neurons occurred independently of the NR2B/PSD-95 interaction or neuronal nitric oxide synthase activation. These results will facilitate development of neuronal type-specific protective therapies.

Resistance of cytolytic lymphocytes to perforin-mediated killing. Induction of resistance correlates with increase in cytotoxicity.

CTL and NK cells cultured in vitro are known to produce a cytolytic pore-forming protein (PFP, perforin) localized in their cytoplasmic granules. Using purified perforin, we showed here that both cloned CTL and primary killer cell populations, including allospecific CTL, NK/lymphokine-activated killer cells, and MHC-non-restricted CTL, were more resistant to perforin-mediated killing than other lymphocyte populations and cell types. Similar results were obtained with both murine and human cytolytic lymphocyte populations. Resistance of killer cells to perforin correlated in general with their cytolytic capability. Thus, cells that have acquired competence to kill after stimulation with Con A, IL-2, or leukocyte-conditioned medium, were also the more resistant cells. IL-2-independent CTL lines and hybridomas derived in our laboratories could be triggered to become cytotoxic and perforin resistant by short-term stimulation with various cytokines, indicating that the acquisition of resistance to perforin-mediated lysis was independent of cell proliferation. Activation of one IL-2-independent CTL line with IL-2 also resulted in enhanced production of perforin and in enhanced serine esterase activity. The acquisition of cell resistance to perforin by these IL-2-independent cell lines after activation with stimulatory reagents was independent of protein and RNA neosynthesis: emetine, cycloheximide, and actinomycin D, while effectively blocking the incorporation of [35S]methionine into cell proteins, did not affect the induced increase in perforin resistance.

Betagamma-CAT, a non-lens betagamma-crystallin and trefoil factor complex from amphibian skin secretions, caused endothelium-dependent myocardial depression in isolated rabbit hearts.

Previous in vivo study demonstrated that betagamma-CAT, a newly identified non-lens betagamma-crystallin and trefoil factor complex from frog Bombina maxima skin secretions, possessed potent lethal toxicity on mammals resulted from hypotension and cardiorespiratory arrest. However, the mechanism of cardiac dysfunction induced by the protein is unknown. Here, we report that betagamma-CAT, with dosages of 0.8-3.0 nM, elicited an acute negative inotropic effect in isolated rabbit heart Langendorff preparations, which mimicked acute heart failure. In addition, the effect of betagamma-CAT on the hearts was mediated by endothelium-dependent coronary vasoconstriction (P<0.01, compared between endothelium-intact and removal hearts). After betagamma-CAT (3.0 nM) treatment, the positive signal of tumor necrosis factor-alpha (TNF-alpha) was detected mainly around the endothelial cell layer as detected by in situ indirect immunofluorescence, indicating that the release of TNF-alpha occurred. At the same time, a rapid TNF-alpha release was detected in primary cultured rabbit endocardial endothelial cells (REECs) treated with betagamma-CAT. After addition of betagamma-CAT (3.0 nM) for 10 min and 30 min, the TNF-alpha levels were increased to 57.33+/-3.22 pg/ml and 60.00+/-5.35 pg/ml (P<0.05, compared with the control values of 21.67+/-3.45 pg/ml and 33.70+/-6.24 pg/ml, respectively). At high concentrations, betagamma-CAT interfered with the cell viability of REECs (CC(50) about 25 nM). Taken together, betagamma-CAT was able to induce acute myocardial depression and the toxic effect might be partially explained by the release of TNF-alpha. The finding provides new information to understand the patho-physiological roles of non-lens betagamma-crystallins and trefoil factors.

Differential cardiovascular effects of endotoxin derived from Escherichia coli or Pseudomonas aeruginosa.

Sepsis is characterized by various symptoms, signs and underlying pathophysiology. To investigate possible mechanisms underlying this diversity, we compared the cardiovascular effects of lipopolysaccharide (LPS) derived from Escherichia coli (E-LPS) with those of LPS from Pseudomonas aeruginosa (P-LPS) in rats. We also examined the possible roles of tumor necrosis factor-alpha (TNF-alpha) and oxidative stress in LPS-induced cardiovascular damage. E-LPS (10 mg/kg body weight) or P-LPS (2 mg/kg body weight) was administered intravenously to Wistar rats. Echocardiography was serially performed. E-LPS induced an increase in left ventricular fractional shortening that persisted for at least 6 h, whereas P-LPS elicited an initial increase and a subsequent decrease in this parameter. Histological analysis revealed that P-LPS induced interstitial edema, congestion, intramyocardial bleeding, myocardial necrosis, infiltration of inflammatory cells, and formation of fibrin thrombi in the heart, whereas no pathological changes were apparent in the hearts of rats treated with E-LPS. Furthermore, the plasma concentration of TNF-alpha in rats treated with P-LPS was greater than that in rats treated with E-LPS, but the glutathione redox ratio in the heart was not affected by either type of LPS. In conclusion, E-LPS and P-LPS induced distinct patterns of functional and structural responses in the cardiovascular systems of rats. These differential responses may be attributable in part to the difference in the associated increases in the plasma concentration of TNF-alpha. The cardiovascular effects of LPS thus depend on the causative organisms.

[Mycoplasma genitalium lipid-associated membrane proteins induce human monocytic cell express proinflammatory cytokines and apoptosis by activating nuclear factor kappaB].

Designed to investigate the potential pathogenicity of Mycoplasma genitalium (M. genitalium) and its molecular mechanisms responsible for the induction of proinflammatory cytokines gene expression in human monocytic cells (THP-1) stimulated by lipid-associated membrane proteins (LAMPs) prepared from M. genitalium. THP-1 cells were stimulated with LAMPs to analyze the production of proinflammatory cytokines and the expression of mRNA was detected by RT-PCR. Cell apoptosis was detected in THP-1 cells by Annexin V-propidium iodide staining. The activity of transcriptional factors, NF-kappaB, was examined in THP-1 cells treated with LAMPs by EMSA. The effects of pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-kappaB, on the production of proinflammatory cytokines, the expression of mRNA and apoptosis were also examined in THP-1 cells treated with LAMPs. M. genitalium LAMPs stimulate THP-1 cells to produce TNF-alpha, IL-1beta and IL-6 in dose- and time-dependent manner. The mRNA levels and cell apoptosis are also downregulated in response to LAMPs stimulation and inhibited by PDTC treatment. M. genitalium LAMPs are found to trigger NF-kappaB activation, a possible mechanism for the induction of mRNA expression and the cell apoptosis. This study demonstrated that M. genitalium may be an important etiological factor of certain disease due to the ability of LAMPs to stimulated the expression of mRNA and apoptosis, which is probably mediated through the activation of NF-kappaB.

Functional Requirements for DjlA- and RraA-Mediated Enhancement of Recombinant Membrane Protein Production in the Engineered Escherichia coli Strains SuptoxD and SuptoxR.

In previous work, we have generated the engineered Escherichia coli strains SuptoxD and SuptoxR, which upon co-expression of the effector genes djlA or rraA, respectively, are capable of suppressing the cytotoxicity caused by membrane protein (MP) overexpression and of producing dramatically enhanced yields for a variety of recombinant MPs of both prokaryotic and eukaryotic origin. Here, we investigated the functional requirements for DnaJ-like protein A (DjlA)- and regulator of ribonuclease activity A (RraA)-mediated enhancement of recombinant MP production in these strains and show that: (i) DjlA and RraA act independently, that is, the beneficial effects of each protein on recombinant MP production occur through a mechanism that does not involve the other, and in a non-additive manner; (ii) full-length and membrane-bound DjlA is required for exerting its beneficial effects on recombinant MP production in E. coli SuptoxD; (iii) the MP production-promoting properties of DjlA in SuptoxD involve the action of the molecular chaperone DnaK but do not rely on the activation of the regulation of capsular synthesis response, a well-established consequence of djlA overexpression; (iv) the observed RraA-mediated effects in E. coli SuptoxR involve the ribonucleolytic activity of RNase E, but not that of its paralogous ribonuclease RNase G; and (v) DjlA and RraA are unique among similar E. coli proteins in their ability to promote bacterial recombinant MP production. These observations provide important clues about the molecular requirements for suppressed toxicity and enhanced MP accumulation in SuptoxD/SuptoxR and will guide future studies aiming to decipher the exact mechanism of DjlA- and RraA-mediated enhancement of recombinant MP production in these strains.

Functional characterization of human proapoptotic molecules in yeast S. cerevisiae.

The presence of a complete (BH1-3) proapoptotic molecule is necessary for the induction of the intrinsic apoptotic cascade in mammalian cells. It is unclear, however, what distinct roles the members of the large family of BH3-only proapoptotic molecules play in apoptosis. Although biochemical analysis of these molecules can characterize binding efficiencies of BH3 family members, the biologic consequences of these interactions are difficult to predict. We have, therefore, established three functional categories of BH3-only human proapoptotic proteins based on their toxicity after expression in budding yeast: directly killing (tBid), sensitizing in Bax/Bcl-2 expressing cells (Bad or Puma), and non-toxic (BNip3, BNip3L, and Noxa). The mechanism of killing by the proapoptotic molecules in yeast, however, is not due to activation of the recently described yeast metacaspase MCA1.

Antileukemic activity of Flt3 ligand in murine leukemia.

Flt3-ligand (Flt3-L) is an early acting costimulatory cytokine that has been shown to possess antitumor properties in murine solid tumor models. Flt3-L is a trans-membrane protein (tm) but can be proteolytically cleaved to a soluble form, which is also biologically active. In this study, the antitumor effect of both soluble and tmFlt3-L was evaluated in a mouse leukemia model. To mimic the multiorgan involvement characteristic of human leukemia, a factor-dependent cell line FDC.P1 was made leukemogenic by transfection with the human BCR/ABL gene. The resulting cell line, AW, expresses BCR/ABL RNA and protein. It maintains a similar in vitro growth rate as the parent cell line, but unlike the parent cell line, AW cells are factor independent and tumorigenic. Growth of FDC.P1 and AW cells are unaffected by the addition of soluble human Flt3-L to the culture medium. Also, AW growth is unaltered after transduction with a retroviral vector expressing the tm isoform of human Flt3-L (AW/tmFlt3-L). When 10(5) AW cells were i.v. injected into syngeneic DBA/2 mice, fatal leukemia developed in nine of nine (100%) mice within 4-6 weeks with involvement of the blood, bone marrow, spleen, and thymus. Systematic administration of soluble human Flt3-L (500 microg/kg/day) for 10 days protected mice from leukemia, with 11 of 17 mice tumor free at week 8 (64.7%) The tm isoform of Flt3-L also was protective. When 10(4) AW/tmFlt3-L cells were injected i.v. into mice, only 35.7% (5 of 14) developed leukemia versus 100% in control groups. Adoptive transfer of immunity was also demonstrated; T cells obtained from tumor-free animals conferred protection to 87% (seven of eight) naive mice challenged with AW cells. These results demonstrate that both soluble and membrane-bound human Flt3-L has antitumor activity in this leukemia model.

The amino-terminus and membrane-spanning domains of LMP-1 inhibit cell proliferation.

The LMP-1 oncoprotein of EBV is required to maintain proliferation of infected B-cells and shares several features with CD40, TNF-R1, and related receptors. Members of this family can bind TRAF and TRADD molecules and activate NF-kappaB and AP-1, as can LMP-1. While CD40 and TNF-R1 are dependent on binding their ligands for their signaling, LMP-1 apparently is not. We have found that LMP-1 can act as a governor of cell proliferation and thereby limit its own activities. Its inhibition of proliferation is not mediated by apoptosis but results in cytostasis in four cell lines tested. The structural moiety of LMP-1 that distinguishes it from CD40 and TNF-R1, its amino-terminus and multiple membrane spanning segments, alone can mediate its cytostatic activity.