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TRAIL induces apoptosis in a variety of tumor cells. Our laboratory found that human neutrophils contain an intracellular reservoir of prefabricated TRAIL that is released after stimulation with Mycobacterium bovis bacillus Calmette-Guérin. In this study,we examined the subcellular distribution of TRAIL in freshly isolated neutrophils. Neutrophil granules,secretory vesicles (SV),and plasma membrane vesicles were isolated by subcellular fractionation,followed by free-flow electrophoresis,and examined by ELISA and immunoblot. TRAIL was found in all membrane-bound fractions with the highest amounts in the fractions enriched in azurophilic granule (AG) and SV. Immunofluorescence confocal microscopy showed that TRAIL colocalized independently with myeloperoxidase (MPO),lactoferrin (LF),and albumin,respective markers of AG,specific granules,and SV. Furthermore,immunotransmission electron microscopy demonstrated that TRAIL colocalized intracellularly with MPO and albumin. We examined TRAIL expression in PLB-985 cells induced with dimethylformamide and in CD34-positive stem cells treated with G-CSF. Quantitative RT-PCR analysis showed that TRAIL was expressed in each stage of development,whereas MPO and LF were only expressed at distinct times during differentiation. Collectively,these findings suggest that TRAIL is expressed throughout neutrophil development,resulting in a broad distribution among different granule subtypes. View Publication

We have previously developed an antibody fusion protein composed of a mouse/human chimeric IgG3 specific for the human transferrin receptor genetically fused to avidin (anti-hTfR IgG3-Av) as a universal delivery system for cancer therapy. This fusion protein efficiently delivers biotinylated FITC into cancer cells via TfR-mediated endocytosis. In addition,anti-hTfR IgG3-Av alone exhibits intrinsic cytotoxic activity and interferes with hTfR recycling,leading to the rapid degradation of the TfR and lethal iron deprivation in certain malignant B-cell lines. We now report on the cytotoxic effects of a conjugate composed of anti-hTfR IgG3-Av and biotinylated saporin 6 (b-SO6),a toxin derived from the plant Saponaria officinalis that inhibits protein synthesis. Conjugation of anti-hTfR IgG3-Av with b-SO6 enhances the cytotoxic effect of the fusion protein in sensitive cells and also overcomes the resistance of malignant cells that show low sensitivity to the fusion protein alone. Our results show for the first time that loading anti-hTfR IgG3-Av with a biotinylated toxin enhances the cytotoxicity of the fusion protein alone. These results suggest that anti-hTfR IgG3-Av has great potential as a therapeutic agent for a wide range of applications due to its intrinsic cytotoxic activity plus its ability to deliver biotinylated molecules into cancer cells. View Publication

BAFF plays a central role in B-lineage cell biology; however,the regulation of BAFF-binding receptor (BBR) expression during B cell activation and differentiation is not completely understood. In this study,we provide a comprehensive ex vivo analysis of BBRs in human B-lineage cells at various stages of maturation,as well as describe the events that drive and regulate receptor expression. Our data reveal that B-lineage cells ranging from naive to plasma cells (PCs),excluding bone marrow PCs,express BAFF-R uniformly. In contrast,only tonsillar memory B cells (MB) and PCs,from both tonsil and bone marrow tissues,express BCMA. Furthermore,we show that TACI is expressed by MB cells and PCs,as well as a subpopulation of activated CD27(neg) B cells. In this regard,we demonstrate that TACI is inducible early upon B cell activation and this is independent of B cell turnover. In addition,we found that TACI expression requires activation of the ERK1/2 pathway,since its expression was blocked by ERK1/2-specific inhibitors. Expression of BAFF-R and B cell maturation Ag (BCMA) is also highly regulated and we demonstrate that BCMA expression is only acquired in MB cells and in a manner accompanied by loss of BAFF-R expression. This inverse expression coincides with MB cell differentiation into Ig-secreting cells (ISC),since blocking differentiation inhibited both induction of BCMA expression and loss of BAFF-R. Collectively,our data suggest that the BBR profile may serve as a footprint of the activation history and stage of differentiation of normal human B cells. View Publication

Recently,a number of clinical trials used either mesenchymal stem cells (MSCs) or natural killer (NK) cells in an attempt to improve the effectiveness of hematopoietic stem cell transplantation (HSCT). In view of the relevant role of both MSCs and NK cells in HSCT,we have recently explored the result of possible interactions between the 2 cell types. We found that activated NK cells could kill MSCs,whereas MSCs strongly inhibited interleukin-2 (IL-2)-induced NK-cell proliferation. In this study,we further analyzed the inhibitory effect exerted by MSCs on NK cells. We show that MSCs not only inhibit the cytokine-induced proliferation of freshly isolated NK cells but also prevent the induction of effector functions,such as cytotoxic activity and cytokine production. Moreover,we show that this inhibitory effect is related to a sharp down-regulation of the surface expression of the activating NK receptors NKp30,NKp44,and NKG2D. Finally,we demonstrate that indoleamine 2,3-dioxygenase and prostaglandin E2 represent key mediators of the MSC-induced inhibition of NK cells. View Publication

A newly recognized link between the complement system and adaptive immunity is that decay accelerating factor (DAF),a cell surface C3/C5 convertase regulator,exerts control over T cell responses. Extending these results,we show that cultures of Marilyn TCR-transgenic T cells stimulated with DAF-deficient (Daf1(-/-)) APCs produce significantly more IL-12,C5a,and IFN-gamma compared with cultures containing wild-type APCs. DAF-regulated IL-12 production and subsequent T cell differentiation into IFN-gamma-producing effectors was prevented by the deficiency of either C3 or C5a receptor (C5aR) in the APC,demonstrating a link between DAF,local complement activation,IL-12,and T cell-produced IFN-gamma. Bone marrow chimera experiments verified that bone marrow cell-expressed C5aR is required for optimal differentiation into IFN-gamma-producing effector T cells. Overall,our results indicate that APC-expressed DAF regulates local production/activation of C5a following cognate T cell/APC interactions. Through binding to its receptor on APCs the C5a up-regulates IL-12 production,this in turn,contributes to directing T cell differentiation toward an IFN-gamma-producing phenotype. The findings have implications for design of therapies aimed at altering pathologic T cell immunity. View Publication

NK cells express different TLRs,such as TLR3,TLR7,and TLR9,but little is known about their role in NK cell stimulation. In this study,we used specific agonists (poly(I:C),loxoribine,and synthetic oligonucleotides containing unmethylated CpG sequences to stimulate human NK cells without or with suboptimal doses of IL-12,IL-15,or IFN-alpha,and investigated the secretion of IFN-gamma,cytotoxicity,and expression of the activating receptor NKG2D. Poly(I:C) and loxoribine,in conjunction with IL-12,but not IL-15,triggered secretion of IFN-gamma. Inhibition of IFN-gamma secretion by chloroquine suggested that internalization of the TLR agonists was necessary. Also,secretion of IFN-gamma was dependent on MEK1/ERK,p38 MAPK,p70(S6) kinase,and NF-kappaB,but not on calcineurin. IFN-alpha induced a similar effect,but promoted lesser IFN-gamma secretion. However,cytotoxicity (51Cr release assays) against MHC class I-chain related A (MICA)- and MICA+ tumor targets remained unchanged,as well as the expression of the NKG2D receptor. Excitingly,IFN-gamma secretion was significantly increased when NK cells were stimulated with poly(I:C) or loxoribine and IL-12,and NKG2D engagement was induced by coculture with MICA+ tumor cells in a PI3K-dependent manner. We conclude that resting NK cells secrete high levels of IFN-gamma in response to agonists of TLR3 or TLR7 and IL-12,and this effect can be further enhanced by costimulation through NKG2D. Hence,integration of the signaling cascades that involve TLR3,TLR7,IL-12,and NKG2D emerges as a critical step to promote IFN-gamma-dependent NK cell-mediated effector functions,which could be a strategy to promote Th1-biased immune responses in pathological situations such as cancer. View Publication

Unconjugated mAbs have emerged as useful cancer therapeutics. Ab-dependent cellular cytotoxicity (ADCC) is believed to be a major antitumor mechanism of some anticancer Abs. However,the factors that regulate the magnitude of ADCC are incompletely understood. In this study,we described the relationship between Ab affinity and ADCC. A series of human IgG1 isotype Abs was created from the anti-HER2/neu (also named c-erbB2) C6.5 single-chain Fv (scFv) and its affinity mutants. The scFv affinities range from 10(-7) to 10(-11) M,and the IgG Abs retain the affinities of the scFv from which they were derived. The apparent affinity of the Abs ranged from nearly 10(-10) M (the lowest affinity variant) to almost 10(-11) M (the other variants). The IgG molecules were tested for their ability to elicit ADCC in vitro against three tumor cell lines with differing levels of HER2/neu expression using unactivated human PBMC from healthy donors as the effector cells. The results demonstrated that both the apparent affinity and intrinsic affinity of the Abs studied regulate ADCC. High-affinity tumor Ag binding by the IgGs led to the most efficient and powerful ADCC. Tumor cells expressing high levels of HER2/neu are more susceptible to the ADCC triggered by Abs than the cells expressing lower amounts of HER2/neu. These findings justify the examination of high affinity Abs for ADCC promotion. Because high affinity may impair in vivo tumor targeting,a careful examination of Ab structure to function relationships is required to develop optimized therapeutic unconjugated Abs. View Publication

Regulated adhesion of T cells by the integrins LFA-1 (lymphocyte function-associated antigen-1) and VLA-4 (very late antigen-4) is essential for T-cell trafficking. The small GTPase Rap1 is a critical activator of both integrins in murine lymphocytes and T-cell lines. Here we examined the contribution of the Rap1 regulatory pathway in integrin activation in primary CD3(+) human T cells. We demonstrate that inactivation of Rap1 GTPase in human T cells by expression of SPA1 or Rap1GAP blocked stromal cell-derived factor-1alpha (SDF-1alpha)-stimulated LFA-1-ICAM-1 (intercellular adhesion molecule-1) interactions and LFA-1 affinity modulation but unexpectedly did not significantly affect binding of VLA-4 to its ligand VCAM-1 (vascular cell adhesion molecule 1). Importantly,silencing of the Rap1 guanine exchange factor CalDAG-GEFI inhibited SDF-1alpha- and phorbol 12-myristate 13-acetate (PMA)-induced adhesion to ICAM-1 while having no effect on adhesion to VCAM-1. Pharmacologic inhibition of Phospholipase C (PLC) blocked Rap1 activation and inhibited cell adhesion and polarization on ICAM-1 and VCAM-1. Protein kinase C (PKC) inhibition led to enhanced levels of active Rap1 concomitantly with increased T-cell binding to ICAM-1,whereas adhesion to VCAM-1 was reduced. Thus,PLC/CalDAG-GEFI regulation of Rap1 is selectively required for chemokine- and PMA-induced LFA-1 activation in human T cells,whereas alternate PLC- and PKC-dependent mechanisms are involved in the regulation of VLA-4. View Publication

1,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) can modulate immune responses,but whether it directly affects B cell function is unknown. Patients with systemic lupus erythematosus,especially those with antinuclear Abs and increased disease activity,had decreased 1,25(OH)(2)D(3) levels,suggesting that vitamin D might play a role in regulating autoantibody production. To address this,we examined the effects of 1,25(OH)(2)D(3) on B cell responses and found that it inhibited the ongoing proliferation of activated B cells and induced their apoptosis,whereas initial cell division was unimpeded. The generation of plasma cells and postswitch memory B cells was significantly inhibited by 1,25(OH)(2)D(3),although the up-regulation of genetic programs involved in B cell differentiation was only modestly affected. B cells expressed mRNAs for proteins involved in vitamin D activity,including 1 alpha-hydroxylase,24-hydroxylase,and the vitamin D receptor,each of which was regulated by 1,25(OH)(2)D(3) and/or activation. Importantly,1,25(OH)(2)D(3) up-regulated the expression of p27,but not of p18 and p21,which may be important in regulating the proliferation of activated B cells and their subsequent differentiation. These results indicate that 1,25(OH)(2)D(3) may play an important role in the maintenance of B cell homeostasis and that the correction of vitamin D deficiency may be useful in the treatment of B cell-mediated autoimmune disorders. View Publication

Bone marrow mesenchymal stem cells (MSC) have potent immunosuppressive properties and have been advocated for therapeutic use in humans. The nature of their suppressive capacity is poorly understood but is said to be a primitive stem cell function. Demonstration that adult stromal cells such as fibroblasts (Fb) can modulate T cells would have important implications for immunoregulation and cellular therapy. In this report,we show that dermal Fb inhibit allogeneic T cell activation by autologously derived cutaneous APCs and other stimulators. Fb mediate suppression through soluble factors,but this is critically dependent on IFN-gamma from activated T cells. IFN-gamma induces IDO in Fb,and accelerated tryptophan metabolism is at least partly responsible for suppression of T cell proliferation. T cell suppression is reversible,and transient exposure to Fb during activation reprograms T cells,increasing IL-4 and IL-10 secretion upon restimulation. Increased Th2 polarization by stromal cells is associated with amelioration of pathological changes in a human model of graft-vs-host disease. Dermal Fb are highly clonogenic in vitro,suggesting that Fb-mediated immunosuppression is not due to outgrowth of rare MSC,although dermal Fb remain difficult to distinguish from MSC by phenotype or transdifferentiation capacity. These results suggest that immunosuppression is a general property of stromal cells and that dermal Fb may provide an alternative and accessible source of cellular therapy. View Publication