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Cell-to-cell virus transmission is one of the most efficient mechanisms of human immunodeficiency virus (HIV) spread,requires CD4 and coreceptor expression in target cells,and may also lead to syncytium formation and cell death. Here,we show that in addition to this classical coreceptor-mediated transmission,the contact between HIV-producing cells and primary CD4 T cells lacking the appropriate coreceptor induced the uptake of HIV particles by target cells in the absence of membrane fusion or productive HIV replication. HIV uptake by CD4 T cells required cellular contacts mediated by the binding of gp120 to CD4 and intact actin cytoskeleton. HIV antigens taken up by CD4 T cells were rapidly endocytosed to trypsin-resistant compartments inducing a partial disappearance of CD4 molecules from the cell surface. Once the cellular contact was stopped,captured HIV were released as infectious particles. Electron microscopy revealed that HIV particles attached to the surface of target cells and accumulated in large (0.5-1.0 microm) intracellular vesicles containing 1-14 virions,without any evidence for massive clathrin-mediated HIV endocytosis. The capture of HIV particles into trypsin-resistant compartments required the availability of the gp120 binding site of CD4 but was independent of the intracytoplasmic tail of CD4. In conclusion,we describe a novel mechanism of HIV transmission,activated by the contact of infected and uninfected primary CD4 T cells,by which HIV could exploit CD4 T cells lacking the appropriate coreceptor as an itinerant virus reservoir. View Publication

Hematopoietic progenitor/stem cell homing to the bone marrow requires the concerted action of several adhesion molecules. Endothelial P- and E-selectins play an important role in this process,but their ligands on a large subset of neonate-derived human CD34+ cells are absent,leading to a reduced ability to interact with the bone marrow (BM) microvasculature. We report here that this deficiency results from reduced alpha1,3-fucosyltransferase (FucT) expression and activity in these CD34+ cells. Incubation of CD34+ cells with recombinant human FucTVI rapidly corrected the deficiency in nonbinding CD34+ cells and further increased the density of ligands for both P- and E-selectins on all cord blood-derived CD34+ cells. Intravital microscopy studies revealed that these FucTVI-treated CD34+ cells displayed a marked enhancement in their initial interactions with the BM microvasculature,but unexpectedly,homing into the BM was not improved by FucTVI treatment. These data indicate that,although exogenous FucT enzyme activity can rapidly modulate selectin binding avidity of cord blood CD34+ cells,further studies are needed to understand how to translate a positive effect on progenitor cell adhesion in bone marrow microvessels into one that significantly influences migration and lodgement into the parenchyma. View Publication

NK cells play a critical role in the rejection of xenografts. In this study,we report on an investigation of the effect of complement regulatory protein,a decay accelerating factor (DAF: CD55),in particular,on NK cell-mediated cytolysis. Amelioration of human NK cell-mediated pig endothelial cell (PEC) and pig fibroblast cell lyses by various deletion mutants and point substitutions of DAF was tested,and compared with their complement regulatory function. Although wild-type DAF and the delta-short consensus repeat (SCR) 1-DAF showed clear inhibition of both complement-mediated and NK-mediated PEC lyses,delta-SCR2-DAF and delta-SCR3-DAF failed to suppress either process. However,delta-SCR4-DAF showed a clear complement regulatory effect,but had no effect on NK cells. Conversely,the point substitution of DAF (L147 x F148 to SS and KKK(125-127) to TTT) was half down-regulated in complement inhibitory function,but the inhibition of NK-mediated PEC lysis remained unchanged. Other complement regulatory proteins,such as the cell membrane-bound form factor H,fH-PI,and C1-inactivator,C1-INH-PI,and CD59 were also assessed,but no suppressive effect on NK cell-mediated PEC lysis was found. These data suggest,for DAF to function on NK cells,SCR2-4 is required but no relation to its complement regulatory function exists. View Publication

NK cells protect hosts against viral pathogens and transformed cells,and dendritic cells (DCs) play important roles in activating NK cells. We now find that murine IL-15Ralpha-deficient DCs fail to support NK cell cytolytic activity and elaboration of IFN-gamma,despite the fact that these DCs express normal levels of costimulatory molecules and IL-12. By contrast,IL-15Ralpha expression on NK cells is entirely dispensable for their activation by DCs. In addition,blockade with anti-IL-15Ralpha and anti-IL-2Rbeta but not anti-IL-2Ralpha-specific Abs prevents NK cell activation by wild-type DCs. Finally,presentation of IL-15 by purified IL-15Ralpha/Fc in trans synergizes with IL-12 to support NK cell priming. These findings suggest that murine DCs require IL-15Ralpha to present IL-15 in trans to NK cells during NK cell priming. View Publication

Mixed chimaerism and graft rejection are higher after reduced-intensity allogeneic stem cell transplantation (RIST) with T-cell depleted (TCD) allografts. As host immune status before RIST affects engraftment,we hypothesized that targeted depletion of host lymphocytes prior to RIST would abrogate graft rejection and promote donor chimaerism. Lymphocyte-depleting chemotherapy was administered at conventional doses to subjects prior to RIST with the intent of decreasing CD4(+) counts to textless0.05 x 10(9)cells/l. Subjects (n = 18) then received reduced-intensity conditioning followed by ex vivo TCD human leucocyte antigen-matched sibling allografts. All evaluable patients (n = 17) were engrafted; there were no late graft failures. At day +28 post-RIST,12 patients showed complete donor chimaerism. Mixed chimaerism in the remaining five patients was associated with higher numbers of circulating host CD3(+) cells (P = 0.0032) after lymphocyte-depleting chemotherapy and was preferentially observed in T lymphoid rather than myeloid cells. Full donor chimaerism was achieved in all patients after planned donor lymphocyte infusions. These data reflect the importance of host immune status prior to RIST and suggest that targeted host lymphocyte depletion facilitates the engraftment of TCD allografts. Targeted lymphocyte depletion may permit an individualized approach to conditioning based on host immune status prior to RIST. View Publication

Thrombopoietin (Tpo) is the primary cytokine regulating megakaryocyte development and platelet production. Tpo signaling through its receptor,c-mpl,activates multiple pathways including signal transducer and activator of transcription (STAT)3,STAT5,phosphoinositide 3-kinase-Akt,and p42/44 mitogen-activated protein kinase (MAPK). The adaptor protein Lnk is implicated in cytokine receptor and immunoreceptor signaling. Here,we show that Lnk overexpression negatively regulates Tpo-mediated cell proliferation and endomitosis in hematopoietic cell lines and primary hematopoietic cells. Lnk attenuates Tpo-induced S-phase progression in 32D cells expressing mpl,and Lnk decreases Tpo-dependent megakaryocyte growth in bone marrow (BM)-derived megakaryocyte culture. Consistent with this result,we found that in both BM and spleen,Lnk-deficient mice exhibited increased numbers of megakaryocytes with increased ploidy compared with wild-type mice. In addition,Lnk-deficient megakaryocytes derived from BM and spleen showed enhanced sensitivity to Tpo during culture. The absence of Lnk caused enhanced and prolonged Tpo induction of STAT3,STAT5,Akt,and MAPK signaling pathways in CD41+ megakaryocytes. Furthermore,the Src homology 2 domain of Lnk is essential for Lnk's inhibitory function. In contrast,the conserved tyrosine near the COOH terminus is dispensable and the pleckstrin homology domain of Lnk contributes to,but is not essential for,inhibiting Tpo-dependent 32D cell growth or megakaryocyte development. Thus,Lnk negatively modulates mpl signaling pathways and is important for Tpo-mediated megakaryocytopoiesis in vivo. View Publication

Lipid rafts accumulate in the immunological synapse formed by an organized assembly of the TCR/CD3,LFA-1,and signaling molecules. However,the precise role of lipid rafts in the formation of the immunological synapse is unclear. In this study,we show that LFA-1 on CTL is constitutively active and mediates Ag-independent binding of CTL to target cells expressing its ligands. LFA-1 and CD3 on CTL,but not resting T cells,colocalize in lipid rafts. Binding of LFA-1 on CTL to targets initiates the formation of the immunological synapse,which is formed by LFA-1,CD3,and ganglioside GM1 distributed in the periphery of the cell contact site and cholesterol is more widely distributed. The formation of this synapse is Ag independent,but the recognition of Ag by the TCR induces accumulation of tyrosine phosphorylated proteins in the synapse as well as redistribution of the microtubule organization center toward the cell contact site. Our results suggest that LFA-1 recruits lipid rafts and the TCR/CD3 to the synapse,and facilitates efficient and rapid activation of CTL. View Publication

PURPOSE: Allogeneic T lymphocytes can induce regression of metastatic breast cancer through an immune-mediated graft-versus-tumor (GVT) effect in murine models. To determine if a clinical GVT effect exists against metastatic breast cancer,allogeneic lymphocytes were used as adoptive cellular therapy after a reduced-intensity chemotherapy conditioning regimen and allogeneic hematopoietic stem-cell transplantation (HSCT) from human leukocyte antigen-matched siblings. PATIENTS AND METHODS: Sixteen patients with metastatic breast cancer that had progressed after treatment with anthracyclines,taxanes,hormonal agents,and trastuzumab,received allogeneic HSCT. The reduced-intensity transplant conditioning regimen consisted of cyclophosphamide and fludarabine. To distinguish an immunological GVT effect from any antitumor effect of cytotoxic chemotherapy in the transplant-conditioning regimen,allogeneic T lymphocytes were removed from the stem-cell graft and were subsequently administered late postallogeneic HSCT. Allogeneic lymphocytes containing 1 x 10(6),5 x 10(6),and 10 x 10(6) CD3(+) cells/kg were infused on days +42,+70,and +98 post-allogeneic HSCT,respectively. RESULTS: Objective tumor regressions occurred after day +28 post-allogeneic HSCT in six patients and were attributed to allogeneic lymphocyte infusions. Two of these responding patients had disease progression post-allogeneic HSCT before subsequent tumor regression. Tumor regressions occurred concomitantly with the establishment of complete donor T-lymphoid engraftment,were associated with the development of graft-versus-host disease (GVHD),and were abrogated by subsequent systemic immunosuppression for GVHD. CONCLUSION: Allogeneic lymphocytes can induce regression of advanced metastatic breast cancer. These results indicate that an immunological GVT effect from allogeneic lymphocytes exists against metastatic breast cancer and provide rationale for further development of allogeneic cellular therapy for this largely incurable disease. View Publication

Molecular mimicry between microbial and self-components is postulated as the mechanism that accounts for the antigen and tissue specificity of immune responses in postinfectious autoimmune diseases. Little direct evidence exists,and research in this area has focused principally on T cell-mediated,antipeptide responses,rather than on humoral responses to carbohydrate structures. Guillain-Barré syndrome,the most frequent cause of acute neuromuscular paralysis,occurs 1-2 wk after various infections,in particular,Campylobacter jejuni enteritis. Carbohydrate mimicry [Galbeta1-3GalNAcbeta1-4(NeuAcalpha2-3)Galbeta1-] between the bacterial lipooligosaccharide and human GM1 ganglioside is seen as having relevance to the pathogenesis of Guillain-Barré syndrome,and conclusive evidence is reported here. On sensitization with C. jejuni lipooligosaccharide,rabbits developed anti-GM1 IgG antibody and flaccid limb weakness. Paralyzed rabbits had pathological changes in their peripheral nerves identical with those present in Guillain-Barré syndrome. Immunization of mice with the lipooligosaccharide generated a mAb that reacted with GM1 and bound to human peripheral nerves. The mAb and anti-GM1 IgG from patients with Guillain-Barré syndrome did not induce paralysis but blocked muscle action potentials in a muscle-spinal cord coculture,indicating that anti-GM1 antibody can cause muscle weakness. These findings show that carbohydrate mimicry is an important cause of autoimmune neuropathy. View Publication

Using whole-cell patch-clamp,fluorescence microscopy and flow cytometry,we demonstrate a switch in potassium channel expression during differentiation of human B cells from naive to memory cells. Naive and IgD(+)CD27(+) memory B cells express small numbers of the voltage-gated Kv1.3 and the Ca(2+)-activated intermediate-conductance IKCa1 channel when quiescent,and increase IKCa1 expression 45-fold upon activation with no change in Kv1.3 levels. In contrast,quiescent class-switched memory B cells express high levels of Kv1.3 ( approximately 2000 channels/cell) and maintain their Kv1.3(high) expression after activation. Consistent with their channel phenotypes,proliferation of naive and IgD(+)CD27(+) memory B cells is suppressed by the specific IKCa1 inhibitor TRAM-34 but not by the potent Kv1.3 blocker Stichodactyla helianthus toxin,whereas the proliferation of class-switched memory B cells is suppressed by Stichodactyla helianthus toxin but not TRAM-34. These changes parallel those reported for T cells. Therefore,specific Kv1.3 and IKCa1 inhibitors may have use in therapeutic manipulation of selective lymphocyte subsets in immunological disorders. View Publication