scholarly journals Liver-Derived Dendritic Cells Induce Donor-Specific Hyporesponsiveness: Use of Sponge Implant as a Cell Transplant Model

2001 ◽  
Vol 10 (3) ◽  
pp. 343-350 ◽  
Author(s):  
Yang-Jen Chiang ◽  
Lina Lu ◽  
John J. Fung ◽  
Shiguang Qian
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
Mouse Liver ◽  
Cytotoxic T Lymphocyte ◽  
Tolerance Induction ◽  
Cell Transplant ◽  
Spleen Cells ◽  
Infiltrating Cells ◽  
Transplant Model ◽  
Ctl Activity

Spontaneously accepted mouse liver allografts are capable of protecting subsequently transplanted donor organs from rejection; however, the underlying mechanisms are unclear. Dendritic cells (DC) residing in liver grafts are likely important in tolerance induction. DC propagated from mouse liver with GM-CSF are phenotypically and functionally immature. They are poor allostimulators in MLR and prolong survival of pancreatic islet allografts. It has been problematic to perform mechanistic studies in an islet transplant model because of difficulties in obtaining sufficient graft infiltrating cells. In this study, we used a sponge allograft model [i.e., a subcutaneously implanted sponge matrix loaded with B10 (H2b) spleen cells]. To investigate the influence of administration of donor (B10) liver-derived DC on alloimmune reactivity of C3H (H2k) hosts, sponge graft infiltrating cells (SGIC) and recipient spleen cells were isolated, and their immunopheno-type and donor-specific cytotoxic T lymphocyte (CTL) activity were examined. The results illustrate that donor-specific CTL activity of T cells are lower in recipients that had received systemic treatment with liver-derived immature DC, associated with a decrease in CD8+ cell population and an increase in Gr-1+ cells in SGIC, compared with recipients treated with mature bone marrow (BM)-derived DC. Interestingly, administration of liver DC directly into the sponge did not inhibit T cell responses. These data suggest that systemic administration of donor liver DC induces donor-specific hyporesponsiveness, probably not by direct inhibition of graft infiltrating T cells. The increased Gr-1+ cells may play immune regulatory roles in induction of host donor-specific hyporesponsiveness.

scholarly journals Induction of neonatal tolerance to H-2k in B6 mice does not allow the emergence of T cells specific for H-2k plus vaccinia virus.

1982 ◽  
Vol 156 (3) ◽  
pp. 810-821 ◽  
Author(s):  
D H Schwartz ◽  
P C Doherty
Keyword(s):  
T Cells ◽  
T Cell ◽  
Vaccinia Virus ◽  
Somatic Mutation ◽  
T Lymphocyte ◽  
Cytotoxic T Lymphocyte ◽  
Spleen Cells ◽  
Cell Ontogeny ◽  
Stimulation Of ◽  
Tolerized Mouse

Thymocytes and spleen cells from C57BL/6 mice (H-2b) neonatally tolerized to H-2k alloantigens do not generate an anti-vaccinia response restricted to H-2Kk when adoptively transferred to appropriate irradiated hosts. This is in sharp contrast to the case for negatively selected C57BL/6 spleen cells acutely depleted of alloreactivity. No evidence for suppression was found in cell mixture experiments. We have shown elsewhere that our neonatally tolerized animals have a centrally induced delection-type tolerance in the absence of obvious suppression.2 We now suggest that in the neonatally tolerized mouse, chronic, central delection of anti-H-2k clones during early T cell ontogeny eliminates the major source of cells able to give rise, via somatic mutation and expansion, to anti-H-2Kk + vaccinia specific cytotoxic T lymphocyte precursors (CTL-P) in the adult. A similar mechanism may operate in the (k + b) leads to b chimera; however, the presence of H-2kxb accessory and presenting cells may permit the eventual generation (via cross-stimulation) of an H-2k-restricted vaccinia-specific repertoire. This would account for our observation of such "aberrant recognition" CTL-P emerging in the spleens of older (k x b) leads to b chimeras.

scholarly journals Haplotype-specific suppression of cytotoxic T cell induction by antigen inappropriately presented on T cells.

1983 ◽  
Vol 157 (1) ◽  
pp. 141-154 ◽  
Author(s):  
P J Fink ◽  
I L Weissman ◽  
M J Bevan
Keyword(s):  
T Cells ◽  
Cytotoxic T Lymphocyte ◽  
Mixed Lymphocyte Culture ◽  
Lymphocyte Culture ◽  
Cytotoxic T Cell ◽  
Spleen Cells ◽  
Specific Suppression ◽  
Veto Cells

To detect a strong cytotoxic T lymphocyte (CTL) response to minor histocompatibility (H) antigens in a 5-d mixed lymphocyte culture, it is necessary to use a responder that has been primed in vivo with antigen-bearing cells. It has previously been shown that minor-H-specific CTL can be primed in vivo both directly by foreign spleen cells and by presentation of foreign minor H antigens on host antigen-presenting cells. This latter route is evident in the phenomenon of cross-priming, in which H-2 heterozygous (A x B)F1 mice injected 2 wk previously with minor H-different H-2A (A') spleen cells generate both H-2A- and H-2B-restricted minor-H-specific CTL. In a study of the kinetics of direct- vs. cross-priming to minors in F1 mice, we have found that minor H-different T cells actually suppress the induction of virgin CTL capable of recognizing them. CTL activity measured from F1 mice 3-6 d after injection with viable A' spleen cells is largely H-2B restricted. The H-2A-restricted response recovers such that roughly equal A- and B-restricted activity is detected in mice as early as 8-10 d postinjection. This temporary hyporeactivity does not result from generalized immunosuppression--it is specific for those CTL that recognize the foreign minor H antigen in the context of the H-2 antigens on the injected spleen cells. The injected spleen cells that mediate this suppression are radiosensitive T cells; Lyt-2+ T cells are highly efficient at suppressing the induction of CTL in vivo. No graft vs. host reaction by the injected T cells appears to be required, as suppression of direct primed CTL can be mediated by spleen cells that are wholly tolerant of both host H-2 and minor H antigens. Suppression cannot be demonstrated by in vitro mixing experiments. Several possible mechanisms for haplotype-specific suppression are discussed, including inactivation of responding CTL by veto cells and in vivo sequestration of responding CTL by the injected spleen cells.

scholarly journals Indirect allorecognition of platelets by T helper cells during platelet transfusions correlates with anti-major histocompatibility complex antibody and cytotoxic T lymphocyte formation [published erratum appears in Blood 1995 Dec 15;86(12):4710]

Blood ◽  
1995 ◽  
Vol 86 (2) ◽  
pp. 805-812 ◽  
Author(s):  
JW Semple ◽  
ER Speck ◽  
YP Milev ◽  
V Blanchette ◽  
J Freedman
Keyword(s):  
T Cells ◽  
Major Histocompatibility Complex ◽  
T Cell ◽  
Mhc Class I ◽  
T Lymphocyte ◽  
Nk Cell ◽  
Cytotoxic T Lymphocyte ◽  
Spleen Cells ◽  
Histocompatibility Complex ◽  
Platelet Transfusions

To study the cellular immunology of platelet-induced alloimmunization, a murine transfusion model was developed. BALB/c (H-2d) recipient mice were transfused weekly with 2 x 10(8) platelets or 10(3) leukocytes from C57BL/6 (H-2b) donor mice. Recipient antidonor major histocompatibility complex (MHC) class I alloantibodies could be detected in flow cytometric assays by the fifth platelet transfusion. In contrast, when leukocytes only were transfused, alloantibodies were not detected. In vitro assays demonstrated that murine H-2b platelets were positive for MHC class I expression but lacked MHC class II molecules on their membranes and were unable to stimulate proliferation or cytokine production when incubated with naive H-2d spleen cells. In vivo, however, platelet transfusions induced two distinct patterns of cell-mediated reactivity. First, during the initial transfusions and before alloantibody formation, there was induction of T-cell anergy, characterized by the inability of recipient T cells to respond to Concanavalin A (ConA) or to proliferate in an antidonor mixed lymphocyte reaction (MLR), together with suppressed natural killer (NK) cell activity. This unresponsiveness was associated with a transient increase in nitric oxide (NO)-dependent cytotoxicity and interleukin-1 (IL-1) production. Second, once alloantibodies developed, significantly increased antidonor CD8+ cytotoxic T lymphocyte (CTL) and NK cell responses were observed. At this time, when recipient spleen cells were depleted of CD8+ T cells and incubated with only donor platelets in 7- day antigen-presenting cell (APC) assays, enhanced proliferation and IL- 2 production occurred. These cellular responses were not seen when 10(3) allogeneic leukocytes were transfused. Thus, the results suggest that leukoreduced platelet transfusions induce antidonor MHC antibodies and CD8+ CTL responses in recipient mice. At the same time, the transfusions induced recipient CD4+ T-cell activation when incubated with donor platelets in the presence of syngeneic APCs, an indirect recognition pathway that correlates with the time of alloantibody production.

scholarly journals Immunization with dendritic cells can break immunological ignorance toward a persisting virus in the central nervous system and induce partial protection against intracerebral viral challenge

2004 ◽  
Vol 85 (8) ◽  
pp. 2379-2387 ◽  
Author(s):  
Ulrike Fassnacht ◽  
Andreas Ackermann ◽  
Peter Staeheli ◽  
Jürgen Hausmann
Keyword(s):  
Central Nervous System ◽  
T Cells ◽  
Nervous System ◽  
Dendritic Cells ◽  
Cd8 T Cells ◽  
Cytotoxic T Lymphocyte ◽  
Recombinant Vaccinia Virus ◽  
Immune Memory ◽  
Cervical Lymph Nodes ◽  
The Central Nervous System

Dendritic cells (DCs) have been used successfully to induce CD8 T cells that control virus infections and growth of tumours. The efficacy of DC-mediated immunization for the control of neurotropic Borna disease virus (BDV) in mice was evaluated. Certain strains of mice only rarely develop spontaneous neurological disease, despite massive BDV replication in the brain. Resistance to disease is due to immunological ignorance toward BDV antigen in the central nervous system. Ignorance in mice can be broken by immunization with DCs coated with TELEISSI, a peptide derived from the N protein of BDV, which represents the immunodominant cytotoxic T lymphocyte epitope in H-2k mice. Immunization with TELEISSI-coated DCs further induced solid protective immunity against intravenous challenge with a recombinant vaccinia virus expressing BDV-N. Interestingly, however, this immunization scheme induced only moderate protection against intracerebral challenge with BDV, suggesting that immune memory raised against a shared antigen may be sufficient to control a peripherally replicating virus, but not a highly neurotropic virus that is able to avoid activation of T cells. This difference might be due to the lack of BDV-specific CD4 T cells and/or inefficient reactivation of DC-primed, BDV-specific CD8 T cells by the locally restricted BDV infection. Thus, a successful vaccine against persistent viruses with strong neurotropism should probably induce antiviral CD8 (as well as CD4) T-cell responses and should favour the accumulation of virus-specific memory T cells in cervical lymph nodes.

Effective Deletion of Anti-Donor Host Memory Effector Cells by Anti-3rd Party Veto CTLs: Implications to Tolerance Induction in Presensitized Bone Marrow Recipients.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 44-44 ◽  
Author(s):  
Shlomit Reich-Zeliger ◽  
Esther Bachar-Lustig ◽  
Yair Reisner
Keyword(s):  
T Cells ◽  
Cd8 T Cells ◽  
Memory T Cells ◽  
Tolerance Induction ◽  
Annexin V ◽  
Memory Cells ◽  
Spleen Cells ◽  
Memory Cd8 T Cells ◽  
Effector Cells ◽  
Veto Cells

Abstract Recently we demonstrated that veto CTLs enhance engraftment of mismatched T cell depleted BM in recipient mice following reduced intensity conditioning. This desirable tolerance induction can be further enhanced by combining veto CTLs with CD4+CD25+ cells and Rapamycin. While these results are encouraging, they were largely based on models in which the resistant effector T cells mediating the allorejection are naive CTLp. However, considering that many patients undergoing BMT are presensitized by transfusions of different blood products, memory T cells could play an important role in graft rejection and, therefore, their sensitivity to veto cells could be critical to the implementation of the latter cells in BMT. Clearly, memory T cells respond under less stringent conditions to foreign antigens, compared to their naïve counterparts. In particular, they are programmed to be activated promptly, with a reduced requirement for costimulatory signals and therefore they might be more resistant to veto cells. To address this question we used the 2C mouse model, the CD8 T cells of which express a transgenic TCR against H-2d. The CD8 T cells bearing the TCR transgene can be followed by FACS using staining with a clontypic antibody (1B2) against the transgene. In this model, addition of veto CTLs was shown to inhibit expansion of CD8+1B2+ effector cells by induction of apoptosis which can be monitored by annexin V staining. Thus, in a total of 10 experiments the addition of 5% veto cells to 3 day MLR culture of naive 2C effector cells in the presence of H-2d stimulator cells, led to 76%±9% inhibition of expansion. In order to compare the sensitivity of memory cells in the same model, memory cells were established by immunizing 2C transgenic mice with 1x106 irradiated splenocytes from Balb/c donors (H-2d origin). Six weeks later, splenocytes were harvested and after Ficoll separation were shown to be enriched with memory CD8 T cells(CD44+high CD45Rb+ CD62L+, average in 16 different experiments was 73%±11). Upon addition of 5% veto cells to MLR culture of memory 2C spleen cells in the presence of stimulator cells, 78%±7% inhibition of 2C expansion was found. This veto activity was associated with increased apoptosis of allospecific memory CD8 T cells. Thus, in the absence of veto cells the CD8+1B2+ memory cells exhibited a low level of Annexin V (6%±3%) while in the presence of 5% veto cells, a high level of Annexin V (25%±9%) was detected. The deletion of the 2C memory effectors, as previously shown for naive 2C cells, is largely dependent on the presence of Fas-FasL interaction, as indicated by using memory cells from 2C- lpr mice that lack Fas receptor on the cell surface. Upon addition of veto cells to MLR culture with 2C memory spleen cells from lpr mice, only a minor reduction of expansion (5.5%±6% in the presence of 10% veto CTLs) was detected. In conclusion, these results suggest that veto cells can delete memory effector cells as efficiently as exhibited on naive effector cells and by a similar Fas-FasL dependent mechanism. This finding might have significant implications not only for BMT, but also for the treatment of autoimmune diseases in which memory T cells play a major role.

Concomitant Induction of CMVpp65-Specific CD4+ and CD8+ T Cells Using Dendritic Cells Transfected with mRNA Encoding an Invariant Chain-pp65 Fusion Protein.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 3243-3243
Author(s):  
Ngocdiep Le ◽  
Jens Dannull ◽  
Nelson Chao ◽  
Johannes Vieweg
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
Fusion Protein ◽  
Mhc Class Ii ◽  
Cellular Immunity ◽  
Invariant Chain ◽  
Cell Transplant ◽  
Presentation Pathway ◽  
Cmv Disease ◽  
Ctl Responses

Abstract Human cytomegalovirus (CMV) disease is increasingly recognized as a major cause of morbidity and mortality in post-stem cell transplant (SCT) recipients due to a lack of cellular immunity. Thus, novel therapies that offer the restoration of cellular immunity in SCT patients are highly desirable for clinical use. Cytotoxic T lymphocyte (CTL) responses against CMV represent a major effector arm of the immune system to control viremia. However, it is well established that the efficient induction and persistence of CTL responses in vivo requires the concomitant induction of antigen-specific CD4+ T helper cells. In this study, we sought to determine whether human dendritic cells (DC) transfected with mRNA encoding an invariant chain-CMVpp65 fusion protein (Ii-pp65) were capable of inducing concomitant CMV-specific CTL and CD4+ responses, thereby constituting a useful strategy for immunotherapy of CMV disease. We show that transfection of DC with Ii-pp65 mRNA leads to enhanced stimulation of CMV-specific CTL in vitro (Figure 1). Furthermore, DC expressing Ii-pp65 are potent inducers of primary CMV-specific CD4+ T cell responses as evidenced by ELISPOT analyses of primed CD4+CD45RA+ T cells (Figure 2). Lastly, efficient routing of Ii-pp65 into the MHC class II presentation pathway is demonstrated by confocal microscopy (data not shown). Based on these preclinical findings, we propose a clinical trial to administer DC, transfected with mRNA encoding a chimeric Ii-pp65, to post-SCT patients. Our primary goal will be to prevent CMV infection and reactivation by inducing strong immune reactivities against CMV. Figure Figure

scholarly journals Positive Selection of γδ CTL by TL Antigen Expressed in the Thymus

1996 ◽  
Vol 184 (6) ◽  
pp. 2175-2184 ◽  
Author(s):  
Kunio Tsujimura ◽  
Toshitada Takahashi ◽  
Akimichi Morita ◽  
Hitomi Hasegawa-Nishiwaki ◽  
Shigeru Iwase ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Positive Selection ◽  
Transgenic Mouse ◽  
Mouse Strains ◽  
Skin Grafts ◽  
Spleen Cells ◽  
C3h Mice ◽  
Ctl Activity ◽  
Selection Of

To elucidate the function of the mouse TL antigen in the thymus, we have derived two TL transgenic mouse strains by introducing Tlaa-3 of A strain origin with its own promoter onto a C3H background with no expression of TL in the thymus. These transgenic mouse strains, both of which express high levels of Tlaa-3-TL antigen in their thymus, were analyzed for their T cell function with emphasis on cytotoxic T lymphocyte (CTL) generation. A T cell response against TL was induced in Tg.Tlaa-3-1, Tg.Tlaa-3-2, and control C3H mice by skin grafts from H-2Kb/T3b transgenic mice, Tg.Con.3-1, expressing T3b-TL ubiquitously. Spleen cells from mice that had rejected the T3b-TL positive skin grafts were restimulated in vitro with Tg.Con.3-1 irradiated spleen cells. In mixed lymphocyte cultures (MLC), approximately 20% and 15% of Thy-1+ T cells derived from Tg.Tlaa-3-1 and Tg.Tlaa-3-2, respectively, expressed TCRγδ, whereas almost all those from C3H expressed TCRαβ. The MLC from Tg.Tlaa-3-2 and C3H demonstrated high CTL activity against TL, while those from Tg.Tlaa-3-1 had little or none. The generation of γδ CTL recognizing TL in Tg.Tlaa-3-2, but not C3H mice, was confirmed by the establishment of CTL clones. A total of 14 γδ CTL clones were established from Tg.Tlaa-3-2, whereas none were obtained from C3H. Of the 14 γδ CTL clones, 8 were CD8+ and 6 were CD4−CD8− double negative. The CTL activity of all these clones was TL specific and inhibited by anti-TL, but not by anti-H-2 antibodies, demonstrating that they recognize TL directly without antigen presentation by H-2. The CTL activity was blocked by antibodies to TCRγδ and CD3, and also by antibodies to CD8α and CD8β in CD8+ clones, showing that the activity was mediated by TCRγδ and coreceptors. The thymic origin of these γδ CTL clones was indicated by the expression of Thy-1 and Ly-1 (CD5), and also CD8αβ heterodimers in CD8+ clones on their surfaces and by the usage of TCR Vγ4 chains in 12 of the 14 clones. Taken together, these results suggest that Tlaa-3-TL antigen expressed in the thymus engages in positive selection of a sizable population of γδ T cells.

Tolerogenic dendritic cells inhibit antiphospholipid syndrome derived effector/memory CD4+ T cell response to β2GPI

2011 ◽  
Vol 71 (1) ◽  
pp. 120-128 ◽  
Author(s):  
Honorio Torres-Aguilar ◽  
Miri Blank ◽  
Shaye Kivity ◽  
Mudi Misgav ◽  
Jacob Luboshitz ◽  
...  
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Proliferative Response ◽  
Memory T Cells ◽  
Tolerance Induction ◽  
Effector Memory ◽  
Effector Memory T Cells ◽  
Tolerogenic Dendritic Cells ◽  
Specific Tolerance

ObjectivesThe importance of β2-glycoprotein I (β2GPI)-specific CD4+ T cells in the development of pathogenic processes in patients with antiphospholipid syndrome (APS) and APS mouse models is well established. Therefore, our objective is to manipulate the β2GPI specific CD4+ T cells using tolerogenic dendritic cells (tDCs) to induce tolerance. We aim to evaluate the capability of tDCs to induce antigen-specific tolerance in effector/memory T cells from patients with APS and to elucidate the involved mechanism.MethodsDCs and tDCs were produced from patients with APS peripheral-blood-monocytes, using specific cytokines. β2GPI-specific tolerance induction was investigated by coculturing control DC (cDC) or tDC, β2GPI-loaded, with autologous effector/memory T cells, evaluating the proliferative response, phenotype, cytokines secretion, viability and regulatory T cells.ResultsHuman monocyte-derived DCs treated with interleukin (IL)-10 and transforming growth factor β-1 (10/TGF-DC) induced β2GPI-specific-unresponsiveness in effector/memory CD4+ T cells (46.5%±26.0 less proliferation) in 16 of 20 analysed patients with APS, without affecting the proliferative response to an unrelated candidin. In five analysed patients, 10/TGF-DC-stimulated T cells acquired an IL-2lowinterferon γlowIL-10high cytokine profile, with just a propensity to express higher numbers of Foxp3+CTLA-4+ cells, but with an evident suppressive ability. In four of 10 analysed patients, 10/TGF-DC-stimulated T cell hyporesponsiveness could not be reverted and showed higher percentages of late apoptosis, p<0.02.ConclusionsThe inherent tolerance induction resistance of activated T cells present during the development of autoimmune diseases has delayed the application of tDC as an alternative therapy. This study highlights the 10/TGF-DC feasibility to induce antigen-specific unresponsiveness in autoreactive T cells generated in patients with APS by inducing apoptosis or T cells with regulatory abilities.

scholarly journals Surface markers of cloned human T cells with various cytolytic activities.

1981 ◽  
Vol 154 (2) ◽  
pp. 569-574 ◽  
Author(s):  
L Moretta ◽  
M C Mingari ◽  
P R Sekaly ◽  
A Moretta ◽  
B Chapuis ◽  
...  
Keyword(s):  
T Cells ◽  
Cytotoxic T Lymphocyte ◽  
Mixed Lymphocyte Culture ◽  
Lymphocyte Culture ◽  
Target Cells ◽  
Surface Markers ◽  
Human T Cells ◽  
Dependent Cell ◽  
Blast Cells ◽  
Ctl Activity

Human T cells stimulated in secondary allogeneic mixed lymphocyte culture (MLC) were cloned under limiting conditions in microculture systems using T cell growth factor and irradiated allogeneic cells. Clones with lytic activity against either phytohemagglutinin-induced blast cells bearing the stimulating alloantigen(s) (cytotoxic T lymphocyte [CTL] activity), L1210 mouse lymphoma cells coated with rabbit antibody (antibody-dependent cell-mediated cytotoxicity [ADCC]), or K562 human target cells were selected, expanded, and then analyzed for different surface markers, including rosette formation with sheep erythrocytes (E rosettes), receptors for the fc portion of IgG or IgM (Fc gamma R and Fc mu R), and a group of antigens recognized by monoclonal antibodies including Ia, 4F2, OKT8,a nd OKT4. All the cytotoxic cells were E rosette+, Ia+ and 4f2+. Expression of Fc gamma R was restricted to the clones active in ADCC. CTL clones were either OKT8+ or OKT8-. Furthermore, three of the OKT8- CTL clones were OKT4+. In addition, some cytolytic clones devoid of specific CTL activity were OKT8+. It thus appears that the claim that human CTL are OKT8+, OKT4-, and Ia- is not supported by the analysis of their phenotype at the clonal level.

Synergistic activation of dendritic cells by combined Toll-like receptor ligation induces superior CTL responses in vivo

Blood ◽  
2006 ◽  
Vol 108 (2) ◽  
pp. 544-550 ◽  
Author(s):  
Tobias Warger ◽  
Philipp Osterloh ◽  
Gerd Rechtsteiner ◽  
Melanie Fassbender ◽  
Valeska Heib ◽  
...  
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
Cytotoxic T Lymphocyte ◽  
Signaling Cascades ◽  
Full Potential ◽  
Inhibitory Effects ◽  
Synergistic Activation ◽  
Simultaneous Activation ◽  
Receptor Ligation

Toll-like receptors (TLRs) are able to interact with pathogen-derived products and their signals induce the coordinated activation of innate and adaptive immune mechanisms. Dendritic cells (DCs) play a central role in these events. As the different TLRs are able to trigger MyD88/TRIF-dependent and -independent signaling pathways, we wondered if the simultaneous activation of these signaling cascades would synergize with respect to DC activation and induce superior cytotoxic T-lymphocyte (CTL) activity in vivo. We observed that indeed the combined activation of MyD88-dependent and -independent signaling induced by TLR7 and TLR3 ligands provoked a more rapid and more sustained bone marrow–derived DC (BMDC) activation with regard to the secretion of proinflammatory cytokines, like IL-6 and IL-12p70, and the expression of costimulatory molecules like CD40, CD70, and CD86. Furthermore, in the presence of combined TLR ligand–stimulated DCs, CD4+ and CD8+ T cells were insensitive toward the inhibitory effects of regulatory T cells. Most importantly, peptide-loaded BMDCs stimulated by TLR ligand combinations resulted in a marked increase of CTL effector functions in wild-type mice in vivo. Thus, our results provide evidence that unlocking the full potential of DCs by advanced activation protocols will boost their immunogenic potential and improve DC-based vaccination strategies.

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