Inhibition of Dendritic Cell Activation and Modulation of T Cell Polarization by the Platelet Secretome.

Platelet transfusions are a frequently administered therapy for especially hemato-oncological patients with thrombocytopenia. Next to their primary function in hemostasis, currently there is increased attention for the capacity of platelets to affect the function of various cells of the immune system. Here, we investigate the capacity of platelets to immuno-modulate monocyte-derived dendritic cells (moDC) as well as primary dendritic cells and effects on subsequent T cell responses. Platelets significantly inhibited pro-inflammatory (IL-12, IL-6, TNFα) and increased anti-inflammatory (IL-10) cytokine production of moDCs primed with toll-like receptor (TLR)-dependent and TLR-independent stimuli. Transwell assays and ultracentrifugation revealed that a soluble factor secreted by platelets, but not microvesicles, inhibited DC activation. Interestingly, platelet-derived soluble mediators also inhibited cytokine production by human ex vivo stimulated myeloid CD1c+ conventional DC2. Moreover, platelets and platelet-derived soluble mediators inhibited T cell priming and T helper differentiation toward an IFNγ+ Th1 phenotype by moDCs. Overall, these results show that platelets are able to inhibit the pro-inflammatory properties of DCs, and may even induce an anti-inflammatory DC phenotype, with decreased T cell priming capacity by the DC. The results of this study provide more insight in the potential role of platelets in immune modulation, especially in the context of platelet transfusions.

Adaptation to replating of dendritic cells synergizes with Toll-like receptor stimuli and enhances the pro-inflammatory cytokine profile.

BACKGROUND: As initiators of the adaptive immune response, dendritic cells (DCs) can be used for anti-cancer immunotherapy. On addition of proper maturation stimuli DCs mature and produce pro-inflammatory cytokines that skew T cells in the direction needed for anti-cancer therapy. Further optimization of DC maturation might improve the efficacy of DCs for clinical application. We describe that replating and a subsequent resting period enhance the inflammatory properties of the DCs. METHODS: Cultured immature monocyte-derived DCs were harvested and, after replating, were stimulated immediately or after 2 h of rest. Cytokine production was assessed using enzyme-linked immunosorbent assay (ELISA). Dynamics of mitogen-activated protein kinase (MAPK) and nuclear factor kappa b (NFκB) activation in DCs was analyzed using flow cytometry and imaging flow cytometry. RESULTS: Resting immature DCs after replating, before addition of Toll-like receptor (TLR) ligands, increased the production of pro-inflammatory but not anti-inflammatory cytokines. In addition, the speed of MAPK phosphorylation and nuclear translocation of NFκB was increased when DCs were allowed to rest before TLR stimulation. The effect was imprinted, transient and did not reflect a temporary loss of responsiveness, indicating that signaling induced by culture adaptation of DCs synergizes with TLR signals to increase cytokine production. DCs rested before TLR stimulation induced more interferon (IFN)-γ production in CD4-positive and CD8-positive T cells. CONCLUSION: Introduction of a resting step in the DC maturation method, which is cheap and easy to implement, will improve the generation of pro-inflammatory DCs for cancer immunotherapy. These DCs enhanced Th1 polarization and IFN-γ production by CD8 T cells, both important hallmarks for the induction of efficient anti-cancer immunity.

Comparison of media and serum supplementation for generation of monophosphoryl lipid A/interferon-γ-matured type I dendritic cells for immunotherapy.

BACKGROUND AIMS: Ex vivo-generated monocyte-derived dendritic cells (DCs) matured with monophosphoryl lipid A (MPLA) and interferon-γ (IFN-γ) can be used as cancer immunotherapy. MPLA/IFN-γ DCs induce Th1 T cell responses and have migratory capacity. Different culture regimens have been used for generation of immunotherapeutic DCs, with varying results. In the present study, culture conditions for MPLA/IFN-γ-matured type I DCs were optimized for clinical application. METHODS: DCs were generated from monocytes in the clinical grade culture media CellGro DC, AIM V or X-VIVO 15 in the absence or presence of 2% human serum (HS) and matured with the use of MPLA/IFN-γ. DC yield and DC functionality were assessed. DC functionality was determined by means of analysis of cytokines in culture supernatant, migratory capacity, expression of co-stimulatory molecules, T cell stimulatory capacity of DCs and T helper cell (Th) polarization by the DCs. RESULTS: DCs generated in the presence of 2% HS produced low amounts of pro-inflammatory cytokines and could not migrate irrespective of the medium used. In the absence of HS, MPLA/IFN-γ DCs generated in X-VIVO did not migrate either. MPLA/IFN-γ DCs generated in AIM V have slightly lower capacity to induce Th1 cells than do DCs generated in CellGro or X-VIVO. CONCLUSIONS: Addition of HS to different GMP culture media is detrimental for pro-inflammatory DC maturation and migration. In the absence of serum, CellGro is the most optimal medium tested for generation of migratory and Th1-inducing MPLA/IFN-γ DCs for cancer immunotherapy.

TLR4-mediated pro-inflammatory dendritic cell differentiation in humans requires the combined action of MyD88 and TRIF.

TLR4 ligation can activate both the MyD88 and the Toll-IL-1 receptor domain-containing adaptor inducing IFN-ß (TRIF) signaling route. Whereas MyD88 is generally recognized as a universal adaptor for pro-inflammatory responses, TRIF is mainly thought to contribute to specific type I IFN responses. Here, we investigated the contribution of both MyD88 and TRIF to TLR4-mediated pro-inflammatory dendritic cell (DC) differentiation in human. Pro-inflammatory cytokine induction was strongly decreased in monophosphoryl lipid A- and LPS-matured monocyte-derived DCs when either MyD88 or TRIF were down-regulated by small interfering RNA electroporation. Induction of co-stimulatory molecule expression was entirely dependent on the TRIF pathway. Our results demonstrate that in human DCs the TRIF pathway is important for overall pro-inflammatory DC differentiation via TLR4 by mediating co-stimulation and playing a non-redundant role in pro-inflammatory cytokine induction.

Crosstalk between Toll like receptors and C5a receptor in human monocyte derived DCs suppress inflammatory cytokine production.

The complement anaphylatoxin, C5a has been implicated in regulation of adaptive immune responses through modulation of APC function as shown mainly in studies in mice. C5a was shown to enhance cytokine production in immature DCs, but the effect of C5a on DC function during DC activation has not been elucidated in human. In this study we investigated the effect of C5a on human monocyte derived DCs when simultaneously stimulated with TLR ligands. While C5a indeed enhanced cytokine production of immature DCs, the addition of C5a inhibited production of IL-12, IL-23 and TNFα induced by various TLR ligands such as LPS, R848 and Pam(3)CSK(4). The inhibitory effect of C5a on LPS induced IL-6 production was less pronounced and LPS induced IL-10 was not affected at all. This indicates that C5aR signaling has a differential effect on human DC differentiation depending on the crosstalk with other receptors. Furthermore we found that C5a affects the LPS induced cytokines in a small time frame, and requires almost concurrent signaling of C5a receptor and TLR4. These data emphasize the complexity of DC regulation by anaphylatoxins. While complement activation may provide proinflammatory signals to immature DCs in the absence of pathogens, the same products may serve to downmodulate or deviate immune responses upon combat against infections. These context depending effects of anaphylatoxins on immune responses may have important implications for the emerging use of complement inhibitors in clinical practice.

Monophosphoryl lipid A plus IFNgamma maturation of dendritic cells induces antigen-specific CD8+ cytotoxic T cells with high cytolytic potential.

Dendritic cells (DCs) are promising antigen presenting cells for cancer treatment. Previously, we showed that the combination of monophosphoryl lipid A (MPLA) with IFNgamma generates mature DCs that produce IL-12 and polarize CD4(+) T cells towards a Th1 phenotype. Here, we extended these observations by showing that the DCs generated with the clinical grade maturation cocktail of MPLA/IFNgamma induce superior tumour antigen-specific CD8(+) CTL responses compared to the cytokine cocktail matured DCs that are currently used in the clinic. MPLA/IFNgamma DCs can induce CTL responses in healthy individuals as well as in melanoma patients. The CTL induction was mainly dependent on the IL-12 produced by the MPLA/IFNgamma DCs. The high amounts of induced CTLs are functional as they produce IFNgamma and lyse target cells and this cytolytic activity is antigen specific and HLA restricted. Furthermore, the CTLs proved to kill tumour cells expressing endogenous tumour antigen in vitro. Therefore, MPLA/IFNgamma DCs are very promising for the use in future cancer immunotherapy.

CTL escape and increased viremia irrespective of HIV-specific CD4+ T-helper responses in two HIV-infected individuals.

We investigated whether development of mutations leads to loss of CD8 T-cell recognition in HIV-1 infection and is possibly linked to alterations in HIV-1-specific CD4(+) T-cell responses in 2 HIV-infected individuals. In patient, H434 full genome sequencing of HIV-1 biological clones at early and late time points during disease progression showed development of fixed mutations in 16 predicted HIV-specific CTL epitopes. Loss of T-cell recognition and reactivity against wild-type and mutant epitopes was observed primarily for the HLA-B27-restricted KK10 epitope and HLA-A2-restricted SL9 epitope. Similarly, in patient H671, decreasing numbers of HLA-A3-restricted CD8(+) T cells specific for the wild-type RK9 epitope was observed after CTL escape. Only in patient H434 loss of CTL responses was paralleled by a decrease in HIV-specific IL-2(+) CD4(+) T-helper responses. This suggests that loss of T-cell reactivity may not be directly linked to HIV-specific CD4(+) T-cell responses but that increased viremia after CTL escape may influence CD4(+) T-helper responses.

Direct ex vivo detection of HLA-DR3-restricted cytomegalovirus- and Mycobacterium tuberculosis-specific CD4+ T cells.

In order to detect epitope-specific CD4+ T cells in mycobacterial or viral infections in the context of human class II major histocompatibility complex protein human leukocyte antigen (HLA)-DR3, two HLA-DR3 tetrameric molecules were successfully produced. One contained an immunodominant HLA-DR3-restricted T-cell epitope derived from the 65-kDa heat-shock protein of Mycobacterium tuberculosis, peptide 1-13. For the other tetramer, we used an HLA-DR3-restricted T-cell epitope derived from cytomegalovirus (CMV) pp65 lower matrix protein, peptide 510-522, which induced high levels of interferon (IFN)-gamma-producing CD4+ T cells in three of four HLA-DR3-positive CMV-seropositive individuals up to 0.84% of CD4+ T cells by intracellular cytokine staining. In peripheral blood mononuclear cells from M. tuberculosis-exposed, Mycobacterium bovis bacille Calmette-Guérin (BCG)-vaccinated, or CMV-seropositive individuals, we were able to directly detect with both tetramers epitope-specific T cells up to 0.62% and 0.45% of the CD4+ T-cell population reactive to M. tuberculosis and CMV, respectively. After a 6-day culture with peptide p510-522, the frequency of CMV-specific tetramer-binding T cells was expanded up to 9.90% tetramer+ CFSElow (5,6-carboxyfluorescein diacetate succinimidyl ester) cells within the CD4+ T-cell population, further confirming the specificity of the tetrameric molecules. Thus, HLA-DR3/peptide tetrameric molecules can be used to investigate HLA-DR3-restricted antigen-specific CD4+ T cells in clinical disease or after vaccination.

Targeting primary human Ph(+) B-cell precursor leukemia-engrafted SCID mice using radiolabeled anti-CD19 monoclonal antibodies.

UNLABELLED: The Philadelphia chromosome translocation (Ph(+)) confers a poor prognosis in patients with acute lymphocytic leukemia (ALL). CD19 is highly expressed (CD19(+)) on ALL cells and is an attractive target for antibody-based therapies. CLB-CD19 is an IgG1kappa murine monoclonal antibody (mAb) directed against an epitope on the CD19 antigen. METHODS: Radiolabeled CLB-CD19 antibody was evaluated for targeting ALL in a severe combined immunodeficient (SCID) mouse model engrafted with primary human leukemia cells. Lodgment of CD19(+) ALL cells in spleen and liver was confirmed using immunohistochemistry analyses. Circulating CD19(+) ALL cells in blood were also detected by flow cytometry. RESULTS: Antibody was labeled directly with the radiohalogen (125)I and radiometal (111)In via the bifunctional metal ion chelate CHX-A"-diethylenetriaminepentaacetic acid (DTPA) with retention of immunoreactivities. After intravenous injection of radioconjugates, biodistribution studies showed rapid localization of the (111)In-conjugate to leukemia-infiltrated spleen, reaching a maximum (mean +/- SD) of 72.78 +/- 13.67 % injected dose per gram of tissue (%ID/g) by 24 h after injection. In contrast, peak localization of coinjected (125)I-CLB-CD19 occurred by 4 h and was significantly lower (11.41 +/- 12.79 %ID/g) (P < 0.001). Uptake of (111)In-conjugate in the liver containing tumor was also evident but not in other normal tissues. Uptake of radiolabeled CLB-CD19 in tumor-bearing organs was specific, as uptake of radiolabeled isotype-matched antibody control was low. Gamma-camera imaging detected the uptake of (111)In-CHX-A"-DTPA CLB-CD19 in enlarged tumor-bearing spleen of engrafted mice. A single injection of 32 micro g CLB-CD19 mAb had a delayed suppressive effect on the level of circulatory leukemia cells in surviving mice and extended the median survival from 48.5 to 58 d (n = 8; P = 0.03). CONCLUSION: The radiolabeled anti-CD19 antibody showed specific targeting and rapid internalization in ALL cell-engrafted SCID mice and may also be used for selective intracellular delivery of cytotoxic radionuclides with beta-, Auger, or alpha-emissions.

Lethal T cell immunodeficiency induced by chronic costimulation via CD27-CD70 interactions.

It has been proposed that HIV-1, in addition to directly infecting and killing CD4+ T cells, causes T cell dysfunction and T cell loss by chronic immune activation. We analyzed the effects of chronic immune activation in mice that constitutively expressed CD70, the ligand for the tumor necrosis factor receptor family member CD27, on B cells. CD70 transgenic (CD70 Tg) mice showed a progressive conversion of naive T cells into effector-memory cells, which culminated in the depletion of naive T cells from lymph nodes and spleen. T cell changes depended on continuous CD27-CD70 interactions and T cell antigen receptor stimulation. Despite this hyperactive immune system, CD70 Tg mice died aged 6-8 months from Pneumocystis carinii infection, a hallmark of T cell immunodeficiency. Thus, persistent delivery of costimulatory signals via CD27-CD70 interactions, as may occur during chronic active viral infections, can exhaust the T cell pool and is sufficient to induce lethal immunodeficiency.

Expression of the murine CD27 ligand CD70 in vitro and in vivo.

The interaction between TNFR family member CD27 and its ligand CD70 promotes lymphocyte expansion and effector cell formation. In humans, control of CD27 function is partly regulated by the restricted expression of CD70. We used newly developed mAbs to characterize murine (m) CD70 expression in vitro and in vivo. On resting lymphocytes and immature dendritic cells (DC), mCD70 is absent. In vitro, Ag receptor triggering induced mCD70 mRNA in T cells, but cell surface protein expression was very low. Activated B cells synthesized much higher levels of mCD70 mRNA than activated T cells and clearly expressed mCD70 at the cell surface. mCD70 cell surface expression could also be induced on the DC line D1 and on in vitro-generated murine DC upon maturation. In lymphoid organs of naive mice, virtually no mCD70-expressing cells were found, with exception of cells in the thymic medulla, which may be epithelial in origin. However, after intranasal infection with influenza virus, lung-infiltrating T cells and T and B cells in draining lymph nodes expressed mCD70 according to immunohistology. In such activated lymphocytes, mCD70 protein is largely retained intracellularly. Plasma membrane expression of mCD70 was only detectable by flow cytometry on a small proportion of lung-infiltrating T cells and peaked at the height of the primary response. Thus, expression of CD70 in the mouse is highly regulated at the transcriptional and posttranslational level. This most likely serves to limit excessive effector cell formation after antigenic stimulation.