Monocyte-derived dendritic cells display a highly activated phenotype and altered function in patients with familial Mediterranean fever

Dendritic cells (DCs) are sentinels of the immune system that bridge innate and adaptive immunity. By capturing antigens in peripheral tissue, processing and presenting them with concurrent expression of co‐stimulatory molecules and cytokine secretion they control and modulate immune reactions. Through pattern recognition receptors, DCs sense molecules that are associated with infection or tissue damage, frequently resulting in the formation of inflammasomes upon intracellular stimulation. The inherited autoinflammatory familial Mediterranean fever (FMF) is associated with deregulated activity of the pyrin inflammasome leading to acute inflammatory episodes. However, differentiation and function of DCs in this disease are as yet unclear. Therefore, we first determined DC subpopulation frequency in peripheral blood of a cohort of FMF patients. Joint evaluation without classification according to specific patient characteristics, such as mutational status, did not disclose significant differences compared to healthy controls. For the further examination of phenotype and function, we used immature and mature monocyte‐derived DCs (imMo‐DCs, mMo‐DCs) that were generated in vitro from FMF patients. Immunophenotypical analysis of imMo‐DCs revealed a significantly elevated expression of CD83, CD86 and human leukocyte antigen D‐related (HLA‐DR) as well as a significant down‐regulation of CD206, CD209 and glycoprotein NMB (GPNMB) in our FMF patient group. Furthermore, FMF imMo‐DCs presented a significantly higher capacity to migrate and to stimulate the proliferation of unmatched allogeneic T cells. Finally, the transition towards a more mature, and therefore activated, phenotype was additionally reinforced by the fact that peripheral blood DC populations in FMF patients exhibited significantly increased expression of the co‐stimulatory molecule CD86.

The Deubiquitinase Inhibitor b-AP15 and Its Effect on Phenotype and Function of Monocyte-Derived Dendritic Cells

The ubiquitin-proteasome system is elementary for cellular protein degradation and gained rising attention as a new target for cancer therapy due to promising clinical trials with bortezomib, the first-in class proteasome inhibitor meanwhile approved for multiple myeloma and mantle cell lymphoma. Both bortezomib and next-generation proteasome inhibitors mediate their effects by targeting the 20S core particle of the 26S proteasome. The novel small molecule inhibitor b-AP15 affects upstream elements of the ubiquitin-proteasome cascade by suppressing the deubiquitinase activity of both proteasomal regulatory 19S subunits and showed promising anticancer activity in preclinical models. Nonetheless, effects of inhibitors on the ubiquitin-proteasome system are not exclusively restricted to malignant cells: alteration of natural killer cell-mediated immune responses had already been described for drugs targeting either 19S or 20S proteasomal subunits. Moreover, it has been shown that bortezomib impairs dendritic cell (DC) phenotype and function at different levels. In the present study, we comparatively analyzed effects of bortezomib and b-AP15 on monocyte-derived DCs. In line with previous results, bortezomib exposure impaired maturation, antigen uptake, migration, cytokine secretion and immunostimulation, whereas treatment with b-AP15 had no compromising effects on these DC features. Our findings warrant the further investigation of b-AP15 as an alternative to clinically approved proteasome inhibitors in the therapy of malignancies, especially in the context of combinatorial treatment with DC-based immunotherapies.

The novel deubiquitinase inhibitor b-AP15 induces direct and NK cell-mediated antitumor effects in human mantle cell lymphoma

The first therapeutic proteasome inhibitor bortezomib has clinical efficacy in mantle cell lymphoma (MCL) which resulted in its incorporation in treatment algorithms for this disease. Impairment of proteasomal function by bortezomib is mediated via inhibition of the 20S core particle. However, proteasome function can also be modified by targeting upstream components of the ubiquitin-proteasome system. Recently, b-AP15 has been identified as a small molecule achieving proteasome inhibition by targeting the deubiquitinase (DUB) activity of the 19S regulatory subunit and was found to inhibit cancer cell growth in preclinical analyses. In the present study, both direct antitumor effects and the possibility to induce natural killer group 2 member D ligands (NKG2DL) to reinforce NK cell immunity with b-AP15 were investigated to provide a rational basis for clinical evaluation of this novel DUB inhibitor in MCL. Treatment with b-AP15 resulted in reduced viability as well as induction of apoptosis in a time- and dose-dependent manner, which could be attributed to caspase activation in MCL cells. In addition, treatment with b-AP15 differentially induced NKG2DL expression and subsequent NK cell lysis of MCL cells. These results indicate that the DUB inhibitor b-AP15 displays substantial antitumor activity in human MCL and suggest that b-AP15 might be a novel therapeutic option in the treatment of MCL that warrants clinical investigation.

The BCR-ABL inhibitor nilotinib influences phenotype and function of monocyte-derived human dendritic cells

In chronic myeloid leukemia (CML), the translocation t(9;22) results in the fusion protein BCR-ABL (breakpoint cluster region-abelson murine leukemia), a tyrosine kinase mediating oncogenic signaling which is successfully targeted by treatment with BCR-ABL inhibitors like imatinib. However, BCR-ABL inhibitors may also affect antitumor immunity. For instance, it was reported that imatinib impairs the function of dendritic cells (DCs) that play a central role in initiating and sustaining T cell responses. Meanwhile, second generation BCR-ABL inhibitors like nilotinib, which inhibits BCR-ABL with enhanced potency have become standard of treatment, at least in patients with BCR-ABL kinase domain mutations. In this study we analyzed the influence of therapeutic concentrations of nilotinib on human monocyte-derived DCs and compared its effects to imatinib. We found that both tyrosine kinase inhibitors (TKI) comparably and significantly impaired differentiation of monocytes to DCs as revealed by curtated downregulation of CD14 and reduced upregulation of CD1a and CD83. This was only partially restored after withdrawal of the TKI. Moreover, both TKI significantly reduced activation-induced IL-12p70 and C-C motif chemokine ligand (CCL) 3 secretion, while divergent TKI effects for CCL2 and CCL5 were observed. In contrast, only nilotinib significantly impaired the migratory capacity of DCs and their capacity to induce T-cell immune responses in MLRs. Our results indicate that imatinib and nilotinib may differ significantly with regard to their influence on antitumor immunity. Thus, for future combinatory approaches and particularly stop studies in CML treatment, choice of the most suitable BCR-ABL inhibitor requires careful consideration.

Confirmation and next-generation sequencing of allele HLA-B*35:279 found in a family of a leukaemia patient with Western Asia origin

The confirmation of novel allele HLA-B*35:279 in a family of a leukaemia patient with Western Asia origin is reported. Moreover, next-generation sequencing (NGS) resulted in whole-gene sequence data and revealed the inheritance of HLA-B*35:279 on the paternal haplotype.

Profiling of primary peripheral blood- and monocyte-derived dendritic cells using monoclonal antibodies from the HLDA10 Workshop in Wollongong, Australia

Dendritic cells (DCs) arise from hematopoietic stem cells and develop into a discrete cellular lineage distinct from other leucocytes. Mainly three phenotypically and functionally distinct DC subsets are described in the human peripheral blood (PB): plasmacytoid DCs (pDCs), which express the key marker CD303 (BDCA-2), and two myeloid DC subsets (CD1c(+) DC (mDC1) and CD141(+) DC (mDC2)), which express the key markers CD1c (BDCA-1) and CD141 (BDCA-3), respectively. In addition to these primary cell subsets, DCs can also be generated in vitro from either CD34(+) stem/progenitor cells in the presence of Flt3 (Fms-related tyrosine kinase 3) ligand or from CD14(+) monocytes (monocyte-derived DCs (mo-DCs)) in the presence of granulocyte-macrophage colony-stimulating factor+interleukin-4 (GM-CSF+IL-4). Here we compare the reactivity patterns of HLDA10 antibodies (monoclonal antibody (mAb)) with pDCs, CD1c(+) DCs and CD141(+) DCs, as well as with CD14(+)-derived mo-DCs cultured for 7 days in the presence of 100 ng/ml GM-CSF plus 20 ng/ml IL-4. A detailed profiling of these DC subsets based on immunophenotyping and multicolour flow cytometry analysis is presented. Using the panel of HLDA10 Workshop mAb, we could verify known targets selectively expressed on discrete DC subsets including CD370 as a selective marker for CD141(+) DCs and CD366 as a marker for both myeloid subsets. In addition, vimentin and other markers are heterogeneously expressed on all three subsets, suggesting the existence of so far not identified DC subsets.

The transcription factor MITF is a critical regulator of GPNMB expression in dendritic cells

BACKGROUND

Dendritic cells (DC) are the most potent antigen-presenting cells (APC) with the unique ability to activate naïve T cells and to initiate and maintain primary immune responses. Immunosuppressive and anti-inflammatory stimuli on DC such as the cytokine IL-10 suppress the activity of the transcription factor NF-κB what results in downregulation of costimulatory molecules, MHC and cytokine production. Glycoprotein NMB (GPNMB) is a transmembrane protein, which acts as a coinhibitory molecule strongly inhibiting T cell responses if present on APC. Interestingly, its expression on human monocyte-derived dendritic cells (moDC) is dramatically upregulated upon treatment with IL-10 but also by the BCR-ABL tyrosine kinase inhibitors (TKI) imatinib, nilotinib or dasatinib used for the treatment of chronic myeloid leukemia (CML). However, the molecular mechanisms responsible for GPNMB overexpression are yet unknown.

RESULTS

The immunosuppressive cytokine IL-10 and the BCR-ABL TKI imatinib or nilotinib, that were examined here, concordantly inhibit the PI3K/Akt signaling pathway, thereby activating the downstream serine/threonine protein kinase GSK3ß, and subsequently the microphthalmia-associated transcription factor (MITF) that is phosphorylated and translocated into the nucleus. Treatment of moDC with a small molecule inhibitor of MITF activity reduced the expression of GPNMB at the level of mRNA and protein, indicating that GPNMB expression is in fact facilitated by MITF activation. In line with these findings, PI3K/Akt inhibition was found to result in GPNMB overexpression accompanied by reduced stimulatory capacity of moDC in mixed lymphocyte reactions (MLR) with allogeneic T cells that could be restored by addition of the GPNMB T cell ligand syndecan-4 (SD-4).

CONCLUSIONS

In summary, imatinib, nilotinib or IL-10 congruently inhibit the PI3K/Akt signaling pathway thereby activating MITF in moDC, resulting in a tolerogenic phenotype. These findings extend current knowledge on the molecular mechanisms balancing activating and inhibitory signals in human DC and may facilitate the targeted manipulation of T cell responses in the context of DC-based immunotherapeutic interventions.

Comprehensive analysis of NKG2D ligand expression and release in leukemia: implications for NKG2D-mediated NK cell responses

Ligands of the prototypical activating NK receptor NKG2D render cancer cells susceptible to NK cell-mediated cytolysis if expressed at sufficiently high levels. However, malignant cells employ mechanisms to evade NKG2D-mediated immunosurveillance, such as NKG2D ligand (NKG2DL) shedding resulting in reduced surface expression levels. In addition, systemic downregulation of NKG2D on NK cells of cancer patients has been observed in many studies and was attributed to soluble NKG2DL (sNKG2DL), although there also are conflicting data. Likewise, relevant expression of NKG2DL in leukemia has been reported by some, but not all studies. Hence, we comprehensively studied expression, release, and function of the NKG2D ligands MHC class I chain-related molecules A and B and UL16-binding proteins 1-3 in 205 leukemia patients. Leukemia cells of most patients (75%) expressed at least one NKG2DL at the surface, and all investigated patient sera contained elevated sNKG2DL levels. Besides correlating NKG2DL levels with clinical data and outcome, we demonstrate that sNKG2DL in patient sera reduce NKG2D expression on NK cells, resulting in impaired antileukemia reactivity, which also critically depends on number and levels of surface-expressed NKG2DL. Together, we provide comprehensive data on the relevance of NKG2D/NKG2DL expression, release, and function for NK reactivity in leukemia, which exemplifies the mechanisms underlying NKG2D-mediated tumor immunosurveillance and escape.

The immune inhibitory receptor osteoactivin is upregulated in monocyte-derived dendritic cells by BCR-ABL tyrosine kinase inhibitors

Multiple approaches presently aim to combine targeted therapies using tyrosine kinase inhibitors with immunotherapy. Ex vivo-generated dendritic cells are frequently used in such strategies due to their unique ability to initiate primary T-cell immune responses. Besides governing tumor cell growth, many kinases targeted by tyrosine kinase inhibitors are involved in the development and function of dendritic cells and thus tyrosine kinase inhibitor therapy may cause immunoinhibitory side effects. We here report that exposure of developing human monocyte-derived dendritic cells to the BCR-ABL inhibitors imatinib, dasatinib, and nilotinib results in profound upregulation of the transmembrane glycoprotein osteoactivin that has recently been characterized as a negative regulator of T-cell activation. Thus, in line with osteoactivin upregulation, exposure to tyrosine kinase inhibitors resulted in significantly reduced stimulatory capacity of dendritic cells in mixed lymphocyte reactions that could be restored by the addition of blocking anti-osteoactivin antibody. Our data demonstrate that tyrosine kinase inhibitor-mediated inhibition of dendritic cell function is, at least in great part, mediated by upregulation of the immune inhibitory molecule osteoactivin.

The BCR/ABL-inhibitors imatinib, nilotinib and dasatinib differentially affect NK cell reactivity

In chronic myeloid leukemia (CML), BCR/ABL-mediated oncogenic signaling can be targeted with the BCR/ABL-inhibitors Imatinib, Nilotinib and Dasatinib. However, these agents may also affect anti-tumor immunity. Here, we analyzed the effects of the 3 BCR/ABL-inhibitors on natural killer (NK) cell reactivity. Exposure of CML cells (K562, Meg-01) to pharmacological concentrations of Imatinib, Nilotinib and Dasatinib diminished expression of ligands for the activating immunoreceptor NKG2D to a similar extent. This resulted in comparably reduced NK cell cytotoxicity and IFN-gamma production. When direct effects on NK cell responses to K562 and primary CML cells as well as activating cytokines were studied, Dasatinib was found to abrogate NK cytotoxicity and cytokine production. Nilotinib did not alter cytotoxicity but, at high levels, impaired NK cytokine production, while Imatinib had no direct influence on NK cell reactivity. Of note, Nilotinib, but not the other BCR/ABL-inhibitors increased cell death within the preferentially cytokine-secreting CD56(bright)CD16(-) NK cell subset, which may, at least in part, serve to explain the effect of Nilotinib on NK cytokine production. Analysis of NK cell signaling revealed that Dasatinib inhibited proximal signaling events leading to decreased phosphorylation of PI3K and ERK that are crucial for NK cell reactivity. Imatinib and Nilotinib, in contrast, showed no relevant effect on NK cell PI3K or ERK activity. In light of the potential role of NK cells in the immunesurveillance of residual leukemia and for future combinatory immunotherapeutic approaches, our data indicate that choice and dosing of the most suitable BCR/ABL-inhibitor for a given patient require careful consideration.

Characterization of BAX inhibitor-1 as a novel leukemia-associated antigen

Using dendritic cells (DCs) electroporated with whole RNA isolated from blasts of a patient with acute myeloid leukemia (AML), we were able to generate leukemia-specific cytotoxic T lymphocytes (CTLs) capable of recognizing the leucemic cells. To identify T-cell epitopes mediating lysis of malignant cells, peptides were eluted from the patient's blasts and analyzed by mass spectrometry (LC/MS)-based peptide sequencing. Using this approach, an HLA-A24-binding peptide derived from Bax inhibitor-1 (BI-1), a regulator of apoptosis pathways, was identified as an epitope recognized by the generated CTLs. To further characterize this novel antigenic peptide, CTLs were induced using DCs electroporated with RNA coding for BI-1 or pulsed with the cognate peptide. These CTLs generated from healthy donors in vitro efficiently lysed the patient's blasts as well as other HLA-matched leukemic cells. In conclusion, we identified a BI-1 peptide as a novel immunogenic tumor-associated antigen (TAA) in AML. In vitro induction of BI-1-specific CTLs by RNA transfection or pulsing of DCs with the synthetically generated peptide was a feasible and highly effective method to generate leukemia-specific CTLs. As BI-1 is (over-) expressed in a broad variety of malignancies, it may represent an interesting novel TAA in the context of cancer vaccines.

Post-transcriptional regulation of adapter molecules by IL-10 inhibits TLR-mediated activation of antigen-presenting cells

Toll-like receptors (TLRs) act to sense the environment for microbial products and submit danger signals to antigen-presenting cells (APCs) resulting in activation of complex immune responses. In this study, we analyzed the function of human monocyte-derived APCs generated in vitro in the presence of interleukin (IL)-10 upon activation by TLR ligands. Exposure of these APCs to IL-10 resulted in a skewed phenotypic maturation in response to stimuli provided by the TLR ligands, a reduced cytokine production, such as IL-12, IL-6 or tumor necrosis factor-alpha, and impaired capacity to stimulate T-cell activation. Furthermore, CCR7 upregulation in APCs exposed to TLR stimulation as well as migration towards CCL19/MIP-3beta were strongly reduced. IL-10 was found to downregulate MyD88, IRAK1 (IL-1 receptor-associated kinase) and tumor necrosis factor receptor-associated factor 6, essential adaptor molecules for TLR signaling, and to decrease TLR-induced nuclear expression of the nuclear factor-kappaB transcription factors c-Rel and Rel-B as well as interferon regulatory factor (IRF)-3 and IRF-8. This was not due to the inhibition of the mitogen-activated protein kinase pathway, but was rather mediated by the blockage of the PI3K signaling cascade. Interestingly, the inhibition of proteins involved in TLR signaling, such as MyD88, IRAK1 and mammalian target of rapamycin, was due to a selective post-transcriptional regulation.

Matrilysin (MMP-7) is a novel broadly expressed tumor antigen recognized by antigen-specific T cells

PURPOSE

A prerequisite for the development of vaccination strategies is the identification and characterization of relevant tumor-associated antigen. Using microarray and reverse transcription-PCR analysis, we found matrix metalloproteinase (MMP)-7 to be extensively up-regulated in renal cell carcinomas and expressed in a broad variety of malignant cells. MMP-7 can promote cancer invasion and angiogenesis by proteolytic cleavage of extracellular matrix and basement membrane proteins, thus making it a promising target in the context of immunotherapies.

EXPERIMENTAL DESIGN

To analyze the possible use of MMP-7 as a tumor-associated antigen, specific CTLs were induced using monocyte-derived dendritic cells electroporated with MMP-7-mRNA. In addition, to better characterize the fine specificity of these CTLs, MMP-7 MHC class I ligands were isolated and characterized in renal cell carcinoma tissue, which overexpressed MMP-7, by mass spectrometry-based peptide sequencing. Using this approach, we identified a novel HLA-A3-binding antigenic MMP-7 peptide. CTLs generated from healthy donors by in vitro priming with dendritic cells, pulsed with the novel peptide, were used as effectors in (51)Cr-release assays.

RESULTS

The induced CTLs elicited an antigen-specific and HLA-restricted cytolytic activity against tumor cells endogenously expressing the MMP-7 protein. Furthermore, we were able to induce MMP-7-specific CTLs using peripheral blood mononuclear cells from a patient with acute lymphoblastic leukemia capable of recognizing the autologous leukemic blasts while sparing nonmalignant cells.

CONCLUSIONS

Our study describes the identification of a novel broadly expressed T-cell epitope derived from the MMP-7 protein that represents an interesting candidate to be applied in immunotherapies of human malignancies targeting both tumor cells and neovascularization.

Generation of antigen-specific CTL responses using RGS1 mRNA transfected dendritic cells

Advances in tumor immunology and Identification of tumor-associated antigens (TAAs) provide a basis for the development of novel immunotherapies to treat malignant diseases. In order to identify novel TAAs, we performed comparative microarray analysis of (heterogeneous) tissues and found regulator of G protein-signaling 1 (RGS1) extensively up-regulated in renal cell carcinoma (RCC) tissues. To examine the possible function of this molecule as a novel, broadly applicable TAA, synthetic full-length RGS1-mRNA was synthesized for the transfection of monocyte-derived dendritic cells (DCs). These modified antigen-presenting cells (APCs) were then used to induce RGS1-specific cytotoxic T cells (CTLs) in vitro. The CTLs generated from several healthy donors and a patient with chronic lymphocytic leukemia (CLL) elicited an antigen-specific and HLA-A2- and -A3-restricted cytolytic activity against tumor cells endogenously expressing the RGS1 protein including renal cell carcinomas (RCCs), melanoma, ovarian carcinoma and the primary autologous CLL-blasts. In conclusion, our study demonstrates that the in vitro induction of RGS1-specific CTLs by RNA-transfected DCs is feasible and highly effective. Since this molecule is (over-) expressed in a broad variety of malignancies it might represent an interesting novel TAA in the context of cancer vaccines designed to target RGS1 expressing tumor cells.

The use of dendritic cells in cancer immunotherapy

Cancer immunotherapy aims at eliciting an immune response directed against tumor antigens to help fight off residual tumor cells and thereby improve survival and quality of life of cancer patients. Different immunotherapeutic approaches share the use of dendritic cells (DCs) to present tumor-associated antigens to T-lymphocytes. Ex vivo generated DCs can be loaded with antigens and re-infused to the patients, or they can be used for ex vivo expansion of antitumor lymphocytes. Alternatively, methods exist to target antigens to DCs in vivo without need for ex vivo cell manipulations. The clinical studies have shown that DC administration to patients is safe and induces antigen-specific immunity. However, it seldom elicits objective clinical responses in patients with advanced-stage malignancies. Novel insights into DC and lymphocyte regulation are expected to lead to more effective vaccines in the near future. Meanwhile, efforts are directed at identifying the most appropriate clinical targets for active specific immunotherapies. Data suggests that vaccinations may indeed be beneficial when given in the adjuvant setting rather than to treat metastatic cancers. These issues are discussed here together with an overview of the DC-based antitumor immunotherapy studies.

Histone deacetylase inhibitors affect dendritic cell differentiation and immunogenicity

PURPOSE

Histone deacetylases (HDAC) modulate gene transcription and chromatin assembly by modifying histones at the posttranscriptional level. HDAC inhibitors have promising antitumor activity and are presently explored in clinical studies. Cumulating evidence in animal models of immune disorders also suggests immunosuppressive properties for these small molecules, although the underlying mechanisms remain at present poorly understood. Here, we have evaluated the effects of two HDAC inhibitors currently in clinical use, sodium valproate and MS-275, on human monocyte-derived DCs.

EXPERIMENTAL DESIGN

DCs were generated from monocytes through incubation with granulocyte macrophage colony-stimulating factor and interleukin-4. DC maturation was induced by addition of polyinosinic-polycytidylic acid. DC phenotype, immunostimulatory capacity, cytokine secretion, and migratory capacity were determined by flow cytometry, mixed leukocyte reaction, ELISA, and Transwell migration assay, respectively. Nuclear translocation of RelB, IFN regulatory factor (IRF)-3, and IRF-8 were determined by immunoblotting.

RESULTS

HDAC inhibition skews DC differentiation by preventing the acquisition of the DC hallmark CD1a and by affecting the expression of costimulation and adhesion molecules. In addition, macrophage inflammatory protein-3beta/chemokine, motif CC, ligand 19-induced migration, immunostimulatory capacity, and cytokine secretion by DCs are also profoundly impaired. The observed defects in DC function on exposure to HDAC inhibitors seem to reflect the obstruction of signaling through nuclear factor-kappaB, IRF-3, and IRF-8.

CONCLUSIONS

HDAC inhibitors exhibit strong immunomodulatory properties in human DCs. Our results support the evaluation of HDAC inhibitors in inflammatory and autoimmune disorders.

Identification and characterization of T-cell epitopes deduced from RGS5, a novel broadly expressed tumor antigen

PURPOSE

Identification of tumor-associated antigens and advances in tumor immunology resulted in the development of vaccination strategies to treat patients with malignant diseases. In a novel experimental approach that combined comparative mRNA expression analysis of defined cell types with the characterization of MHC ligands by mass spectrometry, we found that regulator of G protein signaling 5 (RGS5) is extensively up-regulated in a broad variety of malignant cells, and we identified two HLA-A2- and HLA-A3-binding peptides derived from the RGS5 protein. Interestingly, RGS5 was recently shown to be involved in tumor angiogenesis.

EXPERIMENTAL DESIGN

We used monocyte-derived dendritic cells pulsed with these novel antigenic peptides or transfected with RGS5-mRNA for the in vitro induction of CTLs, generated from healthy donors, to analyze the presentation of RGS5-deduced epitopes by malignant cells.

RESULTS

The generated CTL lines elicited an antigen-specific and HLA-restricted cytolytic activity against tumor cells endogenously expressing the RGS5 protein. Furthermore, we were able to induce RGS5-specific CTLs using peripheral blood mononuclear cells from a patient with acute myeloid leukemia capable of recognizing the autologous leukemic blasts while sparing nonmalignant cells.

CONCLUSIONS

These results indicate that the RGS5 peptides represent interesting candidates for the development of cancer vaccines designed to target malignant cells and tumor vessels.

hDectin-1 is involved in uptake and cross-presentation of cellular antigens

Human Dectin-1 (hDectin-1) is a member of the C-type lectin-like receptor family that was shown to be the major receptor for fungal beta-glucans and to play an important role in the cellular responses mediated by these carbohydrates. In this study, we demonstrate that hDectin-1 is involved in the uptake and cross-presentation of cellular antigens. Furthermore, activation of monocyte-derived dendritic cells (MDCs) with toll-like receptor 3 (TLR3) ligand but not with TLR2 ligand or TLR7 ligand resulted in down-regulation of hDectin-1 expression and reduced phagocytosis of apoptotic tumor cells as well as presentation of pp65-derived T-cell epitopes upon engulfment of cytomegalovirus (CMV)-infected human foreskin fibroblasts.

BCR-ABL Activity Is Critical for the Immunogenicity of Chronic Myelogenous Leukemia Cells

Chronic myelogenous leukemia (CML) is a myeloproliferative disorder caused by excessive granulopoiesis due to the formation of the constitutively active tyrosine kinase BCR-ABL. An effective drug against CML is imatinib mesylate, a tyrosine kinase inhibitor acting on Abl kinases, c-KIT, and platelet-derived growth factor receptor. Recently, a study revealed that patients treated with imatinib showed impaired CTL responses compared with patients treated with IFN-alpha, which might be due to a treatment-induced reduction in immunogenicity of CML cells or immunosuppressive effects. In our study, we found that inhibition of BCR-ABL leads to a down-regulation of immunogenic antigens on the CML cells in response to imatinib treatment, which results in the inhibition of CML-directed immune responses. By treating CML cells with imatinib, we could show that the resulting inhibition of BCR-ABL leads to a decreased expression of tumor antigens, including survivin, adipophilin, hTERT, WT-1, Bcl-x(L), and Bcl-2 in correlation to a decreased development of CML-specific CTLs. In contrast, this reduction in immunogenicity was not observed when a CML cell line resistant to the inhibitory effects of imatinib was used, but could be confirmed by transfection with specific small interfering RNA against BCR-ABL or imatinib treatment of primary CML cells.

Zoledronic acid inhibits the function of Toll-like receptor 4 ligand activated monocyte-derived dendritic cells

Zoledronic acid (ZA) is a nitrogen-containing bisphosphonate with antitumor activity used to treat patients with malignant diseases. ZA treatment induces, as a side effect, inflammatory responses, which are accompanied by expansion of gammadelta T cells. In our study, we analyzed the function and differentiation of monocyte-derived immature and lipopolysaccharide (LPS)-stimulated dendritic cells (moDCs) treated with different ZA concentrations, which are achieved in patients. We found that moDC activation with TLR4 ligand LPS is modulated by ZA. The expression of maturation markers was diminished with increasing ZA levels upon LPS activation. The migratory capacity, interleukin-12 secretion and generation of cytotoxic- T-cell responses were reduced at higher ZA levels. Increasing ZA concentrations downregulated nuclear factor-kappaB family members and interferon-regulatory factor (IRF)-3. Surprisingly, in immature moDCs, low ZA concentrations caused upregulation of RelB, c-Rel, IRF-3 and IRF-8. We conclude that ZA concentrations used to treat patients have inhibitory effects on DC activation. This might lead to immunosuppression or result in infectious complications.

TLR ligands differentially affect uptake and presentation of cellular antigens

Dendritic cells (DCs) have the unique ability to efficiently present T-cell epitopes from exogenous antigens on MHC class I molecules, a process called cross-presentation. In our study we demonstrate that stimulation of monocyte-derived DCs with Toll-like receptor (TLR) ligands differentially affects the uptake and cross-presentation of cellular antigens. Activation of DCs with TLR3 or TLR4 but not with TLR2 or TLR7/8 ligands inhibited phagocytosis of apoptotic tumor cells and resulted in a reduced cross-presentation of pp65-derived T-cell epitopes on MHC class I molecules upon engulfment of cytomegalovirus (CMV)–infected fibroblasts. These results have an important impact on the understanding of the interactions between the immune system and pathogens and the development of vaccination strategies to treat malignant diseases.

Proteasome inhibitors: antitumor effects and beyond

Proteasome inhibitors are emerging as effective drugs for the treatment of multiple myeloma and possibly certain subtypes of non-Hodgkin's lymphoma. Bortezomib (Velcade) is the first proteasome inhibitor proven to be clinically useful and will soon be followed by a second generation of small molecule inhibitors with improved pharmacological properties. Although it is now understood that certain types of malignancies have an exquisite dependence on a functional proteasome for their survival, the underlying reason(s) remain unclear as of now. In this context, addiction to nuclear factor-kappaB (NF-kappaB)-induced survival signals, activation of the unfolded protein response as well as a reduced proteasomal activity in differentiated plasma cells have all been proposed to justify proteasome inhibitors' activity in susceptible tissues. In addition to their anticancer properties, bortezomib and related drugs modulate inflammatory and immune responses by affecting function and survival of immune cells such as lymphocytes and dendritic cells. The present review offers an overview of the biological effects that have been involved in proteasome inhibitors' antitumor activity and suggests prospective future applications for these drugs based on their recently characterized anti-inflammatory and immunomodulatory effects.

Identification of RGS5 as a tumor-associated antigen expressed in a broad range of human malignancies and recognized by antigen specific cytotoxic T cells

2569

Background: Identification of tumor-associated antigens (TAA) have resulted in the development of therapeutic vaccines for the treatment of cancer. We applied an integrated functional genomics approach to identify TAA in malignant tissues of patients with renal cell carcinoma (RCC). Methods: A comparative DNA chip analysis of tumor and the corresponding non-malignant tissue from patients with RCC followed by sequencing of peptides bound to the HLA-class I molecules by mass spectrometry was applied to identify novel TAA in RCC. To confirm the immunogenicity of identified epitopes cytotoxic T lymphocytes (CTL) were generated using dendritic cells (DC). Results: RGS5 was found to be overexpressed in 16 of 29 analyzed RCC (5.7–29.9 fold) as compared to non-malignant renal tissue. Two peptides derived from RGS5 binding to either HLA-A*02 or 03 were identified. RGS5 was previously shown to be expressed in pericytes and promote tumor angiogenesis. Using RT-PCR analysis we found that RGS5 is expressed on a broad variety of tumor cells including RCC, colorectal, breast and ovarian cancer, malignant melanoma and multiple myeloma as well as in acute and chronic leukemias making this protein an interesting candidate for the development of vaccination strategies to target the tumor cells and the tumor vessels. CTL that were induced using the RGS5 peptides lysed autologous DC pulsed with the cognate peptide or transfected with in vitro transcribed RGS5 RNA as well as HLA-matched tumor cell lines. The specificity and HLA restriction was confirmed using blocking monoclonal antibodies and in cold-target inhibition assays. We next utilized DC transfected with RGS5 RNA to generate specific CTL. Using this approach we confirmed the processing and presentation of the identified peptides by malignant cells. These CTL lysed tumor cells in antigen specific manner while sparing non-malignant cells. In an ongoing vaccine trial RGS5 peptides could safely be given to RCC patients resulting in the induction of peptide specific CTL responses. Conclusions: Our results demonstrate that RGS5 is a novel tumor rejection antigen expressed in a wide range of malignancies that can be applied to target malignant cells and tumor angiogenesis.

[Table: see text]

BCR-ABL Is Not an Immunodominant Antigen in Chronic Myelogenous Leukemia

In the present study, we analyzed the involvement of the BCR-ABL protein in the induction of antigen-specific CTL in order to develop an immunotherapeutic approach in patients with chronic myelogenous leukemia (CML). To accomplish this, we generated dendritic cells (DC) in vitro and electroporated them with various sources of RNA harboring the chimeric bcr-abl transcript. These genetically engineered DCs were used as antigen-presenting cells for the induction of CTLs. By applying this approach, we found that the CTLs induced by DCs transfected with RNA extracted from bcr-abl-positive K-562 cells or CML blasts lysed DCs transfected with the corresponding RNA, but failed to recognize epitopes derived from the chimeric BCR-ABL fusion protein in (51)Cr-release assays. In contrast, they were able to lyse autologous DCs electroporated with RNA isolated from patients with acute myeloid leukemia, indicating that antigens shared among these malignant cells are involved and recognized by these CTLs. In patients with CML in complete cytogenetic remission during IFN-alpha treatment, we detected some reactivity of CD8(+) T cells against BCR-ABL in IFN-gamma ELISPOT assays, which was weaker as compared with proteinase 3 (PR3)- or prame-directed responses, suggesting that the BCR-ABL protein is less immunogenic as compared with other CML-derived antigens.

Epithelial-specific transcription factor ESE-3 is involved in the development of monocyte-derived DCs

Dendritic cells (DCs) are recognized as the most potent antigen-presenting cells of the immune system with the unique ability to initiate and maintain primary immune responses. In order to better characterize the functional and phenotypic features of DCs, a subtractive cDNA library to identify differentially expressed genes in monocyte-derived DCs (MDCs) was constructed. Using this approach, we found that the epithelial transcription factor ESE-3, which was previously shown to be exclusively expressed in cells of epithelial origin, is differentially expressed in MDCs. This was further confirmed by reverse transcriptase–polymerase chain reaction (RT-PCR) and Western blot analyses. The expression of ESE-3 is up-regulated upon maturation of MDCs and inhibited by treating the cells with IL-10 or IFN-γ. Knockdown experiments using siRNA suggest that ESE-3 plays an important role during MDC development. Our results might help to improve the phenotypic characterization of DCs and lead to a better understanding of the cellular mechanisms involved in antigen presentation and T-cell stimulation.

Proteasome inhibitor bortezomib modulates TLR4-induced dendritic cell activation

Evidence from the animal model suggests that proteasome inhibitors may have immunosuppressive properties; however, their effects on the human immune system remain poorly investigated. Here, we show that bortezomib, a proteasome inhibitor with anticancer activity, impairs several immune properties of human monocyte-derived dendritic cells (DCs). Namely, exposure of DCs to bortezomib reduces their phagocytic capacity, as shown by FITC-labeled dextran internalization and mannose-receptor CD206 down-regulation. DCs treated with bortezomib show skewed phenotypic maturation in response to stimuli of bacterial (lipopolysaccharide [LPS]) and endogenous sources (including TNF-alpha and CD40L), as well as reduced cytokine production and immunostimulatory capacity. LPS-induced CCL-2/MCP-1 and CCL5/RANTES secretions by DCs were prevented by DC treatment with bortezomib. Finally, CCR7 up-regulation in DCs exposed to LPS as well as migration toward CCL19/MIP-3beta were strongly impaired. As a suitable mechanism for these effects, bortezomib was found to down-regulate MyD88, an essential adaptor for TLR signaling, and to relieve LPS-induced activation of NF-kappaB, IRF-3, and IRF-8 and of the MAP kinase pathway. In summary, inhibition of DC function may represent a novel mechanism by which proteasome inhibitors exert immunomodulatory effects. These compounds could prove useful for tuning TLR signaling and for the treatment of inflammatory and immune-mediated disorders.

PPAR-γ agonists inhibit toll-like receptor-mediated activation of dendritic cells via the MAP kinase and NF-κB pathways

Dendritic cells (DCs) play an important role in initiating and maintaining primary immune responses. However, mechanisms involved in the resolution of these responses are elusive. We analyzed the effects of 15d-PGJ2 and the synthetic peroxisome proliferator-activated receptor (PPAR)-γ ligand troglitazone (TGZ) on the immunogenicity of human monocyte-derived DCs upon stimulation with toll-like receptor (TLR) ligands. Activation of PPAR-γ resulted in a reduced stimulation of DCs via the TLR ligands 2, 3, 4, and 7, characterized by down-regulation of costimulatory and adhesion molecules and reduced secretion of cytokines and chemokines involved in T-lymphocyte activation and recruitment. MCP-1 (monocyte chemotactic protein-1) production was increased due to PPAR-γ activation. Furthermore, TGZ-treated DCs showed a significantly reduced capacity to stimulate T-cell proliferation, emphasizing the inhibitory effect of PPAR-γ activation on TLR-induced DC maturation. Western blot analyses revealed that these inhibitory effects on TLR-induced DC activation were mediated via inhibition of the NF-κB and mitogen-activated protein (MAP) kinase pathways while not affecting the PI3 kinase/Akt signaling. Our data demonstrate that inhibition of the MAP kinase and NF-κB pathways is critically involved in the regulation of TLR and PPAR-γ-mediated signaling in DCs.

Cotransfection of dendritic cells with RNA coding for HER-2/neu and 4-1BBL increases the induction of tumor antigen specific cytotoxic T lymphocytes

Ribonucleic acid (RNA) transfection of dendritic cells (DCs) was shown to be highly efficient in eliciting CD8+ and CD4+ T-cell responses. We analyzed whether electroporation of DCs with RNA coding for a tumor-associated antigen (TAA) would elicit antigen-specific effector cytotoxic T lymphocyte (CTL) responses and whether these responses could be modulated by cotransfection with a second specific synthetic RNA. Therefore in vitro generated human monocyte-derived DCs were electroporated with in vitro transcribed RNA (in vitro transcript, IVT) encoding the TAA HER-2/neu. Additionally, these cells were cotransfected with IVT coding for human 4-1BBL. Transfection of DCs with 4-1BBL-IVT did not alter their typical phenotype. However, it increased the expression of the costimulatory molecules CD80 and CD40. Coadministration of HER-2/neu- and 4-1BBL-IVT resulted in an increased specific lysis of target cells by the in vitro induced CTL lines, indicating that 4-1BBL enhances their ability to elicit primary CTL responses. Interestingly, transfection of DCs with 4-1BBL-IVT did not augment their capacity to stimulate allogeneic lymphocyte responses. The here established approach of cotransfection of DCs with tumor-RNA and a second specific IVT could improve and optimize the in vitro manipulation of DCs for the induction of antigen-specific CTL responses.

Transfection of dendritic cells with in vitro-transcribed CMV RNA induces polyclonal CD8+- and CD4+-mediated CMV-specific T cell responses

Transfection of dendritic cells (DCs) with RNA was shown to be effective in the generation of antigen-specific T cells, probably due to the induction of a polyclonal T cell response directed against multiple antigens. To verify this assumption we used DCs, generated from cytomegalovirus (CMV)-negative or -positive donors, that were electroporated with in vitro-transcribed RNA (in vitro transcript, IVT) coding for the CMV pp65 antigen. We found that transfection of DCs with pp65 IVT induces an expansion of polyclonal CD8(+) T lymphocytes that recognize peptide antigens presented on different HLA molecules. These T lymphocytes are able to lyse DCs pulsed with pp65-derived peptides or transfected with the cognate IVT. Furthermore, this approach allowed the identification of immunodominant epitopes presented upon IVT transfection. Interestingly, transfection of DCs with pp65 IVT resulted in the induction of CD4(+)-specific T cells. Cotransfection of DCs with IVTs coding for the CMV antigens pp65 and IE1 elicited polyclonal T lymphocytes specific for peptides derived from both antigens. More importantly, cytotoxic T cells could be generated in two of three CMV-negative donors. Finally, functional CMV-specific autologous cytotoxic T lymphocytes were successfully generated from immunosuppressed patients after allogeneic hematopoietic stem cell transplantation.

CDCP1 identifies a broad spectrum of normal and malignant stem/progenitor cell subsets of hematopoietic and nonhematopoietic origin

CUB-domain-containing protein 1 (CDCP1) is a novel transmembrane molecule that is expressed in metastatic colon and breast tumors as well as on the surface of hematopoietic stem cells. In this study, we used multiparameter flow cytometry and antibodies against CDCP1 to analyze the expression of CDCP1 on defined hematopoietic cell subsets of different sources. In addition, CDCP1 expression on leukemic blasts and on cells with nonhematopoietic stem/progenitor cell phenotypes was determined. Here we demonstrate that a subset of bone marrow (BM), cord blood (CB), and mobilized peripheral blood (PB) CD34+ cells expressed this marker and that CDCP1 was detected on CD34(+)CD38- BM stem/progenitor cells but not on mature PB cells. Analysis of leukemic blasts from patients with acute lymphoblastic leukemia, acute myeloid leukemia, and chronic myeloid leukemia in blast crisis revealed that CDCP1 is predominantly expressed on CD34(+)CD133+ myeloid leukemic blasts. However, CDCP1 was not strictly correlated with CD34 and/or CD133 expression, suggesting that CDCP1 is a novel marker for leukemia diagnosis. Stimulation of CD34+ BM cells with CDCP1-reactive monoclonal antibody CUB1 resulted in an increased (approximately twofold) formation of erythroid colony-forming units, indicating that CDCP1 plays an important role in early hematopoiesis. Finally, we show that CDCP1 is also expressed on cells phenotypically identical to mesenchymal stem/progenitor cells (MSCs) and neural progenitor cells (NPCs). In conclusion, CDCP1 is not only a novel marker for immature hematopoietic progenitor cell subsets but also unique in its property to recognize cells with phenotypes reminiscent of MSC and NPC.

Effects of imatinib on monocyte-derived dendritic cells are mediated by inhibition of nuclear factor-kappaB and Akt signaling pathways

Dendritic cells are the most powerful antigen-presenting cells playing a decisive role for the initiation and maintenance of primary immune responses. However, signaling pathways involved in the differentiation of these cells have not been fully determined. Imatinib is a novel tyrosine kinase inhibitor effective against Abl kinases, c-Kit, and platelet-derived growth factor receptor. Using this compound, we show that human monocyte-derived dendritic cells generated in the presence of therapeutic concentrations of imatinib show a reduced expression of CD1a, MHC class I and II, and costimulatory molecules as well as decreased secretion of chemokines and cytokines resulting in an impaired capacity of dendritic cells to elicit primary T-cell responses. Using Western blot analyses, we found that these effects are mediated by inhibition of phosphatidylinositol 3-kinase/Akt pathways and a pronounced down-regulation of nuclear localized protein levels of nuclear factor-kappaB family members. Importantly, using blocking antibodies and tyrosine kinase inhibitors, we show that the inhibitory effects of imatinib on dendritic cell differentiation are not mediated via platelet-derived growth factor receptor and c-Kit. Taken together, our study reveals that imatinib inhibits dendritic cell differentiation and function via Akt and nuclear factor-kappaB signal transduction. Importantly, we show that imatinib can inhibit the function of normal, nonmalignant cells that may result in immunosuppression of these patients.

New developments in dendritic cell-based vaccinations: RNA translated into clinics

Dendritic cells (DCs) are the most powerful antigen-presenting cells that induce and maintain primary immune responses in vitro and in vivo. The development of protocols for the ex vivo generation of DCs provided a rationale for designing and developing DC-based vaccination studies for the treatment of infectious and malignant diseases. Recently, it was shown that DCs transfected with ribonucleic acid (RNA) coding for a tumour-associated antigen or whole tumour RNA are able to induce potent antigen and tumour-specific T-cell responses directed against multiple epitopes. The first RNA-transfected-DC-based clinical studies have shown that this form of vaccination is feasible and safe. In some cases, clinical responses were observed, but the preliminary data require further extensive investigations that should address the technical and biological problems of manipulating human DCs, as well as the development of standardised protocols and definitions of clinical settings.

RNA transfection of dendritic cells

Dendritic cells (DC) are the most powerful antigen-presenting cells that induce and maintain primary immune responses in vitro and in vivo. The development of protocols for the ex vivo generation of DC provided a rationale to design and develop DC-based vaccination studies for the treatment of infectious and malignant diseases. The efficacy of antigen loading and delivery into DC is pivotal for the optimal induction of T-cell-mediated immune responses. Recently it was shown that DC transfected with RNA coding for a tumor-associated antigen (TAA) or whole-tumor RNA are able to induce potent antigen- and tumor-specific T-cell responses directed against multiple epitopes. The latter technique does not require the definition of the TAA or HLA haplotype of the patients and has the potential of broad clinical application. Such a polyvalent vaccine might be able to reduce the probability of clonal tumor escape and to elicit CTL responses directed against naturally processed and presented immuno-dominant tumor antigens. Additional targeting of HLA class II restricted epitopes may further amplify and prolong the induced T-cell responses.

Processing and presentation of HLA class I and II epitopes by dendritic cells after transfection with in vitro-transcribed MUC1 RNA

RNA transfection of dendritic cells (DCs) was shown to be highly efficient in eliciting CD8+ and CD4+ T-cell responses. However, antigen presentation pathways involved in generation of human leukocyte antigen (HLA) class I and class II peptides have remained elusive. To analyze this we incubated mucin 1 (MUC1) RNA-transfected DCs with compounds known to inhibit HLA class I presentation and used these cells in chromium 51 (51Cr)-release assays. As effectors, we used cytotoxic T lymphocyte (CTL) lines specific for the MUC1 peptides M1.1 and M1.2. We observed that the presentation of HLA-A*02 epitopes is inhibited by brefeldin A and lactacystin. To determine the requirement of a functional transporter associated with antigen processing (TAP), we cotransfected DCs with MUC1 and infected cell peptide 47 (ICP47) RNA. ICP47 could only inhibit the presentation of the M1.1 but not the M1.2 peptide, indicating that this epitope derived from the signal sequence is presented independently of TAP. Cocultivation of MUC1 RNA-transfected DCs with MUC1-specific CD4+ T lymphocytes revealed that the presentation of HLA class II peptides is sensitive to proteasomal inhibitors and brefeldin A. Furthermore, the presentation pathway requires lysosomal and endosomal processing and is mediated by autophagy. Our results demonstrate that the efficient presentation of cytosolic proteins on major histocompatibility complex (MHC) class II combines the proteolytic and lysosomal pathways.

Rituximab consolidation after high-dose chemotherapy and autologous blood stem cell transplantation in follicular and mantle cell lymphoma: a prospective, multicenter phase II study

BACKGROUND

Patients with follicular (FL) or mantle cell lymphoma (MCL) are incurable with conventional therapy. We investigated the safety and efficacy of rituximab consolidation after autologous stem cell transplantation (ASCT) in order to prevent relapse by clearance of minimal residual disease (MRD).

METHODS

Rituximab was given approximately 8 weeks after CD34+ cell enriched ASCT at 375 mg/m2, weekly for 4 weeks. Monitoring of MRD was performed by repetitive PCR analyses.

RESULTS

Thirty-one patients were included; one died early after ASCT before rituximab administration. Thirty patients (20 FL, 10 MCL) were evaluable after rituximab consolidation, and 27 of these were assessable for MRD detection. Rituximab consolidation post-ASCT was safe, the most common toxicity being infection. At a median follow-up of 42 months (range 13-96) after ASCT, 25 patients were censored with an actuarial event-free survival (EFS) of 81% at 4 and 5 years. Four patients (two FL, two MCL) relapsed, and one additional MCL patient died unexpectedly in complete remission. PCR-negativity was observed in 22% of the patients before ASCT, 53% post-ASCT (P=0.0547), 72% after rituximab (P=0.0018) and 100% at 6 months post-transplant (P < 0.001).

CONCLUSIONS

One single course of rituximab consolidation given after ASCT is safe, may help to eliminate MRD and may translate into improved EFS in both FL and MCL patients.

Identification of C-Met Oncogene as a Broadly Expressed Tumor-Associated Antigen Recognized by Cytotoxic T-Lymphocytes

PURPOSE

C-Met proto-oncogene is a receptor tyrosine kinase that mediates the oncogenic activities of the hepatocyte growth factor. Using a DNA chip analysis of tumor samples from patients with renal cell carcinoma and sequencing of peptides bound to the HLA-A*0201 molecules on tumor cells a peptide derived from the c-Met protein was identified recently.

EXPERIMENTAL DESIGN

We used this novel HLA-A*0201 peptide for the induction of specific CTLs to analyze the presentation of this epitope by malignant cells.

RESULTS

The induced CTL efficiently lysed target cells pulsed with the cognate peptide, as well as HLA-A*0201-matched tumor cell lines in an antigen-specific and HLA-restricted manner. Furthermore, the induced c-Met-specific CTLs recognized autologous dendritic cells (DCs) pulsed with the peptide or transfected with whole-tumor mRNA purified from c-Met-expressing cell lines. We next induced c-Met-specific CTLs using peripheral blood mononuclear cells and DC from an HLA-A*0201-positive patient with plasma cell leukemia to determine the recognition of primary autologous malignant cells. These CTLs lysed malignant plasma cells while sparing nonmalignant B- and T-lymphocytes, monocytes, and DCs.

CONCLUSION

Our results demonstrate that c-Met oncogene is a novel tumor rejection antigen recognized by CTL and expressed on a broad variety of epithelial and hematopoietic malignant cells.

Cyclopentenone prostaglandins induce lymphocyte apoptosis by activating the mitochondrial apoptosis pathway independent of external death receptor signaling

15-Deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) is a naturally occurring cyclopentenone metabolite of PGD(2) that possesses both peroxisome proliferator-activated receptor gamma (PPAR-gamma)-dependent and PPAR-gamma-independent anti-inflammatory properties. Recent studies suggest that cyclopentenone PGs may play a role in the down-regulation of inflammation-induced immune responses. In this study, we report that 15d-PGJ(2) as well as synthetic PPAR-gamma agonists inhibit lymphocyte proliferation. However, only 15d-PGJ(2), but not the specific PPAR-gamma activators, induce lymphocyte apoptosis. We found that blocking of the death receptor pathway in Fas-associated death domain(-/-) or caspase-8(-/-) Jurkat T cells has no effect on apoptosis induction by 15d-PGJ(2). Conversely, overexpression of Bcl-2 or Bcl-x(L) completely inhibits the initiation of apoptosis, indicating that 15d-PGJ(2)-mediated apoptosis involves activation of the mitochondrial pathway. In line with these results, 15d-PGJ(2) induces mitochondria disassemblage as demonstrated by dissipation of mitochondrial transmembrane potential (Deltapsi(m)) and cytochrome c release. Both of these events are partially inhibited by the broad spectrum caspase inhibitor benzyloxycarbonil-Val-Ala-Asp-fluoromethylketone, suggesting that caspase activation may amplify the mitochondrial alterations initiated by 15d-PGJ(2). We also demonstrate that 15d-PGJ(2) potently stimulates reactive oxygen species production in Jurkat T cells, and Deltapsi(m) loss induced by 15d-PGJ(2) is prevented by the reactive oxygen species scavenger N-acetyl-L-cysteine. In conclusion, our data indicate that cyclopentenone PGs like 15d-PGJ(2) may modulate immune responses even independent of PPAR-gamma by activating the mitochondrial apoptosis pathway in lymphocytes in the absence of external death receptor signaling.

Induction of Adipophilin-Specific Cytotoxic T Lymphocytes Using a Novel HLA-A2-Binding Peptide That Mediates Tumor Cell Lysis

Identification of tumor-associated antigens and advances in tumor immunology resulted in the development of vaccination strategies to treat patients with malignant diseases. Using a novel approach that combines DNA chip analysis of tumor samples with isolation of peptides on the surface of tumor cells, a HLA-A*0201-binding peptide derived from the adipophilin protein was identified. Adipophilin is involved in lipid storage and was thought to be expressed only in adipocytes, but it can be found in other cell types such as macrophages or tumor cells. In the present study, we analyzed the possible use of this peptide as a T-cell epitope presented by malignant cells. To accomplish this, we induced CTL responses using this HLA-A*0201-binding peptide. The in vitro-induced CTLs efficiently lysed cells pulsed with the adipophilin peptide and HLA-matched tumor cell lines in an antigen-specific and HLA-restricted manner. Finally, the induced CTLs recognized autologous dendritic cells (DCs) pulsed with the antigenic peptide or transfected with tumor RNA purified from an adipophilin-expressing tumor cell line. To further analyze the possible use of this peptide in immunotherapies of human malignancies, we induced adipophilin-specific CTLs using peripheral blood mononuclear cells and DCs from HLA-A*0201-positive patients with chronic lymphatic leukemia and plasma cell leukemia. The in vitro-generated CTLs recognized autologous chronic lymphatic leukemia cells and malignant plasma cells, whereas they spared nonmalignant resting or activated B and T lymphocytes, monocytes, or DCs. Our results demonstrate that this peptide might represent an interesting candidate for the development of cancer vaccines designed to target adipophilin-derived epitopes in a wide range of malignancies.

Induction of chronic lymphocytic leukemia (CLL)-specific CD4- and CD8-mediated T-cell responses using RNA-transfected dendritic cells

Recently, it was demonstrated that transfection of dendritic cells (DCs) with tumor-derived RNA can elicit effective T-cell responses. This technique does not require the definition of the tumor antigen or HLA haplotype of the patients. We applied this approach to induce HLA class I- and class II-restricted T-cell responses directed against malignant cells from patients with chronic lymphocytic leukemia (B-CLL). Here, we show that DCs generated from monocytes of patients with B-CLL induce leukemia-specific cytotoxic and proliferative T-cell responses on transfection with total RNA isolated from autologous leukemic B lymphocytes. Standard 51Cr-release assays showed specific major histocompatibility complex (MHC) class I-restricted cytotoxic activity against the autologous leukemic B cells and DCs transfected with CLL-RNA, whereas nonmalignant B cells were spared. The specificity of the cytotoxic T-lymphocyte (CTL) response was confirmed using cold target inhibition assays and by blocking HLA class I molecules. Furthermore, we established a protocol for the amplification of whole B-CLL mRNA. The use of DCs transfected with in vitro amplified B-CLL mRNA elicited specific T-cell responses similar to the results obtained with native mRNA. These data suggest that vaccinations using DCs transfected with RNA might be a potent new strategy in the treatment of CLL.

Imatinib mesylate affects the development and function of dendritic cells generated from CD34+ peripheral blood progenitor cells

Imatinib mesylate (STI571) is a competitive Bcr-Abl tyrosine kinase inhibitor and has yielded encouraging results in treatment of chronic myelogenous leukemia (CML) and gastrointestinal stroma tumors (GISTs). Apart from inhibition of the Abl protein tyrosine kinases, it also shows activity against platelet-derived growth factor receptor (PDGF-R), c-Kit, Abl-related gene (ARG), and their fusion proteins while sparing other kinases. In vitro studies have revealed that imatinib mesylate can inhibit growth of cell lines and primitive malignant progenitor cells in CML expressing Bcr-Abl. However, little is known about the effects of imatinib mesylate on nonmalignant hematopoietic cells. In the current study we demonstrate that in vitro exposure of mobilized human CD34+ progenitors to therapeutic concentrations of imatinib mesylate (1-5 microM) inhibits their differentiation into dendritic cells (DCs). DCs obtained after 10 to 16 days of culture in the presence of imatinib mesylate showed concentration-dependent reduced expression levels of CD1a and costimulatory molecules such as CD80 and CD40. Furthermore, exposure to imatinib mesylate inhibited the induction of primary cytotoxic T-lymphocyte (CTL) responses. The inhibitory effects of imatinib mesylate were accompanied by down-regulation of nuclear localized RelB protein. Our results demonstrate that imatinib mesylate can act on normal hematopoietic cells and inhibits the differentiation and function of DCs, which is in part mediated via the nuclear factor kappaB signal transduction pathway.

Expression of her-2/neu on acute lymphoblastic leukemias: implications for the development of immunotherapeutic approaches

Her-2/neu is a tumor-associated antigen that is expressed on several adenocarcinomas and correlates with poor prognosis. In a previous study (H. J. Bühring et al., Blood, 86: 1916-1923, 1995), it has been demonstrated that Her-2/neu expression can be detected on blast cells from patients with hematological malignancies including acute lymphoblastic leukemia (ALL). Here, we show that Her-2/neu-specific CTLs induced in vitro using peptide-pulsed dendritic cells efficiently lyse primary ALL blasts constitutively expressing both Her-2/neu and human leukocyte antigen A2 in an antigen-specific and MHC-restricted manner. Furthermore, we analyzed the feasibility of this approach in an autologous setting and induced Her-2/neu-specific CTLs using dendritic cells generated from peripheral blood mononuclear cells from an ALL patient that were pulsed with peptides or transfected with in vitro-transcribed Her-2/neu mRNA. Our data demonstrate that Her-2/neu could be used as a potential target for the application of Her-2/neu-directed treatment strategies in ALL including vaccination approaches.

Survivin is a shared tumor-associated antigen expressed in a broad variety of malignancies and recognized by specific cytotoxic T cells

Survivin, a member of the inhibitor of apoptosis protein family, is expressed in almost all types of malignancies, making this protein a useful tool for the development of broadly applicable vaccination therapies. We used a recently identified HLA-A2 binding peptide and dendritic cells (DCs) from healthy donors to induce survivin-specific cytotoxic T lymphocytes (CTLs) in vitro. These T cells efficiently lysed target cells pulsed with the cognate peptide. Furthermore, survivin-specific CTLs recognized HLA-A2-matched tumor cell lines and primary malignant cells from patients with leukemia in an antigen-specific and HLA-restricted manner as demonstrated with the use of cold target inhibition assays and blocking antibodies. To validate the immunogenicity of survivin we performed the experiments in an autologous setting and used monocyte-derived DCs as targets. Interestingly, we found that DCs up-regulate survivin expression on stimulation with tumor necrosis factor alpha (TNF-alpha). However, these mature DCs were not recognized by survivin-specific CTLs, whereas they lysed autologous mature DCs pulsed with the antigenic peptide or transfected with whole tumor RNA purified from a survivin-expressing cell line. To further analyze the possible use of survivin-specific CTLs in cancer therapies, we induced survivin-specific CTLs using peripheral blood mononuclear cells (PBMNCs) and DCs from a patient with chronic lymphocytic leukemia (CLL). The in vitro-generated T cells efficiently recognized autologous malignant CLL cells, whereas they spared autologous-purified nonmalignant B cells or DCs. Our results demonstrate that survivin epitopes are presented on a broad variety of malignancies and can be applied in vaccination therapies.

Transfection of dendritic cells with RNA induces CD4- and CD8-mediated T cell immunity against breast carcinomas and reveals the immunodominance of presented T cell epitopes

Transfection of dendritic cells (DC) with tumor-derived RNA has recently been shown to elicit tumor-specific CTL capable of recognizing and lysing a variety of tumor cells. In our study we analyzed the induction of HLA class I- and II-restricted T cell responses against MCF-7 breast cancer cells. Using this approach we were able to elicit CD4- and CD8-mediated antitumor responses. The CTL specifically lysed MCF-7 cells and DC electroporated with MCF-7 RNA, but spared control cell lines. The specificity of the cytotoxic activity was confirmed in cold target inhibition assays and using mAbs blocking HLA class I molecules. Interestingly, these polyclonal cytotoxic T cells recognized selectively two epitopes derived from the MUC1 and Her-2/neu tumor Ags. The induced Th cells were found to be entirely HLA class II restricted and showed a significant cross-reactivity to a renal cell carcinoma cell line, similar to the results obtained with cytotoxic T cells.

Dendritic cells transfected with tumor RNA for the induction of antitumor CTL in colorectal cancer

Dendritic cells (DC) are the most potent antigen-presenting cells known, currently tested for vaccination studies in cancer patients. The use of tumor-derived RNA to load DC overcomes the requirement of defined HLA types and the identification of tumor antigens expressed by the tumors. Here, we show that human monocyte-derived DC generated under serum-free conditions by GM-CSF, IL-4 and TNF-alpha acquire a mature phenotype and expression of the chemokine receptor CCR-7, which plays a pivotal role in DC migration to the afferent lymph nodes. We demonstrate the feasibility of total RNA transfection into such DC using the renal cell carcinoma (RCC) cell line N43-EGFP, which was stably transfected with an EGFP-encoding vector. Moreover, we show that DC transfected with RNA from colorectal cancer cells present HLA class I-restricted antigenic epitopes to induce a primary antitumor CTL response in vitro. Interestingly, the CTL induced by SW480 RNA also recognized another colon cancer line, HCT116, and the RCC line A498. Our results confirm the feasibility of total RNA transfection of serum-free generated DC for the induction of CTL against colon cancer and RCC cells, and support the relevance of shared tumor rejection epitopes between colorectal cancer and RCC.

Delivery of tumor-derived RNA for the induction of cytotoxic T-lymphocytes

Dendritic cells (DC) are professional antigen-presenting cells playing a central role in the induction of antigen-specific cytotoxic T-lymphocytes (CTL). We analyzed the efficiency of tumor RNA transfection into DC using different sources of RNA as well as delivery strategies including electroporation, lipofection and CD71-receptor-based delivery. To evaluate the sensitivity of these approaches, we utilized in vitro transcribed enhanced green fluorescence protein (EGFP)-RNA and whole tumor RNA from EGFP-transfected renal cell carcinoma cell line N43. We demonstrate that electroporation was the most effective way yielding about 30% EGFP positive cells while less than 1% of DC expressed EGFP using the transferrin receptor transfection system. Delivery of RNA with liposomes resulted in 17.5% of EGFP positive cells depending on the RNA amount. However, when these approaches were applied to transduce DC with RNA derived from the A498 cell line for T-cell priming, tumor-specific CTL could be induced using all delivery strategies suggesting that this technology has the potential to induce cytotoxic T-cell response even when low level of antigen is delivered. Furthermore, we demonstrate that amplification of whole tumor messenger RNA (mRNA) as well as the use of total instead of purified mRNA can be utilized for stimulating tumor-specific CTL responses.