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

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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.

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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.