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

Dendritic Cell Vaccines: A Shift from Conventional Approach to New Generations

In the emerging era of cancer immunotherapy, immune checkpoint blockades (ICBs) and adoptive cell transfer therapies (ACTs) have gained significant attention. However, their therapeutic efficacies are limited due to the presence of cold type tumors, immunosuppressive tumor microenvironment, and immune-related side effects. On the other hand, dendritic cell (DC)-based vaccines have been suggested as a new cancer immunotherapy regimen that can address the limitations encountered by ICBs and ACTs. Despite the success of the first generation of DC-based vaccines, represented by the first FDA-approved DC-based therapeutic cancer vaccine Provenge, several challenges remain unsolved. Therefore, new DC vaccine strategies have been actively investigated. This review addresses the limitations of the currently most adopted classical DC vaccine and evaluates new generations of DC vaccines in detail, including biomaterial-based, immunogenic cell death-inducing, mRNA-pulsed, DC small extracellular vesicle (sEV)-based, and tumor sEV-based DC vaccines. These innovative DC vaccines are envisioned to provide a significant breakthrough in cancer immunotherapy landscape and are expected to be supported by further preclinical and clinical studies.

Dendritic Cells in Anticancer Vaccination: Rationale for Ex Vivo Loading or In Vivo Targeting

Dendritic cells (DCs) have shown great potential as a component or target in the landscape of cancer immunotherapy. Different in vivo and ex vivo strategies of DC vaccine generation with different outcomes have been proposed. Numerous clinical trials have demonstrated their efficacy and safety in cancer patients. However, there is no consensus regarding which DC-based vaccine generation method is preferable. A problem of result comparison between trials in which different DC-loading or -targeting approaches have been applied remains. The employment of different DC generation and maturation methods, antigens and administration routes from trial to trial also limits the objective comparison of DC vaccines. In the present review, we discuss different methods of DC vaccine generation. We conclude that standardized trial designs, treatment settings and outcome assessment criteria will help to determine which DC vaccine generation approach should be applied in certain cancer cases. This will result in a reduction in alternatives in the selection of preferable DC-based vaccine tactics in patient. Moreover, it has become clear that the application of a DC vaccine alone is not sufficient and combination immunotherapy with recent advances, such as immune checkpoint inhibitors, should be employed to achieve a better clinical response and outcome.

NPM-ALK-reactive T-cell responses in children and adolescents with NPM-ALK positive anaplastic large cell lymphoma

The oncoantigen nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) induces cellular and humoral immune responses in patients with NPM-ALK-positive anaplastic large cell lymphoma (ALCL). We characterize the NPM-ALK-specific T-cell responses in a cohort of pediatric and adolescent ALCL-patients in remission without Human Leucocyte Antigen (HLA)-preselection.

First, we assessed NPM-ALK-reactive T-cell responses and their HLA-class I restriction in patients by using dendritic cells (DCs) transfected with in vitro transcribed (IVT) NPM-ALK-RNA for CD8 (n = 20) or CD3 (n = 9) T-cell stimulation. NPM-ALK-specific T-cells were detected in twelve of 29 patients (nine of 20 with CD8-selected and three of nine with CD3-selected cells). Recognition of NPM-ALK was restricted by HLA-C alleles in six of eight, and by HLA-B alleles in four of eight analyzed patients. No NPM-ALK-reactivity was detected in 20 healthy individuals.

Second, in order to define possible immunogenic NPM-ALK-epitope regions, DCs pulsed with pools of overlapping long NPM-ALK-peptides were used to stimulate T-cells in further 22 patients and ten controls. Responsive T-cells were detected in 15 patients and in five controls. A peptide pool located in the middle of the kinase domain induced ALK-reactive T-cells in 14 of 15 responsive patients. We could narrow to single peptides between p327-p370 of NPM-ALK in four patients.

In conclusion, using IVT-RNA, 40% of NPM-ALK-positive ALCL-patients in remission had detectable NPM-ALK-specific T-cell responses which were mainly restricted by HLA-B and -C alleles. Peptide stimulation of T-cells revealed responses in almost 70% of patients and allowed describing an immunogenic region located in the ALK-kinase domain.

An autologous tumor vaccine for CLL

Chronic Lymphocytic Leukemia B cells (CLL) are malignant cells which retain at least some functions of normal B cells. Paramount amongst the latter is that when such cells are appropriately stimulated, they are able to present antigens, including any potential tumor antigens, making them excellent choices as a candidate tumor vaccine. We show that following stimulation of CLL cells with Phorbol myristic acetate, IL-2, the TLR7 agonist imiquimod (P2I) and ionomycin (P2Iio), markedly increased expression of CD54 and CD83 was seen, indicative of B cell activation and a transition to antigen-presenting cells. However, this occurred in the context of augmented expression of the known immunoregulatory molecule, CD200. Accordingly we explored the effect of stimulation of CLL cells with P2Iio, followed by coating of cells with a non-depleting anti-CD200mAb, on the ability of those cells to immunize PBL in vitro to become cytotoxic to CLL cells, or to protect NOD-SCIDγc^null (NSG) mice from subsequent CLL tumor challenge. Our data indicate that this protocol is effective in inducing CD8⁺ CTL able to lyse CLL cells in vitro, and decrease tumor burden in vivo in spleen and marrow of mice injected with CLL cells. Pre-treatment of mice with a CD8 depleting antibody before vaccination with P2Iio/anti-CD200 coated cells abolished any protection seen. These data suggest a potential role for blockade of CD200 expression on CLL cells as a component of a tumor vaccination strategy.

Hematologic neoplasms: Dendritic cells vaccines in motion

Dendritic cells (DCs) are bone-marrow-derived immune cells accounted for a key role in cancer vaccination as potent antigen-presenting cells within the immune system. Cancer microenvironment can modulate DCs maturation resulting in their accumulation into functional states associated with a reduced antitumor immune response. In this regard, a successful cancer vaccine needs to mount a potent antitumor immune response able to overcome the immunosuppressive tumor milieu. As a consequence, DCs-based approaches are a safe and promising strategy for improving the therapeutic efficacy in hematological malignancies, particularly in combinations with additional treatments. This review summarizes the most significant evidence about the immunotherapeutic strategies performed to target hematologic neoplasms including the tumoral associated antigens (TAA) pulsed on DCs, whole tumor cell vaccines or leukemia-derived DCs.

Dendritic cell-based immunotherapy

Immunotherapy using dendritic cell (DC)-based vaccination is an approved approach for harnessing the potential of a patient's own immune system to eliminate tumor cells in metastatic hormone-refractory cancer. Overall, although many DC vaccines have been tested in the clinic and proven to be immunogenic, and in some cases associated with clinical outcome, there remains no consensus on how to manufacture DC vaccines. In this review we will discuss what has been learned thus far about human DC biology from clinical studies, and how current approaches to apply DC vaccines in the clinic could be improved to enhance anti-tumor immunity.

Dendritic Cell Vaccines

Exploitation of the patient's own immune system to induce antitumor immune responses using dendritic cell (DC) immunotherapy has been established in early clinical trials as a safe and promising therapeutic approach for cancer. However, their limited success in larger clinical trials highlights the need to optimize DC vaccine preparations. This chapter describes the methodologies utilized for the preparation of the DC vaccine most commonly used in clinical trials. Optional variations at different stages in DC vaccine preparation, based on the nature of antigen, delivery of antigen, maturation stimuli, and mode of administration for DC vaccines, are also presented for consideration as these are often dependent on the disease setting, desired immune response, and/or resources available.

Pluripotent state induction in mouse embryonic fibroblast using mRNAs of reprogramming factors

Reprogramming of somatic cells has great potential to provide therapeutic treatments for a number of diseases as well as provide insight into mechanisms underlying early embryonic development. Improvement of induced Pluripotent Stem Cells (iPSCs) generation through mRNA-based methods is currently an area of intense research. This approach provides a number of advantages over previously used methods such as DNA integration and insertional mutagenesis. Using transfection of specifically synthesized mRNAs of various pluripotency factors, we generated iPSCs from mouse embryonic fibroblast (MEF) cells. The genetic, epigenetic and functional properties of the iPSCs were evaluated at different times during the reprogramming process. We successfully introduced synthesized mRNAs, which localized correctly inside the cells and exhibited efficient and stable translation into proteins. Our work demonstrated a robust up-regulation and a gradual promoter de-methylation of the pluripotency markers, including non-transfected factors such as Nanog, SSEA-1 (stage-specific embryonic antigen 1) and Rex-1 (ZFP-42, zinc finger protein 42). Using embryonic stem cells (ESCs) conditions to culture the iPS cells resulted in formation of ES-like colonies after approximately 12 days with only five daily repeated transfections. The colonies were positive for alkaline phosphatase and pluripotency-specific markers associated with ESCs. This study revealed the ability of pluripotency induction and generation of mouse mRNA induced pluripotent stem cells (mRNA iPSCs) using transfection of specifically synthesized mRNAs of various pluripotency factors into mouse embryonic fibroblast (MEF) cells. These generated iPSCs exhibited molecular and functional properties similar to ESCs, which indicate that this method is an efficient and viable alternative to ESCs and can be used for further biological, developmental and therapeutic investigations.

HLA-DRB1*0410-Restricted Recognition of XAGE-1b37-48 Peptide by CD4 T Cells

XAGE-1b belongs to cancer/testis (CT) antigens, and has been shown to be expressed frequently in lung cancers and to elicit an antibody response in patients with XAGE-1b-expressing tumors. In this study, we investigated an XAGE-1b peptide recognized by CD4 T cells. CD4 T cells were purified from PBMC of a healthy donor and stimulated with pooled 25-mer peptides overlapped with 15 amino acids spanning the entire XAGE-1b protein. The generation of XAGE-1b-specific CD4 T cells was shown by IFNgamma secretion assay. A CD4 T cell clone OHD1 was obtained by limiting dilution. OHD1 recognized two overlapping peptides, XAGE1-b(33-49) and XAGE-1b(37-52), by ELISPOT assay. A peptide XAGE-1b(38-46) which was included in both XAGE-1b(33-49) and XAGE-1b(37-52) was predicted to be a DRB1*0410-restricted 9-mer peptide by a computer-based program. We identified the 12-mer peptide XAGE-1b(37-48) as a new XAGE-1b epitope restricted to HLA-DRB1*0410.

Dendritic cell immunotherapy in ovarian cancer

Ovarian cancer is one of the most frequent gynecological malignancies. However, as there is no effective screening method to detect early disease, it is usually only diagnosed when already widespread in the abdomen. The majority of patients diagnosed with advanced-stage disease will relapse and require additional therapy. In the search for additional effective treatments for the management of recurrent disease, researchers have focused on the potential usefulness of immunotherapeutic modulation by administering autologous immune cells, such as dendritic cells (DCs), to stimulate antitumor host responses. With the ultimate goal of improved survival, this review addresses mechanisms in ovarian cancer that may limit the expansion of antitumor immunity, discusses the parameters to be considered for optimal DC immunotherapy, outlines evaluation methodology used to monitor the success of treatment regimens and reviews reported DC immunotherapy trials in ovarian cancer.

Increased cytotoxic capacity of tumor antigen specific human T cells after in vitro stimulation with IL21 producing dendritic cells

Monocyte derived dendritic cells (moDC) electroporated with tumor associated antigen derived mRNA can elicit specific T cells against tumor cells in vivo. IL21 has been shown to enhance activation and cytotoxicity in CD8+ T cells. We therefore investigated in vitro effects on human CD8+ T-cells after stimulation with IL21 mRNA electroporated moDC. Codon modification of the IL21 gene significantly enhanced IL21 production upon electroporation of moDC. Tumor associated antigen specific CTL induction efficiency was significantly enhanced when codon modified IL21 mRNA was co-electroporated with tumor associated antigen mRNA. Tumor associated antigen specific T cells induced by codon modified IL21-DC demonstrated increased cytotoxic capacity and killing compared to control cultures. In conclusion, ectopic expression of codon modified IL21 by moDC enhances the priming efficiency of the DC as well as the cytotoxic potential of the induced CTL.

Immunomodulatory drugs and active immunotherapy for chronic lymphocytic leukemia

BACKGROUND

The last decade witnessed the emergence of several therapeutic options for patients with chronic lymphocytic leukemia (CLL) for first-line and relapsed settings. The vast majority of patients with relapsed or refractory CLL carry poor prognostic features, which are strong predictors of shorter overall survival and resistance to first-line treatment, particularly fludarabine-based regimens.

METHODS

This article highlights the current role of immunomodulatory drugs (IMiDs) and active immunotherapy as treatment options for this select group. The rationale of using IMiDs is discussed from the perspective of lenalidomide as a novel active agent. Relevant clinical trials using IMiDs alone or in combinations are discussed. New immunotherapeutic experimental approaches are also described.

RESULTS

As a single agent, lenalidomide offers an overall response rate of 32% to 47% in patients with relapsed/refractory disease. Recent studies have shown promising activity as a single agent in treatment-naive patients. The combination of lenalidomide with immunotherapy (rituximab and ofatumumab) has also shown clinical responses. Encouraging preclinical and early clinical data have been observed with different immunotherapeutic approaches.

CONCLUSIONS

The use of IMiDs alone or in combination with immunotherapy represents a treatment option for relapsed/refractory or treatment-naive patients. Mature data and further studies are needed to validate overall and progression-free survival. The toxicity profile of lenalidomide might limit its use and delay further studies. Immunotherapy offers another potential alternative, but further understanding of the immunogenicity of CLL cells and the mechanisms of tumor fl are reaction is needed to improve the outcomes in this field.

The characterization and role of leukemia cell-derived dendritic cells in immunotherapy for leukemic diseases

Usually, an effective anti-leukemia immune response cannot be initiated effectively in patients with leukemia. This is probably related to immunosuppression due to chemotherapy, down-regulation of major histocompatibility complex (MHC) II molecules, and the lack of co-stimulatory molecules on dendritic cells (DC). In light of this problem, some methods had been used to induce leukemia cells to differentiate into mature DCs, causing them to present leukemia-associated antigens and activating naïve T cells. Furthermore, leukemia-derived DCs could be modified with tumor antigens or tumor-associated antigens to provide a new approach to anti-leukemia therapy. Numerous studies have indicated factors related to the induction and functioning of leukemia-derived DCs and the activation of cytotoxic T-lymphocytes (CTLs). These include the amount of purified DCs, cytokine profiles appropriate for inducing leukemia-derived DCs, effective methods of activating CTLs, reasonable approaches to DC vaccines, and the standardization of their clinical use. Determining these factors could lead to more effective leukemia treatment and benefit both mankind and scientific development. What follows in a review of advances in and practices of inducing leukemia-derived DCs and the feasibility of their clinical use.

Tumour-loaded α-type 1-polarized dendritic cells from patients with chronic lymphocytic leukaemia produce a superior NK-, NKT- and CD8+ T cell-attracting chemokine profile

Tumour-loaded dendritic cells (DCs) from patients with chronic lymphocytic leukaemia (CLL) matured using an α-type 1-polarized DC cocktail (IL-1β/TNF-α/IFN-α/IFN-γ/poly-I:C;αDC1) were recently shown to induce more functional CD8(+) T cells against autologous tumour cells in vitro than DCs matured with the 'standard' cocktail (IL-1β/TNF-α/IL-6/PGE(2) ;PGE(2) DCs). However, the ability of vaccine DCs to induce a type 1-polarized immune response in vivo probably relies on additional features, including their ability to induce a CXCR3-dependent recruitment of NK cells into vaccine-draining lymph nodes. Moreover, their guiding of rare tumour-specific CD8(+) T cells to sites of DC-CD4(+) T cell interactions by secretion of CCL3 and CCL4 is needed. We therefore analysed the chemokine profile and the lymphocyte-attracting ability in vitro of monocyte-derived PGE(2) DCs and αDC1s from patients with CLL. αDC1s produced much higher levels of CXCR3 ligands (CXCL9/CXCL10/CXCL11) than PGE(2) DCs. Functional studies further demonstrated that αDC1s were superior recruiters of both NK and NKT cells. Moreover, αDC1s produced higher levels of CCL3/CCL4 upon CD40 ligation. These findings suggest that functional αDC1s, derived from patients with CLL, produce a desirable NK-, NKT- and CD8(+) T cell-attracting chemokine profile which may favour a guided and Th1-deviated priming of CD8(+) T cells, supporting the idea that αDC1-based vaccines have a higher immunotherapeutic potential than PGE(2) DCs.

Intradermal vaccinations with RNA coding for TAA generate CD8+ and CD4+ immune responses and induce clinical benefit in vaccinated patients

The aim of this phase I/II nonrandomized trial was to assess feasibility, safety as well as immunological and clinical responses of a mRNA-based vaccination in patients with stage IV renal cell cancer using granulocyte-macrophage colony stimulating factor (GM-CSF) as adjuvant. Intradermal injections of in vitro transcribed naked mRNA, which was generated using plasmids coding for the tumor-associated antigens mucin 1(MUC1), carcinoembryonic (CEA), human epidermal growth factor receptor 2 (Her-2/neu), telomerase, survivin, and melanoma-associated antigen 1 (MAGE-A1) were performed in 30 enrolled patients. In the first 14 patients (cohort A) vaccinations were administered on days 0, 14, 28, and 42 (20 µg/antigen) while in the consecutive 16 patients (cohort B) an intensified protocol consisting of injections at days 0-3, 7-10, 28, and 42 (50 µg/antigen) was used. In both cohorts, after this induction period, vaccinations were repeated monthly until tumor progression analyzed by Response Evaluation Criteria In Solid Tumors criteria (RECIST). Vaccinations were well tolerated with no severe side effects and induced clinical responses [six stable diseases (SD) and one partial response in cohort A and nine SD in cohort B]. In cohort A, 35.7% survived 4 years (median survival 24 months) compared to 31.25% in cohort B (median survival 29 months). Induction of CD4(+) and CD8(+) T cell responses was shown for several tumor-associated antigens (TAA) using interferon-γ (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) and Cr-release assays.

Directing dendritic cell immunotherapy towards successful cancer treatment

The use of dendritic cells (DCs) for tumor immunotherapy represents a powerful approach for harnessing the patient's own immune system to eliminate tumor cells. However, suboptimal conditions for generating potent immunostimulatory DCs, as well as the induction of tolerance and suppression mediated by the tumors and its microenvironment have contributed to limited success. Combining DC vaccines with new approaches that enhance immunogenicity and overcome the regulatory mechanisms underlying peripheral tolerance may be the key to achieving effective and durable anti-tumor immune responses that translate to better clinical outcomes.

Toll-like receptor 9 signaling by CpG-B oligodeoxynucleotides induces an apoptotic pathway in human chronic lymphocytic leukemia B cells

Chronic lymphocytic leukemia (CLL) is the most prevalent human leukemia and is characterized by the progressive accumulation of long-lived malignant B cells. Here we show that human B-CLL cells selectively express high levels of Toll-like receptor 9 (TLR9) mRNA and proteins. Treating B-CLL cells with TLR9 agonists, type B CpG oligodeoxynucleotides (CpG-B ODNs), induces significant morphologic and phenotypic activation, altered cytokine production, reversal of signal transducer, and activator of transcription 1 (STAT1) phosphorylation state, followed by profound apoptosis of B-CLL cells that is CpG-B ODN treatment time- and dose-dependent. TLR9-CpG ODN ligation-induced apoptosis of B-CLL cells is confirmed by viable cell counts, annexin V/propidium iodide and tetramethyl-rhodamine ethylester staining, Western blots of the activation, and cleaved caspases and poly (ADP-ribose) polymerase. Triggering TLR9 by CpG-B ODN leads to nuclear factor-kappaB-dependent production of autocrine interleukin-10, which activates JAK/STAT pathway-dependent tyrosine phosphorylation of STAT1 proteins and thereby provokes an apoptosis pathway in B-CLL cells. Treating B-CLL cells in vitro or in vivo with CpG-B ODN reduces the number of leukemia cells that engraft in NOD-scid mice. These findings provide new understanding of CpG ODN-mediated antitumor effects and support for the development of TLR9-targeted therapy for human CLL.

Autologous dendritic cells pulsed with eluted peptide as immunotherapy for advanced B-cell malignancies

We have studied the feasibility, safety and efficacy of vaccination with autologous dendritic cells pulsed with eluted peptide in patients with advanced low-grade B-cell malignancies. This study demonstrates that autologous dendritic cell vaccines can be successfully produced from patients with advanced disease and be delivered without significant toxicity. Furthermore, we have demonstrated immunological and clinical responses in two of ten patients treated. These results provide further evidence for the use of immunotherapy in the management of B-cell malignancies, but also suggest that sustained responses may only be possible in patients with low bulk disease early in the disease course.

Survivin is an essential mediator of arthritis interacting with urokinase signalling

Proto-oncogene survivin has recently been identified as a prognostic marker distinguishing patients with destructive rheumatoid arthritis (RA). In the present material of 132 RA patients and 82 controls, the levels of survivin correlated to urokinase (uPA) (r= 0.46), a plasminogen activator over-expressed in inflamed joints and known to exhibit potent arthritogenic properties. Here we evaluate the functional relationship between these proteins using primary synovial fibroblasts and leucocytes of RA patients, human monocytic (THP-1) and fibroblast (MRC-5) cell lines. Using inhibitors of intracellular signalling, we show that uPA and survivin share common transduction pathways in synovial fibroblasts being dependent on the activity of tyrosine kinases, phosphatidylinositide 3 kinase and mitogen effector kinase. Moreover, uPA production is significantly reduced in fibroblasts if survivin synthesis has been silenced by siRNA. Importantly, silencing of survivin in fibroblasts prevented their invasive growth in knee joints of severe combined immune deficient mice. Interaction of uPA with receptor up-regulates survivin expression in leucocytes. In turn, survivin is required for the up-regulation of uPA receptor on the cell surface. These findings indicate that survivin is an essential mediator of arthritogenic properties of uPA regulating its synthesis in synovial fibroblasts and uPAR expression in leucocytes. Close correlation between survivin and uPA levels in patients with RA supports the importance of this connection for the pathogenesis of arthritis.

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.

Dendritic cell-Ewing's sarcoma cell hybrids enhance antitumor immunity

Given the effective immunotherapy of DC-based vaccine in other cancers, we hypothesized DC-based vaccines would induce effective immune responses against Ewing's sarcoma. To verify this hypothesis and develop the most effective dendritic cell vaccine against Ewing's sarcoma, we evaluated the antitumor efficacy of dendritic cell-Ewing's sarcoma hybrids and dendritic cells pulsed with other antigen-loading methods, including cell lysates and the characteristic EWS-FLI1 gene of Ewing's sarcoma, using an A673 cell line as a model. The hybrids were generated by electrofusion with fusion efficiency and viability determined by flow cytometry and fluorescent microscopy analyses. By interferon-gamma secretion assay, the capacity of hybrids to stimulate cytotoxic T-lymphocytes (CTLs) is higher than that of other antigen-loading methods showing stronger tumor antigen-specific CTL cytotoxicity to A673. By in vivo experiment in SCID mice, all dendritic cell-based strategies induced specific immune responses to Ewing's sarcoma after mice-human immune system reconstitution by inoculating human peripheral blood mononuclear cells into the peritoneal cavity of SCID mice. However, the hybrids most inhibited the subcutaneous tumor growth in SCID mice compared with dendritic cells pulsed with other loading methods. The data suggest A673 cells respond to dendritic cell-based immunotherapy.

Type 1-polarized dendritic cells loaded with autologous tumor are a potent immunogen against chronic lymphocytic leukemia

Induction of active tumor-specific immunity in patients with chronic lymphocytic leukemia (CLL) and other hematologic malignancies is compromised by the deficit of endogenous dendritic cells (DCs). In attempt to develop improved vaccination strategies for patients with CLL and other tumors with poorly identified rejection antigens, we tested the ability of ex vivo-generated DCs to cross-present the antigens expressed by CLL cells and to induce CLL-specific, functional CTL responses. Monocyte-derived DCs from CLL patients were induced to mature using a "standard" cytokine cocktail (in IL-1beta, TNF-alpha, IL-6, and PGE2) or using an alpha-type 1-polarized DC (alphaDC1) cocktail (in IL-1beta, TNF-alpha, IFN-alpha, IFN-gamma, and polyinosinic:polycytidylic acid) and were loaded with gamma-irradiated, autologous CLL cells. alphaDC1 from CLL patients expressed substantially higher levels of multiple costimulatory molecules (CD83, CD86, CD80, CD11c, and CD40) than standard DCs (sDCs) and immature DCs, and their expression of CCR7 showed intermediate level. alphaDC1 secreted substantially higher (10-60 times) levels of IL-12p70 than sDCs. Although alphaDC1 and sDCs showed similar uptake of CLL cells, alphaDC1 induced much higher numbers (range, 2.4-38 times) of functional CD8+ T cells against CLL cells. The current demonstration that autologous tumor-loaded alphaDC1 are potent inducers of CLL-specific T cells helps to develop improved immunotherapies of CLL.

Novel approaches to immunotherapy for B-cell malignancies

Immunotherapy for cancer refers to a wide array of novel therapeutic interventions that harness the immune system to target and eradicate malignant cells in the host. Advances in the understanding of how tumor cells evade host immune detection, coupled with improved gene transduction technologies, have enabled investigators to propose and test novel immune-based therapies for B-cell malignancies. As a result, more immunogenic vaccination strategies, able to elicit immune responses to otherwise poorly immunogenic tumor antigens, are being tested in early clinical trials. Furthermore, with the development of efficient T-cell transduction methodologies, investigators are able to generate autologous antitumor T-cell responses through the introduction of chimeric antigen receptors able to target tumor antigens. However, whether the promising preclinical and phase I clinical data presented here will ultimately translate into improved survival of patients with B-cell malignancies remains largely unknown.

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.

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.

T cell responses in melanoma patients after vaccination with tumor-mRNA transfected dendritic cells

We have developed an individualized melanoma vaccine based on autologous dendritic cells (DCs) transfected with autologous tumor-mRNA. The vaccine targets the unique spectrum of tumor antigens in each patient and may recruit multiple T cell clones. In a recent phase I/II trial, we demonstrated T cell responses against vaccine antigens in 9/19 patients evaluable by T cell assays. Here, we report a follow-up study that was conducted to characterize interesting T cell responses and to investigate the effects of long-term booster vaccination. Two patients were selected for continued vaccine therapy. The clinical follow-up suggested a favorable clinical development in both patients. The immunological data (T cell proliferation/IFNgamma ELISPOT/Bioplex cytokine assays) indicated sustained T cell responses and suggested an enhancing effect of booster vaccinations. Both CD4(+) and CD8(+) T cell responses were demonstrated. From post-vaccination samples, we generated 39 T cell clones that responded specifically to stimulation by mRNA-transfected DCs and 12 clones that responded to mock-transfected DCs. These data clearly indicate a two-component vaccine response, against transfected and non-transfected antigens. T cell receptor (TCR) clonotype mapping, performed on 11 tDC-specific clones, demonstrated that 10/11 clones had different TCRs. The results thus indicate a broad spectrum T cell response against antigens encoded by the transfected tumor-mRNA. We generally observed mixed Th1/Th2 cytokine profiles, even in T cell clones that were confirmed to be derived from a single cell. This finding suggests that cytokine patterns after cancer vaccination may be more complex than indicated by the classic Th1/Th2 dichotomy.

Comparative analysis of DC fused with tumor cells or transfected with tumor total RNA as potential cancer vaccines against hepatocellular carcinoma

BACKGROUND

DC vaccination with the use of tumor cells provides the potential to generate a polyclonal immune response to multiple known and unknown tumor Ag. Our study comparatively analyzed DC fused with tumor cells or transfected with tumor total RNA as potential cancer vaccines against hepatocellular carcinoma (HCC).

METHODS

Immature DC generated from PBMC of patients with HCC were fused with HepG2-GFP (HepG2 cell line transfected stably with plasmid pEGFP-C3) cells or transfected with their total RNA. Matured DC were used to stimulate autologous T cells, and the resultant Ag-specific effector T cells were analyzed by IFN-gamma ELISPOT assay.

RESULTS

DC were capable of further differentiation into mature DC after fusion with HepG2-GFP cells or transfection with HepG2-GFP cell total RNA, and were able to elicit specific T-cell responses in vitro. Both methods of Ag loading could result in stimulating CD4+ and CD8+ T cells, but with the indication that fusion loading was more efficient than RNA loading in priming the Th1 response, while RNA loading was more effective in CTL priming.

DISCUSSION

Our results indicate that DC fused with tumor cells or transfected with tumor total RNA represent promising strategies for the development of cancer vaccines for treatment of HCC. They may have potential as an adjuvant immunotherapy for patients with HCC.

Full-length EBNA1 mRNA-transduced dendritic cells stimulate cytotoxic T lymphocytes recognizing a novel HLA-Cw*0303- and -Cw*0304-restricted epitope on EBNA1-expressing cells

Epstein–Barr virus (EBV)-encoded nuclear antigen 1 (EBNA1) is an attractive target for immunotherapy against EBV-associated malignancies because it is expressed in all EBV-positive cells. Although CD8+ cytotoxic T-lymphocyte (CTL) epitope presentation is largely prevented by its glycine–alanine-repeat domain (GAr), the use of mRNA-transduced dendritic cells (DCs) would offer the advantage of priming EBNA1-specific CTLs. After stimulation with GAr-containing EBNA1-transduced monocyte-derived DCs, two EBNA1-specific CTL clones, B5 and C6, were isolated successfully from a healthy donor. These CTLs recognize peptides in the context of HLA-B*3501 and HLA-Cw*0303, respectively. A novel epitope, FVYGGSKTSL, was then identified, presented by both HLA-Cw*0303 and -Cw*0304, which are expressed by >35 % of Japanese, >20 % of Northern Han Chinese and >25 % of Caucasians. The mixed lymphocyte–peptide culture method revealed that FVYGGSKTSL-specific CTL-precursor frequencies in HLA-Cw*0303- or -Cw*0304-positive donors were between 1×10−5 and 1×10−4 CD8+ T cells. Moreover, both CTL clones inhibited growth of HLA-matched EBV-transformed B lymphocytes in vitro, and B5 CTLs produced a gamma interferon response to EBNA1-expressing gastric carcinoma cells in the context of HLA-Cw*0303. These data demonstrate that EBNA1 mRNA-transduced DCs may be useful tools for inducing EBNA1-specific CTLs that might be of clinical interest for CTL therapy of EBV-associated malignancies.

An improved protocol for generation of immuno-potent dendritic cells through direct electroporation of CD14+ monocytes

In this study we demonstrate a novel protocol showing that electroporation of CD14+ monocytes directly isolated from blood with green fluorescent protein (GFP) RNA results in a 3-fold higher yield of antigen presenting dendritic cells (DCs) when compared to conventional methods employing immature DCs for electroporation. We further show a stable electroporation efficacy resulting in 60% of GFP positive cells. Expression of co-stimulatory molecules and maturation markers such as CD80, CD86, CD83 as well of the chemokine receptor 7 (CCR7) was found in 90% of the mature DCs. Importantly, production of IL-12p70 was 10 times higher in cells electroporated at the monocyte stage compared to cells electroporated at the immature DC stage. Stimulation of autologous naïve lymphocytes by DCs electroporated at monocytes stage elicited proliferation of CD8+ T-cell with 7-fold increase in IFN-gamma release. Blocking of the MHC-Class I molecules significantly inhibited the IFN-gamma release, indicating that antigen presentation was MHC-Class I mediated. In summary, electroporation of CD14+ monocytes with RNA results in a high yield of antigen presenting DCs with high immuno-stimulatory capacity and antigen presentation on MHC-Class I molecules. This improved method may represent an attractive approach for RNA-based DC immunotherapy.

Targets and strategies for T-cell based vaccines in patients with B-cell chronic lymphocytic leukemia

T-cell based immunotherapies might be a novel option for the treatment of B-cell chronic lymphocytic leukemia (B-CLL), a disease characterized by a prolonged natural course. Different strategies of active immunotherapy have been tested in vitro to enhance a specific T-cell response against tumor cells and an anti-leukemic effect has been observed in B-CLL patients after allogenic stem cell transplantation. Several antigens have been characterized as tumor/leukemia associated antigens (T/LAAs) in B-CLL with the potential to elicit specific anti-tumor response encompassing idiotype immunoglobulin, oncofetal antigen-immature laminin receptor protein (OFAiLRP), survivin, as well as fibromodulin, the receptor for hyaluronic acid mediated motility (RHAMM/CD168) and the murine double-minute 2 oncoprotein (MDM2). This study presents an overview of possible targets and genetherapeutical maneuvers for future immunotherapies of B-CLL patients and summarizes recent clinical vaccination trials with dendritic cells (DCs) for B-CLL.

Prolongation of the survival of breast cancer-bearing mice immunized with GM-CSF-secreting syngeneic/allogeneic fibroblasts transfected with a cDNA expression library from breast cancer cells

Breast cancer cells, like other types of neoplastic cells, form weakly immunogenic tumor-associated antigens. The antigenic properties of the tumor-associated antigens can be enhanced if they are expressed by highly immunogenic cells. In this study, a cancer vaccine was prepared by transfer of a cDNA expression library from SB5b breast carcinoma into mouse fibroblast cells of C3H/He mouse origin (H-2(k)), that had been previously modified to secrete GM-CSF and to express allogeneic class I-determinants (H-2(b)). The transfected syngeneic/allogeneic fibroblasts secreting GM-CSF were used as a vaccine in C3H/He mice. Robust cell-mediated immunity toward the breast cancer cells was generated in mice immunized with the cDNA-based vaccine. The immunity, mediated predominantly by CD8(+) T lymphocytes, was directed toward the breast cancer cells, but not against either of two other non-cross-reactive neoplasms of C3H/He mice. The immunity was sufficient to prolong the survival of mice with established breast cancer. Among other advantages, preparation of the vaccine by cDNA-transfer into a fibroblast cell line enabled the recipient cells to be modified in advance of DNA-transfer to augment their immunogenic properties. As the transferred DNA is replicated as the transfected cells divide, the vaccine could be prepared from microgram quantities of tumor tissue.

Enhanced immunity to breast cancer in mice immunized with fibroblasts transfected with a complementary DNA expression library from breast cancer cells: Enrichment of the vaccine for immunotherapeutic cells

Breast cancer cells express an array of weakly immunogenic tumor-associated antigens (TAAs). Under appropriate circumstances, immunity to breast cancer can be induced, with potential benefits for patients with the disease. Here, we report a new cell-based vaccination strategy resulting in enhanced immunity to breast cancer in tumor-bearing mice. The strategy was designed to enrich the vaccine for highly immunogenic cells. The vaccine was prepared by transfer of unfractionated complementary DNA (cDNA) derived from a highly malignant breast neoplasm that arose spontaneously in a C3H/He mouse (SB5b) into an immunogenic fibroblast cell line. As the transferred cDNA spontaneously integrates into the genome of the recipient cells and is replicated as the cells divide, sufficient DNA to prepare the vaccine could be obtained from as few as 10(7) cells (4-mm tumor). Because only a small proportion of the transfected cell population was expected to have incorporated genes responsible for inducing immunity to the breast cancer, we devised a novel approach designed to enrich the transfected cell population for cells that induced immunity to the neoplasm. Aliquots of the transfected population were divided into small pools (initial inoculum = 4 x 10). Afterward, the cell number from each pool was allowed to expand in vitro. Pools containing greater numbers of immunogenic cells (identified by 2 independent assays) were subdivided for additional rounds of immune selection. Enhanced immunity to the neoplasm was detected in tumor-bearing mice treated solely by immunization with the enriched cell population. The immunity, mediated by CD8+ T cells, was sufficient to prolong the survival of mice with established breast cancer.

Nonviral delivery of cancer genetic vaccines

The potential use of genetic vaccines to address numerous diseases including cancer is promising, but currently unrealized. Here, we review advances in the nonviral delivery of antigen-encoded plasmid DNA for the purpose of treating cancer through the human immune system, as this disease has drawn the most attention in this field to date. Brief overviews of dendritic cell immunobiology and the mechanism of immune activation through genetic vaccines set the stage for the desirability of delivery technology. Several promising nonviral delivery techniques are discussed along with a mention of targeting strategies aimed at improving the potency of vaccine formulations. Implications for the future of genetic vaccines are also presented.

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.

An improved method for RNA isolation and removal of melanin contamination from melanoma tissue: implications for tumor antigen detection and amplification

Several kits are available to isolate RNA(1) from tissues. However, melanoma tissue is often rich in melanin that co-purifies with DNA/RNA and inhibits subsequent PCR reactions, hampering tumor antigen detection and amplification. This problem has not yet been addressed systematically. Here we generated a photometric protocol to determine both the melanin and RNA concentration by correcting the latter for the absorption coefficient of melanin at 260 nm. Subsequently, different combinations of silica-based RNA-binding, size-exclusion, and ion-exchange columns were used in 8 protocols for isolation of RNA from melanoma tissue to compare efficacy of melanin removal and yield of RNA. Furthermore, the capability of the different RNA preparations to function as template in RT-PCRs with products of different length, i.e. GAP-DH, tyrosinase, and gp100, was tested. We found that the combination of silica-based RNA-binding and size-exclusion columns was not sufficient to remove melanin from highly contaminated tumor samples, and subsequent RT-PCR failed to give larger products. However, protocols including ion-exchange columns resulted in efficient removal of melanin, while retaining reasonable RNA yields in samples from highly pigmented melanomas. Efficient RT-PCR of larger products turned out to be inversely correlated to the melanin contamination. This RNA-purification method will help scientists to isolate polynucleotides from melanin-containing tumor samples, which subsequently can be used in antigen detection assays and vaccination strategies using amplified total tumor RNA.

Effective induction of anti-melanoma immunity following genetic vaccination with synthetic mRNA coding for the fusion protein EGFP.TRP2

RNA-based genetic immunization represents an alternative novel strategy for antigen-specific cancer vaccines. In the present paper we investigate the use of synthetic messenger RNA in an experimental melanoma model. We show that gene gun-based immunization using synthetic RNA mediates gene expression in the epidermis and effectively induces antigen-specific cellular and humoral immunity in mice in vivo. Importantly, bombardment of the skin with RNA coding for the melanocytic self-antigen TRP2 linked to the immunogenic protein EGFP was associated with protection against experimentally induced B16 melanoma lung metastases and vitiligo-like fur depigmentation. Our results provide a scientific basis for clinical trials using synthetic mRNA encoding melanocytic antigens linked to immunogenic helper proteins for vaccination of patients with melanoma.

T and B cells in B-chronic lymphocytic leukaemia: Faust, Mephistopheles and the pact with the Devil

A large number of human malignancies are associated with decreased numbers of circulating T cells. B-CLL, in this regard, represents an anomaly since there is not only high numbers of circulating B cells, characteristic of the malignancy, but also a massive expansion of both CD4 and CD8 T cells. These T cells for the most part may probably not represent a leukaemia-specific TCR-dependent expansion. On the contrary, these T cells, especially the CD4 subset, might support a "microenvironment" sustaining the growth of the leukaemic B cell clone. Conversely, the leukaemic B cells may produce membrane-bound as well as soluble factors that stimulate the proliferation of these T cells in an antigen independent manner. In addition to these T cells lacking anti-leukaemic reactivity, there exist spontaneously occurring leukaemia-specific T cells recognizing several leukaemia-associated antigens, e.g. the tumour derived idiotype, survivin and telomerase. Both CD4 and CD8 leukaemia-specific T cells have been identified using proliferation and gamma-IFN assays. These reactive T cells can lyse autologous tumour cells in an MHC class I and II restricted manner. Spontaneously occurring leukaemia-specific T cells are more frequently noted at an indolent stage rather than in progressive disease. Preliminary results from vaccination trials using whole tumour cell preparations as vaccine have demonstrated that vaccination may induce a leukaemia-specific T cell response, which might be associated with clinical benefits. Extended clinical trials are required to establish the therapeutic effects of vaccination in B-CLL. Studies in our laboratory as well as those of others indicate that whole tumour cell antigen in the form of apoptotic bodies or RNA loaded on to dendritic cells may be a suitable vaccine candidate. Patients with low stage disease may maximally benefit from this form of therapy.

Monoclonal antibody therapy of chronic lymphocytic leukemia

Cure of patients with chronic lymphocytic leukemia (CLL) has been an elusive goal. The recent availability of active monoclonal antibodies has rekindled enthusiasm for new and innovative therapeutic approaches. Alemtuzumab, induces responses in about a third of patients with relapsed or refractory CLL following therapy with fludarabine and an alkylating agent. Whereas, rituximab has limited activity in previously treated patients, response rates of 50-70% have been reported in those without prior therapy. Recent data on combinations with rituximab and chemotherapy have shown promise for improving patient outcome. Newer antibodies in development include the primatized monoclonal antibody lumiliximab (IDEC-152), directed against CD23. Other biological approaches include the use of antisense oligonucleotides, proapoptic small molecules, and vaccines directed against the malignant B cells. The rational development of combinations of these promising approaches may eliminate the need for chemotherapy, leading to safer and more effective approaches for patients with CLL.

Dendritic cell-based cancer immunotherapy targeting MUC-1

Vaccination therapy using dendritic cells (DC) as antigen presenting cells (APC) has shown significant promise in laboratory and animal studies as a potential treatment for malignant diseases. Pulsing of autologous DCs with tumor-associated antigens (TAA) is a method often used for antigen delivery and choice of suitable antigens plays an important role in designing an effective vaccine. We identified two HLA-A2 binding novel 9-mer peptides of the TAA MUC1, which is overexpressed on various hematological and epithelial malignancies. Cytotoxic T cells generated after pulsing DC with these peptides were able to induce lysis of tumor cells expressing MUC1 in an antigen-specific and HLA-restricted fashion. Within two clinical studies, we demonstrated that vaccination of patients with advanced cancer using DCs pulsed with MUC1 derived peptides is well tolerated without serious side effects and can induce immunological responses. Of 20 patients with metastatic renal cell carcinoma, 6 patients showed regression of metastases with 3 objective responses (1 CR, 2 PR). Furthermore, we found that in patients responding to treatment T cell responses for antigens not used for treatment occurred suggesting that antigen spreading in vivo might be a possible mechanism of mediating antitumor effects. These results demonstrate that immunotherapy in patients with advanced malignancies using autologous DCs pulsed with MUC1 derived peptides can induce immunological and clinical responses. However, further clinical studies are needed to identify the most potent treatment regimen that can consistently mediate an antitumor immune response in vivo.

Vaccine strategies to treat lymphoproliferative disorders

Lymphoproliferative disorders, including follicular lymphoma (FL), multiple myeloma (MM) and chronic lymphatic leukaemia (CLL), are slowly progressive malignancies which remain incurable despite advances in therapy. Harnessing the immune system to recognise and destroy tumours is a promising new approach to treating these diseases. Dendritic cells (DC) are unique antigen-presenting cells that play a central role in the initiation and direction of immune responses. DC loaded ex vivo with tumour-associated antigens and administered as a vaccine have already shown promise in early clinical trials for a number of lymphoproliferative disorders, but the need for improvement is widely agreed. Recent advances in the understanding of basic DC biology and lessons from early clinical trials have provided exciting new insights into the generation of anti-tumour immune responses and the design of vaccine strategies. In this review we provide an overview of our current understanding of DC biology and their function in patients with lymphoproliferative disorders. We discuss the current status of clinical trials and new approaches to exploit the antigen presenting capacity of DC to design vaccines of the future.

T cell-mediated graft-versus-leukemia reactions after allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation represents the only curative approach for many hematological malignancies. During the last years the impact of the conditioning regimen has been re-assessed. With the advent of reduced-intensity conditioning the paradigm has changed from cytoreduction executed by high-dose radio-chemotherapy to immunological surveillance of leukemia by donor cells. Distinct subsets of T cells and NK cells contribute to graft-versus-leukemia reactions. So far, cytotoxic T lymphocytes are the mainstay of allogeneic immunotherapy. Here, we summarise the current knowledge of T cell-mediated graft-versus-leukemia reactions and present results from pre-clinical and clinical studies of T cell-based adoptive immunotherapy. We address the issues of feasibility and specificity of adoptive immunotransfer from a clinical point of view and discuss the prerequisites for successful clinical applications. Finally, the prospects for immunological research that have evolved with the increasing use of reduced-intensity conditioning and allogeneic stem cell transplantation are highlighted.

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.

Recent advances in immunotherapy of B-CLL using ex vivo modified dendritic cells

Chronic lymphocytic leukemia (CLL) results from the relentless accumulation of small mature, slowly dividing, monoclonal B-lymphocytes. The clinical course is heterogeneous, some patients with aggressive form of the disease progressing rapidly with early death while others exhibit a more stable, possibly, non-progressing indolent type of the disease lasting many years. Despite progress in modern treatment modalities, relapse invariably occurs and disease still remains incurable. The clinical management of CLL is therefore challenging and considerable effort has been directed towards novel therapeutic strategies aimed at reducing minimal residual disease which can increase remission duration. Recent insight into the role of dendritic cells (DCs) as pivotal antigen presenting cells that initiate immune responses may provide the basis for generating more specific and effective immune responses. Ex-vivo modified and monocyte-derived DCs represents a promising approach within the context of CLL. However, understanding the relationship between DCs and the cellular immune response is crucial in devising strategies for manipulating immune responses. After a brief survey of general properties of DCs, this review focuses on the different approaches exploiting monocyte-derived DCs in CLL, which may help to design novel strategies for phase-I clinical trials.

Antigen-specific cellular immunotherapy of leukemia

Advances in cellular and molecular immunology have led to the characterization of leukemia-specific T-cell antigens and to the development of strategies for effective augmentation of T-cell immunity in leukemia patients. While several leukemia-related antigens have been identified, this review focuses on the Wilms' tumor 1 (WT1) antigen and the proteinase 3 (Pr3) antigen that are overexpressed in leukemic cells and are already being used in the clinical setting. Moreover, WT1 is also overexpressed in a vast number of nonhematological solid tumors, thereby expanding its use as a promising target for cancer vaccines. Examples of spontaneous immune responses against WT1 and Pr3 in leukemia patients are presented and the potential of WT1 and Pr3 for adoptive T-cell immunotherapy of leukemia is discussed. We also elaborate on the use of professional antigen-presenting cells loaded with mRNA encoding WT1 exploiting the advantage of broad HLA coverage for therapeutic vaccination purposes. Finally, the summarized data underscore the potential of WT1 for the manipulation of T-cell immunity in leukemia and in cancer in general, that will likely pave the way for the development of more effective and generic cancer vaccines.

Allogeneic dendritic cells pulsed with tumor lysates or apoptotic bodies as immunotherapy for patients with early-stage B-cell chronic lymphocytic leukemia

Recently, immunotherapies with allogeneic dendritic cells (DCs) pulsed with tumor antigens to generate specific T-cell responses have been tested in clinical trials for patients with solid tumors. This is the first report on a clinical vaccination study with DCs for patients with B-cell chronic lymphocytic leukemia (B-CLL). The potential of allogeneic DCs pulsed ex vivo with tumor cell lysates or apoptotic bodies to stimulate antitumor immunity in patients with B-CLL in early stages was evaluated. Monocyte-derived DCs were obtained from unrelated healthy donors. Nine patients (clinical stage 0 and 1 according to Rai) were vaccinated five times with a mean number of 32 x 10(6) stimulated DCs administered intradermally once every 2-3 weeks. No signs of autoimmunity were detected, and only mild local skin reactions were noted. During the treatment period, we observed a decrease of peripheral blood leukocytes and CD19+/CD5+ leukemic cells. In one patient, a significant increase of specific cytotoxic T lymphocytes against RHAMM/CD168, a recently characterized leukemia-associated antigen, could be detected after DC vaccination. Taken together, the study demonstrated that DC vaccination in CLL patients is feasible and safe. Immunological and to some extent hematological responses could be noted, justifying further investigation on this immuno-therapeutical approach.

Chronic lymphocytic leukemia cells induce changes in gene expression of CD4 and CD8 T cells

To examine the impact of tumors on the immune system, we compared global gene expression profiles of peripheral blood T cells from previously untreated patients with B cell chronic lymphocytic leukemia (CLL) with those from age-matched healthy donors. Although the cells analyzed were not part of the malignant clone, analysis revealed differentially expressed genes, mainly involved in cell differentiation in CD4 cells and defects in cytoskeleton formation, vesicle trafficking, and cytotoxicity in CD8 cells of the CLL patients. In coculture experiments using CLL cells and T cells from healthy allogeneic donors, similar defects developed in both CD4 and CD8 cells. These changes were induced only with direct contact and were not cytokine mediated. Identification of the specific pathways perturbed in the T cells of cancer-bearing patients will allow us to assess steps to repair these defects, which will likely be required to enhance antitumor immunity.

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.