Deliver Tumor Antigens Research Articles

Improving Cancer Vaccine Efficiency by Nanomedicine.

Cancer vaccines, which have been widely investigated in the past few decades, are one of the most attractive strategies for cancer immunotherapy. Through the precise delivery of antigens and adjuvants to lymphoid organs or lymphocytes via nanotechnology, innate and adaptive immunity can be boosted to prevent the growth and relapse of malignant tumors. Indeed, nanomedicine offers great opportunities to improve the efficiency of vaccines. Various functional platforms are used to deliver small molecules, peptides, nucleic acids, and even whole cell antigens to the target area of interest, achieving enhanced antitumor immunity and durable therapeutic benefits. Herein, the recent progress in cancer vaccines based on nanotechnology is summarized. Novel platforms used for delivering tumor antigens, promoting adjuvant functions, and combining other therapeutic strategies are discussed. Moreover, possible striving directions and major challenges of nanomedicine for vaccination are also reviewed.

Polyethyleneimine modification of aluminum hydroxide nanoparticle enhances antigen transportation and cross-presentation of dendritic cells.

BackgroundThe aim of this study was to explore the feasibility of delivering tumor antigens and enhancing the antigen cross-presentation of dendritic cells (DCs) by aluminum hydroxide nanoparticle with polyethyleneimine (PEI) modification (LV@HPA/PEI).Materials and methodsThe LV@HPA nanoparticles were modified by PEI first, then the influence of LV@HPA/PEI on DCs was examined. The distinct expression of ovalbumin (OVA) protein transported into DCs by LV@HPA/PEI was observed by flow cytometry and Western blot. The biocompatibility of LV@HPA/PEI, maturity and antigen cross-presentation of DCs was observed in vitro. Tumor derived autophagosomes (DRibbles) combined with LV@HPA/PEI were loaded into DCs, and DC vaccines were used to immunize mice. The percentage of CD3+CD8+IFN-γ+ T cells in immunized mice was determined by flow cytometry. Additionally, the functional properties of the LV@HPA/PEI-DRibble-DCs vaccine were examined in vivo in PancO2 tumor-bearing mice.ResultsIn our study, we described how LV@HPA/PEI can be a functionalized antigen delivery system with notable antigen transport effect and negligible cytotoxicity. It was found that LV@HPA/PEI could be easily internalized into DCs to assist antigen release into the cytoplasm. In addition, DCs matured gradually after loading with LV@HPA/PEI-OVA, which increased significantly the cytokine IL-12 secretion and expression of surface molecules CD80 and CD86. Interestingly, DCs loaded with LV@HPA/PEI-DRibbles could promote the activation of tumor-specific T cells both in murine and in human T cells. In the following in vivo experiments, the vaccine of LV@HPA/PEI-DRibble-DCs significantly inhibited tumor growth and improved the survival rate of the PancO2 tumor-bearing mice.ConclusionWe established a high-performance anti-tumor vaccine of DCs loaded with LV@ HPA/PEI nanoparticles and tumor-associated antigens in autophagosomes (DRibbles), which could serve as a therapeutic strategy in cancer immunotherapy.

Molecular regulation of dendritic cell development and function in homeostasis, inflammation, and cancer

Dendritic cells (DCs) are the principal antigen-presenting cells of the immune system and play key roles in controlling immune tolerance and activation. As such, DCs are chief mediators of tumor immunity. DCs can regulate tolerogenic immune responses that facilitate unchecked tumor growth. Importantly, however, DCs also mediate immune-stimulatory activity that restrains tumor progression. For instance, emerging evidence indicates the cDC1 subset has important functions in delivering tumor antigens to lymph nodes and inducing antigen-specific lymphocyte responses to tumors. Moreover, DCs control specific therapeutic responses in cancer including those resulting from immune checkpoint blockade. DC generation and function is influenced profoundly by cytokines, as well as their intracellular signaling proteins including STAT transcription factors. Regardless, our understanding of DC regulation in the cytokine-rich tumor microenvironment is still developing and must be better defined to advance cancer treatment. Here, we review literature focused on the molecular control of DCs, with a particular emphasis on cytokine- and STAT-mediated DC regulation. In addition, we highlight recent studies that delineate the importance of DCs in anti-tumor immunity and immune therapy, with the overall goal of improving knowledge of tumor-associated factors and intrinsic DC signaling cascades that influence DC function in cancer.

Engineered outer membrane vesicle is potent to elicit HPV16E7-specific cellular immunity in a mouse model of TC-1 graft tumor.

PurposeCurrently, therapeutic tumor vaccines under development generally lack significant effects in human clinical trials. Exploring a powerful antigen delivery system is a potential approach to improve vaccine efficacy. We sought to explore engineered bacterial outer membrane vesicles (OMVs) as a new vaccine carrier for efficiently delivering tumor antigens and provoking robust antitumor immune responses.Materials and methodsFirst, the tumoral antigen human papillomavirus type 16 early protein E7 (HPV16E7) was presented on Escherichia coli-derived OMVs by genetic engineering methods, acquiring the recombinant OMV vaccine. Second, the ability of recombinant OMVs delivering their components and the model antigen green fluorescent protein to antigen-presenting cells was investigated in the macrophage Raw264.7 cells and in bone marrow-derived dendritic cells in vitro. Third, it was evaluated in TC-1 graft tumor model in mice that the recombinant OMVs displaying HPV16E7 stimulated specific cellular immune response and intervened the growth of established tumor.ResultsE. coli DH5α-derived OMVs could be taken up rapidly by dendritic cells, for which vesicle structure has been proven to be important. OMVs significantly stimulated the expression of dendritic cellmaturation markers CD80, CD86, CD83 and CD40. The HPV16E7 was successfully embedded in engineered OMVs through gene recombinant techniques. Subcutaneous immunization with the engineered OMVs induced E7 antigen-specific cellular immune responses, as shown by the increased numbers of interferon-gamma-expressing splenocytes by enzyme-linked immunospot assay and interferon-gamma-expressing CD4+ and CD8+ cells by flow cytometry analyses. Furthermore, the growth of grafted TC-1 tumors in mice was significantly suppressed by therapeutic vaccination. The recombinant E7 proteins presented by OMVs were more potent than those mixed with wild-type OMVs or administered alone for inducing specific cellular immunity and suppressing tumor growth.ConclusionThe results indicated that the nano-grade OMVs might be a useful vaccine platform for antigen delivery in cancer immunotherapy.

Oral delivery of tumor microparticle vaccines activates NOD2 signaling pathway in ileac epithelium rendering potent antitumor T cell immunity

ABSTRACTExploiting gut mucosal immunity to design new antitumor vaccination strategy remains unexplored. Tumor cell-derived microparticles (T-MP) are natural biomaterials that are capable of delivering tumor antigens and innate signals to dendritic cells (DC) for tumor-specific T cell immunity. Here, we show that T-MPs by oral vaccination route effectively access and activate mucosal epithelium, leading to subsequent antitumor T cell responses. Oral vaccination of T-MPs generated potent inhibitory effect against the growth of B16 melanoma and CT26 colon cancer in mice, which required both T cell and DC activation. T-MPs, once entering intestinal lumen, were mainly taken up by ileac intestinal epithelial cells (IEC), where T-MPs activated NOD2 and its downstream MAPK and NF-κB, leading to chemokine releasing, including CCL2, from IECs to attract CD103+ CD11c+ DCs. Furthermore, ileac IECs could transcytose T-MPs to the basolateral site, where T-MPs were captured by those DCs for cross-presentation of loaded antigen contents. Elucidating these molecular and cellular mechanisms highlights T-MPs as a novel antitumor oral vaccination strategy with great potential of clinical applications.

Abstract 1648: Ionizing radiation switches the function of tumor-derived exosomes from messengers of tolerance to inducers of antitumor immunity

Abstract Tumor-derived exosomes (TEX) are constantly shed by cancer cells and have been shown to carry tumor-derived antigens to dendritic cells (DCs). However, presentation of tumor antigens derived from TEX in the absence of activation signals for DCs leads to immune tolerance. Our lab has demonstrated that ionizing radiotherapy (RT) can convert the irradiated tumor into an in situ vaccine, leading to anti-tumor immune responses. We hypothesized that TEX derived from irradiated cancer cells play a role in RT-induced anti-tumor immunity by delivering tumor antigens together with pro-inflammatory signals that activate DCs and prime tumor-specific effector T cells. To begin to address this hypothesis we first studied how RT modifies TEX molecular composition and their ability to induce DC activation in vitro. Mouse carcinoma cells TSA cultured in exosome-free media were treated in vitro with sham RT (control TEX), or 3 fractions of 8Gy (RT-TEX). TEX were isolated from supernatants 48 hr later using differential ultracentrifugation and purified with a sucrose gradient. Electron microscopy was used to confirm TEX size and morphology. Mass spectrometry (LFQ-MS) followed by MS/MS analyses was used to characterize protein composition. miRNA were analyzed by nanoString nCounter Mouse miRNA expression assay kit using a panel of 578 mouse miRNAs. Normalized results were analyzed with MultiExperiment Viewer. Mouse bone marrow-derived dendritic cells (BMDC) were cultured with TEX for 48 hours. Cells were analyzed by flow cytometry for expression of activation markers. Significant changes in microRNA and protein compositions were seen in RT-TEX compared to control TEX. Specifically, RT-TEX showed increase in proteins involved in the Antigen Processing and Presentation pathway. Additionally, 17 unique proteins were present only in RT-TEX and included proteins involved in T cell development, MHC class I peptide processing, and pro-inflammatory lipid signaling. Analysis of DCs cultured with RT-TEX, but not control TEX, revealed an increase in cell surface expression of CD80 (1428 MFI vs. 963 MFI) and CD86 (3487 MFI vs. 2578 MFI). Interestingly, culturing BMDC with RT-TEX also resulted in an increase in DCs expressing CD103 and CD8a (2% vs 1.2% of CD11c+ cells), suggesting that RT-TEX may influence differentiation of BMDC towards this subset, which is critical for cross-presentation of tumor antigens to T cells. Obtained data support the hypothesis that RT-TEX may switch tolerogenic DCs into activated DCs by providing activation signals together with tumor-derived antigens. Further in vivo experiments are ongoing to determine the ability of RT-TEX to stimulate anti-tumor immune responses. Citation Format: Julie M. Diamond, Jessica R. Chapman, Beatrix Ueberheide, Silvia C. Formenti, Sandra Demaria. Ionizing radiation switches the function of tumor-derived exosomes from messengers of tolerance to inducers of antitumor immunity. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1648.

Cationic liposomes produced via ethanol injection method for dendritic cell therapy

Cationic liposomes can be designed and developed in order to be an efficient gene delivery system for mammalian cells. Dendritic cell (DC) vaccines can be used to treat cancer, as cationic liposomes can deliver tumor antigens to cells while cells remain active. However, most methods used for liposome production are not able to reproduce in large scale the physicochemical and biological properties of liposomes produced in laboratory scale. In this context, ethanol injection method achieved promising results, although requiring post-treatment for size reduction and/or to remove residual ethanol. Thus, the purpose of this study was to generate cationic liposomes suitable for gene therapies via ethanol injection method in only one step (VEI) and compared to those submitted to a size reduction processes by microfluidization (MFV). For this, the method to produce cationic liposomes composed of egg phosphatidylcholine (EPC), 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) and 1,2-dioleoylphosphatidylethanolamine (DOPE) was optimized using a statistical design approach. As a result, the size of VEI decreased from 290 nm to 110 nm and the polydispersity from 0.54 to 0.17. In the case of MFV, size decreased from 128 nm to 107 nm and polydispersity from 0.40 to 0.18. ST and MFV before and after optimization were also characterized in terms of morphology by transmission electron microscopy (TEM) and structure by differential scanning calorimetry (DSC). Finally, to show their potential in gene/immune therapies applications, DCs were stimulated by such liposomes. Cells internalized liposomes, increasing expression of the costimulatory molecule CD86 and inducing T lymphocyte proliferation.

The Endoplasmic Reticulum Chaperone GRP170: From Immunobiology to Cancer Therapeutics.

Glucose-regulated protein 170 (GRP170) is the largest member of glucose-regulated protein family that resides in the endoplasmic reticulum (ER). As a component of the ER chaperone network, GRP170 assists in protein folding, assembly, and transportation of secretory or transmembrane proteins. The well documented cytoprotective activity of intracellular GRP170 due to its intrinsic chaperoning property has been shown to provide a survival benefit in cancer cells during tumor progression or metastasis. Accumulating evidence shows that extracellular GRP170 displays a superior capacity in delivering tumor antigens to specialized antigen-presenting cells for cross-presentation, resulting in generation of an anti-tumor immune response dependent on cytotoxic CD8+ T cells. This unique feature of GRP170 provides a molecular basis for using GRP170 as an immunostimulatory adjuvant to develop a recombinant vaccine for therapeutic immunization against cancers. This review summarizes the latest findings in understanding the biological effects of GRP170 on cell functions and tumor progression. The immunomodulating activities of GRP170 during interactions with the innate and adaptive arms of the immune system as well as its therapeutic applications in cancer immunotherapy will be discussed.

Attenuated Listeria monocytogenes: a powerful and versatile vector for the future of tumor immunotherapy.

For over a century, inactivated or attenuated bacteria have been employed in the clinic as immunotherapies to treat cancer, starting with the Coley's vaccines in the 19th century and leading to the currently approved bacillus Calmette-Guérin vaccine for bladder cancer. While effective, the inflammation induced by these therapies is transient and not designed to induce long-lasting tumor-specific cytolytic T lymphocyte (CTL) responses that have proven so adept at eradicating tumors. Therefore, in order to maintain the benefits of bacteria-induced acute inflammation but gain long-lasting anti-tumor immunity, many groups have constructed recombinant bacteria expressing tumor-associated antigens (TAAs) for the purpose of activating tumor-specific CTLs. One bacterium has proven particularly adept at inducing powerful anti-tumor immunity, Listeria monocytogenes (Lm). Lm is a gram-positive bacterium that selectively infects antigen-presenting cells wherein it is able to efficiently deliver tumor antigens to both the MHC Class I and II antigen presentation pathways for activation of tumor-targeting CTL-mediated immunity. Lm is a versatile bacterial vector as evidenced by its ability to induce therapeutic immunity against a wide-array of TAAs and specifically infect and kill tumor cells directly. It is for these reasons, among others, that Lm-based immunotherapies have delivered impressive therapeutic efficacy in preclinical models of cancer for two decades and are now showing promise clinically. In this review, we will provide an overview of the history leading up to the development of current Lm-based immunotherapies, the advantages and mechanisms of Lm as a therapeutic vaccine vector, the preclinical experience with Lm-based immunotherapies targeting a number of malignancies, and the recent findings from clinical trials along with concluding remarks on the future of Lm-based tumor immunotherapies.

Immunotherapy at Large: Balancing tumor immunity and inflammatory pathology

Immunotherapy at Large: Balancing tumor immunity and inflammatory pathology

Cationic Liposomes as Non-viral Vector for RNA Delivery in Cancer Immunotherapy

This review presents the current status in the use of liposomes as non-viral vector for nucleic acid delivery in cancer immunotherapy. Currently, cancer treatment uses surgery, radiotherapy and/or chemotherapy. The search for new strategies to improve the efficiency of conventional treatments is a challenge, and biological therapy has emerged as a promising technique. Immunotherapy is a branch of biological therapy that uses the body's immune system to detect and destroy cancer cells. One immunotherapy approach is the activation of T lymphocytes from cancer patients by dendritic cells (DCs) loaded with tumor antigens. Among different antigens, mRNA coding the tumor antigens is advantageous due to its capability to be amplified from small amounts of tumor tissue, its safety because it is easily degraded without integrating into the host genome, and it does not need to cross the nuclear barrier to exert its biological activity. Nanotechnology is an approach to deliver tumor antigens into DCs. Specially; we review the use of nanoliposomes in the field of cancer therapy because cationic liposomes can be used as non-viral vectors for mRNA delivery. Aside from the promise of liposomes, the development of scalable processes and facilities to the use this individualized therapy is still a challenge. Thus, we also present the recent techniques used for liposome production. In this context, the integration between technological knowledge in the production of cationic liposomes and immunotherapy using mRNA may contribute to the development of new strategies for cancer therapy.

Part I: Targeted Particles for Cancer Immunotherapy

Dendritic cells (DCs) are the key antigen presenting cells that link innate and adaptive immunity. In the periphery, DCs capture antigens, process them and migrate into the regional lymph nodes where they could initiate antigen specific T cell immune responses. Immunotherapeutic strategies that aim to deliver tumor antigens specifically to DCs could not only boost anti-tumor immune responses but also could alleviate non-specific immune activation and/or unwanted side effects. Nano-sized particulate delivery systems are efficient modalities that can deliver tumor antigens to DCs in a targeted and specific manner. This review will provide general information on the rationale behind targeting antigens to DCs and the crucial role of DCs in initiating antigen specific T cell responses. Different strategies that have been employed in delivering antigens to DCs will be also discussed. A special emphasis will be put on specific targeting of cancer vaccine formulations to DC-specific receptors (e.g. CD11c, CD40, Fcγ, CCR6, pathogenic recognition receptors such as Toll-like receptors (TLRs) and C-type lectin receptors (CLRs)).

Cellular Vaccine Approaches

Therapeutic cancer vaccines aim to generate immunologic targeting of cancer cells through the induction of effective cellular and antibody-mediated responses specific for antigens selectively expressed by the tumor. Exploiting the adaptive immune system as a targeted tool against cancer is appealing in its capacity for exact specificity and avoidance of unintended tissue damage seen by other conventional agents such as chemotherapy. There are a multitude of challenges to designing effective vaccine strategies. The components of a vaccine strategy start with the challenges of selecting immunogenic, tumor-specific antigen targets, choosing a platform with which to deliver the antigens, and enhancing the immunostimulatory context in which the vaccines are delivered. Although understanding the components of effective T-cell activation is essential, successful effector T cells can only be produced if there is also an understanding of the natural processes that tumors exploit to down-modulate active immune responses. These processes are normally used to down-regulate excessive tissue-destructive immune responses against infectious agents once the infecting agent is cleared or to prevent autoimmunity. Advances in molecular and cellular technologies continue to provide insights into the regulation of immune responses both to infectious agents and to cancer that may be manipulated to tip the balance in favor of tumor regression over immune tolerance. This review focuses primarily on cellular vaccines. For the purpose of this review, cellular vaccines are defined as vaccines that use whole cells or cell lysates either as the source of antigens or the platform in which to deliver the antigens. Dendritic cell (DC)-based vaccines focus on ex vivo antigen delivery to DCs. Other platforms such as GVAX (tumor cells genetically engineered to produce granulocyte-macrophage colony-stimulating factor) aim to deliver tumor antigens in vivo in an immune stimulatory context to endogenous DCs. Because data continue to emerge regarding the importance of the maturation status of DCs and the importance of the particular subset of DCs being targeted, these insights will be integrated into vaccine strategies that are likely to produce more effective vaccines.

Allogeneic Tumor Vaccine Produced by Electrofusion between Osteosarcoma Cell Line and Dendritic Cells in the Induction of Antitumor Immunity

Objective: Fusion of dendritic cells, DCs, with tumor cells is an effective approach for delivering tumor antigens to DCs, and DC-tumor fusion cells are potent stimulators of T cells. However, the integration of allogeneic DC-osteosarcoma fusion cells has not been fully examined. This study was designed to investigate the antitumor effects of tumor vaccine produced by electrofusion between rat osteosarcoma cells and allogeneic DCs. Methods: In the present study, we eletrofused Wistar rat bone marrow-derived DCs to SD rat osteosarcoma cells (UMR106) and purified them by monoclonal antibody OX62 and magnetic beads. Coculture of SD or Wistar bone marrow derived T lymphocytes with DC-tumor fusion cells resulted in activation of T cells, and the proportion of CD8+, CD4+ cells was determined using flow cytometry. Then cytotoxic T lymphocytes, CTLs, assay was assessed according to results of MTT assay. Results: After T cells were cultured with allogeneic DC-osteosarcoma fusion cells, DOF, and effective activation of T cells was observed. The proportion of CD8+ cells in the SD T cell group increases from 34.16% before induction to 74.85%, while that of CD4+ cells is from 63.35% to 71.75% in Wistar T cell group. The immunization using allogeneic DC-osteosarcoma vaccine induced UMR106-spcific CTL responses which were statistically significant (P < 0.05) and the cytotoxic activity was inhibited by the treatment with anti-CD8 and anti-MHC-class I monoclonal antibodies but not with anti-CD4 and anti-MHC-class II antibodies. Conclusion: The present study provided valid evidence of integration of rat allogeneic DCs electrofused with tumor cells and analyzed their properties in T cell activation. The fusion cells may thus represent a promising strategy for DC-based immunotherapy of patients with osteosarcoma.

UP-02.22: Superior anti-tumor immune response of dendritic cells fused with prostate cancer cells compared with tumor lysate-pulsed dendritic cells

Dendritic cells(DCs) are recognized as the most potent antigen-presenting cells and methods for delivering tumor antigens into DCs are one of the major concerns of intensive investigation in DC-based tumor vaccines. Fusion of DCs with tumor cells is an effective approach for delivering tumor antigens to DCs, and DC-tumor fusion cells are potent stimulators of immune response against tumor cells. We compared anti-tumor immune response of the DC-tumor fusion cells versus the tumor lysate-pulsed DCs in hormone refractory prostate cancer cell lines.

Reduced expression of the transporter associated with antigen processing 1 molecule in malignant glioma cells, and its restoration by interferon-γ and -β

It remains unclear whether malignant glioma cells can deliver tumor antigens efficiently to major histocompatibility complex (MHC) Class I molecules. To elucidate the mechanism of antigen presentation in malignant gliomas, the authors examined the expression of the transporter associated with antigen processing 1 (TAP1), which transports antigens to MHC Class I molecules, and low-molecular-mass polypeptide 2 (LMP2), which is a subunit of a proteasome. They also analyzed the effects of interferon (IFN)-gamma and IFN-beta on the expression of these molecules. Five glioma cells expressed undetectable or very low levels of TAP1 protein and did not express TAP1 messenger (m)RNA. Normal brain tissue and glioma tissue specimens also showed undetectable levels of TAP1 protein and the same levels of LMP2 protein as lymphoblastoid B cells. Treatments of the tumor cells with IFN-gamma, or -beta enhanced the expression of both TAP1 protein and mRNA as well as the expression of MHC Class I molecules. The expression of LMP2 protein was not altered by the IFN treatments. The authors analyzed structural alterations in the TAP1 promoter region in eight malignant glioma cell lines. Single nucleotide polymorphism was found in 446 bp up-stream of the translation start site of the TAP1 gene, and a point mutation was found in 34 bp upstream of the TAP1 gene. Malignant glioma cells may be less immunogenic due to low levels of TAP1 expression. Upregulated expression of TAP1 and MHC Class I molecules by IFN-gamma and -beta may enhance antigen presentation in malignant glioma cells.

Dendritic cells fused with human cancer cells: morphology, antigen expression, and T cell stimulation

Fusion of human dendritic cells (DC) with tumor cells is an effective approach for delivering tumor antigens to DC, and DC/tumor fusion cells are potent stimulators of autologous T cells. However, the integration and morphology of DC/tumor fusion cells has not been examined. In the present study, we fused patient-derived DC to autologous breast or ovarian carcinoma cells. The fusion cells possessed the properties of both parent cells. After fusion, the cytoplasm of the two cells was integrated, whereas their nuclei remained separate entities. Colocalization of MUC1 peptide and HLA-DR molecules was observed on fusion cells under the immunoelectron microscope. Coculture of patient-derived peripheral blood mononuclear cells (PBMC) with DC/tumor fusion cells resulted in activation of CD4 and CD8 T cells as assessed by IFN-γ secretion, HLA-A*0201-MUC1 tetramer, and standard cytotoxic T lymphocyte (CTL) assays. The present study provides first evidence of integration of human DC and tumor cells and links their properties to T cell activation.

Cross-presentation of a human tumor antigen delivered to dendritic cells by HSV VP22-mediated protein translocation.

Dendritic cells (DC) capture antigens from apoptotic and/or necrotic tumor cells and cross-present them to T cells, and various ways of delivering tumor antigens to DC in vitro and in vivo are being pursued. Since fusions of antigenic proteins with the HSV integument protein VP22 are capable of intercellular trafficking, this approach has been exploited for delivery of antigens to antigen-presenting cells. Adenoviral vectors were used to express the tumor-associated-but-self-antigen MART-1 fused to HSV VP22 in MART-1-negative A375 melanoma cells and in DC. When expressed in A375 cells and allowed to spread to DC across a transwell barrier, the VP22-MART-1 fusion protein localized to both early and late endosomal structures of the DC. The DC loaded with the VP22-MART-1 fusion by intercellular trafficking efficiently presented the MART-1(27-35) epitope to MART-1(27-35)-specific CTL. Furthermore, transloaded DC were capable of expanding the population of MART-1(27-35)-specific CTL. Thus, a tumor antigen acquired by intercellular trafficking can be cross-presented by DC. This experimental approach should therefore be useful not only for studying the mechanism of cross-presentation but also for vaccine development.

Peptide-based cancer vaccines

The characterization of tumor antigens recognized by T lymphocytes has provided the opportunity to immunize cancer patients with well-defined peptides. Differentiation and tumor-specific antigens are expressed in a significant proportion of patients with cancer. Pilot studies have involved many patients with melanoma. No major toxicity has been reported after peptide vaccination. The clinical efficacy of peptide vaccines is limited to a minority of patients and the response rate is less than 20%. Some regressions have been complete and long-lasting. The development of this approach, and that of other methods to deliver tumor antigens, depends on clinical empirism to improve the therapeutic efficacy of the vaccine as well as the accurate understanding of the immune mechanisms involved in vivo. Semin Oncol 29:494-502. Copyright 2002, Elsevier Science (USA). All rights reserved.

Dendritic cell vaccination for the treatment of skin cancer.

Reasons for failure of the immune system to fight cancer include tumor immune escape mechanisms, limited availability of tumor-specific antigens, and failure to deliver tumor antigens in the right immunological context. Progress in molecular biology and immunology has provided technologies that can detect an ever-widening choice of new tumor-specific antigens. One of the most important questions remains the delivery of these tumor antigens in an effective way to the immune system of a cancer patient. This task is performed in normal circumstances by dendritic cells (DCs). DCs are sentinels of the immune system located at sites of antigen entry such as skin. They take up antigen and carry it to secondary lymphoid organs. They are highly specialized antigen-presenting cells (APCs) for the activation of specific effector T cells recirculating in secondary lymphoid organs. In recent years an enormous increase in our understanding of DC biology has opened up new ways of applying these cells for immunotherapy of cancer.