Genetic approaches for the induction of a CD4+ T cell response in cancer immunotherapy

Immortalized B Cells Transfected with mRNA of Antigen Fused to MITD (IBMAM): An Effective Tool for Antigen-Specific T-Cell Expansion and TCR Validation

Peripheral mononuclear blood cells (PBMCs) are the most widely used study materials for immunomonitoring and antigen-specific T-cell identification. However, limited patient PBMCs and low-frequency antigen-specific T cells remain as significant technical challenges. To address these limitations, we established a novel platform comprised of optimized HLA-matched immortalized B cells transfected with mRNA of a prototype viral or tumor antigen conjugated to MHC class-I trafficking domain protein (MITD) to increase the efficiency of epitope expression in antigen-presenting cells (APCs) essential to expanding antigen-specific T cells. When applied to CMV as a model, the IBMAM platform could successfully expand CMV-specific T cells from low-frequency CMV PBMCs from seropositive donors. Additionally, this platform can be applied to the validation of antigen specific TCRs. Together, compared to using APCs with synthesized peptides, this platform is an unlimited, highly efficient, and cost-effective resource in detecting and expanding antigen-specific T cells and validating antigen-specific TCRs.

A Necroptosis-Related Gene Signature to Predict the Prognosis of Skin Cutaneous Melanoma

The prognosis of skin cutaneous melanoma (SKCM) remains poor, and patients with SKCM show a poor response to immunotherapy. Thus, we aimed to identify necroptosis-related biomarkers, which can help predict the prognosis of SKCM and improve the effectiveness of precision medicine. Data of SKCM were obtained from The Cancer Genome Atlas (TCGA) and GEO databases. TCGA samples were classified into two clusters by consensus clustering of necroptosis-related genes. Univariate Cox and least absolute shrinkage and selection operator regression analyses led to the identification of 11 genes, which were used to construct a prognostic model. GSE65904 was used as the test set. Principal component, t-distributed stochastic neighbor embedding, and Kaplan–Meier survival analyses indicated that samples in the train and test sets could be divided into two groups, with the high-risk group showing a worse prognosis. Univariate and multivariate Cox regression analyses were performed, and a nomogram, calibration curve, and time-dependent receiver operating characteristic curve were constructed to verify the efficacy of our model. The 1-, 3-, and 5-year areas under the receiver operating characteristic curves for the train set were 0.702, 0.663, and 0.701 and for the test set were 0.613, 0.627, and 0.637, respectively. Moreover, we performed Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses between the high- and low-risk groups. Single sample gene set enrichment analysis, immune cell infiltration analysis, tumor microenvironment scores, immune checkpoint analysis, and half-maximal inhibitory concentration prediction indicated that the high-risk group showed weaker antitumor immunity; further, the response to immune checkpoint inhibitors was worse, and the high-risk group was sensitive to fewer antitumor drugs. Tumor mutational burden analysis, Kaplan–Meier survival analysis, and correlation analysis between risk score and RNA stemness score revealed that the high-risk group with low tumor mutational burden and high RNA stemness score was potentially associated with poor prognosis. To conclude, our model, which was based on 11 necroptosis-related genes, could predict the prognosis of SKCM; in addition, it has guiding significance for the selection of clinical treatment and provides new research directions to enhance necroptosis against SKCM.

Emerging applications of nanobodies in cancer therapy

Cancer is a heterogeneous disease, requiring treatment tailored to the unique phenotype of the patient's tumor. Monoclonal antibodies (mAbs) and variants thereof have enabled targeted therapies to selectively target cancer cells. Cancer cell-specific mAbs have been used for image-guided surgery and targeted delivery of radionuclides or toxic agents, improving classical treatment strategies. Cancer cell-specific mAbs can further inhibit tumor cell growth or can stimulate immune-mediated destruction of cancer cells, a feature that has also been achieved through mAb-mediated manipulation of immune cells and pathways. Drawbacks of mAbs and their variants, together with the discovery of camelid heavy chain-only antibodies and the many advantageous features of their variable domains, referred to as V_HHs, single domain antibodies or nanobodies (Nbs), resulted in the exploration of Nbs as an alternative targeting moiety. We therefore review the state-of-the-art as well as novel exploitation strategies of Nbs for targeted cancer therapy.

H2-M and H2-O as Targeting Vehicles for the MHC Class II Processing Compartment Promote Antigen-Specific CD4+ T Cell Activation

CD8 and CD4 T cell activation are both required for a strong and long-lasting T cell immune response. Endogenously expressed proteins are readily processed by the MHC class I antigen presentation pathway, enabling activation of CD8+ T cells. However, the MHC class II antigen presentation pathway, necessary for CD4+ T cell activation, is generally not sufficiently accessible to endogenously expressed proteins, limiting the efficiency of mRNA- or DNA-based vaccines. In the current study, we have evaluated the feasibility of using antigen sequences fused to sequences derived from the H2-M and H2-O proteins, two complexes known to participate in MHC class II antigen processing, for the enhancement of CD4 T-cell activation. We analyzed T cell activation after genetic immunization with mRNA-encoding fusion proteins with the model antigen ovalbumin and sequences derived from H2-M or H2-O. Our results show that H2-M- or H2-O-derived sequences robustly improve antigen-specific CD4 T-cell activation when fused to the antigen of interest and suggest that the approach could be used to improve the efficiency of mRNA- or DNA-based vaccines.

Targeting the MHC Class II antigen presentation pathway in cancer immunotherapy

The success of immunotherapy relies on the participation of all arms of the immune system and the role of CD4+ T lymphocytes in preventing tumor growth is now well established. Understanding how tumors evade immune responses holds the key to the development of cancer immunotherapies. In this review, we discuss how MHC Class II expression varies in cancer cells and how this influences antitumor immune responses. We also discuss the means that are currently available for harnessing the MHC Class II antigen presentation pathway for the development of efficient vaccines to activate the immune system against cancer.

Neo-Antigen mRNA Vaccines

The interest in therapeutic cancer vaccines has caught enormous attention in recent years due to several breakthroughs in cancer research, among which the finding that successful checkpoint blockade treatments reinvigorate neo-antigen-specific T cells and that successful adoptive cell therapies are directed towards neo-antigens. Neo-antigens are cancer-specific antigens, which develop from somatic mutations in the cancer cell genome that can be highly immunogenic and are not subjected to central tolerance. As the majority of neo-antigens are unique to each patient's cancer, a vaccine technology that is flexible and potent is required to develop personalized neo-antigen vaccines. In vitro transcribed mRNA is such a technology platform and has been evaluated for delivery of neo-antigens to professional antigen-presenting cells both ex vivo and in vivo. In addition, strategies that support the activity of T cells in the tumor microenvironment have been developed. These represent a unique opportunity to ensure durable T cell activity upon vaccination. Here, we comprehensively review recent progress in mRNA-based neo-antigen vaccines, summarizing critical milestones that made it possible to bring the promise of therapeutic cancer vaccines within reach.

Strategies to Genetically Modulate Dendritic Cells to Potentiate Anti-Tumor Responses in Hematologic Malignancies

Dendritic cell (DC) vaccination has been investigated as a potential strategy to target hematologic malignancies, while generating sustained immunological responses to control potential future relapse. Nonetheless, few clinical trials have shown robust long-term efficacy. It has been suggested that a combination of surmountable shortcomings, such as selection of utilized DC subsets, DC loading and maturation strategies, as well as tumor-induced immunosuppression may be targeted to maximize anti-tumor responses of DC vaccines. Generation of DC from CD34+ hematopoietic stem and progenitor cells (HSPCs) may provide potential in patients undergoing allogeneic HSPC transplantations for hematologic malignancies. CD34+ HSPC from the graft can be genetically modified to optimize antigen presentation and to provide sufficient T cell stimulatory signals. We here describe beneficial (gene)-modifications that can be implemented in various processes in T cell activation by DC, among which major histocompatibility complex (MHC) class I and MHC class II presentation, DC maturation and migration, cross-presentation, co-stimulation, and immunosuppression to improve anti-tumor responses.

mRNA Electroporation of Dendritic Cells with WT1, Survivin, and TriMix (a Mixture of caTLR4, CD40L, and CD70)

The immune system is a crucial player in the development of cancer. Once it is in imbalance and immunosuppressive mechanisms supporting tumor growth take over control, dendritic cell immunotherapy might offer a solution to restore the balance. There are several methods to manufacture dendritic cells but none of them has yet proven to be superior to others. In this chapter, we discuss the methodology using electroporation of mRNA encoding Wilms' tumor gene 1, survivin, and TriMix (mixture of caTLR4, CD40L, and CD70) to simultaneously load and mature dendritic cells.

Dendritic cell immunotherapy in uterine cancer

Uterine cancer is the most common pelvic gynecological malignancy. Uterine sarcomas and relapsed uterine carcinomas have limited treatment options. The search for new therapies is urgent. Dendritic cell (DC) immunotherapy holds much promise, though has been poorly explored in uterine cancer. This commentary gives an insight in existing DC immunotherapy studies in uterine cancer and summarizes the possibilities and the importance of the loading of tumor antigens onto DC and their subsequent maturation. However, the sole application of DC immunotherapy to target uterine cancer will be insufficient because of tumor-induced immunosuppression, which will hamper the establishment of an effective anti-tumor immune response. The authors give an overview on the limited existing immunosuppressive data and propose a novel approach on DC immunotherapy in uterine cancer.

mRNA-based dendritic cell vaccines

Cancer immunotherapy has been proposed as a powerful treatment modality. Active immunotherapy aspires to stimulate the patient's immune system, particularly T cells. These cells can recognize and kill cancer cells and can form an immunological memory. Dendritic cells (DCs) are the professional antigen-presenting cells of our immune system. They take up and process antigens to present them to T cells. Consequently, DCs have been investigated as a means to stimulate cancer-specific T-cell responses. An efficient strategy to program DCs is the use of mRNA, a well-defined and safe molecule that can be easily generated at high purity. Importantly, vaccines consisting of mRNA-modified DCs showed promising results in clinical trials. Therefore, we will introduce cancer immunotherapy and DCs and give a detailed overview on the application of mRNA to generate cancer-fighting DC vaccines.

Cancer immunotherapy using virally transduced dendritic cells: animal studies and human clinical trials

The immune system uses a process known as 'immunosurveillance' to help prevent the outgrowth of tumors. In cancer immunotherapy, a major goal is for immunity against tumor-associated antigens to be generated or strengthened in patients. To achieve this goal, several approaches have been tested, including the use of highly potent antigen-presenting cells called dendritic cells (DCs), which can activate T cells efficiently. Presentation of peptides derived from tumor antigens on the surface of DCs can stimulate strong antitumor immunity. Using recombinant viral vectors encoding tumor-associated antigens, DCs can be engineered efficiently to express sustained levels of tumor-antigen peptides. This review discusses the effectiveness of virally transduced DCs in treating tumors and generating antigen-specific T-cell responses. It covers mouse and nonhuman primate studies, preclinical in vitro human cell experiments and clinical trials.

The effect of helper epitopes and cellular localization of an antigen on the outcome of gene gun DNA immunization

In DNA vaccination, CD4(+) T-cell help can be enhanced by fusion of a gene encoding an immunization protein with a foreign gene or its part providing T(h) epitopes. To study the effect of helper epitope localization in a protein molecule, the influence of the vicinity of the helper epitope, and the impact of chimeric protein cellular localization, we fused the helper epitope p30 from tetanus toxin (TT, aa 947-967) with the N- or C-terminus of the mutated E7 oncoprotein (E7GGG) of human papillomavirus type 16, enlarged the p30 epitope with the flanking residues containing potential protease-sensitive sites and altered the cellular localization of the fusion constructs by signal sequences. The p30 epitope enhanced the E7-specific response, but only in constructs without added signal sequences. After localization of the fusion proteins into the endoplasmic reticulum and endo/lysosomal compartment, the TT-specific T(h)2 response was increased. The synthetic Pan DR epitope (PADRE) induced a stronger E7-specific response than the p30 epitope and its stimulatory effect was not limited to nuclear/cytoplasmic localization of the E7 antigen. These results suggest that in the optimization of immune responses by adding helper epitopes to DNA vaccines delivered by the gene gun, the cellular localization of the antigen needs to be taken into account.

Dendritic cell-based vaccines: barriers and opportunities

Dendritic cells (DCs) have several characteristics that make them an ideal vehicle for tumor vaccines, and with the first US FDA-approved DC-based vaccine in use for the treatment of prostate cancer, this technology has become a promising new therapeutic option. However, DC-based vaccines face several barriers that have limited their effectiveness in clinical trials. A major barrier includes the activation state of the DC. Both DC lineage and maturation signals must be selected to optimize the antitumor response and overcome immunosuppressive effects of the tumor microenvironment. Another barrier to successful vaccination is the selection of target antigens that will activate both CD8(+) and CD4(+) T cells in a potent, immune-specific manner. Finally, tumor progression and immune dysfunction limit vaccine efficacy in advanced stages, which may make DC-based vaccines more efficacious in treating early-stage disease. This review underscores the scientific basis and advances in the development of DC-based vaccines, focuses on current barriers to success and highlights new research opportunities to address these obstacles.

RNA pulsed dendritic cells: an approach for cancer immunotherapy

The immunotherapy of cancer is aimed at evoking both branches of immune system to elicite specific immune responses directed against tumor antigens to deal with residual tumor cells upon interaction, and thereby decreases mortality as well as morbidity of cancer patients. As dendritic cells (DCs) are specialized for antigen presentation, and their immunogenicity leads to the induction of antigen specific immune responses, various immunotherapeutic approaches have been designed for using DCs to present tumor-associated antigens to T-lymphocytes. As a part of proposed strategy ex vivo generated DCs might be loaded with antigens and re-infused to the patients and/or they can be used for the ex vivo expansion of anti-tumor lymphocytes. The DCs loaded ex vivo with RNA can be safely administered which proves to be an asset for producing antigen specific immune responses. Furthermore, already conducted studies have prompted clinical trials to be designed to investigate immunological and clinical effects of RNA pulsed DCs administered as an engineered therapeutic vaccine in cancer patients. However, selection of the antigens of interest, methods for introducing TAAgs into MHC class I and II processing pathways, methods for isolation and activation of DCs, and route of administration are the parameters to be considered for designing and conducting clinical trials with engineered DCs. The enhanced RNA transfection efficiency would further improve antigen processing and presentation and T-cell co-stimulation, resulting in the induction of heightened anti-tumor immune responses. Therefore, RNA transfected dendritic cells continue to hold promise for cellular immunotherapy and opens new avenues to devising further strategies for cancer therapeutic interventions.

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.

Dendritic cells loaded with mRNA encoding full-length tumor antigens prime CD4+ and CD8+ T cells in melanoma patients

It is generally thought that dendritic cells (DCs) loaded with full-length tumor antigen could improve immunotherapy by stimulating broad T-cell responses and by allowing treatment irrespective of the patient's human leukocyte antigen (HLA) type. To investigate this, we determined the specificity of T cells from melanoma patients treated with DCs loaded with mRNA encoding a full-length tumor antigen fused to a signal peptide and an HLA class II sorting signal, allowing presentation in HLA class I and II. In delayed-type hypersensitive (DTH)-biopsies and blood, we found functional CD8(+) and CD4(+) T cells recognizing novel treatment-antigen-derived epitopes, presented by several HLA types. Additionally, we identified a CD8(+) response specific for the signal peptide incorporated to elicit presentation by HLA class II and a CD4(+) response specific for the fusion region of the signal peptide and one of the antigens. This demonstrates that the fusion proteins contain newly created immunogenic sequences and provides evidence that ex vivo-generated mRNA-modified DCs can induce effector CD8(+) and CD4(+) T cells from the naive T-cell repertoire of melanoma patients. Thus, this work provides definitive proof that DCs presenting the full antigenic spectrum of tumor antigens can induce T cells specific for novel epitopes and can be administered to patients irrespective of their HLA type.

Targeting lentiviral vectors for cancer immunotherapy

Delivery of tumour-associated antigens (TAA) in a way that induces effective, specific immunity is a challenge in anti-cancer vaccine design. Circumventing tumour-induced tolerogenic mechanisms in vivo is also critical for effective immunotherapy. Effective immune responses are induced by professional antigen presenting cells, in particular dendritic cells (DC). This requires presentation of the antigen to both CD4(+) and CD8(+) T cells in the context of strong co-stimulatory signals. Lentiviral vectors have been tested as vehicles, for both ex vivo and in vivo delivery of TAA and/or activation signals to DC, and have been demonstrated to induce potent T cell mediated immune responses that can control tumour growth. This review will focus on the use of lentiviral vectors for in vivo gene delivery to DC, introducing strategies to target DC, either targeting cell entry or gene expression to improve safety of the lentiviral vaccine or targeting dendritic cell activation pathways to enhance performance of the lentiviral vaccine. In conclusion, this review highlights the potential of lentiviral vectors as a generally applicable 'off-the-shelf' anti-cancer immunotherapeutic.

Engineering dendritic cells to enhance cancer immunotherapy

Cancer immunotherapy aims to establish immune-mediated control of tumor growth by priming T-cell responses to target tumor-associated antigens. Three signals are required for T-cell activation: (i) presentation of cognate antigen in self MHC molecules; (ii) costimulation by membrane-bound receptor-ligand pairs; and (iii) soluble factors to direct polarization of the ensuing immune response. The ability of dendritic cells (DCs) to provide all three signals required for T-cell activation makes them an ideal cancer vaccine platform. Several strategies have been developed to enhance and control antigen presentation, costimulation, and cytokine production. In this review, we discuss progress toward developing DC-based cancer vaccines by genetic modification using RNA, DNA, and recombinant viruses. Furthermore, the ability of DC-based vaccines to activate natural killer (NK) and B-cells, and the impact of gene modification strategies on these populations is described. Clinical trials using gene-modified DCs have shown modest results, therefore, further considerations for DC manipulation to enhance their clinical efficacy are also discussed.

Developing dendritic cell-based therapies to condition immune responses to novel oncogenic proteins and stem cells

Cancer vaccines have been disappointing when utilized as stand-alone therapy, especially in late disease settings. However, recent clinical studies in prostate cancer have suggested that dendritic cellular (DC) vaccines may impact patient survival, reviving the notion that cancer vaccines can impact established cancer. In this review we will highlight the advances that have been made in the development of DC-based therapies activated by Toll-like receptor agonists with the capacity to condition toward strong Th1 cellular responses, through the production of cytokines and chemokines, and a capacity to induce apoptosis of tumor cells. Used in early cancer settings, these DCs induce clinically effective immune responses, thus shifting the emphasis toward using these cells earlier in the disease process. We will also discuss targeting novel molecules and cancer stem cells that can eliminate cells with high metastatic potential, moving DC-based therapies into mainstream cancer therapy.

Targeting the MHC class II pathway of antigen presentation enhances immunogenicity and safety of allergen immunotherapy

BACKGROUND

Current s.c. allergen-specific immunotherapy (SIT) leads to amelioration of IgE-mediated allergy, but it requires numerous allergen injections over several years and is frequently associated with severe side-effects. The aim of this study was to test whether modified recombinant allergens can improve therapeutic efficacy in SIT while reducing allergic side-effects.

METHODS

The major cat allergen Fel d 1 was fused to a TAT-derived protein translocation domain and to a truncated invariant chain for targeting the MHC class II pathway (MAT-Fel d 1). The immunogenicity was evaluated in mice, while potential safety issues were assessed by cellular antigen stimulation test (CAST) using basophils from cat-dander-allergic patients.

RESULTS

MAT-Fel d 1 enhanced induction of Fel d 1-specific IgG2a antibody responses as well as the secretion of IFN-gamma and IL-2 from T cells. Subcutaneous allergen-specific immunotherapy of mice using the modified Fel d 1 provided stronger protection against anaphylaxis than SIT with unmodified Fel d 1, and MAT-Fel d 1 caused less degranulation of human basophils than native Fel d 1.

CONCLUSION

MAT-Fel d 1 allergen enhanced protective antibody and Th1 responses in mice, while reducing human basophil degranulation. Immunotherapy using MAT-Fel d 1 allergen therefore has the potential to enhance SIT efficacy and safety, thus, shortening SIT. This should increase patient compliance and lower treatment costs.

Dendritic cell-based cancer vaccination: quo vadis?

Dendritic cells (DCs) play a central role in the initiation and regulation of primary immune responses. DCs loaded with tumor-associated antigens induce anti-tumoral cytotoxic T cells in vitro and in vivo. However, clinical trials using ex vivo-generated DCs have failed to demonstrate clinical efficacy. This review summarizes recent advances in concepts and techniques that are providing new impulses to DC-based cancer vaccination. Improvements in protocols for ex vivo-generation of DCs, innovations in immunomonitoring, strategies to overcome tumor-induced immunosuppression and insights into the mutual beneficial effects of vaccines and chemotherapy are all considered. Furthermore, we highlight novel developments in cell-free vaccines targeting DCs in vivo.

Functional T-cell responses generated by dendritic cells expressing the early HIV-1 proteins Tat, Rev and Nef

The limitations of highly active anti-retroviral therapy (HAART) have necessitated the development of alternative therapeutic strategies. One of the approaches that has gained prominence in recent years is therapeutic vaccination. We decided to assess the capacity of mature dendritic cells, derived from blood monocytes of HIV-1 infected patients, to generate functional T-cell responses. For this purpose, we constructed a chimeric mRNA encoding the proteins Tat, Rev and Nef. The TaReNef encoding information was linked to the HLA class II-targeting sequence of DC-LAMP. Broadly directed HIV-specific CD4(+) and CD8(+) cytotoxic T cells exhibiting a poly-functional cytokine secretion pattern were generated by co-culturing with autologous chimeric mRNA electroporated dendritic cells. Thus, administration of ex vivo generated dendritic cells expressing the early proteins Tat, Rev and Nef might offer a promising approach for therapeutic vaccination in HIV-1 infection.

Increased antigen presentation efficiency by coupling antigens to MHC class I trafficking signals

Genetic modification of vaccines by linking the Ag to lysosomal or endosomal targeting signals has been used to route Ags into MHC class II processing compartments for improvement of CD4+ T cell responses. We report in this study that combining an N-terminal leader peptide with an MHC class I trafficking signal (MITD) attached to the C terminus of the Ag strongly improves the presentation of MHC class I and class II epitopes in human and murine dendritic cells (DCs). Such chimeric fusion proteins display a maturation state-dependent subcellular distribution pattern in immature and mature DCs, mimicking the dynamic trafficking properties of MHC molecules. T cell response analysis in vitro and in mice immunized with DCs transfected with Ag-encoding RNA showed that MITD fusion proteins have a profoundly higher stimulatory capacity than wild-type controls. This results in efficient expansion of Ag-specific CD8+ and CD4+ T cells and improved effector functions. We used CMVpp65 and NY-ESO-1 Ags to study preformed immune responses in CMV-seropositive individuals and cancer patients. We show that linking these Ags to the MITD trafficking signal allows simultaneous, polyepitopic expansion of CD8+ and CD4+ T cells, resulting in distinct CD8+ T cell specificities and a surprisingly broad and variable Ag-specific CD4+ repertoire in different individuals.

Simultaneous ex vivo quantification of antigen-specific CD4+ and CD8+ T cell responses using in vitro transcribed RNA

Assessment of antigen-specific T-cell responses has been greatly facilitated by development of ELISPOT and intracellular cytokine flow cytometry (CFC) assays. The use of autologous antigen presenting cells transfected with in vitro transcribed RNA as stimulators allows in principle quantification of antigen-specific T-cells independent of the knowledge of the epitopes. We describe here a cytokine secretion assay that enables simultaneous assessment of both antigen-specific CD4+ as well as CD8+ T-cells directly from clinical samples without the need for generation of dendritic cells. To this aim, bulk PBMCs were electroporated with RNA encoding the antigen fused to trafficking signal sequences derived from a MHC class I molecule and used as stimulators. With human cytomegalovirus (HCMV) phosphoprotein 65 (pp65) as antigen we show that for measuring ex vivo T-cell responses in ELISPOT and CFC such stimulators are superior or at least equivalent to a pool of overlapping peptides representing the entire pp65 sequence as well as to untagged pp65 encoding RNA. This approach avoids the time consuming generation of dendritic cells as immune stimulators and, in particular when used in the context of the CFC, is robust, broadly applicable and fast.

T-cell receptor gene therapy for cancer: the progress to date and future objectives

In the last decade research has begun into the use of T-cell receptor (TCR) gene therapy as a means to control and eradicate malignancies. There is now a large body of evidence to demonstrate that through the use of this technology one can redirect T-cell antigen specificity to produce both cytotoxic and helper T cells, which are functionally competent both in vitro and in vivo and show promising antitumour effects in humans. This review focuses on the means by which TCR gene transfer is achieved and the recent advances to modify the TCRs and vector delivery systems which aim to enhance the efficiency and safety of TCR gene transfer protocols.

Activation of human CD4+ T cells by targeting MHC class II epitopes to endosomal compartments using human CD1 tail sequences

Distinct CD4(+) T-cell epitopes within the same protein can be optimally processed and loaded into major histocompatibility complex (MHC) class II molecules in disparate endosomal compartments. The CD1 protein isoforms traffic to these same endosomal compartments as directed by unique cytoplasmic tail sequences, therefore we reasoned that antigen/CD1 chimeras containing the different CD1 cytoplasmic tail sequences could optimally target antigens to the MHC class II antigen presentation pathway. Evaluation of trafficking patterns revealed that all four human CD1-derived targeting sequences delivered antigen to the MHC class II antigen presentation pathway, to early/recycling, early/sorting and late endosomes/lysosomes. There was a preferential requirement for different CD1 targeting sequences for the optimal presentation of an MHC class II epitope in the following hierarchy: CD1b > CD1d = CD1c > > > CD1a or untargeted antigen. Therefore, the substitution of the CD1 ectodomain with heterologous proteins results in their traffic to distinct intracellular locations that intersect with MHC class II and this differential distribution leads to specific functional outcomes with respect to MHC class II antigen presentation. These findings may have implications in designing DNA vaccines, providing a greater variety of tools to generate T-cell responses against microbial pathogens or tumours.

mRNA-based cancer vaccine: prevention of B16 melanoma progression and metastasis by systemic injection of MART1 mRNA histidylated lipopolyplexes

Immunization with mRNA encoding tumor antigen is an emerging vaccine strategy for cancer. In this paper, we demonstrate that mice receiving systemic injections of MART1 mRNA histidylated lipopolyplexes were specifically and significantly protected against B16F10 melanoma tumor progression. The originality of this work concerns the use of a new tumor antigen mRNA formulation as vaccine, which allows an efficient protection against the growth of a highly aggressive tumor model after its delivery by intravenous route. Synthetic melanoma-associated antigen MART1 mRNA was formulated with a polyethylene glycol (PEG)ylated derivative of histidylated polylysine and L-histidine-(N,N-di-n-hexadecylamine)ethylamide liposomes (termed histidylated lipopolyplexes). Lipopolyplexes comprised mRNA/polymer complexes encapsulated by liposomes. The tumor protective effect was induced with MART1 mRNA carrying a poly(A) tail length of 100 adenosines at an optimal dose of 12.5 microg per mouse. MART1 mRNA lipopolyplexes elicited a cellular immune response characterized by the production of interferon-gamma and the induction of cytotoxic T lymphocytes. Finally, the anti-B16 response was enhanced using a formulation containing both MART1 mRNA and MART1-LAMP1 mRNA encoding the antigen targeted to the major histocompatibility complex class II compartments by the lysosomal sorting signal of LAMP1 protein. Our results provide a basis for the development of mRNA histidylated lipopolyplexes for cancer vaccine.

Processing sites are different in the generation of HLA-A2.1-restricted, T cell reactive tumor antigen epitopes and viral epitopes

In order to improve the processing efficiency of T cell tumor antigen epitopes, this bioinformatic study compares proteolytic sites in the generation of 47 experimentally identified HLA-A2.1-restricted immunodominant tumor antigen epitopes to those of 52 documented HLA-A2.1-restricted immunodominant viral antigen epitopes. Our results show that the amino acid frequencies in the C-terminal cleavage sites of the tumor antigen epitopes, as well as several positions within the 10 amino acid (aa) flanking regions, are significantly different from those of the viral antigen epitopes. In the 9 amino acid epitope region, frequencies differed somewhat in the secondary-anchored amino acid residues on E3 (the third aa of the epitope), E4, E6, E7 and E8; however, frequencies in the primary-anchored positions, on E2 and E9, for binding in the HLA-A2.1 groove, remained almost identical. The most frequently occurring amino acid pairs in both N-terminal and C-terminal cleavage sites in the generation of tumor antigen epitopes were different from those of the viral antigen epitopes. Our findings demonstrate for the first time that these two groups of epitopes may be cleaved by distinct sets of proteasomes and peptidases or similar enzymes with lower efficiencies for tumor epitopes. In the future, in order to more effectively generate tumor antigen epitopes, targeted activation of the immunoproteasomes and peptidases that mediate the cleavage of viral epitopes could be achieved, thus enhancing our potential for antigen-specific tumor immunotherapy.

Therapeutic implications of the TLR and VDR partnership

The innate immune system provides the host with an immediate and rapid defense against invading microbes. Detection of foreign invaders is mediated by a class of receptors that are known as the pattern recognition receptors, such as the family of Toll-like receptors (TLRs). In humans, ten functional TLRs have been identified and they respond to conserved pathogen-associated molecular patterns derived from bacteria, mycoplasma, fungi and viruses. TLR activation leads to direct antimicrobial activity against both intracellular and extracellular bacteria, and induces an antiviral gene program. Recently, it was reported that TLR2 activation leads to the use of vitamin D3 as a mechanism to combat Mycobacterium tuberculosis. Here, we focus on recent findings concerning the TLR-induced antimicrobial mechanisms in humans and the therapeutic implications of these findings. Owing to their capability to combat a wide array of pathogens, TLRs are attractive therapeutic targets. However, additional knowledge about their antimicrobial mechanisms is needed.

Mast cells and T-lymphocytes in juvenile angiofibromas

Juvenile angiofibroma (JA) is regarded as a benign fibrovascular tumour of unknown aetiology. Due to its fibrovascular architecture the fibrous and vascular tumour component have been in the focus of most studies. This investigation aimed at characterizing inflammatory cells in JAs by immunohistochemical stainings and western blot analysis. Number and type of mast cells as well as T-lymphocytes were evaluated in a series of 10 JAs and 5 nasal mucosa (NM) specimens used as control tissue. A remarkable number of mast cells were found in JAs (14.6% of all cells). By using a combination of the mast cell markers tryptase and chymase three distinct mast cell populations could be identified: 12% expressed tryptase (T+) only, 3% stained for chymase (C+) only, and 85% were positive for both tryptase and chymase (TC+). Western blot analysis supported finding of remarkable expression of the mast cell markers tryptase and chymase in JAs and indicated for both proteins similar but also different molecular weights than being observed in NM. Furthermore an infiltration of the tumour by CD4- and CD8-positive T-lymphocytes (15.4% of all cells) was evident in immunofluorescent stainings. Compared to NM, a significantly higher number of TC+ (6.9% in JAs versus 2.7% in NM) and CD8-positive (9.7% in JAs versus 5.8% in NM) cells were found in the tumour tissue. Thus, mast cells and T-lymphocytes were identified as predominant cell types in JAs representing 30% of the cells in the tumour specimens analysed. Regarding these observations JAs are certainly not only built up by vascular cells and fibrous stroma cells. High rates of inflammatory cells like mast cells and T-lymphocytes have to be considered in this tumour.

Characterization of a permissive epitope insertion site in adenovirus hexon

A robust immune response is generated against components of the adenovirus capsid. In particular, a potent and long-lived humoral response is elicited against the hexon protein. This is due to the efficient presentation of adenovirus capsid proteins to CD4+ T cells by antigen-presenting cells, in addition to the highly repetitive structure of the adenovirus capsids, which can efficiently stimulate B-cell proliferation. In the present study, we take advantage of this immune response by inserting epitopes against which an antibody response is desired into the adenovirus hexon. We use a B-cell epitope from Bacillus anthracis protective antigen (PA) as a model antigen to characterize hypervariable region 5 (HVR5) of hexon as a site for peptide insertion. We demonstrate that HVR5 can accommodate a peptide of up to 36 amino acids without adversely affecting virus infectivity, growth, or stability. Viruses containing chimeric hexons elicited antibodies against PA in mice, with total immunoglobulin G (IgG) titers reaching approximately 1 x 10(3) after two injections. The antibody response contained both IgG1 and IgG2a subtypes, suggesting that Th1 and Th2 immunity had been stimulated. Coinjection of wild-type adenovirus and a synthetic peptide from PA produced no detectable antibodies, indicating that incorporation of the epitope into the capsid was crucial for immune stimulation. Together, these results indicate that the adenovirus capsid is an efficient vehicle for presenting B-cell epitopes to the immune system, making this a useful approach for the design of epitope-based vaccines.

Antigen targeting to endosomal pathway in dendritic cell vaccination activates regulatory T cells and attenuates tumor immunity

Lymphoma cells are malignant cells of the T- or B-cell lineage that often express many surface markers inappropriately, yet are not recognized as abnormal by the immune system. We modeled this situation by inoculating ovalbumin-expressing E.G7-OVA lymphoma cells into mice that expressed ovalbumin as a self antigen in pancreatic islets, and investigated the efficacy of dendritic cell (DC) vaccination in these mice. Although vaccination with DC-expressing ovalbumin induced strong cytotoxic T-cell immunity, which led to clearance of E.G7-OVA lymphoma cells in naive C57BL/6 mice, DC vaccination was ineffective in mice expressing ovalbumin as a self antigen. Antigen modification to increase its processing via the endosomal processing pathway dramatically increased CD4 T-cell activation but paradoxically, impaired the protective effect of DC vaccination even in naive mice. Depletion of CD25(+) T cells (regulatory T cells [Tregs]) prior to vaccination restored the efficacy of DC vaccination and allowed eradication of lymphoma also in mice expressing ovalbumin as a self antigen. We conclude that lymphoma cells may be eradicated using DC vaccination if activation of CD25(+) Tregs is simultaneously inhibited, and that intentionally enhanced endosomal antigen processing in DC vaccines may shift the balance from CD4 T-cell help toward stimulation of Tregs.

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.