Processing and presentation of tumor antigens and vaccination strategies

Caged aminoluciferin probe for bioluminescent immunoproteasome activity analysis

The immunoproteasome (iCP) can be expressed under inflammatory conditions, such as exposure to interferon-gamma (IFN-γ), that alerts the cell to begin generating iCP preferentially over the standard proteasome (sCP). With the iCP becoming a widely targeted isoform in a variety of diseases, there is a need to understand its activity and expression in cells and in vivo. Activity-based probes for the iCP have been developed but their application has been limited due to their difficult synthesis and cannot be used in tissues or whole animals. Our lab has previously demonstrated we can monitor iCP activity using a 4-mer peptide linked to a fluorophore and a peptoid. This was utilized in the development of the first cell-permeable iCP activity-based probe that did not include a covalent reactive moiety. Here, we demonstrate that this same peptide recognition sequence can be appended to aminoluciferin, caging it, until its interaction with the iCP. This probe should be applicable to monitor iCP activity in animal models where tumor or other tissue has been engineered to produce luciferase. We anticipate it could also be applied to observe iCP activity as tumors are formed in vivo.

In vitro proteasome processing of neo-splicetopes does not predict their presentation in vivo

Proteasome-catalyzed peptide splicing (PCPS) of cancer-driving antigens could generate attractive neoepitopes to be targeted by T cell receptor (TCR)-based adoptive T cell therapy. Based on a spliced peptide prediction algorithm, TCRs were generated against putative KRASG12V- and RAC2P29L-derived neo-splicetopes with high HLA-A*02:01 binding affinity. TCRs generated in mice with a diverse human TCR repertoire specifically recognized the respective target peptides with high efficacy. However, we failed to detect any neo-splicetope-specific T cell response when testing the in vivo neo-splicetope generation and obtained no experimental evidence that the putative KRASG12V- and RAC2P29L-derived neo-splicetopes were naturally processed and presented. Furthermore, only the putative RAC2P29L-derived neo-splicetopes was generated by in vitro PCPS. The experiments pose severe questions on the notion that available algorithms or the in vitro PCPS reaction reliably simulate in vivo splicing and argue against the general applicability of an algorithm-driven 'reverse immunology' pipeline for the identification of cancer-specific neo-splicetopes.

Naringenin Enhances the Antitumor Effect of Therapeutic Vaccines by Promoting Antigen Cross-Presentation

Dendritic cells (DCs) can internalize and cross-present exogenous Ags to CD8⁺ T cells for pathogen or tumor cell elimination. Recently, growing evidences suggest the possible immunoregulatory role of flavonoids through modulating the Ag presentation of DCs. In this study, we report that naringenin, a grapefruit-derived flavonoid, possesses the ability to increase the Ag cross-presentation in both murine DC line DC2.4 as well as bone marrow-derived DCs, and naringenin-induced moderate intracellular oxidative stress that contributed to the disruption of lysosomal membrane enhanced Ag leakage to cytosol and cross-presentation. Moreover, in a murine colon adenocarcinoma model, naringenin induced more CD103⁺ DCs infiltration into tumor and facilitated the activation of CD8⁺ T cells and strengthened the performance of therapeutic E7 vaccine against TC-1 murine lung cancer. Our investigations may inspire novel thoughts for vaccine design and open a new field of potential applications of flavonoids as immunomodulators to improve host protection against infection and tumor.

Monitoring the Immunoproteasome in Live Cells Using an Activity-Based Peptide-Peptoid Hybrid Probe

Activity-based probes have greatly improved our understanding of the intrinsic roles and expression levels of various proteins within cells. To be useful in live cells, probes must be cell permeable and provide a read-out that can be measured without disrupting the cells or the activity of the target. Unfortunately, probes for the various forms of the proteasome that can be utilized in intact cells are limited; commercially available probes are most effectively used with purified protein or cell lysate. The proteasome, both the 26S and various isoforms of the 20S CP, is an important target with reported roles in cancer, autoimmune disorders, and neurodegenerative diseases. Here, we present the development of a selective probe for the immunoproteasome, a specialized isoform of the 20S proteasome, that becomes expressed in cells that encounter an inflammatory signal. Using a one-bead, one-compound library of small peptides, we discovered a trimer sequence efficiently cleaved by the immunoproteasome with significant selectivity over the standard proteasome. Upon conjugating this sequence to rhodamine 110 and a peptoid, we generated a probe with a considerable improvement in sensitivity compared to that of current aminomethylcoumarin-based proteasome probes. Importantly, our probe was capable of labeling immunoproteasome-expressing cells while maintaining its selectivity over other cellular proteases in live cell cultures. We anticipate this probe to find wide utility for those that wish to study the immunoproteasome's activity in a variety of cell lines and to be used as a reporter to discover small molecules that can perturb the activity of this proteasome isoform.

Targeting Autophagy in ALK-Associated Cancers

Autophagy is an evolutionarily conserved catabolic process, which is used by the cells for cytoplasmic quality control. This process is induced following different kinds of stresses e.g., metabolic, environmental, or therapeutic, and acts, in this framework, as a cell survival mechanism. However, under certain circumstances, autophagy has been associated with cell death. This duality has been extensively reported in solid and hematological cancers, and has been observed during both tumor development and cancer therapy. As autophagy plays a critical role at the crossroads between cell survival and cell death, its involvement and therapeutic modulation (either activation or inhibition) are currently intensively studied in cancer biology, to improve treatments and patient outcomes. Over the last few years, studies have demonstrated the occurrence of autophagy in different Anaplastic Lymphoma Kinase (ALK)-associated cancers, notably ALK-positive anaplastic large cell lymphoma (ALCL), non-small cell lung carcinoma (NSCLC), Neuroblastoma (NB), and Rhabdomyosarcoma (RMS). In this review, we will first briefly describe the autophagic process and how it can lead to opposite outcomes in anti-cancer therapies, and we will then focus on what is currently known regarding autophagy in ALK-associated cancers.

Glycopeptides as Targets for Dendritic Cells: Exploring MUC1 Glycopeptides Binding Profile toward Macrophage Galactose-Type Lectin (MGL) Orthologs

The macrophage galactose-type lectin (MGL) recognizes glycan moieties exposed by pathogens and malignant cells. Particularly, mucin-1 (MUC1) glycoprotein presents an altered glycosylation in several cancers. To estimate the ability of distinct MGL orthologs to recognize aberrant glycan cores in mucins, we applied evanescent-field detection to a versatile MUC1-like glycopeptide microarray platform. Here, as binding was sequence-dependent, we demonstrated that not only sugars but also peptide region impact the recognition of murine MGL1 (mMGL1). In addition, we observed for all three MGL orthologs that divalent glycan presentation increased the binding. To assess the utility of the glycopeptide binders of the MGL orthologs for MGL targeting, we performed uptake assays with fluorescein-MUC1 using murine dendritic cells. A diglycosylated MUC1 peptide was preferentially internalized in an MGL-dependent fashion, thus showing the utility for divalent MGL targeting. These findings may be relevant to a rational design of antitumor vaccines targeting dendritic cells via MGL.

Molecular mechanisms involved in dendritic cell dysfunction in cancer

Dendritic cells (DC) play a pivotal role in the tumor microenvironment (TME). As the primary antigen-presenting cells in the tumor, DCs modulate anti-tumor responses by regulating the magnitude and duration of infiltrating cytotoxic T lymphocyte responses. Unfortunately, due to the immunosuppressive nature of the TME, as well as the inherent plasticity of DCs, tumor DCs are often dysfunctional, a phenomenon that contributes to immune evasion. Recent progresses in our understanding of tumor DC biology have revealed potential molecular targets that allow us to improve tumor DC immunogenicity and cancer immunotherapy. Here, we review the molecular mechanisms that drive tumor DC dysfunction. We discuss recent advances in our understanding of tumor DC ontogeny, tumor DC subset heterogeneity, and factors in the tumor microenvironment that affect DC recruitment, differentiation, and function. Finally, we describe potential strategies to optimize tumor DC function in the context of cancer therapy.

Increased Activity of the Immunoregulatory Enzyme Indoleamine-2,3-Dioxygenase with Consecutive Tryptophan Depletion Predicts Death in Patients with Neuroendocrine Neoplasia

BACKGROUND/AIMS

Data from a considerable number of malignancies demonstrate that depletion of the essential amino acid tryptophan via induction of the immunoregulatory enzyme indoleamine-2,3-dioxygenase (IDO) serves as an important tumour escape strategy and is of prognostic importance. Here we investigate the predictive value of the activity of IDO as well as levels of tryptophan and respective downstream catabolites in a large cohort of patients with neuroendocrine neoplasms (NEN).

METHODS

142 consecutive Caucasian patients (62 male, aged 60.3 ± 11.9 years) with histologically confirmed NEN were systematically analysed in a retrospective blinded end point analysis. Patients were followed up for a mean period of about 3.9 ± 1.9 years. Clinical outcome, levels of established biomarkers, and tryptophan degradation markers (assessed using tandem mass spectrometry) including estimated IDO activity were recorded. Cox proportional hazards regression models were performed for the assessment of prognostic power.

RESULTS

We found that baseline tryptophan levels were significantly lower and IDO activity was significantly increased in non-survivors. The risk for death inclined stepwise and was highest in patients in the upper tertile of IDO activity. Cox proportional regression models identified IDO activity as an independent predictor of death.

CONCLUSIONS

In this retrospective analysis, we observed that baseline activity of the immunoregulatory enzyme IDO was significantly increased in non-survivors. IDO activity was identified as an independent predictor of death in this cohort of NEN patients. Whether IDO activity or tryptophan depletion serves to guide future therapeutic interventions in NEN remains to be established.

Personalized approaches to active immunotherapy in cancer

Immunotherapy is emerging as a promising anti-cancer curative modality. However, in contrast to recent advances obtained employing checkpoint blockade agents and T cell therapies, clinical efficacy of therapeutic cancer vaccines is still limited. Most vaccination attempts in the clinic represent "off-the shelf" approaches since they target common "self" tumor antigens, shared among different patients. In contrast, personalized approaches of vaccination are tailor-made for each patient and in spite being laborious, hold great potential. Recent technical advancement enabled the first steps in the clinic of personalized vaccines that target patient-specific mutated neo-antigens. Such vaccines could induce enhanced tumor-specific immune response since neo-antigens are mutation-derived antigens that can be recognized by high affinity T cells, not limited by central tolerance. Alternatively, the use of personalized vaccines based on whole autologous tumor cells, overcome the need for the identification of specific tumor antigens. Whole autologous tumor cells could be administered alone, pulsed on dendritic cells as lysate, DNA, RNA or delivered to dendritic cells in-vivo through encapsulation in nanoparticle vehicles. Such vaccines may provide a source for the full repertoire of the patient-specific tumor antigens, including its private neo-antigens. Furthermore, combining next-generation personalized vaccination with other immunotherapy modalities might be the key for achieving significant therapeutic outcome.

T-cell mediated anti-tumor immunity after photodynamic therapy: why does it not always work and how can we improve it?

Photodynamic therapy (PDT) uses the combination of non-toxic photosensitizers and harmless light to generate reactive oxygen species that destroy tumors by a combination of direct tumor cell killing, vascular shutdown, and activation of the immune system. It has been shown in some animal models that mice that have been cured of cancer by PDT, may exhibit resistance to rechallenge. The cured mice can also possess tumor specific T-cells that recognize defined tumor antigens, destroy tumor cells in vitro, and can be adoptively transferred to protect naïve mice from cancer. However, these beneficial outcomes are the exception rather than the rule. The reasons for this lack of consistency lie in the ability of many tumors to suppress the host immune system and to actively evade immune attack. The presence of an appropriate tumor rejection antigen in the particular tumor cell line is a requisite for T-cell mediated immunity. Regulatory T-cells (CD25+, Foxp3+) are potent inhibitors of anti-tumor immunity, and their removal by low dose cyclophosphamide can potentiate the PDT-induced immune response. Treatments that stimulate dendritic cells (DC) such as CpG oligonucleotide can overcome tumor-induced DC dysfunction and improve PDT outcome. Epigenetic reversal agents can increase tumor expression of MHC class I and also simultaneously increase expression of tumor antigens. A few clinical reports have shown that anti-tumor immunity can be generated by PDT in patients, and it is hoped that these combination approaches may increase tumor cures in patients.

Dasatinib promotes the expansion of a therapeutically superior T-cell repertoire in response to dendritic cell vaccination against melanoma

Dasatinib (DAS) is a potent inhibitor of the BCR-ABL, SRC, c-KIT, PDGFR, and ephrin tyrosine kinases that has demonstrated only modest clinical efficacy in melanoma patients. Given reports suggesting that DAS enhances T cell infiltration into the tumor microenvironment, we analyzed whether therapy employing the combination of DAS plus dendritic cell (DC) vaccination would promote superior immunotherapeutic benefit against melanoma. Using a M05 (B16.OVA) melanoma mouse model, we observed that a 7-day course of orally-administered DAS (0.1 mg/day) combined with a DC-based vaccine (VAC) against the OVA_257–264 peptide epitope more potently inhibited tumor growth and extended overall survival as compared with treatment with either single modality. The superior efficacy of the combinatorial treatment regimen included a reduction in hypoxic-signaling associated with reduced levels of immunosuppressive CD11b⁺Gr1⁺ myeloid-derived suppressor cells (MDSC) and CD4⁺Foxp3⁺ regulatory T (Treg) populations in the melanoma microenvironment. Furthermore, DAS + VAC combined therapy upregulated expression of Type-1 T cell recruiting CXCR3 ligand chemokines in the tumor stroma correlating with activation and recruitment of Type-1, vaccine-induced CXCR3⁺CD8⁺ tumor-infiltrating lymphocytes (TILs) and CD11c⁺ DC into the tumor microenvironment. The culmination of this bimodal approach was a profound “spreading” in the repertoire of tumor-associated antigens recognized by CD8⁺ TILs, in support of the therapeutic superiority of combined DAS + VAC immunotherapy in the melanoma setting.

Advances in host and vector development for the production of plasmid DNA vaccines

Recent developments in DNA vaccine research provide a new momentum for this rather young and potentially disruptive technology. Gene-based vaccines are capable of eliciting protective immunity in humans to persistent intracellular pathogens, such as HIV, malaria, and tuberculosis, for which the conventional vaccine technologies have failed so far. The recent identification and characterization of genes coding for tumor antigens has stimulated the development of DNA-based antigen-specific cancer vaccines. Although most academic researchers consider the production of reasonable amounts of plasmid DNA (pDNA) for immunological studies relatively easy to solve, problems often arise during this first phase of production. In this chapter we review the current state of the art of pDNA production at small (shake flasks) and mid-scales (lab-scale bioreactor fermentations) and address new trends in vector design and strain engineering. We will guide the reader through the different stages of process design starting from choosing the most appropriate plasmid backbone, choosing the right Escherichia coli (E. coli) strain for production, and cultivation media and scale-up issues. In addition, we will address some points concerning the safety and potency of the produced plasmids, with special focus on producing antibiotic resistance-free plasmids. The main goal of this chapter is to make immunologists aware of the fact that production of the pDNA vaccine has to be performed with as much as attention and care as the rest of their research.

Photodynamic therapy of murine mastocytoma induces specific immune responses against the cancer/testis antigen P1A

Photodynamic therapy (PDT) involves the intravenous administration of photosensitizers followed by illumination of the tumor with visible light, leading to local production of reactive oxygen species that cause vascular shutdown and tumor cell death. Antitumor immunity is stimulated after PDT because of the acute inflammatory response that involves activation of the innate immune system, leading to stimulation of adaptive immunity. We carried out PDT using benzoporphyrin derivative and 690-nm light after 15 minutes, in DBA/2 mice bearing either the mastocytoma, P815, which expresses the naturally occurring cancer/testis antigen P1A, or the corresponding tumor P1.204 that lacks P1A expression. Tumor cures, significantly higher survival, and rejection of tumor rechallenge were obtained with P815, which were not seen with P1.204 or seen with P815 growing in nude mice. Both CD4 and CD8 T cells had higher levels of intracellular cytokines when isolated from mice receiving PDT of P815 tumors than P1.204 tumors and CD8 T cells from P815-cured mice recognized the peptide epitope of the P1A antigen (LPYLGWLVF) using pentamer staining. Taken together, these findings show that PDT can induce a potent antigen- and epitope-specific immune response against a naturally occurring mouse tumor antigen.

Dendritic cells in cancer immunotherapy: vaccines and combination immunotherapies

Dendritic cells (DCs) are specialized immunostimulatory cells involved in the induction and regulation of immune responses. The feasibility of large-scale ex vivo generation of DCs from patients' monocytes allows for therapeutic application of ex vivo-cultured DCs to bypass the dysfunction of endogenous DCs, restore immune surveillance, induce cancer regression or stabilization or delay or prevent its recurrence. While the most common paradigm of the therapeutic application of DCs reflects their use as cancer 'vaccines', additional and potentially more effective possibilities include the use of patients' autologous DCs as parts of more comprehensive therapies involving in vivo or ex vivo induction of tumor-reactive T cells and the measures to counteract systemic and local immunosuppression in tumor-bearing hosts. Ex vivo-cultured DCs can be instructed to acquire distinct functions relevant for the induction of effective cancer immunity (DC polarization), such as the induction of different effector functions or different homing properties of tumor-specific T cells (delivery of 'signal 3' and 'signal 4'). These considerations highlight the importance of the application of optimized conditions for the ex vivo culture of DCs and the potential combination of DC therapies with additional immune interventions to facilitate the entry of DC-induced T cells to tumor tissues and their local antitumor functions.

Oncolytic viruses as therapeutic cancer vaccines

Oncolytic viruses (OVs) are tumor-selective, multi-mechanistic antitumor agents. They kill infected cancer and associated endothelial cells via direct oncolysis, and uninfected cells via tumor vasculature targeting and bystander effect. Multimodal immunogenic cell death (ICD) together with autophagy often induced by OVs not only presents potent danger signals to dendritic cells but also efficiently cross-present tumor-associated antigens from cancer cells to dendritic cells to T cells to induce adaptive antitumor immunity. With this favorable immune backdrop, genetic engineering of OVs and rational combinations further potentiate OVs as cancer vaccines. OVs armed with GM-CSF (such as T-VEC and Pexa-Vec) or other immunostimulatory genes, induce potent anti-tumor immunity in both animal models and human patients. Combination with other immunotherapy regimens improve overall therapeutic efficacy. Coadministration with a HDAC inhibitor inhibits innate immunity transiently to promote infection and spread of OVs, and significantly enhances anti-tumor immunity and improves the therapeutic index. Local administration or OV mediated-expression of ligands for Toll-like receptors can rescue the function of tumor-infiltrating CD8⁺ T cells inhibited by the immunosuppressive tumor microenvironment and thus enhances the antitumor effect. Combination with cyclophosphamide further induces ICD, depletes Treg, and thus potentiates antitumor immunity. In summary, OVs properly armed or in rational combinations are potent therapeutic cancer vaccines.

In vitro and in vivo evaluations of human papillomavirus type 16 (HPV16)-derived peptide-loaded dendritic cells (DCs) with a CpG oligodeoxynucleotide (CpG-ODN) adjuvant as tumor vaccines for immunotherapy of cervical cancer

PURPOSE

To evaluate the immunotherapeutic potentials for human dendritic cells (DCs) loaded with different HPV16-associated antigens, including HPV16E7 (E) protein, HPV16E7 polypeptide (P), as well as CpG-oligodeoxynucleotide (ODN) 2006 as a promising immune adjuvant for vaccination against cervical carcinoma.

METHODS

DCs derived from human peripheral blood and cord blood were isolated and loaded with HPV-derived protein or peptides, in combination with CpG-ODN2006 as a potential adjuvant. The IL-12 level, the allogeneic T cell-stimulatory capacity and the cytotoxicity of cytotoxic T lymphocytes (CTLs) were evaluated in vitro. Furthermore, an immune reconstitution model of human cervical carcinoma in SCID mice was used to assess the anti-tumor effects in vivo. The tumor sizes, the expression of IgG and IFN-γ, and the presence of the human CD3(+), CD4(+) and CD8(+) T cells were measured in the mice inoculated with different DCs.

RESULTS

The antigen-loaded DCs displayed obvious anti-tumor activities in vitro and in vivo, and showed no toxicity to normal cells. The level of IL-12, an important cytokine for immune response, was up-regulated in all mice inoculated with antigen-loaded DCs. Stimulation and activity of CTLs were increased after treatment with antigen-loaded DCs. Significantly, DCs loaded with HPV16E7 polypeptide (P) showed the most distinguished immunotherapeutic activities, and such effect was further enhanced when HPV16E7 polypeptide (P) was used in combination with CpG-ODN2006. Interestingly, the same results were obtained in vivo: the tumor size was decreased, and IgG and IFN-γ levels were increased after the SCID mice were inoculated with the loaded DCs.

CONCLUSIONS

HPV16E7 polypeptide combined with the immune adjuvant CpG-ODN2006 could be a suitable HPV16-associated tumor antigen. The research provides a new strategy for generating DCs vaccines for immunotherapy of cervical cancer.

MHC class I antigen processing and presenting machinery: organization, function, and defects in tumor cells

The surface presentation of peptides by major histocompatibility complex (MHC) class I molecules is critical to all CD8(+) T-cell adaptive immune responses, including those against tumors. The generation of peptides and their loading on MHC class I molecules is a multistep process involving multiple molecular species that constitute the so-called antigen processing and presenting machinery (APM). The majority of class I peptides begin as proteasome degradation products of cytosolic proteins. Once transported into the endoplasmic reticulum by TAP (transporter associated with antigen processing), peptides are not bound randomly by class I molecules but are chosen by length and sequence, with peptidases editing the raw peptide pool. Aberrations in APM genes and proteins have frequently been observed in human tumors and found to correlate with relevant clinical variables, including tumor grade, tumor stage, disease recurrence, and survival. These findings support the idea that APM defects are immune escape mechanisms that disrupt the tumor cells' ability to be recognized and killed by tumor antigen-specific cytotoxic CD8(+) T cells. Detailed knowledge of APM is crucial for the optimization of T cell-based immunotherapy protocols.

Characterization of small spheres derived from various solid tumor cell lines: are they suitable targets for T cells?

T cell based immunotherapy has been investigated in a variety of malignancies and analyses have been mostly founded on in vitro data with tumor cell monolayers. However, three-dimensional (3D) culture models might mimic more closely the 'in vivo' conditions than 2D monolayers. Therefore, we analyzed the expression of tumor-associated antigens (TAA) and of molecules involved in antigen processing and presentation (APM) in tumor spheres, which served as an in vitro model for micrometastasis which might be enriched in tumor propagating cancer stem cells. For enrichment of sphere cells 12 human solid tumor cell lines were cultured in serum-free medium. Expression of a variety of TAA and APM were analyzed by RT-PCR and/or flow cytometry and compared to expression in corresponding adherent bulk cells grown in regular growth medium. Compared to adherent cells, spheres showed equal or higher mRNA expression levels of LMP2, LMP7 and MECL-1, of TAP1 and TAP2 transporters and, surprisingly, also of TAA including differentiation antigens. However, downregulation or loss of HLA-I and HLA-II molecules in spheres was observed in 8 of 10 and 1 of 2 cell lines, respectively, and was unresponsive to stimulation with IFN-γ. Although tumor spheres express TAA and molecules of intracellular antigen processing, they are defective in antigen presentation due to downregulation of HLA surface expression which may lead to immune evasion.

Tumor microenvironment and myeloid-derived suppressor cells

Tumor progression has been demonstrated to be supported by chronic inflammatory conditions developed in the tumor microenvironment and characterized by the long-term secretion of various inflammatory soluble factors (including cytokines, chemokines, growth factors, reactive oxygen and nitrogen species, prostaglandins etc.) and strong leukocyte infiltration. Among leukocytes infiltrating tumors, myeloid-derived suppressor cells (MDSCs) represent one of the most important players mediating immunosuppression. These cells may not only strongly inhibit an anti-tumor immune reactions mediated by T cells but also directly stimulate tumorigenesis, tumor growth and metastasis by enhancing neoangiogenesis and creating a suitable environment for the metastatic formation. This review provides an overview of interactions between MDSCs and tumor cells leading to MDSC generation, activation and migration to the tumor site, where they can strongly enhance tumor progression. Better understanding of the MDSC-tumor interplay is critical for the development of new strategies of tumor immunotherapy.

Using intein catalysis to probe the origin of major histocompatibility complex class I-presented peptides

All vertebrate nucleated cells generate peptides from their expressed gene products and then display them at the cell surface bound to MHC class I molecules. This allows CD8(+) T cells to detect and eliminate abnormal cells that are synthesizing foreign proteins, e.g., from viruses or mutations. To permit the immune system to more uniformly monitor a cell's proteins, regardless of their half-life or location, it has been thought that the products of rapid degradation of the mistakes of protein synthesis (defective ribosomal products, DRiPs) preferentially contribute to the class I-presented peptides. However, using intein catalysis to generate peptide sequences exclusively by posttranslational splicing of mature proteins, we show here that presented peptides can be generated from fully folded and functional proteins. Remarkably, the presentation of peptides from two model mature proteins is just as efficient as from newly synthesized proteins subject to errors in translation or folding. These results indicate that for the constructs we have analyzed, DRiPs are not a more efficient source of class I peptides for antigen presentation than the turnover of mature functional proteins. Accordingly, our data suggest that one of the major ways the immune system evaluates the health of cells is by monitoring the breakdown products of the proteome.

Proteasome inhibitors as immunosuppressants: biological rationale and clinical experience

Accumulating evidence supports the potential of proteasome inhibitors as immunosuppressants. Proteasome inhibitors interfere with antigen processing and presentation, as well as with the signaling cascades involved in immune cell function and survival. Both myeloma and healthy plasma cells appear to be highly susceptible to proteasome inhibitors due to impaired proteasomal activity in both cell types. As a consequence, these agents can be used to reduce antibody production and thus prevent antibody-induced tissue damage. Several clinical studies have explored the potential of bortezomib, a peptide boronate proteasome inhibitor, for treating immune disorders, such as antibody-mediated organ rejection and graft-versus-host disease (GVHD), with encouraging results. Here, we discuss the biological rationale for the use of proteasome inhibitors as immunosuppressive agents and review the clinical experience with bortezomib in immune-mediated diseases.

Dendritic cells in cancer immunotherapy: vaccines or autologous transplants?

Dendritic cells (DCs) are the most powerful immunostimulatory cells specialized in the induction and regulation of immune responses. Their properties and the feasibility of their large-scale ex vivo generation led to the application of ex vivo-educated DCs to bypass the dysfunction of endogenous DCs in cancer patients and to induce therapeutic anti-cancer immunity. While multiple paradigms of therapeutic application of DCs reflect their consideration as cancer "vaccines", numerous features of DC-based vaccination resemble those of autologous transplants, resulting in challenges and opportunities that distinguish them from classical vaccines. In addition to the functional heterogeneity of DC subsets and plasticity of the individual DC types, the unique features of DCs are the kinetic character of their function, limited functional stability, and the possibility to imprint in maturing DCs distinct functions relevant for the induction of effective cancer immunity, such as the induction of different effector functions or different homing properties of tumor-specific T cells (delivery of "signal 3" and "signal 4"). These considerations highlight the importance of the application of optimized, potentially patient-specific conditions of ex vivo culture of DCs and their delivery, with the logistic and regulatory implications shared with transplantation and other surgical procedures.

Involvement of indoleamine 2,3-dioxygenase in impairing tumor-infiltrating CD8 T-cell functions in esophageal squamous cell carcinoma

The indoleamine 2,3-dioxygenase-(IDO-) mediated microenvironment plays an important role in tumor immune escape. However, the inhibitory effects of IDO on the CD8⁺ tumour-infiltrating lymphocytes (CD8⁺ TILs) in esophageal squamous cell carcinoma (ESCC) have not been clarified yet. Here, we found that the level of IDO expression in ESCC tumor specimens correlated with a reduction in the number of CD8⁺ TILs. Patients with high IDO expression and a low number of CD8⁺ TILs had significantly impaired overall survival time. IDO expression and functional enzyme activity in ESCC cell lines could be induced by IFNγ. When exposed to the milieu generated by IDO-expressing Eca109 cells, the CD8⁺ TILs were suppressed in proliferation, and their cytolytic functions against target tumor cells were lost. These results suggested that impairing CD8⁺ TIL functions by IDO expressed in ESCC possibly contributed to the finding that patients with higher IDO expression have more aggressive disease progression and shorter overall survival time.

A novel tumor antigen derived from enhanced degradation of bax protein in human cancers

Cancer cells frequently exhibit defects in apoptosis, which contribute to increased survival and chemotherapeutic resistance. For example, genetic mutations or abnormal proteasomal degradation can reduce expression of Bax which limits apoptosis. In cancers where abnormal proteasomal degradation of Bax occurs, we hypothesized that Bax peptides that bind to human leukocyte antigen (HLA) class I molecules would be generated for presentation to CD8(+) T cells. To test this hypothesis, we generated T cells against pooled Bax peptides, using the blood of healthy human donors. Although T-cell responses were of low frequency (0.15%), a CD8(+) T-cell clone (KSIVB17) was isolated that optimally recognized Bax(136-144) peptide (IMGWTLDFL) presented by HLA-A*0201. KSIVB17 was able to recognize and kill a variety of HLA-matched cancer cells including primary tumor cells from chronic lymphocytic leukemia (CLL). No reactivity was seen against HLA-matched, nontransformed cells such as PHA blasts and skin fibroblasts. Furthermore, KSIVB17 reactivity corresponded with the proteasomal degradation patterns of Bax protein observed in cancer cells. Taken together, our findings suggest a new concept for tumor antigens based on regulatory proteins that are ubiquitously expressed in normal cells, but that have abnormally enhanced degradation in cancer cells. Bax degradation products offer candidate immune antigens in cancers such as CLL in which increased Bax degradation correlates with poor clinical prognosis.

Autophagy shapes inflammation

Autophagy is a basic cell biological process ongoing under physiologic circumstances in almost all cell types of the human organism and upregulated by various stress conditions including those leading to inflammation. Since autophagy affects the effector cells of innate and adaptive immunity mediating the inflammatory response, its activity in these cells influences the antimicrobial response, the development of an effective cognate immune defense, and the course of the normal sterile inflammatory reactions. The level of autophagic activity may determine whether tissue cells die by apoptosis, necrosis, or through autophagy, and, as a consequence, whether the clearance of these dying cells is a silent process or results in an inflammatory response. Loss or decreased autophagy may lead to necrotic death that can initiate an inflammatory reaction in phagocytes through their surface and cytosolic receptors. Engulfment of certain cells dying through autophagy can activate the inflammasome. The intertwining regulatory connections between inflammation and immunity extend to pathologic conditions including chronic inflammatory diseases, autoimmunity and cancer.

Photodynamic therapy of tumors can lead to development of systemic antigen-specific immune response

BACKGROUND

The mechanism by which the immune system can effectively recognize and destroy tumors is dependent on recognition of tumor antigens. The molecular identity of a number of these antigens has recently been identified and several immunotherapies have explored them as targets. Photodynamic therapy (PDT) is an anti-cancer modality that uses a non-toxic photosensitizer and visible light to produce cytotoxic reactive oxygen species that destroy tumors. PDT has been shown to lead to local destruction of tumors as well as to induction of anti-tumor immune response.

METHODOLOGY/PRINCIPAL FINDINGS

We used a pair of equally lethal BALB/c colon adenocarcinomas, CT26 wild-type (CT26WT) and CT26.CL25 that expressed a tumor antigen, β-galactosidase (β-gal), and we treated them with vascular PDT. All mice bearing antigen-positive, but not antigen-negative tumors were cured and resistant to rechallenge. T lymphocytes isolated from cured mice were able to specifically lyse antigen positive cells and recognize the epitope derived from beta-galactosidase antigen. PDT was capable of destroying distant, untreated, established, antigen-expressing tumors in 70% of the mice. The remaining 30% escaped destruction due to loss of expression of tumor antigen. The PDT anti-tumor effects were completely abrogated in the absence of the adaptive immune response.

CONCLUSION

Understanding the role of antigen-expression in PDT immune response may allow application of PDT in metastatic as well as localized disease. To the best of our knowledge, this is the first time that PDT has been shown to lead to systemic, antigen- specific anti-tumor immunity.

An integrated approach to epitope analysis II: A system for proteomic-scale prediction of immunological characteristics

Background

Improving our understanding of the immune response is fundamental to developing strategies to combat a wide range of diseases. We describe an integrated epitope analysis system which is based on principal component analysis of sequences of amino acids, using a multilayer perceptron neural net to conduct QSAR regression predictions for peptide binding affinities to 35 MHC-I and 14 MHC-II alleles.

Results

The approach described allows rapid processing of single proteins, entire proteomes or subsets thereof, as well as multiple strains of the same organism. It enables consideration of the interface of diversity of both microorganisms and of host immunogenetics. Patterns of binding affinity are linked to topological features, such as extracellular or intramembrane location, and integrated into a graphical display which facilitates conceptual understanding of the interplay of B-cell and T-cell mediated immunity.

Patterns which emerge from application of this approach include the correlations between peptides showing high affinity binding to MHC-I and to MHC-II, and also with predicted B-cell epitopes. These are characterized as coincident epitope groups (CEGs). Also evident are long range patterns across proteins which identify regions of high affinity binding for a permuted population of diverse and heterozygous HLA alleles, as well as subtle differences in reactions with MHCs of individual HLA alleles, which may be important in disease susceptibility, and in vaccine and clinical trial design. Comparisons are shown of predicted epitope mapping derived from application of the QSAR approach with experimentally derived epitope maps from a diverse multi-species dataset, from Staphylococcus aureus, and from vaccinia virus.

Conclusions

A desktop application with interactive graphic capability is shown to be a useful platform for development of prediction and visualization tools for epitope mapping at scales ranging from individual proteins to proteomes from multiple strains of an organism. The possible functional implications of the patterns of peptide epitopes observed are discussed, including their implications for B-cell and T-cell cooperation and cross presentation.

Recent advances in antigen-loaded dendritic cell-based strategies for treatment of minimal residual disease in acute myeloid leukemia

Therapeutic vaccination with dendritic cells (DCs) is recognized as an important experimental therapy for the treatment of minimal residual disease in acute myeloid leukemia. Many sources of leukemia-associated antigens and different methods for antigen loading of DCs have been used in an attempt to optimize anti-tumor responses. For instance, monocyte-derived DCs have been loaded with apoptotic whole-cell suspensions, necrotic cell lysates, tumor-associated peptides, eluted peptides and cellular DNA or RNA. Furthermore, monocyte-derived DCs can be chemically or electrically fused with leukemic blasts, and DCs have been cultured out of leukemic blasts. However, it remains a challenge in cancer immunotherapy to identify which of these methods is the most optimal for antigen loading and activation of DCs. This review discusses recent advances in DC research and the application of this knowledge towards new strategies for antigen loading of DCs in the treatment of minimal residual disease in acute myeloid leukemia.

Phase I clinical trial of the vaccination for the patients with metastatic melanoma using gp100-derived epitope peptide restricted to HLA-A*2402

BACKGROUND

The tumor associated antigen (TAA) gp100 was one of the first identified and has been used in clinical trials to treat melanoma patients. However, the gp100 epitope peptide restricted to HLA-A*2402 has not been extensively examined clinically due to the ethnic variations. Since it is the most common HLA Class I allele in the Japanese population, we performed a phase I clinical trial of cancer vaccination using the HLA-A*2402 gp100 peptide to treat patients with metastatic melanoma.

METHODS

The phase I clinical protocol to test a HLA-A*2402 gp100 peptide-based cancer vaccine was designed to evaluate safety as the primary endpoint and was approved by The University of Tokyo Institutional Review Board. Information related to the immunologic and antitumor responses were also collected as secondary endpoints. Patients that were HLA-A*2402 positive with stage IV melanoma were enrolled according to the criteria set by the protocol and immunized with a vaccine consisting of epitope peptide (VYFFLPDHL, gp100-in4) emulsified with incomplete Freund's adjuvant (IFA) for the total of 4 times with two week intervals. Prior to each vaccination, peripheral blood mononuclear cells (PBMCs) were separated from the blood and stored at -80°C. The stored PBMCs were thawed and examined for the frequency of the peptide specific T lymphocytes by IFN-γ- ELISPOT and MHC-Dextramer assays.

RESULTS

No related adverse events greater than grade I were observed in the six patients enrolled in this study. No clinical responses were observed in the enrolled patients although vitiligo was observed after the vaccination in two patients. Promotion of peptide specific immune responses was observed in four patients with ELISPOT assay. Furthermore, a significant increase of CD8+ gp100-in4+ CTLs was observed in all patients using the MHC-Dextramer assay. Cytotoxic T lymphocytes (CTLs) clones specific to gp100-in4 were successfully established from the PBMC of some patients and these CTL clones were capable of lysing the melanoma cell line, 888 mel, which endogenously expresses HLA-restricted gp100-in4.

CONCLUSION

Our results suggest this HLA-restricted gp100-in4 peptide vaccination protocol was well-tolerated and can induce antigen-specific T-cell responses in multiple patients. Although no objective anti-tumor effects were observed, the effectiveness of this approach can be enhanced with the appropriate modifications.

Bacteria-induced gap junctions in tumors favor antigen cross-presentation and antitumor immunity

Antigen-presenting dendritic cells (DCs) trigger the activation of cytotoxic CD8 T cells that target and eliminate cells with the antigen on their surface. Although DCs usually pick up and process antigens themselves, they can also receive peptide antigens from other cells via gap junctions. We demonstrate here that infection with Salmonella can induce, in both human and murine melanoma cells, the up-regulation of connexin 43 (Cx43), a ubiquitous protein that forms gap junctions and that is normally lost during melanoma progression. Bacteria-treated melanoma cells can establish functional gap junctions with adjacent DCs. After bacterial infection, these gap junctions transferred preprocessed antigenic peptides from the tumor cells to the DCs, which then presented those peptides on their surface. These peptides activated cytotoxic T cells against the tumor antigen, which could control the growth of distant uninfected tumors. Melanoma cells in which Cx43 had been silenced, when infected in vivo with bacteria, failed to elicit a cytotoxic antitumor response, indicating that this Cx43 mechanism is the principal one used in vivo for the generation of antitumor responses. The Cx43-dependent cross-presentation pathway is more effective than standard protocols of DC loading (peptide, tumor lysates, or apoptotic bodies) for generating DC-based tumor vaccines that both inhibit existing tumors and prevent tumor establishment. In conclusion, we exploited an antimicrobial response present in tumor cells to activate cytotoxic CD8 T cells specific for tumor-generated peptides that could directly recognize and kill tumor cells.

Linear and branched glyco-lipopeptide vaccines follow distinct cross-presentation pathways and generate different magnitudes of antitumor immunity

BACKGROUND

Glyco-lipopeptides, a form of lipid-tailed glyco-peptide, are currently under intense investigation as B- and T-cell based vaccine immunotherapy for many cancers. However, the cellular and molecular mechanisms of glyco-lipopeptides (GLPs) immunogenicity and the position of the lipid moiety on immunogenicity and protective efficacy of GLPs remain to be determined.

METHODS/PRINCIPAL FINDINGS

We have constructed two structural analogues of HER-2 glyco-lipopeptide (HER-GLP) by synthesizing a chimeric peptide made of one universal CD4(+) epitope (PADRE) and one HER-2 CD8(+) T-cell epitope (HER(420-429)). The C-terminal end of the resulting CD4-CD8 chimeric peptide was coupled to a tumor carbohydrate B-cell epitope, based on a regioselectively addressable functionalized templates (RAFT), made of four alpha-GalNAc molecules. The resulting HER glyco-peptide (HER-GP) was then linked to a palmitic acid moiety, attached either at the N-terminal end (linear HER-GLP-1) or in the middle between the CD4+ and CD8+ T cell epitopes (branched HER-GLP-2). We have investigated the uptake, processing and cross-presentation pathways of the two HER-GLP vaccine constructs, and assessed whether the position of linkage of the lipid moiety would affect the B- and T-cell immunogenicity and protective efficacy. Immunization of mice revealed that the linear HER-GLP-1 induced a stronger and longer lasting HER(420-429)-specific IFN-gamma producing CD8(+) T cell response, while the branched HER-GLP-2 induced a stronger tumor-specific IgG response. The linear HER-GLP-1 was taken up easily by dendritic cells (DCs), induced stronger DCs maturation and produced a potent TLR- 2-dependent T-cell activation. The linear and branched HER-GLP molecules appeared to follow two different cross-presentation pathways. While regression of established tumors was induced by both linear HER-GLP-1 and branched HER-GLP-2, the inhibition of tumor growth was significantly higher in HER-GLP-1 immunized mice (p<0.005).

SIGNIFICANCE

These findings have important implications for the development of effective GLP based immunotherapeutic strategies against cancers.

Concomitant tumor and autoantigen vaccination supports renal cell carcinoma rejection

Efficient tumor vaccination frequently requires adjuvant. Concomitant induction of an autoimmune response is discussed as a means to strengthen a weak tumor Ag-specific response. We asked whether the efficacy of dendritic cell (DC) vaccination with the renal cell carcinoma Ags MAGE-A9 (MAGE9) and G250 could be strengthened by covaccination with the renal cell carcinoma autoantigen GOLGA4. BALB/c mice were vaccinated with DC loaded with MHC class I-binding peptides of MAGE9 or G250 or tumor lysate, which sufficed for rejection of low-dose RENCA-MAGE9 and RENCA-G250 tumor grafts, but only retarded tumor growth at 200 times the tumor dose at which 100% of animals will develop a tumor. Instead, 75-100% of mice prevaccinated concomitantly with Salmonella typhimurium transformed with GOLGA4 cDNA in a eukaryotic expression vector rejected 200 times the tumor dose at which 100% of animals will develop tumor. In a therapeutic setting, the survival rate increased from 20-40% by covaccination with S. typhimurium-GOLGA4. Autoantigen covaccination significantly strengthened tumor Ag-specific CD4(+) and CD8(+) T cell expansion, particularly in peptide-loaded DC-vaccinated mice. Covaccination was accompanied by an increase in inflammatory cytokines, boosted IL-12 and IFN-gamma expression, and promoted a high tumor Ag-specific CTL response. Concomitant autoantigen vaccination also supported CCR6, CXCR3, and CXCR4 upregulation and T cell recruitment into the tumor. It did not affect regulatory T cells, but slightly increased myeloid-derived suppressor cells. Thus, tumor cell eradication was efficiently strengthened by concomitant induction of an immune response against a tumor Ag and an autoantigen expressed by the tumor cell. Activation of autoantigen-specific Th cells strongly supports tumor-specific Th cells and thereby CTL activation.

Improved secretion of the cancer-testis antigen SSX2 in Pichia pastoris by deletion of its nuclear localization signal

The cancer-testis (CT) antigen synovial sarcoma X break point 2 (SSX2) was expressed in Pichia pastoris as a means to produce a delayed-type hypersensitivity skin test reagent for monitoring SSX2-specific anti-cancer immune responses. SSX2 was detected intracellularly in P. pastoris despite the addition of the Saccharomyces cerevisiae alpha-mating factor secretion signal. Increasing the SSX2 gene copy number did not improve its secretion but did enhance intracellular SSX2 levels. SSX2 with its C-terminal nuclear localization signal (NLS) deleted (SSX2NORD), however, was secreted. Indirect immunofluorescence indicated that SSX2 containing the NLS did not translocate to the nucleus but accumulated in the endoplasmic reticulum (ER). Experimental results further suggested that SSX2 containing the NLS was misfolded in the ER, while deletion of the NLS facilitated correct folding of SSX2 inside the ER and improved its secretion. Production of SSX2NORD was scaled-up to a 2-L fermentor using a fed-batch protocol to maintain methanol at a concentration of 1 g L(-1). Decreasing the cultivation temperature from 25 degrees C to 16 degrees C improved protein stability in the culture supernatant. In this process, after 120 h cultivation, the wet cell weight of P. pastoris reached 280 mg mL(-1), and the yield of SSX2NORD was 21.6 mg L(-1).

The chemotherapeutic agents XK469 (2-{4-[(7-chloro-2-quinoxalinyl)oxy]phenoxy}propionic acid) and SH80 (2-{4-[(7-bromo-2-quinolinyl)oxy]phenoxy}propionic acid) inhibit cytokinesis and promote polyploidy and induce senescence

The therapeutic usefulness of the quinoxaline derivatives XK469 (2-{4-[(7-chloro-2-quinoxalinyl)oxy]phenoxy}propionic acid) and SH80 (2-{4-[(7-bromo-2-quinolinyl)oxy]phenoxy}propionic acid) has been attributed to their abilities to induce G(2)/M arrest and apoptotic or autophagic cell death. Concentrations of XK469 or SH80 > or = 5 microM were cytostatic to cultures of the normal murine melanocyte cell line Melan-a. Higher concentrations caused dose-dependent cytotoxicity. Concentrations > or =10 microM provoked dramatic morphological changes typified by marked increases in cell size and granularity. XK469/SH80-treated cultures accumulated tetraploid (4N) DNA-containing cells within 24 h of treatment, an 8N population within 3 days, and a 16N population within 5 days. Increases in ploidy correlated with the appearance of multinucleated cells. Under no circumstances did cells exhibit evidence of furrow formation. Both drugs suppressed cytokinesis in additional mammalian cell lines. Cytotoxic concentrations of XK469 elevated DEVDase activities (a measure of procaspase-3/7 activation) and enhanced cellular staining by a fluorescent analog of the pan caspase inhibitor valine-alanine-aspartic acid-fluoromethyl ketone within 48 to 96 h of treatment. Within 48 h of treatment, cytostatic and cytotoxic concentrations of XK469 elevated p21 contents, reduced Bcl-2 and Bcl-XL contents, and induced autophagy, as monitored by the accumulation of phosphatidylethanolamine-modified cleavage product of microtubule-associated protein light chain 3 (LC3-II). Cultures treated with > or =10 microM XK469 or SH80 for 5 days could not be induced to divide upon removal of drugs. Such cultures maintained high LC3-II contents, exhibited reduced cyclin E and D1 contents, and extensively expressed senescence-associated beta-galactosidase within 14 to 17 days of cessation of drug treatment. Hence, XK469 and SH80 inhibit cytokinesis, promote polyploidy, and induce senescence in Melan-a cells.

Use of tumour-responsive T cells as cancer treatment

The stimulation of a tumour-specific T-cell response has several theoretical advantages over other forms of cancer treatment. First, T cells can home in to antigen-expressing tumour deposits no matter where they are located in the body-even in deep tissue beds. Additionally, T cells can continue to proliferate in response to immunogenic proteins expressed in cancer until all the tumour cells are eradicated. Finally, immunological memory can be generated, allowing for eradication of antigen-bearing tumours if they reoccur. We will highlight two direct methods of stimulating tumour-specific T-cell immunity: active immunisation with cancer vaccines and infusion of competent T cells via adoptive T-cell treatment. Preclinical and clinical studies have shown that modulation of the tumour microenvironment to support the immune response is as important as stimulation of the most appropriate effector T cells. The future of T-cell immunity stimulation to treat cancer will need combination approaches focused on both the tumour and the T cell.

Methods for constructing and evaluating antitumor DNA vaccines

An antitumor DNA vaccine is a bacterial DNA plasmid that encodes the complementary DNA (cDNA) of a tumor antigen. When injected into recipients, antitumor DNA vaccines have been shown to elicit both humoral and cellular immunity against the encoded tumor antigen. These vaccines represent a relatively new immunotherapeutic technique being investigated as a means to deliver a target antigen and elicit or augment antitumor antigen-specific immune responses. One of the primary advantages of DNA vaccines as opposed to some other methods of antigen delivery is that they can be easily constructed, purified, and delivered to recipients. In this review we describe this process, detailing the procedures used to construct, purify, deliver, and evaluate the efficacy of DNA vaccines. We begin by describing the process of molecularly constructing the vaccine, from selecting a bacterial plasmid to form the backbone of the vaccine, cloning the antigen cDNA into this plasmid, and confirming the sequence and orientation of the completed vaccine. This is then followed by a series of experiments that can be used to ensure that the antigen encoded by the vaccine is transcribed and translated after being taken up by eukaryotic cells. We then describe large-scale purification procedures that can be used to obtain sufficient quantities of plasmid DNA to conduct in vivo immunization experiments. Finally, we provide an immunization protocol that can be used to evaluate the immunological efficacy of the constructed DNA vaccine. By following these protocols, it is possible to construct, purify, deliver, and evaluate the efficacy of antitumor DNA vaccines.

Liposome-based Systems for Anti-tumor Vaccination: Influence of Lipopeptide Adjuvants

We have developed liposome-based synthetic constructs incorporating peptide epitope(s) (ErbB2 p63-67 CTL which is overexpressed in many tumors and/or HA 307-319 T-helper) and lipopeptide adjuvants (Pam3CysSerSer, Pam3CysAlaGly) in order to elicit an anti-tumor immune response. The epitopes, derivatized with a linker containing a cysteine residue, were conjugated on preformed vesicles (dia. approximately 100 nm) containing lipopeptides functionalized with thiol reactive groups (maleimide or bromoacetyl). The therapeutic efficacy of these constructs was evaluated on a Balb/c mice tumor model inoculated with syngenic murine renal carcinoma (Renca) cells expressing human ErbB2 (Her2/neu) receptor. A successful therapeutic vaccination was obtained which was antigen specific. Furthermore, it appeared that the nature of the polar head group of the lipopeptide adjuvant and also its type of functionalization influence the efficacy of the construct. In our study, the best results were obtained with formulations containing a Pam3CSS anchor in association with the CTL and Th epitopes. Considering these promising results studies are in progress with a new generation of liposomes that incorporate a neutral lipid--lacking adjuvant properties--that serves as anchor of the peptide epitopes and new adjuvants synthesized in our laboratory, which are screened for their antitumour activity in a therapeutic setting.

Cancer immunotherapy by dendritic cells

Cancerous lesions promote tumor growth, motility, invasion, and angiogenesis via oncogene-driven immunosuppressive leukocyte infiltrates, mainly myeloid-derived suppressor cells, tumor-associated macrophages, and immature dendritic cells (DCs). In addition, many tumors express or induce immunosuppressive cytokines such as TGF-beta and IL-10. As a result, tumor-antigen crosspresentation by DCs induces T cell anergy or deletion and regulatory T cells instead of antitumor immunity. Tumoricidal effector cells can be generated after vigorous DC activation by Toll-like receptor ligands or CD40 agonists. However, no single immunotherapeutic modality is effective in established cancer. Rather, chemotherapies, causing DC activation, enhanced crosspresentation, lymphodepletion, and reduction of immunosuppressive leukocytes, act synergistically with vaccines or adoptive T cell transfer. Here, I discuss the considerations for generating promising therapeutic antitumor vaccines that use DCs.

Gamma-IFN-inducible-lysosomal thiol reductase modulates acidic proteases and HLA class II antigen processing in melanoma

HLA class II-restricted antigen (Ag) processing and presentation are important for the activation of CD4+ T cells, which are the central orchestrating cells of immune responses. The majority of melanoma cells either expresses, or can be induced to express, HLA class II proteins. Thus, they are prime targets for immune mediated elimination by class II-restricted CD4+ T cells. We have previously shown that human melanoma cells lack an important enzyme, gamma interferon-inducible lysosomal thiol-reductase (GILT), capable of perturbing immune recognition of these tumors. Here, we show that GILT expression in human melanoma cells enhances Ag processing and presentation via HLA class II molecules. We also show that GILT expression influences the generation of active forms of cysteinyl proteases, cathepsins B, L and S, as well as an aspartyl protease cathepsin D in melanoma cells. Mechanistic studies revealed that GILT does not regulate acidic cathepsins at the transcriptional level; rather it colocalizes with the cathepsins and influences HLA class II Ag processing. GILT expression in melanoma cells also elevated HLA-DM molecules, which favor epitope loading onto class II in the endolysosomal compartments, enhancing CD4+ T cell recognition. These data suggest that GILT-expressing melanoma cells could prove to be very promising for direct antigen presentation and CD4+ T cell recognition, and may have direct implications for the design of cancer vaccines.

Neutrophil-dependent tumor rejection and priming of tumoricidal CD8+ T cell response induced by dendritic cells overexpressing CD95L

Overexpression of CD95 (Fas/Apo-1) ligand (CD95L) has been shown to induce T cell tolerance but also, neutrophilic inflammation and rejection of allogeneic tissue. We explored the capacity of dendritic cells (DCs) genetically engineered to overexpress CD95L to induce an antitumor response. We first found that DCs overexpressing CD95L, in addition to MHC class I-restricted OVA peptides (CD95L-OVA-DCs), induced increased antigen-specific CD8(+) T cell responses as compared with DCs overexpressing OVA peptides alone. The enhanced T cell responses were associated with improved regression of a tumor expressing OVA, allowing survival of all animals. When DCs overexpressing CD95L (CD95L-DCs) were injected with the tumor expressing OVA, in vivo tumor proliferation was strikingly inhibited. A strong cellular apoptosis and a massive neutrophilic infiltrate developed in this setting. Neutrophil depletion prevented tumor regression as well as enhanced IFN-gamma production induced by CD95L-OVA-DCs. Furthermore, the CD8(+) T cell response induced by the coadministration of tumor cells and CD95L-DCs led to rejection of a tumor implanted at a distance from the DC injection site. In summary, DCs expressing CD95L promote tumor rejection involving neutrophil-mediated innate immunity and CD8(+) T cell-dependent adaptative immune responses.

Spontaneous and treatment-induced cancer rejection in humans

BACKGROUND

Experimental observations suggest that human cancer cells actively interact with normal host cells and this cross-talk results, in most instances, in an increased potential of cancer cells to survive. On the other hand, it is also well documented that on rare occasions tumors can be dramatically destroyed by the host's immune response.

OBJECTIVE

In this review, we argue that understanding the mechanisms that bring about the immune response and lead to cancer destruction is of paramount importance for the design of future rational therapies.

METHODS

Here we summarize the present understanding of the phenomenology leading to cancer regression in humans and propose novel strategies for a more efficient study of human cancer under natural conditions and during therapy.

CONCLUSION

The understanding of tumor/host interactions within the tumor microenvironment is a key component of the study of tumor immunology in humans, much can be learned by a dynamic study of such interactions at time points related to the natural history of the disease or its response to therapy. Such understanding will eventually lead to novel and more effective therapies.

Diversity of proteasomal missions: fine tuning of the immune response

The majority of cellular proteins are degraded by proteasomes within the ubiquitin-proteasome ATP-dependent degradation pathway. Products of proteasomal activity are short peptides that are further hydrolysed by proteases to single amino acids. However, some peptides can escape this degradation, being selected and taken up by major histocompatibility complex (MHC) class I molecules for presentation to the immune system on the cell surface. MHC class I molecules are highly selective and specific in terms of ligand binding. Variability of peptides produced in living cells arises in a variety of ways, ensuring fast and efficient immune responses. Substitution of constitutive proteasomal subunits with immunosubunits leads to conformational changes in the substrate binding channels, resulting in a modified protein cleavage pattern and consequently in the generation of new antigenic peptides. The recently discovered event of proteasomal peptide splicing opens new horizons in the understanding of additional functions that proteasomes apparently possess. Whether peptide splicing is an occasional side product of proteasomal activity still needs to be clarified. Both gamma-interferon-induced immunoproteasomes and peptide splicing represent two significant events providing increased diversity of antigenic peptides for flexible and fine-tuned immune response.

Induction of potent CD4+ T cell-mediated antitumor responses by a helper HER-2/neu peptide linked to the Ii-Key moiety of the invariant chain

The Ii-Key fragment from the MHC class II-associated invariant chain (or Ii protein) has been shown to facilitate direct charging of MHC class II epitopes to the peptide binding groove. The purpose of the present study was to test the potential of a series of Ii-Key/HER-2/neu776-790 hybrid peptides to generate increased frequencies of peptide-specific CD4+ T cells over the native peptide in mice transgenic (Tg) for a chimeric human mouse class II molecule (DR4-IE) (H-2b) as well as their antitumor potency. Following in vivo priming, such hybrid peptides induced increased proliferation and frequencies of IFN-gamma producing CD4+ T cells in response to either syngeneic dendritic cells pulsed with native peptide, or HLA-DR4+ human tumor cell lines expressing HER-2/neu. Hybrid peptides were more stable in an off-rate kinetics assay compared to the native peptide. In addition, antigen-specific CD4+ T cells from hybrid peptide immunized DR4-IE Tg mice synergized with HER-2/neu(435-443)-specific CD8+ T cells from HLA-A2.1 Tg HHD (H-2b) mice in producing antitumor immunity into SCID mice xenografted with the HER-2/neu+, HLA-A2.1+ and HLA-DR4+ FM3 human melanoma cell line. High proportions of these adoptively transferred HER-2/neu peptide-specific CD4+ and CD8+ T cells infiltrated FM3-induced tumors (tumor infiltrating lymphocytes; TIL) in SCID mice. CD8+ TIL exhibited long-lasting antitumor activity when cotransferred with CD4+ TIL, inducing regression of FM3 tumors in a group of untreated, tumor-bearing SCID mice, following adoptive transfer. Our data show that Ii-Key modified HER-2/neu776-790 hybrid peptides are sufficiently potent to provide antigen-specific CD4+ TH cells with therapeutic antitumor activity.

A melanoma multiepitope polypeptide induces specific CD8+ T-cell response

Strategies using epitope-based vaccination are being considered for melanoma immunotherapy, in an attempt to overcome failure of other modalities. In the present study, we designed and produced a multiepitope polypeptide for melanoma (MEP-mel), which contains three repeats of four antigenic epitopes (gp100: 209-217 (210M); gp100: 280-288 (288V); Mart1: 26-35 (27L); tyrosinase: 368-376 (370D). The peptides were attached to each other by linkers containing sequences recognized by the proteasome, to improve protein cleavage and antigen presentation. The results show that peptide-specific T cells produced IFN-gamma when stimulated with MEP-mel-transfected dendritic cells. The presentation of peptides by MEP-mel-transfected dendritic cells was proteasome-dependent and was more long-lasting than the presentation of exogenously delivered native peptides. When dendritic cells were loaded with MEP-mel protein, weak cross presentation was induced. The production of multiepitope molecules based on several peptides linked by sequences sensitive to proteasomal cleavage represents a promising new tool for the improvement of cancer immunotherapy.

Tumor-associated Tn-MUC1 glycoform is internalized through the macrophage galactose-type C-type lectin and delivered to the HLA class I and II compartments in dendritic cells

The type of interaction between tumor-associated antigens and specialized antigen-presenting cells such as dendritic cells (DCs) is critical for the type of immunity that will be generated. MUC1, a highly O-glycosylated mucin, is overexpressed and aberrantly glycosylated in several tumor histotypes. This results in the expression of tumor-associated glycoforms and in MUC1 carrying the tumor-specific glycan Tn (GalNAcalpha1-O-Ser/Thr). Glycopeptides corresponding to three tandem repeats of MUC1, enzymatically glycosylated with 9 or 15 mol of GalNAc, were shown to specifically bind and to be internalized by immature monocyte-derived DCs (iDCs). Binding required calcium and the GalNAc residue and was competed out by GalNAc polymer and Tn-MUC1 or Tn-MUC2 glycopeptides. The macrophage galactose-type C-type lectin (MGL) receptor expressed on iDCs was shown to be responsible for the binding. Confocal analysis and ELISA done on subcellular fractions of iDCs showed that the Tn-MUC1 glycopeptides colocalized with HLA class I and II compartments after internalization. Importantly, although Tn-MUC1 recombinant protein was bound and internalized by MGL, the glycoprotein entered the HLA class II compartment, but not the HLA class I pathway. These data indicate that MGL expressed on iDCs is an optimal receptor for the internalization of short GalNAcs carrying immunogens to be delivered into HLA class I and II compartments. Such glycopeptides therefore represent a new way of targeting the HLA class I and II pathways of DCs. These results have possible implications in designing cancer vaccines.