Inhibition of serine-peptidase activity enhances the generation of a survivin-derived HLA-A2-presented CTL epitope in colon-carcinoma cells

Cytotoxic T lymphocytes eliminate tumor cells expressing antigenic peptides in the context of MHC-I molecules. Peptides are generated during protein degradation by the proteasome and resulting products, surviving cytosolic amino-peptidases activity, may be presented by MHC-I molecules. The MHC-I processing pathway is altered in a large number of malignancies and modulation of antigen generation is one strategy employed by cells to evade immune control. In this study we analyzed the generation and presentation of a survivin-derived CTL epitope in HLA-A2-positive colon-carcinoma cells. Although all cell lines expressed the anti-apoptotic protein survivin, some tumors were poorly recognized by ELTLGEFLKL (ELT)-specific CTL cultures. The expression of MHC-I or TAP molecules was similar in all cell lines suggesting that tumors not recognized by CTLs may present defects in the generation of the ELT-epitope which could be due either to lack of generation or to subsequent degradation of the epitope. The cells were analyzed for the expression and the activity of extra-proteasomal peptidases. A significant overexpression and higher activity of TPPII was observed in colon-carcinoma cells which are not killed by ELT-specific CTLs, suggesting a possible role of TPPII in the degradation of the ELT-epitope. To confirm the role of TPPII in the degradation of the ELT-peptide, we showed that treatment of colon-carcinoma cells with a TPPII inhibitor resulted in a dose-dependent increased sensitivity to ELT-specific CTLs. These results suggest that TPPII is involved in degradation of the ELT-peptide, and its overexpression may contribute to the immune escape of colon-carcinoma cells.

Human lymphocyte activation gene-3 molecules expressed by activated T cells deliver costimulation signal for dendritic cell activation

Data have been reported on the in vivo adjuvant role of soluble lymphocyte activation gene-3 (LAG-3) recombinant protein in mouse models and on its ability to support the in vitro generation of human, tumor-specific CTLs. In this study, we show that soluble human rLAG-3 protein (hLAG-3Ig) used in vitro as a single maturation agent induces phenotypic maturation of monocyte-derived dendritic cells and promoted the production of chemokines and TNF-alpha inflammatory cytokine. When given in association with optimal or suboptimal doses of CD40/CD40L, hLAG-3Ig functions as a strong costimulatory factor and induces full functional activation of monocyte-derived dendritic cells that includes the production of high level of IL-12p70. Moreover, evidence is here provided that this costimulatory function licensing dendritic cells to produce IL-12p70 is also a functional property of LAG-3 molecules when expressed in a physiological context by CD4(+) activated T cells. Altogether, these data show for the first time a role of LAG-3 in mediating dendritic cell activation when expressed on the T cell surface or released after specific Ag stimulation in the interspaces of immunological synapses.

NKG2D-mediated antitumor activity by tumor-infiltrating lymphocytes and antigen-specific T-cell clones isolated from melanoma patients

PURPOSE

The role of NKG2D receptor in antitumor immunosurveillance has not been completely clarified. We addressed this issue by investigating the involvement of this receptor in tumor-specific immunologic response in melanoma patients.

EXPERIMENTAL DESIGN

We determined the presence of NKG2D+ T cells among tumor-infiltrating lymphocytes (TIL) of 10 (one primary and 9 metastatic) melanoma samples and the expression of NKG2D ligands (NKG2DL) by these tumor cells. Moreover, the expression of NKG2D was assessed in a panel of antigen-specific T lymphocytes isolated from melanoma patients and the engagement of NKG2D in antitumor activity mediated by these T cells was determined.

RESULTS

TILs located either in the periphery or within the tumor mass of melanoma samples expressed NKG2D and the expression of this receptor by T cells was retained after in vitro culture. However, NKG2DLs were weakly expressed, or not expressed, by most metastatic lesions with only the primary tumor being positive for all these molecules. In contrast, these ligands were expressed, although heterogeneously, by all in vitro established melanoma lines. Moreover, the engagement of NKG2D occurred in antitumor activity by both freshly isolated and in vitro cultured TILs. However, this receptor was involved to a different extent in the antitumor activity of antigen-specific T-cell clones.

CONCLUSIONS

These findings indicate that NKG2D+ T cells have a role in the immunologic response against tumor. Thus, new immunotherapeutic treatments for melanoma patients should be designed aimed at augmenting the NKG2D+ T lymphocyte-mediated immune response.

PTPRK negatively regulates transcriptional activity of wild type and mutated oncogenic beta-catenin and affects membrane distribution of beta-catenin/E-cadherin complexes in cancer cells

Previous reports showed that receptor-type protein-tyrosine phosphatase PTPRK co-localizes with beta-catenin at adherens junctions, and in vitro experiments suggested that beta-catenin could be substrate of PTPRK-mediated phosphatase activity. beta-catenin is a molecule endowed with a dual function being involved both in cell adhesion and in Wnt signaling pathway. Here we provide evidence for the role of PTPRK in negatively regulating the beta-catenin transcriptional activity by modulating its intracellular and membrane distribution. Expression of PTPRK protein in HEK293 cells and in PTPRK-null melanoma cell lines, one of which harbors a mutated oncogenic beta-catenin, impairs nuclear accumulation of wild type and oncogenic forms of beta-catenin, limits cytosolic levels of tyrosine-phosphorylated beta-catenin, and leads to re-localization of E-cadherin/beta-catenin complexes in ordered membrane phase along cell-cell contacts. This re-modulation of beta-catenin cellular distribution results in the inhibition of cyclin D1 and c-myc protein expression, whose genes are targets of beta-catenin. Tumor cells upon re-expression of PTPRK have a reduced proliferative and migration capacity. Moreover we show that PTPRK is also active in negatively regulating the transactivating function of beta-catenin in normal melanocytes as confirmed by experiments with silenced PTPRK by specific siRNA. Our data show that PTPRK influences transactivating activity of beta-catenin in non-tumoral and neoplastic cells by regulating the balance between signaling and adhesive beta-catenin, thus providing biochemical basis for the hypothesis of PTPRK as a tumor suppressor gene.

Identification of a new subset of myeloid suppressor cells in peripheral blood of melanoma patients with modulation by a granulocyte-macrophage colony-stimulation factor-based antitumor vaccine

PURPOSE

Phenotypic and functional features of myeloid suppressor cells (MSC), which are known to serve as critical regulators of antitumor T-cell responses in tumor-bearing mice, are still poorly defined in human cancers. Here, we analyzed myeloid subsets with suppressive activity present in peripheral blood of metastatic melanoma patients and evaluated their modulation by a granulocyte-macrophage colony-stimulating factor (GM-CSF)--based antitumor vaccine.

PATIENTS AND METHODS

Stage IV metastatic melanoma patients (n = 16) vaccinated with autologous tumor-derived heat shock protein peptide complex gp96 (HSPPC-96) and low-dose GM-CSF provided pre- and post-treatment whole blood specimens. Peripheral-blood mononuclear cells (PBMCs) were analyzed by flow cytometry, separated into cellular subsets, and used for in vitro proliferation assays. PBMCs from stage-matched metastatic melanoma patients (n = 12) treated with non-GM-CSF-based vaccines (ie, HSPPC-96 alone or interferon alfa/melanoma-derived peptides) or sex- and age-matched healthy donors (n = 16) were also analyzed for comparison.

RESULTS

The lack of or low HLA-DR expression was found to identify a CD14+ cell subset highly suppressive of lymphocyte functions. CD14+HLA-DR-/lo cells were significantly expanded in all metastatic melanoma patients, whereas they were undetectable in healthy donors. Suppressive activity was mediated by transforming growth factor beta (TGF-beta), whereas no involvement of the arginase and inducible nitric oxide synthase pathways could be detected. CD14+HLA-DR-/lo cells, as well as spontaneous ex vivo release and plasma levels of TGF-beta, were augmented after administration of the HSPPC-96/GM-CSF vaccine. No enhancement of the CD14+-mediated suppressive activity was found in patients receiving non-GM-CSF-based vaccines.

CONCLUSION

CD14+HLA-DR-/lo cells exerting TGF-beta-mediated immune suppression represent a new subset of MSC potentially expandable by the administration of GM-CSF-based vaccines in metastatic melanoma patients.

Phenotypic characterization of human colorectal cancer stem cells

Recent observations indicate that, in several types of human cancer, only a phenotypic subset of cancer cells within each tumor is capable of initiating tumor growth. This functional subset of cancer cells is operationally defined as the "cancer stem cell" (CSC) subset. Here we developed a CSC model for the study of human colorectal cancer (CRC). Solid CRC tissues, either primary tissues collected from surgical specimens or xenografts established in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice, were disaggregated into single-cell suspensions and analyzed by flow cytometry. Surface markers that displayed intratumor heterogeneous expression among epithelial cancer cells were selected for cell sorting and tumorigenicity experiments. Individual phenotypic cancer cell subsets were purified, and their tumor-initiating properties were investigated by injection in NOD/SCID mice. Our observations indicate that, in six of six human CRC tested, the ability to engraft in vivo in immunodeficient mice was restricted to a minority subpopulation of epithelial cell adhesion molecule (EpCAM)(high)/CD44+ epithelial cells. Tumors originated from EpCAM(high)/CD44+ cells maintained a differentiated phenotype and reproduced the full morphologic and phenotypic heterogeneity of their parental lesions. Analysis of the surface molecule repertoire of EpCAM(high)/CD44+ cells led to the identification of CD166 as an additional differentially expressed marker, useful for CSC isolation in three of three CRC tested. These results validate the stem cell working model in human CRC and provide a highly robust surface marker profile for CRC stem cell isolation.

Unique human tumor antigens: immunobiology and use in clinical trials

The individual, unique tumor Ags, which characterize each single tumor, were described 50 years ago in rodents but their molecular characterization was limited to few of them and obtained during the last 20 years. Here we summarize the evidence for the existence and the biological role of such Ags in human tumors, although such evidence was provided only during the last 10 years and by a limited number of studies, a fact leading to a misrepresentation of unique Ags in human tumor immunology. This was also due to the increasing knowledge on the shared, self-human tumor Ags, which have been extensively used as cancer vaccines. In this review, we highlight the biological and clinical importance of unique Ags and suggest how they could be used in clinical studies aimed at assessing their immunogenic and clinical potential both in active and adoptive immunotherapy of human tumors.

Melanoma immunology: past, present and future

PURPOSE OF REVIEW

Metastatic melanoma is a disease for which no effective therapeutic options have been developed during the last 30 years with the possible exception of high dose interferon-alpha in the adjuvant setting of stage III patients. The immunotherapy approach was initiated decades ago using cell-based vaccines and adoptive immunotherapy with functionally ill-defined lymphocytes. This paper aims to evaluate the last three decades of research in melanoma immunotherapy and to provide insights in the future of this strategy.

RECENT FINDINGS

Thanks to the development of knowledge in basic and applied immunology, clinical studies of immunotherapy have been followed by trials based on molecular characterization of melanoma antigens and availability of ex-vivo assays allowing the quantitative assessment of the immune response against the given vaccine and against patient tumor cells. This second generation of immunotherapy trials, along with additional preclinical studies, while not yet resulting in a convincing clinical outcome, provided a wealth of data on immunogenicity of different melanoma antigens, mechanism of antigen presentation and factors that impair immune recognition of melanoma cells.

SUMMARY

We discuss how this information will be exploited for designing new and more successful clinical trials of both active and adoptive antigen-specific immunotherapy of metastatic melanoma patients.

Opposite immune functions of GM-CSF administered as vaccine adjuvant in cancer patients

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been and is still widely used as an adjuvant in clinical trials of vaccination with autologous tumor cells, peptides and/or dendritic cells in a variety of human neoplasms. This cytokine was administered either as product of gene-transduced tumor cells or as recombinant protein together with the vaccine given subcutaneously or intradermally. Results of these trials were heterogeneous in terms of induction of vaccine-specific immune response and of clinical response. Though in some of these studies GM-CSF appeared to help in generating an immune response, in others no effect or even a suppressive effect was reported. Here, we review the literature dealing with the immune adjuvant activity of GM-CSF both in animal models and clinical trials. As a consequence of such analysis, we conclude that GM-CSF may increase the vaccine-induced immune response when administered repeatedly at relatively low doses (range 40-80 microg for 1-5 days) whereas an opposite effect was often reported at dosages of 100-500 microg. The potential mechanisms of the GM-CSF-mediated immune suppression are discussed at the light of studies describing the activation and expansion of myeloid suppressor cells by endogenous tumor-derived or exogenous GM-CSF.

Soluble human LAG-3 molecule amplifies the in vitro generation of type 1 tumor-specific immunity

The adjuvant activities of the human lymphocyte activation gene-3 (LAG-3) molecule have been evaluated in a human setting by investigating the ability of a soluble recombinant human LAG-3 protein (hLAG-3Ig) to enhance the in vitro induction of viral- and tumor-specific CTLs. We found that soluble human LAG-3 significantly sustained the generation and expansion of influenza matrix protein Melan-A/MART-1 and survivin-specific CD8+ T lymphocytes in peripheral blood mononuclear cells (PBMC) of both cancer patients and healthy donors, showing its ability to boost CD8+ T-cell memory response or to prime naive T cells in vitro. The peptide-specific T cells generated in the presence of hLAG-3Ig were endowed with cytotoxic activity and enhanced release of type 1 cytotoxic T (Tc1) cytokines and were able to recognize tumor cells expressing their nominal antigen. Phenotype and cytokine/chemokines produced by antigen-presenting cells (APC) of PBMCs exposed in vitro for 2 days to peptide and hLAG-3Ig indicate that the LAG-3-mediated adjuvant effect may depend on a direct activation of circulating APCs. Our data revealed the activity of hLAG-3Ig in inducing tumor-associated, antigen-specific CD8+ T-cell responses in a human setting and strongly support the conclusion that this recombinant protein is a potential candidate adjuvant for cancer vaccines.

Escape strategies and reasons for failure in the interaction between tumour cells and the immune system: how can we tilt the balance towards immune-mediated cancer control?

The last decade has witnessed an exponential increase in the attempts to demonstrate that adaptive immunity can effectively detect cancer cells and impair their growth in vivo in cancer patients. However, clinical trials of immunotherapy with a broad array of immunisation strategies have depicted a rather disappointing scenario, suggesting that successful control of tumour growth by immunotherapeutic treatments may not be an easy task to achieve. The attention of tumour immunologists has thus been switched to the potential reasons of failure, and extensive efforts are being made in defining the cellular and molecular pathways interfering with the capacity of the immune system to develop powerful immunological reactions against tumour cells. Although many of these pathways have been well characterised in murine models, little and controversial information about their role in determining neoplastic progression in cancer patients is available. This discrepancy at the moment represents one of the major limitations in understanding the obstacles to the in vivo development of protective T cell-mediated immune responses against tumours, and how pharmacological or biological interventions aimed at bypassing tumour escape mechanisms would indeed result in a clinical benefit. The study of the reasons for the failure of the immune system to control tumour growth, which have to be ascribed to highly interconnected phenomena occurring at both tumour and immune levels, could in the near future provide adequate tools to fight cancer by finely tuning the host environment through biological therapies.

Photosensitizing properties of 6-methoxy-2-naphthylacetic acid, the major metabolite of the phototoxic non-steroidal anti-inflammatory and analgesic drug nabumetone

The photobiological properties of 6-methoxy-2-naphthylacetic acid (6-MNAA) were studied using a variety of in vitro phototoxicity assays: photohemolysis, photoperoxidation of linoleic acid, photosensitized degradation of histidine and thymine and the Candida phototoxicity test. 6-MNAA was phototoxic in vitro. 6-MNAA reduced nitro blue tetrazolium (NBT) when irradiated with lambda > or = 300 nm in deoxygenated aqueous buffer solution (pH 7.4). NBT can be reduced by reaction with the excited state of 6-MNAA subject to interference with molecular oxygen. The photohemolysis rate was inhibited by the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO), sodium azide (NaN3) and reduced glutathione (GSH). Photoperoxidation of linoleic acid and photosensitized degradation of histidine and thymine were significantly inhibited by sodium azide and reduced glutathione. 6-MNAA was phototoxic to C. albicans, C. lipolytica and C. tropicalis. A mechanism involving singlet oxygen, radicals, and electron transfer reactions is suggested for the observed phototoxicity.

Natural killer and NK-Like T-cell activation in colorectal carcinoma patients treated with autologous tumor-derived heat shock protein 96

Heat shock proteins (HSPs) are involved in the activation of both adaptive and innate immune systems. Here, we report that vaccination with autologous tumor-derived HSP96 of colorectal cancer patients, radically resected for liver metastases, induced a significant boost of natural killer (NK) activity detected as cytokine secretion and cytotoxicity in the presence of NK-sensitive targets. Increased NK activity was associated with a raise in CD3-CD56+ NK and/or CD3+CD56+ NK-like T cells, displaying enhanced expression of NKG2D and/or NKp46 receptors. Up-regulated expression of CD83 and CD40 and increased interleukin-12 release on stimulation were observed in CD14+ cells from post-HSP96 peripheral blood mononuclear cells, suggesting an indirect pathway of NK stimulation by HSP96-activated monocytes. Additionally, CD3-CD56+ and CD3+CD56+ lymphocytes were found to undergo functional and phenotypic activation on in vitro exposure to HSP96 even in the absence of monocytes, supporting a potential direct activity of HSP96 on these cell subsets. This evidence was confirmed by the specific binding of FITC-conjugated HSP96 to a subset of both CD3-CD56+ and CD3+CD56+ cells in peripheral blood mononuclear cells from colorectal cancer patients. Altogether, these findings identify the activation of the NK compartment as an additional immunologic effect of autologous tumor-derived HSP96 administration in cancer patients.

Reconstitution of human telomerase reverse transcriptase expression rescues colorectal carcinoma cells from in vitro senescence: evidence against immortality as a constitutive trait of tumor cells

Although in vitro establishment of new colorectal carcinoma (CRC) cell lines is an infrequent event, we have observed that primary cultures of CRC can be repeatedly and reproducibly initiated following in vitro plating of tumor-derived epithelial cells. These cultures, however, usually display a short life span as they undergo a limited number of cell passages before entering a state of irreversible growth arrest. In this study, we show that short-lived CRC primary cultures lack constitutive telomerase activity and undergo a senescence process characterized by progressive telomere shortening. Moreover, transduction of these cells with a retroviral vector encoding human telomerase reverse transcriptase (hTERT) is sufficient to reconstitute telomerase activity and allow immortalization. Detailed molecular characterization of hTERT-immortalized CRC cell lines confirms their individual tumor origin by showing expression of colonic epithelial differentiation markers, such as cytokeratin-20 (CK20), full match with class I and class II human leukocyte antigen genotyping of autologous B-lymphoblastoid cells, and presence of somatic mutations in key cancer genes (KRAS2, APC) identical to those of the corresponding autologous original tumor tissues. Moreover, functional characterization of hTERT-immortalized CRC cell lines shows that they have a transformed phenotype, being able to form colonies in soft agar and tumors in severe combined immunodeficient mice. Most interestingly, immunohistochemical analysis of original tumor tissues indicates that short-lived CRC primary cultures, although hTERT-negative in vitro, derive from hTERT-positive tumors. Taken together, our data show that, in a least subset of CRC, biochemical pathways involved in maintenance of telomere length, such as telomerase, are not activated in a constitutive way in all tumor cells.

A listing of human tumor antigens recognized by T cells: March 2004 update

The technological advances occurred in the last few years have led to a great increase in the number of tumor associated antigens (TAA) that are currently available for clinical applications. In this review we provide a comprehensive list of human tumor antigens as reported in the literature updated at February 2004. The list includes all T cell-defined epitopes, while excluding analogs or artificially modified epitopes, as well as virus-encoded and antibodies-recognized antigens. TAAs are listed in alphabetical order along with the epitope sequence and the HLA allele which restricts recognition by T cells. Data on the tissue distribution of each antigen are also provided together with an extensive bibliography that allows a rapid search for any additional information may be needed on each single antigen or epitope. Overall, the updated list is a database tool for clinicians, scientists and students who have an interest in the field of tumor immunology and immunotherapy.

Heat shock proteins: biological functions and clinical application as personalized vaccines for human cancer

Heat shock proteins (HSPs) are a large family of proteins with different molecular weights and different intracellular localizations. These proteins undertake crucial functions in maintaining cell homeostasis, and therefore they have been conserved during evolution. Hsp70 and Grp94/gp96, due to their peptide chaperone capacity and their ability to actively interact with professional antigen-presenting cells (APCs), are also endowed with crucial immunological functions. The immunological properties of these proteins and their implications for vaccine in human cancer will be discussed. Immunological and clinical data of phase I/II studies in melanoma and colorectal cancer patients will be reviewed.

Effect Of Human Natural Killer and γδ T Cells on the Growth of Human Autologous Melanoma Xenografts in SCID Mice

Natural killer (NK) cells were first identified for their ability to kill tumor cells of different origin in vitro. Similarly, gammadelta T lymphocytes display strong cytotoxic activity against various tumor cell lines. However, the ability of both the NK and gammadelta cells to mediate natural immune response against human malignant tumors in vivo is still poorly defined. Severe combined immunodeficient (SCID) mice have been successfully engrafted with human tumors. In this study, the antitumor effect of local as well as of systemic treatments based on NK cells or Vdelta1 or Vdelta2 gamma/delta T lymphocytes against autologous melanoma cells was investigated in vivo. The results show that all three of the populations were effective in preventing growth of autologous human melanomas when both tumor and lymphoid cells were s.c. inoculated at the same site. However, when lymphoid cells were infused i.v., only NK cells and Vdelta1 gamma/delta T lymphocytes could either prevent or inhibit the s.c. growth of autologous melanoma. Accordingly, both NK cells and Vdelta1 gammadelta T lymphocytes could be detected at the s.c. tumor site. In contrast, Vdelta2 gammadelta T lymphocytes were only detectable in the spleen of the SCID mice. Moreover, NK cells maintained their inhibitory effect on tumor growth even after discontinuation of the treatment. Indeed they were present at the tumor site for a longer period. These data support the possibility to exploit NK cells and Vdelta1 gammadelta T lymphocytes in tumor immunotherapy. Moreover, our study emphasizes the usefulness of human tumor/SCID mouse models for preclinical evaluation of immunotherapy protocols against human tumors.

Human tumor-derived heat shock protein 96 mediates in vitro activation and in vivo expansion of melanoma- and colon carcinoma-specific T cells

Heat shock proteins (hsp) 96 play an essential role in protein metabolism and exert stimulatory activities on innate and adaptive immunity. Vaccination with tumor-derived hsp96 induces CD8(+) T cell-mediated tumor regressions in different animal models. In this study, we show that hsp96 purified from human melanoma or colon carcinoma activate tumor- and Ag-specific T cells in vitro and expand them in vivo. HLA-A*0201-restricted CD8(+) T cells recognizing Ags expressed in human melanoma (melanoma Ag recognized by T cell-1 (MART-1)/melanoma Ag A (Melan-A)) or colon carcinoma (carcinoembryonic Ag (CEA)/epithelial cell adhesion molecule (EpCAM)) were triggered to release IFN-gamma and to mediate cytotoxic activity by HLA-A*0201-matched APCs pulsed with hsp96 purified from tumor cells expressing the relevant Ag. Such activation occurred in class I HLA-restricted fashion and appeared to be significantly higher than that achieved by direct peptide loading. Immunization with autologous tumor-derived hsp96 induced a significant increase in the recognition of MART-1/Melan-A(27-35) in three of five HLA-A*0201 melanoma patients, and of CEA(571-579) and EpCAM(263-271) in two of five HLA-A*0201 colon carcinoma patients, respectively, as detected by ELISPOT and HLA/tetramer staining. These increments in Ag-specific T cell responses were associated with a favorable disease course after hsp96 vaccination. Altogether, these data provide evidence that hsp96 derived from human tumors can present antigenic peptides to CD8(+) T cells and activate them both in vitro and in vivo, thus representing an important tool for vaccination in cancer patients.