Identification of the immunodominant peptides of the MART-1 human melanoma antigen recognized by the majority of HLA-A2-restricted tumor infiltrating lymphocytes

A HLA-Cw*0701 restricted Melan-A/MART1 epitope presented by melanoma tumor cells to CD8+ tumor infiltrating lymphocytes

Melan-A/MART1 is a melanocytic differentiation antigen recognized on melanoma tumor cells by CD8+ and CD4+ T cells. In this study, we describe a new epitope of this protein recognized in the context of HLA-Cw*0701 molecules by a CD8+ tumor infiltrating lymphocyte (TIL) clone. This CD8+ TIL clone specifically recognized and killed a fraction of melanoma cells lines expressing Melan-A/MART1 and HLA-Cw*0701. We further show that the Melan-A/MART1(51-61) peptide is the optimal peptide recognized by this clone. Together, these data significantly enlarge the fraction of melanoma patients susceptible to benefit from a Melan-A/MART1 vaccine approach.

Cell- and peptide-based immunotherapeutic approaches for glioma

Glioblastoma multiforme (GBM) is the most common and lethal primary malignant brain tumor. Although considerable progress has been made in surgical and radiation treatment for glioma patients, the impact of these advances on clinical outcome has been disappointing. Therefore, the development of novel therapeutic approaches is essential. Recent reports demonstrate that systemic immunotherapy using dendritic cells (DCs) or peptide vaccines is capable of inducing an antiglioma response. These approaches successfully induce an antitumor immune response and prolong survival in patients with glioma without major side effects. There are several types of glioma, so to achieve effective therapy, it might be necessary to evaluate the molecular genetic abnormalities in individual patient tumors and design novel immunotherapeutic strategies based on the pharmacogenomic findings. Here, we review recent advances in DC- and peptide-based immunotherapy approaches for patients with gliomas.

A novel population of human melanoma-specific CD8 T cells recognizes Melan-AMART-1 immunodominant nonapeptide but not the corresponding decapeptide

HLA-A2-restricted cytolytic T cells specific for the immunodominant human tumor Ag Melan-A(MART-1) can kill most HLA-matched melanoma cells, through recognition of two naturally occurring antigenic variants, i.e., Melan-A nonamer AAGIGILTV and decamer EAAGIGILTV peptides. Several previous studies have suggested a high degree of TCR cross-reactivity to the two peptides. In this study, we describe for the first time that some T cell clones are exclusively nonamer specific, because they are not labeled by A2/decamer-tetramers and do not recognize the decamer when presented endogenously. Functional assays with peptides gave misleading results, possibly because decamers were cleaved by exopeptidases. Interestingly, nonapeptide-specific T cell clones were rarely Valpha2.1 positive (only 1 of 19 clones), in contrast to the known strong bias for Valpha2.1-positive TCRs found in decamer-specific clones (59 of 69 clones). Molecular modeling revealed that nonapeptide-specific TCRs formed unfavorable interactions with the decapeptide, whereas decapeptide-specific TCRs productively created a hydrogen bond between CDR1alpha and glutamic acid (E) of the decapeptide. Ex vivo analysis of T cells from melanoma metastases demonstrated that both nonamer and decamer-specific T cells were enriched to substantial frequencies in vivo, and representative clones showed efficient tumor cell recognition and killing. We conclude that the two peptides should be regarded as distinct epitopes when analyzing tumor immunity and developing immunotherapy against melanoma.

Less yin, more yang: confronting the barriers to cancer immunotherapy

Clinical trials involving T cell-based immunotherapy for the treatment of human cancer have shown limited degrees of success. In cancer vaccine trials conducted at multiple centers worldwide, immunization has often resulted in the robust elicitation of T cells that specifically recognize antigens expressed on the surface of tumor cells. However, to date, objective clinical responses resulting from these approaches have remained relatively rare. By contrast, adoptive transfer of laboratory-expanded T cells into patients has had more success, producing impressive clinical regressions in a subset of advanced metastatic melanoma patients. The failure of activated T cells to consistently induce clinical responses in many other patients has pushed us toward a deeper understanding of natural immunoregulatory mechanisms that are directly responsible for diminishing tumor-specific T-cell activation, migration, and effector function in vivo. Such immunosuppressive factors likely evolved to prevent autoimmunity, but are frequently co-opted by tumors to evade tumor-specific immune responses. With this knowledge, it now becomes imperative to develop specific clinical interventions capable of eliminating tumor-specific immunosuppression, with the goal of shifting the balance to favor effector T-cell function and tumor cell killing.

Identification of human leukocyte antigen-A24-restricted epitope peptides derived from gene products upregulated in lung and esophageal cancers as novel targets for immunotherapy

For the development of cancer vaccine therapies, we have searched for possible epitope peptides that can elicit cytotoxic T lymphocytes (CTL) to the TTK protein kinase (TTK), lymphocyte antigen 6 complex locus K (LY6K) and insulin-like growth factor (IGF)-II mRNA binding protein 3 (IMP-3), which were previously identified to be transactivated in the majority of lung and esophageal cancers. We screened 31, 17 and 17 candidate human leukocyte antigen (HLA)-A*2402-binding peptides to parts of TTK, LY6K and IMP-3, respectively. As a result, we successfully established strong CTL clones stimulated by TTK-567 (SYRNEIAYL), LY6K-177 (RYCNLEGPPI) and IMP-3-508 (KTVNELQNL) that have specific cytotoxic activities against the HLA-A24-positive target cells pulsed with the candidate peptides. Subsequent analysis of the CTL clones also revealed their cytotoxic activities against lung and esophageal tumor cells that endogenously express TTK, LY6K or IMP-3. A cold target inhibition assay further confirmed that the CTL cell clones specifically recognized the MHC class I–peptide complex. Our results strongly imply that TTK, LY6K and IMP-3 are novel tumor-associated antigens recognized by CTL, and TTK-567 (SYRNEIAYL), LY6K-177 (RYCNLEGPPI) and IMP-3-508 (KTVNELQNL) are HLA-A24-restricted epitope peptides that can induce potent and specific immune responses against lung and esophageal cancer cells expressing TTK, LY6K and IMP-3.

A HLA-DQ5 restricted Melan-A/MART-1 epitope presented by melanoma tumor cells to CD4+ T lymphocytes

Melan-A/MART1 is a melanocytic differentiation antigen expressed by tumor cells of the majority of melanoma patients and, as such, is considered as a good target for melanoma immunotherapy. Nonetheless, the number of class I and II restricted Melan-A epitopes identified so far remains limited. Here we describe a new Melan-A/MART-1 epitope recognized in the context of HLA-DQa1*0101 and HLA-DQb1*0501, -DQb1*0502 or -DQb1*0504 molecules by a CD4+ T cell clone. This clone was obtained by in vitro stimulation of PBMC from a healthy donor by the Melan-A51-73 peptide previously reported to contain a HLA-DR4 epitope. The Melan-A51-73 peptide, therefore contains both HLA-DR4 and HLA-DQ5 restricted epitope. We further show that Melan-A51-63 is the minimal peptide optimally recognized by the HLA-DQ5 restricted CD4+ clone. Importantly, this clone specifically recognizes and kills tumor cell lines expressing Melan-A and either HLA-DQb1*0501, -DQb1*0504 or -DQb1*0502 molecules. Moreover, we could detect CD4+ T cells secreting IFN-gamma in response to Melan-A51-63 and Melan-A51-73 peptides among tumor infiltrating and blood lymphocytes from HLA-DQ5+ patients. This suggests that spontaneous CD4+ T cell responses against this HLA-DQ5 epitope occur in vivo. Together these data significantly increase the fraction of melanoma patients susceptible to benefit from a Melan-A class II restricted vaccine approach.

Human heat shock protein 70 enhances tumor antigen presentation through complex formation and intracellular antigen delivery without innate immune signaling

Heat shock proteins (HSPs) have shown promise for the optimization of protein-based vaccines because they can transfer exogenous antigens to dendritic cells and at the same time induce their maturation. Great care must be exercised in interpretating HSP-driven studies, as by-products linked to the recombinant generation of these proteins have been shown to mediate immunological effects. We generated highly purified human recombinant Hsp70 and demonstrated that it strongly enhances the cross-presentation of exogenous antigens resulting in better antigen-specific T cell stimulation. Augmentation of T cell stimulation was a direct function of the degree of complex formation between Hsp70 and peptides and correlated with improved antigen delivery to endosomal compartments. The Hsp70 activity was independent of TAP proteins and was not inhibited by exotoxin A or endosomal acidification. Consequently, Hsp70 enhanced cross-presentation of various antigenic sequences, even when they required different post-uptake processing and trafficking, as exemplified by the tumor antigens tyrosinase and Melan-A/MART-1. Furthermore, Hsp70 enhanced cross-presentation by different antigen-presenting cells (APCs), including dendritic cells and B cells. Importantly, enhanced cross-presentation and antigen-specific T cell activation were observed in the absence of innate signals transmitted by Hsp70. As Hsp70 supports the cross-presentation of different antigens and APCs and is inert to APC function, it may show efficacy in various settings of immune modulation, including induction of antigen-specific immunity or tolerance.

Vitiligo puzzle: the pieces fall in place

Over the years, the role of biochemical, immunological, genetic, and other biological aspects in the pathogenesis of vitiligo has been studied. So far, no convincing model describing the interplay of these contributing factors has been formulated. Based on existing research, we propose that vitiligo has a multi-factorial etiology, characterized by multiple steps, but always involving an increase of external or internal phenol/catechol concentration, serving as a preferred surrogate substrate of tyrosinase, competing with its physiological substrate tyrosine. The conversion of these substrates into reactive quinones is reinforced by a disturbed redox balance (increasing hydrogen peroxide). Such reactive quinones can be covalently bound to the catalytic centre of tyrosinase (haptenation). This could give rise to a new antigen, carried by Langerhans cells to the regional lymph node, stimulating the proliferation of cytotoxic T cells. However, the activation of such cytotoxic cells is only a first step in skin melanocyte killing, which also depends on a shift in the balance between immune defence and tolerance, e.g. resulting from a decrease in properly functioning T-regulatory cells. With this new model, based on a synthesis of several of the existing theories, in mind, the external and internal factors involved in the etiopathogenesis of vitiligo are reviewed, against the background of reported clinical data, experimental studies and existing and potential new therapies. A similar complex mechanism may also lead to some other autoimmune diseases.

Novel antibodies as anticancer agents

In recent years antibodies, whether generated by traditional hybridoma technology or by recombinant DNA strategies, have evolved from Paul Ehrlich's 'magic bullets' to a modern age 'guided missile'. In the recent years of immunologic research, we are witnessing development in the fields of antigen screening and protein engineering in order to create specific anticancer remedies. The developments in the field of recombinant DNA, protein engineering and cancer biology have let us gain insight into many cancer-related mechanisms. Moreover, novel techniques have facilitated tools allowing unique distinction between malignantly transformed cells, and regular ones. This understanding has paved the way for the rational design of a new age of pharmaceuticals: monoclonal antibodies and their fragments. Antibodies can select antigens on both a specific and a high-affinity account, and further implementation of these qualities is used to target cancer cells by specifically identifying exogenous antigens of cancer cell populations. The structure of the antibody provides plasticity resonating from its functional sites. This review will screen some of the many novel antibodies and antibody-based approaches that are being currently developed for clinical applications as the new generation of anticancer agents.

Structures of MART-126/27-35 Peptide/HLA-A2 complexes reveal a remarkable disconnect between antigen structural homology and T cell recognition

Small structural changes in peptides presented by major histocompatibility complex (MHC) molecules often result in large changes in immunogenicity, supporting the notion that T cell receptors are exquisitely sensitive to antigen structure. Yet there are striking examples of TCR recognition of structurally dissimilar ligands. The resulting unpredictability of how T cells will respond to different or modified antigens impacts both our understanding of the physical bases for TCR specificity as well as efforts to engineer peptides for immunomodulation. In cancer immunotherapy, epitopes and variants derived from the MART-1/Melan-A protein are widely used as clinical vaccines. Two overlapping epitopes spanning amino acid residues 26 through 35 are of particular interest: numerous clinical studies have been performed using variants of the MART-1 26-35 decamer, although only the 27-35 nonamer has been found on the surface of targeted melanoma cells. Here, we show that the 26-35 and 27-35 peptides adopt strikingly different conformations when bound to HLA-A2. Nevertheless, clonally distinct MART-1(26/27-35)-reactive T cells show broad cross-reactivity towards these ligands. Simultaneously, however, many of the cross-reactive T cells remain unable to recognize anchor-modified variants with very subtle structural differences. These dichotomous observations challenge our thinking about how structural information on unligated peptide/MHC complexes should be best used when addressing questions of TCR specificity. Our findings also indicate that caution is warranted in the design of immunotherapeutics based on the MART-1 26/27-35 epitopes, as neither cross-reactivity nor selectivity is predictable based on the analysis of the structures alone.

Vaccine therapy for melanoma: current status and future directions

A vaccine is typically defined as any preparation used as a preventive inoculation to confer immunity against a specific disease. Vaccines for infectious diseases are highly effective, acting by inducing antigen-specific immunity that prevents subsequent infection. Unfortunately, the success of vaccines in infectious diseases has not been mirrored in oncology. This failure is the result of several challenges facing cancer vaccines, including the conceptual shift from disease prevention to disease treatment, tumor-induced immunosuppression and other mechanisms of immune escape, the similarity between tumor antigens and self antigens to which the patient is tolerant, unfavorable effector-to-target ratios in patients with established tumors, and financial and regulatory issues. Despite this, cancer remains a promising target for vaccine therapy. Melanoma in particular is known for its inherent immunogenicity on the basis of many anecdotal reports of spontaneous immune-based tumor regression, and thus has been the focus of immunotherapeutic approaches. Rare but significant vaccine-induced clinical regression of melanoma has spurred intensive investigations to augment vaccine efficacy. This review explores the many vaccine strategies that have been clinically tested for the treatment of melanoma and considers future approaches of cancer immunotherapy.

Identification of HLA-CW3, GNAS and IMPA as cytotoxic T-lymphocyte (CTL) target antigens using an allogeneic mixed lymphocyte tumor cell culture (MLTC) system and subsequent cDNA library screening

Allogeneic mixed lymphocyte tumor cell cultures (MLTCs) were established using lymphocytes from non-small-cell lung cancer (NSCLC) patient UKY-53 and HLA-A2+ NSCLC tumor cells (UKY-29). The tumor cells expressed the lymphocyte costimulatory molecule CD80 (UKY29.7). Cytolytic activity showed the cytotoxic T-lymphocytes (CTL) lysed UKY-29, but not K562 or Daudi. The CTL also lysed: HLA-A2+ and -A24+ tumor cell lines from a number of tumor histologies. The CTL also lysed Epstein Barr virus transformed (EBV) B-cells, UKY-29EBV, autologous to the stimulating cell line, UKY29TC. These data suggested the presence of both tumor-specific and allogeneic reactivities in the bulk CTL population. Subsequent cDNA cloning analysis and sequencing demonstrated that the bulk CTL population was recognizing: (i) allogeneic target HLA-CW3, and two minor histocompatibility antigens; (ii) guanine nucleotide-binding protein, G(S) (GNAS), and (iii) inositol myophosphatase (IMPA). All three antigens, we believe, were restricted by HLA-A2. Whereas the system described was initially intended to identify tumor-associated antigens recognized by CTL, the nature of the allogeneic system provides a unique opportunity for the identification of epitopes that confer both allo and minor antigen recognition.

Peptide-based immunotherapeutic approaches to glioma: a review

Despite advances in surgery, radiation and chemotherapy, the prognosis of patients with malignant glioma is still very poor; therefore, the development of a novel therapeutic modality is essential. There are increasing reports demonstrating that systemic immunotherapy using dendritic cells or a peptide vaccine is capable of inducing an antiglioma response. Peptide-based immunotherapy strategies appear promising as an approach to successfully induce an antitumor immune response and prolong survival in patients with glioma without major side effects. Now, peptide-based immunotherapy could be a new treatment modality for patients with brain tumors.

Antigenic profiling of glioma cells to generate allogeneic vaccines or dendritic cell-based therapeutics

PURPOSE

Allogeneic glioma cell lines that are partially matched to the patient at class I human leukocyte antigen (HLA) loci and that display tumor-associated antigens (TAA) or antigenic precursors [tumor antigen precursor proteins (TAPP)] could be used for generating whole tumor cell vaccines or, alternatively, for extraction of TAA peptides to make autologous dendritic cell vaccines.

EXPERIMENTAL DESIGN

Twenty human glioma cell lines were characterized by molecular phenotyping and by flow cytometry for HLA class I antigen expression. Twelve of the 20 cell lines, as well as analyses of freshly resected glioma tissues, were further characterized for protein and/or mRNA expression of 16 tumor antigen precursor proteins or TAA.

RESULTS

These 20 human glioma cell lines potentially cover 77%, 85%, and 78% of the U.S. Caucasian population at HLA-A, HLA-B, and HLA-C alleles, respectively. All cells exhibited multiple TAA expressions. Most glioma cells expressed antigen isolated from immunoselected melanoma-2 (Aim-2), B-cyclin, EphA2, GP100, beta1,6-N-acetylglucosaminyltransferase V (GnT-V), IL13Ralpha2, Her2/neu, hTert, Mage, Mart-1, Sart-1, and survivin. Real-time PCR technology showed that glioblastoma specimens expressed most of the TAA as well. Tumor-infiltrating lymphocytes and CD8(+) CTL killed T2 cells when loaded with specific HLA-A2(+) restricted TAA, or gliomas that were both HLA-A2(+) and also positive for specific TAA (Mart-1, GP100, Her2/neu, and tyrosinase) but not those cells negative for HLA-A2 and/or lacking the specific epitope.

CONCLUSIONS

These data provide proof-in-principle for the use of allogeneic, partially HLA patient-matched glioma cells for vaccine generation or for peptide pulsing with allogeneic glioma cell extracts of autologous patient dendritic cells to induce endogenous CTL in brain tumor patients.

Potential functional role of plasmacytoid dendritic cells in cancer immunity

Plasmacytoid dendritic cells (pDCs), as well as myeloid dendritic cells (mDCs), have a dual role not only in initiating immune responses but also in inducing tolerance to exogenous and endogenous antigens. Tumour antigens originate from endogenous self-antigens, which are poorly immunogenic and also subject to change during tumour progression. In general, tumour antigens derived from apoptotic cells are captured by immature mDCs, antigen presentation by which is most likely to result in immune tolerance. In contrast, tumour antigens may be taken up by pDCs through Toll-like receptor 9 (TLR9) via receptor-mediated endocytosis. TLR9-dependent activation of pDCs results in the secretion of pro-inflammatory cytokines such as interleukin (IL)-12 and type I interferons (IFNs) through a MyD88-dependent pathway. Type I IFNs also activate mDCs for T-cell priming. Although pDCs recruited to the tumour site are implicated in facilitating tumour growth via immune suppression, they can be released from the tumour as a result of cell death caused by primary systemic chemotherapy, and can then be activated through TLR9. Thus, synergistically with mDCs, pDCs may also play a crucial role in mediating cancer immunity. In this review, the potential functional duality and plasticity of pDCs mediated by TLR9 ligation in cancer immunity will be discussed.

Enhancement of immunologic tumor regression by intratumoral administration of dendritic cells in combination with cryoablative tumor pretreatment and Bacillus Calmette-Guerin cell wall skeleton stimulation

PURPOSE

We developed an effective immunotherapy, which could induce antitumor immune responses against shared and unique tumor antigens expressed in autologous tumors.

EXPERIMENTAL DESIGN

Intratumoral administration of dendritic cells is one of the individualized immunotherapies; however, the antitumor activity is relatively weak. In this study, we attempted to enhance the antitumor efficacy of the i.t. dendritic cell administration by combining dendritic cells stimulated with Bacillus Calmette-Guerin cell wall skeleton (BCG-CWS) additionally with cryoablative pretreatment of tumors and analyzed the therapeutic mechanisms.

RESULTS

These two modifications (cryoablation of tumors and BCG-CWS stimulation of dendritic cells) significantly increases the antitumor effect on both the treated tumor and the untreated tumor, which was distant at the opposite side, in a bilateral s.c. murine CT26 colon cancer model. Further analysis of the augmented antitumor effects revealed that the cryoablative pretreatment enhances the uptake of tumor antigens by the introduced dendritic cells, resulting in the induction of tumor-specific CD8(+) T cells responsible for the in vivo tumor regression of both treated and remote untreated tumors. This novel combination i.t. dendritic cell immunotherapy was effective against well-established large tumors. The antitumor efficacy was further enhanced by depletion of CD4(+)CD25(+)FoxP3(+) regulatory T cells.

CONCLUSIONS

This novel dendritic cell immunotherapy with i.t. administration of BCG-CWS-treated dendritic cells following tumor cryoablation could be used for the therapy of cancer patients with multiple metastases.

Synthetic anticancer vaccine candidates: rational design of antigenic peptide mimetics that activate tumor-specific T-cells

A rational design approach was followed to develop peptidomimetic analogues of a cytotoxic T-cell epitope capable of stimulating T-cell responses as strong as or stronger (heteroclytic) than those of parental antigenic peptides. The work described herein focused on structural alterations of the central amino acids of the melanoma tumor-associated antigenic peptide Melan-A/MART-1(26-35) using nonpeptidic units. A screening was first realized in silico to select altered peptides potentially capable of fitting at the interface between the major histocompatibilty complex (MHC) class-I HLA-A2 molecule and T-cell receptors (TCRs). Two compounds appeared to be high-affinity ligands to the HLA-A2 molecule and stimulated several Melan-A/MART-1 specific T-cell clones. Most remarkably, one of them even managed to amplify the response of one clone. Together, these results indicate that central TCR-contact residues of antigenic peptides can be replaced by nonpeptidic motifs without loss of binding affinity to MHC class-I molecules and T-cell triggering capacity.

Macrophages as stimulators of MART-1 27-35 epitope-specific human cytolytic T lymphocytes in vitro

BACKGROUND

Activation and expansion of antigen-specific cytolytic T lymphocytes (CTL) require epitope presented by antigen-presenting cells (APC). Presently, dendritic cells (DC) are viewed as the most efficient APC. Since the recognition of DCs as the professional APC, the paradigm has emerged that macrophage (MPhi) are scavengers and are incapable of activating T cells.

METHOD

The melanoma-associated MART-1(27-35) peptide-loaded MPhi from HLA-A2-positive donors were used to activate MART-1(27-35) epitope-specific CTL in vitro.

RESULTS

We show that peptide-pulsed MPhi stimulate MART-1(27-35) epitope-specific precursors to proliferate and to express effector functions. We also show that upon restimulation with the peptide pulsed MPhi, a fraction of the epitope-specific CTLs undergoes activation-induced cell death. The activation-induced cell death is induced in an epitope-specific manner and through apoptosis.

CONCLUSION

MPhi can function as APC and are also capable of modulating expansion and contraction of CTL response in vitro.

Development of Effective Antigen Delivery Carrier to Dendritic Cells via Fc Receptor in Cancer Immunotherapy

In cancer immunotherapy with dendritic cells (DCs), which are the most potent antigen-presenting cells, it is important that DCs present peptides derived from tumor-associated antigens on major histocompatibility complex (MHC) class I molecules and activate tumor-specific cytotoxic T lymphocytes. However, exogenous antigens are generally presented on MHC class II but not class I molecules. To develop effective immunotherapy for cancer, an antigen delivery carrier that can induce MHC class I presentation of exogenous antigens is necessary. Several strategies to induce DCs to present exogenous antigens on MHC class I molecules have been reported. First, DCs that phagocytosed a particulate form of antigens present peptides derived from the antigens on MHC class I molecules. Second, DCs that incorporated antigens via certain endocytic receptors such as Fc receptors efficiently present peptides on MHC class I molecules. We combined these two strategies and prepared antigen-containing IgG-conjugated liposomes (IgG-liposomes). In this study, we investigated the feasibility of IgG-liposomes as antigen delivery carriers in cancer immunotherapy with DCs. Immunization of mice with DCs that endocytosed ovalbumin (OVA)-containing IgG-liposomes, but not OVA-containing bare liposomes or soluble OVA, completely prevented the growth of OVA-expressing lymphoma cells. These results suggest that IgG-liposomes represent an efficient antigen delivery carrier for DCs in cancer immunotherapy.

Direct class I HLA antigen discovery to distinguish virus-infected and cancerous cells

Class I human leukocyte antigen molecules are nature's proteome-scanning chips, presenting thousands of endogenously loaded peptides on the surface of virtually every cell in the body. Cytotoxic T cells survey the class I human leukocyte antigen peptide cargo presented, recognize peptides unique to unhealthy cells and destroy diseased cells. A precise understanding of how class I molecules distinguish diseased cells is positioned to drive immune-based diagnostics, therapies and vaccines. When identifying epitopes unique to unhealthy cells, the most experimentally direct approach is to examine the class I-presented peptides of infected/cancerous cells. Here we discuss the strategies adapted for protein production, protein/peptide purification, peptide separation and for maintaining experimental reproducibility during the direct characterization of class I human leukocyte antigen peptides.

Spontaneous CD8 T cell responses against the melanocyte differentiation antigen RAB38/NY-MEL-1 in melanoma patients

The melanocyte differentiation Ag RAB38/NY-MEL-1 was identified by serological expression cloning (SEREX) and is expressed in the vast majority of melanoma lesions. The immunogenicity of RAB38/NY-MEL-1 has been corroborated previously by the frequent occurrence of specific Ab responses in melanoma patients. To elucidate potential CD8 T cell responses, we applied in vitro sensitization with overlapping peptides spanning the RAB38/NY-MEL-1 protein sequence and the reverse immunology approach. The identified peptide RAB38/NY-MEL-1(50-58) exhibited a marked response in ELISPOT assays after in vitro sensitization of CD8 T cells from HLA-A *0201(+) melanoma patients. In vitro digestion assays using purified proteasomes provided evidence of natural processing of RAB38/NY-MEL-1(50-58) peptide. Accordingly, monoclonal RAB38/NY-MEL-1(50-58)-specific T cell populations were capable of specifically recognizing HLA-A2(+) melanoma cell lines expressing RAB38/NY-MEL-1. Applying fluorescent HLA-A2/RAB38/NY-MEL-1(50-58) multimeric constructs, we were able to document a spontaneously developed memory/effector CD8 T cell response against this peptide in a melanoma patient. To elucidate the Ag-processing pathway, we demonstrate that RAB38/NY-MEL-1(50-58) is produced efficiently by the standard proteasome and the immunoproteasome. In addition to the identification of a RAB38/NY-MEL-1-derived immunogenic CD8 T cell epitope, this study is instrumental for both the onset and monitoring of future RAB38/NY-MEL-1-based vaccination trials.

MHC Class I Antigens and Immune Surveillance in Transformed Cells

MHC class I antigens play a crucial role in the interaction of tumor cells with the host immune system, in particular, in the presentation of peptides as tumor-associated antigens to cytotoxic lymphocytes (CTLs) and in the regulation of cytolytic activity of natural killer (NK) cells. In this review we discuss the role of MHC class I antigens in the recognition and elimination of transformed cells and in the generation of tumor immune escape routes when MHC class I losses occur in tumors. The different altered MHC class I phenotypes and their distribution in different human tumors are the main topic of this review. In addition, molecular defects that underlie MHC alterations in transformed cells are also described in detail. Future research directions in this field are also discussed, including the laboratory analysis of tumor MHC class I-negative variants and the possible restoration of MHC class I expression.

Gene transfer of tumor-reactive TCR confers both high avidity and tumor reactivity to nonreactive peripheral blood mononuclear cells and tumor-infiltrating lymphocytes

Cell-based antitumor immunity is driven by CD8(+) cytotoxic T cells bearing TCR that recognize specific tumor-associated peptides bound to class I MHC molecules. Of several cellular proteins involved in T cell:target-cell interaction, the TCR determines specificity of binding; however, the relative amount of its contribution to cellular avidity remains unknown. To study the relationship between TCR affinity and cellular avidity, with the intent of identifying optimal TCR for gene therapy, we derived 24 MART-1:27-35 (MART-1) melanoma Ag-reactive tumor-infiltrating lymphocyte (TIL) clones from the tumors of five patients. These MART-1-reactive clones displayed a wide variety of cellular avidities. alpha and beta TCR genes were isolated from these clones, and TCR RNA was electroporated into the same non-MART-1-reactive allogeneic donor PBMC and TIL. TCR recipient cells gained the ability to recognize both MART-1 peptide and MART-1-expressing tumors in vitro, with avidities that closely corresponded to the original TCR clones (p = 0.018-0.0003). Clone DMF5, from a TIL infusion that mediated tumor regression clinically, showed the highest avidity against MART-1 expressing tumors in vitro, both endogenously in the TIL clone, and after RNA electroporation into donor T cells. Thus, we demonstrated that the TCR appeared to be the core determinant of MART-1 Ag-specific cellular avidity in these activated T cells and that nonreactive PBMC or TIL could be made tumor-reactive with a specific and predetermined avidity. We propose that inducing expression of this highly avid TCR in patient PBMC has the potential to induce tumor regression, as an "off-the-shelf" reagent for allogeneic melanoma patient gene therapy.

Efficient priming and expansion of antigen-specific CD8+T cells by a novel cell-based artificial APC

The ex vivo priming and expansion of human CTL by APC, such as autologous monocyte-derived dendritic cells (DC), has the potential for use in immunotherapy for infectious diseases and cancer. To overcome the difficulty of obtaining sufficient number of autologous DC from patients, we have developed cell-based artificial APC (aAPC), designated Med-APC. These aAPC rapidly activate and expand the corresponding Ag-specific CD8+ T cells when pulsed with CTL epitope peptide(s) as efficiently as mature DC (mDC). We have also shown that Med-APC possess an innate cellular machinery that is sufficient to support the processing of complete Ag into immunodominant peptides, which considerably extends the usefulness of this technology. In addition, we have developed a novel expression vector system that expresses ubiquitinated Ag, resulting in an enhanced APC function of this system. Genetically encoded Ag can be easily introduced into Med-APC by transfection with this vector. Med-APC transfected with ubiquitinated Ag can efficiently expand the corresponding Ag-specific CTL without exogenous peptides. Therefore, Med-APC may have important therapeutic implications for adoptive immunotherapy and can be used for the detection of Ag-specific CTL for immunomonitoring.

Melan-A/MART-1-Specific CD4 T Cells in Melanoma Patients: Identification of New Epitopes and Ex Vivo Visualization of Specific T Cells by MHC Class II Tetramers

Over the past decade, many efforts have been made to identify MHC class II-restricted epitopes from different tumor-associated Ags. Melan-A/MART-1(26-35) parental or Melan-A/MART-1(26-35(A27L)) analog epitopes have been widely used in melanoma immunotherapy to induce and boost CTL responses, but only one Th epitope is currently known (Melan-A51-73, DRB1*0401 restricted). In this study, we describe two novel Melan-A/MART-1-derived sequences recognized by CD4 T cells from melanoma patients. These epitopes can be mimicked by peptides Melan-A27-40 presented by HLA-DRB1*0101 and HLA-DRB1*0102 and Melan-A25-36 presented by HLA-DQB1*0602 and HLA-DRB1*0301. CD4 T cell clones specific for these epitopes recognize Melan-A/MART-1+ tumor cells and Melan-A/MART-1-transduced EBV-B cells and recognition is reduced by inhibitors of the MHC class II presentation pathway. This suggests that the epitopes are naturally processed and presented by EBV-B cells and melanoma cells. Moreover, Melan-A-specific Abs could be detected in the serum of patients with measurable CD4 T cell responses specific for Melan-A/MART-1. Interestingly, even the short Melan-A/MART-1(26-35(A27L)) peptide was recognized by CD4 T cells from HLA-DQ6+ and HLA-DR3+ melanoma patients. Using Melan-A/MART-1(25-36)/DQ6 tetramers, we could detect Ag-specific CD4 T cells directly ex vivo in circulating lymphocytes of a melanoma patient. Together, these results provide the basis for monitoring of naturally occurring and vaccine-induced Melan-A/MART-1-specific CD4 T cell responses, allowing precise and ex vivo characterization of responding T cells.

Substitution analog peptide derived from HER-2 can efficiently induce HER-2-specific, HLA-A24 restricted CTLs

In order to broaden the possibility for anti-HER-2/neu (HER-2) immune targeting, it is important to identify HLA-A24 restricted peptide epitopes derived from HER-2, since HLA-A24 is one of the most common alleles in Japanese and Asian people. In the present study, we have screened HER-2-derived, HLA-A24 binding peptides for cytotoxic T lymphocyte (CTL) epitopes. A panel of HER-2-derived peptides with HLA-A24 binding motifs and the corresponding analogs designed to enhance HLA-A24 binding affinity were selected. Identification of HER-2-reactive and HLA-A24 restricted CTL epitopes were performed by a reverse immunology approach. To induce HER-2-reactive and HLA-A24 restricted CTLs, PBMCs from healthy donors were repeatedly stimulated with monocytes-derived, mature DCs pulsed with HER-2 peptide. Subsequent peptide-induced T cells were tested for the specificity by enzyme linked immunospot, cytotoxicity and tetramer assays. CTL clones were then obtained from the CTL lines by limiting dilution. Of the peptides containing HLA-A24 binding motifs, 16 peptides (nine mers) including wild type peptides (IC50 <1,000 nM) and substituted analog peptides (IC50 <50 nM) were selected for the present study. Our studies show that an analog peptide, HER-2(905AA), derived from HER-2(905) could efficiently induce HER-2-reactive and HLA-A24 restricted CTLs. The reactivity of the HER-2(905AA)-induced CTL (CTL905AA) was confirmed by different CTL assays. The CTL905AA clones also were able to lyse HER-2(+), HLA-A24(+) tumor cells and cytotoxicity could be significantly reduced in cold target inhibition assays using cold targets pulsed with the HER-2(905) wild type peptide as well as the inducing HER-2(905AA) analog peptide. A newly identified HER-2(905) peptide epitope is naturally processed and presented as a CTL epitope on HER-2 overexpressing tumor cells, and an MHC anchor-substituted analog, HER-2(905AA), can efficiently induce HER-2-specific, HLA-A24 restricted CTLs.

Identification of two Melan-A CD4+ T cell epitopes presented by frequently expressed MHC class II alleles

Because of its expression pattern restricted to cells of the melanocytic lineage and to melanoma cells, Melan-A is an important target of immunotherapeutic approaches for the treatment of melanoma. Identification of Melan-A derived sequences recognized by specific T cells is therefore of great interest for the development of these therapeutic strategies. Using circulating CD4(+) T cells from healthy donors, we identified two Melan-A-derived CD4(+) T cell epitopes mapping to the 1-20 and 91-110 regions of the protein and restricted by HLA-DR11 and HLA-DR52 molecules, respectively. CD4(+) T cells specific for the identified epitopes were able to recognize the native antigen when endogenously expressed by antigen presenting cells and tumor cells. In addition, CD4(+) T cells specific for Melan-A 91-110 recognized the epitope after exogenous processing and presentation of Melan-A recombinant protein. Identification of these epitopes will be instrumental for the evaluation of the immune response to Melan-A in cancer patients.

Human T cell responses against melanoma

Many antigens recognized by autologous T lymphocytes have been identified on human melanoma. Melanoma patients usually mount a spontaneous T cell response against their tumor. But at some point, the responder T cells become ineffective, probably because of a local immunosuppressive process occurring at the tumor sites. Therapeutic vaccination of metastatic melanoma patients with these antigens is followed by tumor regressions only in a small minority of the patients. The T cell responses to the vaccines show correlation with the tumor regressions. The local immunosuppression may be the cause of the lack of vaccination effectiveness that is observed in most patients. In patients who do respond to the vaccine, the antivaccine T cells probably succeed in reversing focally this immunosuppression and trigger a broad activation of other antitumor T cells, which proceed to destroy the tumor.

Adoptive T-Cell Therapy of Cancer

Adoptive therapy involves the transfer of ex vivo expanded immune effector cells to patients as a means of augmenting the antitumor immune response. In general, this transfer is accomplished by harvesting cells from the peripheral blood, tumor sites, or draining lymph nodes and expanding effector cells in a specific or nonspecific fashion for adoptive transfer. This article describes the rationale for adoptive T-cell therapy, the developments that have led to the translational application of this strategy for the treatment of cancer, the challenges that have been addressed, and future approaches to the development of adoptive therapy as a treatment modality.

Cannibalism of live lymphocytes by human metastatic but not primary melanoma cells

The phenomenon of cell cannibalism, which generally refers to the engulfment of cells within other cells, was described in malignant tumors, but its biological significance is still largely unknown. In the present study, we investigated the occurrence, the in vivo relevance, and the underlying mechanisms of cannibalism in human melanoma. As first evidence, we observed that tumor cannibalism was clearly detectable in vivo in metastatic lesions of melanoma and often involved T cells, which could be found in a degraded state within tumor cells. Then, in vitro experiments confirmed that cannibalism of T cells was a property of metastatic melanoma cells but not of primary melanoma cells. In particular, morphologic analyses, including time-lapse cinematography and electron microscopy, revealed a sequence of events, in which metastatic melanoma cells were able to engulf and digest live autologous melanoma-specific CD8(+) T cells. Importantly, this cannibalistic activity significantly increased metastatic melanoma cell survival, particularly under starvation condition, supporting the evidence that tumor cells may use the eating of live lymphocytes as a way to "feed" in condition of low nutrient supply. The mechanism underlying cannibalism involved a complex framework, including lysosomal protease cathepsin B activity, caveolae formation, and ezrin cytoskeleton integrity and function. In conclusion, our study shows that human metastatic melanoma cells may eat live T cells, which are instead programmed to kill them, suggesting a novel mechanism of tumor immune escape. Moreover, our data suggest that cannibalism may represent a sort of "feeding" activity aimed at sustaining survival and progression of malignant tumor cells in an unfavorable microenvironment.

Melanoma-specific tumor-infiltrating lymphocytes but not circulating melanoma-specific T cells may predict survival in resected advanced-stage melanoma patients

PURPOSE

To study the effect of autologous tumor cell vaccinations on the presence and numbers of circulating CD8+ T cells specific for tumor-associated antigens (TAA) in metastatic melanoma patients. To investigate the correlation between the presence of tumor-infiltrating lymphocytes (TIL) and circulating TAA-specific CD8+ T cells before and after autologous tumor cell vaccination with overall survival.

EXPERIMENTAL DESIGN

Twenty-five stage III and resected stage IV metastatic melanoma patients were adjuvantly treated with a series of intracutaneously injected autologous tumor cell vaccinations, of which the first two contained BCG as an immunostimulatory adjuvant. Tumor samples and blood samples obtained before and after vaccination of these patients were studied for the presence of TAA-specific T cells using HLA-tetramers and results were correlated with survival.

RESULTS

In 5 of 17 (29%) melanoma patients, circulating TAA-specific T cells were detectable prior to immunizations. No significant changes in the frequency and specificity were found during the treatment period in all patients. Presence of circulating TAA-specific T cells was not correlated with survival (log rank, P=0.215). Inside melanoma tissue, TAA-specific TIL could be detected in 75% of 16 available tumor samples. In case of detectable TAA-specific TIL, median survival was 22.5 months compared to median survival of 4.5 months in case of absence of TAA-specific T cells (log rank, P=0.0094). In none of the patients, TAA-specific T cells were found both in tumor tissue and blood at the same time.

CONCLUSIONS

These data suggest that the presence of TAA-specific TILs forms a prognostic factor, predicting improved survival in advanced-stage melanoma patients. The absence of TAA-specific T cells in the circulation suggests that homing of the tumor-specific T cell population to the tumor site contributes to the effectiveness of antitumor immunity.

Covalent modification of a melanoma-derived antigenic peptide with a natural quinone methide. Preliminary chemical, molecular modelling and immunological evaluation studies

A LigandFit shape-directed docking methodology was used to identify the best position at which the melanoma-derived MHC class-I HLA-A2-binding antigenic peptide ELAGIGILTV could be modified by attaching a small molecule capable of fitting at the interface of complementary determining regional (CDR) loops of a T-cell receptor (TCR) while triggering T-cell responses. The small molecule selected here for determining the feasibility of this alternative track to chemical alteration of antigenic peptides was the electrophilic quinone methide (+)-puupehenone (), a natural product that belongs to a family of marine metabolites capable of expressing immunomodulatory activities. A preliminary chemical reactivity model study revealed the efficacy of the thiol group of a cysteine (C) side-chain in its nucleophilic addition reaction with in a regio- and diastereoselective manner. The best TCR/HLA-A2 ligand [i.e., ELAGCGILTV-S-puupehenol ()] then identified by the LigandFit docking procedure was synthesized and used to pulse HLA-A2(+) T2 cells for T-cell stimulation. Among the ELAGIGILTV-specific T-cell clones we tested, five of them recognized the conjugate in spite of its low binding affinity for the HLA-A2 molecules. The resulting T-cell stimulation was determined through the intracytoplasmic secretion of IFN-gamma and the percentage of T-cells thus activated. These highly encouraging results indicate that small non-peptidic natural product-derived molecules attached onto the central part of an antigenic peptide can fit at the TCR/HLA-A2 interface with induction of T-cell responses.

A Phase I Trial of Vaccination of CA9-Derived Peptides for HLA-A24-Positive Patients with Cytokine-Refractory Metastatic Renal Cell Carcinoma

PURPOSE

A phase I peptide vaccination trial was done in patients with progressive cytokine-refractory metastatic renal cell carcinoma (RCC) to assess both the toxicity and capability to induce immune responses of three peptides (CA9p219-227, p288-296, and p323-331) derived from CA9, a tumor-associated antigen ubiquitously expressed in RCC.

EXPERIMENTAL DESIGN

Twenty-three patients positive for human leukocyte antigen (HLA)-A24 with histologically confirmed RCC were enrolled. Eligibility included progressive disease after standard cytokine therapy with interleukin-2 and/or IFN-alpha. Patients were vaccinated s.c. with the three peptides emulsified in incomplete Freund's adjuvant at 2-week intervals. Pre- and post-vaccination blood samples were obtained for toxicity assessment and immunologic studies. Patients were monitored for clinical responses on a 3-monthly basis.

RESULTS

Vaccinations were well tolerated without any major adverse event. Most of the patients developed peptide-specific CTLs and/or immunoglobulin G reactive to the peptides after the 6th or 9th vaccination, followed by a gradual increase in both CTL frequency and levels of peptide-reactive serum IgG. Three patients with multiple lung metastases showed partial responses with disappearance and shrinking of metastatic lesions. Additionally, stable disease for >6 months was observed in six patients (median duration, 12.2 months). Moreover, the median survival time of all patients who were progressive at trial enrollment after failing immunotherapy was 21.0 months (5-35 months).

CONCLUSIONS

These results suggest that vaccination of these peptides is safe and recommended for further trials for HLA-A24-positive metastatic RCC patients.

Dendritic cell immunizations alone or combined with low doses of interleukin-2 induce specific immune responses in melanoma patients

Dendritic cell (DC)-based therapy has proved to be effective in patients with a variety of malignancies. However, an optimal immunization protocol using DCs and the best means for delivering antigens has not yet been described. In this study, 20 patients with malignant melanoma in stages III or IV were vaccinated with autologous DCs pulsed with a melanoma cell lysate, alone (n = 13) or in combination with low doses of subcutaneous (s.c.) interleukin (IL)-2 injections (n = 7), to assess toxicity, immunological and clinical responses. Monocyte-derived DCs were morphological, phenotypic and functionally characterized in vitro. Peripheral blood mononuclear cells (PBMC), harvested from patients either prior to and after the treatment, were analysed using enzyme-linked immunosorbent spot (ELISPOT). After vaccination, 50% of the patients tested (seven of 13) from the first group and (three of seven) from the second, showed an increase in interferon (IFN)-gamma production in response to allogeneic melanoma cell lines but not to controls. Four of five tested human leucocyte antigen (HLA)-A2(+) patients with anti-melanoma activity also showed specific T cell responses against peptides derived from melanoma-associated antigens. Delayed type IV hypersensitivity reaction (DTH) against melanoma cell lysate was observed in six of 13 patients from the group treated with DC vaccines only and four of seven from the group treated with the combination of DCs and IL-2. Significant correlations were found between DTH-positive responses against tumour lysate and both disease stability and post-vaccination survival on the stage IV patients. There were no toxicities associated with the vaccines or evidence of autoimmunity including vitiligo. Furthermore, no significant enhancement was observed as a result of combining DC vaccination with IL-2. Our data suggest that autologous DCs pulsed with tumour lysate may provide a standardized and widely applicable source of melanoma specific antigens for clinical use. It is safe and causes no significant side effects and has been demonstrated to be partially efficient at triggering effective anti-melanoma immunity.

Fusion proteins of Hsp70 with tumor-associated antigen acting as a potent tumor vaccine and the C-terminal peptide-binding domain of Hsp70 being essential in inducing antigen-independent anti-tumor response in vivo

Hsp70s are a family of ATP-dependent chaperones of relative molecular mass around 70 kDa. Immunization of mice with Hsp70 isolated from tumor tissues has been proved to elicit specific protective immunity against the original tumor challenge. In this work, we investigated whether Hsp70 can be used as vehicle to elicit immune response to its covalence-accompanying antigen. A recombinant protein expression vector was constructed that permitted the production of recombinant protein fusing tumor-associated antigen (eg, Mela) to the C terminus of Hsp70. We found that the Hsp70-Mela fusion protein can elicit strong cellular immune responses against murine tumor B16, which expresses protein Mela. The Hsp70 peptide-binding domain deletion mutant of the fusion protein was sufficient for inducing Mela-specific cytotoxic T lymphocyte but was not sufficient for engendering potent anti-tumor immunity against B16. We also found that host natural killer (NK) cells were stimulated in vivo by C-terminal domain of Hsp70. We thus presume that Hsp70 fusion proteins suppress tumor growth via at least 2 distinct pathways: one is covalence-accompanying antigen dependent; another is antigen independent. The C-terminal domain of Hsp70 seemed to be the crucial part in eliciting antigen-independent responses, including NK cell stimulation, against tumor challenges. Furthermore, we found that immunization with multiple Hsp70 fusion proteins resulted in a better anti-tumor effect.

Immunogenic HER-2/neu peptides as tumor vaccines

During the last decade, a large number of tumor-associated antigens (TAA) have been identified, which can be recognized by T cells. This has led to renewed interest in the use of active immunization as a modality for the treatment of cancer. HER-2/neu is a 185-KDa receptor-like glycoprotein that is overexpressed by a variety of tumors including breast, ovarian, lung, prostate and colorectal carcinomata. Several immunogenic HER-2/neu peptides recognized by cytotoxic T lymphocytes (CTL) or helper T lymphocytes (TH) have been identified thus far. Patients with HER-2/neu over-expressing cancers exhibit increased frequencies of peripheral blood T cells recognizing immunogenic HER-2/neu peptides. Various protocols for generating T cell-mediated immune responses specific for HER-2/neu peptides have been examined in pre-clinical models or in clinical trials. Vaccination studies in animals utilizing HER-2/neu peptides have been successful in eliminating tumor growth. In humans, however, although immunological responses have been detected against the peptides used for vaccination, no clinical responses have been described. Because HER-2/neu is a self-antigen, functional immune responses against it may be limited through tolerance mechanisms. Therefore, it would be interesting to determine whether abrogation of tolerance to HER-2/neu using appropriate adjuvants and/or peptide analogs may lead to the development of immune responses to HER-2/neu epitopes that can be of relevance to cancer immunotherapy. Vaccine preparations containing mixtures of HER-2/neu peptides and peptide from other tumor-related antigens might also enhance efficacy of therapeutic vaccination.

Cutaneous melanoma: available therapy for metastatic disease

Survival of melanoma varies widely by stage, from a potentially highly curable disease when detected in early stages, to a disease with dismal prognosis when it reaches advanced inoperable stages. Stage IV melanoma defines distant metastasis and continues to comprise an ominous prognosis, with a median survival of 6-9 months. Currently, there is no therapeutic agent known to prolong survival in patients with metastatic melanoma. Therapeutic approaches studied in metastatic melanoma include chemotherapy, biochemotherapy, nonspecific immune adjuvants, cancer-specific vaccines, cytokines, monoclonal antibodies, and specific immunostimulants. Chemotherapy with single-agent dacarbazine is the only United States Food and Drug Administration (US-FDA)-approved chemotherapy agent for metastatic melanoma. Immunological approaches have yielded the only newly US-FDA-approved agent for metastatic disease in 30 years, high-dose bolus IL-2, based on durable responses in some patients with metastatic melanoma, but with associated high toxicity rate and cost. A number of novel therapeutic agents are undergoing active clinical investigation.

Immunity to melanoma antigens: from self-tolerance to immunotherapy

The development of effective immune therapy for cancer is a central goal of immunologists in the 21st century. Our laboratories have been deeply involved in characterization of the immune response to melanoma and translation of laboratory discoveries into clinical trials. We have identified a cohort of peptide antigens presented by Major Histocompatibility Complex (MHC) molecules on melanoma cells and widely recognized by T cells from melanoma patients. These have been incorporated into peptide-based vaccines that induce CD8(+) and CD4(+) T-cell responses in 80-100% of patients. Major objective clinical tumor regressions have been observed in some patients, and overall survival in vaccinated patients exceeds expected stage-specific survival. New clinical trials will determine the value of combination of melanoma helper peptides (MHP) into multipeptide vaccines targeting CD8 cells. New trials will also evaluate new approaches to modulating the host-tumor relationship and will develop new combination therapies. Parallel investigations in murine models are elucidating the immunobiology of the melanoma-host relationship and addressing issues that are not feasible to approach in human trials. Based on the fact that the largest cohort of melanoma antigens are derived from normal proteins concerned with pigment production, we have evaluated the mechanisms of self-tolerance to tyrosinase (Tyr) and have determined how T cells in an environment of self-tolerance are impacted by immunization. Using peptide-pulsed dendritic cells as immunogens, we have also used the mouse model to establish strategies for quantitative and qualitative enhancement of antitumor immunity. This information creates opportunities for a new generation of therapeutic interventions using cancer vaccines.

Identification of the HLA-Cw*0702-restricted tumor-associated antigen recognized by a CTL clone from a lung cancer patient

PURPOSE

A large number of tumor-associated antigens have been used in vaccination trials for mainly melanomas. Our purpose of this study is to identify a novel tumor antigen useful for immunotherapy of lung cancer patients.

EXPERIMENTAL DESIGN

Analysis of an autologous tumor-specific CTL clone F2a that was established from regional lymph node lymphocytes of a patient with lung cancer (A904) by a mixed lymphocyte-tumor cell culture.

RESULTS

F2a recognized and killed autologous tumor cells (A904L), whereas it did not respond to autologous EBV-transformed B cells, phytohemagglutinin-blastoid T cells, and K562 cells. cDNA clone 31.2 was isolated by using cDNA expression cloning method as a gene encoding antigen. This gene was identical to the reported gene whose function was unknown. The antigen encoded by the cDNA was recognized by the CTL in a HLA-Cw*0702-restricted manner. Furthermore, a 9-mer peptide at positions 659 to 685 in cDNA clone 31.2 was identified as a novel epitope peptide. The CTL recognized some allogeneic cancer cell lines with HLA-Cw*0702 as well as some HLA-Cw*0702-negative cell lines when transfected with HLA-Cw*0702, thus indicating that the identified antigen was a cross-reactive antigen.

CONCLUSIONS

Although exact mechanism to process the encoded protein and present the antigen in the context of HLA class I remains to be elucidated, the CTL recognized some of tumor cells in the context of HLA-Cw*0702 but did not recognize a variety of normal cells and also autologous EBV-transformed B cells. These results indicated that the antigen identified in this study may therefore be a possible target of tumor-specific immunotherapy for lung cancer patients.

Induction of Th1-type immunity and tumor protection with a prostate-specific antigen DNA vaccine

Prostate specific antigen (PSA) is a serum marker that is widely used in the detection and monitoring of prostate cancer. Though PSA is a self-antigen, T cell responses to PSA epitopes have been detected in healthy men and prostate cancer patients, suggesting it may be used as a target for active immunotherapy of prostate cancer. A PSA DNA vaccine (pPSA) was evaluated in mice and monkeys for its ability to induce antigen-specific immune responses. Mice immunized intradermally with pPSA demonstrated strong PSA-specific humoral and cellular immunity. The anti-PSA immune responses were skewed toward Th1, as shown by high IFNgamma and IL-2 production. The immune response was sufficient to protect mice from challenge with PSA-expressing tumor cells. Tumor protection was durable in the absence of additional vaccination, as demonstrated by protection of vaccinated mice from tumor rechallenge. Furthermore, pPSA vaccination induced PSA-specific antibody titers in male cynomolgus monkeys, which express a closely related PSA gene. These results demonstrate that vaccination with pPSA may be able to break tolerance and can induce an immune response that mediates tumor protection.

Immunogenicity, including vitiligo, and feasibility of vaccination with autologous GM-CSF-transduced tumor cells in metastatic melanoma patients

PURPOSE

To determine the feasibility, toxicity, and immunologic effects of vaccination with autologous tumor cells retrovirally transduced with the GM-CSF gene, we performed a phase I/II vaccination study in stage IV metastatic melanoma patients.

PATIENTS AND METHODS

Sixty-four patients were randomly assigned to receive three vaccinations of high-dose or low-dose tumor cells at 3-week intervals. Tumor cell vaccine preparation succeeded for 56 patients (88%), but because of progressive disease, the well-tolerated vaccination was completed in only 28 patients. We analyzed the priming of T cells against melanoma antigens, MART-1, tyrosinase, gp100, MAGE-A1, and MAGE-A3 using human leukocyte antigen/peptide tetramers and functional assays.

RESULTS

The high-dose vaccination induced the infiltration of T cells into the tumor tissue. Three of 14 patients receiving the high-dose vaccine showed an increase in MART-1- or gp100-specific T cells in the peripheral blood during vaccination. Six patients experienced disease-free survival for more than 5 years, and two of these patients developed vitiligo at multiple sites after vaccination. MART-1- and gp100-specific T cells were found infiltrating in vitiligo skin. Upon vaccination, the T cells acquired an effector phenotype and produced interferon-gamma on specific antigenic stimulation.

CONCLUSION

We conclude that vaccination with GM-CSF-transduced autologous tumor cells has limited toxicity and can enhance T-cell activation against melanocyte differentiation antigens, which can lead to vitiligo. Whether the induction of autoimmune vitiligo may prolong disease-free survival of metastatic melanoma patients who are surgically rendered as having no evidence of disease before vaccination is worthy of further investigation.

Mechanisms of the self/non-self-survey in the defense against cancer: Potential for chemoprevention?

When compared to a reference population, several large epidemiological studies with long-term follow-up have reported a three- to five-fold increased risk of neoplasia amongst patients who have received organ transplants, with an incidence curve that rises in a linear fashion with time. The relationship between the immune system and cancer is complex. The ability to discriminate "self" from "non-self" is one of the central roles of the immune system. Since tumors arise from transformation of host cells, it is not surprising that some aspects of tumor immunity resemble autoimmunity. The immune response to tumors shares aspects of both self- and non-self-immune recognition. What accounts for the apparent failure of immunity? In this review article, we address the role of the self/non-self-survey in the immune response to tumors, we describe mechanisms of immune surveillance against tumor cells, and we discuss models of ignorance, tolerance and tumor evasion of the immune response. The overall aim of the article is to demonstrate the scope for prevention of cancer in individuals at increased risk of developing malignancy due to immune compromise. Interventional strategies may involve the use of pro-differentiation agents such as retinoids, modifiers of polyamine biosynthesis or inhibitors of cyclooxygenase isozymes.

Melanoma cell necrosis facilitates transfer of specific sets of antigens onto MHC class II molecules of dendritic cells

Vaccine strategies that target dendritic cells (DC) in order to elicit immunity against tumors are the subject of intense research. For the induction and maintenance of anti-tumor immunity, CD4+ helper T cells are often required, which need to see appropriate MHC class II-peptide complexes on DC. So far, it remained widely unclear what type of tumor cells can feed the MHC class II processing pathway of DC with what type of antigens. Here, we report that peptide loading onto MHC class II molecules of myeloid DC is facilitated by melanoma cells undergoing necrotic rather than apoptotic cell death. Importantly, the set of MHC class II-associated peptides induced by necrotic tumor cells differed from those found upon engagement of apoptotic tumor cells. This may be due to the fact that only necrotic cells liberated heat shock proteins, which bind tumor-derived peptides and thereby may promote processing by DC. The potential of DC to activate T cells was kinetically controlled through their antigen receptivity: CD4+ T cells were easily stimulated upon encountering antigen early in DC maturation, whereas antigen capture at later maturation stages favored activation of CD8+ T cells. These findings may aid in designing future vaccination strategies and in identifying novel tumor-specific helper T cell antigens.

Ring finger protein 43 as a new target for cancer immunotherapy

We have performed genome-wide exploration by using cDNA microarray profiling, and successfully identified a new tumor-associated antigen (TAA) that can induce potent cytotoxic T lymphocytes (CTLs) specific to tumor cells. In our preceding study, we identified multiple new genes by using gene expression profiling with a genome-wide cDNA microarray containing 23,040 genes. Among them, we selected RNF43 (ring finger protein 43) as a promising candidate for a TAA expressed by colon cancer cells. In this study, we examined whether the RNF43 protein contains antigenic epitope peptides restricted to HLA-A*0201 or HLA-A*2402. The CTL clones were successfully induced with stimulation by using the peptides binding to HLA-A*0201 (ALWPWLLMA and ALWPWLLMAT) and HLA-A*2402 (NSQPVWLCL), and these CTL clones showed the cytotoxic activity specific to not only the peptide-pulsed targets but also the tumor cells expressing RNF43 and respective HLAs. Lytic activities mediated by two HLA-A2-restricted epitopes were marginal, whereas tumor lysis mediated by the HLA-A24 epitope was clearly better. These findings might be caused by the poor natural presentation of RNF43-11(IX) and RNF43-11(X) by tumors or poor T-cell receptor avidity for these specific epitopes. These results strongly suggest that RNF43 is a new TAA of colon cancer. Furthermore, these results also suggest that our strategy might be a promising one to efficiently discover clinically useful TAAs.

T cell avidity and tumor recognition: implications and therapeutic strategies

In the last two decades, great advances have been made studying the immune response to human tumors. The identification of protein antigens from cancer cells and better techniques for eliciting antigen specific T cell responses in vitro and in vivo have led to improved understanding of tumor recognition by T cells. Yet, much remains to be learned about the intricate details of T cell – tumor cell interactions. Though the strength of interaction between T cell and target is thought to be a key factor influencing the T cell response, investigations of T cell avidity, T cell receptor (TCR) affinity for peptide-MHC complex, and the recognition of peptide on antigen presenting targets or tumor cells reveal complex relationships. Coincident with these investigations, therapeutic strategies have been developed to enhance tumor recognition using antigens with altered peptide structures and T cells modified by the introduction of new antigen binding receptor molecules. The profound effects of these strategies on T cell – tumor interactions and the clinical implications of these effects are of interest to both scientists and clinicians. In recent years, the focus of much of our work has been the avidity and effector characteristics of tumor reactive T cells. Here we review concepts and current results in the field, and the implications of therapeutic strategies using altered antigens and altered effector T cells.