Multiple HLA class II-restricted melanocyte differentiation antigens are recognized by tumor-infiltrating lymphocytes from a patient with melanoma

The ATG8 Family Proteins GABARAP and GABARAPL1 Target Antigen to Dendritic Cells to Prime CD4+ and CD8+ T Cells

Vaccine therapy is a promising method of research to promote T cell immune response and to develop novel antitumor immunotherapy protocols. Accumulating evidence has shown that autophagy is involved in antigen processing and presentation to T cells. In this work, we investigated the potential role of GABARAP and GABARAPL1, two members of the autophagic ATG8 family proteins, as surrogate tumor antigen delivery vectors to prime antitumor T cells. We showed that bone marrow-derived dendritic cells, expressing the antigen OVALBUMIN (OVA) fused with GABARAP or GABARAPL1, were able to prime OVA-specific CD4+ T cells in vitro. Interestingly, the fusion proteins were also degraded by the proteasome pathway and the resulting peptides were presented by the MHC class I system. We then asked if the aforementioned fusion proteins could improve tumor cell immunogenicity and T cell priming. The B16-F10 melanoma was chosen as the tumor cell line to express the fusion proteins. B16-F10 cells that expressed the OVA-ATG8 fused proteins stimulated OVA-specific CD8+ T cells, but demonstrated no CD4+ T cell response. In the future, these constructions may be used in vaccination trials as potential candidates to control tumor growth.

Therapeutic Cancer Vaccines—Antigen Discovery and Adjuvant Delivery Platforms

For decades, vaccines have played a significant role in protecting public and personal health against infectious diseases and proved their great potential in battling cancers as well. This review focused on the current progress of therapeutic subunit vaccines for cancer immunotherapy. Antigens and adjuvants are key components of vaccine formulations. We summarized several classes of tumor antigens and bioinformatic approaches of identification of tumor neoantigens. Pattern recognition receptor (PRR)-targeting adjuvants and their targeted delivery platforms have been extensively discussed. In addition, we emphasized the interplay between multiple adjuvants and their combined delivery for cancer immunotherapy.

Identification of neoantigens for individualized therapeutic cancer vaccines

Somatic mutations in cancer cells can generate tumour-specific neoepitopes, which are recognized by autologous T cells in the host. As neoepitopes are not subject to central immune tolerance and are not expressed in healthy tissues, they are attractive targets for therapeutic cancer vaccines. Because the vast majority of cancer mutations are unique to the individual patient, harnessing the full potential of this rich source of targets requires individualized treatment approaches. Many computational algorithms and machine-learning tools have been developed to identify mutations in sequence data, to prioritize those that are more likely to be recognized by T cells and to design tailored vaccines for every patient. In this Review, we fill the gaps between the understanding of basic mechanisms of T cell recognition of neoantigens and the computational approaches for discovery of somatic mutations and neoantigen prediction for cancer immunotherapy. We present a new classification of neoantigens, distinguishing between guarding, restrained and ignored neoantigens, based on how they confer proficient antitumour immunity in a given clinical context. Such context-based differentiation will contribute to a framework that connects neoantigen biology to the clinical setting and medical peculiarities of cancer, and will enable future neoantigen-based therapies to provide greater clinical benefit.

Proteomic Implications of Tumoral Infiltrating Lymphocytes in Melanoma: PD-L1, CD4 and CD8 - Short Review

Melanoma is a tumor developed by malignancy of melanocytes, being one of the most lethal cancers. Usually, it is associated with exposure to ultraviolet radiations, being most common in the skin, but can also be located extracutaneously as in the digestive tract, leptomeninges or uvea. Histopathologically it presents a phase of radial growth and a vertical one, often accompanied by an intra and peritumoral inflammatory infiltrate. Immunohistochemically, the confirmation of the diagnosis of melanoma should be accompanied by the assessment of proteomic markers of lymphocytic infiltrate such as PD-L1, CD4 and CD8. Those have a role in evaluating the prognosis and a possible prediction of the immunotherapeutic response.

Expression of Potential Targets for Cell-Based Therapies on Melanoma Cells

Tumor antigen-specific redirection of cytotoxic T cells (CTLs) or natural killer (NK) cells including chimeric antigen receptor (CAR-) and T cell receptor (TCR-) cell therapy is currently being evaluated in different tumor entities including melanoma. Expression of melanoma-specific antigen recognized by the respective CAR or TCR directly or presented by HLA molecules is an indispensable prerequisite for this innovative therapy. In this study, we investigated in 168 FFPE tumor specimens of patients with stage I-IV melanoma the protein expression of HER2, TRP2, ABCB5, gp100, p53, and GD2 by immunohistochemistry (IHC). These results were correlated with clinical parameters. Membrane expression of HER2 and GD2 was also investigated in ten melanoma cell lines by flow cytometry for which corresponding tumors were analyzed by IHC. Our results demonstrated that gp100 was the most frequently overexpressed protein (61%), followed by TRP2 (50%), GD2 (38%), p53 (37%), ABCB5 (17%), and HER2 (3%). TRP2 expression was higher in primary tumors compared to metastases (p = 0.005). Accordingly, TRP2 and ABCB5 expression was significantly associated with lower tumor thickness of the primary (p = 0.013 and p = 0.025). There was no association between protein expression levels and survival in advanced melanoma patients. Flow cytometric analysis revealed abundant surface expression of GD2 and HER2 in all melanoma cell lines. The discordant HER2 expression in situ and in vitro suggests a tissue culture associated induction. In summary, our data support the use of gp100 and GD2 as a potential target for developing engineered TCR- or CAR-cell therapies, respectively, against melanoma.

The HLA-DR mediated signalling increases the migration and invasion of melanoma cells, the expression and lipid raft recruitment of adhesion receptors, PD-L1 and signal transduction proteins

The constitutive expression of Major Histocompatibility Complex (MHC) class II molecules is restricted to professional Antigen-Presenting Cells (APCs), nevertheless almost 50% of melanomas express constitutively the MHC class II molecules. Therefore, in two MHC class II constitutive expressing melanoma cell lines we studied the signalling mediated by the HLA-DR molecules in the aim to understand the consequence of class II mediated signalling on metastatic dissemination of melanoma. In particular, we reported that the HLA-DR mediated signalling play a new role in melanoma progression, increasing the migration and invasion of melanoma cells. Furthermore, we showed that the HLA-DR mediated signalling increases the expression and the lipid raft localisation of class II molecules, PD-L1 receptor, Integrin and CAM adhesion receptors, FAK, AKT and STAT3 signalling proteins. We also showed that the HLA-DR mediated signalling increases the activation of FAK, AKT, ERK, PKC and STAT3 signalling proteins and the expression of ILK, PAX, BRAF, ERK and PKC. Indeed, the results showed suggest that the HLA-DR mediated signalling provides a platform useful to frustrate an effective anti-tumour response and to increase melanoma migration and metastatic dissemination of this cancer.

CD4+ T cell-mediated cytotoxicity eliminates primary tumor cells in metastatic melanoma through high MHC class II expression and can be enhanced by inhibitory receptor blockade

Metastatic melanoma is a rapidly progressing disease with high mortality rate and limited treatment options. Immunotherapy based on tumor-targeting cytotoxic T cell responses represents a promising strategy. To assist in its development, we examined the possibility and efficacy of using CD4+ cytotoxic T cells. The regulatory mechanisms controlling CD4+ T cell-mediated cytotoxicity were also investigated. We found that naturally occurring granzyme B and perforin-expressing CD4+ cytotoxic T cells can be recovered from metastatic melanoma patients at significantly elevated frequencies compared to those from healthy controls. These CD4+ cytotoxic T cells were also capable of killing autologous tumor cells harvested from metastatic melanoma, independent of CD8+ T cells or any other cell types. However, several restricting factors were observed. First, the cytolytic activity by CD4+ T cells required high MHC class II expression on melanoma cells, which was not satisfied in a subset of melanomas. Second, the granzyme B and perforin release by activated CD4+ cytotoxic T cells was reduced after coculturing with autologous melanoma cells, characterized by low LAMP-1 expression and low granzyme B and perforin secretion in the supernatant. This suggested that inhibitory mechanisms were present to suppress CD4+ cytotoxic T cells. Indeed, blockade of PD-1 and CTLA-4 had increased the cytolytic activity of CD4+ T cells but was only effective in MHC class II high but not MHC class II low melanomas. Together, our study showed that CD4+ T cell-mediated cytotoxicity could eliminate primary melanoma cells but the efficacy depended on MHC class II expression.

CD8 T Cell-Independent Antitumor Response and Its Potential for Treatment of Malignant Gliomas

Malignant brain tumors continue to represent a devastating diagnosis with no real chance for cure. Despite an increasing list of potential salvage therapies, standard-of-care for these patients has not changed in over a decade. Immunotherapy has been seen as an exciting option, with the potential to offer specific and long lasting tumor clearance. The “gold standard” in immunotherapy has been the development of a tumor-specific CD8 T cell response to potentiate tumor clearance and immunological memory. While many advances have been made in the field of immunotherapy, few therapies have seen true success. Many of the same principles used to develop immunotherapy in tumors of the peripheral organs have been applied to brain tumor immunotherapy. The immune-specialized nature of the brain should call into question whether this approach is appropriate. Recent results from our own experiments require a rethinking of current dogma. Perhaps a CD8 T cell response is not sufficient for an organ as immunologically unique as the brain. Examination of previously elucidated principles of the brain’s immune-specialized status and known immunological preferences should generate discussion and experimentation to address the failure of current therapies.

Predictors of tumor-infiltrating lymphocyte efficacy in melanoma

In the past decades, the increasing knowledge in cellular immunology and tumor-host immune interactions, led to the development of immunotherapy approaches. Immunotherapy, based on adoptive cell transfer of ex vivo activated and expanded tumor-infiltrating T lymphocytes (TILs), has shown promising clinical results in patients with metastatic melanoma. TIL therapy yields response rates of around 50% and significant survival benefit in refractory melanoma patients, even after failing other immunotherapies, such as checkpoint inhibitors or cytokine-based therapy. Identifying predictors of TIL efficacy and detection of TIL subsets with specific reactivity against the patient's tumor might be an important milestone toward further improvement of clinical responses and prolonged survival.

The Tumor Antigen NY-ESO-1 Mediates Direct Recognition of Melanoma Cells by CD4+ T Cells after Intercellular Antigen Transfer

NY-ESO-1-specific CD4(+) T cells are of interest for immune therapy against tumors, because it has been shown that their transfer into a patient with melanoma resulted in tumor regression. Therefore, we investigated how NY-ESO-1 is processed onto MHC class II molecules for direct CD4(+) T cell recognition of melanoma cells. We could rule out proteasome and autophagy-dependent endogenous Ag processing for MHC class II presentation. In contrast, intercellular Ag transfer, followed by classical MHC class II Ag processing via endocytosis, sensitized neighboring melanoma cells for CD4(+) T cell recognition. However, macroautophagy targeting of NY-ESO-1 enhanced MHC class II presentation. Therefore, both elevated NY-ESO-1 release and macroautophagy targeting could improve melanoma cell recognition by CD4(+) T cells and should be explored during immunotherapy of melanoma.

Tumor-infiltrating lymphocytes for the treatment of metastatic cancer

Over the past few years melanoma incidence has been rising steadily, resulting in an increase in melanoma related mortality. Until recently, therapeutic options for metastatic melanoma were scarce. Chemotherapy and, in some countries, IL-2 were the only registered treatment modalities. In the last five years, treatment with immunotherapy (anti CTLA-4, anti PD-1, or the combination of these antibodies) has shown very promising results and was able to improve survival in patients with metastatic melanoma. Adoptive cell therapy using tumor-infiltrating lymphocytes is yet another, but highly promising, immunotherapeutic strategy for patients with metastatic melanoma. This review will discuss the development of TIL as a treatment option for melanoma, its mode of action and simplification over time, and the possibilities to expand this therapy to other types of cancer. Also, the future directions of TIL based therapies will be highlighted.

Aberrant Expression of MHC Class II in Melanoma Attracts Inflammatory Tumor-Specific CD4+ T- Cells, Which Dampen CD8+ T-cell Antitumor Reactivity

In the absence of a local inflammatory response, expression of MHC class II molecules is restricted mainly to hematopoietic cells and thymus epithelium. However, certain tumors, such as melanoma, may acquire aberrant constitutive expression of MHC class II. In a set of primary melanoma cell populations and correspondingly expanded autologous tumor-infiltrating lymphocytes (TIL), we show how MHC class II expression on melanoma cells associates with strong MHC class II-restricted CD4(+) T-cell responses that are specific for tumors. Notably, we found that tumor-specific CD4(+) T-cell responses were dominated by TNF production. TNF reduced CD8(+) T-cell activation in IFNγ-rich environments resembling a tumor site. Conversely, direct CD4(+) T-cell responses had no influence on either the proliferation or viability of melanoma cells. Taken together, our results illustrate a novel immune escape mechanism that can be activated by aberrant expression of MHC class II molecules, which by attracting tumor-specific CD4(+) T cells elicit a local inflammatory response dominated by TNF that, in turn, inhibits cytotoxic CD8(+) T-cell responses

An exhaustion-like phenotype constrains the activity of CD4+ T cells specific for a self and melanoma antigen

While the immune system has the capacity to recognize and destroy melanoma, tolerance mechanisms often hinder the development of effective anti-tumor immune responses. Since many melanoma antigens are self proteins expressed in normal melanocytes, self antigen exposure before tumor development can negatively impact the function of T cells specific for these self/tumor antigens. However, the contribution of self tolerance to anti-melanoma T cell dysfunction remains largely unexplored. We have previously described a TCR transgenic (Tg) mouse model in which T cells specific for the self/melanoma antigen, tyrosinase-related protein 1 (TRP1), develop in the presence of endogenous TRP1 expression (Ag+) and diminished antigen presentation due to the absence of gamma-interferon-inducible lysosomal thiol reductase (GILT-/-). We show that TRP1-specific T cells from these Ag+GILT-/-Tg mice do not protect from melanoma tumor growth, fail to induce autoimmune vitiligo, and undergo diminished proliferation compared to T cells from Ag-GILT+/+Tg mice. Despite an increased frequency of TRP1-specific Treg cells in Ag+GILT-/-Tg mice compared to Ag-GILT+/+Tg animals, Treg cell depletion only partially rescues the proliferative capacity of T cells from TRP1-expressing mice, suggesting the involvement of additional suppressive mechanisms. An increased percentage of melanoma-specific T cells from Ag+GILT-/-Tg animals express PD-1, an inhibitory receptor associated with the maintenance of T cell exhaustion. Antibody blockade of PD-1 partially improves the ability of TRP1-specific T cells from Ag+GILT-/-Tg mice to produce IL-2. These findings demonstrate that melanoma-specific T cells exposed to a self/melanoma antigen in healthy tissue develop an exhaustion-like phenotype characterized by PD-1-mediated immunosuppression prior to encounter with tumor.

GILT: Shaping the MHC Class II-Restricted Peptidome and CD4(+) T Cell-Mediated Immunity

The MHC class II-restricted antigen processing pathway generates peptide:MHC complexes in the endocytic pathway for the activation of CD4(+) T cells. Gamma-interferon-inducible lysosomal thiol reductase (GILT) reduces protein disulfide bonds in the endocytic compartment, thereby exposing buried epitopes for MHC class II binding and presentation. T cell hybridoma responses and elution of MHC class II bound peptides have identified GILT-dependent epitopes, GILT-independent epitopes, and epitopes that are more efficiently presented in the absence of GILT termed GILT-prevented epitopes. GILT-mediated alteration in the MHC class II-restricted peptidome modulates T cell development in the thymus and peripheral tolerance and influences the pathogenesis of autoimmunity. Recent studies suggest an emerging role for GILT in the response to pathogens and cancer survival.

Tumor-specific CD4+ melanoma tumor-infiltrating lymphocytes

Adoptive cell therapy using tumor-infiltrating lymphocytes (TIL) can mediate objective and durable tumor regressions in patients with metastatic melanoma. CD8+ tumor-reactive TIL are well studied in humans and animals, yet the function of tumor-infiltrating CD4+ T lymphocytes in patient treatments remains controversial. We recently demonstrated that CD4+ TILs are not necessary for objective responses in patients. Coinfusion with tumor-specific CD4 TIL may enhance or increase the durability of tumor regressions, but the number of patients with tumor-reactive CD4 TIL is unknown. We screened 44 CD8+-depleted TIL for in vitro reactivity against autologous tumor. Nine (20%) showed specific reactivity by interferon-γ release assay, of which 8 were specifically blocked by an anti-HLA-DR antibody. Flow-cytometric analysis of these reactive TIL confirmed a high CD4+ composition (median 89%). Highlighting the contribution of CD4+ TIL to tumor regression, a patient with widespread metastatic disease was administered TIL containing HLA class II-restricted tumor activity with high-dose interleukin-2 therapy after lymphodepletion that mediated regression of extensive metastatic disease in the liver and spleen. These results demonstrate that at least 20% of metastatic melanomas contain CD4+ lymphocytes with specific tumor recognition and suggest a possible role for CD4+ cells in the effectiveness of adoptive cell therapy.

Expression and functions of galectin-7 in human and murine melanomas

The identification of galectin-7 as a p53-induced gene and its ability to induce apoptosis in many cell types support the hypothesis that galectin-7 has strong antitumor activity. This has been well documented in colon cancer. However, in some cases, such as breast cancer and lymphoma, its high expression level correlates with aggressive subtypes of cancer, suggesting that galectin-7 may have a dual role in cancer progression. In fact, in breast cancer, overexpression of galectin-7 alone is sufficient to promote metastasis to the bone and lung. In the present work, we investigated the expression and function of galectin-7 in melanoma. An analysis of datasets obtained from whole-genome profiling of human melanoma tissues revealed that galectin-7 mRNA was detected in more than 90% of biopsies of patients with nevi while its expression was more rarely found in biopsies collected from patients with malignant melanoma. This frequency, however, was likely due to the presence of normal epidermis tissues in biopsies, as shown our studies at the protein level by immunohistochemical analysis. Using the experimental melanoma B16F1 cell line, we found that melanoma cells can express galectin-7 at the primary tumor site and in lung metastasis. Moreover, we found that overexpression of galectin-7 increased the resistance of melanoma cells to apoptosis while inducing de novo egr-1 expression. Overexpression of galectin-7, however, was insufficient to modulate the growth of tumors induced by the subcutaneous injection of B16F1 cells. It also failed to modulate the dissemination of B16F1 cells to the lung.

MELOE-1 antigen contains multiple HLA class II T cell epitopes recognized by Th1 CD4+ T cells from melanoma patients

MELOE-1 is an overexpressed melanoma antigen containing a HLA-A2 restricted epitope, involved in melanoma immunosurveillance of patients adoptively transferred with tumour infiltrating lymphocytes (TIL). The use of the full-length antigen (46 aa) for anti-melanoma vaccination could be considered, subject to the presence of Th epitopes all along MELOE-1 sequence. Thus, in this study we evaluated in vitro the immunoprevalence of the different regions of MELOE-1 (i.e. their ability to induce CD4 T cell responses in vitro from PBMC). Stimulation of PBMC from healthy subjects with MELOE-1 induced the amplification of CD4 T cells specific for various regions of the protein in multiple HLA contexts, for each tested donor. We confirmed these results in a panel of melanoma patients, and documented that MELOE-1 specific CD4 T cells, were mainly Th1 cells, presumably favourable to the amplification of CD8 specific T cells. Using autologous DC, we further showed that these class II epitopes could be naturally processed from MELOE-1 whole protein and identified minimal epitopes derived from each region of MELOE-1, and presented in four distinct HLA contexts. In conclusion, vaccination with MELOE-1 whole polypeptide should induce specific Th1 CD4 responses in a majority of melanoma patients, stimulating the amplification of CD8 effector cells, reactive against melanoma cells.

Effector CD4 and CD8 T cells and their role in the tumor microenvironment

T cells in tumors—the so-called tumor infiltrating lymphocytes (TIL) have been studied intensively over the past years. Compelling evidence point to a clinical relevance for high numbers of T cells at the tumor site with CD8 memory T cells as a key denominator for overall survival (OS) in patients with colo-rectal cancer (CRC), and also for others solid cancers. These data goes hand in hand with studies of clonality of TIL showing the T cells among TIL are expanded clonally, and also that tumor specific T cells of CD4 as well as CD8 type are enriched at the tumor site. The tumor microenvironment is hostile to T cell function e.g., due to expression of enzymes that depletes the amino acids tryptophan and arginine, high concentration of tumor secreted lactate, and presence innate cells or regulatory T cells both with suppressive activity. Analyses of the specificity of TILs in melanoma demonstrate that quite few known antigens are in fact recognized by these cultures underscoring patient unique and/or mutated antigens may represent important target for recognition.

Methods to improve adoptive T-cell therapy for melanoma: IFN-γ enhances anticancer responses of cell products for infusion

Further development of adoptive T-cell therapy (ACT) with autologous tumor-infiltrating lymphocytes (TILs) has the potential to markedly change the long-term prognosis of patients with metastatic melanoma, and modifications of the original protocol that can improve its clinical efficacy are highly desirable. In this study, we demonstrated that a high in vitro tumor reactivity of infusion products was associated with clinical responses upon adoptive transfer. In addition, we systematically characterized the responses of a series of TIL products to relevant autologous short term-cultured melanoma cell lines from 12 patients. We provide evidence that antitumor reactivity of both CD8(+) and CD4(+) T cells could be enhanced in most TIL products by autologous melanoma sensitization by pretreatment with low-dose IFN-γ. IFN-γ selectively enhanced responses to tumor-associated antigens other than melanoma differentiation antigens. In addition, IFN-γ treatment was invariably associated with restored/increased cancer immunogenicity as demonstrated by upregulation of major histocompatibility complex molecules. These findings suggest a potential synergism between IFN-γ and ACT, and have important implications for clinical development of combination strategies for the treatment of metastatic melanoma.

Variation of tumor-infiltrating lymphocytes in human cancers: controversy on clinical significance

Tumors develop and progress under the influence of a microenvironment comprising a variety of immune cell subsets and their products. Recent studies have shown that tumor-infiltrating lymphocytes (TILs) are not randomly distributed, but organized to accumulate more or less densely in different regions within tumors, and interact with each other. Substantial evidence has suggested that not only CD8(+) and/or CD4(+) αβ T cells but also other lymphocyte subsets, including γδ T cells, B cells, NK cells, and NKT cells, infiltrate tumor tissues in variable quantities and play a key role in the regulation of antitumor immunity. In this article, we summarize available information regarding the diversity and composition of TILs, which may positively or negatively affect tumor growth and patient clinical outcomes. The clinical significance of TILs in human cancers remains unclear and is a subject of considerable controversy; largely due to the lack of functional data for TILs, as well as due to enormous variability of TILs in different tumors. A great deal more functional data about TILs needs to be obtained for individual tumors before TILs can be considered as a prognostic parameter in human cancers.

GILT modulates CD4+ T-cell tolerance to the melanocyte differentiation antigen tyrosinase-related protein 1

Gamma-IFN-inducible lysosomal thiol reductase (GILT) facilitates major histocompatibility complex class II-restricted processing through endocytic reduction of protein disulfide bonds and is necessary for efficient class II-restricted processing of melanocyte differentiation antigen, tyrosinase-related protein 1 (TRP1). Using class II-restricted, TRP1-specific T-cell receptor transgenic mice, we identify a role, to our knowledge, previously unreported, for GILT in the maintenance of tolerance to TRP1. TRP1-specific thymocytes are centrally deleted in the presence of GILT and TRP1. In contrast, CD4 single-positive thymocytes and peripheral T cells develop in the absence of GILT or TRP1, demonstrating that GILT is required for negative selection of TRP1-specific thymocytes. Although TRP1-specific T cells escape thymic deletion in the absence of GILT, they are tolerant to TRP1 and do not induce vilitigo. TRP1-specific T cells that develop in the absence of GILT have diminished IL-2 and IFN-γ production. Furthermore, GILT-deficient mice have a 4-fold increase in the percentage of TRP1-specific regulatory T (Treg) cells compared with TRP1-deficient mice, and depletion of Treg cells partially restores the ability of GILT-deficient TRP1-specific CD4(+) T cells to induce vitiligo. Thus, GILT has a critical role in regulating CD4(+) T-cell tolerance to an endogenous skin-restricted antigen relevant to controlling autoimmunity and generating effective immunotherapy for melanoma.

Optimal epitope composition after antigen screening using a live bacterial delivery vector: application to TRP-2

Immunotherapeutic approaches, based on the generation of tumor-specific cytotoxic T-lymphocytes (CTL), are currently emerging as promising strategies of anti-tumor therapy. The potential use of attenuated bacteria as engineered vectors for vaccine development offers several advantages, including the stimulation of innate immunity. We developed an attenuated live bacterial vector using the type III secretion system (TTSS) of Pseudomonas aeruginosa to deliver in vivo tumor antigens. Using an inducible and rapid expression plasmid, vaccination with several antigens of different length and epitope composition, including TRp-2, gp100 and MUC18, was evaluated against glioma tumor cells. We observed similar CTL immunity and T-cell receptor (TCR) repertoire diversity with the vaccines, TRP2(125-243), TRP2L(125-376) and TRP2S(291-376). However, only immunization with TRP2L(125-376) induced significant anti-tumor immunity. Taken together, our data indicate the importance of the epitopes composition and/or peptide length of these peptides for inducing cytotoxic T-lymphocyte (CTL) mediated immunity. Characteristics that consistently improved anti-tumor immunity include: long peptides with immunodominant and cryptic CD8(+) epitopes, and strong CD4(+) Th epitopes. Our bacterial vector is versatile, easy-to-use and quick to produce. This vector is suitable for rapid screening and evaluation of antigens of varying length and epitope composition.

Disulfide reduction in the endocytic pathway: immunological functions of gamma-interferon-inducible lysosomal thiol reductase

Gamma-interferon-inducible lysosomal thiol reductase (GILT) is constitutively expressed in most antigen presenting cells and is interferon γ inducible in other cell types via signal transducer and activator of transcription 1. Normally, N- and C-terminal propeptides are cleaved in the early endosome, and the mature protein resides in late endosomes and lysosomes. Correspondingly, GILT has maximal reductase activity at an acidic pH. Monocyte differentiation via Toll-like receptor 4 triggers secretion of a disulfide-linked dimer of the enzymatically active precursor, which may contribute to inflammation. GILT facilitates major histocompatibility complex (MHC) class II-restricted processing through reduction of protein disulfide bonds in the endocytic pathway and is hypothesized to expose buried epitopes for MHC class II binding. GILT can also facilitate the transfer of disulfide-containing antigens into the cytosol, enhancing their cross-presentation by MHC class I. A variety of antigens are strongly influenced by GILT-mediated reduction, including hen egg lysozyme, melanocyte differentiation antigens, and viral envelope glycoproteins. In addition, GILT is conserved among lower eukaryotes and likely has additional functions. For example, GILT expression increases the stability of superoxide dismutase 2 and decreases reactive oxygen species, which correlates with decreased cellular proliferation. It is also a critical host factor for infection with Listeria monocytogenes.

GILT accelerates autoimmunity to the melanoma antigen tyrosinase-related protein 1

Melanocyte differentiation Ags, including tyrosinase-related protein (TRP) 1, are relevant to both autoimmune skin depigmentation (vitiligo) and tumor immunity, because they are expressed by both benign melanocytes and many malignant melanomas. Melanoma patients generate CD4(+) T cells that specifically recognize these proteins. TRP1 contains internal disulfide bonds and is presented by MHC class II molecules. Gamma-IFN-inducible lysosomal thiol reductase (GILT) facilitates the generation of class II-binding peptides by the endocytic reduction of protein disulfide bonds. We show in this study that GILT is required for efficient MHC class II-restricted processing of a TRP1 epitope in vitro and accelerates the onset of vitiligo in TRP1-specific TCR transgenic mice. The presence of GILT confers a small increase in the percentage of autoreactive T cells with an effector memory phenotype that may contribute to earlier disease onset. The onset of vitiligo is associated with a greater increase in the percentage of autoreactive T cells with an effector memory phenotype. Given that many self and tumor Ags have disulfide bonds and are presented on MHC class II, GILT is likely to be important in the pathogenesis of other CD4(+) T cell-mediated autoimmune diseases and for the development of effective cancer immunotherapy.

HLA Class II Antigen Presentation in Prostate Cancer Cells: A Novel Approach to Prostate Tumor Immunotherapy

Prostate cancer is a deadly disease that is in drastic need of new treatment strategies for late stage and metastatic prostate cancer. Immunotherapy has emerged as a viable option to fill this void. Clinical trials have been conducted that induce tumor clearance through cytotoxic T lymphocyte (CTL) activation, these studies have had mixed outcomes with the overlying problem being the lack of a complete immune response with sustained killing and the formation of tumor specific memory cells. To overcome this, we have outlined the need for activating the HLA class II pathway in inducing a sustained CD8+ T cell response and the development of effective memory. We have also discussed the ability of prostate cancer cells to express stable HLA class II molecules that can be manipulated for tumor antigen (Ag) processing and presentation. This review also sets to outline new directions that exist for the use of class II-restricted Ags/peptides in devising cancer vaccines as well as combined chemoimmunotherapy. A better understanding of these concepts will improve future cancer vaccine studies and further the field of cancer immunobiology.

Autologous MUC1-specific Th1 effector cell immunotherapy induces differential levels of systemic TReg cell subpopulations that result in increased ovarian cancer patient survival

Adoptive T cell immunotherapy using autologous lymphocytes is a viable treatment for patients with cancer and requires participation of Ag-specific CD4 and CD8 T cells. Here, we assessed the immunotherapeutic effects of autologous MUC1 peptide-stimulated CD4(+) effector cells following adoptive transfer in patients with ovarian cancer. Using MUC1 peptide and IL-2 for ex vivo CD4(+)/Th1 effector cell generation, we show that three monthly treatment cycles of peripheral blood T cell restimulation and intraperitoneal re-infusion selectively modulated endogenous T cell-mediated immune responses that correlated with diminished serum CA125 tumor marker levels and enhanced patient survival. One patient remains disease-free, another patient survived long-term for nearly 16 months with recurrent disease and two patients expired within 3-5 months following final infusion. Although PBL from all patients showed elevated MUC1 cytolytic activity following therapy, such responses did not correlate with therapeutic efficacy. Long-term survivors showed elevated levels of systemic memory (CD45RO) and naïve (CD45RA) CD3/CD4/CD25(+) T cells when compared to that of pre-treatment levels and similarly treated short-term survivors. Such cells co-expressed different levels of Foxp3 and CTLA-4 that resulted in progressively lower systemic Foxp3/CTLA-4 memory T cell ratios that further correlated with disease-free survival. Lastly, these patients showed elevated levels of MUC1-specific T cells expressing the CCR5 and CCR1 chemokine receptors and the chemokine CCL4 associated with Th1 cell differentiation/memory. We suggest that effective immunotherapy with autologous MUC1-stimulated CD4(+) effector cells induces differential levels of systemic "Ag-experienced" and "Ag-inexperienced" CD4/CD25(+) TReg cell subpopulations that influence long-term tumor immunity in ovarian cancer patients.

HLA and melanoma: multiple alterations in HLA class I and II expression in human melanoma cell lines from ESTDAB cell bank

Altered HLA class I and class II cell surface expression has been reported in many types of malignancy and represents one of the major mechanism by which tumour cells escape from T lymphocytes. In this report, we review the results obtained from the study of constitutive and IFN-gamma-induced expression of HLA class I and II molecules in 91 human melanoma cell lines from the European Searchable Tumour Cell Line Database, and compare them with published data on HLA expression in other types of cancer. Various types of alterations in HLA class I cell surface expression were found in a high percentage (67%) of the studied cell lines. These alterations range from total to selective HLA class I loss and are associated with beta2-microglobulin gene mutations, transcriptional downregulation of HLA class I genes and antigen processing machinery components, or with the loss of heterozygosity in chromosome 6. The most frequently observed phenotype is selective downregulation of HLA-B locus, reversible after treatment with IFN-gamma. The expression of constitutive- or IFN-gamma induced-surface expression of at least one HLA class II locus is positive in 71.5% of the analysed cell lines. Four different HLA class II expression phenotypes were defined, and a positive correlation between the expression of class I and II molecules is discussed. More detailed information on the HLA expression patterns and others immunological characteristics of these melanoma cell lines can be found on the following website http://www.ebi.ac.uk/ipd/estdab .

Focus on TILs: prognostic significance of tumor infiltrating lymphocytes in human melanoma

Tumors contain variable numbers of lymphocytes, referred to as tumor infiltrating lymphocytes (TILs). In melanoma, the intensity of this lymphocytic infiltrate is believed to correlate with outcome, though there is some debate about the applicability of this finding for all melanomas. Much research has gone into classifying TILs with respect to antigen receptor structure and the antigen to which melanoma-specific T cells react. However, these studies for the most part did not immunophenotype TILs, and recent data has revealed that the composition of tumoral lymphocytes is not homogenous, but rather represents varying contributions from many lymphocytic subsets. Furthermore, the function of TILs is often compromised as a result of the accumulation of immunoregulatory cells and various tumor escape mechanisms. These recent insights stress the need to collect more data on the composition and function of TIL infiltrates before definitive conclusions about the prognostic significance of TILs can be drawn. Advances in immunology have also facilitated the development of immunotherapeutic strategies, examples of which will be discussed with a special emphasis on blocking antibodies against CTLA-4, which are prototypical immunotherapeutic agents. This flurry of novel "biological" therapies will undoubtedly complicate our already incomplete understanding of TIL immunobiology as each of these agents has the potential to uniquely distort the series of immunological events which normally occur in untreated melanoma. Therefore, considerable research is needed to better elucidate the function and prognostic significance of TILs in both untreated melanoma and tumors treated with "biological" therapy.

MHC class II presentation of gp100 epitopes in melanoma cells requires the function of conventional endosomes and is influenced by melanosomes

Many human solid tumors express MHC class II (MHC-II) molecules, and proteins normally localized to melanosomes give rise to MHC-II-restricted epitopes in melanoma. However, the pathways by which this response occurs have not been defined. We analyzed the processing of one such epitope, gp100(44-59), derived from gp100/Pmel17. In melanomas that have down-regulated components of the melanosomal pathway, but constitutively express HLA-DR*0401, the majority of gp100 is sorted to LAMP-1(high)/MHC-II(+) late endosomes. Using mutant gp100 molecules with altered intracellular trafficking, we demonstrate that endosomal localization is necessary for gp100(44-59) presentation. By depletion of the AP-2 adaptor protein using small interfering RNA, we demonstrate that gp100 protein internalized from the plasma membrane to such endosomes is a major source for gp100(44-59) epitope production. The gp100 trapped in early endosomes gives rise to epitopes that are indistinguishable from those produced in late endosomes but their production is less sensitive to inhibition of lysosomal proteases. In melanomas containing melanosomes, gp100 is underrepresented in late endosomes, and accumulates in stage II melanosomes devoid of MHC-II molecules. The gp100(44-59) presentation is dramatically reduced, and processing occurs entirely in early endosomes or stage I melanosomes. This occurrence suggests that melanosomes are inefficient Ag-processing compartments. Thus, melanoma de-differentiation may be accompanied by increased presentation of MHC-II restricted epitopes from gp100 and other melanosome-localized proteins, leading to enhanced immune recognition.

Unique tumor antigens: evidence for immune control of genome integrity and immunogenic targets for T cell-mediated patient-specific immunotherapy

The molecular identification and characterization of antigenic epitopes recognized by T cells on human cancers has rapidly evolved since the cloning in 1991 of MAGEA1, the first gene reported to encode a CTL-defined human tumor antigen. In the expanding field of human tumor immunology, unique tumor antigens constitute a growing class of T cell-defined epitopes that exhibit strong immunogenicity. Some of these antigens, which often derive from mutation of genes that have relevant biological functions, are less susceptible to immunoselection and may be retained even in advanced tumors. Immunogenicity and constitutive expression of the unique tumor antigens provide a strong rationale for the design of novel, patient-tailored therapies that target such determinants. Here we discuss the immunologic relevance of unique tumor antigens in the light of the prospects for exploiting such epitopes as targets for patient-specific immune intervention strategies.

Ii-Key/MHC class II epitope hybrids: a strategy that enhances MHC class II epitope loading to create more potent peptide vaccines

Life-threatening diseases, such as cancer and pandemic influenza, demand new efforts towards effective vaccine design. Peptides represent a simple, safe and adaptable basis for vaccine development; however, the potency of peptide vaccines is insufficient in most cases for significant therapeutic efficacy. Several methods, such as Ligand Epitope Antigen Presentation System and ISCOMATRIX, have been developed to enhance the potency of peptide vaccines. One way of increasing the loading of MHC class II peptides occurs through the use of Ii-Key technology. Ii-Key (LRMK), a portion of the MHC class II-associated invariant chain (Ii), facilitates the direct loading of epitopes to the MHC class II molecule groove. Linking the Ii-Key moiety via a simple polymethylene bridge to an MHC class II epitope, to generate an Ii-Key/MHC class II epitope hybrid, greatly enhances the vaccine potency of the tethered epitope. The combination of such Ii-Key/MHC class II epitope hybrids with MHC class I epitope-containing peptides might generate a potent peptide vaccine for malignancies and infectious diseases. The Ii-Key hybrid technology is compared with other methods that enhance the potency of a peptide vaccine.

Prolongation of the survival of breast cancer-bearing mice immunized with GM-CSF-secreting syngeneic/allogeneic fibroblasts transfected with a cDNA expression library from breast cancer cells

Breast cancer cells, like other types of neoplastic cells, form weakly immunogenic tumor-associated antigens. The antigenic properties of the tumor-associated antigens can be enhanced if they are expressed by highly immunogenic cells. In this study, a cancer vaccine was prepared by transfer of a cDNA expression library from SB5b breast carcinoma into mouse fibroblast cells of C3H/He mouse origin (H-2(k)), that had been previously modified to secrete GM-CSF and to express allogeneic class I-determinants (H-2(b)). The transfected syngeneic/allogeneic fibroblasts secreting GM-CSF were used as a vaccine in C3H/He mice. Robust cell-mediated immunity toward the breast cancer cells was generated in mice immunized with the cDNA-based vaccine. The immunity, mediated predominantly by CD8(+) T lymphocytes, was directed toward the breast cancer cells, but not against either of two other non-cross-reactive neoplasms of C3H/He mice. The immunity was sufficient to prolong the survival of mice with established breast cancer. Among other advantages, preparation of the vaccine by cDNA-transfer into a fibroblast cell line enabled the recipient cells to be modified in advance of DNA-transfer to augment their immunogenic properties. As the transferred DNA is replicated as the transfected cells divide, the vaccine could be prepared from microgram quantities of tumor tissue.

Enhanced immunity to breast cancer in mice immunized with fibroblasts transfected with a complementary DNA expression library from breast cancer cells: Enrichment of the vaccine for immunotherapeutic cells

Breast cancer cells express an array of weakly immunogenic tumor-associated antigens (TAAs). Under appropriate circumstances, immunity to breast cancer can be induced, with potential benefits for patients with the disease. Here, we report a new cell-based vaccination strategy resulting in enhanced immunity to breast cancer in tumor-bearing mice. The strategy was designed to enrich the vaccine for highly immunogenic cells. The vaccine was prepared by transfer of unfractionated complementary DNA (cDNA) derived from a highly malignant breast neoplasm that arose spontaneously in a C3H/He mouse (SB5b) into an immunogenic fibroblast cell line. As the transferred cDNA spontaneously integrates into the genome of the recipient cells and is replicated as the cells divide, sufficient DNA to prepare the vaccine could be obtained from as few as 10(7) cells (4-mm tumor). Because only a small proportion of the transfected cell population was expected to have incorporated genes responsible for inducing immunity to the breast cancer, we devised a novel approach designed to enrich the transfected cell population for cells that induced immunity to the neoplasm. Aliquots of the transfected population were divided into small pools (initial inoculum = 4 x 10). Afterward, the cell number from each pool was allowed to expand in vitro. Pools containing greater numbers of immunogenic cells (identified by 2 independent assays) were subdivided for additional rounds of immune selection. Enhanced immunity to the neoplasm was detected in tumor-bearing mice treated solely by immunization with the enriched cell population. The immunity, mediated by CD8+ T cells, was sufficient to prolong the survival of mice with established breast cancer.

Generation of tumour-specific cytotoxic T-cell clones from histocompatibility leucocyte antigen-identical siblings of patients with melanoma

Lymphodepletion and infusion of autologous expanded tumour-infiltrating lymphocytes is effective therapy for patients with malignant melanoma. Antitumour responses are likely to be mediated by HLA class I- and II-restricted immune responses directed at tumour antigens. We assessed whether the peripheral blood of normal HLA-matched siblings of patients with melanoma could be used to generate lymphocytes with antimelanoma activity for adoptive immunotherapy after allogeneic blood or marrow transplantation. Melanoma cell lines were derived from two donors and were used to stimulate the mononuclear cells of three HLA-identical siblings. CD4(+) clones dominated cultures. Of these, approximately half were directly cytotoxic towards recipient melanoma cells and secreted interferon-gamma in response to tumour stimulation. More than half of the noncytotoxic clones also secreted interferon-gamma after melanoma stimulation. No CD4(+) clones responded to stimulation with recipient haemopoietic cells. The majority of CD8(+) clones directly lysed recipient melanoma, but did not persist in long-term culture in vitro. No crossreactivity with recipient haemopoietic cells was observed. The antigenic target of one CD4(+) clone was determined to be an HLA-DR11-restricted MAGE-3 epitope. Antigenic targets of the remaining clones were not elucidated, but appeared to be restricted through a non-HLA-DR class II molecule. We conclude that the blood of allogeneic HLA-matched sibling donors contains melanoma-reactive lymphocyte precursors directed at tumour-associated antigens. Adoptive immunotherapy with unselected or ex vivo-stimulated donor lymphocytes after allogeneic stem cell transplantation has a rational basis for the treatment of malignant melanoma.

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.

Striking Immunodominance Hierarchy of Naturally Occurring CD8+ and CD4+ T Cell Responses to Tumor Antigen NY-ESO-1

Immunodominance has been well-demonstrated in many antiviral and antibacterial systems, but much less so in the setting of immune responses against cancer. Tumor Ag-specific CD8+ T cells keep cancer cells in check via immunosurveillance and shape tumor development through immunoediting. Because most tumor Ags are self Ags, the breadth and depth of antitumor immune responses have not been well-appreciated. To design and develop antitumor vaccines, it is important to understand the immunodominance hierarchy and its underlying mechanisms, and to identify the most immunodominant tumor Ag-specific T cells. We have comprehensively analyzed spontaneous cellular immune responses of one individual and show that multiple tumor Ags are targeted by the patient's immune system, especially the "cancer-testis" tumor Ag NY-ESO-1. The pattern of anti-NY-ESO-1 T cell responses in this patient closely resembles the classical broad yet hierarchical antiviral immunity and was confirmed in a second subject.

Yeast whole glucan particle (WGP) beta-glucan in conjunction with antitumour monoclonal antibodies to treat cancer

Beta-glucans, biological response modifiers (BRMs) derived from the cell walls of yeast and other sources, have been demonstrated to prime leukocyte complement receptor 3 (CR3), thus enabling these cells to kill tumours opsonised with complement fragment iC3b. Many tumours activate complement via the classical pathway mediated by antitumour monoclonal antibodies (mAbs) or natural antibodies. Studies into the cellular and molecular mechanisms of action have demonstrated that orally administrated yeast beta-glucans are ingested and processed by macrophages. These macrophages secrete the active moiety that primes neutrophil CR3 to kill iC3b-opsonised tumour cells. Extensive studies in preclinical animal tumour models have demonstrated the efficacy of combined oral particulate yeast beta-glucan with antitumour mAb therapy in terms of tumour regression and long-term survival. It is proposed that the addition of beta-glucan will further improve the clinical therapeutic efficacy of antitumour mAbs in cancer patients.

The response of autologous T cells to a human melanoma is dominated by mutated neoantigens

Our understanding of pathways leading to antitumor immunity may depend on an undistorted knowledge of the primary antigenic targets of patients' autologous T cell responses. In the melanoma model derived from patient DT, we applied cryopreserved short-term autologous mixed lymphocyte-tumor cell cultures (MLTCs) in combination with an IFN-gamma enzyme-linked immunospot (ELISPOT) assay to cDNA expression screening. We identified three previously unknown peptides processed from melanosomal proteins tyrosinase (presented by HLA-A(*)2601 and -B(*)3801) and gp100 (presented by HLA-B(*)07021) and five neoantigens generated by somatic point mutations in the patient's melanoma. The mutations were found in the genes SIRT2, GPNMB, SNRP116, SNRPD1, and RBAF600. Peptides containing the mutated residues were presented by HLA-A(*)03011, -B(*)07021, and -B(*)3801. Mutation-induced functional impairment was so far demonstrated for SIRT2. Within MLTC responder populations that were independently expanded from the patient's peripheral blood lymphocytes of different years, T cells against mutated epitopes clearly predominated. These results document a high degree of individuality for the cellular antitumor response and support the need for individualizing the monitoring and therapeutic approaches to the primary targets of the autologous T cell response, which may finally lead to a more effective cancer immunotherapy.

Detection of Spontaneous CD4+ T-Cell Responses in Melanoma Patients against a Tyrosinase-Related Protein-2–Derived Epitope Identified in HLA-DRB1*0301 Transgenic Mice

PURPOSE

The frequently expressed differentiation antigen tyrosinase-related protein-2 (TRP-2) has repeatedly been described as a target of spontaneous cytotoxic T-cell responses in melanoma patients, suggesting that it might be an ideal candidate antigen for T cell-based immunotherapy. As a prerequisite for immunization, T-cell epitopes have to be identified. Whereas a number of HLA class I-presented TRP-2-derived epitopes are known, information about HLA class II-presented antigenic ligands recognized by CD4+ T helper (Th) cells is limited.

EXPERIMENTAL DESIGN

The search for TRP-2-derived Th epitopes was carried out by competitive in vitro peptide binding studies with predicted HLA-DRB1*0301 ligands in combination with peptide and protein immunizations of HLA-DRB1*0301 transgenic mice. In vivo selected candidate epitopes were subsequently verified for their immunogenicity in human T-cell cultures.

RESULTS

This strategy led to the characterization of TRP-2(60-74) as an HLA-DRB1*0301-restricted Th epitope. Importantly, TRP-2(60-74)-reactive human CD4+ Th cell lines, specifically recognizing target cells loaded with recombinant TRP-2 protein, could be established by repeated peptide stimulation of peripheral blood lymphocytes from several HLA-DRB1*03+ melanoma patients. Even short-term peptide stimulation of patients' peripheral blood lymphocytes showed the presence of TRP-2(60-74)-reactive T cells, suggesting that these T cells were already activated in vivo.

CONCLUSION

Peptide TRP-2(60-74) might be a useful tool for the improvement of immunotherapy and immune monitoring of melanoma patients.

Immunological detection of altered signaling molecules involved in melanoma development

To understand immune responses to human cancer and develop more effective immunotherapy, human tumor antigens has been isolated using various immunological methods with tumor reactive T cells or antibodies obtained from patients with melanoma. During the process of tumor antigen isolation, various molecules with genetic alterations or over-expression in tumor cells, which may be involved in proliferation, differentiation, or survival of various cancer cells, were identified. In melanoma, abnormal molecules with mutations including beta -catenin, CDK4, and BRAF, and molecules with increased expression including Survivin, were immunologically detected. Therefore, immunological isolation of human tumor antigens contributes to the identification of important molecules including altered signaling molecules involved in melanoma formation.

Immunity to breast cancer in mice immunized with fibroblasts transfected with a cDNA expression library derived from small numbers of breast cancer cells

Immunotherapy of breast cancer at an early stage of the disease increases the likelihood of success. Here, in a mouse model, we report a new strategy that enables vaccines to be prepared from microgram amounts of tumor tissue. The vaccine is prepared by transfer of a cDNA expression library from relatively small numbers of breast cancer cells into a highly immunogenic cell line, where genes specifying TAA are expressed. As the transferred DNA is integrated and replicated as the recipient cells divide, the number of vaccine cells can be conveniently expanded for repeated immunizations. A cDNA expression library prepared from a breast cancer that arose spontaneously in a C3H/He mouse (H-2(k)) was transferred into a mouse fibroblast cell line derived from C3H/He mice. To augment their nonspecific immunogenic properties, the fibroblasts were genetically modified before DNA transfer to secrete IL-2 and to express allogeneic MHC class I H-2K(b)-determinants. C3H/He mice, highly susceptible to growth of the breast cancer cells, were immunized with the cDNA-transfected cells. Robust breast cancer-specific CD8(+) T-cell-mediated immunity was generated in the mice, raising the possibility that an analogous treatment strategy could be used to treat breast cancer patients at an early stage of the disease.

Bcl-2 overexpression enhances tumor-specific T-cell survival

Although immunotherapy based on the adoptive transfer of tumor-specific T lymphocytes has been shown to result in dramatic clinical responses in some patients, the relatively low levels of engraftment and persistence of the adoptively transferred cells may limit these responses in many patients. In an attempt to develop strategies for prolonging the survival of adoptively transferred T cells, we have carried out studies in which T cells obtained from healthy donors as well as tumor-specific T cells were transduced with a retrovirus expressing the human Bcl-2 gene. Our results indicate that these transduced T cells overexpress Bcl-2, are resistant to death, and have a survival advantage following interleukin-2 withdrawal compared with control T cells transduced with a retrovirus expressing green fluorescent protein. Tumor-specific T cells overexpressing Bcl-2 maintained their ability to specifically recognize and respond to target cells. Furthermore, we show that adoptive immunotherapy of an established B16 tumor can be significantly enhanced by overexpressing Bcl-2 in melanoma-specific T-cell receptor transgenic T cells. Our data suggest that adoptive immunotherapy approaches to the treatment of cancer patients may be enhanced using Bcl-2-modified tumor-reactive T cells.

Induction of CD4+ Th1 lymphocytes that recognize known and novel class II MHC restricted epitopes from the melanoma antigen gp100 by stimulation with recombinant protein

CD4+ T helper cells may play a critical role in the induction and maintenance of a therapeutic immune response to cancer. To evaluate the efficacy with which a recombinant tumor-associated protein can induce antigen-reactive CD4+ T cells, we stimulated peripheral blood lymphocytes from patients with melanoma in vitro with the purified melanoma antigen gp100 produced in Escherichia coli. In preliminary experiments, we observed that peripheral blood mononuclear cells could process and present known HLA-DRbeta1*0401 and HLA-DRbeta1*0701 restricted epitopes to gp100-reactive CD4+ T cell lines after being loaded exogenously with protein. Therefore, we used autologous protein-loaded peripheral blood mononuclear cells as antigen presenting cells. From four of nine patients who expressed both HLA-DRbeta1*0401 and HLA-DRbeta1*0701, we raised five gp100-reactive CD4+ T cell populations that secreted TH1 type cytokines in response to exogenously loaded protein as well as target cells that endogenously expressed gp100 and MHC class II molecules, including transfectants and melanoma cells. Four of the five cultures specifically recognized the known HLA-DRbeta1*0401 and HLA-DRbeta1*0701 restricted epitopes gp100:44-59 and gp100:170-190, respectively. The fifth culture, and 30 T cell clones derived from it, specifically recognized a new peptide, gp100:420-435, in the context of HLA-DRbeta1*0701. These results suggest that recombinant tumor-associated proteins may be clinically applicable for the generation of CD4+ T helper cells in active vaccination strategies or adoptive cellular immunotherapies.

A tumor-associated glycoprotein that blocks MHC class II-dependent antigen presentation by dendritic cells

Tumors evade immune surveillance despite the frequent expression of tumor-associated Ags (TAA). Tumor cells escape recognition by CD8(+) T cells through several mechanisms, including down-regulation of MHC class I molecules and associated Ag-processing machinery. However, although it is well accepted that optimal anti-tumor immune responses require tumor-reactive CD4(+) T cells, few studies have addressed how tumor cells evade CD4(+) T cell recognition. In this study, we show that a common TAA, GA733-2, and its murine orthologue, mouse epithelial glycoprotein (mEGP), function in blocking MHC class II-restricted Ag presentation by dendritic cells. GA733-2 is a common TAA that is expressed normally at low levels by some epithelial tissues and a subset of dendritic cells, but at high levels on colon, breast, lung, and some nonepithelial tumors. We show that ectopic expression of mEGP or GA733-2, respectively, in dendritic cells derived from murine bone marrow or human monocytes results in a dose-dependent inability to stimulate proliferation of Ag-specific or alloreactive CD4(+) T cells. Dendritic cells exposed to cell debris from tumors expressing mEGP are similarly compromised. Furthermore, mice immunized with dendritic cells expressing mEGP from a recombinant adenovirus vector exhibited a muted anti-adenovirus immune response. The inhibitory effect of mEGP was not due to down-regulation of functional MHC class II molecules or active suppression of T cells, and did not extend to T cell responses to superantigen. These results demonstrate a novel mechanism by which tumors may evade CD4(+) T cell-dependent immune responses through expression of a TAA.

Cutting edge: induction of the antigen-processing enzyme IFN-gamma-inducible lysosomal thiol reductase in melanoma cells Is STAT1-dependent but CIITA-independent

Presentation and CD4(+) T cell responses to Ag in the context of MHC class II molecules require processing of native proteins into short peptide fragments. Within this pathway, IFN-gamma-inducible lysosomal thiol reductase (GILT) functions to catalyze thiol bond reduction, thus unfolding native protein Ag and facilitating further processing via cellular proteases. In contrast with professional APCs such as B cells, class II-positive human melanomas expressed relatively little to no GILT protein or mRNA. Tumor cell GILT expression was partially restored with IFN-gamma treatment but unlike other genes required for class II Ag presentation, GILT was not regulated by CIITA. Rather, studies revealed STAT1 plays a direct role in IFN-gamma-inducible GILT expression. These results define a molecular mechanism for the uncoupled regulation of MHC class II genes and the processing enzyme GILT in human melanomas.

Tc1 and Tc2 effector cell therapy elicit long-term tumor immunity by contrasting mechanisms that result in complementary endogenous type 1 antitumor responses

Cytolytic CD8(+) effector cells fall into two subpopulations based on cytokine secretion. Type 1 CD8(+) T cells (Tc1) secrete IFN-gamma, whereas type 2 CD8(+) T cells (Tc2) secrete IL-4 and IL-5. Both effector cell subpopulations display predominantly perforin-dependent cytolysis in vitro. Using an OVA-transfected B16 lung metastases model, we show that adoptively transferred OVA-specific Tc1 and Tc2 cells induce considerable suppression, but not cure, of pulmonary metastases. However, long-term tumor immunity prolonged survival times indefinitely and was evident by resistance to lethal tumor rechallenge. At early stages after therapy, protection by Tc2 and Tc1 effector cells were dependent in part on effector cell-derived IL-4, IL-5, and IFN-gamma, respectively. Whereas effector cell-derived perforin was not necessary. Over time the numbers of both donor cells diminished to low, yet still detectable, levels. Concomitantly, Tc1 and Tc2 effector cell therapies potentiated endogenous recipient-derived antitumor responses by inducing 1) local T cell-derived chemokines associated with type 1-like immune responses; 2) elevated levels of recipient-derived OVA tetramer-positive CD8 memory T cells that were CD44(high), CD122(+), and Ly6C(high) that predominantly produced IFN-gamma and TNF-alpha; and 3) heightened numbers of activated recipient-derived Th1 and Tc1 T cell subpopulations expressing CD25(+), CD69(+), and CD95(+) cell surface activation markers. Moreover, both Tc2 and Tc1 effector cell therapies were dependent in part on recipient-derived IFN-gamma and TNF-alpha for long-term survival and protection. Collectively, Tc1 and Tc2 effector cell immunotherapy mediate long-term tumor immunity by different mechanisms that subsequently potentiate endogenous recipient-derived type 1 antitumor responses.