Identification of the genes encoding cancer antigens: implications for cancer immunotherapy

T Cell Based Immunotherapy for Cancer: Approaches and Strategies

T cells are critical in destroying cancer cells by recognizing antigens presented by MHC molecules on cancer cells or antigen-presenting cells. Identifying and targeting cancer-specific or overexpressed self-antigens is essential for redirecting T cells against tumors, leading to tumor regression. This is achieved through the identification of mutated or overexpressed self-proteins in cancer cells, which guide the recognition of cancer cells by T-cell receptors. There are two main approaches to T cell-based immunotherapy: HLA-restricted and HLA-non-restricted Immunotherapy. Significant progress has been made in T cell-based immunotherapy over the past decade, using naturally occurring or genetically engineered T cells to target cancer antigens in hematological malignancies and solid tumors. However, limited specificity, longevity, and toxicity have limited success rates. This review provides an overview of T cells as a therapeutic tool for cancer, highlighting the advantages and future strategies for developing effective T cell cancer immunotherapy. The challenges associated with identifying T cells and their corresponding antigens, such as their low frequency, are also discussed. The review further examines the current state of T cell-based immunotherapy and potential future strategies, such as the use of combination therapy and the optimization of T cell properties, to overcome current limitations and improve clinical outcomes.

A New Concept of Enhancing Immuno-Chemotherapeutic Effects Against B16F10 Tumor via Systemic Administration by Taking Advantages of the Limitation of EPR Effect

The enhanced permeability and retention (EPR) effect has been comfortably accepted, and extensively assumed as a keystone in the research on tumor-targeted drug delivery system. Due to the unsatisfied tumor-targeting efficiency of EPR effect being one conspicuous drawback, nanocarriers that merely relying on EPR effect are difficult to access the tumor tissue and consequently trigger efficient tumor therapy in clinic. In the present contribution, we break up the shackles of EPR effect on nanocarriers thanks to their universal distribution characteristic. We successfully design a paclitaxel (PTX) and alpha-galactosylceramide (αGC) co-loaded TH peptide (AGYLLGHINLHHLAHL(Aib)HHIL-Cys) -modified liposome (PTX/αGC-TH-Lip) and introduce a new concept of immuno-chemotherapy combination via accumulation of these liposomes at both spleen and tumor sites naturally and simultaneously. The PTX-initiated cytotoxicity attacks tumor cells at tumor sites, meanwhile, the αGC-triggered antitumor immune response emerges at spleen tissue. Different to the case that liposomes are loaded with sole drug, in this concept two therapeutic processes effectively reinforce each other, thereby elevating the tumor therapy efficiency significantly. The data demonstrates that the PTX/αGC-TH-Lip not only possess therapeutic effect against highly malignant B16F10 melanoma tumor, but also adjust the in vivo immune status and induce a more remarkable systemic antitumor immunity that could further suppress the growth of tumor at distant site. This work exhibits the capability of the PTX/αGC-TH-Lip in improving immune-chemotherapy against tumor after systemic administration.

Adoptive T-Cell Therapy for Cancer

Recent developments have demonstrated that immunotherapies are capable of achieving durable antitumor responses in patients with metastatic cancer. One modality that has been able to induce durable complete regressions in patients with melanoma has been adoptive cell therapy (ACT). This has slowly been expanded to other cancer types using new approaches such as genetically engineered T-cells and other methods of antigen targeting. It now appears that immune targeting of mutated "neoantigens" plays a major role in successful ACT, as well as in other immunotherapies such as checkpoint inhibitors. This realization presents not only new challenges to ACT but also new opportunities in that all tumors now may have potential antigens to attack that can be revealed by tumor genomic sequencing. There are a variety of exciting approaches to translate these new findings into clinical trials applying ACT to the majority of cancer types.

Cancer immunotherapy in clinical practice -- the past, present, and future

Considerable progress has been made in the field of cancer immunotherapy in recent years. This has been made possible in large part by the identification of new immune-based cellular targets and the development of novel approaches aimed at stimulating the immune system. The role played by the immunosuppressive microenvironment in the development of tumors has been established. The success of checkpoint-inhibiting antibodies and cancer vaccines has marked the beginning of a new era in cancer treatment. This review highlights the clinically relevant principles of cancer immunology and various immunotherapeutic approaches that have either already entered mainstream oncologic practice or are currently in the process of being evaluated in clinical trials. Furthermore, the current barriers to the development of effective immunotherapies and the potential strategies of overcoming them are also discussed.

Strong spontaneous tumor neoantigen responses induced by a natural human carcinogen

A key to improving cancer immunotherapy will be the identification of tumor-specific "neoantigens" that arise from mutations and augment the resultant host immune response. In this study we identified single nucleotide variants (SNVs) by RNA sequencing of asbestos-induced murine mesothelioma cell lines AB1 and AB1-HA. Using the NetMHCpan 2.8 algorithm, the theoretical binding affinity of predicted peptides arising from high-confidence, exonic, non-synonymous SNVs was determined for the BALB/c strain. The immunoreactivity to 20 candidate mutation-carrying peptides of increased affinity and the corresponding wild-type peptides was determined using interferon-γ ELISPOT assays and lymphoid organs of non-manipulated tumor-bearing mice. A strong endogenous immune response was demonstrated to one of the candidate neoantigens, Uqcrc2; this response was detected in the draining lymph node and spleen. Antigen reactive cells were not detected in non-tumor bearing mice. The magnitude of the response to the Uqcrc2 neoantigen was similar to that of the strong influenza hemagglutinin antigen, a model tumor neoantigen. This work confirms that the approach of RNAseq plus peptide prediction and ELISPOT testing is sufficient to identify natural tumor neoantigens.

Immunotherapy for solid tumors--a review for surgeons

Immunotherapy has evolved considerably in the last decade and is becoming an integral component of the armamentarium for the treatment of patients with advanced solid tumors. It is important for clinicians, especially surgeons, to understand the basic principles of novel immunotherapies and the immune system. This review summarizes the evolution of the most relevant immunotherapies, their mechanisms of action, the data supporting their clinical use, and integration of immunotherapy into multidisciplinary management of solid tumors. This review should serve as a primer for clinicians and surgeons to understand the rapidly evolving field of immunotherapy.

Reflections upon human cancer immune responsiveness to T cell-based therapy

Immune-mediated rejection of human cancer is a relatively rare but well-documented phenomenon. Its rate of occurrence progressively increases from the occasional observation of spontaneous regressions to the high rate of complete remissions observed in response to effective treatments. For two decades, our group has focused its interest in understanding this phenomenon by studying humans following an inductive approach. Sticking to a sequential logic, we dissected the phenomenon by studying to the best of our capability both peripheral and tumor samples and reached the conclusion that immune-mediated cancer rejection is a facet of autoimmunity where the target tissue is the cancer itself. As we are currently defining the strategy to effectively identify the mechanisms leading in individual patients to rejection of their own tumors, we considered useful to summarize the thought process that guided us to our own interpretation of the mechanisms of immune responsiveness.

PLGA nanoparticle-mediated delivery of tumor antigenic peptides elicits effective immune responses

The peptide vaccine clinical trials encountered limited success because of difficulties associated with stability and delivery, resulting in inefficient antigen presentation and low response rates in patients with cancer. The purpose of this study was to develop a novel delivery approach for tumor antigenic peptides in order to elicit enhanced immune responses using poly(DL-lactide-co-glycolide) nanoparticles (PLGA-NPs) encapsulating tumor antigenic peptides. PLGA-NPs were made using the double emulsion-solvent evaporation method. Artificial antigen-presenting cells were generated by human dendritic cells (DCs) loaded with PLGA-NPs encapsulating tumor antigenic peptide(s). The efficiency of the antigen presentation was measured by interferon-γ ELISpot assay (Vector Laboratories, Burlingame, CA). Antigen-specific cytotoxic T lymphocytes (CTLs) were generated and evaluated by CytoTox 96^® Non-Radioactive Cytotoxicity Assay (Promega, Fitchburg, WI). The efficiency of the peptide delivery was compared between the methods of emulsification in incomplete Freund’s adjuvant and encapsulation in PLGA-NPs. Our results showed that most of the PLGA-NPs were from 150 nm to 500 nm in diameter, and were negatively charged at pH 7.4 with a mean zeta potential of −15.53 ± 0.71 mV; the PLGA-NPs could be colocalized in human DCs in 30 minutes of incubation. Human DCs loaded with PLGA-NPs encapsulating peptide induced significantly stronger CTL cytotoxicity than those pulsed with free peptide, while human DCs loaded with PLGA-NPs encapsulating a three-peptide cocktail induced a significantly greater CTL response than those encapsulating a two-peptide cocktail. Most importantly, the peptide dose encapsulated in PLGA-NPs was 63 times less than that emulsified in incomplete Freund’s adjuvant, but it induced a more powerful CTL response in vivo. These results demonstrate that the delivery of peptides encapsulated in PLGA-NPs is a promising approach to induce effective antitumor CTL responses in vivo.

Cytotoxic T lymphocyte responses against melanocytes and melanoma

Background

Vitiligo is a common toxicity associated with immunotherapy for melanoma. Cytotoxic T lymphocytes (CTLs) against melanoma commonly target melanoma-associated antigens (MAAs) which are also expressed by melanocytes. To uncouple vitiligo from melanoma destruction, it is important to understand if CTLs can respond against melanoma and melanocytes at different levels.

Methods

To understand the dichotomous role of MAA-specific CTL, we characterized the functional reactivities of established CTL clones directed to MAAs against melanoma and melanocyte cell lines.

Results

CTL clones generated from melanoma patients were capable of eliciting MHC-restricted, MAA-specific lysis against melanocyte cell lines as well as melanoma cells. Among the tested HLA-A*0201-restricted CTL clones, melanocytes evoked equal to slightly higher degranulation and cytolytic responses as compared to melanoma cells. Moreover, MAA-specific T cells from vaccinated patients responded directly ex vivo to melanoma and melanocytes. Melanoma cells express slightly higher levels of MART-1 and gp100 than melanocytes as measured by quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) and immunohistochemistry.

Conclusions

Our data suggest that CTLs respond to melanoma and melanocytes equally in vitro and directly ex vivo.

GM-CSF Gene-Modifed Cancer Cell Immunotherapies: Of Mice and Men

GVAX cancer immunotherapies are composed of whole tumor cells genetically modified to secrete the immune stimulatory cytokine, granulocyte-macrophage colony-stimulating factor (GM-CSF), and then irradiated to prevent further cell division. Both autologous (patient specific) and allogeneic (non-patient specific) GVAX platforms have been evaluated either as single agents or in combination with other immunomodulatory strategies. Many early-phase clinical trials have now been completed. Results have consistently demonstrated a favorable safety profile manifested primarily by injection site reactions and flu-like symptoms. Consistent evidence of immune activation and clinical activity, including radiologic tumor regressions, has been seen across multiple cancer indications in both early- and late-stage disease. Phase 3 trials evaluating an allogeneic GVAX immunotherapy product in prostate cancer are under way.

Effects of Combined Oral Administration and Intravenous Injection on Maintaining Decreased Systemic Tyrosine Levels in Rats

Our previous studies have indicated that encapsulated tyrosinase and crosslinked hemoglobin with tyrosinase (polyhemoglobin-tyrosinase) decrease systemic tyrosine level significantly in rats. However, we need a few days of oral administration of encapsulated tyrosinase before the systemic tyrosine level starts to decrease. Although intravenous injection of polyhemoglobin tyrosinase can lower the systemic tyrosine to about 10% within an hour, the level increases towards normal after 24 h. We therefore investigate the effects of intravenous injection of polyhemoglobin-tyrosinase combined with oral administration of encapsulated tyrosinase on lowering the systemic tyrosine level. In addition, we further optimize this combined method for lowering systemic tyrosine in animal studies and have found out that two intravenous injections of polyhemoglobin-tyrosinase followed by three times a day oral administration of encapsulated tyrosinase could immediately lower the body tyrosine and maintain this low level as long as the oral administration is continued.

Physiological role of plasmacytoid dendritic cells and their potential use in cancer immunity

Dendritic cells (DCs) play a pivotal role in the control of innate and adaptive immune responses. They are a heterogeneous cell population, where plasmacytoid dendritic cells (pDCs) are a unique subset capable of secreting high levels of type I IFNs. It has been demonstrated that pDCs can coordinate events during the course of viral infection, atopy, autoimmune diseases, and cancer. Therefore, pDC, as a main source of type I IFN, is an attractive target for therapeutic manipulations of the immune system to elicit a powerful immune response against tumor antigens in combination with other therapies. The therapeutic vaccination with antigen-pulsed DCs has shown a limited efficacy to generate an effective long-lasting immune response against tumor cells. A rational manipulation and design of vaccines which could include DC subsets outside “Langerhans cell paradigm” might allow us to improve the therapeutic approaches for cancer patients.

Secretion of biologically active recombinant human granulocyte-macrophage colony-stimulating factor by transduced gastric cancer cells

PURPOSE

Gastric cancer has the highest incidence rate among cancers in Asia. The advanced type of signet ring cell carcinoma has poor prognosis compared to other types of gastric cancer. The immuno-gene therapy with cytokine-based tumor vaccines has not yet been investigated for gastric cancer. The granulocyte macrophage colony-stimulating factor (GM-CSF)-based tumor vaccine has been demonstrated as the most potent stimulator for specific and long-lasting systemic tumor immunity.

MATERIALS AND METHODS

In the present study, KATO III cells, the human signet ring cell gastric carcinoma cell line, were genetically modified by the transduction with the human GM-CSF cDNA or the modified hGM-CSF in replication-deficient retroviruses. The genomic integrations and mRNA expressions of the transgenes were determined by Southern and Northern blot analyses.

RESULTS

Wild type (wt) or modified hGM-CSF was integrated into the genome of KATO III cells. The modified hGM-CSF mRNA was more stable than that of wt. The KATO III cells with the modified hGM-CSF produced higher level of hGM-CSF (12.4-19 ng/10(6)cells/48hrs) than that with wt hGM-CSF, when determined by enzyme-linked immunosorbent assay (ELISA). The secreted recombinant hGM-CSF could support the proliferation of the GM-CSF-dependent cell line, indicating that the hGM-CSF secreted by the transduced KATO III cells has biological activities. Irradiated, transduced KATO III cells continued to secret hGM-CSF without proliferation.

CONCLUSION

Our results suggest that GM-CSF secreting KATO III cells could be tested for the treatment of gastric cancer as an allogeneic tumor vaccine as a part of immunotherapeutic treatment.

Spontaneous and treatment-induced cancer rejection in humans

BACKGROUND

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

OBJECTIVE

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

METHODS

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

CONCLUSION

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

A novel murine model of allogeneic vaccination against prostate cancer

Prostate cancer continues to be a major cause of death in men. Surgical and medical treatments of the disease have improved, but metastasic disease remains a significant clinical problem. Novel therapies such as whole cell vaccination offer the potential of treating disease by stimulating the immune system. To study the efficacy of a whole cell vaccine in prostate cancer two strains of mice were used: C57BL/6 (H-2Kb) and C3H/HeJ (H-2K(k)) in combination with four different cell lines. Thus, a model was constructed of allogeneic and syngeneic vaccine, as well as a challenge tumour for each strain. Two novel cell lines were developed during this study. Firstly, the non tumourigeneic PMC-1 was derived from a normal mouse prostate and immortalized with HPV16. Secondly, the tumourigeneic PMC-1 C6ras1p1 was transformed with human ras gene which formed tumours in both SCID and C3H/HeJ mice. Protection, and the nature of the immune response to syngeneic and allogeneic vaccine, in males and females was examined in both strains. Vaccination with both syngeneic and allogeneic irradiated whole cell vaccines induced protection from syngeneic challenge in females. However, no protection was observed when allogeneic vaccine was given to male mice. This correlated with the immune response. Two types of cellular immune responses were generated in females. A NK-mediated response was observed in C57BL/6 mice, whilst C3H/HeJ mice developed a CTL response. Little or no cellular immune response was observed in males. The cytokine profile in C3H/HeJ females was a mixture of Th1 and Th2 whilst a mainly Th1 profile was observed in C57BL/6 mice. Male mice showed a diminished cytokine secretion compared to females which was further depressed after challenge. The difference in immunity was largely as expected, since tolerance to prostate antigens should not normally develop in female mice. However, this makes this model particularly relevant clinically since it directly mimics the human situation and thus may accelerate the development of whole cell vaccines for clinical use.

Treatment of Oligometastases After Successful Immunotherapy

Local destruction of individual metastases by any of a number of effective modalities fails as a treatment for most patients with disseminated cancer because of the presence of either undetected micrometastases or simply too many lesions. The availability of a systemic therapy that could reduce the number of metastases to a manageable few would dramatically increase the utility of surgical metastasectomy or other locally ablative measures. Interleukin-2-based immunotherapy can serve exactly this function in some patients with renal cancer or melanoma. We review the effectiveness of surgery in treating limited relapses or residual disease in patients who have responded to systemic immunotherapy. These data indicate that a surprising percentage of such patients can enjoy durable disease-free survival after surgical removal of their oligometastases, and, for a significant minority, it appears to be curative.

Identification of HLA-DQα and -DRβ Residues Associated With Susceptibility and Protection to Epithelial Ovarian Cancer

Substantial evidence has been accumulated suggesting that T cells in patients with epithelial ovarian carcinoma (EOC) exhibit an antigen-driven immune response directed against the tumor cells. In the context of human leukocyte antigen (HLA), this suggests its possible involvement in the disease. Therefore, we examined the distribution of the HLA-DRB1*, -DQA1*, and -DQB1* alleles in 47 patients with EOC and 67 healthy Caucasian women. The frequency of D(70) and E(71) polymorphic residues of the DRB1 alleles was significantly reduced in EOC patients versus controls (pD(70)E(71) = 0.009), suggesting a protective role against the disease. The DQalpha residues R(52) and Y(11)R(55) were increased in the patients (p = 0.008 and 0.012, respectively). Because residues 11 and 55 participate in the formation of pocket 1, they may be functionally important amino acid positions that influence disease susceptibility. The frequency of the DQalpha susceptibility epitope (R(52)Y(11)R(55)) among the DRbetaD(70)E(71)-positive EOC patients was increased when compared with DRbetaD(70)E(71)-positive controls (EOC, 100%; control, 52%; p = 0.028). Among individuals without the DQalpha susceptibility epitope, the distribution of DRbetaD(70)E(71)-positive cases was significantly different between EOC patients and controls (EOC, 0%; control, 60%; p = 0.039). Therefore, it appears that the presence of DQalpha susceptibility elements overrides the protective effect of the DRbetaD(70)E(71) epitope and suggests an interactive relationship between DRbeta and DQalpha epitopes that may be of importance for disease susceptibility. Because positions DRbeta 70,71 and DQalpha 52 have been implicated in immunologic diseases, it is likely that besides being critical for T-cell recognition, they may also play a role in T-cell development and acquisition of the T-cell repertoire.

DNA fusion gene vaccines against cancer: from the laboratory to the clinic

Vaccination against target antigens expressed by cancer cells has now become a realistic goal. DNA vaccines provide a direct link between identification of genetic markers in tumors and vaccine formulation. Simplicity of manufacture facilitates construction of vaccines against disease subsets or even for individual patients. To engage an immune system that exists to fight pathogens, we have developed fusion gene vaccines encoding tumor antigens fused to pathogen-derived sequences. This strategy activates high levels of T-cell help, the key to induction and maintenance of effective immunity. We have dissected the immunogenic tetanus toxin to obtain specific sequences able to activate antibody, CD4+, or CD8+ T cells to attack selected fused tumor antigens. Principles established in preclinical models are now being tested in patients. So far, objective immune responses against idiotypic antigen of neoplastic B cells have been observed in patients with B-cell malignancies and in normal transplant donors. These responses provide a platform for testing physical methods to improve DNA delivery and strategies to boost responses. For cancer, demands are high, because vaccines have to activate powerful immunity against weak antigens, often in a setting of immune damage or tolerance. Vaccination strategies against cancer and against microbes are sharing knowledge and technology for mutual benefit.

MART-1 adenovirus-transduced dendritic cell immunization in a murine model of metastatic central nervous system tumor

Dendritic cells (DCs) are potent antigen-presenting cells that have been shown to play a critical role in the initiation of host immune responses against tumor antigens. In this study, a recombinant adenovirus vector encoding the melanoma-associated antigen, MART-1, was used to transduce murine DCs, which were then tested for their ability to activate cytotoxic T lymphocytes (CTLs) and induce protective immunity against B16 melanoma tumor cells implanted intracranially. Genetic modifications of murine bone marrow-derived DCs to express MART-1 was achieved through the use of an E1-deficient, recombinant adenovirus vector. Sixty-two C57BL/6 mice were immunized subcutaneously with AdVMART-1-transduced DCs (n = 23), untransduced DCs (n = 17), or sterile saline (n = 22). Using the B16 murine melanoma, which naturally expresses the MART-1 antigen, all the mice were then challenged intracranially with viable, unmodified syngeneic B16 tumor cells 7 days later. Splenocytes from representative animals in each group were harvested for standard cytotoxicity (CTL) and enzyme-linked immunospot (ELISPOT) assays. The remaining mice were followed for survival. Immunization of C57BL/6 mice with DCs transduced with an adenoviral vector encoding the MART-1 antigen elicited the development of antigen-specific CTL responses. As evidenced by a prolonged survival curve when compared to control-immunized mice with intracranial B16 tumors, AdMART-1-DC vaccination was able to elicit partial protection against central nervous system tumor challenge in vivo.

Cancer vaccines

Although cancer immunotherapy was initiated by William Coley more than a century ago, the field of cancer vaccines is in an early stage of development. Only recently, major advances in cellular and molecular immunology have allowed a comprehensive understanding of the complex and high rate of interactions between the immune system and tumor cells. We have learned that these tumor-immune system interactions may result either in strong immune antitumor response or tolerance to tumor-associated antigens. This article will discuss the profound interest in cancer vaccines derived from their potential to induce antitumor responses in vivo. Substantial data from several preclinical models and early human clinical trials have confirmed the ability of cancer vaccines to induce immune responses that are tumor-specific and, in some cases, associated with clinical responses. One future challenge will be to determine how to appropriately stimulate the pathways leading to effective interaction among antigen-presenting cells, T lymphocytes, and tumor cells. It also is critical to develop monitoring strategies that may allow the identification of patients who may benefit from cancer vaccines.

Clinical immunotherapy for brain tumors

As an immunization platform for brain tumors, dendritic cells supply an impressive host of advantages. On the simplest level, they provide the safety and tumor-specificity so wanted by current therapeutic options. Yet, in addition, as the fundamental antigen-presenting cell, they circumvent many of the immunologic challenges that gliomas and the CNS proffer and that other immunotherapeutic modes fail to overcome. Directions to take now include the identification of new tumor-specific and tumor-associated antigens; the determination of the optimal dendritic cell subtype, generation, loading method, maturation state, dose, and route of delivery for immunizations; the further characterization of dendritic cells and their activities; and, potentially, the discovery of ways to pulse dendritic cells efficiently in vivo. Preclinical studies continue to play an important role in refining this form of active immunotherapy.

GM-CSF-based cellular vaccines: a review of the clinical experience

Immunotherapy is playing an increasing role in the treatment of many cancers. The recent advances in antibody therapy gives much optimism that both passive (antibody therapy) as well as active (vaccine therapy) immunotherapeutic interventions will acquire an increasing presence in oncology. Granulocyte macrophage-colony stimulation factor (GM-CSF)-based vaccines have now been tested in several diseases in a variety of formulations. The success and broad applicability of such an approach rests on the development of an ideal vaccine formulation administered in the appropriate clinical context. This review summarizes the results from the clinical trials performed to date and discusses the future directions of GM-CSF-based cellular vaccine strategies aimed at maximizing the therapeutic benefit.

Induction of tumor-reactive cytotoxic T-lymphocytes using a peptide from NY-ESO-1 modified at the carboxy-terminus to enhance HLA-A2.1 binding affinity and stability in solution

NY-ESO-1 is an attractive candidate tumor antigen for the development of immunotherapy for a wide variety of cancers. It is expressed in multiple types of tumors, but its normal tissue distribution is predominantly limited to the testes and ovaries; furthermore, both humoral and cellular immune responses can be mounted against this protein. Three overlapping HLA-A2.1-restricted T-cell epitopes have been identified within NY-ESO-1. In this investigation, the authors evaluated the in vitro immunogenicity of these peptides. From 2 of 12 HLA-A2.1+ patients with metastatic melanoma, peptide-reactive cytotoxic T-lymphocytes were generated using either NY-ESO-1:157-167 or NY-ESO-1:157-165 but not NY-ESO-1:155-163. Because NY-ESO-1:157-165 is a 9 amino acid peptide completely contained within NY-ESO-1:157-167, it seemed likely that this peptide was the minimal determinant, and thus it was selected for continued study. An amino acid substitution of C to V was introduced into NY-ESO-1:157-165 at P9 to attempt to improve its immunogenicity by enhancing its binding affinity to HLA-A2.1 and increasing its stability in solution, because the C residue is readily oxidized, leading to dimerization of the peptide. From 5 of 20 HLA-A2.1+ patients with metastatic melanoma, NY-ESO-1:157-165(165V) stimulated cytotoxic T-lymphocytes in vitro, which recognized peptide-pulsed target cells and HLA-A2.1+ NY-ESO-1+ tumor cells, suggesting that this peptide may be clinically valuable for the treatment of patients with NY-ESO-1+ tumors.

Expression of gp100, MART-1, tyrosinase, and S100 in paraffin-embedded primary melanomas and locoregional, lymph node, and visceral metastases: implications for diagnosis and immunotherapy. A study conducted by the EORTC Melanoma Cooperative Group

With the recent availability of novel antibodies against melanoma antigens tyrosinase and MART-1, it is important to validate their usefulness in pathology practice and in screening patients for immunotherapy treatment. In the present study conducted by the Melanoma Cooperative Group of the European Organization for Research and Treatment of Cancer (EORTC-MCG), immunohistochemical staining for gp100 (antibodies NKI-beteb and HMB-45), MART-1 (A103), tyrosinase (T311), and S100 (S100) was compared on formalin-fixed and paraffin-embedded tumour lesions from 80 patients with 130 malignant melanoma lesions, comprising 44 primary tumours, 18 locoregional metastases, 41 lymph node metastases, and 27 visceral metastases from the lung, liver, and brain. A score between 0 and 5 was allocated to each immunohistochemically stained section. These scores were evaluated in a statistical analysis. S100 was by far the most sensitive marker in all four types of lesions tested. Apart from a significantly better performance for T311 in primary melanomas compared with HMB-45, no significant differences were observed between the four remaining antigens tested. Three settings were next investigated to determine whether the expression of melanoma antigens decreases with tumour progression. First, within the primary melanomas, only NKI-beteb and A103 staining showed a nearly significant negative correlation with Clark's level of invasion and a similar tendency was observed for these antibodies with Breslow thickness. Second, when comparing primary melanoma-metastasis pairs from the same patient, lymph node metastases showed less staining with NKI-beteb, HMB-45, A103, and T311, at a level near significance. This difference was not significant when comparing the primary tumour with visceral metastases, probably due to the lower numbers of pairs. Third, regarding tumour progression from primary melanoma to locoregional, to lymph node, to visceral metastasis, a significant decrease with progression was found only for T311. The apparently stable expression of most of the melanoma antigens, and the small contribution of decreased expression in melanoma tumour progression, supports the rationale for immunotherapy based on the melanoma immunogens gp100, MART-1, and tyrosinase.

Novel allogeneic granulocyte-macrophage colony-stimulating factor-secreting tumor vaccine for pancreatic cancer: a phase I trial of safety and immune activation

PURPOSE

Allogeneic granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting tumor vaccines can cure established tumors in the mouse, but their efficacy against human tumors is uncertain. We have developed a novel GM-CSF-secreting pancreatic tumor vaccine. To determine its safety and ability to induce antitumor immune responses, we conducted a phase I trial in patients with surgically resected adenocarcinoma of the pancreas.

PATIENTS AND METHODS

Fourteen patients with stage 1, 2, or 3 pancreatic adenocarcinoma were enrolled. Eight weeks after pancreaticoduodenectomy, three patients received 1 x 10(7) vaccine cells, three patients received 5 x 10(7) vaccine cells, three patients received 10 x 10(7) vaccine cells, and five patients received 50 x 10(7) vaccine cells. Twelve of 14 patients then went on to receive a 6-month course of adjuvant radiation and chemotherapy. One month after completing adjuvant treatment, six patients still in remission received up to three additional monthly vaccinations with the same vaccine dose that they had received originally.

RESULTS

No dose-limiting toxicities were encountered. Vaccination induced increased delayed-type hypersensitivity (DTH) responses to autologous tumor cells in three patients who had received >or= 10 x 10(7) vaccine cells. These three patients also seemed to have had an increased disease-free survival time, remaining disease-free at least 25 months after diagnosis.

CONCLUSION

Allogeneic GM-CSF-secreting tumor vaccines are safe in patients with pancreatic adenocarcinoma. This vaccine approach seems to induce dose-dependent systemic antitumor immunity as measured by increased postvaccination DTH responses against autologous tumors. Further clinical evaluation of this approach in patients with pancreatic cancer is warranted.

Treatment of a patient by vaccination with autologous dendritic cells pulsed with allogeneic major histocompatibility complex class I-matched tumor peptides. Case Report

Dendritic cells (DCs) are antigen-presenting cells that play a central role in the initiation and modulation of antitumor immune responses. In this pilot study, we investigated the ability of autologous DCs pulsed ex vivo with allogeneic major histocompatibility complex class I-matched glioblastoma peptides to stimulate host antitumor immune responses when injected as a vaccine. A patient with recurrent brainstem glioblastoma multiforme (GBM) received a series of three intradermal immunizations of antigen-pulsed DCs on an outpatient basis following surgical debulking of her posterior fossa tumor. Dendritic cell vaccination was well tolerated, and no clinical signs of autoimmunity or experimental allergic encephalomyelitis were detected. She developed a measurable cellular immune response against the allogeneic glioblastoma peptides used in her vaccine preparation, as demonstrated by in vitro T-cell proliferation assays. In addition, increased T-cell infiltration was noted within the intracranial tumor site in the biopsy sample obtained following DC vaccination. An objective clinical response, however, was not evident, and this patient eventually died 21 months after her disease was diagnosed. To our knowledge, this is the first patient with brain cancer ever to be treated with DC-based immunotherapy. This case illustrates that vaccination with DCs pulsed with acid-eluted glioblastoma peptides is feasible and can induce systemic antigen-specific immunity in a patient with recurrent GBM. Additional studies are necessary to determine the optimum DC doses and antigen loading conditions that may translate into clinical effectiveness and survival benefit for patients with brain tumors. Phase I trials for malignant glioma are currently underway.

Recombinant adenovirus-transduced dendritic cell immunization in a murine model of central nervous system tumor

Object

Dendritic cells (DCs) are potent antigen-presenting cells that have been shown to play a critical role in the initiation of host immune responses against tumor antigens. In this study, a recombinant adenovirus vector encoding the melanoma-associated antigen, MART-1, was used to transduce murine DCs, which were then tested for their ability to activate cytotoxic T lymphocytes (CTLs) and induce protective immunity against B16 melanoma tumor cells implanted intracranially.

Methods

Genetic modification of murine bone marrrow–derived DCs to express MART-1 was achieved through the use of an E1-deficient, recombinant adenovirus vector (AdVMART1). Sixty-two C57BL/6 mice were immunized by subcutaneous injection of AdVMART-1-transduced DCs (23 mice), untransduced DCs (17 mice), or sterile saline (22 mice). Using the B16 murine melanoma, which naturally expresses the MART-1 antigen, all the mice were then challenged intracranially with viable, unmodified syngeneic B16 tumor cells 7 days later. Splenocytes obtained from representative animals in each group were harvested for standard cytotoxicity and enzyme-linked immunospot assays. The remaining mice were followed for survival.

Immunization of C57BL/6 mice with DCs transduced with AdVMART1-DC elicited the development of antigen-specific CTL responses. As evidenced by a prolonged survival curve when compared with control-immunized mice harboring intracranial B16 tumors, AdMART1-DC vaccination was able to elicit partial protection against central nervous system (CNS) tumor challenge in vivo. However, this CNS antitumor immunity was weaker than that previously demonstrated against subcutaneous B16 tumors in which the same vaccination strategy was used.

Conclusions

These data suggest that immune responses generated against CNS tumors by DC-based vaccines may be different from those obtained against subcutaneous tumors.

Expression of the SART3 tumor-rejection antigen in brain tumors and induction of cytotoxic T lymphocytes by its peptides

The authors recently reported on the SART3 tumor-rejection antigen, which possesses epitopes that can induce cytotoxic T lymphocytes (CTLs) in patients with epithelial cancer. To explore a new modality for treatment of patients with brain tumors, this study investigated the expression of the SART3 antigen in patients with brain tumors and the ability of SART3 peptides to induce CTLs from peripheral blood mononuclear cells (PBMCs) of these patients. The SART3 antigen was detected in the cytoplasmic fraction of all 18 glioma cell lines examined and in the majority (31 of 34; 91%) of brain tumor tissues irrespective of their histologies. It was also expressed in the nuclear fraction of all 18 glioma cell lines and in the majority (26 of 34; 76%) of brain tumor tissues. In contrast, the SART3 was not expressed in nontumorous brain tissues. Cytotoxic T lymphocytes were induced in patients with glioma by stimulation with two epitope peptides of SART3. These CTLs could eliminate glioma cells in a HLA-A24-restricted manner. Therefore, the SART3 peptides may be appropriate molecules for use in peptide-based specific immunotherapy of HLA-A24+ patients with brain tumors.

Tumour immunotherapy: the adjuvant treatment of the 21st century?

In the course of a century, tumour immunology has revealed a picture of a very complex immune system involving the recognition and eradication of malignancies. Many tumours evade the immune system, and understanding of tumour escape mechanisms is the key to a successful immunotherapy for cancer. A wide array of tumour immunotherapy modalities have been developed, many of which have reached the phase of clinical trials, with some satisfactory results. Based on the available clinical, data and the techniques available for further improvement, we analyse the prospects for the different treatment modalities, and predict an important role for tumour immunotherapy in the near future.

Immunology and immunotherapy of human cancer: present concepts and clinical developments

Immunotherapy of cancer is entering into a new phase of active investigation both at the pre-clinical and clinical level. This is due to the exciting developments in basic immunology and tumour biology that have allowed a tremendous increase in our understanding of mechanisms of interactions between the immune system and tumour cells. This review briefly summarizes the state of the art in basic tumour immunology before discussing the clinical applications of the new concepts in the clinical setting. Clinical approaches are diverse but can now be based on strong scientific rationales. The analysis of the available clinical results suggests that, despite some disappointments, there is room for optimism that both active immunotherapy (vaccination) and adoptive immunotherapy may soon become part of the therapeutic arsenal to combat cancer in a more efficient way.

Immunotherapy of cancer

The goal of cancer treatment is to develop modalities that specifically target tumor cells, thereby avoiding unnecessary side effects to normal tissue. Vaccine strategies that result in the activation of the immune system specifically against proteins expressed by a cancer have the potential to be effective treatment for this purpose. An early vaccine approach that was developed by our group involves the insertion of the granulocyte-macrophage colony stimulating factor (GM-CSF) gene into cancer cells that are then used to immunize patients. These genetically modified tumor cells produce the immune activating protein GM-CSF in the local environment of the tumor cells, specifically activating the patient's T cells to eradicate cancer at metastatic sites. We have performed many studies that demonstrate that this vaccine can cure mice of cancer. We recently demonstrated that this approach can activate an immune response in patients with renal cell carcinoma. We are currently testing a similar approach in patients with pancreatic cancer. Until recently, whole tumor cells were used to produce the vaccine because the proteins expressed by the tumor cells that can be recognized by the immune system were unknown. However, recent advances have allowed the identification of many of the proteins expressed by some cancers. In addition, significant attention has been focused on the mechanisms by which antitumor immunity can be modulated. These active areas of research will undoubtably lead to the development of more specific and more potent vaccine strategies in the near future. The first part of this paper focuses on data from two recent clinical trials that evaluated the whole tumor cell approach. The second part of this paper discusses some of the more exciting antigen-specific vaccine approaches that are under development for the treatment of cancer.

The density of peptides displayed by dendritic cells affects immune responses to human tyrosinase and gp100 in HLA-A2 transgenic mice

Several HLA-A*0201-restricted peptide epitopes that can be used as targets for active immunotherapy have been identified within melanocyte differentiation proteins. However, uncertainty exists as to the most effective way to elicit CD8+ T cells with these epitopes in vivo. We report the use of transgenic mice expressing a derivative of HLA-A*0201, and dendritic cells, to enhance the activation of CD8+ T cells that recognize peptide epitopes derived from human tyrosinase and glycoprotein 100. We find that by altering the cell surface density of the immunizing peptide on the dendritic cells, either by pulsing with higher concentrations of peptide, or by changing the MHC-peptide-binding affinity by generating variants of the parent peptides, the size of the activated CD8+ T cell populations can be modulated in vivo. Significantly, the density of peptide that produced the largest response was less than the maximum density achievable through short-term peptide pulsing. We have also found, however, that while some variant peptides are effective at eliciting both primary and recall CD8+ T cell responses that can recognize the parental epitope, other variant epitopes lead to the outgrowth of CD8+ T cells that only recognize the variant. HLA-A*0201 transgenic mice provide an important model to define which peptide variants are most likely to stimulate CD8+ T cell populations that recognize the parental, melanoma-specific peptide.

Immunotherapeutic approaches to sarcoma

In the last decade, the most important factor in the rekindled interest in immune therapy for cancer is the development of new methods to identify tumor antigens that can be recognized by T-cells and other immune effectors. In addition, greater knowledge about tolerance and mechanisms of tumor cell evasion from immune effectors has made the prospect of developing clinically effective immune therapies for cancer seem promising. Research in immune therapies for sarcoma has been limited, mainly because of the previous lack of defined tumor antigens in this disease and the low prevalence of sarcoma in the general population. We will review the fundamental concepts of tumor immunobiology, both cellular and humoral, and highlight the new, powerful methods for identifying novel tumor antigens. Further, we will focus on the unique situation presented by sarcoma as the only solid tumor in which many cytogenetic abnormalities have been characterized which encode for unique, tumor-specific fusion proteins that are ideal targets for immune-based therapy. We will review the specifics of vaccine therapy approach to this disease, with emphasis on strategies to improve the immunogenicity of newly defined tumor antigens in sarcoma.

Cancer vaccines with emphasis on a viral oncolysate melanoma vaccine

Biotherapy of malignant diseases has become the fourth treatment modality besides surgery, chemo- and radiotherapy. Whole cell melanoma vaccines with or without BCG and other adjuvants, purified ganglioside and shed antigens, recombinant viruses carrying tumor antigens, dendritic cells pulsed with antigenic peptides etc. are in clinical trials. Efficacious viral oncolysate vaccines induce the host to mount tumor-specific cytotoxic T-cell response and prevention of relapses is supported by clinical trials. The use of "polyvalent" whole cell vaccines vs. purified or genetically engineered single antigen vaccines is justified as i. only very few single tumor antigens are present in all tumors of a given histological type; and ii. antigen modulation occurs in tumors rendering them resistant to immune attack generated by vaccine against a single antigen. Thus polyvalent vaccines immunize against several antigens vs. against a selected antigen.

Ex vivo delivery of suicide genes into melanoma cells using epidermal growth factor receptor-specific Fab immunogene

The Fab fragment of monoclonal antibody B4G7 against human epidermal growth factor (EGF) receptor was conjugated with cationic poly-L-lysine and the resulting conjugate was further complexed with reporter genes or therapeutic genes. This Fab/DNA complex was designated as "Fab immunogene." The Fab immunogene transfer in vitro was mediated through the EGF receptors in two melanoma cell lines. The frequency of cells expressing beta-galactosidase (beta-Gal) reporter gene was approximately 1%. The induction of suicide effects after Fab immunogene transfer of herpes simplex virus thymidine kinase (TK) or Escherichia coli cytosine deaminase (CD) gene was quite remarkable, and the growth of melanoma cells was inhibited for over 7 days in the presence of ganciclovir (GCV) or 5-fluorocytosine (5-FC). Similarly, when melanoma cells treated in vitro with the Fab immunogene carrying TK or CD were transplanted into the back of nude mouse, subsequent systemic administration of GCV or 5-FC effectively suppressed the growth of tumors, indicating the occurrence of in vivo suicide effects.

Adoptive immunotherapy prevents prostate cancer in a transgenic animal model

Cancer-related mortality can be decreased by prevention, early detection and improved therapies. Although animal models should be used to evaluate the success of cancer therapies, their usefulness is controversial. Many cancer therapies that have cured tumors in mice have not met with similar success when attempted in humans. Current animal models rely mainly on inoculating cell lines into animals, a method that does not reproduce the natural development of the tumor, both for the kinetics of induction and the anatomical site concerned. In this study, we have used an SV40 T-antigen-transgenic mouse model of prostate cancer in which the tumor spontaneously develops orthotopically with a disease progression that closely resembles the progression of human prostate cancer. We have used this model to test the suitability of adoptive cellular immunotherapy. Transfer of naive cells obtained from a T-antigen-negative congenic animal had significant but partial effects: it prevented development of malignant tumors, leaving just minor foci of residual tumor and/or hyperplasia. Adoptive transfer of memory lymphocytes specific for T-antigen, which is a prostatic self antigen in this model, prevented tumor development and progression without affecting the morphology and function of involved tissues. Treated animals were able to breed, and their survival was greatly increased. These results strongly suggest that adoptive immunotherapy should be successful in treating early stages of human prostate cancer.

Down-regulation of HLA class I antigen-processing molecules in malignant melanoma: association with disease progression

Expression of the proteasome subunits LMP2 and LMP7, the MHC-encoded transporter subunits TAP1 and TAP2, and HLA Class I antigens was examined by immunoperoxidase staining in 10 nevi and 98 melanoma lesions (60 primary and 38 metastatic), because these molecules play an important role in the presentation of melanoma-associated peptide antigens to cytotoxic T cells. LMP2 was less frequently expressed than LMP7 in primary and metastatic melanoma lesions. TAP1, TAP2, and HLA Class I antigen expression was more frequently (P < 0.05) down-regulated in metastatic than in primary melanoma lesions and in nevi. A synchronous TAP1, TAP2, and HLA Class I antigen down-regulation was observed in 58% of primary and 52% of metastatic lesions. TAP and HLA Class I antigen down-regulation in primary lesions was significantly associated with lesion thickness, stage of disease, reduced time to disease progression, and reduced survival. These results suggest that TAP down-regulation plays a role in the clinical course of malignant melanoma, probably by providing melanoma cells with a mechanism to escape from cytotoxic T lymphocyte recognition during disease progression.

Identification of New Melanoma Epitopes on Melanosomal Proteins Recognized by Tumor Infiltrating T Lymphocytes Restricted by HLA-A1, -A2, and -A3 Alleles

To isolate melanoma Ags recognized by T cells, cDNA libraries made from melanoma cell lines were screened with four CTLs derived from tumor infiltrating lymphocytes (TIL) that were able to recognize melanoma cells in a HLA-A1, -A2, or -A3 restricted manner. Although cDNAs encoding the previously identified melanoma Ags, tyrosinase and gp100, were isolated, these TIL were found to recognize previously unidentified peptides. An HLA-A1-restricted CTL, TIL1388, was found to recognize a tyrosinase peptide (SSDYVIPIGTY), and an HLA-A3-restricted CTL, TIL1351, recognized a gp100 peptide (LIYRRRLMK). CTL clones isolated from the HLA-A2-restricted TIL1383 recognized a gp100 peptide (RLMKQDFSV). HLA-A2-restricted CTL, TIL1200, recognized a gp100 peptide (RLPRIFCSC). Replacement of either cysteine residue with α-amino butyric acid in the gp100 peptide, RLPRIFCSC, enhanced CTL recognition, suggesting that the peptide epitope naturally presented on the tumor cell surface may contain reduced cysteine residues. Oxidation of these cysteines might have occurred during the course of the synthesis or pulsing of the peptide in culture. These modifications may have important implications for the development of efficient peptide-based vaccines. These newly identified peptide epitopes can extend the ability to perform immunotherapy using synthetic peptides to a broader population of patients, especially those expressing HLA-A1 or HLA-A3 for whom only a few melanoma epitopes have previously been identified.

Mutated Ras peptides as vaccines in immunotherapy of cancer

Mutations in codon 12 and 13 of K-RAS are frequently found in human cancer, including pancreatic- and colorectal adenocarcinomas. T cell responses specific for individual RAS mutations can be elicited in vitro by stimulation with synthetic peptides and in vivo following vaccination with antigen presenting cells pulsed ex vivo with synthetic peptides. The peptide-responding T cells are capable of responding to intact p21 ras, and can recognise and kill tumour cell lines and isolated tumour cells harbouring the corresponding RAS mutation. The responding cells can be of both CD4+ and CD8+ phenotype, and these T cell subsets recognise nested epitopes within the vaccine peptides. Mutant ras peptides are therefore possibly an important vaccine for specific immunotherapy in patients with pancreatic and colorectal carcinomas, and are currently being tested in vivo together with GM-CSF as an adjuvant in these cancer patients.

The susceptibility to natural killer cell-mediated lysis of HLA class I-positive melanomas reflects the expression of insufficient amounts of different HLA class I alleles

NK cells selectively lyse tumor cells which do not express one or more MHC class I alleles. The ability to discriminate between self normal or tumor cells is due to the expression of MHC class I-specific killer inhibitory receptors (KIR). In the present study we analyzed melanoma cell lines which were highly susceptible to NK cell-mediated lysis in spite of the expression of a complete set of HLA class I alleles. Quantitative analysis of the HLA class I expression using allele-specific monoclonal antibodies (mAb) revealed a down-regulation of all HLA class I molecules. Treatment of melanoma cells with IFN-gamma resulted in up-regulation of all HLA class I alleles that was paralleled by the acquisition of resistance to lysis. That resistance to lysis reflected the up-regulation of HLA class I molecules was revealed by the finding that mAb-mediated masking of either KIR or their HLA class I ligands completely restored the melanoma cell lysis. These results were obtained by the use of selected NK cell clones derived either from allogeneic or autologous donors. In addition, similar results were obtained using in vitro expanded autologous NK cell populations. Our data indicate that NK cells can lyse not only melanoma cells which have lost the expression of one or more HLA class I alleles but also cells expressing a decreased amount of class I molecules.

Human Melanoma-Reactive CD4+ and CD8+ CTL Clones Resist Fas Ligand-Induced Apoptosis and Use Fas/Fas Ligand-Independent Mechanisms for Tumor Killing

Tumor cells have been shown recently to escape immune recognition by developing resistance to Fas-mediated apoptosis and acquiring expression of Fas ligand (FasL) molecule that they may use for eliminating activated Fas+ lymphocytes. In this study, we report that tumor-specific T lymphocytes isolated from tumor lesions by repeated in vitro TCR stimulation with relevant Ags (mostly represented by normal self proteins, such as MART-1/Melan A and gp100) can develop strategies for overcoming these escape mechanisms. Melanoma cells (and normal melanocytes) express heterogeneous levels of Fas molecule, but they result homogeneously resistant to Fas-induced apoptosis. However, CD4+ and CD8+ CTL clones kill melanoma cells through Fas/FasL-independent, granule-dependent lytic pathway. In these lymphocytes, Ag/MHC complex interaction with TCR does not lead to functional involvement of FasL, triggered, on the contrary, by T cell activation with nonspecific stimuli such as PMA/ionomycin. Additionally, melanoma cells express significant levels of FasL (detectable on the cell surface only after treatment with metalloprotease inhibitors), although to a lesser extent than professional immune cells such as Th1 clones. Nevertheless, antimelanoma CTL clones resist apoptosis mediated by FasL either in soluble form or expressed by Th1 lymphocytes or FasL+ melanoma cells. These results demonstrate that CD4+ and CD8+ antimelanoma T cell clones can be protected against Fas-dependent apoptosis, and thus be useful reagents of immunotherapeutic strategies aimed to potentiate tumor-specific T cell responses.

Gene therapy for melanoma in humans

As melanoma evolves, it interacts with the immune system. Based on this immunobiology, there are now a number of rationally designed attempts to develop genetically modified melanoma vaccines. This article outlines immunologic and other strategies in gene therapy for melanoma and provides an overview of current clinical trials.

Enhanced tumor protection by granulocyte-macrophage colony-stimulating factor expression at the site of an allogeneic vaccine

Murine tumor models have demonstrated that whole tumor cell vaccines engineered to secrete certain cytokines in a paracrine fashion elicit systemic immune responses capable of eliminating small amounts of established tumor. In particular, autologous tumors that express the cytokine GM-CSF induce potent systemic immune responses against poorly immunogenic murine tumors. However, phase I clinical trials have demonstrated the technical difficulty of routinely expanding primary autologous human tumor cells to the numbers required for vaccination, making the generalization of autologous vaccines impractical. Dissection of the mechanism by which antitumor immunity is generated has demonstrated that GM-CSF recruits professional antigen-presenting cells that act as intermediates in presenting tumor antigen to and activating effector T cells. Furthermore, the identification of commonly recognized murine and human tumor antigens indicates that many are shared rather than unique. These findings would suggest that allogeneic as well as autologous tumor cells can be used as the vaccinating cells for activating antitumor immunity. A major concern in the application of allogeneic vaccines relates to the potential interference of allogeneic MHC expression at the vaccine site with priming of tumor-specific T cell responses. Here we describe a series of experiments that directly examines the effects of allogeneic MHC molecules on the immune-priming capabilities of a whole cell tumor vaccine engineered to secrete GM-CSF. The results demonstrate that the expression of an allogeneic MHC molecule by a vaccine cell can actually enhance the induction of systemic antitumor immunity. In addition, allogeneic MHC expression has no inhibitory effect on the ability of GM-CSF-transduced vaccines to induce systemic antitumor immunity. These findings support the design of clinical trials for testing this more feasible and generalizable allogeneic whole tumor cell vaccine approach.

Immunogenicity of the ALLAVGATK (gp100[17-25]) peptide in HLA-A3.1 melanoma patients

A T cell line recognizing autologous and allogeneic HLA-A3.1 melanomas was obtained from a disease-free melanoma patient (patient 15392). By transfection of a tumor cDNA library and in vitro sensitization experiments, the ALLAVGATK gp100/Mel17-derived peptide was found to be the epitope recognized by this melanoma-specific T cell line. The role of the ALLAVGATK peptide in the systemic immune response to melanoma of this patient was evaluated. When pulsed on the autologous peripheral blood mononuclear cells, the ALLAVGATK peptide generated tumor-specific HLA-A3-restricted T lymphocytes and a single restimulation in vitro was sufficient to raise gp100-specific T lymphocytes, indicating a high frequency of epitope-specific T cells. gp100-specific T cells were also induced from T lymphocytes purified from tumor-invaded lymph nodes (tumor-associated lymphocytes, TAL). TAL-derived effectors displayed lower peptide affinity and lower tumor recognition than effectors elicited from peripheral blood lymphocytes (PBL). To further evaluate its immunogenicity, ALLAVGATK was used to stimulate PBL derived from six additional HLA-A3.1 melanoma patients and seven healthy donors. After 7 weeks of peptide stimulation in vitro the generation of anti-gp100 and tumor-specific T cell lines was achieved in one out of the six patients analyzed. Taken together these data indicate that an in vivo priming leading to a systemic immunity against gp100 in HLA-A3 melanoma patients may occasionally occur and that the immunogenicity of ALLAVGATK peptide in melanoma patients is comparable to that of other HLA-A2-restricted epitopes derived from gp100/Mel 17 protein.