Overlapping epitopes encompassing a point mutation (12 Gly-->Arg) in p21 ras can be recognized by HLA-DR, -DP and -DQ restricted T cells

Prophylactic vaccines against cancers of non-infectious origin: a dream or a real possibility?

The dramatic progress in tumour biology and immunology in the past several years has opened new avenues for the treatment and prevention of cancer. One of the great contributions of the immunotherapeutic approaches is an increasing understanding of the immunology of cancer, which is, gradually creating conditions for the development of prophylactic anti-cancer vaccines. Efficient vaccines have been developed and employed for the prophylaxis of two frequent cancers of viral origin, namely cervical cancer and liver cancer. The new knowledge on the interactions between the immune system and the malignant tumors seems to provide means for the development of prophylactic vaccines against cancers developing due to the mutations in the proto-oncogenes converting their products into oncoproteins. According to the present estimates, these cancers form a great majority of human malignancies. Recent evidence has indicated that the immune system recognizes such mutated proteins, and that the development of cancer is due to the failure of the immune system to eliminate neoplastic cells. Followingly, it can be expected that inducing immunity against the mutated epitopes will increase the capacity of the body to deal with the initiated precancerous cells. In the present paper this hypothesis is primarily discussed in the relationship with colorectal cancer (CRC), which seems to be a well-fitting candidate for prophylactic vaccination. CRC is the third most frequent malignancy and the fourth most common cause of cancer mortality. Mutations of two proto-oncogenes, namely RAS and RAF, are involved in the majority of CRC cases and, in addition, they are shared with other human malignancies. Therefore, the strategy to be used for prophylaxis of CRC is discussed together with several other frequent human cancers, namely lung cancer, pancreatic duct cancer and melanoma. The prophylactic vaccines proposed are aimed at the reduction of the incidence of these and, to a lesser extent, some other cancers.

Post-translational modifications such as citrullination are excellent targets for cancer therapy

Under conditions of cellular stress, proteins can be post-translationally modified causing them to be recognized by the immune system. One such stress-induced post-translational modification (siPTM) is citrullination, the conversion of arginine residues to citrulline by peptidylarginine deiminase (PAD) enzymes. PAD enzymes are activated by millimolar concentrations of calcium which can occur during apoptosis, leading to precipitation of proteins, their subsequent uptake by B cells and stimulation of antibody responses. Detection of anti-citrullinated protein antibodies (ACPAs) is a diagnostic of rheumatoid arthritis (RA), where immune complexes stimulate inflammation around the joints. More recently, autophagy has been shown to play a role in the presentation of citrullinated peptides on MHC class II molecules to CD4⁺ helper T cells, suggesting that citrullination may be a way of alerting immune cells to cellular stress. Additionally, inflammation-induced IFNγ and concomitant MHC class II expression on target cells contributes to immune activation. Stressful conditions in the tumor microenvironment induce autophagy in cancer cells as a pro-survival mechanism. Cancer cells also over express PAD enzymes and in light of this the hypothesis that citrullinated peptides stimulate CD4⁺ T cell responses that would recognize these siPTM's produced during autophagy has been investigated. The induction of potent citrullinated peptide-specific CD4 responses has been shown in both humans and HLA transgenic mouse models. Responses in mouse models resulted in potent anti-tumour responses against tumours expressing either constitutive or IFNγ-inducible MHC class II. The anti-tumour effect relied upon direct recognition of tumours by specific CD4 T cells suggesting that citrullinated peptides are attractive targets for cancer vaccines.

T cell repertoire to citrullinated self-peptides in healthy humans is not confined to the HLA-DR SE alleles; Targeting of citrullinated self-peptides presented by HLA-DP4 for tumour therapy

Post-translational modifications are induced in stressed cells which cause them to be recognised by the system. One such modification is citrullination where the positive charged arginine is modified to a neutral citrulline. We demonstrate most healthy donors show an oligoclonal CD4 response in vitro to at least one citrullinated vimentin or enolase peptide. Unlike rheumatoid arthritis patients, these T cell responses were not restricted by HLA-DRB1 shared epitope (SE) alleles, suggesting they could be presented by other MHC class II alleles. As HLA-DP is less polymorphic than HLA-DR, we investigated whether the common allele, HLA-DP4 could present citrullinated epitopes. The modification of arginine to citrulline enhanced binding of the peptides to HLA-DP4 and induced high-frequency CD4 responses in HLA-DP4 transgenic mouse models. Our previous studies have shown that tumours present citrullinated peptides restricted through HLA-DR4 which are good targets for anti-tumour immunity. In this study, we show that citrullinated vimentin and enolase peptides also induced strong anti-tumour immunity (100% survival, p < 0.0001) against established B16 tumours and against the LLC/2 lung cancer model (p = 0.034) both expressing HLA-DP4. Since most tumours do not constitutively express MHC class II molecules, models were engineered that expressed MHC class II under the control of an IFNγ inducible promoter. Immunisation with citrullinated peptides resulted in 90% survival (p < 0.001) against established B16 HHD tumour expressing IFNγ inducible DP4. These studies show that citrullinated peptides can be presented by a range of MHC class II molecules, including for the first time HLA-DP4, and are strong targets for anti-tumour immunity.

Immunotherapy: Pancreatic Cancer and Extrahepatic Biliary Tract Cancer

Pancreatic ductal adenocarcinoma (PDAC) and extrahepatic biliary tract cancer (BTC) are among the malignancies with the highest morbidity and mortality. Despite increasing knowledge on biology and novel therapies, outcome remains poor in these patients. Recent progress in immunotherapies created new hopes in the treatment of PDAC and extrahepatic BTC. Several trials tested immunotherapies in various therapeutic situations as monotherapies or in combinations. Although responses were seen in some of the trials, the value of immunotherapy in PDAC and extrahepatic BTC remains unclear in the current situation, especially regarding the complex biological characteristics with a high stroma component, intrinsic resistance mechanisms and an immunosuppressive, hypoxic microenvironment. These major hurdles have to be taken into account and overcome if immunotherapies should be successful in these tumor entities. Thereby, combinational approaches that allow on the one hand targeted therapy and on the other restore or boost the function of immune cells are promising.

Long-peptide vaccination with driver gene mutations in p53 and Kras induces cancer mutation-specific effector as well as regulatory T cell responses

Mutated proteins arising from somatic mutations in tumors are promising targets for cancer immunotherapy. They represent true tumor-specific antigens (TSAs) as they are exclusively expressed in tumors, reduce the risk of autoimmunity and are more likely to overcome tolerance compared to wild-type (wt) sequences. Hence, we designed a panel of long peptides (LPs, 28–35 aa) comprising driver gene mutations in TP35 and KRAS frequently found in gastrointestinal tumors to test their combined immunotherapeutic potential. We found increased numbers of T cells responsive against respective mutated and wt peptides in colorectal cancer patients that carry the tested mutations in their tumors than patients with other mutations. Further, active immunization of HLA(-A2/DR1)-humanized mice with mixes of the same mutated LPs yielded simultaneous, polyvalent CD8⁺/CD4⁺ T cell responses against the majority of peptides. Peptide-specific T cells possessed a multifunctional cytokine profile with CD4⁺ T cells showing a T_H1-like phenotype. Two mutated peptides (Kras[G12V], p53[R248W]) induced significantly higher T cell responses than corresponding wt sequences and comprised HLA-A2/DR1-restricted mutated epitopes. However, vaccination with the same highly immunogenic LPs strongly increased systemic regulatory T cells (T_reg) numbers in a syngeneic sarcoma model over-expressing these mutated protein variants and resulted in accelerated tumor outgrowth. In contrast, tumor outgrowth was delayed when vaccination was directed against tumor-intrinsic Kras/Tp53 mutations of lower immunogenicity. Conclusively, we show that LP vaccination targeting multiple mutated TSAs elicits polyvalent, multifunctional, and mutation-specific effector T cells capable of targeting tumors. However, the success of this therapeutic approach can be hampered by vaccination-induced, TSA-specific T_regs.

Cancer immunotherapy targeting neoantigens

Neoantigens are antigens encoded by tumor-specific mutated genes. Studies in the past few years have suggested a key role for neoantigens in cancer immunotherapy. Here we review the discoveries of neoantigens in the past two decades and the current advances in neoantigen identification. We also discuss the potential benefits and obstacles to the development of effective cancer immunotherapies targeting neoantigens.

Therapeutic options for the management of pancreatic cancer

Since its initial characterization, pancreatic ductal adenocarcinoma has remained one of the most devastating and difficult cancers to treat. Pancreatic cancer is the fourth leading cause of death in the United States, resulting in an estimated 38460 deaths annually. With few screening tools available to detect this disease at an early stage, 94% of patients will die within five years of diagnosis. Despite decades of research that have led to a better understanding of the molecular and cellular signaling pathways in pancreatic cancer cells, few effective therapies have been developed to target these pathways. Other treatment options have included more sophisticated pancreatic cancer surgeries and combination therapies. While outcomes have improved modestly for these patients, more effective treatments are desperately needed. One of the greatest challenges in the future of treating this malignancy will be to develop therapies that target the tumor microenvironment and surrounding pancreatic cancer stem cells in addition to pancreatic cancer cells. Recent advances in targeting pancreatic stellate cells and the stroma have encouraged researchers to shift their focus to the role of desmoplasia in pancreatic cancer pathobiology in the hopes of developing newer-generation therapies. By combining novel agents with current cytotoxic chemotherapies and radiation therapy and personalizing them to each patient based on specific biomarkers, the goal of prolonging a patient’s life could be achieved. Here we review the most effective therapies that have been used for the treatment of pancreatic cancer and discuss the future potential of therapeutic options.

Phase II study of the GI-4000 KRAS vaccine after curative therapy in patients with stage I-III lung adenocarcinoma harboring a KRAS G12C, G12D, or G12V mutation

INTRODUCTION

Patients with early-stage lung cancer have a high risk of recurrence despite multimodality therapy. KRAS-mutant lung adenocarcinomas are the largest genetically defined subgroup, representing 25% of patients. GI-4000 is a heat-killed recombinant Saccharomyces cerevisiae yeast-derived vaccine expressing mutant KRAS proteins. The present phase II study assessed the feasibility, immunogenicity, and safety of the GI-4000 vaccine in patients with early-stage, KRAS-mutant lung cancer.

MATERIALS AND METHODS

Patients with stage I-III KRAS-mutant lung cancer who completed curative therapy were enrolled. The patients received the genotype matched GI-4000 vaccine for ≤ 3 years or until intolerance, disease recurrence, or death. The KRAS antigen T-cell response was assessed using the interferon-gamma enzyme-linked immunospot assay in peripheral blood mononuclear cells. The study was powered to detect an immune response in ≥ 25% of patients.

RESULTS

A total of 24 patients were enrolled over 28 months. No vaccine-related serious adverse events occurred. One patient withdrew consent because of pain at the injection site. The study met its primary endpoint, with 50% of patients developing an immune response to mutant KRAS. The median number of vaccinations received was 15 (range, 1-19). Ten patients experienced disease recurrence, and 6 died. Compared with the genotypically matched historical controls, the recurrence rates were equivalent but overall survival showed a favorable trend.

CONCLUSION

GI-4000 was well tolerated and immunogenic when used as consolidation therapy in patients with stage I-III KRAS-mutant lung cancer. The patterns of recurrence and death observed in the present study can be used to design a randomized study of GI-4000 with overall survival as the primary endpoint.

RNA vaccines in cancer treatment

The Cancer Report from the World Health Organization states that in the year 2000 12% of all death cases worldwide were caused by cancer. In the western world, the cancer death rates are often devastating, being at about 25%. This fact stresses the urgency to find effective cures against malignant diseases. New approaches in the treatment of cancer focus on the development of immunotherapies to fight the disease. Besides other methods, the usage of tumor-specific RNA as part of vaccines is investigated lately. RNA, administered alone or used for transfection of dendritic cells, shows several advantages as a vaccine including feasibility, applicability, safeness, and effectiveness when it comes to the generation of immune responses. This review concentrates on results from in vitro experiments and recent trials using RNA vaccines to present an overview about this specific strategy.

Five HLA-DP molecules frequently expressed in the worldwide human population share a common HLA supertypic binding specificity

Compared with DR and DQ, knowledge of the binding repertoires and specificities of HLA-DP alleles is somewhat limited. However, a growing body of literature has indicated the importance of DP-restricted responses in the context of cancer, allergy, and infectious disease. In the current study, we developed high-throughput binding assays for the five most common HLA-DPB1 alleles in the general worldwide population. Using these assays on a comprehensive panel of single-substitution analogs and large peptide libraries, we derived novel detailed binding motifs for DPB1*0101 and DPB1*0501. We also derived more detailed quantitative motifs for DPB1*0201, DPB1*0401, and DPB1*0402, which were previously characterized on the basis of sets of eluted ligands and/or limited sets of substituted peptides. Unexpectedly, all five DP molecules, originally selected only on the basis of their frequency in human populations, were found to share largely overlapping peptide motifs. Testing panels of known DP epitopes and a panel of peptides spanning a set of Phleum pratense Ags revealed that these molecules also share largely overlapping peptide-binding repertoires. This demonstrates that a previously hypothesized DP supertype extends far beyond what was originally envisioned and includes at least three additional very common DP specificities. Taken together, these DP supertype molecules are found in >90% of the human population. Thus, these findings have important implications for epitope-identification studies and monitoring of human class II-restricted immune responses.

Unconventional cytokine profiles and development of T cell memory in long-term survivors after cancer vaccination

Cancer vaccine trials frequently report on immunological responses, without any clinical benefit. This paradox may reflect the challenge of discriminating between effective and pointless immune responses and sparse knowledge on their long-term development. Here, we have analyzed T cell responses in long-term survivors after peptide vaccination. There were three main study aims: (1) to characterize the immune response in patients with a possible clinical benefit. (2) To analyze the long-term development of responses and effects of booster vaccination. (3) To investigate whether the Th1/Th2-delineation applies to cancer vaccine responses. T cell clones were generated from all nine patients studied. We find that surviving patients harbor durable tumor-specific responses against vaccine antigens from telomerase, RAS or TGFbeta receptor II. Analyses of consecutive samples suggest that booster vaccination is required to induce robust T cell memory. The responses exhibit several features of possible clinical advantage, including combined T-helper and cytotoxic functionality, recognition of naturally processed antigens and diverse HLA-restriction and fine-specificity. CD4(-)CD8(-) T cell clones display unconventional cytotoxicity and specifically kill tumor cells expressing mutated TGFbeta receptor II. Cytokine profiling on the long-term survivors demonstrates high IFN gamma/IL10-ratios, favoring immunity over tolerance, and secretion of multiple chemokines likely to mobilize the innate and adaptive immune system. Interestingly, these pro-inflammatory cytokine profiles do not follow a Th1/Th2-delineation. Most IFN gamma(high)/IL4(low)/IL10(low) cultures include high concentrations of hallmark Th2-cytokines IL-5 and IL-13. This does not reflect a mixture of Th1- and Th2-clones, but applies to 19/20 T cell clones confirmed to be monoclonal through TCR clonotype mapping. The present study identifies several factors that may promote clinical efficacy and suggests that cytokine profiling should not rely on the Th1/Th2-paradigm, but assess the overall inflammatory milieu and the balance between key cytokines.

Cancer vaccine development

A new era involving the evaluation of recombinant cancer vaccines has begun with the concurrent emergence of insights and technologies in the fields of molecular biology and immunology. These advances include: The identification and cloning of an array of genes associated with the neoplastic process, such as oncogenes, suppressor genes, genes encoding oncofoetal antigens and tissue-lineage determinants. The development of a variety of viral and bacterial vectors to deliver and present gene products. The identification of numerous T-cell costimulatory molecules and an understanding of their mode of action. The cloning and analysis of the modes of action of an array of cytokines and other immunomodulatory molecules. More sophisticated knowledge of the mode(s) of antigen presentation and T-cell activation. One current challenge in cancer therapy is the delineation of strategies toward the rational design and implementation of recombinant vaccines that will be of therapeutic benefit to cancer patients and/or members of groups at high risk for specific neoplasias. Numerous concepts are emerging in this regard. The study of immunologic intervention using laboratory animal models demonstrates that no one approach will prevail for all cancer types or, perhaps, for the various stages of the neoplastic process of a given tumour type. The immunological role(s) of CD8+, CD4+, natural killer and other cell types, as well as the roles of antibodies, must all be taken into consideration. This article reviews some of the strategies currently undergoing evaluation toward the development of recombinant vaccines for several carcinoma types.

Specific T-cell immunity against Ki-ras peptides in patients with pancreatic and colorectal cancers

Mutations of codon 12 in the Ki-ras gene are frequently found in pancreatic and colorectal cancers. It has been demonstrated that human T-cells have the potential to recognise tumours expressing mutated ras-derived peptides. However, it remains unclear whether T-cells from a given individual can recognise the mutant peptides, which are expressed in that individual's tumour tissues. Mutations of the Ki-ras oncogene were analysed by the mutant-allele-specific amplification (MASA) method in pancreatic and colorectal tumour tissues, and T-cell responses against mutated Ki-ras-derived peptides were measured by [(3)H]thymidine incorporation and IFN-gamma production assays. Specific T-cell responses against Ki-ras-products were found in cancer patients, whereas no immune response was observed in normal individuals (P<0.01). Six of the eight pancreatic cancer patients (75%) and nine of 26 colorectal cancer patients (35%) had T-cell responses to mutated Ki-ras-derived-peptides. T-cell response in a given individual cannot recognise the same mutated ras peptide, which is expressed in that individual's tumour tissues. However, pancreatic and colorectal cancer patients have T-cell immunity against Ki-ras-peptides, and this provides potential target for cancer immunotherapy.

Specific immunotherapy of cancer in elderly patients

The concept of immunotherapy of cancer is more than a century old, but only recently have molecularly defined therapeutic approaches been developed. In this review, we focus on the most promising approach, active therapeutic vaccination. The identification of tumour antigens can now be accelerated by methods allowing the amplification of gene products selectively or preferentially transcribed in the tumour. However, determining the potential immunogenicity of such gene products remains a demanding task, since major histocompatibility complex (MHC) restriction of T cells implies that for any newly defined antigen, immunogenicity will have to be defined for any individual MHC haplotype. Tumour-derived peptides eluted from MHC molecules of tumour tissue are also a promising source of antigen. Tumour antigens are mostly of weak immunogenicity, because the vast majority are tumour-associated differentiation antigens already 'seen' by the patient's immune system. Effective therapeutic vaccination will thus require adjuvant support, possibly by new approaches to immunomodulation such as bispecific antibodies or antibody-cytokine fusion proteins. Tumour-specific antigens, which could be a more potent target for immunotherapy, mostly arise by point mutations and have the disadvantage of being not only tumour-specific, but also individual-specific. Therapeutic vaccination will probably focus on defined antigens offered as protein, peptide or nucleic acid. Irrespective of the form in which the antigen is applied, emphasis will be given to the activation of dendritic cells as professional antigen presenters. Dendritic cells may be loaded in vitro with antigen, or, alternatively, initiation of an immune response may be approached in vivo by vaccination with RNA or DNA, given as such or packed into attenuated bacteria. The importance of activation of T helper cells has only recently been taken into account in cancer vaccination. Activation of cytotoxic T cells is facilitated by the provision of T helper cell-derived cytokines. T helper cell-dependent recruitment of elements of non-adaptive defence, such as leucocytes, natural killer cells and monocytes, is of particular importance when the tumour has lost MHC class I expression. Barriers to successful therapeutic vaccination include: (i) the escape mechanisms developed by tumour cells in response to immune attack; (ii) tolerance or anergy of the evoked immune response; (iii) the theoretical possibility of provoking an autoimmune reaction by vaccination against tumour-associated antigens; and (iv) the advanced age of many patients, implying reduced responsiveness of the senescent immune system.

Frameshift-mutation-derived peptides as tumor-specific antigens in inherited and spontaneous colorectal cancer

The functional role and specificity of tumor infiltrating lymphocytes (TIL) is generally not well characterized. Prominent lymphocyte infiltration is the hallmark of the most common form of hereditary colon cancer, hereditary nonpolyposis colon cancer (HNPCC) and the corresponding spontaneous colon cancers with the microsatellite instability (MSI) phenotype. These cancers are caused by inherited or acquired defects in the DNA mismatch-repair machinery. The molecular mechanism behind the MSI phenotype provides a clue to understanding the lymphocyte reaction by allowing reliable prediction of potential T cell epitopes created by frameshift mutations in candidate genes carrying nucleotide repeat sequences, such as TGF beta RII and BAX. These tumors therefore represent an interesting human system for studying TIL and characterizing tumor-specific T cells. We here describe T cell reactivity against several T helper cell epitopes, representing a common frameshift mutation in TGF beta RII, in TIL and peripheral blood lymphocytes from patients with MSI(+) tumors. The peptide SLVRLSSCVPVALMSAMTTSSSQ was recognized by T cells from two of three patients with spontaneous MSI(+) colon cancers and from all three patients with HNPCC. Because such mutations are present in 90% of cancers within this patient group, these newly characterized epitopes provide attractive targets for cancer vaccines, including a prophylactic vaccine for individuals carrying a genetic disposition for developing HNPCC.

Successful induction of immune responses against mutant ras in melanoma patients using intradermal injection of peptides and GM-CSF as adjuvant

The rapidly increasing incidence and mortality rate of malignant melanoma, together with the lack of efficient treatment of the late stages, makes it a serious threat to public health. Innovative new treatments are needed. The proteins of the ras-family of proto-oncogenes, functioning as relay switches for signalling pathways between cell surface and nucleus, are involved in cell proliferation, differentiation, apoptosis and transformation. If over-expressed or mutated they can induce and/or maintain a transformed state of a cell. Codon 61 mutations of N-ras seem to be involved in melanoma development on sun exposed sites. In order to induce an immune response towards mutated N-ras proteins we performed a phase 1 feasibility study. Ten melanoma patients were immunized intradermally 6 times with N-ras peptides (residue 49-73) with 4 codon 61 mutations using GM-CSF as adjuvant. HLA typing was not used as an inclusion criterion. Eight patients responded with strong delayed type hypersensitivity reactions. In 2 of the patients an in vitro response to the vaccine could also be detected. The specificity of the reaction could be confirmed by cloning of peptide-specific CD4 positive T cells from peripheral blood of the patients. Intradermal injection of ras peptides using GM-CSF as adjuvant is simple to perform and seems to be efficient in inducing cellular immune responses. Since a majority of the patients showed positive skin reactions and 2 of the patients analysed showed a T-helper response to this melanoma specific antigen, these promiscuous HLA class II binding mutant ras peptides may be candidates for inclusion into vaccine cocktails containing various established CTL epitopes.

Intradermal ras peptide vaccination with granulocyte-macrophage colony-stimulating factor as adjuvant: Clinical and immunological responses in patients with pancreatic adenocarcinoma

K-RAS mutations are frequently found in adenocarcinomas of the pancreas, and induction of immunity against mutant ras can therefore be of possible clinical benefit in patients with pancreatic cancer. We present data from a clinical phase I/II trial involving patients with adenocarcinoma of the pancreas vaccinated by i.d. injection of synthetic mutant ras peptides in combination with granulocyte-macrophage colony-stimulating factor. Forty-eight patients (10 surgically resected and 38 with advanced disease) were treated on an outpatient basis. Peptide-specific immunity was induced in 25 of 43 (58%) evaluable patients, indicating that the protocol used is very potent and capable of eliciting immune responses even in patients with end-stage disease. Patients followed-up for longer periods showed evidence of induction of long-lived immunological memory against the ras mutations. CD4(+) T cells reactive with an Arg12 mutation also present in the tumor could be isolated from a tumor biopsy, demonstrating that activated, ras-specific T cells were able to selectively accumulate in the tumor. Vaccination was well tolerated in all patients. Patients with advanced cancer demonstrating an immune response to the peptide vaccine showed prolonged survival from the start of treatment compared to non-responders (median survival 148 days vs. 61 days, respectively; p = 0.0002). Although a limited number of patients were included in our study, the association between prolonged survival and an immune response against the vaccine suggests that a clinical benefit of ras peptide vaccination may be obtained for this group of patients.

Molecular technology and pancreatic cancer

BACKGROUND

Pancreatic cancer is the fifth leading cause of cancer death in the Western world. Despite improvement in operative mortality rates, little impact has been made on overall 5-year survival. This review discusses the molecular changes peculiar to pancreatic cancer and how the use of molecular technology might affect detection, screening, diagnosis and treatment of the disease.

METHODS

A literature review was performed using the National Library of Medicine's Pubmed database; this was combined with ongoing work within the Queen Elizabeth Hospital, Birmingham.

RESULTS

Over the past 20 years great strides have been made in our understanding of the molecular basis of disease. Advances in molecular biology are now reshaping how diseases are screened for, diagnosed, investigated and treated. In recent years collaboration between clinicians and basic scientists has revealed a unique pattern of genetic and molecular events in pancreatic cancer. This review discusses how these advances may impact on patients with this disease.

CONCLUSION

The past decade has seen some improvement in outlook for patients with pancreatic cancer, but the 'molecular age' promises to deliver even better results.

Enhanced growth of primary tumors in cancer-prone mice after immunization against the mutant region of an inherited oncoprotein

One major objective of tumor immunologists is to prevent cancer development in individuals at high risk. (TG.AC x C57BL/6)F1 mice serve as a model for testing the feasibility of this objective. The mice carry in the germline a mutant ras oncogene that has an arginine at codon 12 instead of glycine present in the wild-type, and after physical (wounding) or chemical promotion, these mice have a high probability for developing papillomas that progress to cancer. Furthermore, F1 mice immunized with Arg(12) mutant ras peptide in complete Freund's adjuvant (CFA) develop T cells within 10 d that proliferate in vitro on stimulation with the Arg(12) mutant ras peptide. Within 14 d, these mice have delayed-type hypersensitivity to the peptide. Immunization with CFA alone or with a different Arg(12) mutant ras peptide in CFA induced neither response. To determine the effect of immunization on development of tumors, mice immunized 3 wk earlier were painted on the back with phorbol 12-myristate 13-acetate every 3 d for 8 wk. The time of appearance and the number of papillomas were about the same in immunized and control mice, but the tumors grew faster and became much larger in the mice immunized with the Arg(12) mutant ras peptide. Thus, the immunization failed to protect against growth of papillomas. The peptide-induced CD4(+) T cells preferentially recognized the peptide but not the native mutant ras protein. On the other hand, mice immunized with Arg(12) mutant ras peptide and bearing papillomas had serum antibodies that did bind native mutant ras protein. Together, these studies indicate that active immunization of cancer-prone individuals may result in immune responses that fail to eradicate mutant oncogene-expressing tumor cells, but rather induce a remarkable enhancement of tumor growth.

Cancer therapy: new concepts on active immunization

There is increasing evidence that tumors express putative target molecules for a therapeutic immune reaction. Yet, tumor cells lack the prerequisites for appropriate antigen presentation and--hence--the immune system does not respond. This difficulty can probably be circumvented when tumor antigens are processed by conventional antigen presenting cells. Thus, the identification of immunogenic tumor-associated antigens may allow new modes of vaccination with the hope of adding a fourth and hopefully powerful weapon to surgery, radiation and chemotherapy in the fight against cancer.

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.

Identification of a human CD8+ T lymphocyte neo-epitope created by a ras codon 12 mutation which is restricted by the HLA-A2 allele

Point mutations in the ras proto-oncogenes, notably at codon 12, are found in high frequency of human malignancies and, thus, may be appropriate targets for the induction of tumor-specific T cell responses in cancer immunotherapy. In this study, we examined the mutant ras protein sequence reflecting the substitution of Gly to Val at position 12 as a putative point-mutated determinant for potential induction of an HLA-A2-reactive, CD8+ cytotoxic T lymphocyte (CTL) response. We identified the ras 4-12(Val12) sequence as a minimal 9-mer peptide, which displayed specific binding to HLA-A2 by T2 bioassays. Peptide binding to HLA-A2 on T2 cells was weak and required coincubation with exogenous beta(2)-microglobulin to facilitate and enhance complex formation. In contrast, the wild-type ras 4-12(Gly12) peptide failed to bind to HLA-A2 even in the presence of beta(2)-microglobulin, consistent with the hypothesis that the point mutation creates a C-terminus anchor residue. A CD8+ CTL line against the ras 4-12(Val12) peptide was derived in vitro from a normal HLA-A2+ donor using a model culture system consisting of T2 cells as antigen presenting cells pulsed with exogenous mutant ras peptide and beta(2)-microglobulin plus cytokines (interleukin-2 and 12). Functional characterization of CD8+ CTL line revealed (1) peptide-specific and HLA-A2-restricted cytotoxicity against a panel of peptide-pulsed targets; (2) no specific lysis using the normal ras peptide sequence; (3) half-maximal lysis with exogenous peptide of approximately 0.3 microM; (4) lysis of HLA-A2+ B cell lines infected with a recombinant vaccinia virus construct encoding the point-mutated human K-ras gene; and (5) specific lysis of the HLA-A2+ SW480 colon carcinoma cell line expressing the naturally occurring K-ras Val12 mutation. Maximal lysis of SW480 cells occurred following interferon (IFN)-gamma pretreatment, which correlated with enhanced HLA-A2 and ICAM-1 (CD54) expression. Specificity of lysis was revealed by the absence of lysis against a HLA-A2+ melanoma cell line (+/- IFN-gamma), which lacked the mutant Val12 mutation, and the inability of an irrelevant CD8+ CTL line to lyse SW480 (+/- IFN-gamma) unless the appropriate exogenous peptide was added. These findings demonstrated that tumor cells may endogenously process and express mutant ras epitopes, such as the 4-12(Val12) sequence, albeit in limiting amounts that may be potentiated by IFN-gamma treatment. These data support the biological relevance of this sequence and, thus, may have important implications for the generation of ras oncogene-specific CTL responses in clinical situations.

Generation of stable CD4+ and CD8+ T cell lines from patients immunized with ras oncogene-derived peptides reflecting codon 12 mutations

Previous studies have identified and characterized both murine in vivo and human in vitro T cell responses reflecting specific mutations in the ras proto-oncogenes at codon 12, 13, or 61. In an attempt to determine whether peptide epitopes reflecting point mutations in the ras oncogenes are immunogenic in humans for the production of CD4+ and/or CD8+ T cell responses, a phase I clinical trial was initiated in metastatic carcinoma patients whose primary tumors harbor mutations in the K-ras proto-oncogenes at codon 12. The peptides used here as immunogens, which were administered in Detox adjuvant, spanned the ras sequence 5-17 and reflected the amino acid substitution of glycine (Gly) at position 12 to aspartic acid (Asp), cysteine (Cys), or valine (Val). Three of eight evaluable patients have demonstrated peptide-specific cell-mediated immunity, as determined by the production of T cell lines resulting from the vaccination. First, an antigen (Ag)-specific, major histocompatibility complex (MHC) class II (DP)-restricted CD4+ T cell line was established in vitro from postvaccination lymphocytes of a non-small cell lung carcinoma patient whose primary tumor contained a Cys12 mutation when cultured on the immunizing peptide. Moreover, CD4+ proliferation was inducible against the corresponding mutant K-ras protein, suggesting productive T cell receptor recognition of exogenously processed Ag. Second, an Ag-specific, MHC class I (HLA-A2)-restricted CD8+ cytotoxic T lymphocyte (CTL) line was established in vitro from postvaccination lymphocytes of a colon carcinoma patient whose primary tumor contained an Asp12 mutation. To that end, a 10-mer peptide, nested within the 13-mer immunizing peptide, was identified [i.e., ras5-14(Asp12)], which was shown to bind to HLA-A2 and display specific functional capacity for expansion of the in vivo primed CD8+ CTL precursors. Third, both Ag-specific, MHC class II (DQ)-restricted CD4+ and MHC class I-restricted (HLA-A2) CD8+ T cell lines were generated from a single patient with duodenal carcinoma whose primary tumor contained a Val12 mutation when cultured on the immunizing 13-mer peptide or a nested 10-mer peptide [i.e., ras5-14(Val12)], respectively. Evidence is thus provided that vaccination with mutant ras oncogene peptides in adjuvant may induce specific anti-ras cellular immune responses, with no detectable cross-reactivity toward normal proto-ras sequences. Moreover, we have identified for the first time human HLA-A2-restricted, CD8+ CTL epitopes reflecting specific point mutations in the K-ras oncogenes at codon 12 which, in concert with the activation of the CD4+ T cell response, may have important implications for both active and passive immunotherapies in selected cancer patients.

Augmentation of immune response by an analog of the antigenic peptide in a human T-cell clone recognizing mutated Ras-derived peptides

T-cells that recognize mutated p21 Ras are relevant to immune surveillance systems against cancer. We report here evidence that immune responses of a T-cell clone recognizing mutated p21 Ras can be augmented by an analog peptide. Using spleen cells from a gastric cancer patient, we established the CD4+ alpha beta Th1-like clone C27 that recognizes wild-type (3EYKLVVVGAGGVGKS17) and mutated p21 Ras protein molecules and peptides, in an HLA-DR1-restricted manner. C27 responded prominently to mutated Ras peptides carrying Val or Ala at position 12, as compared to wild-type and other mutated peptides. C27 also exhibited a much stronger response to a mutated p21 Ras whole-protein molecule-carrying Val at position 12, as compared with the wild-type protein. The proliferative response and production of GM-CSF, TNF-alpha, and IFN-gamma by C27 were further augmented by replacing the possible first DR anchor 4Tyr of the mutated Ras peptide with Trp, a more potent anchor residue for the DR1 molecule. Enhancement of peptide antigenicity by substituting the HLA anchor residue of an antigenic peptide recognized by tumor-reactive T-cells may prove to be a novel strategy for antigen-specific cancer immunotherapy.

Characterisation of immune responses in pancreatic carcinoma patients after mutant p21 ras peptide vaccination

This is a study of immune responses generated by mutant ras peptide vaccination of patients with pancreatic adenocarcinoma. Responding T cells from one patient were cloned and two CD4+ T-lymphocyte clones (TLC) specific for the 12 Val peptide and restricted by HLA-DR6 or DQ2 were obtained. These class II molecules have not previously been found to bind or present mutant ras peptides to T cells. The DR6-restricted TLC showed marked cytotoxicity against autologous target cells pulsed with the 12 Val peptide. Target cells pulsed with the control peptide were not killed. Responding T cells from another patient showed cross-reactivity towards the homologous ras peptides. Investigation by limiting dilution analysis (LDA) revealed different T-cell precursor frequencies for the immunising, mutant ras peptide (1:28000), compared with the normal ras peptide (1:110000).

Ex vivo ras peptide vaccination in patients with advanced pancreatic cancer: results of a phase I/II study

In a pilot I/II study we have tested synthetic ras peptides used as a cancer vaccine in 5 patients with advanced pancreatic carcinoma. The treatment principle used was based on loading professional antigen-presenting cells (APCs) from peripheral blood with a synthetic ras peptide corresponding to the ras mutation found in tumour tissue from the patient. Peptide loading was performed ex vivo and the next day APCs were re-injected into the patients after washing to remove unbound peptide. Patients were vaccinated in the first and second week and thereafter every 4-6 weeks. In 2 of the 5 patients treated, an immune response against the immunising ras peptide could be induced. None of the patients showed evidence of a T-cell response against any of the ras peptides before vaccination. The treatment was well tolerated and could be repeated multiple times in the same patient. Side effects were not observed even if an immunological response against the ras peptide was evident. We conclude that ras peptide vaccination according to the present protocol is safe and may result in a potentially beneficial immune response even in patients with advanced malignant disease.

Identification of two epitopes on the dengue 4 virus capsid protein recognized by a serotype-specific and a panel of serotype-cross-reactive human CD4+ cytotoxic T-lymphocyte clones

We analyzed the CD4+ T-lymphocyte response of a donor who had received an experimental live-attenuated dengue 4 virus (D4V) vaccine. Bulk culture proliferative responses of peripheral blood mononuclear cells (PBMC) to noninfectious dengue virus (DV) antigens showed the highest proliferation to D4V antigen, with lesser, cross-reactive proliferation to D2V antigen. We established CD4+ cytotoxic T-lymphocyte clones (CTL) by stimulation with D4 antigen. Using recombinant baculovirus antigens, we identified seven CTL clones that recognized D4V capsid protein. Six of these CTL clones were cross-reactive between D2 and D4, and one clone was specific for D4. Using synthetic peptides, we found that the D4V-specific CTL clone recognized an epitope between amino acids (aa) 47 and 55 of the capsid protein, while the cross-reactive CTL clones each recognized epitopes in a separate location, between aa 83 and 92, which is conserved between D2V and D4V. This region of the capsid protein induced a variety of CD4+ T-cell responses, as indicated by the fact that six clones which recognized a peptide spanning this region showed heterogeneity in their recognition of truncations of this same peptide. The bulk culture response of the donor's PBMC to the epitope peptide spanning aa 84 to 92 was also examined. Peptides containing this epitope induced proliferation of the donor's PBMC in bulk culture, but peptides not containing the entire epitope did not induce proliferation. Also, PBMC stimulated in bulk culture with noninfectious D4V antigen lysed autologous target cells pulsed with peptides containing aa 84 to 92. These results indicate that this donor exhibits memory CD4+ T-cell responses directed against the DV capsid protein and suggest that the response to the capsid protein is dominant not only in vitro at the clonal level but in bulk culture responses as well. Since previous studies have indicated that the CTL responses to DV infection seem to be directed mainly against the envelope (E) and NS3 proteins, these results are the first to indicate that the DV capsid protein is also a target of the antiviral T-cell response.

Polymorphic structural features of modelled HLA-DQ molecules segregate according to susceptibility or resistance to IDDM

The structural features of HLA-DQ alleles which are susceptible and resistant to insulin-dependent diabetes mellitus (IDDM) have been examined using a model of their three-dimensional structure obtained by energy minimisation, based on the published structure of HLA-DR1. The model shows DQ molecules to have an overall shape nearly identical to that of DR molecules, but with significant differences in the fine structure: 1) the antigen-binding groove of DQ molecules has a polymorphic first pocket; this pocket can be either amphiphilic or hydrophilic, 2) The beta 49-56 dimerisation domain of DQ is polymorphic: hydrophobic, or amphiphilic, or hydrophilic and positively charged, leading to spontaneous or T-cell receptor-induced homodimer formation, or T-cell receptor-induced homodimer formation, or difficulty of the formation of such dimers, respectively; 3) a prominent Arg-Gly-Asp loop is formed by some DQ alleles (beta 167-169) and probably functions in cell adhesion. There are also small differences in the residues and sequences implicated in CD4 binding (mostly in DQ beta 134-148) but the significance of these differences cannot be evaluated at present. All seven DQ alleles which confer susceptibility to IDDM possess a hydrophilic first pocket in the antigen-binding groove, a hydrophobic or amphiphilic beta 49-56 dimerisation patch that allows for spontaneous or T-cell receptor-induced dimerisation, and the Arg-Gly-Asp loop. By contrast, in the protective alleles at least one of these three features is absent. This segregation of phenotypes according to susceptibility or resistance can well explain the model of tighter autoantigen binding by the protective alleles compared to the susceptible alleles, previously proposed for the pathogenesis of IDDM.

A human melanoma cell line, recognized by both HLA class I and class II restricted T cells, is capable of initiating both primary and secondary immune responses

We have characterized a melanoma cell line, FM3, established from a metastasis of a 75 year old female patient (HLA-A2, HLA-DQ7) with malignant melanoma. This cell line expresses both HLA class I and class II antigens, as well as several important accessory molecules at high levels. FM3 cells were shown to function as a stimulator of both allogeneic as well as autologous mixed lymphocyte tumour cell culture (MLTC). From these autologous MLTC we were able to generate cytotoxic T cell clones indicating that FM3 is capable of processing and presenting endogenous antigens. We have used this cell line in a model system to investigate whether these cells were able to initiate and support an immune response with specificity for selected peptide antigens. The FM3 cell line was capable of presenting a HLA-DQ7 restricted ras derived peptide (5-21, 13Gly- >Asp) to a previously established T cell clone, RM70. The ability of FM3 to function as an antigen presenting cell (APC) was comparable to that of an autologous Epstein Barr virus (EBV) transformed B cell line. The CD4+ T cell clone RM70 showed a peptide-specific anti-proliferative effect on FM3 cells. This growth inhibition was not due to cytotoxicity as measured in a standard 4 h chromium release assay. The FM3 cell line also presented a HLA-A2 restricted nonapeptide derived from the influenza matrix protein, M1(58-66) to a CD8+ T cell line specific for this peptide. This resulted in an effective killing of the melanoma cells. Together, these data suggest that some melanomas may initiate an immune response by presenting their own specific antigens in an immunogenic context, and subsequently serve as targets for T cells of both the CD4+ and CD8+ phenotype.

CD8+ T cells from a patient with colon carcinoma, specific for a mutant p21-Ras-derived peptide (Gly13-->Asp), are cytotoxic towards a carcinoma cell line harbouring the same mutation

Several T lymphocyte clones (TLC), specific for a p21-Ras-derived peptide expressing a Gly13-->Asp mutation and of the CD8+ subtype, were generated from peripheral blood of a colon carcinoma patient. The TLC exerted cytotoxicity against an interferon-gamma (IFN gamma)-pretreated colon carcinoma cell line, HCT116, which harbours the Gly13-->Asp mutation and shares both HLA-A2 and HLA-B12(44) with the patient. This cytotoxic effect could be blocked by a monoclonal antibody (mAb) against CD8 molecules, as well as with a mAb against HLA class I molecules and a polyclonal antiserum against HLA-B12, identifying B12(44) as the antigen-presenting molecule. In growth-inhibition experiments, the growth of both IFN gamma-pretreated and untreated target cells were strongly inhibited by the presence of the CD8+ TLC. Together these data indicate that human cancer cells harbouring a spontaneous ras mutation can process aberrant p21 Ras and express peptide/HLA-class-I complexes on their surface in sufficient density to be recognized by Ras-specific cytotoxic T lymphocytes.

T cell epitope analysis with peptides simultaneously synthesized on cellulose membranes: fine mapping of two DQ dependent epitopes

Several MHC class II restricted, CD4+ human T cell clones from three donors were induced with soluble matrix protein of influenza virus. The epitopes recognized by these clones were mapped using a complete set of overlapping 15-mer peptides synthesized with the newly developed SPOT method which allows the simple simultaneous synthesis of numerous peptides on cellulose membranes. Fine analysis of two clones by truncation of the stimulatory peptide by single subsequent amino acids from either the NH2- or the COOH-terminus revealed the minimal stimulatory determinants of two DQ dependent T cell epitopes.

A K-ras 13Gly-->Asp mutation is recognized by HLA-DQ7 restricted T cells in a patient with colorectal cancer. Modifying effect of DQ7 on established cancers harbouring this mutation?

We have characterized and described in detail 2 CD4+ T-lymphocyte clones (TLC) from a colonic cancer patient. These TLC specifically recognize a K-ras-derived peptide carrying the 13Asp mutation commonly found in adenocarcinomas of the colon. The TLC were independently derived, as they carried 2 different T-cell receptors. The TLC recognized partly overlapping epitopes within the 13Asp peptide, presented by HLA-DQ7 molecules, suggesting that this molecule might confer some protective immunity against the mutation. On the basis of analysis of 251 colonic carcinomas, the presence of HLA-DQ7 did not seem to protect against the establishment of carcinomas carrying the 13Asp mutation, since the frequency of the DQ7 haplotype was not decreased among patients having this mutation. A modifying effect of DQ7 on the development of carcinomas with a 13Asp mutation was, however, observed, resulting in fewer tumours reaching advanced Dukes stages when DQ7 was present.

Binding of ras oncogene peptides to purified HLA-DQ(alpha 1*0102,beta 1*0602) and -DR(alpha,beta 1*0101) molecules

Mutated oncogene peptides may be presented to T cells by HLA molecules. To be able to design the optimal peptides for stimulation of T cells in individuals with different HLA molecules, it is important to analyse the binding characteristics of oncogene peptides to HLA. HLA-DQ6 (DQ(alpha 1*0102,beta 1*0602)) and HLA-DR1 (DR(alpha,beta 1*0101)) molecules were purified from lysates of homozygous EBV-transformed cell lines. Purified HLA molecules were then tested for their ability to bind synthetic peptides in gel filtration assays. A p21 ras oncogene peptide (previously found to stimulate DQ6-restricted T-cell clones) and an influenza matrix peptide were labelled with 125I and served as indicator peptides for binding to DQ6 and DR1 respectively. Binding of homologous truncated and mutated p21 ras peptides and unrelated peptides was then evaluated by their capacity to inhibit binding of the indicator peptides. p21 ras-derived peptides were found to bind to both DQ6 and DR1 molecules indicating the existence of a promiscuous binding motif in these peptides. The binding affinities seemed to vary between the different peptides, but the amino acid substitutions resulting from natural mutations were not critical for binding. Notably, the results obtained for DQ6 in the biochemical peptide binding assay correlated well with results obtained in a functional assay using T-cell clones as probes.

T cell epitopes encompassing the mutational hot spot position 61 of p21 ras. Promiscuity in ras peptide binding to HLA

Activated ras carry a point mutation either in codon 12, 13 or 61 which is tumor specific. Peptides derived from this oncoprotein are therefore potential tumor antigens. Essential for the feasibility of using ras-derived peptides in therapy of cancer is whether p21 ras-derived peptides can be processed, bind to human histocompatibility leukocyte antigen (HLA) and be recognized by T cells. Here we report the fine specificity and HLA restriction of several T lymphocyte clones (TLC) specific for a peptide which is derived from the second mutational hot spot in ras encoding residue 61. These TLC were generated from memory T cells present in the blood of a cancer patient and recognized a ras-derived peptide carrying Leu instead of Gln at residue 61. By sequencing of the T cell receptor (TcR) genes three sets of "sister" TLC carrying highly different TcR were identified. Two of the TLC recognized a peptide carrying the 61 Leu mutation presented by HLA-DQ8 and one recognized the same peptide presented by HLA-DQ4. By using truncated peptides derived from residues 51 to 69 of p21 ras, partially overlapping minimal epitopes could be defined. All three TLC recognized the corresponding recombinant mutant p21 ras oncoprotein carrying Leu at residue 61 presented by autologous B-lymphoblastoid cell lines (B-LCL). This demonstrates that naturally derived ras peptides from this region of p21 ras encompass the three epitopes recognized by the TLC. These results indicate that immunogenic ras-derived peptides may be used in immunotherapy of cancer where transforming ras oncoproteins are involved.

p21-ras-peptide-specific T-cell responses in a patient with colorectal cancer. CD4+ and CD8+ T cells recognize a peptide corresponding to a common mutation (13Gly-->Asp)

Peptides derived from mutated ras are immunogenic in mice and humans, and represent a group of specific tumor antigens that are potential targets for immunotherapy. T-cell responses against mutant p21 ras can be initiated in vitro by repeated stimulation of peripheral-blood mononuclear cells with mutant ras-derived peptides. Patients with tumors commonly harbouring ras mutations may therefore show evidence of in vivo reactivity against such mutations. Peripheral-blood mononuclear cells from 10 patients with colorectal adenocarcinoma were screened for reactivity against synthetic ras-derived peptides corresponding to the most commonly found mutations in this type of cancer. In one patient, T-cell reactivity against the 1-25,13Gly-->Asp peptide was detected. From this patient, both CD4+ and CD8+ T-cell clones specific for the 1-25,13Gly-->Asp mutation could be raised. We were not, however, able to detect the corresponding mutation in the cancer. The 13Gly-->Asp mutation in the ras oncogene is frequent and constitutes 9 to 27% of all K ras mutations found in biopsies from patients with colorectal carcinomas. Our study demonstrates a mutant ras-specific T-cell response of both the CD4+ and the CD8+ phenotype in a cancer patient. We speculate that in this patient a specific T-cell response resulted in eradication of tumor cells harboring the 13Gly-->Asp mutation.