Potential immunogenicity of oncogene and tumor suppressor gene products

Targeting Artificial Tumor Stromal Targets for Molecular Imaging of Tumor Vascular Hypoxia

Developed and tested for many years, a variety of tumor hypoxia detection methods have been inconsistent in their ability to predict treatment outcomes or monitor treatment efficacy, limiting their present prognostic capability. These variable results might stem from the fact that these approaches are based on inherently wide-ranging global tumor oxygenation levels based on uncertain influences of necrotic regions present in most solid tumors. Here, we have developed a novel non-invasive and specific method for tumor vessel hypoxia detection, as hypoxemia (vascular hypoxia) has been implicated as a key driver of malignant progression, therapy resistance and metastasis. This method is based on high-frequency ultrasound imaging of α-pimonidazole targeted-microbubbles to the exogenously administered hypoxia marker pimonidazole. The degree of tumor vessel hypoxia was assessed in three mouse models of mammary gland carcinoma (4T1, SCK and MMTV-Wnt-1) and amassed up to 20% of the tumor vasculature. In the 4T1 mammary gland carcinoma model, the signal strength of α-pimonidazole targeted-microbubbles was on average 8-fold fold higher in tumors of pimonidazole-injected mice than in non-pimonidazole injected tumor bearing mice or non-targeted microbubbles in pimonidazole-injected tumor bearing mice. Overall, this provides proof of principle for generating and targeting artificial antigens able to be ‘created’ on-demand under tumor specific microenvironmental conditions, providing translational diagnostic, therapeutic and treatment planning potential in cancer and other hypoxia-associated diseases or conditions.

"Glowing head" mice: a genetic tool enabling reliable preclinical image-based evaluation of cancers in immunocompetent allografts

Preclinical therapeutic assessment currently relies on the growth response of established human cell lines xenografted into immunocompromised mice, a strategy that is generally not predictive of clinical outcomes. Immunocompetent genetically engineered mouse (GEM)-derived tumor allograft models offer highly tractable preclinical alternatives and facilitate analysis of clinically promising immunomodulatory agents. Imageable reporters are essential for accurately tracking tumor growth and response, particularly for metastases. Unfortunately, reporters such as luciferase and GFP are foreign antigens in immunocompetent mice, potentially hindering tumor growth and confounding therapeutic responses. Here we assessed the value of reporter-tolerized GEMs as allograft recipients by targeting minimal expression of a luciferase-GFP fusion reporter to the anterior pituitary gland (dubbed the "Glowing Head" or GH mouse). The luciferase-GFP reporter expressed in tumor cells induced adverse immune responses in wildtype mouse, but not in GH mouse, as transplantation hosts. The antigenicity of optical reporters resulted in a decrease in both the growth and metastatic potential of the labeled tumor in wildtype mice as compared to the GH mice. Moreover, reporter expression can also alter the tumor response to chemotherapy or targeted therapy in a context-dependent manner. Thus the GH mice and experimental approaches vetted herein provide concept validation and a strategy for effective, reproducible preclinical evaluation of growth and response kinetics for traceable tumors.

Prospects for T cell immunotherapy of tumours by vaccination with immunodominant and subdominant peptides

Immunotherapy of tumours by adoptive transfer of cytotoxic T lymphocytes (CTL) is now feasible in experimental murine systems. These CTL recognize peptide sequences of defined length presented by major histocompatibility complex (MHC) class I molecules. Effective eradication of large tumour masses requires co-administration of interleukin 2. Tumour escape strategies are numerous but in various instances can be counteracted by defined measures. Initiation of CTL responses against poorly immunogenic virally induced tumours and other tumours requires novel strategies to overcome T cell inertia. We propose a strategy in which CTL are raised against target molecules of choice including differentiation antigens of restricted tissue distribution (autoantigens) or mutated/overexpressed oncogene products. The steps proposed include: (1) identification of target molecules of choice. (2) Identification in these target molecules of peptides fitting MHC allele-specific peptide motifs involved in peptide binding to MHC molecules. (3) Evaluation of actual binding of such peptides to specific MHC class I molecules. (4) In vitro CTL response induction by such peptides, presented by highly efficient antigen-presenting cells such as antigen processing-defective cells carrying empty MHC class I molecules loaded with a single peptide or dendritic cells. Both types of cells are capable of primary CTL response induction in vitro. (5) Evaluation of proper processing by the demonstration of tumour cell lysis by these CTL. (6) Adoptive transfer of tumour-specific CTL generated in vitro or vaccination with peptides. These various steps have now been taken for several viruses, virally induced tumours and other types of tumours and the first indications that this strategy is useful have been obtained.

Lymphoproliferative disorders: prospects for gene therapy

The lymphoproliferative disorders represent a large group of diseases with a significant variation in presentation and clinical course. There has been a trend of increasing incidence for some of these disorders, and despite advances in therapies, a significant number of patients either respond poorly or have early relapses. For this reason there is a need to investigate novel therapies to be used either alone or as adjunct treatment in combination with conventional therapies. Gene therapy is a relatively new field that takes advantage of our increased understanding of molecular biology with the aim of treating a variety of diseases including cancer. It is defined as the introduction of genetic material into cells for therapeutic intent. Methods to improve gene delivery efficiency have been the focus of a large amount of research and to date the optimal procedure uses viruses such as oncoretroviruses, lentiviruses, adenoviruses, adeno-associated viruses and herpes simplex viruses. There are four main gene therapy strategies that might be used for the treatment of lymphoproliferative disorders. First, immunotherapy using tumour vaccines or techniques to enhance the function of immune effector cells has been investigated with some success in patients with B-cell malignancies. Second, the introduction of prodrug-activated 'suicide' genes into cells has been explored, in particular in patients with post-transplantation lymphoproliferative disease. Third, direct lysis of tumour cells using viruses shows some early promise, especially in the treatment of B-cell disorders by manipulating the measles virus to target the CD20 antigen. Finally, anti-gene strategies such as anti-sense therapy, ribozymes, and most recently RNA interference, could be used to suppress expression of specific target genes. RNA interference in particular has tremendous potential and has been studied in the context of anaplastic large cell lymphoma as well as Epstein-Barr virus-associated malignancies. Whilst we are still in the early days of this field and to date results have been modest, there is still a significant potential for gene therapy to play a role in the future treatment of these disorders.

Identification of a naturally processed HLA-A*0201 HPV18 E7 T cell epitope by tumor cell mediated in vitro vaccination

Immunotherapy of HPV-associated disease such as cervical cancer is moving from preclinical investigation to clinical trials. The viral oncoproteins E6 and E7 are ideal target antigens because their expression is mandatory in HPV-transformed tumor cells. T cells are the most important effector cells for therapeutic vaccination strategies. Therefore, the identification and characterization of HPV E6 and E7 T cell epitopes is necessary. Methods to date rely on screening for immunogenicity of peptides predicted by algorithms. Presentation of the identified peptides on tumor cells, however, needs to be confirmed. In our study, we have improved the method to identify peptide epitopes of HPV18 E7 that are actually presented by tumor cells. We induced allogeneic T-cell lines by stimulation with HPV18-positive, CD80 and HLA-A*0201 transfected cervical cancer cells. Sensitized T cells were probed against an array of a HPV18 E7 20mer peptide-library. We found specific reactivity to one of the 20mer peptides. This sequence was then screened via algorithms for putative epitopes. One putative HLA-A2 restricted epitope was confirmed to bind to HLA-A2, to be immunogenic and to induce IFN gamma-release in ELISpot assays. Epitope-specific T cells were cytolytic toward autologous peptide pulsed targets and HPV18 transformed tumor cells. The identification of epitope-specific T cells in tumor infiltrating lymphocytes of a HPV18-positive HLA-matched cervical cancer patient suggests an in vivo relevance of the identified epitope. We suggest that our approach is advantageous over conventional methods, because it yields candidate peptides that are relevant CTL epitopes that are expressed, processed and presented by tumor cells.

Biological considerations in lung cancer

Our understanding of lung cancer biology has rapidly expanded in recent years. Lung cancer, unlike most human cancers, can be traced to an environmental risk factor in the majority of cases, and this fact is reflected in the vast number of genetic alterations discovered in lung tumors whose pathogenesis is believed to be mediated by carcinogen exposure. The discovery of these alterations has led to a greater understanding of tumor development. The dramatic progress in the understanding of the genetic and molecular basis of oncogenesis and the induction of immunity has led to a rejuvenation of efforts to apply this new knowledge to this common and refractory disease. Further, the resurgent interest in cancer immunology and tumor-host interactions holds promise for the development of new approaches to treatment based on harvesting the immune systems ability to recognize these alterations. Hopefully, this understanding will lead to novel approaches with real and convincing clinical efficacy once some of these strategies are tested in carefully performed randomized clinical trials with appropriate power to detect meaningful differences.

Gene transfer and the treatment of haematological malignancy

Gene therapy offers an additional therapeutic modality for treating haematological malignancy. Because gene therapies could be truly specific for the malignancy, they should ultimately prove both safe and effective. We have far to go before this full potential is realized, but gene transfer strategies are already showing therapeutic promise. Gene transfer may be used to correct the genetic defect in the tumour, to render it more susceptible to conventional therapies, or the normal host cells more resistant, to induce or amplify an antitumour immune response, or simply as a means of tracking the tumour or cells used for treatment. This article describes examples of each approach and discusses future prospects for the field.

CD4+ T cell responses to self- and mutated p53 determinants during tumorigenesis in mice

We analyzed CD4+ T helper responses to wild-type (wt) and mutated (mut) p53 protein in normal and tumor-bearing mice. In normal mice, we observed that although some self-p53 determinants induced negative selection of p53-reactive CD4+ T cells, other p53 determinants (cryptic) were immunogenic. Next, BALB/c mice were inoculated with J774 syngeneic tumor cell line expressing mut p53. BALB/c tumor-bearing mice mounted potent CD4+ T cell responses to two formerly cryptic peptides on self-p53. This response was characterized by massive production of IL-5, a Th2-type lymphokine. Interestingly, we found that T cell response was induced by different p53 peptides depending upon the stage of cancer. Mut p53 gene was shown to contain a single mutation resulting in the substitution of a tyrosine by a histidine at position 231 of the protein. Two peptides corresponding to wt and mutated sequences of this region were synthesized. Both peptides bound to the MHC class II-presenting molecule (Ed) with similar affinities. However, only mut p53.225-239 induced T cell responses in normal BALB/c mice, a result strongly suggesting that high-affinity wt p53.225-239 autoreactive T cells had been eliminated in these mice. Surprisingly, CD4+ T cell responses to both mut and wt p53.225-239 peptides were recorded in J774 tumor-bearing mice, a phenomenon attributed to the recruitment of low-avidity p53.225-239 self-reactive T cells.

Induction in transgenic mice of HLA-A2.1-restricted cytotoxic T cells specific for a peptide sequence from a mutated p21ras protein

Cytotoxic T cells (CTL) recognize short peptides that are derived from the proteolysis of endogenous cellular proteins and presented on the cell surface as a complex with MHC class I molecules. CTL can recognize single amino acid substitutions in proteins, including those involved in malignant transformation. The mutated sequence of an oncogene may be presented on the cell surface as a peptide, and thus represents a potential target antigen for tumour therapy. The p21ras gene is mutated in a wide variety of tumours and since the transforming mutations result in amino acid substitutions at positions 12, 13 and 61 of the protein, a limited number of ras peptides could potentially be used in the treatment of a wide variety of malignancies. A common substitution is Val for Gly at position 12 of p21ras. In this study, we show that the peptide sequence from position 5 to position 14 with Val at position 12-ras p5-14 (Val-12)-has a motif which allows it to bind to HLA-A2.1. HLA-A2.1-restricted ras p5-14 (Val-12)-specific CTL were induced in mice transgenic for both HLA-A2.1 and human beta2-microglobulin after in vivo priming with the peptide. The murine CTL could recognize the ras p5-14 (Val-12) peptide when they were presented on both murine and human target cells bearing HLA-A2.1. No cross-reactivity was observed with the native peptide ras p5-14 (Gly-12), and this peptide was not immunogenic in HLA-A2.1 transgenic mice. This represents an interesting model for the study of an HLA-restricted CD8 cytotoxic T cell response to a defined tumour antigen in vivo.

Pathobiologic identification of two distinct breast carcinoma subsets with diverging clinical behaviors

Many different pathological and biological variables which characterize breast carcinomas have been found to be associated. The aim of this work was to analyze the complex relationship among these parameters. The pathologic, biologic, and clinical characteristics of a series of primary breast carcinomas from 676 patients were retrospectively investigated. Multiple correspondence analysis of 13 factors revealed clustering of eight pathobiologic variables, that is histologic grade, necrosis, lymphoid infiltration, number of mitoses, c-erbB-2 overexpression, p53, progesterone receptor, and bcl2 expression. An index for each tumor calculated on the basis of these eight factors served to distinguish two different tumor phenotypes, designated A and B. Phenotype A is represented by tumors sharing most of the biologic features of normal breast tissues: indeed, these tumors are characterized by a relatively high degree of differentiation, low proliferation, no necrosis or leukocyte infiltration, and no gene alterations. By contrast, phenotype B is quite divergent from the normal tissue because of its poor differentiation, high proliferation, frequent gene alterations and evidence of a host immune reaction. As regards the disease progression, these two subsets showed marked differences: phenotype A tumors had a low recurrence rate per year that remained constant over time and affected more frequently elderly patients, whereas group B tumors showed high aggressivity in the first years after surgery followed by a low long-term recurrence rate and were more frequently seen in younger patients. These data suggest that breast carcinoma consists of two different subsets that can be identified on the basis of pathobiologic features.

The optimization of helper T lymphocyte (HTL) function in vaccine development

Helper T lymphocyte (HTL) responses play an important role in the induction of both humoral and cellular immune responses. Therefore, HTL epitopes are likely to be a crucial component of prophylactic and immunotherapeutic vaccines. For this reason, Pan DR helper T cell epitopes (PADRE), engineered to bind most common HLA-DR molecules with high affinity and act as powerful immunogens, were developed. Short linear peptide constructs comprising PADRE and Plasmodium-derived B cell epitopes induced antibody responses comparable to more complex multiple antigen peptides (MAP) constructs in mice. These antibody responses were composed mostly of the IgG subclass, reactive against intact sporozoites, inhibitory of schizont formation in liver invasion assays, and protective against sporozoite challenge in vivo. The PADRE HTL epitope has also been shown to augment the potency of vaccines designed to stimulate a cellular immune response. Using a HBV transgenic murine model, it was found that CTL tolerance was broken by PADRE-CTL epitope lipopeptide, but not by a similar construct containing a conventional HTL epitope. There are a number of prophylactic vaccines that are of limited efficacy, require multiple boosts, and/or confer protection to only a fraction of the immunized population. Also, in the case of virally infected or cancerous cells, new immunotherapeutic vaccines that induce strong cellular immune responses are desirable. Therefore, optimization of HTL function by use of synthetic epitopes such as PADRE or pathogen-derived, broadly crossreactive epitopes holds promise for a new generation of highly efficacious vaccines.

Cytotoxic T lymphocyte responses to wild-type and mutant mouse p53 peptides

Cytotoxic T lymphocytes (CTL) recognize peptides presented at the cell surface in association with major histocompatibility complex (MHC) class I molecules. The finding that peptides binding to MHC class I molecules share common amino acid motifs renders feasible the selection of antigenic peptides by simply scanning protein sequences, and thus, provides the possibility of inducing CTL to pre-defined specificities. Tumor cells possess antigens known to generate MHC class I-restricted CD8+ CTL responses. Thus, these antigens represent good targets to induce tumor-specific immunity. Among these antigens, the p53 tumor suppressor gene product is an attractive candidate for cancer immunotherapy. Mutations in the p53 gene have been found to be very frequently associated with a malignant transformation and often lead to p53 protein overexpression. Thus, we investigated the possibility of inducing CTL to wild-type or mutant p53 peptides in a BALB/c (H-2d) mouse model. Peptides possessing the H2-Kd binding motif were selected and tested for binding to the H-2Kd molecules in vitro. Synthetic peptides p53(122-130) wild-type or "mutant" (Lys --> Glu substitution at position 129) were shown to be the best binder peptides and were tested for their immunogenicity in mice. H-2Kd-restricted p53-specific CD8+ CTL were generated following immunization of mice with either wild-type (wt) p53(122-130) or mutant (mut) p53(122-130) (E129) peptides. Only low-affinity CTL can be obtained by immunization with the wt sequence. In contrast, CTL elicited with the mut peptide recognized the mut sequence at a 10-100-fold lower concentration. This indicates that CTL elicited with the mut peptide recognized the mut sequence very efficiently, whereas the wt sequence is poorly recognized, if at all. Taken together, these results thus suggest that p53-specific tumor immunotherapy may be successful only if the mutated protein is taken into consideration.

Emerging applications of gene transfer in the hematopoietic cancers

PURPOSE

Originally conceived as a means to replace or correct defective genes in patients with inherited disorders, gene transfer has shown broad potential for medical intervention in the hematopoietic cancers and for study of hematopoietic stem cell biology. The purpose of this article is to review emerging applications of gene therapy with special reference to hematopoietic neoplasia.

RESULTS

Gene transfer strategies now under investigation in the hematopoietic cancers focus on (a) repair of one or more genetic defects associated with the malignant process, (b) delivery of a prodrug-metabolizing enzyme that causes tumor cells to become sensitive to the corresponding anticancer drug, (c) modification of immune responses to the cancer, or (d) introduction of drug resistance genes to increase the therapeutic index of cytotoxic agents. Finally, by marking normal or malignant cells with readily detectable genes, one can monitor the efficacy of therapy or study the dynamics of stem cell behavior in vivo.

CONCLUSION

Despite their undisputed contributions to our knowledge of the hematopoietic cancers, gene transfer studies have been limited by the quality of vector technologies. As transduction efficiencies and gene regulatory mechanisms improve, gene transfer can be expected to evolve into a major therapeutic modality in its own right.

Spontaneous human squamous cell carcinomas are killed by a human cytotoxic T lymphocyte clone recognizing a wild-type p53-derived peptide

A cytotoxic T lymphocyte (CTL) clone generated in vitro from the peripheral blood of a healthy HLA-A2-positive individual against a synthetic p53 protein-derived wild-type peptide (L9V) was shown to kill squamous carcinoma cell lines derived from two head and neck carcinomas, which expressed mutant p53 genes, in a L9V/HLA-A2 specific and restricted fashion. Thus, the normal tolerance against endogenously processed p53 protein-derived self-epitopes can be broken by peptide-specific in vitro priming. p53 protein-derived wild-type peptides might thus represent tumor associated target molecules for immunotherapeutical approaches.

Gene transfer in haematological malignancy

Although gene transfer was first suggested to treat inherited monogenic disorders, at present most clinical protocols are intended to treat patients with malignant disease. Although current vector technologies profoundly limit the potential therapeutic applications of gene transfer, the technique is already being successfully used to complement longer established therapies. This article reviews current and forthcoming applications of gene transfer to treat haematological malignancies.

Immunotherapy II: Antigens, receptors and costimulation

To generate a cytotoxic T-lymphocyte (CTL) response to cancer cells requires tumour-specific antigens appropriately processed and displayed by the MHC proteins; T-lymphocytes with receptors of appropriate specificity to recognise these; and initial antigen presentation to the immune system in an immunogenic context. In vitro, autologous tumour-specific CTL have been raised against a number of tumours, thus at least some patients have a suitable combination of antigen and receptor. Vaccination with antigen, or with DNA or viral vectors encoding the antigen, leading to the presentation of identified antigens in an immunogenic context, can activate T-cells which provide protection from tumour in animal models. An alternative approach uses gene transfer to T-cells, causing them to express novel receptors which direct their cytotoxic activity towards the tumour. Non-specific immune adjuvants, and expression of novel antigens on tumour cells, are briefly discussed. Recent advances in understanding the requirements for T-cell activation suggest that failure to efficiently present antigen in an immunogenic context may explain the apparent lack of tumour-specific CTL activation in vivo. In mice, expression of the costimulatory molecule B7-1 on tumour cells, following gene transfer, allows the modified tumour cells to act as antigen-presenting cells, inducing protective and therapeutic CTL responses in some cases. Clinical trials of some approaches have commenced, with some encouraging results which provide a basis for further development of immunological gene therapy.

Gene transfer and therapeutic drug monitoring

During the next decade, gene therapy will evolve from a medical curiosity into an essential component of medical practice. One of the elements necessary for this transition will be the development of simple and accurate ways of monitoring both the vectors used to transfer the genes of interest and the function of the genes themselves. This article reviews the difficulties in achieving these aims and describes ways in which the technology of gene transfer offers a novel means of monitoring current therapies.

A recombinant adenovirus expressing an Epstein-Barr virus (EBV) target antigen can selectively reactivate rare components of EBV cytotoxic T-lymphocyte memory in vitro

While the bulk of a virus-induced cytotoxic T-lymphocyte (CTL) response may focus on a few immunodominant viral antigens, in certain tumor virus systems the detectability of clones recognizing other, subdominant antigens can assume particular importance. By using the human CTL response to Epstein-Barr virus (EBV) as a model system, here we show that even rare components of virus-specific memory can be selectively reactivated in vitro when the relevant target antigen is expressed in autologous stimulator cells from a recombinant adenovirus (RAd) vector. We generated a replication-deficient adenovirus, RAd-E3C, which in skin fibroblast cultures expressed the EBV nuclear antigen EBNA3C at a 10- to 100-fold-higher level than that naturally present in EBV-transformed lymphoblastoid cell lines (LCLs). Initial experiments with a donor whose polyclonal CTL response to LCL stimulation contained a strong EBNA3C-specific component showed that these CTLs could be efficiently reactivated by in vitro stimulation either with RAd-E3C-infected fibroblasts or with RAd-E3C-infected peripheral blood mononuclear cells. Then we studied donors whose responses to LCL stimulation contained little if any detectable EBNA3C reactivity but were dominated by clones recognizing other EBV target antigens; in vitro stimulation with RAd-E3C-infected peripheral blood mononuclear cells selectively reactivated EBNA3C-specific CTL clones from these individuals, with the epitope specificities of responses subsequently identified at the peptide level. This RAd-based approach could be applied more generally to screen for human CTL responses against any candidate target antigen expressed by tumor cells.

The next wave of recombinant and synthetic anticancer vaccines

The identification of tumor-associated antigens (TAA) recognized by T lymphocytes makes the development of antigen-specific synthetic and recombinant vaccines possible. The expression of TAA within a recombinant vector increases control over the kinetics and quantity, the molecular form, and the subcellular location of the immunogen delivered. The next generation of antitumor vaccines employs cytokines and costimulatory molecules expressed in concert with TAA that are capable of augmenting the activation and proliferation of antitumor immune responses. The ultimate goal of these new strategies, the treatment of established cancer, is now being realized in animal models.

The impact of gene therapy on T cell function in cancer

Studies of signal transduction by T cells are slowly identifying the intracellular messengers that must be generated for full T cell activation to take place. The recent, convincing identification of several tumor-associated antigens (TAA) has transformed our task into trying to define the mechanisms that underlie the failure of T cells to destroy antigenic tumor cells. Although there are a variety of hypotheses that explain why tumors grow progressively, even if they are antigenic, recent evidence suggests that T cells from tumor-bearing patients exhibit abnormalities in signal transduction that render them unable to respond to appropriate activation signals, even following proper stimulation. Gene therapy with interleukin-2 (IL-2)-secreting tumor cells in an animal model has been effective in preventing the onset of these signaling defects. Discovery of the molecular mechanisms by which such cytokine-secreting tumor cells induce immune responses and how they may best be applied clinically may provide clearer indications of the directions to pursue to alter the balance between the T cell and the tumor cell in the patient's favor.

The contribution of marker gene studies to hemopoietic stem cell therapies

Although the transfer of "therapeutic" genes into hemopoietic stem cells (HSC) offers many opportunities to treat a wide range of human disease, the low efficiency of transfer and limited expression of the transferred gene have so far largely prevented any direct beneficial effect from being obtained. However, gene marker studies in which the transferred genes are used simply to track the individual components of the infused HSC have already shown their utility. Genetic marking may be used to identify cells capable of causing relapse after autologous bone marrow transplantation and to distinguish cells in the graft capable of preventing malignant disease. Marking may also be used to analyze the consequences of ex vivo or in vivo manipulations of the HSC which are intended to accelerate engraftment or augment gene transfer efficiencies. Information obtained from these studies should therefore not only improve the outcome of HSC based therapies, but also aid in the introduction of successful gene therapy protocols.

Mapping and ranking of potential cytotoxic T epitopes in the p53 protein: effect of mutations and polymorphism on peptide binding to purified and refolded HLA molecules

In many cancer cells, the p53 gene displays point mutations that result in stabilization and accumulation of the p53 protein. Therefore, p53 peptides could be presented to the immune system by tumor cells; thus, p53 might be a suitable target antigen for developing an immunotherapy against tumors using cytotoxic T lymphocytes (CTL). To map candidate CTL epitopes, we synthesized 150 peptides of 8-11 residues that contained putative anchor motifs required for binding to common HLA class I molecules. They were tested for their capacity to promote the assembly of purified and refolded HLA-A1, A2, B7 and B8 molecules. The following wild-type p53 peptides were found to be reactive with the HLA molecules tested: 196-205 and 226-234 bound moderately to HLA-A1; 25-35, 65-73, 129-137, 187-197, 263-272 and 264-272 bound strongly, and 187-195 and 256-264 moderately to HLA-A2; 26-35, 63-73, 189-197, 249-257 and 321-330 bound strongly to HLA-B7; and 135-143, 210-218 and 375-383 bound weakly to HLA-B8. We also analyzed the effects of p53 mutations occurring naturally in tumors on peptide/HLA assembly. We found substitutions that enhanced, diminished or had no effect on the peptide binding to HLA molecules. Polymorphism at position 72 mainly affected peptide/HLA-B7 binding, the proline allele P72 giving a less-reactive peptide (63-73) than the arginine allele R72. We have ranked potential p53 epitopes according to their reactivity for purified HLA molecules, allowing the selection of appropriate peptides and HLA molecules to attempt CTL induction in vitro.

Induction and characterization of cytotoxic T-lymphocytes recognizing a mutated p21ras peptide presented by HLA-A*0201

The ras oncogene is frequently found to be activated in human cancer through point mutations at codons 12, 13 or 61. We explored whether these altered p21ras protein sequences contain peptide sequences that can activate naive CD8+ cytotoxic T lymphocytes (CTL). Several wild-type and mutated p21ras peptides were identified that carry a binding motif for human leukocyte antigen (HLA)-A*0201. Two peptides were found to bind strongly to this allele. CD8+ CTL bulk cultures specifically reacting with one of these peptides could be induced, using processing-defective T2 cells loaded with peptide CLLDILDTAGL as stimulators. The peptide is derived from p21ras, position 51-61, and carries a 61 Gln-->Leu mutation. In contrast, a 9-mer peptide CLLDILDTA corresponding to amino acid sequence 51-59 of wild-type p21ras did not yield reactive CTL cultures. T-cell clones with low affinity for the 11-mer peptide were isolated from CLLDILDTAGL-reactive bulk cultures. These T cells did not lyse melanoma cells transfected with 61-Leu N-ras, although lysis was found when these transfectants were pulsed with the 11-mer peptide. Possibly, T cells of higher affinity may be required to demonstrate processed peptide on the cell surface. The combined experiments suggest that a peptide derived from mutated p21ras can be recognized by HLA class I-restricted CTL, whereas an analogous wild-type p21ras peptide may not be immunogenic.

Human somatic gene therapy: progress and problems

Whilst the potential of gene therapy is considerable, current applications have been restricted by the limitations of available vectors. As yet, no vector is able to produce the desired safe, targeted and efficient transfer of genetic material with regulation of the new gene in the targeted cell. Notwithstanding these limitations, more than 65 clinical gene transfer protocols have been approved in the US. The majority of these are open to patients with malignant disease, in whom the risk:benefit ratio is most appropriate. Current progress and problems in gene transfer are illustrated by reference to gene transfer into haemopoietic stem cells (HSC), an area that has attracted particular attention, both because of the logistic advantages of these cells and because of the wide range of pathologies that may be corrected in the HSC itself or in its progeny. Because of the low efficiency of transfer into HSC, initial studies have involved transfer of marker genes to determine the origin of relapse after autologous bone marrow transplantation and to learn more about the conditions that enhance gene transfer and expression in haemopoietic tissue. Information gained from these studies is already guiding the practice of autologous and allogeneic marrow transplantation and has contributed to the development of gene therapy protocols for the treatment of malignant disease, immune deficiency syndromes and lysosomal storage disorders. Over the next decade, as the technology of gene transfer advances, many further clinical applications of the approach will become evident.

p53, a potential target for tumor-directed T cells

Cell lineage-specific cellular proteins, oncogenes from viral or cellular origin and tumor suppressor genes encode tumor-specific/associated antigens. Such antigens can elicit an major compatibility complex (MHC) class I-restricted cytotoxic T lymphocyte (CTL) response, either naturally in cancer patients or following appropriate immunostimulation (in vitro or in vivo). The reported immune responses in humans to the melanoma-associated MAGE gene products, GP100 and tyrosinase, all self-proteins, support the idea to use wild-type p53 products as targets for T cells. An important step towards this goal is identification of potential p53 CTL epitopes. We identified the wild-type p53 peptides with the highest affinity to the HLA-A*0201 molecule using two assays: the previously described MHC peptide-binding assay and the peptide competition assay. We obtained CTL against four p53 peptides with a high affinity for the HLA-A*0201 molecule. These findings are discussed next to a short review concerning the p53 literature.

Cytokine therapeutics: lessons from interferon alpha

Cytokines are soluble proteins that allow for communication between cells and the external environment. Interferon (IFN) alpha, the first cytokine to be produced by recombinant DNA technology, has emerged as an important regulator of growth and differentiation, affecting cellular communication and signal transduction pathways as well as immunological control. This review focuses on the biological and clinical activities of the cytokine. Originally discovered as an antiviral substance, the efficacy of IFN-alpha in malignant, viral, immunological, angiogenic, inflammatory, and fibrotic diseases suggests a spectrum of interrelated pathophysiologies. The principles learned from in vivo studies will be discussed, particularly hairy cell leukemia, chronic myelogenous leukemia, certain angiogenic diseases, and hepatitis. After the surprising discovery of activity in a rare B-cell neoplasm, IFN-alpha emerged as a prototypic tumor suppressor protein that represses the clinical tumorigenic phenotype in some malignancies capable of differentiation. Regulatory agencies throughout the world have approved IFN-alpha for treatment of 13 malignant and viral disorders. The principles established with this cytokine serve as a paradigm for future development of natural proteins for human disease.