Tumor vaccines for the management of prostate cancer

Prostate cancer is a significant health problem and one of the leading causes of cancer-related death among men. Given the typically long natural history of the disease, there is considerable interest in developing new therapies to treat or prevent metastatic disease, and cancer vaccines are a particularly attractive immune-based approach. Early clinical studies using non-specific immunomodulatory treatments have met with limited success, but also suggest that improved immunologic approaches might be useful in treating human prostate cancer. Over the last decade, the identification of immune cells responsible for actual destruction of prostate tissue and advances in immunologic and molecular techniques have led to a variety of vaccination approaches that are currently being evaluated in human clinical trials. The present article discusses the rationale in animal models for particular immunization strategies and describes the vaccines currently being used in patients with prostate cancer. The ongoing identification of tumor antigens and proteins involved in prostate cancer progression and the development of better immunologic animal models suggest a hopeful future for the design of effective prostate cancer vaccines.

Cancer Vaccines for the Treatment and Prevention of Non–Small-Cell Lung Cancer

Cancer vaccines targeting non small-cell lung cancer (NSCLC) have been studied for decades; clinical trials, for the most part, have focused on the use of autologous and allogeneic whole-tumor cell vaccines. Recent advances in molecular biology and immunology, however, have allowed the identification of many tumor antigens involved in the generation of immunity to NSCLC. Although small-cell lung cancer (SCLC) is commonly thought of as an immunogenic tumor, it is now clear that NSCLC is also capable of eliciting an endogenous immune response in patients with the disease and, in fact, has a natural history that may make NSCLC more amenable to vaccine therapy as an adjuvant treatment strategy. This review will high-light the major components of the immune system that may potentially interact with tumor-associated proteins as well as outline the immunologic similarities and differences between SCLC and NSCLC. Tumor antigens that elicit immune responses in patients with NSCLC will be discussed. Finally, clinical trials of whole-tumor cell vaccines, both autologous and allogeneic, and tumor antigen-specific vaccines will also be discussed.

Dendritic cells lose ability to present protein antigen after stimulating antigen-specific T cell responses, despite upregulation of MHC class II expression

Immature dendritic cells (DC) take up, process and present protein antigens; mature DC are specialized for stimulating primary T cell responses with increased expression of MHC class II and co-stimulatory molecules, but are incapable of processing and presenting soluble protein. The current study examined whether maturation of DC is triggered by T cell recognition of antigens presented by immature DC. Human DC derived from CD34+ progenitor cells by culture with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-6 (IL-6) in serum-free medium could prime naive CD4+ T cells to keyhole limpet hemocyanin (KLH) and ovalbumin (OVA). The cultured DC retained the ability to prime T cells to native protein for at least 15 days. To test for changes in DC function after participation in an immune response, DC were co-cultured with either allogeneic or autologous CD4+ T cells. DC co-cultured with autologous T cells retained the ability to prime T cells to intact protein antigens. By contrast, DC which had previously stimulated an allogeneic T cell response lost ability to prime T cells to soluble proteins. However, such <<T cell-activated DC>> induced a MLR and stimulated peptide-specific primary CD4+ T cell responses. This indicated that <<T cell-activated DC>> did not die or lose the ability to prime, but lost the ability to process and present subsequent antigens. Following participation in T cell activation, DC increased surface expression of MHC class II, co-stimulatory molecules CD40 and B7.2, and the intercellular adhesion molecule-1 (ICAM-1). In addition, our data suggest that interferon gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) are involved in this T cell-mediated DC maturation.

Delayed-type hypersensitivity response is a predictor of peripheral blood T-cell immunity after HER-2/neu peptide immunization

Many groups that immunize cancer patients with cancer vaccines use the generation of a delayed-type hypersensitivity (DTH) response as the primary measure of the ability to immunize a patient to a tumor cell or specific tumor antigen. This study examines whether the development of a tumor antigen-specific DTH response, measured after vaccination with peptide-based vaccines, correlates to in vitro assessment of peripheral blood antigen-specific T-cell responses. The HER-2/neu protein was used as a model tumor antigen. Thirty-two patients who completed a course of immunization with HER-2/neu peptide-based vaccines were analyzed. HER-2/neu peptide-specific DTH responses (n = 93) and peripheral blood T-cell responses (n = 93) were measured 30 days after the final immunization. Size of DTH induration was correlated with HER-2/neu-specific T-cell proliferative responses assessed from peripheral blood lymphocytes isolated concurrently with peptide skin test placement. HER-2/neu peptide-specific DTH responses > or =10 mm2 correlated significantly to a measurable peptide-specific peripheral blood T-cell response defined as stimulation index >2.0 (P = 0.0006). However, antigen-specific DTH responses with magnitudes between 5 and 9 mm2 were not significantly associated with the development of systemic immunity. DTH responses between 5 and 9 mm2 carried an odds ratio of 1.3 (P = 0.61) in predicting a measurable systemic tumor antigen response. The findings presented here demonstrate that tumor antigen-specific DTH responses > or =10 mm2 correlate with measurable in vitro antigen-specific lymphocytic proliferation and are, in this model system, a reflection of systemic immunization.

Immunotherapeutic approaches for the treatment of breast cancer

The application of immunotherapeutic principles to the treatment and prevention of breast cancer is a relatively new undertaking. Although cytokine infusions, cancer vaccines, and T cell therapy have been extensively studied in solid tumors such as melanoma and renal cell carcinoma, the therapeutic efficacy of these approaches is not well explored in breast cancer. The recent definition of tumor-specific immunity in breast cancer patients and the identification of several breast cancer antigens has generated enthusiasm for the application of immune-based therapies to the treatment of breast malignancies. In general, immunotherapies can be considered either non-specific, such as a general immunomodulator (e.g., a cytokine), or tumor-specific (e.g., a vaccine that targets breast cancer tumor antigens). This review describes three major immunotherapeutic strategies that have the potential to enhance or generate an anti-breast cancer T cell immune response: (i) cytokine therapy; (ii) cancer vaccines; and (iii) T cell therapy, and explores how each strategy has been applied to the treatment of breast cancer.

Antibody immunity to the HER-2/neu oncogenic protein in patients with colorectal cancer

The HER-2/neu protein is overexpressed in approximately 20% of human adenocarcinomas and is a defined tumor antigen in breast cancer. The purpose of this study was to evaluate the endogenous HER-2/neu specific antibody response in 57 patients with colorectal cancer. HER-2/neu specific antibodies, titer > or = 1:100, were detected in 14% (8/57) of patients with colorectal cancer compared to none of the normal control population (0/200). Furthermore, detection of HER-2/neu specific antibodies in the cancer population correlated significantly with HER-2/neu protein overexpression in the patients' tumor (p < 0.01). 46% of patients with HER-2/neu overexpressing tumors (6/13) and 5% of HER-2/neu negative tumors (2/44) had detectable HER-2/neu specific antibodies. The endogenous HER-2/neu antibody response in these patients was predominantly IgG or IgA.

Generation of immunity to the HER-2/neu oncogenic protein in patients with breast and ovarian cancer using a peptide-based vaccine

HER-2/neu is a "self" tumor antigen that is overexpressed in 15-30% of human adenocarcinomas. Vaccine strategies directed against HER-2/neu and other self tumor antigens require development of methods to overcome immune tolerance to self-proteins. In rats, rat neu peptide vaccines have been shown to be an effective way of circumventing tolerance to rat neu protein and generating rat neu-specific immunity. The present report validates that a similar peptide-based vaccine formulation is effective for inducing T-cell immunity to HER-2/neu protein in humans with breast and ovarian cancer. The vaccine formulation included groups of peptides derived from the HER-2/neu extracellular domain (ECD) or intracellular domain (ICD) mixed with granulocyte macrophage colony stimulating factor as an adjuvant. These peptides were 15-18 amino acids in length and designed to elicit a CD4 T helper-specific immune response. Patients underwent intradermal immunization once a month for a total of two to six immunizations. To date, all of the patients immunized with HER-2/neu peptides developed HER-2/neu peptide-specific T-cell responses. The majority of patients (six of eight) also developed HER-2/neu protein-specific responses. Responses to HER-2/neu protein occurred with epitope spreading. Immune T cells elicited by vaccination were shown to migrate outside the peripheral circulation by virtue of generating delayed type hypersensitivity responses distant from the vaccine site, which indicated the potential ability to traffic to the site of tumor. The use of peptide-based vaccines may be a simple, yet effective, vaccine strategy for immunizing humans to oncogenic self-proteins.

Immunization with recombinant human granulocyte-macrophage colony-stimulating factor as a vaccine adjuvant elicits both a cellular and humoral response to recombinant human granulocyte-macrophage colony-stimulating factor

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an important cytokine for the generation and propagation of antigen-presenting cells and for priming a cellular immune response. We report here that use of recombinant human GM-CSF (rhGM-CSF), administered as an adjuvant in a peptide-based vaccine trial given monthly by intradermal injection, led to the development of a T-cell and antibody response to rhGM-CSF. An antibody response occurred in the majority of patients (72%). This antibody response was not found to be neutralizing. In addition, by 48-hour delayed type hypersensitivity (DTH) skin testing, 17% of patients were shown to have a cellular immune response to the adjuvant rhGM-CSF alone. Thymidine incorporation assays also showed a peripheral blood T-cell response to rhGM-CSF in at least 17% of the patients. The generation of rhGM-CSF-specific T-cell immune responses, elicited in this fashion, is an important observation because rhGM-CSF is being used as a vaccine adjuvant in various vaccine strategies. rhGM-CSF-specific immune responses may be incorrectly interpreted as antigen-specific immunity, particularly when local DTH responses to vaccination are the primary means of immunologic evaluation. We found no evidence of hematologic or infectious complications as a result of the development of rhGM-CSF-specific immune responses.

Human HER-2/neu protein immunization circumvents tolerance to rat neu: a vaccine strategy for 'self' tumour antigens

Many newly defined tumour antigens are 'self' proteins. Immunizing cancer patients against these antigens may be difficult due to tolerance. The HER-2/neu oncogenic protein is such a 'self' tumour antigen. Rat neu is homologous with human HER-2/neu and provides a model system for studying vaccination strategies. Rats are tolerant to rat neu. Vaccination with this 'self' protein elicits no detectable immune response. The current studies evaluated whether tolerance to rat neu can be circumvented by immunizing with the highly homologous foreign human HER-2/neu protein. Rats were immunized with human HER-2/neu intracellular domain (hICD) protein that is 92% homologous to rat neu ICD. Animals immunized with hICD developed significant antibody and T-cell responses that were specific for both human HER-2/neu and rat neu. Neu-specific antibodies were present in titres of greater than 1:200,000. Analysis of the specificity of the antibody response using synthetic peptides demonstrated substantial reactivity to an epitope with 100% homology between rat and human protein. Significant T-cell responses (stimulation index > 10) to hICD and rat neu protein (stimulation index > 4) were detected. The T cells also responded to both human and rat ICD. The results imply that immunization with foreign proteins, which are highly homologous to 'self' tumour antigens, may be an effective vaccine strategy for 'self' tumour antigens.

HER-2/neu oncogenic protein: issues in vaccine development

Vaccine studies using whole tumor cells or heterogeneous mixtures of tumor antigens provide intriguing evidence that cancer vaccines might be effective. Now it is possible to test vaccines composed of well-characterized proteins and peptides. Testing vaccine formulations composed of known and defined antigens will allow a more precise determination as to why vaccines work when they work, and why they do not work when they fail. The demonstration that human malignancy is immunogenic and the definition of human tumor antigens has set the stage for a new generation of cancer vaccines directly targeting immunogenic cancer-related peptides and proteins. Many newly defined tumor antigens are self proteins. As an example, screening existent immunity in human melanoma has identified responses to nonmutated self proteins: MAGE, MART, gp100, and tyrosinase. Tolerance to self antigens now emerges as a possible mechanism of tumor immune escape. A new puzzle has emerged for tumor immunologists to solve; how to harness immunity to "self" tumor antigens for cancer therapeutics.

High-titer HER-2/neu protein-specific antibody can be detected in patients with early-stage breast cancer

PURPOSE

To evaluate HER-2/neu-specific antibody immunity in patients with breast cancer, to determine the rate of occurrence of serum antibodies to HER-2/neu in patients with breast cancer, and to relate the presence of specific immunity to overexpression of HER-2/neu protein in primary tumor.

METHODS

The antibody response to HER-2/neu protein was analyzed in 107 newly diagnosed breast cancer patients. Sera was analyzed for the presence of HER-2/neu-specific antibodies with a capture enzyme-linked immunosorbent assay (ELISA) and verified by Western blot. Sera from 200 volunteer blood donors was used as a control population.

RESULTS

The presence of antibodies to HER-2/neu correlated with the presence of breast cancer. HER-2/neu antibodies at titers of > or = 1:100 were detected in 12 of 107 (11%) breast cancer patients versus none of 200 (0%) normal controls (P < .01). The presence of antibodies to HER-2/neu also correlated to overexpression of HER-2/neu protein in the patient's primary tumor. Nine of 44 (20%) patients with HER-2/neu-positive tumors had HER-2/neu-specific antibodies, whereas three of 63 (5%) patients with HER-2/neu-negative tumors had antibodies (P = .03). The antibody responses could be substantial. Titers of greater than 1:5,000 were detected in five of 107 (5%).

CONCLUSION

The presence of HER-2/neu antibodies in breast cancer patients and the correlation with HER-2/neu-positive cancer implies that immunity to HER-2/neu develops as a result of exposure of patients to HER-2/neu protein expressed by their own cancer. These findings should stimulate further studies to develop the detection of immunity to oncogenic proteins as tumor markers, as well as the development and testing of vaccine strategies to induce and augment immunity to HER-2/neu for the treatment of breast cancer or prevention of recurrent disease.

Identification of Her-2/Neu CTL epitopes using double transgenic mice expressing HLA-A2.1 and human CD.8

The Her-2/neu protooncogene is associated with malignant transformation and aggressive disease. Because of its overexpression in tumor cells and because it has been shown to be immunogenic, this protein represents an excellent target for T-cell immunotherapy. By identifying potential HLA-A2.1-binding peptides from the Her-2/neu sequence, peptides were selected as candidate T-cell epitopes. The immunogenicity of each peptide was evaluated by priming double transgenic mice expressing both the human (hu) CD8 and HLA-A2.1 molecules with synthetic peptides corresponding to these sequences. Because of the lack of interaction between murine CD8 and HLA-A2.1, expression of huCD8 on murine cells facilitates recognition of HLA molecules on human tumor cell lines. This led to the identification of two peptides that elicit an A2-restricted CTL response, one of which has not been previously identified. Both peptide-specific CTL populations were able to specifically lyse A2.1 and Her-2/neu expressing human tumor cells originating from a variety of tissues, demonstrating the utility of this murine model in identifying peptides presented by human cells. However, several Her-2/neu peptides previously reported to be immunogenic for human CTL were found not to be immunogenic in transgenic mice. The basis for these discrepancies is discussed.

HER-2/neu protein: a target for antigen-specific immunotherapy of human cancer

The HER-2/neu oncogenic protein is a tumor antigen. Some patients with cancer have a preexistent immune response directed against the HER-2/neu protein. Effective cancer vaccines targeting HER-2/neu will be able to boost this immunity to potentially therapeutic levels. In addition, HER-2/neu-directed monoclonal antibody therapy has been effective in eradicating malignancy in animal models and has shown benefit in the treatment of human HER-2/neu-overexpressing cancers. This review outlines studies that define HER-2/neu-specific immunity in patients with cancer and overviews the current vaccine strategies for generating or augmenting neu-specific immunity. The potential problems associated with eliciting HER-2/neu-specific immunity are addressed, including the question of precipitating autoimmune toxicity against this "self" -protein and the mechanisms of immunological escape that may play a role in preventing effective function of the HER-2/neu-specific immune response. Finally, antibody-based HER-2/neu-directed therapies are overviewed. HER-2/neu is a prototype antigen for groups investigating innovative modifications of monoclonal antibody technology, and cutting edge therapies targeting this antigen are being contemplated for clinical use in the treatment of human malignancy. Immune-based treatments designed to target the HER-2/neu oncogenic protein will soon give the clinical oncologist new therapeutic weapons, directed against a biologically relevant tumor-related protein, with which to fight cancer.

Oncogenic proteins as tumor antigens

Human immune responses to oncogenic proteins have been reported and are continuing to be defined. Immunity to nonmutated overexpressed oncoproteins as well as to mutated or unique cancer-specific oncoproteins has been identified. Immune system based treatments targeting oncogenic proteins have shown therapeutic efficacy in animals models and are currently being translated into human clinical trials.

Granulocyte-macrophage colony-stimulating factor: an effective adjuvant for protein and peptide-based vaccines

The current studies evaluate granulocyte-macrophage colony-stimulating factor (GM-CSF) as a vaccine adjuvant. An important issue for developing vaccine therapy for human malignancy is identifying adjuvants that can elicit T-cell responses to proteins and peptides derived from "self" tumor antigens. GM-CSF, in vitro, stimulates the growth of antigen-presenting cells such as dendritic cells and macrophages. Initial experiments examined whether GM-CSF injected into the skin of rats could affect the number or character of antigen presenting cells, measured as class II major histocompatability complex expressing cells, in lymph nodes draining the injection site. Intradermal (id) inoculation of GM-CSF every 24 hours for a total of five inoculations resulted in an increase of class II+ fluorescing cells that peaked at the fourth inoculation. Subcutaneous (sq) inoculation resulted in an increase of class II+ fluorescing cells that peaked following the second inoculation, then decreased over time. Using this schema for "conditioning" the inoculation site, GM-CSF was administered id or sq for five injections and a foreign antigen, tetanus toxoid (tt), was given at the beginning or the end of the immunization cycle. Id immunization was more effective than sq at eliciting tt specific immunity. In addition, GM-CSF id, administered as a single dose with antigen, compared favorably with complete Freund's adjuvant (CFA) and alum in eliciting tt specific antibody and cellular immunity. We have shown that immunity to rat neu (c-erbB-2) protein, an oncogenic self protein, can be generated in rats by immunization with peptides derived from the normal rat neu sequence plus CFA. The current study demonstrates that rat neu peptides inoculated with GM-CSF could elicit a strong delayed type hypersensitivity reaction (DTH) response, whereas peptides alone were non-immunogenic. GM-CSF was as effective as CFA in generating rat neu specific DTH responses after immunization with a neu peptide based vaccine. Soluble GM-CSF is a potent adjuvant for the generation of immune responses to foreign proteins as well as peptides derived from a self tumor antigen.

Peptide-based, but not whole protein, vaccines elicit immunity to HER-2/neu, oncogenic self-protein

HER-2/neu, an overexpressed oncogenic protein, has been proposed as a human cancer vaccine target. HER-2/neu is a "self" protein, however, and methods of vaccine strategies that would be effective in immunizing patients to a "self" tumor Ag have not been established. Many of the tumor Ags defined in humans are nonmutated self proteins, e.g., MAGE, and overcoming tolerance may be key in the generation of effective anti-tumor immunity. One theory states that tolerance to self proteins is directed only to dominant epitopes of proteins and not to every portion of the protein. Accordingly, tolerance can be circumvented by immunization to peptide fragments, but not whole protein. The studies outlined here demonstrate rat neu-specific immunity could be elicited in rats by vaccination with immunogenic rat neu peptides, but not by immunization with the intact protein. A rat model was used since rat neu protein is 89% homologous to human HER-2/neu protein and has a similar tissue distribution and level of expression. Rats were immunized with groups of peptides derived from the amino acid sequence of the intracellular domain or extracellular domain of rat neu protein and both groups developed CD4+ T cell immunity and Ab immunity to rat neu peptides and protein. Animals immunized in a similar fashion with intact purified rat neu protein did not develop Ab or T cell immunity to rat neu. Furthermore, rats that developed neu-specific immunity showed no histopathologic evidence of autoimmunity directed against organs expressing basal levels of rat neu protein. These studies suggest an immunization strategy that might be effective in human cancer vaccines targeting self tumor Ag.

Peptide-based, but not whole protein, vaccines elicit immunity to HER-2/neu, oncogenic self-protein

HER-2/neu, an overexpressed oncogenic protein, has been proposed as a human cancer vaccine target. HER-2/neu is a "self" protein, however, and methods of vaccine strategies that would be effective in immunizing patients to a "self" tumor Ag have not been established. Many of the tumor Ags defined in humans are nonmutated self proteins, e.g., MAGE, and overcoming tolerance may be key in the generation of effective anti-tumor immunity. One theory states that tolerance to self proteins is directed only to dominant epitopes of proteins and not to every portion of the protein. Accordingly, tolerance can be circumvented by immunization to peptide fragments, but not whole protein. The studies outlined here demonstrate rat neu-specific immunity could be elicited in rats by vaccination with immunogenic rat neu peptides, but not by immunization with the intact protein. A rat model was used since rat neu protein is 89% homologous to human HER-2/neu protein and has a similar tissue distribution and level of expression. Rats were immunized with groups of peptides derived from the amino acid sequence of the intracellular domain or extracellular domain of rat neu protein and both groups developed CD4+ T cell immunity and Ab immunity to rat neu peptides and protein. Animals immunized in a similar fashion with intact purified rat neu protein did not develop Ab or T cell immunity to rat neu. Furthermore, rats that developed neu-specific immunity showed no histopathologic evidence of autoimmunity directed against organs expressing basal levels of rat neu protein. These studies suggest an immunization strategy that might be effective in human cancer vaccines targeting self tumor Ag.

Antibody to ras proteins in patients with colon cancer

The current study examined sera from 160 colon cancer patients and 60 normal individuals to determine whether antibody to mutated p21 ras protein was present. Studies focused on the aspartic acid substitution at amino acid position 12 (denoted D12), one of the most common mutations in colon adenocarcinoma. IgA antibodies directed against mutated p21 ras-D12 protein were detected in 51 (32%) of 160 colon cancer patients, but only in 1 (2.5%) of 40 normal individuals. The greater incidence of antibody in cancer patients provides presumptive evidence that immunization to the ras proteins occurred as a result of the malignancy. Examination of sera for antibody reactivity to wild-type p21 ras protein (denoted p21 ras-G12) as well as p21 ras proteins bearing the D12, V12, S12, or L61 mutations showed that antibody detected was largely to normal segments of the p21 ras protein. Epitope mapping, using peptide neutralization assays with mutated or normal ras peptides as competitors, demonstrated that in 10 (67%) of 15 sera examined the antibody reactivity to p21 ras-G12 protein was neutralized by peptides near the carboxyl terminus of p21 ras protein, but not by peptides spanning the specific point mutation region. Antibody reactivities correlated with peripheral blood lymphocyte count, but did not correlate with patient age, sex, histology, stage, tumor locus, lymph node metastasis, or serum carcinoembryonic antigen.

CD4+ T-cell immunity to mutated ras protein in pancreatic and colon cancer patients

Mutated p21 ras proteins contain single substituted amino acid residues and represent cancer-specific proteins. The current study examined whether primed T cell immunity to mutant p21 ras proteins and/or peptides can be detected in patients with pancreatic or colon cancer. Studies focused on the aspartic acid substitution in amino acid position 12 (denoted D12) as the commonest mutation in gastrointestinal malignancy. Peripheral blood lymphocytes from patients or normal individuals were tested for the ability to proliferate in response to normal or mutated ras peptides or proteins. T-cell responses were defined as a stimulation index of > 2.0. Results showed that 7 of 16 (44%) pancreatic cancer patients responded to ras-D12 peptide. Responses to ras-D12 protein were studied in only the last four patients that responded to D12 peptides. Three of the 4 patients that responded to ras-D12 peptide showed a substantial response to p21 ras-D12 protein (stimulation indices of 12, 8, and 24). Specificity was validated by examining responses to normal and alternate ras peptides and proteins. T-cell responses to ras-D12 peptides were detected in only 2 of 25 (8%) colon cancer patients. None of 11 normal individuals tested had positive responses to normal or mutant ras p21 proteins and/or peptides. Thus, CD4+ T-cell immunity to the mutated segment of ras protein is present in some patients with gastrointestinal cancer.

Generation of immunostimulatory dendritic cells from human CD34+ hematopoietic progenitor cells of the bone marrow and peripheral blood

Dendritic antigen-presenting cells are considered to be the most effective stimulators of T cell immunity. The use of dendritic cells has been proposed to generate therapeutic T cell responses to tumor antigens in cancer patients. One limitation is that the number of dendritic cells in peripheral blood is exceedingly low. Dendritic cells originate from CD34+ hematopoietic progenitor cells (HPC) which are present in the bone marrow and in small numbers in peripheral blood. CD34+ HPC can be mobilized into the peripheral blood by in vivo administration of granulocyte-colony-stimulating factor. The aim of the current study was to determine whether functional dendritic cells could be elicited and grown in vitro from CD34+ HPC derived from bone marrow or granulocyte-colony-stimulating factor-mobilized peripheral blood. Culture of CD34+ HPC with granulocyte-macrophage-colony-stimulating factor and tumor necrosis factor alpha yielded a heterogeneous cell population containing cells with typical dendritic morphology. Phenotypic studies demonstrated a loss of the CD34 molecule over 1 week and an increase in cells expressing surface markers associated with dendritic cells, CD1a, CD80 (B7/BB1), CD4, CD14, HLA-DR, and CD64 (Fc gamma RI). Function was validated in experiments showing that cultured cells could stimulate proliferation of allogeneic CD4+ and CD8+ T lymphocytes. Antigen-presenting capacity was further confirmed in experiments showing that cultured cells could effectively stimulate tetanus toxoid-specific responses and HER-2/neu peptide-specific responses. The derivation and expansion of dendritic cells from cultured bone marrow or granulocyte-colony-stimulating factor-mobilized CD34+ HPC may provide adequate numbers for testing of dendritic cells in clinical studies, such as vaccine and T cell therapy trials.

In vitro generation of human cytolytic T-cells specific for peptides derived from the HER-2/neu protooncogene protein

The development of T-cell therapy for the treatment of human malignancy has been hindered, in large part, by a lack of identifiable tumor antigens. Studies to identify potential T-cell targets in humans have been difficult because of practical problems limiting the use of in vivo immunization and a lack of reproducible in vitro priming methods. Oncogenic proteins are involved in malignant transformation and maintenance of the transformed phenotype and theoretically are potential targets to T-cell therapy. HER-2/neu protein is a protooncogene product overexpressed in a variety of human malignancies and is associated with malignant transformation and aggressive disease in human breast cancer. Previous studies have shown that some patients with breast cancer have existent helper/inducer T-cell immunity to p185HER-2/neu protein and peptides. The current study represents initial attempts to identify candidate cytotoxic T-lymphocyte (CTL) epitopes. Synthetic peptides were constructed identical to HER-2/neu protein segments with amino acid motifs similar to the published motif for HLA-2.1-binding peptides. Four peptides were synthesized and two were shown to be avid binders to HLA-A2.1. Two of the four peptides could be shown to elicit peptide-specific CTL by primary in vitro immunization in a culture system using peripheral blood lymphocytes from a normal individual homozygous for HLA-A2. p185HER-2/neu protooncogene protein contains immunogenic epitopes capable of generating human CD8+ CTL. The identification of candidate CTL epitopes will allow studies to determine whether some cancer patients have existent CTL immunity to HER-2/neu protein. The demonstrated ability to generate human peptide-specific CTL in vitro allows screening of other oncogenic proteins to identify candidate T-cell epitopes potentially useful for future immunotherapy studies.

Existent T-cell and antibody immunity to HER-2/neu protein in patients with breast cancer

The HER-2/neu protooncogene is amplified and overexpressed in 20-40% of invasive breast cancers. HER-2/neu protein overexpression is associated with aggressive disease and is an independent predictor of poor prognosis in several subsets of patients. The protein may also be related to cancer formation, with overexpression being detectable in 50-60% of ductal carcinomas in situ. It has been suggested that it might be possible to develop specific T-cell therapy directed against proteins involved in malignant transformation. One question is whether normal proteins that are overexpressed are appropriate targets for therapeutic immune attack. This report demonstrates that some patients with HER-2/neu-positive breast cancers have both existent CD4+ helper/inducer T-cell immunity and antibody-mediated immunity to HER-2/neu protein. Initial studies performed on 20 premenopausal breast cancer patients identified antibodies to HER-2/neu in 11 individuals. Similar antibody responses have been found in some normal individuals. The patient with the greatest antibody response was studied in detail. In addition to a humoral immune response this patient had evidence of a significant proliferative T-cell response to the HER-2/neu protein and peptides. Similar T-cell responses have been detected in additional patients. It has been assumed that patients would be immunologically tolerant to HER-2/neu as a self-protein and that immunity might be difficult to generate. If immunity could be generated, the result might be destructive autoimmunity. The current data support the notion that HER-2/neu-specific immunity might be used in therapy without destroying normal tissue but also raises questions as to the role of existent immunity in immune surveillance and cancer progression.