Immunoediting of cancers may lead to epithelial to mesenchymal transition

Tumors evade both natural and pharmacologically induced (e.g., vaccines) immunity by a variety of mechanisms, including induction of tolerance and immunoediting. Immunoediting results in reshaping the immunogenicity of the tumor, which can be accompanied by loss of Ag expression and MHC molecules. In this study, we evaluated immunoediting in the neu-transgenic mouse model of breast cancer. A tumor cell line that retained expression of rat neu was generated from a spontaneous tumor of the neu-transgenic mouse and, when injected into the non-transgenic parental FVB/N mouse, resulted in the development of a strong immune response, initial rejection, and ultimately the emergence of neu Ag-loss variants. Morphologic and microarray data revealed that the immunoedited tumor cells underwent epithelial to mesenchymal transition accompanied by an up-regulation of invasion factors and increased invasiveness characteristic of mesenchymal tumor cells. These results suggest that immunoediting of tumor results in cellular reprogramming may be accompanied by alterations in tumor characteristics including increased invasive potential. Understanding the mechanisms by which tumors are immunoedited will likely lead to a better understanding of how tumors evade immune detection.

T-cell immunity to the folate receptor alpha is prevalent in women with breast or ovarian cancer

PURPOSE

Studies have demonstrated that the generation of immunity to tumor antigens is associated with improved prognosis for many cancers. A candidate antigen is the folate receptor alpha (FRalpha), which is overexpressed in breast and ovarian cancers. Our goal in this study was to attain a better understanding of the extent of endogenous FRalpha immunity.

METHODS

Using a CD4+ T cell epitope prediction algorithm, we predicted promiscuous epitopes of FRalpha, and tested for immunity in 30 breast (n = 17) or ovarian (n = 13) cancer patients and 18 healthy donors using enzyme-linked immunospot analysis.

RESULTS

Fourteen peptides were predicted, seven each from the carboxy- and amino-terminus halves of the protein. More than 70% of patients demonstrated immunity to at least one FRalpha peptide. Patients responded to an average of 3 +/- 0.5 peptides, whereas healthy donors responded to 1 +/- 0.4 peptides (P = .004). Five peptides were recognized by more than 25% of patients. Responses to three peptides were higher (P < .05) in patients than in healthy donors, suggesting augmented immunity. Compared with healthy individuals, patients developed higher immunity to the amino-terminus half of the receptor (P = .03). There was no difference between each group in the responses to nonspecific (P = .2) and viral stimuli (P = .5). Lastly, patients demonstrated elevated levels of FRalpha antibodies consistent with a coordinated immune response.

CONCLUSION

These findings demonstrate that the FRalpha is a target of the immune system in breast and ovarian cancer patients. Understanding which antigens are targeted by the immune system may be important for prognosis or immune-based therapies.

IL-2 immunotoxin therapy modulates tumor-associated regulatory T cells and leads to lasting immune-mediated rejection of breast cancers in neu-transgenic mice

Studies in cancer patients have suggested that breast tumors recruit regulatory T cells (Tregs) into the tumor microenvironment. The extent to which local Tregs suppress antitumor immunity in breast cancer is unknown. We questioned whether inhibiting systemic Tregs with an IL-2 immunotoxin in a model of neu-mediated breast cancer, the neu-transgenic mouse, could impact disease progression and survival. As in human breast cancer, cancers that develop in these mice attract Tregs into the tumor microenvironment to levels of approximately 10-25% of the total CD4+ T cells. To examine the role of Tregs in blocking immune-mediated rejection of tumor, we depleted CD4+CD25+ T cells with an IL-2 immunotoxin. The treatment depleted Tregs without concomitant lymphopenia and markedly inhibited tumor growth. Depletion of Tregs resulted in a persistent antitumor response that was maintained over a month after the last treatment. The clinical response was immune-mediated because adoptive transfer of Tregs led to a complete abrogation of the therapeutic effects of immunotoxin treatment. Further, Treg down-modulation was accompanied by increased Ag-specific immunity against the neu protein, a self Ag. These results suggest that Tregs play a major role in preventing an effective endogenous immune response against breast cancer and that depletion of Tregs, without any additional immunotherapy, may mediate a significant antitumor response.

Laboratory analysis of T-cell immunity

Immune-based strategies for treating and preventing cancer are increasingly being tested and include cancer vaccination, adoptive T cell therapy, and cytokine therapy. An important component of testing and development of immune-based strategies is monitoring the immunologic response. The ability to monitor T cell immunity has been suboptimal. The measurement of tumor-specific immunity will aid in defining which strategies should be moved forward in clinical trials and which should be eliminated or evaluated further in the preclinical realm. Immunologic monitoring is necessary for determining if an approach has immunologic efficacy and ultimately whether immunologic responses correlate with a clinical response. This article discusses several important elements of measuring T cell immunity such as validation principles, laboratory issues, current approaches, and new paradigms and concepts for future testing. Informative immunologic monitoring of T cells will be one of the driving forces in advancing the field of tumor immunology.

Antitumor efficacy of CD137 ligation is maximized by the use of a CD137 single-chain Fv-expressing whole-cell tumor vaccine compared with CD137-specific monoclonal antibody infusion

Tumor-destructive immune responses can be generated by engaging CD137 (4-1BB) via infusing a monoclonal antibody specific for CD137 or vaccinating with a single-chain Fv (scFv) CD137-expressing whole-cell tumor vaccine. We assessed whether such a vaccine can induce tumor rejection in the neu-transgenic (neu-Tg) mouse breast cancer model and compared the antitumor efficacy of vaccination with the infusion of a CD137-specific antibody. Mammary carcinoma cells (MMC) from a neu-Tg mouse were transfected to stably express surface scFv derived from the anti-CD137 rat hybridoma 1D8 or 3H3. The anti-CD137 scFv-expressing cells were rejected when transplanted into neu-Tg mice by a mechanism that involved both CD4(+) and CD8(+) T cells, and vaccination with such cells delayed the outgrowth of MMC cells transplanted 3 days previously. T cells from neu-Tg mice that had been vaccinated proliferated and produced IFN-gamma when stimulated by MMC but not by antigen-negative variant breast cancer cells that did not express the neu tumor antigen. In addition, antibodies binding to the MMC but not to antigen-negative variant cells were detected in sera from some but not all of the immunized mice. Complete regression of s.c. transplanted MMC tumors was observed in mice repeatedly immunized against MMC-1D8 starting on the day the MMC cells were transplanted. In contrast, repeated administration of either of two different anti-CD137 monoclonal antibodies did not induce complete tumor regression, although tumor growth was delayed.

Tumor cells transduced with the MHC class II Transactivator and CD80 activate tumor-specific CD4+ T cells whether or not they are silenced for invariant chain

The specificity and potency of the immune system make immunotherapy a potential strategy for the treatment of cancer. To exploit this potential, we have developed cell-based cancer vaccines consisting of tumor cells expressing syngeneic MHC class II and costimulatory molecules. The vaccines mediate tumor regression in mice and activate human CD4+ T cells in vitro. Previous vaccines were generated by transducing MHC II negative tumor cells with a single HLA-DR allele. Because expression of multiple MHC II alleles would facilitate presentation of a broader repertoire of tumor antigens, we have now transduced tumor cells with the MHC class II transactivator (CIITA), a regulatory gene that coordinately increases expression of all MHC II alleles. Previous studies in mice indicated that coexpression of the MHC II accessory molecule invariant chain (Ii) inhibited presentation of endogenously synthesized tumor antigens and reduced vaccine efficacy. To determine if Ii expression affects presentation of MHC class II-restricted endogenously synthesized tumor antigens in human tumor cells, HLA-DR-MCF10 breast cancer cells were transduced with the CIITA, CD80 costimulatory molecule gene, and with or without small interfering RNAs (siRNA) specific for Ii. Ii expression is silenced >95% in CIITA/CD80/siRNA transductants; down-regulation of Ii does not affect HLA-DR expression or stability; and Ii(+) and Ii(-) transductants activate human CD4+ T cells to DRB1*0701-restricted HER-2/neu epitopes. Therefore, tumor cells transduced with the CIITA, CD80, and with or without Ii siRNA present endogenously synthesized tumor antigens and are potential vaccines for activating tumor-specific CD4+ T cells.

Augmenting T helper cell immunity in cancer

Cancer specific immunity elicited with vaccines has traditionally focused on the activation of the CD8 cytolytic T lymphocyte (CTL) often involving direct stimulation of immunity using HLA-class I binding peptide epitopes. Recently it has become clear that activation of the CTL immune effector arm alone is insufficient to mediate an anticancer response. A major problem is that CD8 T cells alone can not be sustained without the concomitant activation of CD4 T helper (Th) cells. In fact, it is now widely recognized that the Th cell regulates nearly all aspects of the adaptive immune response. In addition, Th cells can recruit the innate immune system during immune augmentation. Therefore, the focus of the immune response in cancer has shifted away from activating CTL immunity alone to activating Th cell immunity alone or concurrently with CTL. Evidence suggests that activating the Th cell is sufficient to get a complete adaptive immune response because, once activated, the Th cell will elicit endogenous CD8 T cell and humoral immunity. In this review, we discuss the role of the Th cell in the adaptive immune response to cancer, how peptides that are capable of activation of Th cells are identified, and the clinical translation of newly identified candidate Th cell peptide epitopes to human cancer specific vaccines. Over the next decade, studies should begin to further define how we can manipulate the Th immune effector arm to achieve effective antitumor immunity.

Adoptive T cell therapy of solid cancers

The development of immune-based approaches for the treatment of cancer has been actively investigated for many years. One strategy that has emerged as a potentially effective strategy for the treatment of aggressive established malignancies is adoptive T cell therapy. The power of this approach has been repeatedly observed in preclinical animal models. However, moving from homogeneous animal models to the heterogeneous human clinical setting has been very difficult. It is only in recent times that we have been able to pinpoint the problems of the clinical translation of adoptive T cell therapy. Some of the major problems are sources of tumor-specific T cells, ex vivo expansion, persistence, and anti-tumor activity. This review overviews the nature of these problems and some of the emerging solutions.

Emergence of immune escape variant of mammary tumors that has distinct proteomic profile and a reduced ability to induce “danger signals”

Breast tumors are shaped, in part, by a process termed immunoediting which selects for immunologically evasive phenotypes. In the present study we used the rat neu-transgenic mouse model of breast cancer and its congenic non-transgenic parental strain, FVB, to explore the phenotype of tumors that emerge in the presence of an immune response directed against the neu antigen. When inoculated into parental FVB mice, a neu-overexpressing mouse mammary carcinoma (MMC) cell line isolated from spontaneous breast tumors of the FVB neu (FVBN202) transgenic mouse, elicited a neu-specific immune response resulting in a tumor rejection because of the presence of the rat neu antigen. However, a neu negative variant (ANV) of MMC arose after a long latency in spite of the neu-specific immune response. We show that compared to MMC, ANV tumor cells have a significantly reduced ability to secrete pro-inflammatory cytokines and the CCL5 chemokine, to express immunostimulatory chaperones, and they have a distinct expression of proteins involved in cell motility, and metabolic and signal transduction pathways. These studies suggest that tumor escape through immunoediting can not be explained by the loss of a single tumor antigen, but rather by a selection process of a tumor variant that has a reduced ability to induce "danger signals" together with up-regulation of proteins involved in the tumor survival. Based on these findings, we propose to target novel antigens over-expressed in the escape variant of breast tumors to treat primary tumor and to prevent tumor relapse.

Tumor antigen-specific T helper cells in cancer immunity and immunotherapy

Historically, cancer-directed immune-based therapies have focused on eliciting a cytotoxic T cell (CTL) response, primarily due to the fact that CTL can directly kill tumors. In addition, many putative tumor antigens are intracellular proteins, and CTL respond to peptides presented in the context of MHC class I which are most often derived from intracellular proteins. Recently, increasing importance is being given to the stimulation of a CD4+ T helper cell (Th) response in cancer immunotherapy. Th cells are central to the development of an immune response by activating antigen-specific effector cells and recruiting cells of the innate immune system such as macrophages and mast cells. Two predominant Th cell subtypes exist, Th1 and Th2. Th1 cells, characterized by secretion of IFN-gamma and TNF-alpha, are primarily responsible for activating and regulating the development and persistence of CTL. In addition, Th1 cells activate antigen-presenting cells (APC) and induce limited production of the type of antibodies that can enhance the uptake of infected cells or tumor cells into APC. Th2 cells favor a predominantly humoral response. Particularly important during Th differentiation is the cytokine environment at the site of antigen deposition or in the local lymph node. Th1 commitment relies on the local production of IL-12, and Th2 development is promoted by IL-4 in the absence of IL-12. Specifically modulating the Th1 cell response against a tumor antigen may lead to effective immune-based therapies. Th1 cells are already widely implicated in the tissue-specific destruction that occurs during the pathogenesis of autoimmune diseases, such as diabetes mellitus and multiple sclerosis. Th1 cells directly kill tumor cells via release of cytokines that activate death receptors on the tumor cell surface. We now know that cross-priming of the tumor-specific response by potent APC is a major mechanism of the developing endogenous immune response; therefore, even intracellular proteins can be presented in the context of MHC class II. Indeed, recent studies demonstrate the importance of cross-priming in eliciting CTL. Many vaccine strategies aim to stimulate the Th response specific for a tumor antigen. Early clinical trials have shown that focus on the Th effector arm of the immune system can result in significant levels of both antigen-specific Th cells and CTL, the generation of long lasting immunity, and a Th1 phenotype resulting in the development of epitope spreading.

Humoral Epitope-Spreading Following Immunization with a HER-2/neu Peptide Based Vaccine in Cancer Patients

HER-2/neu is a tumor antigen in patients with breast and ovarian cancer. Multiple varieties of vaccine strategies are being developed to immunize patients against HER-2/neu. Studies in animal models have demonstrated both T cell and antibody immunity are needed to mediate an antitumor response. Thirty-five patients, immunized with HER-2/neu peptide based vaccines, were evaluated for the generation of HER-2/neu-specific antibody immunity. Sixty percent of patients developed HER-2/neu IgG specific antibody responses to at least one peptide included in their vaccine. Twenty-nine percent of patients developed IgG immunity to the native HER-2/neu protein after peptide immunization. Humoral intramolecular epitope-spreading within the HER-2/neu protein occurred in 49% of immunized patients. Intermolecular epitope-spreading to p53 was evident in 20% of vaccinated patients. Of those patients who developed new immunity to p53, 71% had demonstrated antibody epitope-spreading within HER-2/neu.

Specific recruitment of regulatory T cells in ovarian carcinoma fosters immune privilege and predicts reduced survival

Regulatory T (T(reg)) cells mediate homeostatic peripheral tolerance by suppressing autoreactive T cells. Failure of host antitumor immunity may be caused by exaggerated suppression of tumor-associated antigen-reactive lymphocytes mediated by T(reg) cells; however, definitive evidence that T(reg) cells have an immunopathological role in human cancer is lacking. Here we show, in detailed studies of CD4(+)CD25(+)FOXP3(+) T(reg) cells in 104 individuals affected with ovarian carcinoma, that human tumor T(reg) cells suppress tumor-specific T cell immunity and contribute to growth of human tumors in vivo. We also show that tumor T(reg) cells are associated with a high death hazard and reduced survival. Human T(reg) cells preferentially move to and accumulate in tumors and ascites, but rarely enter draining lymph nodes in later cancer stages. Tumor cells and microenvironmental macrophages produce the chemokine CCL22, which mediates trafficking of T(reg) cells to the tumor. This specific recruitment of T(reg) cells represents a mechanism by which tumors may foster immune privilege. Thus, blocking T(reg) cell migration or function may help to defeat human cancer.

Effect of Dose on Immune Response in Patients Vaccinated With an HER-2/neu Intracellular Domain Protein—Based Vaccine

Purpose

To evaluate the safety of an HER-2/neu intracellular domain (ICD) protein vaccine and to estimate whether vaccine dose impacts immunogenicity.

Patients and Methods

Twenty-nine patients with HER-2/neu—overexpressing breast or ovarian cancer and with no evidence of disease after standard therapy received a low- (25 μg), intermediate- (150 μg), or high-dose (900 μg) HER-2/neu ICD protein vaccine. The vaccine was administered intradermally, monthly for 6 months, with granulocyte-macrophage colony-stimulating factor as an adjuvant. Toxicity and both cellular and humoral HER-2/neu—specific immunity was evaluated.

Results

The vaccine was well tolerated. The majority of patients (89%) developed HER-2/neu ICD-specific T-cell immunity. The dose of vaccine did not predict the magnitude of the T-cell response. The majority of patients (82%) also developed HER-2/neu—specific immunoglobulin G antibody immunity. Vaccine dose did not predict magnitude or avidity of the HER-2/neu—specific humoral immune response. Time to development of detectable HER-2/neu—specific immunity, however, was significantly earlier for the high- versus low-dose vaccine group (P = .003). Over half the patients retained HER-2/neu—specific T-cell immunity 9 to 12 months after immunizations had ended.

Conclusion

The HER-2/neu ICD protein vaccine was well tolerated and effective in eliciting HER-2/neu—specific T-cell and antibody immunity in the majority of breast and ovarian cancer patients who completed the vaccine regimen. Although the dose of vaccine did not impact the magnitude of T-cell or antibody immunity elicited, patients receiving the highest dose developed HER-2/neu—specific immunity more rapidly than those who received the lowest dose.

Neu antigen-negative variants can be generated after neu-specific antibody therapy in neu transgenic mice

Prolonged administration of HER-2/neu-specific monoclonal antibody therapy is now widely used for the treatment of HER-2/neu-overexpressing tumors in advanced-stage breast cancer patients. Monoclonal antibody therapy has the potential to promote reduced tumor expression of HER-2/neu by receptor down-modulation and/or the generation of antigen-negative variants. Loss of antigen by either mechanism could potentially impact subsequent therapeutic strategies targeting HER-2/neu. In this study, the effects of chronic neu-specific monoclonal antibody therapy on tumor growth and neu protein expression were examined in a murine model of neu-overexpressing breast cancer. Treatment of neu-overexpressing tumors with neu-specific antibody, in vitro or in vivo, resulted in significant tumor growth inhibition. When neu antibody was used to treat neu-overexpressing tumor cells both in vitro and in vivo in tumor-bearing mice, neu receptor expression was not diminished after cessation of therapy. However, in the setting of clinically undetectable disease in a fraction of animals, antigen-negative variants were generated. An understanding of the effects of monoclonal antibodies on target antigen expression is critical for the future design and testing of novel HER-2/neu-targeted therapies administered in combination with or after HER-2/neu-specific monoclonal antibody therapy.

IL-12 enhances the generation of tumour antigen-specific Th1 CD4 T cells during ex vivo expansion

CD4+ T cells are essential for the immune response against cancer. Vaccination against cancer will likely only be effective at preventing growth of micrometastatic disease while adoptive T cell therapy will be better suited for eradication of bulky pre-existing disease (Knutson et al. Expert Opin Biol Ther 2002; 2:55-66). Problems with the use of adoptive T cell therapy include lack of CD4+ T cell help, low frequency of antigen-specific T cells, and lack of effective ex vivo expansion techniques. In this study, we focused on improving ex vivo expansion of CD4+ T helper cells. The effects of IL-12, along with IL-2, on the ex vivo generation of HER-2/neu antigen-specific T cells were examined. Patients were immunized with a peptide-based vaccine that contained a helper epitope, p776-790, derived from the intracellular domain of HER-2/neu. While T cell immunity to p776-790, assessed by proliferation assays, could be readily measured in short-term cultures, cell line generation by multiple in vitro stimulation with peptide and IL-2 as the only added cytokine resulted in loss of antigen-specific proliferation. The inclusion of IL-12, along with IL-2, restored antigen-specific proliferation in a dose-dependent fashion. The resulting p776-790-specific T cells responded readily to antigen by proliferating and producing type I cytokines (IFN-gamma and TNF-alpha). The increased proliferative response of the cultures was due in part to an increase in the number of HER-2/neu-specific T cells. These results suggest that IL-12 is an important cytokine for ex vivo recovery and maintenance of antigen-specific CD4+ T lymphocytes that would otherwise be lost by using IL-2 alone in combination with antigen. Furthermore, these results have important implications for ex vivo expansion of CD4+ T cell for use in anti-tumour adoptive immunotherapy.

Soluble cytokines can act as effective adjuvants in plasmid DNA vaccines targeting self tumor antigens

There are few vaccination strategies available for the reproducible generation of a cytotoxic T cell (CTL) response, particularly in the setting of immunizing against a tumor antigen. Plasmid-based DNA vaccination offers several advantages as compared to MHC class I peptide-based vaccines or DNA immunization using viral vectors. Plasmid-based DNA vaccines are easily produced, can potentially elicit both an MHC class I and class II response, and have little infectious potential. Plasmid-based vaccines, however, have been poorly immunogenic. The systemic immune response generated after plasmid vaccination relies on in vivo transfection of local antigen presenting cells (APC) and both direct presentation and "cross priming" of antigen by professional and non-professional APC. Therefore, methods to enhance the function of APC, such as simultaneous inoculation with plasmids encoding cytokine genes, has resulted in an enhancement of detectable immunity after vaccination. We questioned whether local application of soluble cytokines would be effective in enhancing the systemic immune response elicited after DNA vaccination. Using a self-tumor antigen model, we vaccinated rats with a plasmid-based rat neu intracellular domain (ICD) DNA construct and either no adjuvant, soluble GM-CSF, or IL-12. We demonstrate that the addition of soluble GM-CSF or IL-12 to rat neu ICD DNA vaccination elicits detectable neu specific T cell immunity; specifically the generation of CTL. Antibodies directed against rat neu were not elicited with this approach, indicating that the neu specific T cell immune response elicited with plasmid DNA was skewed towards cell-mediated rather than humoral immunity.

Peptide-based vaccines in breast cancer

Human tumors are immunogenic and tumor-associated proteins that generate immunity in cancer patients have been defined. Many of these proteins are involved in the malignant transformation and play a role in either initiating or maintaining the malignant phenotype. Furthermore, due to technical advances in basic immunology over the last decade we have a better understanding of the immune effector cell phenotypes that are potentially involved in tumor eradication and have developed methods to quantitate and characterize these immune effectors. Breast cancer is an intriguing model tumor to target with active immunization. Dozens of breast cancer antigens have been defined [1]. Although many patients with breast cancer can be rendered free of disease with standard therapy such as surgery, radiation, and chemotherapy, some patients will have their disease recur. However, relapse may not occur for many months to years after definitive treatment giving an extended period of micrometastatic disease that may be amenable to immune eradication or modulation. Peptide based vaccines are one of the most commonly studied vaccine strategies targeting breast cancer.

Immunization of cancer patients with HER-2/neu-derived peptides demonstrating high-affinity binding to multiple class II alleles

PURPOSE

The purpose of this study was to immunize patients with HER-2/neu-overexpressing cancer with a multipeptide vaccine comprised of four class II HER-2/neu peptides that had been identified as the most immunogenic in a previous clinical trial. Furthermore, we questioned whether MHC binding affinity could predict the in vivo immunogenicity of the HER-2/neu helper peptides.

EXPERIMENTAL DESIGN

Four putative class II HER-2/neu peptides, which were found to generate detectable specific T-cell responses (stimulation index > 2) in a majority of patients in a previous study, were used to formulate a single vaccine. The multipeptide vaccine was administered intradermally with granulocyte macrophage colony-stimulating factor as an adjuvant. Ten patients with HER-2/neu overexpressing breast or lung cancer were enrolled. HER-2/neu peptide-and protein-specific T cell and antibody immune responses were measured. Competitive inhibition assays were used to analyze the class II HER-2/neu peptides for their binding affinity to 14 common HLA-DR alleles.

RESULTS

Twenty-five percent of patients developed HER-2/neu peptide-specific T-cell immunity, and 50% developed HER-2/neu peptide-specific antibody immunity. No patient developed HER-2/neu protein-specific T cell or antibody immunity. The majority of peptides exhibited high binding affinity, in vitro, to >/==" BORDER="0">3 of the 14 DR alleles analyzed.

CONCLUSION

The group of peptides used in this study demonstrated high binding affinity to multiple DR alleles suggesting that in vitro binding affinity may be able to predict the in vivo immunogenicity of class II peptides. However, only a minority of patients immunized with the multipeptide vaccine developed HER-2/neu peptide-specific T cell or antibody immunity, and none developed HER-2/neu protein-specific immunity.

Plasmid-based vaccines encoding rat neu and immune stimulatory molecules can elicit rat neu-specific immunity

DNA vaccines are ideally suited for immunizing against tumor antigens because constructs can be formulated that not only encode the tumor antigen but also encode molecules chosen to improve the ability to elicit an antitumor response. Ligands expressed on antigen-presenting cells associated with stimulating a robust T-cell response are excellent candidates for inclusion in a DNA vaccine. Mice transgenic for the HER-2/neu homologue, rat neu, were immunized with full-length rat neu cDNA given alone or in combination with plasmids encoding costimulatory molecules CD80 or CD86 and the ligand for CD137 (CD137L). Intradermal injection of the plasmid constructs resulted in both plasmid transcript and antigen protein expression being detected in lymph nodes draining the injection site. Immunization with plasmids encoding the neu antigen along with plasmids encoding CD137L and either CD80 or CD86 resulted in the generation of neu-specific antibodies that induced phopshorylation of the neu tyrosine kinase and inhibited the growth of cultured tumor cells overexpressing neu. Survival of animals was significantly prolonged after immunization with vaccines encoding neu together with the costimulatory molecules. Although tumors eventually occurred in the vaccinated animals, they were markedly infiltrated with CD4+ T cells. DNA vaccines encoding neu, when given in combination with both CD137L and either CD80 or CD86, can induce cellular and humoral immunity and result in an antitumor effect.

Immunologic principles and immunotherapeutic approaches in ovarian cancer

Ovarian cancer is an immunogenic tumor, and numerous antigens have been identified in recent years. Several of these antigens are important in regulating tumor growth and may be ideal targets for the development of immune-based strategies. In the absence of immunologic intervention, tumors evade the immune system by several mechanisms, most notably tolerance and immunosuppression. As understanding of the immune response improves, strategies are being designed to circumvent T-cell tolerance to self-antigens through modulation of APC function. In addition, techniques are being developed to identify reverse ovarian cancer-induced immune evasion tactics. The type of the immune-based therapy to apply varies with disease burden. It is hoped that discoveries at the bench along with lessons learned in prior clinical trials soon will allow clinicians to develop rationally based immunologic strategies to treat and prevent ovarian cancer.

Immunotherapy of glioblastoma multiforme

Glioblastoma multiforme is immunogenic and several glioblastoma multiforme-related antigens have now been identified. In addition, the immunologic characteristics of the tumor microenvironment that may affect tumor growth are becoming increasingly understood. The type of immune-based approach selected to treat glioblastoma multiforme will depend on the tumor burden. For minimal disease states, active vaccination may be useful for generating adequate protection from relapse. However, for more advanced stage disease states, more rigorous strategies may need to be applied, such as adoptive T-cell therapy, antibody therapy or a combination of different techniques. The immunosuppressive environment observed during advanced malignancy may need to be reversed for improved efficacy of immune-based therapies.

Blockade of B7-H1 improves myeloid dendritic cell-mediated antitumor immunity

Suppression of dendritic cell function in cancer patients is thought to contribute to the inhibition of immune responses and disease progression. Molecular mechanisms of this suppression remain elusive, however. Here, we show that a fraction of blood monocyte-derived myeloid dendritic cells (MDCs) express B7-H1, a member of the B7 family, on the cell surface. B7-H1 could be further upregulated by tumor environmental factors. Consistent with this finding, virtually all MDCs isolated from the tissues or draining lymph nodes of ovarian carcinomas express B7-H1. Blockade of B7-H1 enhanced MDC-mediated T-cell activation and was accompanied by downregulation of T-cell interleukin (IL)-10 and upregulation of IL-2 and interferon (IFN)-gamma. T cells conditioned with the B7-H1-blocked MDCs had a more potent ability to inhibit autologous human ovarian carcinoma growth in non-obese diabetic-severe combined immunodeficient (NOD-SCID) mice. Therefore, upregulation of B7-H1 on MDCs in the tumor microenvironment downregulates T-cell immunity. Blockade of B7-H1 represents one approach for cancer immunotherapy.

Pilot study of an HLA-A2 peptide vaccine using flt3 ligand as a systemic vaccine adjuvant

A pilot vaccine study was conducted to test the safety and immunological efficacy of four monthly immunizations of an MHC class I peptide vaccine, the E75 HLA-A2 epitope from HER-2/neu, using flt3 ligand as a systemic vaccine adjuvant. Twenty HLA-A2-expressing subjects with advanced stage prostate cancer were randomly assigned to one of four immunization or treatment schedules: (a) Flt3 ligand (20 microg/kg per day) administered subcutaneously daily for 14 days on a 28-day cycle, monthly for four months; (b) flt3 ligand course as above with the E75 peptide vaccine administered on day 7 of each flt3 ligand cycle; (c) flt3 ligand course as above with the E75 peptide vaccine administered on day 14 of each flt3 ligand cycle; or (d) E75 peptide admixed with granulocyte-macrophage colony-stimulating factor and administered intradermally once every 28 days, as has previously been reported. The primary endpoints of the study were the determination of safety and immunological efficacy in generating E75-specific T cells as determined by peptide-specific interferon-gamma ELIspot. Adverse events included one grade 3 skin reaction and the development of grade 2 autoimmune hypothyroidism in two subjects with preexisting subclinical autoimmune hypothyroidism. Dendritic cells were markedly increased in the peripheral blood of subjects receiving flt3 ligand with each repetitive cycle, but augmentation of antigen-presenting cells within the dermis was not observed. Apart from a single subject, no significant peptide-specific T-cell responses were detected by ELIspot, whereas delayed-type hypersensitivity responses were detectable in control subjects and in subjects receiving peptide vaccine early in the course of flt3 ligand administration. The absence of robust peripheral immune responses in the current study may be attributable to the small numbers of subjects or differences in the subject population. In addition, the inability of fit3 ligand to augment the number of peripheral skin antigen-presenting cells may have contributed to the absence of robust peptide-specific immunity detectable in the peripheral blood of immunized subjects treated with flt3 ligand.

Technology evaluation: DCVax, Northwest Biotherapeutics

DCVax, a dendritic cell-based immunotherapy, is an active immunization platform being developed by Northwest Biotherapeutics for the potential treatment of multiple malignancies, including hormone-refractory metastatic prostate cancer, non-small-cell lung cancer, renal cancer and glioblastoma multiforme. The DCVax platform is tailored to a specific cancer type with either purified tumor-specific antigen or tumor cell extracts derived from patients at the time of resection. Phase I/II clinical trials of DCVax-Prostate have been completed, and phase III clinical trials have recently been initiated. DCVax-Brain is currently undergoing phase II clinical trials, and DCVax-Lung recently received approval from the US FDA for phase I clinical trials.

Clonal diversity of the T-cell population responding to a dominant HLA-A2 epitope of HER-2/neu after active immunization in an ovarian cancer patient

Natural antigen processing and presentation of antigen is thought to be important for the generation of a broad functional repertoire of antigen-specific T cells. In this study, the T-cell repertoire to an immunodominant human leukocyte antigen A2 (HLA-A2) binding peptide epitope of HER-2/neu, p369-377, was examined in a patient following immunization with a peptide-based vaccine consisting of helper peptides encompassing HLA-A2 peptide epitopes. The responding T-cell repertoire generated was both phenotypically and functionally diverse. A total of 21 p369-377 clones were generated from this patient. With the exception of two clones, all clones were CD3(+). Sixteen of the clones were CD8(+)/CD4(-). Five of the clones were CD4(+)/CD8(-), despite being generated with an HLA-A2 binding peptide. Nineteen of 21 of clones expressed the alpha beta-T-cell receptor (TCR). The remaining two clones expressed the gamma delta T-cell response (TCR). Selected alpha beta-TCR clones, both CD8(+) and CD4(+), could lyse HLA-A2 transfected HER2 overexpressing tumor cells and p369-377-loaded B-lymphoblastic cell line. In addition to their lytic capabilities these clones could be induced to produce interferon-gamma (IFN-gamma) specifically in response to p369-377 peptide stimulation. The 2 gamma delta-TCR clones expressed CD8 and lysed HLA-A2(+) HER-2/neu(+) tumor cells, but not HLA-A2(-) HER-2/neu(+) tumor cells. One of gamma delta-TCR clones also released IFN-gamma directly in response to p369-377 stimulation. These results suggest that a tumor antigen TCR, directed against a specific epitope, can be markedly polyclonal at multiple levels including CD4/CD8 and TCR.

Generation of T-cell immunity to the HER-2/neu protein after active immunization with HER-2/neu peptide-based vaccines

PURPOSE

The HER-2/neu protein is a nonmutated tumor antigen that is overexpressed in a variety of human malignancies, including breast and ovarian cancer. Many tumor antigens, such as MAGE and gp100, are self-proteins; therefore, effective vaccine strategies must circumvent tolerance. We hypothesized that immunizing patients with subdominant peptide epitopes derived from HER-2/neu, using an adjuvant known to recruit professional antigen-presenting cells, granulocyte-macrophage colony-stimulating factor, would result in the generation of T-cell immunity specific for the HER-2/neu protein.

PATIENTS AND METHODS

Sixty-four patients with HER-2/neu-overexpressing breast, ovarian, or non-small-cell lung cancers were enrolled. Vaccines were composed of peptides derived from potential T-helper epitopes of the HER-2/neu protein admixed with granulocyte-macrophage colony-stimulating factor and administered intradermally. Peripheral-blood mononuclear cells were evaluated at baseline, before vaccination, and after vaccination for antigen-specific T-cell immunity. Immunologic response data are presented on the 38 subjects who completed six vaccinations. Toxicity data are presented on all 64 patients enrolled.

RESULTS

Ninety-two percent of patients developed T-cell immunity to HER-2/neu peptides (stimulation index, 2.1 to 59) and 68% to a HER-2/neu protein domain (stimulation index range, 2 to 31). Epitope spreading was observed in 84% of patients and significantly correlated with the generation of a HER-2/neu protein-specific T-cell immunity (P =.03). At 1-year follow-up, immunity to the HER-2/neu protein persisted in 38% of patients.

CONCLUSION

The majority of patients with HER-2/neu-overexpressing cancers can develop immunity to both HER-2/neu peptides and protein. In addition, the generation of protein-specific immunity, after peptide immunization, was associated with epitope spreading, reflecting the initiation of an endogenous immune response. Finally, immunity can persist after active immunizations have ended.

Immunization of cancer patients with a HER-2/neu, HLA-A2 peptide, p369-377, results in short-lived peptide-specific immunity

Ideally, vaccines should be designed to elicit long-lived immunity. The goal of this study was to determine whether HER-2/neu peptide-specific CD8+ T-cell immunity could be elicited using an immunodominant HER-2/neu-derived HLA-A2 peptide alone in the absence of exogenous help. Granulocyte macrophage colony-stimulating factor (GM-CSF) was used as adjuvant. Six HLA-A2 patients with HER-2/neu-overexpressing cancers received 6 monthly vaccinations with a vaccine preparation consisting of 500 microg of HER-2/neu peptide, p369-377, admixed with 100 microg of GM-CSF. The patients had either stage III or IV breast or ovarian cancer. Immune responses to the p369-377 were examined using an IFN-gamma enzyme-linked immunosorbent spot assay. Before vaccination, the median precursor frequency (range), defined as precursors per 10(6) peripheral blood mononuclear cell, to p369-377 was 0 (no range). After vaccination, the median precursor frequency to p369-377 in four evaluable patients was 0 (0-116). Overall, HER-2/neu peptide-specific precursors developed to p369-377 in two of four evaluable subjects. The responses were short-lived and not detectable at 5 months after the final vaccination. Immunocompetence was evident, because patients had detectable enzyme-linked immunosorbent spot responses to tetanus toxoid and influenza. These results demonstrate that HER-2/neu MHC class I epitopes can induce HER-2/neu peptide-specific IFN-gamma-producing CD8+ T cells. However, the magnitude of the responses were low, as well as short-lived, suggesting that CD4+ T-cell help is required for lasting immunity to this epitope.

Flt3 ligand as a vaccine adjuvant in association with HER-2/neu peptide-based vaccines in patients with HER-2/neu-overexpressing cancers

Dendritic cells (DCs) are potent antigen-presenting cells and have shown promise to function as "natural" vaccine adjuvants. Currently, most cancer vaccine trials using DCs generate autologous DCs ex vivo for each patient. Systemic treatment with Flt3 ligand (FL) results in a marked increase of DCs in tissues such as spleen and lymph nodes in mice and in the peripheral blood and skin of humans. In light of these observations, we questioned whether FL could be used systemically as a vaccine adjuvant to stimulate DC mobilization in vivo, circumventing the need to generate DCs ex vivo. Ten patients with HER-2/neu-overexpressing cancer were enrolled in a phase 1 study to receive a HER-2/neu peptide-based vaccine targeting the intracellular domain of the HER-2/neu protein. All patients received 20 microg/kg FL per day subcutaneously for 14 days. Five patients received the HER-2/neu peptide-based vaccine alone on day 7 of the 14-day cycle, and 5 patients received the vaccine admixed with 150 microg granulocyte macrophage-colony-stimulating factor (GM-CSF) on day 7 of the FL cycle. T-cell proliferative responses to HER-2/neu peptides and intracellular domain protein suggest that vaccine regimens including FL as an adjuvant were not effective in eliciting a significant HER-2/neu protein-specific T-cell proliferative response. However, including FL as a vaccine adjuvant was effective in boosting the precursor frequency of interferon-gamma-secreting HER-2/neu-specific T cells. The small sample size of each group, however, did not allow a statistically significant comparison of immune responses between the FL alone and FL with GM-CSF arms. Finally, vaccine regimens including FL as a vaccine adjuvant were associated with the development of apparent autoimmune phenomena in some patients.

Clinical translation of peptide-based vaccine trials: the HER-2/neu model

In the development of targeted cancer immunotherapies, the choice of antigen is obviously critical to the design of any therapeutic strategy, but particularly so for tumor vaccines, which must distinguish malignant cells from normal cells. Investigations a decade ago focused on mutated tumor antigens, or viral tumor antigens, with the belief that these foreign or abnormal proteins would be best recognized by the host immune system. Within the last 10 years, however, several tumor antigens have been identified on the basis of recognition by infiltrating T cells in tumor samples. Studies on melanoma, in particular, have revealed that in addition to some mutated tumor antigens, several aberrantly expressed normal proteins, as well as tissue-specific differentiation factors, are recognized by the host immune system. Similar studies in other solid tumors have revealed that certain oncogenes overexpressed in malignant cells, such as p53 and HER-2/neu, are also recognized by host T cells. Our group has been investigating the HER-2/neu oncogenic protein as a vaccine target in patients with HER-2/neu-overexpressing cancers. However, several issues unique to the design of human clinical trials of cancer vaccines must be addressed when translating preclinical experiments to human clinical trials. First, HER-2/neu protein expression can vary depending on the tumor type. How would expression differences impact clinical trial design? Secondly, what are the issues in clinical trial design that are critical to the successful execution of a phase I study of a peptide-based vaccine? Thirdly, what types and amounts of clinical material are readily available for immunologic analysis and can be obtained with little distress and risk to the patients enrolled in the study? Finally, what steps must be implemented for a laboratory assay to evolve to meet the validation criteria needed for application as an immunologic monitoring tool?

Vaccination against the HER-2/neu oncogenic protein

The HER-2/neu oncogenic protein is a well-defined tumor antigen. HER-2/neu is a shared antigen among multiple tumor types. Patients with HER-2/neu protein-overexpressing breast, ovarian, non-small cell lung, colon, and prostate cancers have been shown to have a pre-existent immune response to HER-2/neu. No matter what the tumor type, endogenous immunity to HER-2/neu detected in cancer patients demonstrates two predominant characteristics. First, HER-2/neu-specific immune responses are found in only a minority of patients whose tumors overexpress HER-2/neu. Secondly, immunity, if detectable, is of low magnitude. These observations have led to the development of vaccine strategies designed to boost HER-2/neu immunity in a majority of patients. HER-2/neu is a non-mutated self-protein, therefore vaccines must be developed based on immunologic principles focused on circumventing tolerance, a primary mechanism of tumor immune escape. HER-2/neu-specific vaccines have been tested in human clinical trials. Early results demonstrate that significant levels of HER-2/neu immunity can be generated with active immunization. The T-cell immunity elicited is durable after vaccinations have ended. Furthermore, despite the generation of CD8(+) and CD4(+) T-cells responsive to HER-2/neu in a majority of patients, there is no evidence of autoimmunity directed against tissues that express basal levels of the protein. Cancer vaccines targeting the HER-2/neu oncogenic protein may be useful adjuvants to standard therapy and aid in the prevention of relapse in patients whose tumors overexpress the protein. Furthermore, boosting HER-2/neu-specific T-cell frequencies via active immunization may allow the ex vivo expansion of HER-2/neu-specific T-cells for use in adoptive immunotherapy, a therapeutic strategy directed against the treatment of established disease.

Adoptive T-cell therapy for the treatment of solid tumours

Solid tumours can be eradicated by infusion of large amounts of tumour-specific T-cells in animal models. The successes seen in preclinical models, however, have not been adequately translated to human disease due, in part, to the inability to expand tumour antigen-specific T-cells ex vivo. Polyclonality and retention of antigen-specificity are two important properties of infused T-cells that are necessary for successful eradication of tumours. Investigators are beginning to evaluate the impact of attempting to reconstitute full T-cell immunity representing both major T-cell subsets, cytolytic T-cells and T-helper (Th) cells. One of the more important and often overlooked steps of successful adoptive T-cell therapy is the ex vivo expansion conditions, which can dramatically alter the phenotype of the T-cell. A number of cytokines and other soluble activation factors that have been characterised over the last decade are now available to supplement in vitro antigen presentation and IL-2. Newer molecular techniques have been developed and are aimed at genetically altering the characteristics of T-cells including their antigen-specificity and growth in vivo. In addition, advanced imaging techniques, such as positron emission tomography (PET), are being implemented in order to better define the in vivo function of ex vivo expanded tumour-specific T-cells.

GMK (Progenics Pharmaceuticals)

Progenics Pharmaceuticals is developing GMK vaccine (a ganglioside conjugate vaccine coupled to keyhole limpet hemocyanin and formulated with the adjuvant QS-21), licensed from the Memorial Sloan-Kettering Cancer Center, for the potential treatment of melanoma and other cancers [194258], [325284]. It was previously under co-development with Bristol-Myers Squibb, but in May 2001, all rights to the GMK vaccine were returned to Progenics [409168]. It was the first of a new class of ganglioside conjugate vaccine evaluated by Progenics [194258]. GMK vaccination induces antibodies against GM2 ganglioside capable of specifically killing melanoma cells. Melanoma patients with antibodies against GM2 ganglioside have significantly improved disease-free and overall survival compared to antibody-negative subjects. The vaccine is undergoing two phase III trials, the first comparing GMK to high-dose IFNalpha in melanoma patients with more serious disease and at a high risk of relapse, and the second, in collaboration with the European Organization for Research and Treatment of Cancer, comparing GMK (14 doses of GMK over three years) to no treatment other than close monitoring of malignant melanoma patients at immediate risk of relapse [409168]. In February 1999, Lehman Brothers predicted that the vaccine had a 50% probability of reaching market, with an estimated first launch date in 2002. The analysts predicted potential peak sales in 2008 of $150 million in the US and $100 million in the rest of the world at that time [319225]. In January 2000, Lehman Brothers expected that an NDA filing would take place in 2002, with possible launch of the vaccine in 2003. In addition, Lehman Brothers estimated potential peak sales at $500 million [357788]. In August 2000, Punk, Ziegel & Company predicted that Progenics Pharmaceuticals will become sustainably profitable in 2003 following the launch of GMK and PRO-542 in 2002 [390063]. In July 2001, Ladenburg Thalmann predicted a $257 million market potential for GMK in the US, with the non-US market equivalent to the US market. A launch date of 2005 in the US, with a worldwide launch in 2006, was estimated [433347].

Technology evaluation: T-cell activator, Xenova

TA-HPV (therapeutic antigen-human papilloma virus) is a vaccine being developed by Xenova (formerly Cantab) for the potential treatment of cervical cancer. The antigen is intended to activate HPV-specific cytotoxic T-cells to attack tumor cells containing the viral antigen. Over 70% of patients with cervical cancer have tumor cells containing papillomavirus DNA [173070]. TA-HPV has reached phase IIa trials in 60 patients with high-grade anogenital intraepithelial neoplasia, including VIN3 (grade 3 vulvar intraepithelial neoplasia), to evaluate clinical efficacy [381386], [427159], [429895]. In addition, a phase II 'prime-boost' study of TA-HPV in combination with TA-CIN has been initiated at three centers across the UK [427159].

Expansion of HER2/neu-specific T cells ex vivo following immunization with a HER2/neu peptide-based vaccine

The identification and characterization of tumor antigens has facilitated the development of immune-based cancer prophylaxis and therapy. Cancer vaccines, like viral vaccines, may be effective in cancer prevention. Adoptive T-cell therapy, in contrast, may be more efficacious for the eradication of existing malignancies. Our group is examining the feasibility of antigen-specific adoptive T-cell therapy for the treatment of established cancer in the HER2/neu model. Transgenic mice overexpressing rat neu in mammary tissue develop malignancy, histologically similar to human HER2/neu-overexpressing breast cancer. These mice can be effectively immunized against a challenge with neu-positive tumor cells. Adoptive transfer of neu-specific T cells into tumor-bearing mice eradicates malignancy. Effective T-cell therapy relies on optimization of the ex vivo expansion of antigen-specific T cells. Two important elements of ex vivo antigen-specific T-cell growth that have been identified are (1) the preexisting levels of antigen-specific T cells and (2) the cytokine milieu used during ex vivo expansion of the T cells. Phase I clinical trials of HER2/neu-based peptide vaccination in human cancer patients have demonstrated that increased levels of HER2/neu-specific T-cells can be elicited after active immunization. Initiating cultures with greater numbers of antigen-specific T cells facilitates expansion. In addition, cytokines, such as interleukin-12, when added during ex vivo culturing along with interleukin-2 can selectively expand antigen-specific T-cells. Interleukin-12 also enhances antigen-specific functional measurements such as interferon-gamma and tumor necrosis factor-alpha release. Refinements in ex vivo expansion techniques may greatly improve the feasibility of tumor-antigen T-cell-based therapy for the treatment of advanced-stage HER2/neu-overexpressing breast malignancy.

Immunization with a HER-2/neu helper peptide vaccine generates HER-2/neu CD8 T-cell immunity in cancer patients

CD4 T-cell help is required during the generation and maintenance of effective antitumor CD8 T cell-mediated immunity. The goal of this study was to determine whether HER-2/neu-specific CD8 T-cell immunity could be elicited using HER-2/neu-derived MHC class II "helper" peptides, which contain encompassed HLA-A2-binding motifs. Nineteen HLA-A2 patients with HER-2/neu-overexpressing cancers received a vaccine preparation consisting of putative HER-2/neu helper peptides p369-384, p688-703, and p971-984. Contained within these sequences are the HLA-A2-binding motifs p369-377, p689-697, and p971-979. After vaccination, the mean peptide-specific T-cell precursor frequency to the HLA-A2 peptides increased in the majority of patients. In addition, the peptide-specific T cells were able to lyse tumors. The responses were long-lived and detectable for more than 1 year after the final vaccination in select patients. These results demonstrate that HER-2/neu MHC class II epitopes containing encompassed MHC class I epitopes are able to induce long-lasting HER-2-specific IFN-gamma-producing CD8 T cells.

Pre-existent immunity to the HER-2/neu oncogenic protein in patients with HER-2/neu overexpressing breast and ovarian cancer

Immunomodulatory strategies, such as antibody therapy and cancer vaccines, are increasingly being considered as potential adjuvant therapies in patients with advanced stage breast cancer to either treat minimal residual disease or prevent relapse. However, little is known concerning the incidence and magnitude of the pre-existent breast cancer specific immune response in this patient population. Using the HER-2/neu oncogenic protein as a model, a well-defined tumor antigen in breast cancer, we questioned whether patients with advanced stage HER-2/neu overexpressing breast and ovarian cancers (III/IV) had evidence of pre-existent immunity to HER-2/neu. Forty-five patients with stage III or IV HER-2/neu overexpressing breast or ovarian cancer were evaluated for HER-2/neu specific T cell and antibody immunity. Patients enrolled had not received immunosuppressive chemotherapy for at least 30 days (median 5 months, range 1-75 months). All patients were documented to be immune competent prior to entry by DTH testing using a skin test anergy battery. Five of 45 patients (11%) were found to have a significant HER-2/neu specific T cell response as defined by a stimulation index > or = 2.0 (range 2.0-7.9). None of eight patients who were HLA-A2 had a detectable IFNgamma secreting T-cell precursor frequency to a well-defined HER-2/neu HLA-A2 T cell epitope, p369-377. Three of 45 patients (7%) had detectable HER-2/neu specific IgG antibodies, range 1.2-8.9 microg/ml. These findings suggest that patients with advanced stage HER-2/neu overexpressing breast and ovarian cancer can mount a T cell and/or antibody immune response to their tumor. However, in the case of the HER-2/neu antigen, the pre-existent tumor specific immune response is found only in a minority of patients.

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.

Exploitation of host cell signaling machinery: activation of macrophage phosphotyrosine phosphatases as a novel mechanism of molecular microbial pathogenesis

Intracellular pathogens, particularly those that target host mononuclear phagocytes, have evolved strategies to either evade or inhibit cellular mechanisms of host defense. Mycobacterium tuberculosis and Leishmania donovani exemplify a diverse group of microorganisms that have developed the ability to invade and replicate within host macrophages, leading to disease expression. Recent studies have suggested that the pathogenesis of intracellular infection may involve interference with host cell signaling. Drawing upon examples from in vitro models that focused on M. tuberculosis and L. donovani, we review evidence that activation of host cell phosphotyrosine phosphatases may contribute to pathogenesis. A leading candidate appears to be the Src homology 2 domain containing phosphotyrosine phosphatase SHP-1, the activation of which may contribute to the development of infection and disease progression.

1alpha,25-dihydroxyvitamin D(3)-induced myeloid cell differentiation is regulated by a vitamin D receptor-phosphatidylinositol 3-kinase signaling complex

1alpha,25-dihydroxyvitamin D(3) (D(3)) promotes the maturation of myeloid cells and surface expressions of CD14 and CD11b, markers of cell differentiation in response to D(3). To examine how these responses are regulated, THP-1 cells were grown in serum-free medium and incubated with D(3). This was associated with rapid and transient increases in phosphatidylinositol 3-kinase (PI 3-kinase) activity. Furthermore, induction of CD14 expression in response to D(3) was abrogated by (a) the PI 3-kinase inhibitors LY294002 and wortmannin; (b) antisense oligonucleotides to mRNA for the p110 catalytic subunit of PI 3-kinase; and (c) a dominant negative mutant of PI 3-kinase. In THP-1 cells, induction of CD11b expression by D(3) was also abrogated by LY294002 and wortmannin. Similarly, LY294002 and wortmannin inhibited D(3)-induced expression of both CD14 and CD11b in peripheral blood monocytes. In contrast to CD14 and CD11b, hormone-induced expression of the Cdk inhibitor p21 in THP-1 cells was unaffected by either wortmannin or LY294002. These findings suggest that PI 3-kinase selectively regulates D(3)-induced monocyte differentiation, independent of any effects on p21.

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.

Monocyte adherence induced by lipopolysaccharide involves CD14, LFA-1, and cytohesin-1. Regulation by Rho and phosphatidylinositol 3-kinase

Mechanisms regulating lipopolysaccharide (LPS)-induced adherence to intercellular adhesion molecule (ICAM)-1 were examined using THP-1 cells transfected with CD14-cDNA (THP-1wt). THP-1wt adherence to ICAM-1 was LPS dose-related, time-dependent, and inhibited by antibodies to either CD14 or leukocyte function associated antigen (LFA)-1, but was independent of any change in the number of surface expressed LFA-1 molecules. A potential role for phosphatidylinositol (PI) 3-kinase (PI 3-kinase) in LPS-induced adherence was examined using the PI 3-kinase inhibitors LY294002 and Wortmannin. Both inhibitors selectively attenuated LPS-induced, but not phorbol 12-myristate 13-acetate-induced adherence. Inhibition by these agents was unrelated to any changes in either LPS binding to or LFA-1 expression by THP-1wt cells. LPS-induced adherence was also abrogated in U937 cells transfected with a dominant negative mutant of of PI 3-kinase. Toxin B from Clostridium difficile, an inhibitor of the Rho family of GTP-binding proteins, abrogated both PI-3 kinase activation and adherence induced by LPS. Cytohesin-1, a phosphatidylinositol 3,4,5-triphosphate-regulated adaptor molecule for LFA-1 activation, was found to be expressed in THP-1wt cells. In addition, treatment of THP-1wt with cytohesin-1 antisense attenuated LPS-induced adherence. These findings suggest a model in which LPS induces adherence through a process of "inside-out" signaling involving CD14, Rho, and PI 3-kinase. This converts low avidity LFA-1 into an active form capable of increased binding to ICAM-1. This change in LFA-1 appears to be cytohesin-1-dependent.

Lipoarabinomannan of Mycobacterium tuberculosis promotes protein tyrosine dephosphorylation and inhibition of mitogen-activated protein kinase in human mononuclear phagocytes. Role of the Src homology 2 containing tyrosine phosphatase 1

Lipoarabinomannan (LAM) is a putative virulence factor of Mycobacterium tuberculosis that inhibits monocyte functions, and this may involve antagonism of cell signaling pathways. The effects of LAM on protein tyrosine phosphorylation in cells of the human monocytic cell line THP-1 were examined. LAM promoted tyrosine dephosphorylation of multiple cell proteins and attenuated phorbol 12-myristate 13-acetate-induced activation of mitogen-activated protein kinase. To examine whether these effects of LAM could be related to activation of a phosphatase, fractions from LAM-treated cells were analyzed for dephosphorylation of para-nitrophenol phosphate. The data show that LAM induced increased phosphatase activity associated with the membrane fraction. The Src homology 2 containing tyrosine phosphatase 1 (SHP-1) is important for signal termination and was examined as a potential target of LAM. Exposure of cells to LAM brought about (i) an increase in tyrosine phosphorylation of SHP-1, and (ii) translocation of the phosphatase to the membrane. Phosphatase assay of SHP-1 immunoprecipitated from LAM-treated cells, using phosphorylated mitogen-activated protein kinase as substrate, indicated that LAM promoted increased activity of SHP-1 in vivo. LAM also activated SHP-1 directly in vitro. Exposure of cells to LAM also attenuated the expression of tumor necrosis factor-alpha, interleukin-12, and major histocompatibility class II molecules. These results suggest that one mechanism by which LAM deactivates monocytes involves activation of SHP-1.

Subnuclear localization of protein kinase C delta in beta cells

Our laboratory has previously shown that beta cells express multiple isoforms of protein kinase C (PKC) and that some isoforms are located to multiple pools within the cell, including the cytoskeletal elements. In this study we analyzed the localization of the delta, epsilon, zeta, beta, and alpha isoforms of PKC to the nucleus. Nuclei were isolated from insulinoma beta cells and fractionated by centrifugation to give the nuclear soluble fraction, nuclear membrane fraction, and the insoluble matrix. The nuclear pellet was enriched in DNA and contained less than 5% of the total cellular nucleotidase activity. The nuclear membrane contained less than 2% of the total cellular nucleotidase activity, suggesting negligible plasma membrane contamination. Analysis of cellular fractions by immunoblotting with isoform-specific anti-PKC antibodies showed that PKC alpha, beta, zeta, and epsilon could be detected in the soluble fraction of the cell but could not be detected in the nucleus. Only PKC delta could be detected in the nucleus and was mostly present in the nuclear membrane fraction. There was light staining in the nucleocytosol and the nuclear matrix but the enzyme in the nuclear membrane represented approximately 76% of the total nuclear enzyme. Nuclear PKC delta constituted approximately 9% of the total cellular enzyme. Phorbol ester (1 microM, 15 min) increased the levels associated with the nuclear membrane approximately threefold but not to the nuclear matrix or nucleocytosol. Inhibition of PKC with MDL 29152 increased levels of preproinsulin mRNA relative to beta-actin mRNA levels, while chronic phorbol ester treatment led to a slight decrease. Taken together, these data suggest that PKC is constitutively active in the nucleus and may be important in modulating preproinsulin mRNA levels.

Phosphatidylinositol 3-kinase-dependent activation of protein kinase C-zeta in bacterial lipopolysaccharide-treated human monocytes

The isoform identity of activated protein kinase C (PKC) and its regulation were investigated in bacterial lipopolysaccharide (LPS)-treated human monocytes. Resolution of detergent-soluble lysates prepared from LPS-treated, peripheral blood monocytes using Mono Q anion-exchange chromatography revealed two principal peaks of myelin basic protein kinase activity. Immunoblotting and immunoprecipitation with isoform-specific anti-PKC antibodies showed that the major and latest eluting peak is accounted for by PKC-zeta. In addition to primary monocytes, activation of PKC-zeta in response to LPS was also observed in the human promonocytic cell lines, U937 and THP-1. Consistent with its identity as PKC-zeta, the kinase did not depend upon the presence of lipids, Ca2+, or diacylglycerol for activity. In addition, the kinase phosphorylates peptide epsilon and myelin basic protein with equal efficiency but phosphorylates Kemptide and protamine sulfate poorly. Translocation of PKC-zeta from the cytosolic to the particulate membrane fraction upon exposure of monocytes to LPS provided further evidence for activation of the kinase. Preincubation of monocytes with the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitors, wortmannin or LY294002, abrogated LPS-induced activation of PKC-zeta. Furthermore, activation of PKC-zeta failed to occur in U937 cells transfected with a dominant negative mutant of the p85 subunit of PI 3-kinase. PKC-zeta activity was also observed to be enhanced in vitro by the addition of phosphatidylinositol 3,4,5P3. These findings are consistent with a model in which PKC-zeta is activated downstream of PI 3-kinase in monocytes in response to LPS.

Arachidonic acid-induced down-regulation of protein kinase C delta in beta-cells

We have previously identified expression of multiple protein kinase C (PKC) isoforms in insulinoma-derived beta-cells and whole islets. Both PKC delta and PKC alpha appear to be the more abundantly expressed isoforms. In this report we studied the effects of arachidonic acid (AA) on the subcellular distribution of PKC alpha and PKC delta. AA has been reported to activate both PKC alpha and PKC delta and it is thought to be an important second messenger in beta-cells. Here we report that AA interacted with and altered beta-cell pools of PKC delta preferentially over PKC alpha. AA (100 microM) over the course of 45 min reduced cytosolic levels of PKC delta (to 40 +/- 15%, compared to time zero control) leaving membrane- and cytoskeleton-associated levels near control levels. Analysis of whole cell homogenates showed a slight down-regulation of PKC delta indicating proteolysis. The down-regulation of cytosolic PKC delta appeared to be isoform specific since cytosolic PKC alpha remained at control levels over the time course. The response was dose-dependent and negligible at concentrations below 30 microM and occurred, at least partially, in the cytosolic compartment of the cell. Indomethacin also down-regulated cytosolic PKC delta preferentially over PKC alpha possibly through accumulation of AA. These findings suggest that cytosolic PKC delta may be a downstream target of this beta-cell second messenger.

Regulation of distinct pools of protein kinase C delta in beta cells

Previous studies from our laboratory have demonstrated the presence of several isoforms of protein kinase C (PKC), Ca(2+)-independent and Ca(2+)-dependent, in both whole islets and tumor-derived beta cells. In the basal state, a major proportion of the isoform was found in the crude membrane fraction with smaller amounts found in both the cytosolic and cytoskeletal fractions. Whole islets showed a similar distribution of the isoform. These studies were done to analyze the effects of insulin secretagogues on the distribution of PKC delta to different cellular pools in isolated insulinoma beta cells. The phorbol ester, phorbol 12-myristate 13-acetate (PMA), produced a transient association of PKC delta with the beta cell cytoskeleton along with sustained decreases in cytosolic enzyme and transient increases in membrane enzyme. Neither glucose nor carbachol could acutely affect the subcellular distribution of PKC delta. Oleic acid decreased the amount of the enzyme associated with the cytoskeleton and led to a sustained decrease of cytosolic enzyme and a transient increase in membrane enzyme. Oleic acid was also able to prevent the increase in cytoskeletal enzyme induced by PMA. Both oleic acid and PMA potentiated glucose-induced insulin release but oleic acid, in contrast to PMA, was unable to initiate insulin release in the presence of substimulatory concentrations of glucose. These data demonstrate that different activators of PKC may have different effects on localization of the enzyme within the cells and suggest that there are at least three apparently distinct pools of PKC delta within the beta cell which may be important in insulin secretion or other aspects of beta cell function.