Protein vaccination with the HER2/neu extracellular domain plus anti-HER2/neu antibody-cytokine fusion proteins induces a protective anti-HER2/neu immune response in mice

Potent anti-tumor immune response and tumor growth inhibition induced by HER2 subdomain fusion protein in a mouse tumor model

PURPOSE

Several approaches have so far been employed to establish anti-tumor immunity by targeting HER2 protein. Active immunization with recombinant HER2 subdomains has previously been demonstrated to induce potent immune response and tumor growth inhibition. In the present study, we investigated the immunogenicity and tumor inhibitory effect of a fusion protein consisting of human HER2 extracellular subdomain (ECD-DI + II) together with T-helper cell epitopes of Tetanus toxin (p2 and p30).

METHODS

BALB/c mice were immunized with two recombinant proteins (DI + II and p2p30-DI + II) emulsified in 4 different adjuvants. Anti-DI + II antibody response, cytokine profile, frequency of splenic CD25⁺FOXP3⁺ regulatory T cells (Tregs) and CD8⁺CD107a⁺ cytotoxic T lymphocytes (CTLs) were assessed in the immunized mice. To assess the anti-tumor effect, the immunized mice were subcutaneously challenged with HER2-overexpressing tumor cells and the tumor growth was determined.

RESULTS

Both recombinant proteins were able to induce comparable levels of ECD-DI + II-specific antibodies. Immunization with p2p30-DI + II resulted in a significant increase in the level of Interferon-gamma (IFN-γ) secretion compared to DI + II protein and significantly higher frequency of CTLs and lower frequency of Tregs. The number of mice that remained tumor-free until day 120 was significantly higher in p2p30-DI + II vaccinated groups.

CONCLUSIONS

Our data suggest that the p2p30-DI + II fusion protein together with CpG adjuvant induces more potent anti-tumor immune responses in a mouse tumor model. Accordingly, this formulation might be considered as a potential immunotherapeutic approach in HER2⁺ cancers.

A Polypeptide of Tumor-Associated Antigen L6 with Intrinsic Adjuvant Activity Enhances Antitumor Immunity

Peptide vaccines are safe, and aim to elicit and expand tumor-specific immunity so as to eradicate tumors. However, achieving strong and long-lasting anti-tumor immunity with peptide vaccines for the antigen-specific treatment of cancer is challenging, in part because their efficacy depends on strong adjuvants or immunomodulators. We approached this problem by conjugating an epitope-based cancer vaccine with a lipidated sequence (an immunomodulator) to elicit a strong immune response. Lipidated and non-lipidated polyepitope proteins were generated that contained the universal T helper cell epitope (pan-DR), B cell epitopes, and the extended loop sequence of extracellular domain 2 of tumor-associated antigen L6 (TAL6). We show that the lipidated polyepitope cancer vaccine can activate bone marrow-derived dendritic cells, and trigger effective antigen-specific antibody and T helper cell responses, more effectively than the non-lipidated vaccine. Moreover, potent T cell immune responses were elicited in mice inoculated with the lipidated polyepitope cancer vaccine, providing protective antitumor immunity in mice bearing TAL6 tumors. Our study demonstrates that a lipidated polyepitope cancer vaccine could be employed to generate potent anti-tumor immune responses, including humoral and cellular immunity, which could be beneficial in the treatment of TAL6⁺ cancer.

Investigation of the combination of anti-PD-L1 mAb with HER2/neu-loaded dendritic cells and QS-21 saponin adjuvant: effect against HER2 positive breast cancer in mice

BACKGROUND

Human epidermal growth factor receptor 2 (HER2) is overexpressed in a subset of cancers including 25% of breast cancers. Since combination therapy consisting of multiple therapeutic approaches is considered a promising regimen, we examined combination treatment modalities in a xenograft model in Balb/c mice injected with 4T1-HER2 cells. We used HER2/neu-loaded bone marrow-derived dendritic cells (BM-DC's) along with anti-PD-L1 monoclonal antibody in a new combination immunotherapy model.

METHODS

The combination was composed of an active immunotherapy (i.e. BM-DC-based vaccine) designed to boost the immune response against target antigen and was augmented by using anti-PD-L1 mAb to prevent immune evasion by the xenografted tumors. The vaccine combination was further supported using a QS-21 saponin adjuvant and the immune response was evaluated.

RESULTS

Mice treated with HER2/neu-loaded BM-DCs, combined with QS-21 and anti-PD-L1 mAb had significantly decreased tumor sizes and their splenocytes had enhanced cytotoxic activity, based on the lactate dehydrogenase (LDH) assay, compared to vaccine and adjuvant groups alone. The same vaccination group demonstrated a remarkable increase in IFN-γ secreting CD8+ T-cells analyzed by flow cytometry. ELISA data also revealed a significant increase in the serum anti-HER2 IgG1 response; in addition, there was significant splenocyte proliferation upon stimulation with antigen compared to vaccine and adjuvant groups. Consistently, a significant infiltration of CD4+, CD8+ immune cells in and around the tumors was observed.

CONCLUSIONS

Our data suggest that the BM-DC + HER2/neu + QS-21 + anti-PD-L1 vaccine combination paradigm synergistically generates anti-tumor activity and immune responses against HER2 overexpressing breast cancer in mice.

HER2-Positive Breast Cancer Immunotherapy: A Focus on Vaccine Development

Clinical progress in the field of HER2-positive breast cancer therapy has been dramatically improved by understanding of the immune regulatory mechanisms of tumor microenvironment. Passive immunotherapy utilizing recombinant monoclonal antibodies (mAbs), particularly trastuzumab and pertuzumab has proved to be an effective strategy in HER2-positive breast cancer treatment. However, resistance to mAb therapy and relapse of disease are still considered important challenges in clinical practice. There are increasing reports on the induction of cellular and humoral immune responses in HER2-positive breast cancer patients. More recently, increasing efforts are focused on using HER2-derived peptide vaccines for active immunotherapy. Here, we discuss the development of various HER2-derived vaccines tested in animal models and human clinical trials. Different formulations and strategies to improve immunogenicity of the antigens in animal studies are also discussed. Furthermore, other immunotherapeutic approaches to HER2 breast cancer including, CTLA-4 inhibitors, immune checkpoint inhibitors, anti PD-1/PD-L1 antibodies are presented.

Amino acid residues involved in the heparin-binding activity of murine IL-12 in the context of an antibody-cytokine fusion protein

An antibody-cytokine fusion protein, composed of the murine single-chain cytokine interleukin-12 (IL-12) genetically fused to a human IgG3 specific for the human tumor-associated antigen HER2/neu maintains antigen binding, cytokine bioactivity, and IL-12 heparin-binding activity. This latter property is responsible for the binding of the cytokine to glycosaminoglycans (GAGs) on the cell surface and the extracellular matrix and has been implicated in modulating IL-12 bioactivity. Previous studies indicate that the p40 subunit of human and murine IL-12 is responsible for the heparin-binding activity of this heterodimeric cytokine. In the present study we used bioinformatic analysis and site-directed mutagenesis to develop a version of the antibody-(IL-12) fusion protein without heparin-binding activity. This was accomplished by replacing the basic arginine (R) and lysine (K) residues in the cluster of amino acids 254-260 (RKKEKMK) of the murine IL-12 p40 subunit by the neutral non-polar amino acid alanine (A), generating an AAAEAMA mutant fusion protein. ELISA and flow cytometry demonstrated that the antibody fusion protein lacks heparin-binding activity but retains antigen binding. A T-cell proliferation assay showed IL-12 bioactivity in this construct. However, the IL-12 bioactivity is decreased compared to its non-mutated counterpart, which is consistent with an ancillary role of the heparin-binding site of IL-12 in modulating its activity. Thus, we have defined a cluster of amino acid residues with a crucial role in the heparin-binding activity of murine IL-12 in the context of an antibody-cytokine fusion protein.

Human Mast Cells From Adipose Tissue Target and Induce Apoptosis of Breast Cancer Cells

Mast cells (MC) are important immune sentinels found in most tissue and widely recognized for their role as mediators of Type I hypersensitivity. However, they also secrete anti-cancer mediators such as tumor necrosis factor alpha (TNF-α) and granulocyte-macrophage colony-stimulating factor (GM-CSF). The purpose of this study was to investigate adipose tissue as a new source of MC in quantities that could be used to study MC biology focusing on their ability to bind to and kill breast cancer cells. We tested several cell culture media previously demonstrated to induce MC differentiation. We report here the generation of functional human MC from adipose tissue. The adipose-derived mast cells (ADMC) are phenotypically and functionally similar to connective tissue expressing tryptase, chymase, c-kit, and FcεRI and capable of degranulating after cross-linking of FcεRI. The ADMC, sensitized with anti-HER2/neu IgE antibodies with human constant regions (trastuzumab IgE and/or C6MH3-B1 IgE), bound to and released MC mediators when incubated with HER2/neu-positive human breast cancer cells (SK-BR-3 and BT-474). Importantly, the HER2/neu IgE-sensitized ADMC induced breast cancer cell (SK-BR-3) death through apoptosis. Breast cancer cell apoptosis was observed after the addition of cell-free supernatants containing mediators released from FcεRI-challenged ADMC. Apoptosis was significantly reduced when TNF-α blocking antibodies were added to the media. Adipose tissue represents a source MC that could be used for multiple research purposes and potentially as a cell-mediated cancer immunotherapy through the expansion of autologous (or allogeneic) MC that can be targeted to tumors through IgE antibodies recognizing tumor specific antigens.

Recombinant AAV-CEA Tumor Vaccine in Combination with an Immune Adjuvant Breaks Tolerance and Provides Protective Immunity

Carcinoembryonic antigen (CEA) is a human glycoprotein involved in cellular adhesion and expressed during human fetal development. Although expression of CEA largely ceases prior to birth, several human epithelial cancers, including colorectal, gastric, squamous esophageal, and breast carcinomas have been known to overexpress CEA, suggesting its potential as an immunotherapeutic target. Using a transgenic mouse model constitutively expressing human CEA in a spatiotemporal manner as a self-protein and a syngeneic mouse colon cancer cell line, MC38-CEA, overexpressing CEA, we tested the potential of a novel genetic immunotherapy approach against CEA-expressing tumors, using recombinant adeno-associated virus vector encoding CEA (rAAV-CEA) and appropriately timed immune adjuvant application. Results of the study demonstrated breaking of immune tolerance for CEA with this vaccine regimen and an anti-tumor response, resulting in tumor-free survival. Furthermore, tumor challenge of CEA-vaccinated mice with parental MC38 cells not expressing CEA did not result in protection from tumor development, confirming that the protection against tumor development is CEA specific. The study illustrates the feasibility of utilizing rAAV vectors in combination with an immunostimulatory adjuvant to break tolerance to weakly immunogenic self-antigens and for an anti-tumor response.

Generation of HER2-specific antibody immunity during trastuzumab adjuvant therapy associates with reduced relapse in resected HER2 breast cancer

BACKGROUND

Resected HER2 breast cancer patients treated with adjuvant trastuzumab and chemotherapy have superior survival compared to patients treated with chemotherapy alone. We previously showed that trastuzumab and chemotherapy induce HER2-specific antibodies which correlate with improved survival in HER2 metastatic breast cancer patients. It remains unclear whether the generation of immunity required trastuzumab and whether endogenous antibody immunity is associated with improved disease-free survival in the adjuvant setting. In this study, we addressed this question by analyzing serum anti-HER2 antibodies from a subset of patients enrolled in the NCCTG trial N9831, which includes an arm (Arm A) in which trastuzumab was not used. Arms B and C received trastuzumab sequentially or concurrently to chemotherapy, respectively.

METHODS

Pre-and post-treatment initiation sera were obtained from 50 women enrolled in N9831. Lambda IgG antibodies (to avoid detection of trastuzumab) to HER2 were measured and compared between arms and with disease-free survival.

RESULTS

Prior to therapy, across all three arms, N9831 patients had similar mean anti-HER2 IgG levels. Following treatment, the mean levels of antibodies increased in the trastuzumab arms but not the chemotherapy-only arm. The proportion of patients who demonstrated antibodies increased by 4% in Arm A and by 43% in the Arms B and C combined (p = 0.003). Cox modeling demonstrated that larger increases in antibodies were associated with improved disease-free survival in all patients (HR = 0.23; p = 0.04).

CONCLUSIONS

These results show that the increased endogenous antibody immunity observed in adjuvant patients treated with combination trastuzumab and chemotherapy is clinically significant, in view of its correlation with improved disease-free survival. The findings may have important implications for predicting treatment outcomes in patients treated with trastuzumab in the adjuvant setting.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT00005970 . Registered on July 5, 2000.

Immunization with HER2 extracellular subdomain proteins induces cellular response and tumor growth inhibition in mice

AIM

We investigated cellular and protective immune responses in mice vaccinated with recombinant HER2 extracellular subdomains.

MATERIALS & METHODS

Balb/C mice were immunized with recombinant full HER2 extracellular domain and subdomain proteins. Humoral and cellular immune response and antitumor effect was evaluated using a syngeneic mice tumor model.

RESULTS

All recombinant proteins induced secretion of IL-4 and particularly IFN-γ and IL-17 cytokines. Challenging of immunized mice with stable 4T1-HER2 transfected cells resulted in partial but significant tumor growth inhibition in all groups of mice particularly those immunized with fHER2-ECD together with CPG.

CONCLUSION

Our results suggest that the recombinant HER2-ECD subdomains induce mainly Th1 and Th17 responses, which seem to contribute to tumor growth inhibition in syngeneic mice.

Vaccine draining lymph nodes are a source of antigen-specific B cells

PURPOSE

Our research is focused on using vaccine draining lymph nodes as a source of immune cells to better understand the immune response and to attempt to generate new anti-cancer reagents. Following a vaccine, harvesting the lymph node can only be done once. We endeavored to determine the range of times that B cells secreting anti-KLH antibodies were present in the node of KLH-vaccinated mice.

RESULTS

Following vaccination the total number of mononuclear cells (MNCs) increased in the vaccine-draining lymph node (VDN). The percentage of MNCs that were B cells nearly doubled. B cells recovered from the node that secreted anti-KLH antibodies were evident by day 7. The number continued to increase and then slowly decreased over the observed time range to 28days after vaccination. The VDN, compared to the spleen, the bone marrow and the nonVDN, contained a higher percentage of B cells that secreted anti-KLH antibodies.

CONCLUSIONS

After a vaccine, there is a multi-week window of time when an increasing number of B cells are present in a VDN that secrete anti-KLH antibodies. These results support using the VDN as a source for B cells that secrete anti-vaccine antibodies.

In vitro assessment of the effects of anti-HER2 monoclonal antibodies on proliferation of HER2-overexpressing breast cancer cells

BACKGROUND

HER2 proto-oncogene is critical in the biology of breast cancer and an important therapeutic target of monoclonal antibodies (mAbs). We have recently established a panel of anti-HER2 mAbs recognizing different epitopes within the extracellular domain of HER2.

MATERIALS & METHODS

In the present study the antiproliferative effect of these mAbs was investigated on HER2-overexpressing human breast cancer cell line BT474, using radioactive thymidine incorporation assay.

RESULTS

Our results demonstrated that while two of the mAbs (1T0 and 2A8) inhibited cell proliferation dose dependently, similar to trastuzumab, six mAbs (1F2, 1B5, 1H9, 4C7, 1H6 and 2A9) augmented cell proliferation. Treatment of BT474 cells with different combinations of two mAbs induced either synergistic inhibitory or stimulatory effects.

DISCUSSION

Our findings indicate that combination of some stimulatory mAbs could completely abolish the inhibitory effect of other mAbs against HER2. Employment of some combinations of mAbs with significant synergistic inhibitory function may improve the therapeutic efficacy of HER2-specific mAbs.

Active immunotherapy in HER2 overexpressing breast cancer: current status and future perspectives

BACKGROUND

The use of anti-HER2 monoclonal antibodies (mAbs) has improved the clinical outcome of HER2-overexpressing breast cancers (BCs). Unfortunately, often these tumors tend to relapse and, when metastatic, the duration of clinical benefit is limited over time and almost invariably followed by tumor progression. Alternative approaches to this essentially passive immunotherapy are therefore needed in HER2-overexpressing BC patients. As HER2 is one of the most suitable targets for active immunotherapy in BC, manipulating the immune system is a highly attractive approach.

MATERIAL AND METHODS

A computer-based literature search was carried out using PubMed (keywords: breast neoplasm, HER2 vaccine, immunology); data reported at international meetings were included.

RESULTS

This review provides a focus on the following active vaccinal approaches under clinical investigation against HER2-overexpressing BC: (i) peptide and protein based; (ii) DNA based; (iii) whole tumor cell based; (iv) dendritic cell based. Moreover, the review discuss future challenges in the field, trying to define the best setting for the development of this innovative strategy, considering both immunological and clinical aspects of HER2 targeting.

CONCLUSIONS

Development of effective vaccines for BC remains a distinct challenge but is likely to become a substantial advance for patients with HER2-overexpressing BCs.

Polymalic acid nanobioconjugate for simultaneous immunostimulation and inhibition of tumor growth in HER2/neu-positive breast cancer

Breast cancer remains the second leading cause of cancer death among women in the United States. Breast cancer prognosis is particularly poor in case of tumors overexpressing the oncoprotein HER2/neu. A new nanobioconjugate of the Polycefin(TM) family of anti-cancer drugs based on biodegradable and non-toxic polymalic acid (PMLA) was engineered for a multi-pronged attack on HER2/neu-positive breast cancer cells. An antibody-cytokine fusion protein consisting of the immunostimulatory cytokine interleukin-2 (IL-2) genetically fused to an antibody specific for human HER2/neu [anti-HER2/neu IgG3-(IL-2)] was covalently attached to the PMLA backbone to target HER2/neu expressing tumors and ensure the delivery of IL-2 to the tumor microenvironment. Antisense oligonucleotides (AON) were conjugated to the nanodrug to inhibit the expression of vascular tumor protein laminin-411 in order to block tumor angiogenesis. It is shown that the nanobioconjugate was capable of specifically binding human HER2/neu and retained the biological activity of IL-2. We also showed the uptake of the nanobioconjugate into HER2/neu-positive breast cancer cells and enhanced tumor targeting in vivo. The nanobioconjugate exhibited marked anti-tumor activity manifested by significantly longer animal survival and significantly increased anti-HER2/neu immune response in immunocompetent mice bearing D2F2/E2 murine mammary tumors that express human HER2/neu. The combination of laminin-411 AON and antibody-cytokine fusion protein on a single polymeric platform results in a new nanobioconjugate that can act against cancer cells through inhibition of tumor growth and angiogenesis and the orchestration of an immune response against the tumor. The present Polycefin(TM) variant may be a promising agent for treating HER2/neu expressing tumors and demonstrates the versatility of the Polycefin(TM) nanobioconjugate platform.

Peptide vaccines and targeting HER and VEGF proteins may offer a potentially new paradigm in cancer immunotherapy

The ErbB family (HER-1, HER-2, HER-3 and HER-4) of receptor tyrosine kinases has been the focus of cancer immunotherapeutic strategies while antiangiogenic therapies have focused on VEGF and its receptors VEGFR-1 and VEGFR-2. Agents targeting receptor tyrosine kinases in oncology include therapeutic antibodies to receptor tyrosine kinase ligands or the receptors themselves, and small-molecule inhibitors. Many of the US FDA-approved therapies targeting HER-2 and VEGF exhibit unacceptable toxicities, and show problems of efficacy, development of resistance and unacceptable safety profiles that continue to hamper their clinical progress. The combination of different peptide vaccines and peptidomimetics targeting specific molecular pathways that are dysregulated in tumors may potentiate anticancer immune responses, bypass immune tolerance and circumvent resistance mechanisms. The focus of this review is to discuss efforts in our laboratory spanning two decades of rationally developing peptide vaccines and therapeutics for breast cancer. This review highlights the prospective benefit of a new, untapped category of therapies biologically targeted to EGF receptor (HER-1), HER-2 and VEGF with potential peptide 'blockbusters' that could lay the foundation of a new paradigm in cancer immunotherapy by creating clinical breakthroughs for safe and efficacious cancer cures.

Enzymatic discovery of a HER-2/neu epitope that generates cross-reactive T cells

Patients with HER-2/neu-expressing breast cancer remain at risk for relapse following standard therapy. Vaccines targeting HER-2/neu to prevent relapse are in various phases of clinical testing. Many vaccines incorporate the HER-2/neu HLA-A2-binding peptide p369-377 (KIFGSLAFL), because it has been shown that CTLs specific for this epitope can directly kill HER-2/neu-overexpressing breast cancer cells. Thus, understanding how tumors process this epitope may be important for identifying those patients who would benefit from immunization. Proteasome preparations were used to determine if p369-377 was processed from larger HER-2/neu-derived fragments. HPLC, mass spectrometry, cytotoxicity assays, IFN-γ ELISPOT, and human breast cancer cell lines were used to assess the proteolytic fragments. Processing of p369-377 was not detected by purified 20S proteasome and immunoproteasome, indicating that tumor cells may not be capable of processing this Ag from the HER-2/neu protein and presenting it in the context of HLA class I. Instead, we show that other extracellular domain HER-2/neu peptide sequences are consistently processed by the proteasomes. One of these sequences, p373-382 (SLAFLPESFD), bound HLA-A2 stronger than did p369-377. CTLs specific for p373-382 recognized both p373-382 and p369-377 complexed with HLA-A2. CTLs specific for p373-382 also killed human breast cancer cell lines at higher levels than did CTLs specific for p369-377. Conversely, CTLs specific for p369-377 recognized p373-382. Peptide p373-382 is a candidate epitope for breast cancer vaccines, as it is processed by proteasomes and binds HLA-A2.

Targeting of the non-mutated tumor antigen HER2/neu to mature dendritic cells induces an integrated immune response that protects against breast cancer in mice

INTRODUCTION

Given their relative simplicity of manufacture and ability to be injected repeatedly, vaccines in a protein format are attractive for breast and other cancers. However, soluble human epidermal growth factor receptor (HER2)/neu protein as a vaccine has not been immunogenic. When protein is directly targeted to antigen uptake receptors, such as DEC205 (DEC), efficient processing and presentation of antigen take place. The aim of this study was to determine the immunogenicity of a HER2 protein vaccine that directly targets to DEC+ dendritic cells (DCs) in a mouse breast cancer model.

METHODS

We genetically engineered the HER2 extracellular domain into a monoclonal antibody specific for DEC (DEC-HER2). Mice of various genetic backgrounds were immunized with DEC-HER2 in combination with DC maturation stimuli (poly IC ± CD40 Ab). Vaccine-induced T cell immunity was determined by analyzing the ability of CD4+/CD8+ T cell to produce interferon (IFN)-gamma and proliferate upon antigen rechallenge. Sera were assessed for the presence of antigen specific antibody (Ab). For vaccine efficacy, FVB/N mice were immunized with DEC-HER2 in combination with poly IC and protection against neu-expressing mammary tumors was assessed. Protection mechanisms and tumor-specific T cell responses were also evaluated.

RESULTS

We demonstrate that DEC-HER2 fusion mAb, but not Ctrl Ig-HER2, elicits strong, broad and multifunctional CD4+ T cell immunity, CD8+ T cell responses, and humoral immunity specific for HER2 antigen. Cross-reactivity to rat neu protein was also observed. Importantly, mice xeno-primed with DEC-HER2 were protected from a neu-expressing mammary tumor challenge. Both CD4+ and CD8+ T cells mediated the tumor protection. Robust anti-tumor T cell immunity was detected in tumor protected mice.

CONCLUSIONS

Immunization of mice with HER2 protein vaccine targeting DEC+ DCs in vivo induced high levels of T- and B-cell immunity. Non-targeted HER2 protein was poorly immunogenic for CD4+ and CD8+ T cells. This vaccination approach provided long-term survival benefit for mice challenged with neu-expressing tumor following as little as 2.7 μg of HER2 protein incorporated in the vaccine. Vaccine-induced CD4+ and CD8+ T cells were both essential for tumor protection. This immunization strategy demonstrates great potential towards the development of vaccines for breast cancer patients.

Targeting HER2/neu with a fully human IgE to harness the allergic reaction against cancer cells

Breast and ovarian cancer are two of the leading causes of cancer deaths among women in the United States. Overexpression of the HER2/neu oncoprotein has been reported in patients affected with breast and ovarian cancers, and is associated with poor prognosis. To develop a novel targeted therapy for HER2/neu expressing tumors, we have constructed a fully human IgE with the variable regions of the scFv C6MH3-B1 specific for HER2/neu. This antibody was expressed in murine myeloma cells and was properly assembled and secreted. The Fc region of this antibody triggers in vitro degranulation of rat basophilic cells expressing human FcεRI (RBL SX-38) in the presence of murine mammary carcinoma cells that express human HER2/neu (D2F2/E2), but not the shed (soluble) antigen (ECD(HER2)) alone. This IgE is also capable of inducing passive cutaneous anaphylaxis in a human FcεRIα transgenic mouse model, in the presence of a cross-linking antibody, but not in the presence of soluble ECD(HER2). Additionally, IgE enhances antigen presentation in human dendritic cells and facilitates cross-priming, suggesting that the antibody is able to stimulate a secondary T-cell anti-tumor response. Furthermore, we show that this IgE significantly prolongs survival of human FcεRIα transgenic mice bearing D2F2/E2 tumors. We also report that the anti-HER2/neu IgE is well tolerated in a preliminary study conducted in Macaca fascicularis (cynomolgus) monkeys. In summary, our results suggest that this IgE should be further explored as a potential therapeutic against HER2/neu overexpressing tumors, such as breast and ovarian cancers.

The mannosylated extracellular domain of Her2/neu produced in P. pastoris induces protective antitumor immunity

Background

Her2/neu is overexpressed in various human cancers of epithelial origin and is associated with increased metastatic potential and poor prognosis. Several attempts have been made using the extracellular domain of Her2/neu (ECD/Her2) as a prophylactic vaccine in mice with no success in tumor prevention.

Methods

The extracellular domain of Her2/neu (ECD/Her2) was expressed in yeast P. pastoris, in a soluble highly mannosylated form. The immune response of the immunization with this recombinant ECD/Her2 was analyzed using immunoprecipitation and western blot analysis, proliferation and cytotoxicity assays as well as specific tumor growth assays.

Results

Mannosylated ECD/Her2 elicited a humoral response with HER2/neu specific antibodies in vaccinated mice, which were able to reduce the proliferation rate of cancer cells in vitro. Moreover, it elicited a cellular response with Her2/neu-specific CTL capable of lysing tumor cells, in vitro. When immunized Balb/c and HHD mice were challenged with Her2/neu-overexpressing cells, tumor growth was inhibited.

Conclusion

Here we report on the efficacy of the extracellular domain of human Her2/neu produced in yeast P. pastoris, which confers mannosylation of the protein, to act as a potent anti-tumor vaccine against Her2/neu overexpressing tumors. Specific cellular and humoral responses were observed as well as efficacy.

Mannose addition by yeast Pichia Pastoris on recombinant HER-2 protein inhibits recognition by the monoclonal antibody herceptin

We report here the generation of a full-length, highly glycosylated HER-2 oncoprotein using yeast strain, Pichia Pastoris. Upon treatment of secreted HER-2 with alpha-mannosidase, reactivity with the monoclonal antibody Herceptin is significantly increased. This phenomenon is due to glycosylation via mannose of the full-length HER-2 protein that extends over the antigenic epitope, which is recognized by Herceptin. The extensive glycosylation of HER-2 in Pichia Pastoris significantly increases its recognition and uptake by dendritic cells, which could be associated with increased vaccine performance.

Characterisation of an engineered trastuzumab IgE antibody and effector cell mechanisms targeting HER2/neu-positive tumour cells

Trastuzumab (Herceptin), a humanized IgG1 antibody raised against the human epidermal growth factor receptor 2 (HER2/neu), is the main antibody in clinical use against breast cancer. Pre-clinical evidence and clinical studies indicate that trastuzumab employs several anti-tumour mechanisms that most likely contribute to enhanced survival of patients with HER2/neu-positive breast carcinomas. New strategies are aimed at improving antibody-based therapeutics like trastuzumab, e.g. by enhancing antibody-mediated effector function mechanisms. Based on our previous findings that a chimaeric ovarian tumour antigen-specific IgE antibody showed greater efficacy in tumour cell killing, compared to the corresponding IgG1 antibody, we have produced an IgE homologue of trastuzumab. Trastuzumab IgE was engineered with the same light- and heavy-chain variable-regions as trastuzumab, but with an epsilon in place of the gamma-1 heavy-chain constant region. We describe the physical characterisation and ligand binding properties of the trastuzumab IgE and elucidate its potential anti-tumour activities in functional assays. Both trastuzumab and trastuzumab IgE can activate monocytic cells to kill tumour cells, but they operate by different mechanisms: trastuzumab functions in antibody-dependent cell-mediated phagocytosis (ADCP), whereas trastuzumab IgE functions in antibody-dependent cell-mediated cytotoxicity (ADCC). Trastuzumab IgE, incubated with mast cells and HER2/neu-expressing tumour cells, triggers mast cell degranulation, recruiting against cancer cells a potent immune response, characteristic of allergic reactions. Finally, in viability assays both antibodies mediate comparable levels of tumour cell growth arrest. These functional characteristics of trastuzumab IgE, some distinct from those of trastuzumab, indicate its potential to complement or improve upon the existing clinical benefits of trastuzumab.

Humanized ADEPT comprised of an engineered human purine nucleoside phosphorylase and a tumor targeting peptide for treatment of cancer

Immunogenicity caused by the use of nonhuman enzymes in antibody-directed enzyme prodrug therapy has limited its clinical application. To overcome this problem, we have developed a mutant human purine nucleoside phosphorylase, which, unlike the wild-type enzyme, accepts (deoxy)adenosine-based prodrugs as substrates. Among the different mutants of human purine nucleoside phosphorylase tested, a double mutant with amino acid substitutions E201Q:N243D (hDM) is the most efficient in cleaving (deoxy)adenosine-based prodrugs. Although hDM is capable of using multiple prodrugs as substrates, it is most effective at cleaving 2-fluoro-2'-deoxyadenosine to a cytotoxic drug. To target hDM to the tumor site, the enzyme was fused to an anti-HER-2/neu peptide mimetic (AHNP). Treatment of HER-2/neu-expressing tumor cells with hDM-AHNP results in cellular localization of enzyme activity. As a consequence, harmless prodrug is converted to a cytotoxic drug in the vicinity of the tumor cells, resulting in tumor cell apoptosis. Unlike the nonhuman enzymes, the hDM should have minimal immunogenicity when used in antibody-directed enzyme prodrug therapy, thus providing a novel promising therapeutic agent for the treatment of tumors.

Adoptive transfer of HER2/neu-specific T cells expanded with alternating gamma chain cytokines mediate tumor regression when combined with the depletion of myeloid-derived suppressor cells

Adoptive immunotherapy (AIT) using ex vivo-expanded HER-2/neu-specific T cells has shown initial promising results against disseminated tumor cells in the bone marrow. However, it has failed to promote objective responses against primary tumors. We report for the first time that alternating gamma chain cytokines (IL-2, IL-7 and IL-15) ex vivo can expand the neu-specific lymphocytes that can kill breast tumors in vitro. However, the anti-tumor efficacy of these neu-specific T cells was compromised by the increased levels of myeloid-derived suppressor cells (MDSC) during the premalignant stage in FVBN202 transgenic mouse model of breast carcinoma. Combination of AIT with the depletion of MDSC, in vivo, resulted in the regression of neu positive primary tumors. Importantly, neu-specific antibody responses were restored only when AIT was combined with the depletion of MDSC. In vitro studies determined that MDSC caused inhibition of T cell proliferation in a contact-dependent manner. Together, these results suggest that combination of AIT with depletion or inhibition of MDSC could lead to the regression of mammary tumors.

A chaperone protein-enriched tumor cell lysate vaccine generates protective humoral immunity in a mouse breast cancer model

We have documented previously that a multiple chaperone protein vaccine termed chaperone-rich cell lysate (CRCL) promotes tumor-specific T-cell responses leading to cancer regression in several mouse tumor models. We report here that CRCL vaccine generated from a mouse breast cancer (TUBO, HER2/neu positive) is also capable of eliciting humoral immunity. Administration of TUBO CRCL triggered anti-HER2/neu antibody production and delayed the progression of established tumors. This antitumor activity can be transferred through the serum isolated from TUBO CRCL-immunized animals and involved both B cells and CD4(+) T lymphocytes. Further evaluation of the mechanisms underlying TUBO CRCL-mediated humoral immunity highlighted the role of antibody-dependent cell-mediated cytotoxicity. These results suggest that tumor-derived CRCL vaccine has a wider applicability as a cancer vaccine because it can target both T-cell- and B-cell-specific responses and may represent a promising approach for the immunotherapy of cancer.

Antibody-cytokine fusion proteins: applications in cancer therapy

BACKGROUND

Antibody-cytokine fusion proteins consist of cytokines fused to an antibody to improve antibody-targeted cancer immunotherapy. These molecules have the capacity to enhance the tumoricidal activity of the antibodies and/or activate a secondary antitumor immune response.

OBJECTIVE

To review the strategies used to develop antibody-cytokine fusion proteins and their in vitro and in vivo properties, including preclinical and clinical studies focusing on IL-2, IL-12 and GM-CSF.

METHODS

Articles were found by searching databases such as PubMed and Clinical Trials of the US National Institutes of Health.

RESULTS/CONCLUSION

Multiple antibody-cytokine fusion proteins have demonstrated significant antitumor activity as direct therapeutics or as adjuvants of cancer vaccines in preclinical studies, paving the way for their clinical evaluation.

Augmented HER-2 specific immunity during treatment with trastuzumab and chemotherapy

PURPOSE

Passive immunotherapy with antitumor antibodies has the potential to induce active tumor immunity via the opsonic enhancement of immunogenicity of tumor antigen. We have assessed whether immune sensitization to the HER-2/neu tumor antigen occurs during treatment with the anti-HER-2/neu monoclonal antibody trastuzumab.

EXPERIMENTAL DESIGN

Twenty-seven patients treated with trastuzumab and chemotherapy were assessed for the induction of HER-2/neu-specific immunity. Sera and peripheral blood mononuclear cells obtained before and after trastuzumab therapy were compared for the presence of anti-HER-2/neu endogenous Iglambda antibodies and HER-2/neu-specific CD4 responses by ELISA and enzyme-linked immunospot, respectively.

RESULTS

Anti-HER-2/neu antibodies were detectable in 8 of 27 (29%) patients before trastuzumab treatment and in 15 of 27 (56%) patients during trastuzumab treatment. In the overall study population, anti-HER-2/neu humoral responses significantly increased during therapy (P < 0.001) and were not associated with development of an anti-idiotypic response. In 10 evaluable individuals, 6 showed augmented HER-2/neu-specific CD4 T-cell responses during therapy. Of the 22 individuals treated for metastatic disease, those patients showing objective clinical responses exhibited more frequent (P = 0.004) and larger (P = 0.006) treatment-associated anti-HER-2/neu humoral responses.

CONCLUSION

Humoral immune sensitization occurs during treatment with chemotherapy and trastuzumab. Further studies are warranted to investigate whether augmented anti-HER-2/neu humoral and cellular immunity contributes mechanistically to clinical outcome.

Long-term immunity elicited by antibody-cytokine fusion proteins protects against sequential challenge with murine mammary and colon malignancies

We have previously reported that the antibody fusion proteins anti-HER2/neu IgG3 fused to IL-12 [(IL-12)-IgG3] or GM-CSF [IgG3-(GM-CSF)] independently or in combination are effective anti-tumor agents against D2F2/E2 murine mammary cancer cells expressing human HER2/neu in the peritoneum. Importantly, the long-term survivors were immune to the subcutaneous challenge with D2F2/E2 and the parental D2F2 not expressing HER2/neu. We now show that these long-term survivors also exhibit significant protection against subsequent subcutaneous challenge with the murine colon carcinoma CT26-HER2/neu, and later against subcutaneous challenge with the parental CT26. These results suggest that the long-term systemic protection against mammary cancer elicited by treatment with antibody-cytokine fusion proteins can be extended to prevent the growth of a tumor from different origin expressing HER2/neu, and that this protection is not limited to this antigen alone, since it also prevented the growth of the parental tumor cells.

Novel engineered trastuzumab conformational epitopes demonstrate in vitro and in vivo antitumor properties against HER-2/neu

Trastuzumab is a growth-inhibitory humanized Ab targeting the oncogenic protein HER-2/neu. Although trastuzumab is approved for treatment of advanced breast cancer, a number of concerns exist with passive immunotherapy. Treatment is expensive and has a limited duration of action, necessitating repeated administrations of the mAb. Active immunotherapy with conformational B cell epitopes affords the possibility of generating an enduring immune response, eliciting protein-reactive high-affinity anti-peptide Abs. The three-dimensional structure of human HER-2 in complex with trastuzumab reveals that the Ag-binding region of HER-2 spans residues 563-626 that comprises an extensive disulfide-bonding pattern. To delineate the binding region of HER-2, we have designed four synthetic peptides with different levels of conformational flexibility. Chimeric peptides incorporating the measles virus fusion "promiscuous" T cell epitope via a four-residue linker sequence were synthesized, purified, and characterized. All conformational peptides were recognized by trastuzumab and prevented the function of trastuzumab inhibiting tumor cell proliferation, with 563-598 and 597-626 showing greater reactivity. All epitopes were immunogenic in FVB/N mice with Abs against 597-626 and 613-626 recognizing HER-2. The 597-626 epitope was immunogenic in outbred rabbits eliciting Abs which recognized HER-2, competed with trastuzumab for the same epitope, inhibited proliferation of HER-2-expressing breast cancer cells in vitro and caused their Ab-dependent cell-mediated cytotoxicity. Moreover, immunization with the 597-626 epitope significantly reduced tumor burden in transgenic BALB-neuT mice. These results suggest the peptide B cell immunogen is appropriate as a vaccine for HER-2-overexpressing cancers because the resulting Abs show analogous biological properties to trastuzumab.

Engineering antibodies for clinical applications

Molecular engineering has contributed immensely to the clinical success of antibodies in recent years. The modular structure of antibodies has permitted their modification in numerous ways, to meet various clinical requirements. With the help of antibody engineering, it has been possible to modify the molecular size, pharmacokinetics, immunogenicity, binding affinity, specificity and effector function of antibodies. In addition, fusion proteins of antibodies with various proteins and peptides have yielded targeted biological modifiers, toxins and imaging agents. This review focuses on the recent trends in antibody engineering for improving their clinical utility.

Cytokines fused to antibodies and their combinations as therapeutic agents against different peritoneal HER2/neu expressing tumors

We have previously generated antihuman HER2/neu-humanized IgG3 fused to interleukin-2 (IL-2), IL-12, or granulocyte macrophage colony-stimulating factor (GM-CSF) [monofunctional fusion proteins (mono-AbFP)] or fused to IL-2 and IL-12 or IL-12 and GM-CSF [bifunctional fusion proteins (bi-AbFP)]. These AbFPs retained cytokine and antigen-binding activities. We have now further characterized the AbFPs and determined the heparin-binding activity of the fused cytokines, their ability to trigger IFN-gamma secretion and natural killer (NK) activation, and their direct antitumor efficacy. Flow cytometry revealed heparin-binding activity in the AbFPs containing IL-12 and IL-2, although this activity seems to be decreased in the bi-AbFPs. However, both bi-AbFPs retained the capacity to stimulate IL-12-dependent IFN-gamma secretion in the NK cell line KY-1, and IL-12/IL-2 bi-AbFP induced NK activity in splenocytes. The antitumor effectiveness of bi-AbFPs and mono-AbFP combinations was studied in mice challenged i.p. with three different human HER2/neu murine syngeneic models (D2F2/E2, CT26-HER2/neu, and MC38-HER2/neu). Although a significant variability in the profile of antitumor response was observed in the different tumor models, the combination of IL-12 and GM-CSF mono-AbFPs protected 100% of D2F2/E2-challenged and 75% of CT26-HER2/neu-challenged mice. In contrast, bi-AbFPs protected less than the combination of mono-AbFPs and, in some models, even less than mono-AbFPs alone. However, in all cases, most of long-term survivors showed protection after s.c. rechallenge with the tumors and later with the parental tumors not expressing HER2/neu. These results show that, although the pattern of protection is tumor model dependent, treatments with AbFPs can effectively generate high levels of protection against peritoneal tumors expressing HER2/neu, which may be relevant in patients with primary or metastatic peritoneal carcinomatosis that may be observed in ovarian, colon, stomach, bladder, lung, and breast cancers.

Antibody targeted drugs as cancer therapeutics

Treatment of cancer is a double-edged sword: it should be as aggressive as possible to completely destroy the tumour, but it is precisely this aggressiveness which often causes severe side effects - a reason why some promising therapeutics can not be applied systemically. In addition, therapeutics such as cytokines that physiologically function in a para- or autocrine fashion require a locally enhanced level to exert their effect appropriately. An elegant way to accumulate therapeutic agents at the tumour site is their conjugation/fusion to tumour-specific antibodies. Here, we discuss recent preclinical and clinical data for antibody-drug conjugates and fusion proteins with a special focus on drug components that exert their antitumour effects through normal biological processes.

Anti-HER2/neu IgG3–(IL-2) and anti-HER2/neu IgG3–(GM-CSF) promote HER2/neu processing and presentation by dendritic cells: Implications in immunotherapy and vaccination strategies

HER2/neu, a transmembrane glycoprotein overexpressed in several types of human cancers, is a potential target for active immunotherapy. However, this protein and especially its extracellular domain (ECD(HER2)), is weakly immunogenic and is poorly processed by dendritic cells (DCs). Previously, we showed that anti-HER2/neu IgG3-(IL-2) and anti-HER2/neu IgG3-(GM-CSF) fusion proteins can enhance the immunogenicity of ECD(HER2) in mice, and that the non-covalent physical association between each antibody fusion proteins and ECD(HER2) was critical to elicit optimal protective immunity against HER2/neu expressing tumors. We now use the professional antigen-presenting DCs to investigate the effect of the antibody fusion protein binding to ECD(HER2) on its trafficking and presentation. We found that when the extracellular domain of HER2/neu fused to ovalbumin (OVA-ECD(HER2)) is bound by HER2/neu-specific antibody-(IL-2) or antibody-(GM-CSF) fusion proteins, the bound antigen is more efficiently processed by murine bone-marrow-derived dendritic cells (BMDCs) and presented to OVA-specific T-cells than the unbound OVA-ECD(HER2). We also found that ECD(HER2) bound by anti-HER2/neu IgG3-(IL-2) is very efficiently internalized and that the internalized ECD(HER2) is not retained in the early endosomal compartments but traffics to the antigen-processing compartments. These results are consistent with our earlier in vivo studies and suggest that both antibody-(IL-2) and antibody-(GM-CSF) fusion proteins can be used to enhance the immune response to poorly immunogenic antigens including tumor-associated antigens (TAAs).

Anti-HER-2 DNA vaccine protects Syrian hamsters against squamous cell carcinomas

This paper illustrates the efficacy of DNA vaccination through electroporation in the prevention of oral transplantable carcinoma in Syrian hamsters. At 21 and 7 days before tumour challenge, 19 hamsters were vaccinated with plasmids coding for the extracellular and transmembrane domains of rat HER-2 receptor (EC-TM plasmids), whereas 19 control hamsters were injected intramuscularly with the empty plasmid. Immediately following plasmid injection, hamsters of both groups received two square-wave 25 ms, 375 V cm(-1) electric pulses via two electrodes placed on the skin of the injection area. At day 0, all hamsters were challenged in the submucosa of the right cheek pouch with HER-2-positive HCPC I cells established in vitro from an 7,12-dimethylbenz[a]anthracene-induced oral carcinoma. This challenge gave rise to HER-2-positive buccal neoplastic lesions in 14 controls (73.37%), compared with only seven (36.8%, P<0.0027) vaccinated hamsters. In addition, the vaccinated hamsters displayed both a stronger proliferative and cytotoxic response than the controls and a significant anti-HER-2 antibody response. Most of the hamsters that rejected the challenge displayed the highest antibody titres. These findings suggest that DNA vaccination may have a future in the prevention of HER-2-positive human oral cancer.

A Trimeric Anti-HER2/neuScFv and Tumor Necrosis Factor-α Fusion Protein Induces HER2/neuSignaling and Facilitates Repair of Injured Epithelia

Tumor necrosis factor (TNF)-alpha genetically fused to the carboxyl terminus of a single-chain Fv (ScFv) antibody specific for the human HER2/neu (anti-HER2/neu ScFv-TNF-alpha) forms a homotrimeric structure that retains both TNF-alpha activity and the ability to bind HER2/neu. In contrast to anti-HER2/neu IgG3, anti-HER2/neu ScFv-TNF-alpha induces potent HER2/neu signaling, activating the downstream mitogen-activated protein kinase (MAPK) and Akt pathways in SKBR3 cells. Activation of MAPK and Akt by anti-HER2/neu ScFv-TNF-alpha inhibited the apoptosis of SKBR3 cells induced by actinomycin D. Remarkably, anti-HER2/neu ScFv-TNF-alpha facilitated the repair of injured epithelia. Accelerated wound healing required binding to HER2/neu but not TNF-alpha activity since anti-HER2/neu ScFv-TNF-alpha (S147Y), containing a mutant TNF-alpha with significantly decreased biological activity, demonstrated equivalent ability to facilitate wound healing and soluble HER2/neu inhibited the effect. These results suggest that trimeric anti-HER2/neu ScFv has the potential to facilitate wound healing. In addition, fusion with TNF-alpha provides a novel approach to producing polymeric antibodies.

Insights into the mechanism of anti-tumor immunity in mice vaccinated with the human HER2/neu extracellular domain plus anti-HER2/neu IgG3-(IL-2) or anti-HER2/neu IgG3-(GM-CSF) fusion protein

In the present study, we demonstrate that a physical association between the extracellular domain of human HER2/neu receptor (ECDHER2) plus anti-HER2/neu IgG3-(IL-2) or anti-HER2/neu IgG3-(GM-CSF) was required to elicit the most effective anti-tumor immune response against a syngeneic tumor expressing rat HER2/neu. Immune effectors including CD4+, CD8+, and NK cells contributed to protection against tumor growth. Vaccinated B-cell deficient mice did not elicit tumor protection, suggesting a critical role for B-cells in a protective immune response. These results provide insights into the mechanisms responsible for the protective tumor immunity elicited when antibody-(IL-2 or GM-CSF) are used as enhancers of vaccines targeting tumor antigens.

Vaccination with novel combinations of anti-HER2/neu cytokines fusion proteins and soluble protein antigen elicits a protective immune response against HER2/neu expressing tumors

We have previously demonstrated that anti-HER2/neu IgG3-(IL-2), (IL-12)-IgG3, or IgG3-(GM-CSF) antibody fusion proteins (mono-AbFPs) elicit anti-tumor activity against murine tumors expressing HER2/neu when used as adjuvants of extracellular domain of HER2/neu (ECD(HER2)) protein vaccination. We have now studied the effect of combinations of IL-2 and IL-12 or IL-12 and GM-CSF mono-AbFPs during vaccination with ECD(HER2). In addition, we developed two novel anti-HER2/neu IgG3-cytokine fusion proteins in which IL-2 and IL-12 or IL-12 and GM-CSF were fused to the same IgG3 molecule (bi-AbFPs). (IL-12)-IgG3-(IL-2) and (IL-12)-IgG3-(GM-CSF) were properly assembled and retained both cytokine activity and the ability to bind antigen. Vaccination of mice with ECD(HER2) and a combination of cytokines as either bi-AbFPs or two mono-AbFPs activated both Thl and Th2 immune responses and resulted in significant protection against challenge with a HER2/neu expressing tumor. Our results suggest that this approach will be effective in the prevention and/or treatment of HER2/neu expressing tumors.

Gene expression analysis of immune-mediated arrest of tumorigenesis in a transgenic mouse model of HER-2/neu-positive basal-like mammary carcinoma

We previously showed that a vaccine combining interleukin 12 and allogeneic p185(neu)-positive mammary carcinoma cells completely prevented multifocal mammary carcinogenesis in HER-2/neu transgenic mice. To identify the molecular events responsible for effective tumor prevention and to define the tumor gene expression signature, we used microarrays to analyze the expression profile of mammary tissue of untreated transgenic mice and of vaccine-treated, tumor-free mice at different time points. Mammary tissue from vaccinated mice displayed a gene expression profile different from that of untreated, tumor-bearing mice but similar to that of normal/hyperplastic mammary gland. Comparison of treated and untreated mice at 15 weeks of age revealed up-regulation of genes encoding antibodies, chemokines, gamma-interferon-induced genes and inflammatory molecules, and down-regulation of early genes induced by tumor development. The gene expression signature of HER-2/neu-transformed tumor cells showed modulation of genes promoting proliferation, angiogenesis, migration, invasion, and metastasis and inhibiting apoptosis and immune response. Meta-analysis of microarray data on human breast cancer showed that the signature of tumors arising in murine HER-2/neu transgenic model correctly classified human HER-2/neu-expressing tumors and normal breast tissue. Moreover murine and human HER-2/neu-positive tumors share the signature of basal-like breast cancers. This gene expression analysis reveals the immune events associated with prevention of tumor development and shows that HER-2/neu transgenic mice represent a good model of a poor-prognosis group of human breast tumors.

Targeted Delivery of the ErbB2/HER2 Tumor Antigen to Professional APCs Results in Effective Antitumor Immunity

Activation of T cells by professional APCs that present peptide epitopes of tumor-associated Ags is critical for the induction of cell-mediated immunity against tumors. To facilitate targeted delivery of the ErbB2 (HER2, neu) tumor Ag to APCs in vivo, we have generated chimeric proteins that contain the extracellular domain of CTLA-4 for binding to B7 molecules on the APC surface, which is genetically fused to a human ErbB2 fragment as an antigenic determinant. Bacterially expressed CTLA-4-ErbB2 fusion protein and a similar molecule harboring in addition the translocation domain of Pseudomonas exotoxin A as an endosome escape function displayed specific binding to B7-expressing cells, followed by protein internalization and intracellular degradation. Vaccination of BALB/c mice with the fusion proteins resulted in the induction of ErbB2-specific CD8(+) T cells and CTL-dependent protection from subsequent challenge with ErbB2-expressing but not ErbB2-negative murine renal carcinoma cells. In a therapeutic setting, injection of CTLA-4-ErbB2 protein vaccines caused rejection of established ErbB2-expressing tumors. Thereby, immunological memory was induced, leading to long-term systemic immunity and protection against rechallenge several months later. Our results demonstrate that these chimeric protein vaccines are effective tools for the induction of ErbB2-specific, T cell-mediated immunity.

HER-2: A biomarker at the crossroads of breast cancer immunotherapy and molecular medicine

The oncoprotein encoded by the HER-2 oncogene is a member of the HER family of receptor tyrosine kinases and is actually the first successfully exploited target molecule in new biomolecular therapies of solid tumors. The association of HER-2 overexpression with human tumors, its extracellular accessibility, as well as its involvement in tumor aggressiveness are all factors that make this receptor an appropriate target for tumor-specific therapy. In addition, HER-2 overexpression fosters its immunogenicity, as shown by the frequency of B and T cell-mediated responses against this oncoprotein in cancer patients, and it is being investigated as a promising molecule for either passive and active immunotherapy strategies. This review summarizes a number of immune intervention approaches that target HER-2 in breast cancer.

Immunoprevention of HER-2/neu Transgenic Mammary Carcinoma through an Interleukin 12-Engineered Allogeneic Cell Vaccine

This study evaluated the ability of cytokine-engineered allogeneic (H-2(q)) HER-2/neu-positive cells to prevent tumor development in mammary cancer-prone virgin female BALB/c (H-2(d)) mice transgenic for the transforming rat HER-2/neu oncogene (BALB-neuT mice). Repeated vaccinations with cells engineered to release interleukin (IL)-2, IL-12, IL-15, or IFN-gamma showed that IL-12-engineered cell vaccines had the most powerful immunopreventive activity, with >80% of 1-year-old BALB-neuT mice free of tumors. On the contrary all of the untreated mice and all of the mice vaccinated with IL-12-engineered cells lacking either HER-2/neu or allogeneic antigens developed mammary carcinomas within 22 or 33 weeks, respectively. Whole mount, histology, immunohistochemistry, and gene expression profile analysis showed that vaccination with IL-12-engineered cells maintained 26-week mammary glands free of neoplastic growth, with a gene expression profile that clustered with that of untreated preneoplastic glands. The IL-12-engineered cell vaccine elicited a high production of IFN-gamma and IL-4 and a strong anti-HER-2/neu antibody response. Immune protection was lost or markedly impaired in BALB-neuT mice lacking IFN-gamma or antibody production, respectively. The protection afforded by the IL-12-engineered cell vaccine was equal to that provided by the systemic administration of recombinant IL-12 in combination with HER-2/neu H-2(q) cell vaccine. However, IL-12-engineered cell vaccine induced much lower circulating IL-12 and IFN-gamma, and therefore lower potential side effects and systemic toxicity.

Antibody engineering for therapeutics

With the acceptance of antibodies as therapeutics, a diversity of engineered antibody forms have been created to improve their efficacy, including enhancing the effector functions of full-length antibodies, delivering toxins to kill cells or cytokines in order to stimulate the immune system, and bispecific antibodies to target multiple receptors. After years of in vitro investigation, many of these are now moving into clinical trials and are showing promise. A potential new type of effector function for antibodies, that is, the generation of reactive oxygen species that may effect inflammation or bacterial killing, has been elucidated. In addition, the field has expanded beyond a concentration on immunoglobulin G to include immunoglobulin A antibodies as potential therapeutics.