Prevention of spontaneous neu-expressing mammary tumor development in mice transgenic for rat proto-neu by DNA vaccination

Circulating autoantibodies to alpha-enolase (ENO1) and far upstream element-binding protein 1 (FUBP1) are negative prognostic factors for pancreatic cancer patient survival

Pancreatic ductal adenocarcinoma (PDA) has a dismal prognosis due to a lack of early diagnostic markers and effective therapy. In PDA patients, the glycolytic enzyme and plasminogen receptor alpha-enolase (ENO1) and the transcription factor far upstream element-binding protein 1 (FUBP1) are upregulated and elicit the production of autoantibodies (aAb) that discriminate healthy subjects from PDA patients, with the latter mostly directed to post-translational phosphorylated isoforms. Here, the correlation of prognosis with circulating ENO1 and FUBP1aAb, and their protein tissue expression was analyzed in PDA patients. Circulating ENO1 and FUBP1 aAb was analyzed in two cohorts of PDA patients by ELISA (n = 470), while tissues expression was observed by immunohistochemistry (n = 45). Overall survival (OS) was estimated using the Kaplan-Meier method, while the Cox model was used to estimate the hazard ratios (HR) adjusted for the main prognostic factors. Logistic models were applied to assess associations between death and its risk indicators. All statistical analyses were performed with Stata version 15. Unlike ENO1 aAb, there was a significant correlation between FUBP1 aAb and FUBP1 expression in tumors (p = 0.0268). In addition, we found that high ENO1 (p = 0.016) and intermediate FUBP1 aAb levels (p = 0.013) were unfavorable prognostic factors. Notably, it was found that high anti-FUBP1 aAb level is a good prognostic marker for tail-body PDA (p = 0.016). Our results suggest that different levels of circulating aAb to ENO1 and FUBP1 predict a poor outcome in PDA patients and can be used to improve therapeutic strategies.

Single-Cell Immunoblotting based on a Photoclick Hydrogel Enables High-Throughput Screening and Accurate Profiling of Exogenous Gene Expression

Fast and accurate profiling of exogenous gene expression in host cells is crucial for studying gene function in cellular and molecular biology, but still faces the challenge of incomplete co-expression of reporter genes and target genes. Here, a single-cell transfection analysis chip (scTAC) is presented, which is based on the in situ microchip immunoblotting method, for rapid and accurate analysis of exogenous gene expression in thousands of individual host cells. scTAC not only can assign information of exogenous gene activity to specific transfected cells, but enables the acquisition of continuous protein expression even in low co-expression scenarios. It is demonstrated that scTAC can reveal the relationship of expression level between reporter genes and target genes, which is helpful for evaluating transient transfection strategy efficiency. The advantages of this method for the study of fusion protein expression and downstream protein expression in signaling pathway in rare cells are shown. Empirically, an EGFP-TSPAN8 fusion plasmid is transfected into MCF-7 breast cancer cells and the expressions of two cancer stemness biomarkers (ALDHA1 and SOX2) are analyzed. The scTAC method clearly reveals an interesting phenomenon that transfected adherent MCF-7 cells exhibit some stem cell characteristics, but they do not have stem cell appearance.

Cancer Immunoprevention: Current Status and Future Directions

Cancer is one of the most serious diseases affecting health and the second leading cause of death worldwide. Despite the development of various therapeutic modalities to deal with cancer, limited improvement in overall survival of patients has been yielded. Since there is no certain cure for cancer, detection of premalignant lesions, and prevention of their progression are vital to the decline of high morbidity and mortality of cancer. Among approaches to cancer prevention, immunoprevention has gained further attention in recent years. Deep understanding of the tumor/immune system interplay and successful prevention of virally-induced malignancies by vaccines have paved the way toward broadening cancer immunoprevention application. The identification of tumor antigens in premalignant lesions was the turning point in cancer immunoprevention that led to designing preventive vaccines for various malignancies including multiple myeloma, colorectal, and breast cancer. In addition to vaccines, immune checkpoint inhibitors are also being tested for the prevention of oral squamous cell carcinoma (SCC), and imiquimod which is an established drug for the prevention of skin SCC, is a non-specific immunomodulator. Herein, to provide a bench-to-bedside understanding of cancer immunoprevention, we will review the role of the immune system in suppression and promotion of tumors, immunoprevention of virally-induced cancers, identification of tumor antigens in premalignant lesions, and clinical advances of cancer immunoprevention.

Chemo-immunotherapy induces tumor regression in a mouse model of spontaneous mammary carcinogenesis

Tumor-specific immune tolerance represents an obstacle for the development of effective anti-tumor immune responses through cancer vaccines. We here evaluated the efficacy of chemo-immunotherapy in breaking tumor-specific immune tolerance in an almost incurable mouse model of spontaneous carcinogenesis.Transgenic HER-2/neu mice bearing large mammary tumors received the adoptive transfer of splenocytes and serum isolated from immune donors, with or without pre-conditioning with cyclophosphamide. Treatment efficacy was assessed by monitoring tumor growth by manual inspection and by magnetic resonance imaging. The same chemo-immunotherapy protocol was tested on tumor-free HER-2/neu mice, to evaluate the effects on tumor emergence.Our data show that chemo-immunotherapy hampered carcinogenesis and caused the regression of large mammary tumor lesions in tumor-bearing HER-2/neu mice. The complete eradication of a significant number of tumor lesions occurred only in mice receiving cyclophosphamide shortly before immunotherapy, and was associated with increased serum anti HER-2/p185 antibodies and tumor leukocyte infiltration. The same protocol significantly delayed the appearance of mammary tumors when administered to tumor-free HER-2/neu mice, indicating that this chemo-immunotherapy approach acted through the elicitation of an effective anti-tumor immune response. Overall, our data support the immune-modulatory role of chemotherapy in overcoming cancer immune tolerance when administered at lymphodepleting non-myeloablative doses shortly before transfer of antigen-specific immune cells and immunoglobulins. These findings open new perspectives on combining immune-modulatory chemotherapy and immunotherapy to overcome immune tolerance in cancer patients.

Embryonic Lethality in Homozygous Human Her-2 Transgenic Mice Due to Disruption of the Pds5b Gene

The development of antigen-targeted therapeutics is dependent on the preferential expression of tumor-associated antigens (TAA) at targetable levels on the tumor. Tumor-associated antigens can be generated de novo or can arise from altered expression of normal basal proteins, such as the up-regulation of human epidermal growth factor receptor 2 (Her2/ErbB2). To properly assess the development of Her2 therapeutics in an immune tolerant model, we previously generated a transgenic mouse model in which expression of the human Her2 protein was present in both the brain and mammary tissue. This mouse model has facilitated the development of Her2 targeted therapies in a clinically relevant and suitable model. While heterozygous Her2^+/- mice appear to develop in a similar manner to wild type mice (Her2^-/-), it has proven difficult to generate homozygous Her2^+/+ mice, potentially due to embryonic lethality. In this study, we performed whole genome sequencing to determine if the integration site of the Her2 transgene was responsible for this lethality. Indeed, we report that the Her2 transgene had integrated into the Pds5b (precocious dissociation of sisters) gene on chromosome 5, as a 162 copy concatemer. Furthermore, our findings demonstrate that Her2^+/+ mice, similar to Pds5b^-/- mice, are embryonic lethal and confirm the necessity for Pds5b in embryonic development. This study confirms the value of whole genome sequencing in determining the integration site of transgenes to gain insight into associated phenotypes.

The antigenic repertoire of premalignant and high-risk lesions

Prophylactic vaccines have been a major advance in preventing the development of infections after exposure to pathogens. When contemplating an effective approach to cancer prevention, vaccines offer unique advantages over other more standard approaches: First, once appropriately stimulated, antigen-specific T cells will travel to all sites of disease and eradicate cells bearing the proteins to which the T cells have been primed by vaccination. Second, successful immunization will further result in the development of immunologic memory, providing lifelong immunologic surveillance. There is evidence of an adaptive tumor immune infiltrate even at the earliest stages of breast and colon cancer development. Furthermore, there is measurable immunity to lesion-associated antigens present in patients who will eventually develop malignancy even before cancer is clinically evident. Recent studies are beginning to unmask the preinvasive antigenic repertoire for these two malignancies. Preliminary experiments in transgenic mouse models of mammary and intestinal tumors suggest that immunization against antigens expressed in preinvasive and high-risk lesions may be effective in preventing the development of invasive malignancy.

A multiantigen vaccine targeting neu, IGFBP-2, and IGF-IR prevents tumor progression in mice with preinvasive breast disease

A multiantigen multipeptide vaccine, targeting proteins expressed in preinvasive breast lesions, can stimulate type I CD4(+) T cells which have been shown to be deficient in both patients with breast cancer and mice that develop mammary tumors. Transgenic mice (TgMMTV-neu) were immunized with a multiantigen peptide vaccine specific for neu, insulin-like growth factor-binding protein 2 and insulin-like growth factor receptor-I at a time when some of the animals already had preinvasive lesions (18 weeks of age). Although immunization with each individual antigen was partially effective in inhibiting tumor growth, immunization with the multiantigen vaccine was highly effective, blocking development of palpable lesions in 65% of mice and slowing tumor growth in the infrequent palpable tumors, which did arise. Protection was mediated by CD4(+) T cells, and the few slow-growing tumors that did develop demonstrated a significant increase in intratumoral CD8(+) T cells as compared with controls (P = 0.0007). We also combined the vaccine with agents that were, by themselves, partially effective inhibitors of tumor progression in this model; lapatinib and the RXR agonist bexarotene. Although the combination of lapatinib and vaccination performed similarly to vaccination alone (P = 0.735), bexarotene and vaccination significantly enhanced disease-free survival (P < 0.0001), and approximately 90% of the mice showed no pathologic evidence of carcinomas at one year. The vaccine also demonstrated significant clinical efficacy in an additional transgenic model of breast cancer (TgC3(I)-Tag). Chemoimmunoprevention combinations may be an effective approach to breast cancer prevention even when the vaccine is administered in the presence of subclinical disease.

Preclinical HER-2 Vaccines: From Rodent to Human HER-2

Effective prevention of human cancer with vaccines against viruses, such as HBV and HPV, raises the question whether also non-virus related tumors could be prevented with immunological means. Studies in HER-2-transgenic mice showed that powerful anti-HER-2 vaccines, could almost completely prevent the onset of mammary carcinoma. Protective immune responses were orchestrated by T cells and their cytokines, and effected by antibodies against HER-2 gene product p185. Analogous findings were reported in a variety of other cancer immunoprevention systems, thus leading to the definition of oncoantigens, optimal target antigens that are causally involved in carcinogenesis and cancer progression. Prophylactic HER-2 vaccines were also effective in preventing metastasis outgrowth, indicating that concepts and approaches developed for cancer immunoprevention could prove fruitful in cancer immunotherapy as well. The availability of cancer-prone mice carrying a human HER-2 transgene is now fostering the design of novel vaccines against human p185. A further bridge toward human cancer was recently provided by novel immunodeficient models, like Rag2^−/−;Il2rg^−/− mice, which are permissive for metastatic spread of human HER-2+ cancer cells and can be engrafted with a functional human immune system, allowing for the first time the study of vaccines against oncoantigens to elicit human immune responses against human cancer cells in vivo.

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.

Lentivector prime and vaccinia virus vector boost generate high-quality CD8 memory T cells and prevent autochthonous mouse melanoma

Most cancer vaccines, to date, fail to control established tumors. However, their application in preventing tumors is another question that is understudied. In the current study, we investigated the CD8 memory T cell responses of lentivector (lv) immunization and its potential to prevent melanoma using both transplantable B16 tumor and autochthonous melanoma models. We found that lv-expressing xenogenic human gp100 could induce potent CD8 responses that cross-react with mouse gp100. Importantly, the lv-primed CD8 response consisted of a high number of memory precursors and could be further increased by recombinant vaccinia virus vector (vv) boost, resulting in enhanced CD8 memory response. These long-lasting CD8 memory T cells played a critical role in immune surveillance and could rapidly respond and expand after sensing B16 tumor cells to prevent tumor establishment. Although CD8 response plays a dominant role after lv immunization, both CD4 and CD8 T cells are responsible for the immune prevention. In addition, we surprisingly found that CD4 help was not only critical for generating primary CD8 responses, but also important for secondary CD8 responses of vv boost. CD4 depletion prior to lv prime or prior to vv boost substantially reduced the magnitude of secondary CD8 effector and memory responses, and severely compromised the effect of cancer immune prevention. More importantly, the CD8 memory response from lv-vv prime-boost immunization could effectively prevent autochthonous melanoma in tumor-prone transgenic mice, providing a strong evidence that lv-vv prime-boost strategy is an effective approach for cancer immune prevention.

DNA vaccination: using the patient's immune system to overcome cancer

Cancer is one of the most challenging diseases of today. Optimization of standard treatment protocols consisting of the main columns of chemo- and radiotherapy followed or preceded by surgical intervention is often limited by toxic side effects and induction of concomitant malignancies and/or development of resistant mechanisms. This requires the development of therapeutic strategies which are as effective as standard therapies but permit the patients a life without severe negative side effects. Along this line, the development of immunotherapy in general and the innovative concept of DNA vaccination in particular may provide a venue to achieve this goal. Using the patient's own immune system by activation of humoral and cellular immune responses to target the cancer cells has shown first promising results in clinical trials and may allow reduced toxicity standard therapy regimen in the future. The main challenge of this concept is to transfer the plethora of convincing preclinical and early clinical results to an effective treatment of patients.

Analysis of a cholera toxin B subunit (CTB) and human mucin 1 (MUC1) conjugate protein in a MUC1-tolerant mouse model

Since epithelial mucin 1 (MUC1) is associated with several adenocarcinomas at the mucosal sites, it is pertinent to test the efficacy of a mucosally targeted vaccine formulation. The B subunit of the Vibrio cholerae cholera toxin (CTB) has great potential to act as a mucosal carrier for subunit vaccines. In the present study we evaluated whether a MUC1 tandem repeat (TR) peptide chemically linked to CTB would break self-antigen tolerance in the transgenic MUC1-tolerant mouse model (MUC1.Tg) through oral or parenteral immunizations. We report that oral immunization with the CTB-MUC1 conjugate along with mucosal adjuvant, unmethylated CpG oligodeoxynucleotide (ODN) and interleukin-12 (IL-12) did not break self-antigen tolerance in MUC1.Tg mice, but induced a strong humoral response in wild-type C57BL/6 mice. However, self-antigen tolerance in the MUC1.Tg mouse model was broken after parenteral immunizations with different doses of the CTB-MUC1 conjugate protein and with the adjuvant CpG ODN co-delivered with CTB-MUC1. Importantly, mice immunized systemically with CpG ODN alone and with CTB-MUC1 exhibited decreased tumor burden when challenged with a mammary gland tumor cell line that expresses human MUC1.

DNA vaccines in veterinary use

DNA vaccines represent a new frontier in vaccine technology. One important application of this technology is in the veterinary arena. DNA vaccines have already gained a foothold in certain fields of veterinary medicine. However, several important questions must be addressed when developing DNA vaccines for animals, including whether or not the vaccine is efficacious and cost effective compared with currently available options. Another important question to consider is how to apply this developing technology in a wide range of different situations, from the domestic pet to individual fish in fisheries with several thousand animals, to wildlife programs for disease control. In some cases, DNA vaccines represent an interesting option for vaccination, while in others, currently available options are sufficient. This review will examine a number of diseases of veterinary importance and the progress being made in DNA vaccine technology relevant to these diseases, and we compare these with the conventional treatment options available.

DNA vaccines targeting tumor antigens to B7 molecules on antigen-presenting cells induce protective antitumor immunity and delay onset of HER-2/Neu-driven mammary carcinoma

PURPOSE

Presentation of tumor antigens by professional antigen-presenting cells (APC) is critical for the induction of tumor-specific T-cell responses. To facilitate targeted delivery of tumor antigens to APC, we generated DNA vaccines that encode secreted fusion proteins consisting of the extracellular domain of CTLA-4 for binding to costimulatory B7 molecules on APC, fused to residues 1 to 222 of human ErbB2 (HER-2) or a corresponding 224 residues fragment of its rat homologue Neu.

EXPERIMENTAL DESIGN

Induction of humoral and cellular immune responses and antitumoral activity of the DNA vaccines were tested in murine tumor models with transfected renal carcinoma cells expressing the respective antigens and in transgenic BALB-neuT mice developing spontaneous Neu-driven mammary carcinomas.

RESULTS

Vaccination of BALB/c mice with CTLA-4-ErbB2(222) plasmid DNA markedly improved tumor-free survival on challenge with ErbB2-expressing Renca cells in comparison with untargeted ErbB2(222), accompanied by induction of stronger ErbB2-specific antibody and CTL responses. Likewise, a CTLA-4 vaccine carrying the unrelated NY-ESO-1 cancer-germline antigen was more effective than untargeted NY-ESO-1 in the protection of mice from challenge with NY-ESO-1-expressing tumor cells. Importantly, antitumoral activity of such a CTLA-4 fusion vaccine could be reproduced in immunotolerant BALB-neuT mice, where a corresponding CTLA-4-Neu(224) DNA vaccine markedly delayed the onset of spontaneous Neu-driven mammary carcinomas.

CONCLUSIONS

Our results show that plasmid DNA vaccines for in vivo expression of tumor antigens targeted to APC induce potent immune responses and antitumoral activities, providing a rationale for further development of this approach for specific cancer immunotherapy.

Vaccination of fiber-modified adenovirus-transfected dendritic cells to express HER-2/neu stimulates efficient HER-2/neu-specific humoral and CTL responses and reduces breast carcinogenesis in transgenic mice

HER-2/neu transgene-modified dendritic cell (DC)-based vaccines are potent at eliciting HER-2/neu-specific antitumor immunity. In this study, we constructed a recombinant adenovirus (RGD)AdVneu with fiber gene modified by RGD insertion into the viral knob's H1 loop. We transfected DCs with (RGD)AdVneu, and assessed/compared HER-2/neu-specific humoral and cytotoxic T lymphocyte (CTL) responses and antitumor immunity derived from the original AdVneu-transfected DCs (DCneu1) and (RGD)AdVneu-transfected DCs (DCneu2). We demonstrated that DCneu2 displayed increased HER-2/neu expression by 8.3-fold compared to DCneu1. We also demonstrated that DCneu2 vaccination induced stronger HER-2/neu-specific humoral and CTL immune responses than DCneu1 vaccination. DCneu2 vaccination protected all the mice from HER-2/neu-expressing Tg1-1 tumor cell challenge in wild-type FVB/NJ mice, compared to a partial protection in DCneu1-immunized mice. In addition, DCneu2 vaccination also significantly delayed tumor growth than DCneu1 immunization (P<0.05) in Tg FVBneuN mice. Three immunizations of DCneu2 starting at the mouse age of 2 months also significantly delayed breast cancer development in Tg mice compared to DCneu2 vaccine (P<0.05). Importantly, DCneu2 vaccine reduced breast carcinogenesis by 9% in Tg mice with self HER-2/neu tolerance. Therefore, vaccination of fiber-modified adenovirus-transfected DCs to enhance expression of tumor antigens such as HER-2/neu is likely representative of a new direction in DC-based vaccine of breast cancer.

A combination of chemoimmunotherapies can efficiently break self-tolerance and induce antitumor immunity in a tolerogenic murine tumor model

Her-2/neu is a well-characterized tumor-associated antigen overexpressed in human carcinomas such as breast cancer. Because Her-2/neu is a self-antigen with poor immunogenicity due to immunologic tolerance, active immunotherapy targeting Her-2/neu should incorporate methods to overcome immunologic tolerance to self-proteins. In this study, we developed a tolerogenic tumor model in mice using mouse Her-2/neu as self-antigen and investigated whether genetic vaccination with DNA plasmid and/or adenoviral vector expressing the extracellular and transmembrane domain of syngeneic mouse Her-2/neu or xenogenic human Her-2/neu could induce mouse Her-2/neu-specific CTL responses. Interestingly, adenoviral vectors expressing xenogenic human Her-2/neu (AdhHM) proved capable of breaking immune tolerance and of thereby inducing self-reactive CTL and antibodies, but not to the degree required to induce therapeutic antitumor immunity. In attempting to generate therapeutic antitumor immunity against established tumors, we adopted several approaches. Treatment with agonistic anti-glucocorticoid-induced TNFR family-related receptor (GITR) antibody plus AdhHM immunization significantly increased self-reactive CTL responses, and alpha-galactosylceramide (alphaGalCer)-loaded dendritic cells (DC) transduced with AdhHM were shown to break self-tolerance in a tolerogenic murine tumor model. Furthermore, gemcitabine treatment together with either AdhHM plus agonistic anti-GITR antibody administration or alphaGalCer-loaded DC transduced with AdhHM showed potent therapeutic antitumor immunity and perfect protection against preexisting tumors. Gemcitabine treatment attenuated the tumor-suppressive environment by eliminating CD11b(+)/Gr-1(+) myeloid-derived suppressor cells. When combined with immunotherapies, gemcitabine offers a promising strategy for the Ag-specific treatment of human cancer.

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.

HER-2/neu-gene engineered dendritic cell vaccine stimulates stronger HER-2/neu-specific immune responses compared to DNA vaccination

HER-2/neu is a candidate for developing breast cancer-targeted immunotherapeutics. Although DNA-based and HER-2/neu transgene-modified dendritic cell (DC)-based vaccines are potent at eliciting HER-2/neu-specific antitumor immunity, there has been no side-by-side study comparing them directly. The present study utilizes an in vivo murine tumor model expressing HER-2/neu antigen to compare the efficacy between adenovirus (AdVneu)-transfected dendritic cells (DC(neu)) and plasmid DNA (pcDNAneu) vaccine. Our data showed that DC(neu) upregulated the expression of immunologically important molecules and inflammatory cytokines and partially converted regulatory T (Tr)-cell suppression through interleukin-6 (IL-6) secretion. Vaccination of DC(neu) induced stronger HER-2/neu-specific humoral and cellular immune responses than DNA vaccination, which downregulated HER-2/neu expression and lysed HER-2/neu-positive tumor cells in vitro, respectively. In two HER-2/neu-expressing tumor models, DC(neu) completely protected mice from tumor cell challenge compared to partial or no protection observed in DNA-immunized mice. In addition, DC(neu) significantly delayed breast cancer development in transgenic mice in comparison to DNA vaccine (P<0.05). Taken together, we have demonstrated that HER-2/neu-gene-modified DC vaccine is more potent than DNA vaccine in both protective and preventive animal tumor models. Therefore, DCs genetically engineered to express tumor antigens such as HER-2/neu represent a new direction in DC vaccine of breast cancer.

Evaluation of different plasmid DNA delivery systems for immunization against HER2/neu in a transgenic murine model of mammary carcinoma

Studies of DNA vaccination against HER2/neu showed the effectiveness of immunization protocols in models of transplantable or spontaneous tumors; scarce information, however, has been provided to identify the procedure of DNA administration that more effectively contributes to the activation of immune system against spontaneously arising HER2/neu-positive tumors. We compared the effectiveness of different procedures of DNA vaccine delivery (intradermic injection (ID), gene gun (GG) delivery and intramuscular injection (IM) alone or with electroporation) in a murine transgenic model of mammary carcinoma overexpressing HER2/neu. We highlighted the role of DNA delivery system in the success of DNA vaccination showing that, among the analysed methods, intramuscular injection of the vaccine, particularly when associated to electroporation, elicits a better protection against HER2/neu spontaneous tumor development inducing antibody and cell-mediated immune responsiveness against HER2/neu and a Th1 polarization of the immune response.

Early role of CD4+ Th1 cells and antibodies in HER-2 adenovirus vaccine protection against autochthonous mammary carcinomas

HER-2 is an oncogenic tumor-associated Ag that is overexpressed in several human tumors including breast and ovarian cancer. The efficacy and mechanism of a HER-2-expressing recombinant adenoviral vaccine to protect against tumorigenesis was examined using HER-2 transgenic (BALB-neuT) mice, which develop spontaneous breast tumors in all 10 mammary glands, and also using a transplantable mouse tumor model. Vaccination beginning at 6-8 wk of age (through 19 wk of age) prevented development of spontaneous mammary tumors even after 50 wk, whereas the animals in the control groups had tumors in all mammary glands by 25 wk. Such long-term protection after the last boost has not been achieved previously in this transgenic mouse in which the oncogene is continuously spawning tumorigenesis. Using beta(2)-microglobulin-knockout, IFN-gamma-knockout, and B cell-deficient mice, CD4(+) and CD8(+) cell depletion, and Ab transfer studies, we show that induction of anti-HER-2/neu Abs are both necessary and sufficient for protection, and the IgG2a isotype is most effective. In contrast, CD8(+) T cells are not necessary at all, and CD4(+) T cells are necessary for only 36-48 h after immunization to provide help for B cells but not as effector cells. Equal protection in immunized mice deficient in FcgammaRI/III excluded an FcR-mediated mechanism. Anti-HER-2 serum not only inhibited growth of mammary tumor cell lines expressing HER-2 in vitro but also protected mice from tumors in vivo, suggesting a direct action of Ab on the tumor cells. Such a vaccine may provide Ab-mediated protection against HER-2-expressing breast cancers in humans.

Imiquimod and S-27609 as adjuvants of DNA vaccination in a transgenic murine model of HER2/neu-positive mammary carcinoma

DNA vaccination against HER-2/neu is an effective way to induce an immune response able to oppose the spontaneous development of mammary tumours occurring in HER-2/neu transgenic mice. In this study, we have evaluated the potential of Imiquimod and the analogue S-27609 as adjuvants of DNA vaccination against HER-2/neu in transgenic mice. The association of a DNA vaccine encoding a portion of rat HER2/neu with either Imiquimod or S-27609 was found to delay the development of spontaneous mammary tumours and to reduce their incidence, in comparison with DNA vaccination alone. Almost 80 or 40% of tumour-free mice were found at the end of measurement time in mice vaccinated and supplemented with Imiquimod or S-27609, respectively. The antitumour preventive effect was associated with increased antibody and cell-mediated immune responsiveness against HER-2/neu. In mice vaccinated and supplemented with Imiquimod, a small but significant increase of rat p185neu-specific cytotoxicity and of IFN-gamma and IL-2-producing CD8T cells, together with a reduction of IL-4-producing CD4T cells, and a switch from an IgG1 towards a IgG2a phenotype of anti-p185neu antibodies, suggested a TH1 polarization of the immune response. The immunoregulatory efficacy of S-27609 was lower than that observed for Imiquimod. These data highlight the potential of Imiquimod, and, to a lower extent, of S-27609, as immunological adjuvants of therapeutic DNA vaccines.

Induction of antigen-specific immune responses against malignant brain tumors by intramuscular injection of sindbis DNA encoding gp100 and IL-18

We constructed pSin-SV40-HDV-SV40pA, an improved Sindbis DNA expression vector, and evaluated the potential of this vector system for brain tumor therapy. We investigated whether immunizing mice with xenogeneic DNA encoding human gp100 and mouse IL-18 would enhance the antitumor responses. To study the immune mechanisms involved in tumor regression, we examined tumor growth in B16-gp100-implanted brain tumor models using T-cell subset-depleted and IFN-gamma-neutralized mice. Hugp100/mIL-18 vaccination was also investigated for its antitumor effects against the wild-type murine B16 tumor, which expresses the murine gp100 molecule. Genetic immunization using plasmid pSin 9001 DNA codelivery of human gp100 and mouse IL-18 resulted in enhanced protective and therapeutic effects on the malignant brain tumors. The antitumor and protective effects were mediated by both CD4(+)/CD8(+) T cells and IFN-gamma. Vaccination with hugp100/mIL-18 conferred a significant survival merit to wild-type B16 tumor-harboring mice. Immunogene therapy with the improved Sindbis virus vector expressing xenogeneic gp100 and syngeneic IL-18 may be an excellent approach for developing a new treatment protocol. Thus, the Sindbis DNA system may represent a novel approach for the treatment of malignant brain 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.

Cancer immunoprevention

Immunoprevention is a fresh approach to cancer prevention based on the stimulation of the immune system before tumor onset. Immunoprevention was effective in various models of carcinogen-induced or autochthonous tumor progression. Vaccines made of cells or DNA plasmids combined with appropriate adjuvants completely blocked mammary carcinogenesis in HER-2/neu transgenic mice. At variance with cancer immunotherapy, the mediators of immunoprevention are antibodies and T-cell-derived cytokines, rather than cytotoxic T-cells. Immunopreventive approaches and chemoprevention with tamoxifen or cyclooxygenase-2 inhibitors can be combined advantageously. The success obtained in preclinical studies suggests that cancer immunoprevention should progress to clinical testing.

Inhibition of Mammary Carcinoma Development in HER-2/neu Transgenic Mice through Induction of Autoimmunity by Xenogeneic DNA Vaccination

Plasmid DNA vectors encoding the full-length (VR1012/HER-2-FL) or only the extracellular and transmembrane domains (VR1012/HER-2-ECD-TM) of human (h) HER-2/neu proto-oncogene were used to vaccinate HER-2/neu transgenic mice (N202) engineered to overexpress the rat (r) neu proto-oncogene product (r-p185neu). Both the full-length and the deleted vaccines were significantly (P = 0.0001 and P = 0.06, respectively) more active than the empty vector (VR1012/EV) in preventing and delaying HER-2/neu-driven mammary carcinogenesis. A low-level intratumoral infiltrate of dendritic cells, macrophages, CD8 T cells and polymorphonuclear granulocytes in association with low-level cytokine production was observed, which was not detected in tumors from control mice. Morphologic analyses showed that vaccination with VR1012/HER-2-FL or ECD-TM also efficiently hampered the development of terminal ductal lobular units (TDLU). Analyses of sera from vaccinated mice revealed high titers of antihuman HER-2/neu antibodies, which correlated with the delayed time of tumor onset (P = 0.002). These antibodies did not cross-react with r-p185neu. Nontransgenic mice treated with the vaccines produced autoreactive antibodies targeting mouse (m)-p185neu and showed impaired function of the lactating mammary gland and accelerated involution of the gland after weaning. Together, these data indicate that xenogeneic DNA immunization breaks tolerance against the endogenous m-p185neu, impairing the development of mammary TDLU in which m-p185neu expression is concentrated. The reduction in the number of TDLU decreases the number of glandular structures available for r-p185neu-dependent mammary carcinogenesis, resulting in a significant inhibition of mammary carcinoma development.

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.

DNA vaccination against tumors

DNA vaccines have been used to generate protective immunity against tumors in a variety of experimental models. The favorite target antigens have been those that are frequently expressed by human tumors, such as carcinoembryonic antigen (CEA), ErbB2/neu, and melanoma-associated antigens. DNA vaccines have the advantage of being simple to construct, produce and deliver. They can activate all arms of the immune system, and allow substantial flexibility in modifying the type of immune response generated through codelivery of cytokine genes. DNA vaccines can be applied by intramuscular, dermal/epidermal, oral, respiratory and other routes, and pose relatively few safety concerns. Compared to other nucleic acid vectors, they are usually devoid of viral or bacterial antigens and can be designed to deliver only the target tumor antigen(s). This is likely to be important when priming a response against weak tumor antigens. DNA vaccines have been more effective in rodents than in larger mammals or humans. However, a large number of methods that might be applied clinically have been shown to ameliorate these vaccines. This includes in vivo electroporation, and/or inclusion of various immunostimulatory molecules, xenoantigens (or their epitopes), antigen-cytokine fusion genes, agents that improve antigen uptake or presentation, and molecules that activate innate immunity mechanisms. In addition, CpG motifs carried by plasmids can overcome the negative effects of regulatory T cells. There have been few studies in humans, but recent clinical trials suggest that plasmid/virus, or plasmid/antigen-adjuvant, prime-boost strategies generate strong immune responses, and confirm the usefulness of plasmid-based vaccination.

Alphavirus replicon particles containing the gene for HER2/neu inhibit breast cancer growth and tumorigenesis

Introduction

Overexpression of the HER2/neu gene in breast cancer is associated with an increased incidence of metastatic disease and with a poor prognosis. Although passive immunotherapy with the humanized monoclonal antibody trastuzumab (Herceptin) has shown some effect, a vaccine capable of inducing T-cell and humoral immunity could be more effective.

Methods

Virus-like replicon particles (VRP) of Venezuelan equine encephalitis virus containing the gene for HER2/neu (VRP-neu) were tested by an active immunotherapeutic approach in tumor prevention models and in a metastasis prevention model.

Results

VRP-neu prevented or significantly inhibited the growth of HER2/neu-expressing murine breast cancer cells injected either into mammary tissue or intravenously. Vaccination with VRP-neu completely prevented tumor formation in and death of MMTV-c-neu transgenic mice, and resulted in high levels of neu-specific CD8⁺ T lymphocytes and serum IgG.

Conclusion

On the basis of these findings, clinical testing of this vaccine in patients with HER2/neu⁺ breast cancer is warranted.

Immunological Prevention of a Multigene Cancer Syndrome

Vaccines effectively prevent the onset of tumors in transgenic mice carrying activated oncogenes; however, human tumors are caused by combined alterations in oncogenes and oncosuppressor genes. We evaluated the impact of prophylactic vaccines in HER-2/neu transgenic, p53 wild-type/null mice that succumb to an aggressive cancer syndrome comprising mammary and salivary gland carcinomas and rhabdomyosarcoma. A vaccine made of allogeneic mammary carcinoma cells expressing HER-2/neu and interleukin 12 afforded long-term protection from tumor onset. Tumor prevention was mediated by T cell-derived cytokines, in particular gamma-interferon, and by anti-HER-2/neu antibodies. HER-2/neu expression was inhibited in target tissues of vaccinated mice, and somatic loss of the wild-type p53 allele did not occur. A highly effective vaccine against a single oncoprotein induced a powerful immune response that arrested multistep carcinogenesis in distinct target tissues.

Animal models of tumor immunity, immunotherapy and cancer vaccines

Reliable animal models are critical for evaluating immunotherapies and for defining tumor immunology paradigms. Tumor immunologists are moving away from traditional transplantation tumor systems because they do not adequately model human malignancies. Transgenic mouse models in which tumors arise spontaneously have been developed for most cancers. The models use one of three technologies: tissue-specific promoters to drive expression of SV40 large T antigen or tissue-specific oncogenes; deletion of tumor suppressor genes by gene targeting; or, conditional deletion of tumor suppressor genes or activation of oncogenes via Cre-lox technology. Knockin mice expressing human tumor antigens and gene-targeted mice with deletions for immunologically relevant molecules have been integral to advancing knowledge of the tumor-host relationship. Although animal models are becoming more sophisticated, additional improvements are needed so that more realistic models can be developed.

Immunoprevention of Mammary Carcinoma in HER-2/neu Transgenic Mice Is IFN-γ and B Cell Dependent

A vaccine combining IL-12 and allogeneic mammary carcinoma cells expressing p185(neu) completely prevents tumor onset in HER-2/neu transgenic BALB/c mice (NeuT mice). The immune protection elicited was independent from CTL activity. We now formally prove that tumor prevention is mainly based on the production of anti-p185(neu) Abs. In the present studies, NeuT mice were crossed with knockout mice lacking IFN-gamma production (IFN-gamma(-/-)) or with B cell-deficient mice (microMT). Vaccination did not protect NeuT-IFN-gamma(-/-) mice, thus confirming a central role of IFN-gamma. The block of Ab production in NeuT-microMT mice was incomplete. About one third of NeuT-microMT mice failed to produce Abs and displayed a rapid tumor onset. By contrast, those NeuT-microMT mice that responded to the vaccine with a robust production of anti-p185(neu) Ab displayed a markedly delayed tumor onset. In these NeuT-microMT mice, the vaccine induced a lower level of IgG2a and IgG3 and a higher level of IgG2b than in NeuT mice. Moreover, NeuT-microMT mice failed to produce anti-MHC class I Abs in response to allogeneic H-2(q) molecules present in the cell vaccine. These findings show that inhibition of HER-2/neu carcinogenesis depends on cytokines and specific Abs, and that a highly effective vaccine can rescue Ab production even in B cell-deficient mice.

Enhanced efficacy of DNA vaccination against Her-2/neu tumor antigen by genetic adjuvants

Certain types of malignant tumors overexpress Her-2/neu, a transmembrane glycoprotein of the class I receptor tyrosine kinase erbB family. To develop an effective Her-2/neu vaccine for selective immunotherapy of these malignancies, we prepared Her-2/neu DNA plasmid encoding the transmembrane and extracellular domain (pHM) and tested the ability of this construct to induce antitumor immunity in animal models. In addition, we investigated the effects of cytokine used as a genetic adjuvant. Modulation by factors that affect T-cell function or hematopoiesis, including interleukin-12, interleukin-15, interleukin-18, interleukin-23, Eta-1, Flt3L and GM-CSF, was studied in the forms of monocistronic and bicistronic plasmid. Our results demonstrated that vaccination of pHM could induce successful antitumor immunity against Her-2/neu-expressing murine tumor cells in BALB/c mice. We also showed that the antitumor activity of pHM was augmented by coadministration and coexpression of different cytokines. Despite the similar levels of gene expression, the antitumor effects of bicistronic plasmids coexpressing Her-2/neu antigen and cytokine were improved in comparison with coadministration of separate monocistronic plasmid. In particular, coexpression of interleukin-18 or GM-CSF with Her-2/neu increased antitumor activity in both preventive and therapeutic experiments. These findings can help in the decision concerning which of the various cytokine adjuvants should be used for the development of a Her-2/neu DNA vaccine. In addition, our results from a large panel of cytokine adjuvants in the various tumor models may provide an insight into the important immune components of antitumor immunity.

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.

Human ErbB-2 (Her-2) transgenic mice: a model system for testing Her-2 based vaccines

Her-2 transgenic (Tg) mice were generated with wild-type human c-ErbB-2 (Her-2) under the whey acidic protein promoter. They are tolerant to Her-2 and appropriate for testing Her-2 vaccines. The expression of transmembrane ErbB-2 from the whey acidic protein-Her-2 cassette and its up-regulation by insulin and hydrocortisone was verified by in vitro transfection. The transgene cassette was microinjected into fertilized eggs from B6C3 (C3H x C57BL/6) females mated with B6C3 males. Transgene-positive mice were backcrossed onto C57BL/6 mice. Human ErbB-2 was expressed in the secretory mammary epithelia during pregnancy and lactation and expressed constitutively in the Bergman glia cells within the molecular layer of the cerebellum. Overt, neoplastic transformation was not detected in any tissue examined. Tolerance to Her-2 was demonstrated by inoculating mice with a syngenic tumor expressing high levels of human ErbB-2. Tumors grew exclusively in Her-2 Tg mice without inducing an Ab response, while the nontransgenic littermates remained tumor free for 10 mo and mounted a robust anti-ErbB-2 Ab response. When immunized five times with plasmid DNA encoding secErbB-2 and GM-CSF, respectively, approximately 33% of the Her-2 Tg mice rejected a lethal challenge of EL-4/E2 tumor cells, whereas all immunized littermates rejected the tumor. Therefore, Her-2 Tg mice express human ErbB-2 in the brain and mammary gland and demonstrated tolerance to ErbB-2 which was partially overcome by DNA vaccination. The breakable tolerance of Her-2 Tg mice resembles that in human and these mice are particularly suited for testing human ErbB-2 based vaccines.

Antitumor immunopreventive effect in mice induced by DNA vaccine encoding a fusion protein of α-fetoprotein and CTLA4

AIM: To develop a tumor DNA vaccine encoding a fusion protein of murine AFP and CTLA4, and to study its ability to induce specific CTL response and its protective effect against AFP-producing tumor.

METHODS: Murine α-fetoprotein (mAFP) gene was cloned from total RNA of Hepa1-6 cells by RT-PCR. A DNA vaccine was constructed by fusion murine α-fetoprotein gene and extramembrane domain of murine CTLA4 gene. The DNA vaccine was identified by restriction enzyme analysis, sequencing and expression. EL-4 (mAFP) was developed by stable transfection of EL-4 cells with pmAFP. The frequency of cells producing IFN-γ in splenocytes harvested from the immunized mice was measured by ELISPOT. Mice immunized with DNA vaccine were inoculated with EL-4 (mAFP) cells in back to observe the protective effect of immunization on tumor. On the other hand, blood samples were collected from the immunized mice to check the functions of liver and kidney.

RESULTS: 1.8 kb mAFP cDNA was cloned from total RNA of Hepa1-6 cells by RT-PCR. The DNA vaccine encoding a fusion protein of mAFP-CTLA4 was constructed and confirmed by restriction enzyme analysis, sequencing and expression. The expression of mAFP mRNA in EL-4 (mAFP) was confirmed by RT-PCR. The ELISPOT results showed that the number of IFN-γ-producing cells in pmAFP-CTLA4 group was significantly higher than that in pmAFP, pcDNA3.1 and PBS group. The tumor volume in pmAFP-CTLA4 group was significantly smaller than that in pmAFP, pcDNA3.1 and PBS group, respectively. The hepatic and kidney functions in each group were not altered.

CONCLUSION: AFP-CTLA4 DNA vaccine can stimulate potent specific CTL responses and has distinctive antitumor effect on AFP-producing tumor. The vaccine has no impact on the function of mouse liver and kidney.

HSP110-HER2/neu chaperone complex vaccine induces protective immunity against spontaneous mammary tumors in HER-2/neu transgenic mice

Heat shock proteins (HSPs) are shown to be strong immunoadjuvants, eliciting both innate and adaptive immune responses against cancers. HSP110 is related in sequence to HSP70 and is approximately 4-fold more efficient in binding to and stabilizing denatured protein substrates compared with HSP70. In the present study we evaluated the ability of a heat shock complex of HSP110 with the intracellular domain (ICD) of human HER-2/neu to elicit effective antitumor immune responses and to inhibit spontaneous mammary tumors in FVB-neu (FVBN202) transgenic mice. The HSP110-ICD complex was capable of breaking tolerance against the rat neu protein and inhibiting spontaneous mammary tumor development. This vaccine induced ICD-specific IFN-gamma and IL-4 production. Depletion studies revealed that CD8(+) T cells were involved in protection against challenge with mouse mammary tumors, whereas CD4(+) T cells revealed partial protection. Increased IgG2a Ab titer in the sera of tumor-free animals after vaccination and elevated CD4(+) CD25(+) regulatory T cells in the PBL of tumor-bearing animals suggested that IFN-gamma-producing Th1 cells may be responsible for partial protection of CD4(+) T cells against the mammary tumor challenge, whereas CD4(+)CD25(+) regulatory T cells (Th2 cells) may suppress the antitumor immune responses. Together, these results suggest that HSP110-ICD complex can elicit effective IFN-gamma-producing T cells against spontaneous mammary tumors and that up-regulation of CD4(+) CD25(+) regulatory T cells may prevent complete eradication of the tumor following immunotherapy.

Venezuelan Equine Encephalitis Replicon Immunization Overcomes Intrinsic Tolerance and Elicits Effective Anti-tumor Immunity to the ‘Self’ tumor-associated antigen, neu in a Rat Mammary Tumor Model

Many tumor-associated antigens (TAAs) represent 'self' antigens and as such, are subject to the constraints of immunologic tolerance. There are significant barriers to eliciting anti-tumor immune responses of sufficient magnitude. We have taken advantage of a Venezuelan equine encephalitis-derived alphavirus replicon vector system with documented in vivo tropism for immune system dendritic cells. We have overcome the intrinsic tolerance to the 'self' TAA rat neu and elicited an effective anti-tumor immune response using this alphavirus replicon vector system and a designed target antigen in a rigorous rat mammary tumor model. We have demonstrated the capacity to generate 50% protection in tumor challenge experiments (p = 0.004) and we have confirmed the establishment of immunologic memory by both second tumor challenge and Winn Assay (p = 0.009). Minor antibody responses were identified and supported the establishment of T helper type 1 (Th1) anti-tumor immune responses by isotype. Animals surviving in excess of 300 days with established effective anti-tumor immunity showed no signs of autoimmune phenomena. Together these experiments support the establishment of T lymphocyte dependent, Th1-biased anti-tumor immune responses to a non-mutated 'self' TAA in an aggressive tumor model. Importantly, this tumor model is subject to the constraints of immunologic tolerance present in animals with normal developmental, temporal, and anatomical expression of a non-mutated TAA. These data support the continued development and potential clinical application of this alphaviral replicon vector system and the use of appropriately designed target antigen sequences for anti-tumor immunotherapy.

Biologic and therapeutic role of HER2 in cancer

Overexpression of the human epidermal growth factor-2 (HER2) oncogene in human breast carcinomas has been associated with a more aggressive course of disease. The reason for this association is still unclear, although it has been suggested to rest in increased proliferation, vessel formation, and/or invasiveness. Alternatively, prognosis may not be directly related to the presence of the oncoprotein on the cell membrane, but instead to the breast carcinoma subset identified by HER2 overexpression and characterized by a peculiar gene expression profile. HER2 has also been associated with sensitivity to anthracyclins and resistance to endocrine therapy, suggesting that tyrosine kinase receptor and hormone receptor pathways represent two major proliferation pathways exclusively active in breast carcinomas, one sensitive to chemotherapeutic drugs and the other to antiestrogens. HER2 currently represents one of the most appropriate targets for specific therapy. Indeed, trastuzumab, a monoclonal antibody directed against the extracellular domain of HER2, is therapeutically active in HER2-positive breast carcinomas. However, a consistent number of HER2-positive tumors is not responsive to HER2-driven therapy, indicating the need for a better understanding of the mechanism of action of this new biological drug in vivo. While preclinical studies suggest antibody-dependent cell cytotoxicity as the major mechanism, determination of NK activity at the time of treatment remains mandatory, especially in patients treated with immunosuppressive drugs. The efficacy of prophylactic vaccination has been fully demonstrated in preclinical models, whereas ongoing studies of active immunotherapy using a variety of vaccination regimens against HER2 in tumor-bearing mice and patients have met with only moderate success.

Cancer vaccines: between the idea and the reality

Whether vaccines are designed to prepare the immune system for the encounter with a pathogen or with cancer, certain common challenges need to be faced, such as what antigen and what adjuvant to use, what type of immune response to generate and how to make it long lasting. Cancer, additionally, presents several unique hurdles. Cancer vaccines must overcome immune suppression exerted by the tumour, by previous therapy or by the effects of advanced age of the patient. If used for cancer prevention, vaccines must elicit effective long-term memory without the potential of causing autoimmunity. This article addresses the common and the unique challenges to cancer vaccines and the progress that has been made in meeting them. Considering how refractory cancer has been to standard therapy, efforts to achieve immune control of this disease are well justified.

Prevention of HER-2/neu transgenic mammary carcinoma by tamoxifen plus interleukin 12

FVB-NeuN (N#202) female mice transgenic for the HER-2/neu protooncogene driven by the murine mammary tumor virus (MMTV) promoter develop mammary carcinomas with a progression from focal atypical hyperplasia to in situ carcinoma and to invasive carcinoma that closely resembles that of human neoplasia. Here we report that the combination of tamoxifen plus interleukin 12 (IL-12) results in a very effective prevention of mammary carcinogenesis, significantly higher than those obtained with either tamoxifen or IL-12 alone. At 1 year of age, 20% of control mice resulted tumor-free, whereas 80% of mice receiving the combined treatment were tumor-free. At 2 years of age, less than 5% of control mice were tumor-free, as opposed to 70% of mice treated with tamoxifen plus IL-12. The combined treatment inhibited mammary carcinogenesis mainly through a reduction in the number of mammary cells at risk of progression, a reduction in estrogen receptors (ERs) expression and a reduction in the angiogenic support to mammary development, likely due to cross-talk between tamoxifen and interferon-gamma (IFN-gamma) (the main downstream mediator elicited in vivo by IL-12). The addition of IL-12 to the tamoxifen treatment more than doubled mouse lifetime and did not exacerbate known side effects of tamoxifen.

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

Previously protein vaccines consisting of the extracellular domain of HER2/neu (ECD(HER2)) were shown to elicit an immune response that does not provide protection against transplantable tumors expressing HER2/neu. Here, we showed that when mice were vaccinated with a mixture of human ECD(HER2) and anti-human HER2/neu IL-12, IL-2 or GM-CSF fusion proteins, significant retardation of the growth of a syngeneic carcinoma expressing rat HER2/neu, and long-term survivors were observed. Immune sera inhibited the in vitro growth of SK-BR-3, a human breast cancer overexpressing HER2/neu. Transfer of immune sera into mice challenged with TUBO also led to partial inhibition of tumor growth. Splenocytes from mice vaccinated with ECD(HER2) plus IgG3-(GM-CSF) incubated with ECD(HER2) demonstrated significant proliferation and IFN-gamma secretion. Taken together these results suggest that vaccines including ECD(HER2) and Ab-cytokine fusion proteins may be used to elicit both humoral and cell-mediated responses against HER2/neu.

Cancer immunoprevention: tracking down persistent tumor antigens

The immune response can effectively hamper the progression of preclinical stages of tumor growth. Medicine in the postgenomic era offers an increasing possibility of detecting healthy individuals at risk of developing cancer who could benefit from tumor-preventive vaccines. The identification of novel tumor antigens that fulfill two conditions will be crucial for the development of cancer immunoprevention. First, an ideal antigen should have a crucial pathogenetic role in tumor growth to avoid the selection of antigen-loss variants. Second, the antigen should be recognizable by the immune system even in MHC-loss variants and should therefore be recognized both by antibodies and T cells. Identifying such antigens will also provide new targets for cancer immunotherapy.

Comparison of the antitumor efficacies of Her-2/neu DNA vaccines inducing contrasting IgG immunity but comparable CTL activity in mice

The relative importance of CTL and antibodies in rejecting Her-2/neu-expressing tumors was evaluated in preventive and therapeutic models by DNA vaccination. Four human Her-2/neu-expressing plasmids (pNeu(TM), pNeu(ECD), pNeu(TM-gDs), and pNeu(ECD-gDs)) were generated encoding either the transmembrane and extracellular domains or the extracellular domain. Interestingly, these plasmids demonstrated substantial difference in inducing Her-2/neu-specific serum IgG according to their signal sequence when injected in BALB/c mice. pNeu(TM) and pNeu(ECD) induced high serum IgG titers. pNeu(TM-gDs) and pNeu(ECD-gDs) induced low or very low serum IgG titers, respectively. As a result, mice vaccinated with not only pNeu(ECD) but also pNeu(ECD-gDs) exhibited complete eradication of a small number of tumor cells. Nevertheless, when the number of tumor cells was increased in a therapeutic model, only pNeu(ECD) exhibited statistically significant antitumor immunity. These studies demonstrate that strong CTL may be sufficient in tumor prevention, but the collaboration of CTL and antibody may be required in tumor therapy.

Pre-clinical applications of transgenic mouse mammary cancer models

Breast cancer is a leading cause of cancer morbidity and mortality. Given that the majority of human breast cancers appear to be due to non-genetic factors, identifying agents and mechanisms of prevention is key to lowering the incidence of cancer. Genetically engineered mouse models of mammary cancer have been important in elucidating molecular pathways and signaling events associated with the initiation, promotion, and the progression of cancer. Since several transgenic mammary models of human breast cancer progress through well-defined cancer stages, they are useful pre-clinical systems to test the efficacy of chemopreventive and chemotherapeutic agents. This review outlines several oncogenic pathways through which mammary cancer can be induced in transgenic models and describes several types of preventive and therapeutic agents that have been tested in transgenic models of mammary cancer. The effectiveness of farnesyl inhibitors, aromatase inhibitors, differentiating agents, polyamine inhibitors, anti-angiogenic inhibitors, and immunotherapeutic compounds including vaccines have been evaluated in reducing mammary cancer and tumor progression in transgenic models.

Prevention of spontaneous mammary adenocarcinoma in HER-2/neu transgenic mice by foreign DNA

Unmethylated CpG-oligodeoxynucleotides (CpG-ODNs) are recognized as a 'danger signal' and are potent immunostimulators. To test whether tumors might be prevented by maintaining the innate immune system on continuous alert, proto-neu transgenic female mice, which develop spontaneous mammary tumors, were systemically treated with CpG-ODNs at 10-day intervals. Tumor incidence and number of tumors/mouse were significantly lower in treated mice compared with the control group. Moreover, CpG-ODN systemic treatment significantly reduced lung metastases induced by intravenous inoculation of N202.1A cells derived from a spontaneous mammary carcinoma. Growth of established tumors was modestly inhibited after CpG-ODN systemic treatment but strongly on peritumoral application. Our data indicate that systemic repeated injection of CpG-ODN to maintain the innate immune system on continuous alert prevents the onset of genetically determined tumors and confers tumor protection when the tumor load is low.

HER2 peptide-specific CD8(+) T cells are proportionally detectable long after multiple DNA vaccinations

We prepared a plasmid encoding 147 amino acid residues from the N terminus of c-erbB-2/HER2/neu (HER2), which included both a cytotoxic T lymphocyte (CTL) epitope (HER2p63) and a helper epitope (HER2p1), using the mammalian expression vector pCAGGS-New (pCAGGS147HER2). In a parallel analysis with a Tetramer assay and CTL assay, good specificity and sensitivity of a quantitative enzyme-linked immunospot (ELISPOT) assay to detect functional HER2p63-specific CD8(+) T cells were demonstrated after intramuscular immunization of pCAGGS147HER2. In an ELISPOT assay for HER2p63, spots of IFN gamma-producing cells were first detected 10 days after the first immunization, and additional immunizations increased the number of spots. HER2p63-specific CD8(+) T cells were detected over a period of more than 10 months after the last immunization. In hosts receiving more than three immunizations, surprisingly high numbers of specific CD8(+) T cells were persistently detectable. HER2 protein-specific antibodies of IgG class with dominance of IgG2a remain detectable 6 months after single or multiple immunizations. The antibodies however, were not reactive with cell surface HER2 antigens. Total suppression of tumor growth was observed when syngeneic HER2(+) tumor cells (2 x 10(6)) were injected subcutaneously 14 days after a single immunization with pCAGGS147HER2. Furthermore, the number of pulmonary metastases decreased significantly when DNA vaccination was initiated on the day of, or 3 days after, intravenous injection (1 x 10(6) cells).

The potential of DNA vaccination against tumor-associated antigens for antitumor therapy

Conventional treatment approaches for malignant tumors are highly invasive and sometimes have only a palliative effect. Therefore, there is an increasing demand to develop novel, more efficient treatment options. Increased efforts have been made to apply immunomodulatory strategies in antitumor treatment. In recent years, immunizations with naked plasmid DNA encoding tumor-associated antigens have revealed a number of advantages. By DNA vaccination, antigen-specific cellular as well as humoral immune responses can be generated. The induction of specific immune responses directed against antigens expressed in tumor cells and displayed e.g., by MHC class I complexes can inhibit tumor growth and lead to tumor rejection. The improvement of vaccine efficacy has become a critical goal in the development of DNA vaccination as antitumor therapy. The use of different DNA delivery techniques and coadministration of adjuvants including cytokine genes may influence the pattern of specific immune responses induced. This brief review describes recent developments to optimize DNA vaccination against tumor-associated antigens. The prerequisite for a successful antitumor vaccination is breaking tolerance to tumor-associated antigens, which represent "self-antigens." Currently, immunization with xenogeneic DNA to induce immune responses against self-molecules is under intensive investigation. Tumor cells can develop immune escape mechanisms by generation of antigen loss variants, therefore, it may be necessary that DNA vaccines contain more than one tumor antigen. Polyimmunization with a mixture of tumor-associated antigen genes may have a synergistic effect in tumor treatment. The identification of tumor antigens that may serve as targets for DNA immunization has proceeded rapidly. Preclinical studies in animal models are promising that DNA immunization is a potent strategy for mediating antitumor effects in vivo. Thus, DNA vaccines may offer a novel treatment for tumor patients. DNA vaccines may also be useful in the prevention of tumors with genetic predisposition. By DNA vaccination preventing infections, the development of viral-induced tumors may be avoided.