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

Anti-PD-1 antibody therapy potently enhances the eradication of established tumors by gene-modified T cells

PURPOSE

To determine the antitumor efficacy and toxicity of a novel combination approach involving adoptive T-cell immunotherapy using chimeric antigen receptor (CAR) T cells with an immunomodulatory reagent for blocking immunosuppression.

EXPERIMENTAL DESIGN

We examined whether administration of a PD-1 blocking antibody could increase the therapeutic activity of CAR T cells against two different Her-2(+) tumors. The use of a self-antigen mouse model enabled investigation into the efficacy, mechanism, and toxicity of this combination approach.

RESULTS

In this study, we first showed a significant increase in the level of PD-1 expressed on transduced anti-Her-2 CD8(+) T cells following antigen-specific stimulation with PD-L1(+) tumor cells and that markers of activation and proliferation were increased in anti-Her-2 T cells in the presence of anti-PD-1 antibody. In adoptive transfer studies in Her-2 transgenic recipient mice, we showed a significant improvement in growth inhibition of two different Her-2(+) tumors treated with anti-Her-2 T cells in combination with anti-PD-1 antibody. The therapeutic effects observed correlated with increased function of anti-Her-2 T cells following PD-1 blockade. Strikingly, a significant decrease in the percentage of Gr1(+) CD11b(+) myeloid-derived suppressor cells (MDSC) was observed in the tumor microenvironment of mice treated with the combination therapy. Importantly, increased antitumor effects were not associated with any autoimmune pathology in normal tissue expressing Her-2 antigen.

CONCLUSION

This study shows that specifically blocking PD-1 immunosuppression can potently enhance CAR T-cell therapy that has significant implications for potentially improving therapeutic outcomes of this approach in patients with cancer.

IL-15 augments antitumoral activity of an ErbB2/HER2 cancer vaccine targeted to professional antigen-presenting cells

Targeted delivery of tumor-associated antigens to professional antigen-presenting cells (APC) is being explored as a strategy to enhance the antitumoral activity of cancer vaccines. Here, we generated a cell-based system for continuous in vivo production of a CTLA-4-ErbB2 fusion protein as a therapeutic vaccine. The chimeric CTLA-4-ErbB2 molecule contains the extracellular domain of CTLA-4 for specific targeting to costimulatory B7 molecules on the surface of APC, genetically fused to residues 1-222 of human ErbB2 (HER2) as an antigenic determinant. In wild-type BALB/c mice, inoculation of syngeneic epithelial cells continuously secreting the CTLA-4-ErbB2 fusion vaccine in the vicinity of subcutaneously growing ErbB2-expressing renal cell carcinomas resulted in the rejection of established tumors, accompanied by the induction of ErbB2-specific antibodies and cytotoxic T cells. In contrast, treatment with CTLA-4-ErbB2 vaccine-secreting producer cells alone was insufficient to induce tumor rejection in ErbB2-transgenic WAP-Her-2 F1 mice, which are characterized by pronounced immunological tolerance to the human self-antigen. When CTLA-4-ErbB2 producer cells were modified to additionally secrete interleukin (IL)-15, antigen-specific antitumoral activity of the vaccine in WAP-Her-2 F1 mice was restored, documented by an increase in survival, and marked inhibition of the growth of established ErbB2-expressing, but not antigen-negative tumors. Our results demonstrate that continuous in vivo expression of an APC-targeted ErbB2 fusion protein results in antigen-specific immune responses and antitumoral activity in tumor-bearing hosts, which is augmented by the pleiotropic cytokine IL-15. This provides a rationale for further development of this approach for specific cancer immunotherapy.

Modification of a Popular Syngeneic Murine Mammary Tumor Model for Immunotherapy Studies

To facilitate the evaluation of immunotherapeutic intervention against malignant diseases, it is desirable to have a syngeneic tumor model that closely resembles the growth pattern of human tumors. Murine 4T1 breast cancer model is known for its metastatic properties that mimic its human counterpart. However, a drawback of this model is the lack of an identified tumor antigen to function as a therapeutic target for immunologic intervention. We used the piggyBac transposon system to stably transduce a tumor antigen, the human epidermal growth factor receptor 2 gene (HER2), into this tumor cell. In vitro characterization shows that the newly established cells have a similar growth pattern as the parental line. In vivo evaluation shows that host immune response was generated against the HER2 tumor antigen, despite the high homology between HER2 and its murine counterpart (neu gene). When implanted into immune-deficient mice, the HER2-expressing 4T1 cells readily formed sizable tumors, indicating that these cells are useful for evaluating the therapeutic effect of adoptively transferred cytotoxic T cells that are specifically raised or modified to target the HER2 tumor antigen.

Effective antibody therapy induces host-protective antitumor immunity that is augmented by TLR4 agonist treatment

Toll-like receptors are potent activators of the innate immune system and generate signals leading to the initiation of the adaptive immune response that can be utilized for therapeutic purposes. We tested the hypothesis that combined treatment with a Toll-like receptor agonist and an antitumor monoclonal antibody is effective and induces host-protective antitumor immunity. C57BL/6 human mutated HER2 (hmHER2) transgenic mice that constitutively express kinase-deficient human HER2 under control of the CMV promoter were established. These mice demonstrate immunological tolerance to D5-HER2, a syngeneic human HER2-expressing melanoma cell line. This human HER2-tolerant model offers the potential to serve as a preclinical model to test both antibody therapy and the immunization potential of human HER2-targeted therapeutics. Here, we show that E6020, a Toll-like receptor-4 (TLR4) agonist effectively boosted the antitumor efficacy of the monoclonal antibody trastuzumab in immunodeficient C57BL/6 SCID mice as well as in C57BL/6 hmHER2 transgenic mice. E6020 and trastuzumab co-treatment resulted in significantly greater inhibition of tumor growth than was observed with either agent individually. Furthermore, mice treated with the combination of trastuzumab and the TLR4 agonist were protected against rechallenge with human HER2-transfected tumor cells in hmHER2 transgenic mouse strains. These findings suggest that combined treatment with trastuzumab and a TLR4 agonist not only promotes direct antitumor effects but also induces a host-protective human HER2-directed adaptive immune response, indicative of a memory response. These data provide an immunological rationale for testing TLR4 agonists in combination with antibody therapy in patients with cancer.

Chimeric DNA Vaccines against ErbB2+ Carcinomas: From Mice to Humans

DNA vaccination exploits a relatively simple and flexible technique to generate an immune response against microbial and tumor-associated antigens (TAAs). Its effectiveness is enhanced by the application of an electrical shock in the area of plasmid injection (electroporation). In our studies we exploited a sophisticated electroporation device approved for clinical use (Cliniporator, IGEA, Carpi, Italy). As the target antigen is an additional factor that dramatically modulates the efficacy of a vaccine, we selected ErbB2 receptor as a target since it is an ideal oncoantigen. It is overexpressed on the cell membrane by several carcinomas for which it plays an essential role in driving their progression. Most oncoantigens are self-tolerated molecules. To circumvent immune tolerance we generated two plasmids (RHuT and HuRT) coding for chimeric rat/human ErbB2 proteins. Their immunogenicity was compared in wild type mice naturally tolerant for mouse ErbB2, and in transgenic mice that are also tolerant for rat or human ErbB2. In several of these mice, RHuT and HuRT elicited a stronger anti-tumor response than plasmids coding for fully human or fully rat ErbB2. The ability of heterologous moiety to blunt immune tolerance could be exploited to elicit a significant immune response in patients. A clinical trial to delay the recurrence of ErbB2+ carcinomas of the oral cavity, oropharynx and hypopharynx is awaiting the approval of the Italian authorities.

Camouflage and sabotage: tumor escape from the immune system

The field of tumor immunology has made great progress in understanding tumor immune interactions. As a consequence a number of immuno-therapeutic approaches have been successfully introduced into the clinic and a large number of promising therapeutic strategies are investigated in ongoing clinical trials. Evaluation of anti-tumor immunity in such trials as well as in animal models has shown that tumor escape from immune recognition and tumor-mediated suppression of anti-tumor immunity can pose a significant obstacle to successful cancer therapy. Here, we review mechanisms of tumor immune escape and immune-subversion with a focus on the research interests in our laboratory: loss of MHC class I on tumor cells, increased oxidative stress, recruitment of myeloid-derived suppressor cells, and regulatory T cells.

The human splice variant Δ16HER2 induces rapid tumor onset in a reporter transgenic mouse

Several transgenic mice models solidly support the hypothesis that HER2 (ERBB2) overexpression or mutation promotes tumorigenesis. Recently, a HER2 splice variant lacking exon-16 (Δ16HER2) has been detected in human breast carcinomas. This alternative protein, a normal byproduct of HER2, has an increased transforming potency compared to wild-type (wt) HER2 receptors. To examine the ability of Δ16HER2 to transform mammary epithelium in vivo and to monitor Δ16HER2-driven tumorigenesis in live mice, we generated and characterized a mouse line that transgenically expresses both human Δ16HER2 and firefly luciferase under the transcriptional control of the MMTV promoter. All the transgenic females developed multifocal mammary tumors with a rapid onset and an average latency of 15.11 weeks. Immunohistochemical analysis revealed the concurrent expression of luciferase and the human Δ16HER2 oncogene only in the mammary gland and in strict correlation with tumor development. Transgenic Δ16HER2 expressed on the tumor cell plasma membrane from spontaneous mammary adenocarcinomas formed constitutively active homodimers able to activate the oncogenic signal transduction pathway mediated through Src kinase. These new transgenic animals demonstrate the ability of the human Δ16HER2 isoform to transform "per se" mammary epithelium in vivo. The high tumor incidence as well as the short latency strongly suggests that the Δ16HER2 splice variant represents the transforming form of the HER2 oncoprotein.

Genetic modification of natural killer cells for adoptive cellular immunotherapy

Immunotherapy of cancer is a rapidly developing field; one such development is the manipulation and use of natural killer (NK) cells. These cells with 'killer instincts' are an attractive cell to utilize, as they are directly reactive toward tumor and could potentially activate the endogenous adaptive immune system. Their employment in adoptive cell transfer treatments has yielded important results and discoveries, although effective antitumor responses are limited. To address these limitations, NK cells are the target of a new generation of immunotherapy involving gene transfer. The gene modification of immune cells is a relatively recent technique and some groups have targeted NK cells for gene modification to improve their antitumor efficacy. This review will investigate studies describing the gene modification of NK cells and their encouraging antitumor effects.

Enhancing the specificity of T-cell cultures for adoptive immunotherapy of cancer

Adoptive immunotherapy is a promising approach for the treatment of cancer; however, autoimmunity against normal tissue can be a serious complication of this therapy. We hypothesized that T-cell cultures responding maximally only when engaging two antigens would be more specific for tumor cells, and less active against normal cells, as long as the tumor expressed both antigens, while normal cells expressed only one of the antigens. A model system was developed consisting of cell lines expressing either folate binding protein or erbB-2, representing ‘normal’ tissue, and cells expressing both antigens representing tumor tissue. Human T-cell cultures were produced using two chimeric antigen receptor vectors (‘dual transduced’), or using a single chimeric antigen receptor vector (monospecific). Dual-transduced T cells responded less against ‘normal’ cells compared with tumor cells. This relatively simple procedure produced T-cell cultures that were as active against a tumor as the monospecific cultures used traditionally, but had lower activity against model normal cells.

Tumor ablation by gene-modified T cells in the absence of autoimmunity

Adoptive immunotherapy involving genetic modification of T cells with antigen-specific, chimeric, single-chain receptors is a promising approach for the treatment of cancer. To determine whether gene-modified T cells could induce antitumor effects without associated autoimmune pathology, we assessed the ability of T cells expressing an anti-Her-2 chimeric receptor to eradicate tumor in Her-2 transgenic mice that express human Her-2 as a self-antigen in brain and mammary tissues. In adoptive transfer studies, we demonstrated significant improvement in the survival of mice bearing Her-2(+) 24JK tumor following administration of anti-Her-2 T cells compared with control T cells. The incorporation of a lymphoablative step prior to adoptive transfer of anti-Her-2 T cells and administration of IL-2 were both found to further enhance survival. The reduction in tumor growth was also correlated with localization of transferred T cells at the tumor site. Furthermore, an antigen-specific recall response could be induced in long-term surviving mice following rechallenge with Her-2(+) tumor. Importantly, antitumor effects were not associated with any autoimmune pathology in normal tissue expressing Her-2 antigen. This study highlights the therapeutic potential of using gene-engineered T cells as a safe and effective treatment of cancer.

An adenoviral vaccine encoding full-length inactivated human Her2 exhibits potent immunogenicty and enhanced therapeutic efficacy without oncogenicity

PURPOSE

Overexpression of the breast cancer oncogene HER2 correlates with poor survival. Current HER2-directed therapies confer limited clinical benefits and most patients experience progressive disease. Because refractory tumors remain strongly HER2+, vaccine approaches targeting HER2 have therapeutic potential, but wild type (wt) HER2 cannot safely be delivered in immunogenic viral vectors because it is a potent oncogene. We designed and tested several HER2 vaccines devoid of oncogenic activity to develop a safe vaccine for clinical use.

EXPERIMENTAL DESIGN

We created recombinant adenoviral vectors expressing the extracellular domain of HER2 (Ad-HER2-ECD), ECD plus the transmembrane domain (Ad-HER2-ECD-TM), and full-length HER2 inactivated for kinase function (Ad-HER2-ki), and determined their immunogenicity and antitumor effect in wild type (WT) and HER2-tolerant mice. To assess their safety, we compared their effect on the cellular transcriptome, cell proliferation, anchorage-dependent growth, and transformation potential in vivo.

RESULTS

Ad-HER2-ki was the most immunogenic vector in WT animals, retained immunogenicity in HER2-transgenic tolerant animals, and showed strong therapeutic efficacy in treatment models. Despite being highly expressed, HER2-ki protein was not phosphorylated and did not produce an oncogenic gene signature in primary human cells. Moreover, in contrast to HER2-wt, cells overexpressing HER2-ki were less proliferative, displayed less anchorage-independent growth, and were not transformed in vivo.

CONCLUSIONS

Vaccination with mutationally inactivated, nononcogenic Ad-HER2-ki results in robust polyclonal immune responses to HER2 in tolerant models, which translates into strong and effective antitumor responses in vivo. Ad-HER2-ki is thus a safe and promising vaccine for evaluation in clinical trials.

Combining human and rat sequences in her-2 DNA vaccines blunts immune tolerance and drives antitumor immunity

Immune tolerance to tumor-associated self-antigens poses a major challenge in the ability to mount an effective cancer vaccine response. To overcome immune tolerance to HER-2, we formulated DNA vaccines that express both human HER-2 and heterologous rat Neu sequences in separate plasmids or as single hybrid constructs that encode HER-2/Neu fusion proteins. Candidate vaccines were tested in Her-2 transgenic (Tg) mice of BALB/c (BALB), BALB/cxC57BL/6 F1 (F1), or C57BL/6 (B6) background, which exhibit decreasing immune responsiveness to HER-2. Analysis of various cocktails or hybrid vaccines defined a requirement for particular combination of HER/2/Neu sequences to effectively prime immune effector cells in HER-2 Tg mice. In B6 HER-2 Tg mice, rejection of HER-2-positive tumors protected mice from HER-2-negative tumors, providing evidence of epitope spreading. Our findings show that a strategy of combining heterologous antigen with self-antigens could produce a potent DNA vaccine that may be applicable to other tumor-associated antigens.

HER-2/neu mediated down-regulation of MHC class I antigen processing prevents CTL-mediated tumor recognition upon DNA vaccination in HLA-A2 transgenic mice

To study DNA vaccination directed against human HER-2 in the HHD mouse Tg strain, we created a novel HER-2-expressing syngeneic tumor transplantation model. We found that a DNA vaccine encoding the full length HER-2 DNA protected HHD mice from HER-2(+) tumor challenge by a CTL independent mechanism. A more efficient approach to induce HLA-A2 restricted CTLs, through immunization with a multi-epitope DNA vaccine expressing the HLA-A2 restricted HER-2 369-377, 435-443 and 689-697 epitopes, resulted in high numbers of peptide specific T cells but failed to induce tumor protection. Subsequently we discovered that HER-2 transfected tumor cells down-regulated MHC class I antigen expression and exhibited a series of defects in the antigen processing pathway which impaired the capacity to produce and display MHC class I peptide-ligands to specific CTLs. Our data demonstrate that HER-2 transfection is associated with defects in the MHC class I presentation pathway, which may be the underlying mechanism behind the inability of CTLs to recognize tumors in this HLA-A2 transgenic model. As defective MHC class I presentation may be a common characteristic of HER-2 expressing tumors, vaccines targeting HER-2 should aim at inducing an integrated immune response where also CD4(+) T cells and antibodies are important components.

Genetic regulation of the response to Her-2 DNA vaccination in human Her-2 transgenic mice

Genetic regulation of immune reactivity to Her-2 vaccination and the consequent antitumor effect was tested in human Her-2 transgenic (Tg) mice of C57BL/6 (B6), BALB/c (BALB), and (B6x BALB) F1 (F1) background. Mice were electrovaccinated with Her-2 DNA with or without pretreatment with CD25 monoclonal antibody to remove CD25(hi) regulatory T cells. When CD25(+) T cells were intact, BALB Her-2 Tg mice were more responsive than the other two strains in both humoral and cellular immunities, and their tumor growth was significantly delayed. B6 Her-2 Tg mice responded poorly and F1 mice showed modest immune reactivity, but tumor growth did not change in either strain. Depletion of CD25(hi) T cells before vaccination significantly improved protection from tumor challenge in F1 Her-2 Tg mice. This was associated with elevated levels of Her-2 IgG1, IgG2a, and IgG2c antibodies, and some mice also showed IFN-gamma producing T-cell response. The same treatment induced modest improvement in B6 Her-2 Tg mice. In BALB Her-2 Tg mice, however, depletion of CD25(hi) T cells did not further improve antitumor efficacy. Although their Her-2-specific IgG1 and interleukin-5-secreting T cells increased, the levels of IgG2a and IFN-gamma-secreting T cells did not change. These results are the first to show genetic regulation of the response to a cancer vaccine and an unequal effect of removing CD25(hi) T cells on antitumor immunity. These results warrant individualized treatment plans for patients with heterogeneous genetic backgrounds and possibly differential intrinsic immune reactivity to tumor antigens.

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.

Her-2 DNA versus cell vaccine: immunogenicity and anti-tumor activity

Direct comparison and ranking of vaccine formulations in pre-clinical studies will expedite the identification of cancer vaccines for clinical trials. Two human ErbB-2 (Her-2) vaccines, naked DNA and whole cell vaccine, were tested side-by-side in wild type and Her-2 transgenic mice. Both vaccines can induce humoral and cellular immunity to the entire repertoire of Her-2 epitopes. Mice were electro-vaccinated i.m. with a mixture of pGM-CSF and pE2TM, the latter encodes Her-2 extracellular and transmembrane domains. Alternatively, mice were injected i.p. with human ovarian cancer SKOV3 cells that have amplified Her-2. In wild type mice, comparable levels of Her-2 antibodies (Ab) were induced by these two vaccines. However, T cell immunity and protection against Her-2(+) tumors were superior in DNA vaccinated mice. In BALB Her-2 transgenic (Tg) mice, which were tolerant to Her-2, DNA and cell vaccines were administered after regulatory T cells (Treg) were removed by anti-CD25 mAb. Again, comparable levels of Her-2 Ab were induced, but DNA vaccines rendered greater anti-tumor activity. In B6xDR3 Her-2 Tg mice that expressed the autoimmune prone HLA-DR3 allele, higher levels of Her-2 Ab were induced by SKOV3 cell than by Her-2 DNA. But anti-tumor activity was still more profound in DNA vaccinated mice. Therefore, Her-2 DNA vaccine induced greater anti-tumor immunity than cell vaccine, whether mice were tolerant to Her-2 or susceptible to autoimmunity. Through such side-by-side comparisons in appropriate pre-clinical test systems, the more effective vaccine formulations will emerge as candidates for clinical trials.

Adoptive transfer of gene-modified primary NK cells can specifically inhibit tumor progression in vivo

NK cells hold great potential for improving the immunotherapy of cancer. Nevertheless, tumor cells can effectively escape NK cell-mediated apoptosis through interaction of MHC molecules with NK cell inhibitory receptors. Thus, to harness NK cell effector function against tumors, we used Amaxa gene transfer technology to gene-modify primary mouse NK cells with a chimeric single-chain variable fragment (scFv) receptor specific for the human erbB2 tumor-associated Ag. The chimeric receptor was composed of the extracellular scFv anti-erbB2 Ab linked to the transmembrane and cytoplasmic CD28 and TCR-zeta signaling domains (scFv-CD28-zeta). In this study we demonstrated that mouse NK cells gene-modified with this chimera could specifically mediate enhanced killing of an erbB2(+) MHC class I(+) lymphoma in a perforin-dependent manner. Expression of the chimera did not interfere with NK cell-mediated cytotoxicity mediated by endogenous NK receptors. Furthermore, adoptive transfer of gene-modified NK cells significantly enhanced the survival of RAG mice bearing established i.p. RMA-erbB2(+) lymphoma. In summary, these data suggest that use of genetically modified NK cells could broaden the scope of cancer immunotherapy for patients.

ErbB2 transgenic mice: a tool for investigation of the immune prevention and treatment of mammary carcinomas

The epidermal growth factor receptor belongs to a superfamily of receptor tyrosine kinases (RTK) that includes ErbB2. ErbB2 is involved in normal physiological processes, such as embryogenesis, cell proliferation, differentiation, adhesion motility, and apoptosis, while its malfunction or overexpression is responsible for development defects, diabetes, and cancer. The human ortholog of ErbB2 is referred as Her-2 (human ErbB2) while the rat ortholog is referred as neu (rat ErbB2). As ErbB2 is directly involved in carcinogenesis, mice transgenic for the rat neu oncogene allow straightforward assessment of the ability of drugs and vaccines to inhibit the progression of neu-driven cancer. Information from this model may provide indications on the efficacy of similar treatments in patients. This commentary provides key information regarding the use of these transgenic mouse models for evaluation of the efficacy of anti-tumor strategies.

The "A, B and C" of Her-2 DNA vaccine development

INTRODUCTION

The development of Her-2 DNA vaccine has progressed through three phases that can be categorized as phase "A": the pursuit of Her-2 as a tumor-associated "antigen", phase "B": tilting the "balance" between tumor immunity and autoimmunity and phase "C": the on-going "clinical trials".

MATERIALS AND METHODS

In phase "A", a panel of human ErbB-2 or Her-2 plasmids were constructed to encode non-transforming Her-2 derivatives. The immunogenicity and anti-tumor activity of Her-2 DNA vaccines were tested in human Her-2 transgenic mice with or without the depletion of regulatory T cells (Tregs). However, Treg depletion or other immune modulating regimens may increase the risk of autoimmunity. In phase "B", the balance between tumor immunity and autoimmunity was assessed by monitoring the development of experimental autoimmune thyroiditis (EAT). To test the efficacy of Her-2 DNA vaccines in cancer patients, clinical trials have been initiated in phase "C".

RESULTS AND CONCLUSIONS

Significant anti-Her-2 and anti-tumor activity was observed when Her-2 transgenic mice were electro-vaccinated after Treg depletion. Susceptibility to EAT was also enhanced by Treg depletion and there was mutual amplification between Her-2 immunity and EAT development. Although Tregs regulate both EAT and Her-2 immunity, their effector mechanisms may differ. It may be possible to amplify tumor immunity with improved strategies that can by-pass undue autoimmunity. Critical information will be revealed in the next decade to expedite the development of cancer vaccines.

Carcinoembryonic antigen transgenic mouse models for immunotherapy and development of cancer vaccines

The goal of cancer therapy remains as the long-term eradication of tumor cells without adverse effects on normal tissue. Conventional approaches utilizing chemotherapy and radiotherapy are limited by both their toxicity and lack of specificity. In recent years, investigators have carried out several studies designed to evaluate whether human tumor-associated antigens (TAAs) can be exploited as targets for immunotherapy, specifically for human cancer vaccine development. A major limitation in immunotherapy studies of human cancer is the general lack of appropriate preclinical models. Clinical studies can be difficult to implement, particularly when a clear understanding of the potential efficacy, limitation, and safety of an immunotherapeutic strategy is not available from relevant animal investigations. However, mice carrying a transgene for a human tumor self-antigen may provide a more acceptable experimental model in which knowledge about immunotherapeutic strategies aiming at the TAA of interest can be enhanced prior to initiating clinical trials. Since the different strategies in experimental immunotherapy of cancer have been directed to activate different immune system components, a variety of transgenic mouse models have been generated expressing either TAA, human leukocyte antigen (HLA), oncogene, or immune effector cell molecules. These models may serve as an excellent platform for the identification of novel targets for immunotherapy as well as to evaluate the efficacy of targeted therapies and will lead to the development of clinical trials for cancer patients. In this unit, a brief overview of the generation and study of different vaccine approaches in carcinoembryonic antigen (CEA) transgenic mouse models and the experimental findings in mouse models that spontaneously develop gastrointestinal tumors and express the CEA transgene is provided.

Sustained antigen-specific antitumor recall response mediated by gene-modified CD4+ T helper-1 and CD8+ T cells

Given that specific subsets of T helper 1 (Th1) and T helper 2 (Th2) CD4(+) T cells have been shown to play key roles in tumor rejection models, we wanted to assess the contribution of either Th1 or Th2 CD4(+) cell subtypes for redirected T-cell immunotherapy. In this study, we have developed a novel method involving retroviral transduction and in vitro T-cell polarization to generate gene-engineered mouse CD4(+) Th1 and Th2 cells or T helper intermediate (Thi) cells expressing an anti-erbB2-CD28-zeta chimeric receptor. Gene-modified Th1 and Th2 polarized CD4(+) cells were characterized by the preferential secretion of IFN-gamma and interleukin-4, respectively, whereas Thi cells secreted both cytokines following receptor ligation. In adoptive transfer studies using an erbB2(+) lung metastasis model, complete survival of mice was observed when transduced Th1, Th2, or Thi CD4(+) cells were transferred in combination with an equivalent number of transduced CD8(+) T cells. Tumor rejection was consistently associated with transduced T cells at the tumor site and interleukin-2 secretion. However, the surviving mice treated with gene-modified Th1 CD4(+) cells were significantly more resistant to a subsequent challenge with a different erbB2(+) tumor (4T1.2) implanted s.c. This result correlated with both increased expansion of Th1 CD4(+) and CD8(+) T cells in the blood and a greater number of these cells localizing to the tumor site following rechallenge. These data support the use of gene-modified CD4(+) Th1 and CD8(+) T cells for mediating a sustained antitumor response.

T cell precursor frequency differentially affects CTL responses under different immune conditions

Generation of effective CTL responses is the goal of many vaccination protocols. However, to what extant T cell precursor frequencies will generate a CD8(+) CTL response has not been elucidated properly. In this study, we employed a model system, in which naive CD4(+) and CD8(+) T cells derived from ovalbumin (OVA)-specific TCR transgenic OT II and OT I mice were used for adoptive transfer into wild-type, Ia(b-/-) gene knockout and transgenic RIP-mOVA mice, and assessed OVA-pulsed DC (DC(OVA))-stimulated CD8(+) CTL responses in these mice. We demonstrated that (i) a critical threshold exists above which T cells precursor frequency cannot enhance the CTL responses in wild-type C57BL/6 mice, (ii) increasing CD8(+) T cell precursors is required to generate CTL responses but with functional memory defect in absence of CD4(+) T cell help, and (iii) increasing CD4(+) and CD8(+) T cell precursors overcomes immune suppression to DC(OVA)-stimulated CD8(+) CTL responses in transgenic RIP-mOVA mice with OVA-specific self immune tolerance. Taken together, these findings may have important implications for optimizing immunotherapy against cancer.

Control of Her-2 tumor immunity and thyroid autoimmunity by MHC and regulatory T cells

Immune reactivity to self-antigens in both cancer and autoimmune diseases can be enhanced by systemic immune modulation, posing a challenge in cancer immunotherapy. To distinguish the genetic and immune regulation of tumor immunity versus autoimmunity, immune responses to human ErbB-2 (Her-2) and mouse thyroglobulin (mTg) were tested in transgenic mice expressing Her-2 that is overexpressed in several cancers, and HLA-DRB1*0301 (DR3) that is associated with susceptibility to several human autoimmune diseases, as well as experimental autoimmune thyroiditis (EAT). To induce Her-2 response, mice were electrovaccinated with pE2TM and pGM-CSF encoding the extracellular and transmembrane domains of Her-2 and the murine granulocyte macrophage colony-stimulating factor, respectively. To induce EAT, mice received mTg i.v. with or without lipopolysaccharide. Depletion of regulatory T cells (Treg) with anti-CD25 monoclonal antibody enhanced immune reactivity to Her-2 as well as mTg, showing control of both Her-2 and mTg responses by Treg. When immunized with, Her-2xDR3 and B6xDR3 mice expressing H2(b)xDR3 haplotype developed more profound mTg response and thyroid pathology than Her-2 or B6 mice that expressed the EAT-resistant H2(b) haplotype. In Her-2xDR3 mice, the response to mTg was further amplified when mice were also immunized with pE2TM and pGM-CSF. On the contrary, Her-2 reactivity was comparable whether mice expressed DR3 or not. Therefore, induction of Her-2 immunity was independent of DR3 but development of EAT was dictated by this allele, whereas Tregs control the responses to both self-antigens. These results warrant close monitoring of autoimmunity during cancer immunotherapy, particularly in patients with susceptible MHC class II alleles.

Insights from transgenic mouse models of ERBB2-induced breast cancer

One-third of patients with breast cancer overexpress the ERBB2 receptor tyrosine kinase, which is associated not only with a more aggressive phenotype but also reduced responsiveness to hormonal therapies. Over the past two decades, many ERBB2 mouse models for breast cancer have conclusively shown that this receptor has a causal role in breast cancer development. These mouse models have also enabled the mechanisms controlling tumour growth, angiogenesis, metastasis, dormancy and recurrence in ERBB2-positive breast cancer to be elucidated. In addition, a mouse model has recently been described that accurately recapitulates many of the hallmarks associated with the early stages of the human disease.

Viral envelope protein gp64 transgenic mouse facilitates the generation of monoclonal antibodies against exogenous membrane proteins displayed on baculovirus

We have been investigating the functional display of multipass membrane protein such as transporter or G-protein coupled receptor on the budded baculovirus (BV). We tested the use of a viral envelope protein gp64 transgenic mouse for the direct immunization of these membrane proteins displayed on BVs. The gp64 transgenic mice showed only a weak response to virus compared to wild type BALB/c mice. Immunizing gp64 transgenic mice with the BV expressing peptide transporter PepT1, we obtained 47 monoclonal antibodies (mAbs). These mAbs were specific to the PepT1 on the pancreatic cancer cells AsPC-1 by fluorocytometric analysis and exhibited antibody-dependent cellular cytotoxicity or complement-dependent cytotoxicity to AsPC-1. We also generated 7 mAbs by immunizing gp64 transgenic mice on a CCR2-deficient background with the BV expressing chemokine receptor CCR2 together with partially purified CCR2. These mAbs possessed specific binding to CCR2 in CHO cells on fluorocytometric analysis, and exhibited neutralizing activities for ligand-dependent inhibition of cyclic AMP production. This method provides a powerful tool for the generation of therapeutic/diagnostic mAbs against membrane proteins.

Targeting HER-2/neu in Early Breast Cancer Development Using Dendritic Cells with Staged Interleukin-12 Burst Secretion

Overexpression of HER-2/neu (c-erbB2) is associated with increased risk of recurrent disease in ductal carcinoma in situ (DCIS) and a poorer prognosis in node-positive breast cancer. We therefore examined the early immunotherapeutic targeting of HER-2/neu in DCIS. Before surgical resection, HER-2/neu(pos) DCIS patients (n = 13) received 4 weekly vaccinations of dendritic cells pulsed with HER-2/neu HLA class I and II peptides. The vaccine dendritic cells were activated in vitro with IFN-gamma and bacterial lipopolysaccharide to become highly polarized DC1-type dendritic cells that secrete high levels of interleukin-12p70 (IL-12p70). Intranodal delivery of dendritic cells supplied both antigenic stimulation and a synchronized preconditioned burst of IL-12p70 production directly to the anatomic site of T-cell sensitization. Before vaccination, many subjects possessed HER-2/neu-HLA-A2 tetramer-staining CD8(pos) T cells that expressed low levels of CD28 and high levels of the inhibitory B7 ligand CTLA-4, but this ratio inverted after vaccination. The vaccinated subjects also showed high rates of peptide-specific sensitization for both IFN-gamma-secreting CD4(pos) (85%) and CD8(pos) (80%) T cells, with recognition of antigenically relevant breast cancer lines, accumulation of T and B lymphocytes in the breast, and induction of complement-dependent, tumor-lytic antibodies. Seven of 11 evaluable patients also showed markedly decreased HER-2/neu expression in surgical tumor specimens, often with measurable decreases in residual DCIS, suggesting an active process of "immunoediting" for HER-2/neu-expressing tumor cells following vaccination. DC1 vaccination strategies may therefore have potential for both the prevention and the treatment of early breast cancer.

Individual mouse analysis of the cellular immune response to tumor antigens in peripheral blood by intracellular staining for cytokines

Among the experimental animal models, mice remain the most widely used for the evaluation of immunotherapeutic strategies. Vaccines against parasites and viral antigens are commonly administered to the appropriate mouse strain which also allows testing of the therapeutic effect. Similarly, in mice transgenic for human tumor associated antigens (TAA), cancer vaccines must lead to breakage of immune tolerance to elicit a significant effect on the tumor. However, one of the major drawbacks in the monitoring of cellular immune responses induced by vaccination is that functional immunological assays require suppression of the animals to collect the spleen or lymph nodes for analysis. Here, we report the application of a rapid intracellular staining (ICS) method to quantify antigen-specific T cells responses in small volumes of murine blood. Genetic vaccination with plasmid DNA followed by electroporation (DNA-EP) and the use of adenoviral vectors (Ad) encoding CEA as a model target antigen were applied to different strains of mice. Optimal blood volume, number of lymphocytes, sensitivity and reproducibility of intracellular staining for IFN-gamma were determined both in non-tolerant/wild type mice as well as in tolerant CEA transgenic mice upon restimulation of PBMCs with CEA peptides. Groups of vaccinated mice were then sacrificed and PBMCs and splenocytes from individual animals were compared for intracytoplasmic detection of IFN-gamma and TNF-alpha. A significant correlation was observed between splenic and blood immune responses. Finally, the cellular immune response was followed over time in groups of vaccinated mice. The kinetics of IFN-gamma producing effectors were measured after priming and successive boosting with adenoviral vectors. We show that intracellular staining for mouse PBMCs is a rapid and simple method to measure antigen-specific immune responses. It does not require animal euthanasia and mirrors the response observed in lymphoid organs such as the spleen.

Activity of DNA vaccines encoding self or heterologous Her-2/neu in Her-2 or neu transgenic mice

To assess the efficacy of self versus heterologous ErbB-2 vaccines, the reactivity to human and rat ErbB-2 (Her-2 and neu, respectively) DNA vaccines were tested in normal, Her-2 or neu transgenic mice. When immunized with either Her-2 or neu DNA, normal BALB/c and C57BL/6 mice produced cross-reactive T cells, but only antigen specific antibodies. In Her-2 Tg mice, weak to no anti-Her-2 response was induced by either self Her-2 or heterologous neu DNA, demonstrating profound tolerance to Her-2 and the inability to induce anti-Her-2 immunity with either vaccine. In NeuT mice, vaccination with self neu but not heterologous Her-2 DNA induced anti-neu antibodies and delayed spontaneous tumorigenesis. Both neu and Her-2 DNA induced anti-neu T cell response, but depletion of CD8 T cells did not change the delay in tumorigenesis. Therefore, in NeuT mice, both self and heterologous DNA activated anti-neu T cells, although T cell response did not reach sufficient level to suppress spontaneous tumorigenesis. Rather, induction of anti-neu antibodies by self neu DNA is associated with the delay in spontaneous tumor growth. Overall, NeuT mice were more responsive to DNA vaccination than Her-2 Tg mice and this may be associated with the continuous production of neu by the 10 mammary glands undergoing tumor progression.

The ubiquitin-proteasome system plays essential roles in presenting an 8-mer CTL epitope expressed in APC to corresponding CD8+ T cells

MUT1 is an H-2Kb-restricted 8-mer CTL epitope expressed in Lewis lung carcinoma (3LL) tumor cells derived from C57BL/6 (B6) mice. We constructed a chimeric gene encoding ubiquitin-fused MUT1 (pUB-MUT1). By using a gene gun, B6 mice were immunized with the gene prior to challenge with 3LL tumor cells. Tumor growth and lung metastasis were prominently suppressed in mice immunized with pUB-MUT1 but only slightly in those immunized with the MUT1 gene (pMUT) alone. CD8+ T cells were confirmed to be the final effector by in vitro experiments and in vivo removal of the cells with a corresponding antibody. Anti-tumor immunity was profoundly suppressed in mice deficient in an immuno-subunit of proteasome, LMP7. Furthermore, mice deficient in a proteasome regulator, PA28alpha/beta, failed to acquire protective immunity. Thus, application of the ubiquitin-fusion degradation pathway was useful even in immunization with genes encoding a single CTL epitope for induction of specific and active CD8+ T cells.

Adenovirus as vehicle for anticancer genetic immunotherapy

Adenoviruses (Ads) are in the forefront of genetic immunization methods being developed against cancer. Their ability to elicit an effective immune response against tumor-associated antigens has been demonstrated in many model systems. Several clinical trials, which use Ad as vehicle for immunization, are already in progress. Preclinical studies have also demonstrated the efficacy of combining Ad-mediated immunization with adjuvants such as chemotherapeutic agents and cytokines. Issues related to sero-prevalence and safety of Ads, however, continue to pose a challenge and need to be addressed.

Concurrent induction of antitumor immunity and autoimmune thyroiditis in CD4+ CD25+ regulatory T cell-depleted mice

When CD4+ CD25+ regulatory T cells are depleted or inactivated for the purpose of enhancing antitumor immunity, the risk of autoimmune disease may be significantly elevated because these regulatory T cells control both antitumor immunity and autoimmunity. To evaluate the relative benefit and risk of modulating CD4+ CD25+ regulatory T cells, we established a new test system to measure simultaneously the immune reactivity to a tumor-associated antigen, neu, and an unrelated self-antigen, thyroglobulin. BALB/c mice were inoculated with TUBO cells expressing an activated rat neu and treated with anti-CD25 monoclonal antibody to deplete CD25+ cells. The tumors grew, then regressed, and neu-specific antibodies and IFN-gamma-secreting T cells were induced. The same mice were also exposed to mouse thyroglobulin by chronic i.v. injections. These mice produced thyroglobulin-specific antibody and IFN-gamma-secreting T cells with inflammatory infiltration in the thyroids of some mice. The immune responses to neu or thyroglobulin were greater in mice undergoing TUBO tumor rejection and thyroglobulin injection than in those experiencing either alone. To the best of our knowledge, this is the first experimental system to assess the concurrent induction and possible synergy of immune reactivity to defined tumor and self-antigens following reduction of regulatory T cells. These results illustrate the importance of monitoring immune reactivity to self-antigens during cancer immunotherapy that involves immunomodulating agents, and the pressing need for novel strategies to induce antitumor immunity while minimizing autoimmunity.

Induction of effective and antigen-specific antitumour immunity by a liposomal ErbB2/HER2 peptide-based vaccination construct

Efficient delivery of tumour-associated antigens to appropriate cellular compartments of antigen-presenting cells is of prime importance for the induction of potent, cell-mediated antitumour immune responses. We have designed novel multivalent liposomal constructs that co-deliver the p63–71 cytotoxic T Lymphocyte epitope derived from human ErbB2 (HER2), and HA307–319, a T-helper (Th) epitope derived from influenza haemagglutinin. Both peptides were conjugated to the surface of liposomes via a Pam₃CSS anchor, a synthetic lipopeptide with potent adjuvant activity. In a murine model system, vaccination with these constructs completely protected BALB/c mice from subsequent s.c. challenge with ErbB2-expressing, but not ErbB2-negative, murine renal carcinoma (Renca) cells, indicating the induction of potent, antigen-specific immune responses. I.v. re-challenge of tumour-free animals 2 months after the first tumour cell inoculation did not result in the formation of lung tumour nodules, suggesting that long-lasting, systemic immunity had been induced. While still protecting the majority of vaccinated mice, a liposomal construct lacking the Th epitope was less effective than the diepitope construct, also correlating with a lower number of CD8⁺ IFN-γ⁺ T-cells identified upon ex vivo peptide restimulation of splenocytes from vaccinated animals. Importantly, in a therapeutic setting treatment with the liposomal vaccines resulted in cures in the majority of tumour-bearing mice and delayed tumour growth in the remaining ones. Our results demonstrate that liposomal constructs which combine Tc and Th peptide antigens and lipopeptide adjuvants can induce efficient, antigen-specific antitumour immunity, and represent promising synthetic delivery systems for the design of specific antitumour vaccines.

A tat fusion protein-based tumor vaccine for breast cancer

BACKGROUND

We recently reported that dendritic cells (DCs) transduced with a fusion protein between Her2/neu and the protein transduction domain Tat (DC-Tat-extracellular domain [ECD]) induced Her2/neu-specific CD8(+) T cells in vitro. This study tested the in vivo efficacy of DC-Tat-ECD in a murine breast cancer model.

METHODS

FVB/N mice received one or two weekly intraperitoneal immunizations with syngeneic DC-Tat-ECD followed by a tumor challenge with syngeneic neu(+) breast cancer cells, and tumor development was monitored. To test for Her2/neu specificity, CD4(+) and CD8(+) cells were isolated through magnetic bead separation and analyzed for specific interferon gamma release.

RESULTS

Intraperitoneally injected DCs migrated to secondary lymphoid organs, as evidenced by small-animal positron emission tomography studies. Immunized mice developed palpable tumors significantly later than control mice injected with DC-Tat-empty (P = .001 and P < .05 for two immunizations and for one immunization, respectively) or mice that received no DCs (P = .001 and P < .05). Similarly, immunized mice had smaller resulting tumors than mice injected with DC-Tat-empty (P < .05 and P < .01) or untreated mice (P < .001 and P < .001). Significantly more tumor-specific CD8(+) splenocytes were found in twice-immunized mice than in untreated animals (P < .001). Similarly, a T-helper type 1 CD4(+) T-cell response was observed.

CONCLUSIONS

Protein-transduced DCs may be effective vaccines for the treatment of cancer.

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.

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.

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.