The adjuvant activity of BAT antibody enables DNA vaccination to inhibit the progression of established autochthonous Her-2/neu carcinomas in BALB/c mice

DNA vaccination against oncoantigens: A promise

The emerging evidence that DNA vaccines elicit a protective immune response in rodents, dogs and cancer patients, coupled with the US Food and Drug Administration (FDA) approval of an initial DNA vaccine to treat canine tumors is beginning to close the gap between the optimistic experimental data and their difficult application in a clinical setting. Here we review a series of conceptual and biotechnological advances that are working together to make DNA vaccines targeting molecules that play important roles during cancer progression (oncoantigens) a promise with near-term clinical impact.

Engineered exosomes emerging from muscle cells break immune tolerance to HER2 in transgenic mice and induce antigen-specific CTLs upon challenge by human dendritic cells

We recently described a novel biotechnological platform for the production of unrestricted cytotoxic T lymphocyte (CTL) vaccines. It relies on in vivo engineering of exosomes, i.e., nanovesicles constitutively released by all cells, with full-length antigens of choice upon fusion with an exosome-anchoring protein referred to as Nef^mut. They are produced upon intramuscular injection of a DNA vector and, when uploaded with a viral tumor antigen, were found to elicit an immune response inhibiting the tumor growth in a model of transplantable tumors. However, for a possible application in cancer immunotherapy, a number of key issues remained unmet. Among these, we investigated: (i) whether the immunogenic stimulus induced by the engineered exosomes can break immune tolerance, and (ii) their effectiveness when applied in human system. As a model of immune tolerance, we considered mice transgenic for the expression of activated rat HER2/neu which spontaneously develop adenocarcinomas in all mammary glands. When these mice were injected with a DNA vector expressing the product of fusion between Nef^mut and the extracellular domain of HER2/neu, antigen-specific CD8⁺ T lymphocytes became readily detectable. This immune response associated with a HER2-directed CTL activity and a significant delay in tumor development. On the other hand, through cross-priming experiments, we demonstrated the effectiveness of the engineered exosomes emerging from transfected human primary muscle cells in inducing antigen-specific CTLs. We propose our CTL vaccine platform as part of new immunotherapy strategies against tumors expressing self-antigens, i.e., products highly expressed in oncologic lesions but tolerated by the immune system.

KEY MESSAGES

We established a novel, exosome-based method to produce unrestricted CTL vaccines. This strategy is effective in breaking the tolerance towards tumor self-antigens. Our method is also useful to elicit antigen-specific CTL immunity in humans. These findings open the way towards the use of this antitumor strategy in clinic.

Antitumor immunization of mothers delays tumor development in cancer-prone offspring

Maternal immunization is successfully applied against some life-threatening infectious diseases as it can protect the mother and her offspring through the passive transfer of maternal antibodies. Here, we sought to evaluate whether the concept of maternal immunization could also be applied to cancer immune-prevention. We have previously shown that antibodies induced by DNA vaccination against rat Her2 (neu) protect heterozygous neu-transgenic female (BALB-neuT) mice from autochthonous mammary tumor development. We, herein, seek to evaluate whether a similar maternal immunization can confer antitumor protection to BALB-neuT offspring. Significantly extended tumor-free survival was observed in BALB-neuT offspring born and fed by mothers vaccinated against neu, as compared to controls. Maternally derived anti-neu immunoglobulin G (IgG) was successfully transferred from mothers to newborns and was responsible for the protective effect. Vaccinated mothers and offspring also developed active immunity against neu as revealed by the presence of T-cell-mediated cytotoxicity against the neu immunodominant peptide. This active response was due to the milk transfer of immune complexes that were formed between the neu extracellular domain, shed from vaccine-transfected muscle cells, and the anti-neu IgG induced by the vaccine. These findings show that maternal immunization has the potential to hamper mammary cancer in genetically predestinated offspring and to develop into applications against lethal neonatal cancer diseases for which therapeutic options are currently unavailable.

Microenvironment, oncoantigens, and antitumor vaccination: lessons learned from BALB-neuT mice

The tyrosine kinase human epidermal growth factor receptor 2 (HER2) gene is amplified in approximately 20% of human breast cancers and is associated with an aggressive clinical course and the early development of metastasis. Its crucial role in tumor growth and progression makes HER2 a prototypic oncoantigen, the targeting of which may be critical for the development of effective anticancer therapies. The setup of anti-HER2 targeting strategies has revolutionized the clinical outcome of HER2⁺ breast cancer. However, their initial success has been overshadowed by the onset of pharmacological resistance that renders them ineffective. Since the tumor microenvironment (TME) plays a crucial role in drug resistance, the design of more effective anticancer therapies should depend on the targeting of both cancer cells and their TME as a whole. In this review, starting from the successful know-how obtained with a HER2⁺ mouse model of mammary carcinogenesis, the BALB-neuT mice, we discuss the role of TME in mammary tumor development. Indeed, a deeper knowledge of antigens critical for cancer outbreak and progression and of the mechanisms that regulate the interplay between cancer and stromal cell populations could advise promising ways for the development of the best anticancer strategy.

Tailoring DNA Vaccines: Designing Strategies Against HER2-Positive Cancers

The crucial role of HER2 in epithelial transformation and its selective overexpression on cancer tissues makes it an ideal target for cancer immunotherapies such as passive immunotherapy with Trastuzumab. There are, however, a number of concerns regarding the use of monoclonal antibodies which include resistance, repeated treatments, considerable costs, and side effects that make active immunotherapies against HER2 desirable alternative approaches. The efficacy of anti-HER2 DNA vaccination has been widely demonstrated in transgenic cancer-prone mice, which recapitulate several features of human breast cancers. Nonetheless, the rational design of a cancer vaccine able to trigger a long-lasting immunity, and thus prevent tumor recurrence in patients, would require the understanding of how tolerance and immunosuppression regulate antitumor immune responses and, at the same time, the identification of the most immunogenic portions of the target protein. We herein retrace the findings that led to our most promising DNA vaccines that, by encoding human/rat chimeric forms of HER2, are able to circumvent peripheral tolerance. Preclinical data obtained with these chimeric DNA vaccines have provided the rationale for their use in an ongoing Phase I clinical trial (EudraCT 2011-001104-34).

Comparison of adjuvant activity of N- and C-terminal domain of gp96 in a Her2-positive breast cancer model

It has been frequently reported that gp96 acts as a strong biologic adjuvant. Some studies have even investigated adjuvant activity of the gp96 C- or N-terminal domain. The controversy surrounding adjuvant activity of gp96 terminal domains prompted us to compare adjuvant activity of gp96 C- or N-terminal domain toward Her2/neu, as DNA vaccine in a Her2/neu-positive breast cancer model. To do so, mice were immunized with DNA vaccine consisting of transmembrane and extracellular domain (TM + ECD) of rat Her2/neu alone or fused to N- or C-terminal domain of gp96. Treatment with Her2/neu fused to N-terminal domain of gp96 resulted in tumor progression, compared to the groups vaccinated with pCT/Her2 or pHer2. Immunological examination revealed that treatment with Her2/neu fused to N-terminal domain of gp96 led to significantly lower survival rates, higher interferon-γ secretion, and induced infiltration of CD4(+)/CD8(+) cells to the tumor site. However, it could not induce cytotoxic T lymphocyte activity, did not decrease regulatory T cell percentage at the tumor site, and eventually led to tumor progression. Our results reveal that gp96 N-terminal domain does not have adjuvant activity toward Her2/neu. It is also proposed that adjuvant activity and the resultant immune response of gp96 terminal domains may be directed by the antigen applied.

Adjuvant activity of GP96 C-terminal domain towards Her2/neu DNA vaccine is fusion direction-dependent

The Her2 is one of tumor-associated antigens (TAA), regarded as an ideal target of immunotherapy. DNA encoding full-length or truncated rat Her2/neu have shown protective and therapeutics potentials against Her2/neu-expressing mammary tumors. However, the efficacy of active vaccination is limited since Her2 is a self-tolerated antigen. Hence, new strategies are required to enhance both the quality and quantity of the immune response against Her2-expressing tumors. Many studies have used Her2/neu gene with cytokine or other molecules involved in regulation of immune response to enhance the potency of Her2/neu DNA vaccines. Some studies fused adjuvant gene to C-terminal domain of Her2/neu gene, while others fused the adjuvant gene N-terminally to Her2/neu gene, but no comparison on how direction of fusion could affect efficiency of DNA vaccine has ever been made. Based on previous reports demonstrating potent adjuvant activity of gp96 C-terminal domain, we chose it as adjuvant. The aim of this study was to investigate if direction of fusion could affect adjuvant activity of gp96 C-terminal domain or potency of Her2/neu DNA vaccination. To do so, we fused C-terminal domain of gp96 to downstream or C-terminal end of transmembrane and extracellular domain (TM+ECD) of rat Her2/neu and resultant immune response to DNA vaccination was evaluated. The results were compared with that of N-terminally fusion of gp96 C-terminal domain to TM+ECD of rat Her2/neu. Our results revealed that adjuvant activity of gp96 C-terminal domain is enhanced when fused N-terminally to TM+ECD of rat Her2/neu. It suggests that adjuvant activity of gp96 C-terminal domain towards Her2/neu is fusion direction-dependent.

N-terminally fusion of Her2/neu to HSP70 decreases efficiency of Her2/neu DNA vaccine

DNA vaccines consisted of tumor-associated antigen (TAA) are well suited for immunotherapy against tumor. The construct can contain TAA fused to an appropriate molecule (biologic adjuvant) to improve the efficacy of anti-tumor immune response. Heat shock protein 70 (HSP70) has been shown to be an excellent candidate, capable of cross-priming TAA by antigen presenting cells leading to a robust T-cell response. However, the relationship between strong T-cell responses and tumor rejection is not always mutually exclusive, for which TAA loss or activation of suppressive mechanisms may occur. HSP70 fused to downstream of Her2/neu as DNA vaccine has been shown to be efficient against Her2-expressing tumors. In this study, we examined if N-terminally fusion of Her2/neu to HSP70 could also improve efficiency of Her2/neu DNA vaccine. Therefore, mice with an established Her2/neu expressing tumor were immunized with DNA vaccine consisting of extracellular and trans-membrane domain (EC+TM) of rat Her2/neu alone or N-terminally fused to HSP70 and immune response was evaluated. Administration of rat Her2/neu led to partial control of tumor progression. Surprisingly, fusion of HSP70 to N-terminal of rat Her2/neu led to tumor progression. Our result proposes that fusion direction of biologic adjuvant is an important consideration when Her2/neu is used.

GP96 C-terminal improves Her2/neu DNA vaccine

BACKGROUND

DNA vaccines ensure protective immunity against tumors in a variety of experimental models. The favorite target tumor-associated antigens have been those that are frequently expressed by human tumors, such as Her2. However, the efficacy of active vaccination is limited because Her2 is a self-tolerated antigen. Many strategies have been applied to increase the efficacy of DNA vaccination, such as fusion or co-administration of Her2 with cytokine and co-stimulatory molecules. GP96 is involved in innate and adaptive immune responses and evokes potent activation and maturation of dendritic cells along with increased secretion of pro-inflammatory cytokines. On the basis of previous studies, we expected the C-terminal of GP96 to act as a package and as a suitable substitute for both cytokine and co-stimulatory genes.

METHODS

In the present study, the C-terminal of GP96 fused or co-administered with Her2/neu-containing constructs was used and the resultant immune response was evaluated and compared.

RESULTS

The data obtained showed that the construct containing the C-terminal of GP96 fused with Her2/neu, but not the co-administration of the two separated constructs, decreased CD4(+)CD25(+)foxp3(+) regulatory T cells at the tumor site, enhanced cytotoxic T lymphocyte activity and increased interferon-gamma secretion.

CONCLUSIONS

The C-terminal of GP96 has potent adjuvant activity in eliciting a significant immune response when fused with Her2/neu. It may be used as molecular adjuvant along with other tumor or bacterial/viral antigens.

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

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

An oral TLR7 agonist is a potent adjuvant of DNA vaccination in transgenic mouse tumor models

In vivo electroporation of plasmid DNA (DNA-EP) is an efficient and safe method for vaccines resulting in increased DNA uptake, enhanced protein expression and increased immune responses to the target antigen in a variety of species. To further enhance the efficacy of DNA-EP, we have evaluated the toll-like receptor7 (TLR7) agonist-2, 9, substituted 8-hydroxyadenosine derivative or SM360320--as an adjuvant to vaccines against HER2/neu and CEA in BALB-neuT and CEA transgenic mice (CEA.Tg), respectively. SM360320 induced in vivo secretion of interferon alpha (IFNalpha) and exerted a significant antitumor effect in CEA.Tg mice challenged with a syngenic tumor cell line expressing CEA and an additive effect with a CEA vaccine. Additionally, combination of SM360320 with plasmid encoding the extracellular and transmembrane domain of ratHER2/neu affected the spontaneous tumor progression in BALB-neuT mice treated in an advanced disease setting. The antitumor effect in mice treated with DNA-EP and SM360320 was associated with an anti-CEA and anti-p185(neu) antibody isotype switch from IgG1 to IgG2a. These data demonstrate that SM360320 exerts significant antitumor effects and can act in association with DNA-EP for CEA-positive colon cancer and HER2-positive mammary carcinoma. These observations therefore emphasize the potential of SM360320 as immunological adjuvant for therapeutic DNA vaccines.

Peptide vaccine given with a Toll-like receptor agonist is effective for the treatment and prevention of spontaneous breast tumors

Our goal is to develop peptide vaccines that stimulate tumor antigen-specific T-cell responses against frequently found cancers. Previous work has shown that to generate effective T-cell responses, peptides have to be administered in combination with strong adjuvants such as Toll-like receptor agonists. However, most animal tumor model systems used to study peptide vaccines were not truly representative of malignant diseases in humans because they solely used transplantable tumor lines, and instead of true tumor antigens, they used highly immunogenic foreign proteins. Here, we describe a peptide vaccination strategy, which is highly effective in delaying or preventing the occurrence of spontaneous breast tumors. Transgenic female BALB-neuT mice that carry the activated rat HER-2/neu oncogene were vaccinated with a synthetic peptide from the rat HER-2/neu gene product, which represents an epitope for CTLs in combination with a Toll-like receptor agonist adjuvant. Our results show that to obtain tumor antigen-specific CTL responses and antitumor effects, the vaccine had to be administered repetitively, or the function of CD4/CD25 T regulatory cells had to be blocked with anti-CD25 antibody therapy. Mice that were vaccinated with this approach remained tumor-free or were able to control spontaneous tumor growth and exhibited long-lasting CTL responses, not only against the immunizing peptide but also against other peptides derived from rat HER-2/neu product (i.e., epitope spreading). These results suggest that similar strategies should be followed for conducting clinical studies in patients.

Distinct and non-overlapping T cell receptor repertoires expanded by DNA vaccination in wild-type and HER-2 transgenic BALB/c mice

Central tolerance to tumor-associated Ags is an immune-escape mechanism that significantly limits the TCR repertoires available for tumor eradication. The repertoires expanded in wild-type BALB/c and rat-HER-2/neu (rHER-2) transgenic BALB-neuT mice following DNA immunization against rHER-2 were compared by spectratyping the variable (V)beta and the joining (J)beta CDR 3. Following immunization, BALB/c mice raised a strong response. Every mouse used one or more CD8+ T cell rearrangements of the Vbeta9-Jbeta1.2 segments characterized by distinct length of the CDR3 and specific for 63-71 or 1206-1214 rHER-2 peptides. In addition, two CD4+ T cell rearrangements recurred in >50% of mice. Instead, BALB-neuT mice displayed a limited response to rHER-2. Their repertoire is smaller and uses different rearrangements confined to CD4+ T cells. Thus, central tolerance in BALB-neuT mice acts by silencing the BALB/c mice self-reactive repertoire and reducing the size of the CD8+ T cell component. CD8+ and CD4+ T cells from both wild-type and transgenic mice home to tumors. This definition of the T cell repertoires available is critical to the designing of immunological maneuvers able to elicit an effective immune reaction against HER-2-driven carcinogenesis.

Vaccination for Treatment and Prevention of Cancer in Animal Models

Two approaches to immunological intervention in tumor-host interactions in mouse models are discussed in this review. The first is described with reference to experiments in which CD8(+) T lymphocytes are used to kill established transplantable tumors. Peptides and their optimal presentation by dendritic cells and intervention in immune regulatory mechanisms are the key issues for efficient induction of T-killer cell-mediated tumor eradication. The time frame of tumor therapy and the threat imposed by tumor growth in transplantable models and cancer patients require the induction of a robust T-cell reaction. Prevention of the progression of small preneoplastic lesions, on the other hand, requires the significant and prolonged immune protection sought in the second approach. This is based on antibody production and the coordinated activation of multiple low-avidity cell-mediated mechanisms elicited by DNA vaccination in genetically modified cancer-prone mice, transgenic for a mutant Her-2/neu growth factor receptor expressed at the plasma membrane surface of preneoplastic mammary gland epithelial cells. Vaccination with appropriate DNA formulations results in prolonged immune inhibition of the progression of preneoplastic mammary lesions but is ineffective against established tumors. The use of molecularly defined adjuvants and intervention in immune regulatory mechanisms are critical in both the elicitation of an effective T-cell mediated reaction required for tumor debulking in the first set of models and the induction by vaccination of a sustained immune memory able to prevent the expansion of preneoplastic lesions in genetically cancer-prone mice.