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

Gene Gun Her2/neu DNA Vaccination: Evaluation of Vaccine Efficacy in a Syngeneic Her2/neu Mouse Tumor Model

Genetic vaccination using naked plasmid DNA is an immunization strategy both against infectious diseases and cancer.In order to improve efficacy of DNA vaccines, particularly in large animals and humans, different strategies have been pursued. These vaccination strategies are based on different application routes, schedules and coexpression of immunomodulatory molecules as adjuvants. Our mouse tumor model offers the possibility to investigate Her2/neu DNA vaccines in different settings, that is, intramuscular or intradermal application with or without coexpression of adjuvants. The immunogenicity of predicted peptides for Her2/neu specific memory T cells were screened and confirmed after intramuscular and intradermal application. Protection from tumor growth in tumor challenge experiments and both T cell and humoral immune responses against Her2/neu peptides are used as surrogate parameters for vaccine efficacy.

Elevated endoplasmic reticulum stress reinforced immunosuppression in the tumor microenvironment via myeloid-derived suppressor cells

The role of endoplasmic reticulum (ER) stress in cancer has been studied in detail, and ER stress is known to increase tumor cell apoptosis, and thus, reduce tumor growth. However, in our study, persistent ER stress induced by multiple administrations of low-dose thapsigargin (Tg) accelerated tumor growth in mice. Tg-mediated ER stress increased the generation of Ly6G⁺CD11b⁺ myeloid cells, but did not alter anti-tumor effector T cells. 4-Phenylbutyric acid (4-PBA), a chemical chaperone widely used as an ER stress reducer, attenuated Tg-induced myeloid-derived suppressor cell (MDSC) expansion and tumor growth. Tg-mediated ER stress enhanced the immunosuppressive capacity of tumor-infiltrating MDSCs by increasing expression of ARG1, iNOS, and NOX2, although splenic MDSCs were not affected. Consistent with these results, 4-PBA restored the anti-tumor immune response by regulating inflammatory cytokines such as TNF-α and CXCL1/KC, and activated tumor-infiltrating CD8⁺ T cells that were inhibited by Tg-mediated ER stress. These results suggest that significant ER stress in a tumor-bearing host might induce tumor growth mediated by enhancement of MDSC-mediated suppression. Therefore, ER stress reducers such as 4-PBA could restore anti-tumor immunity by inhibiting suppressive MDSCs that are exacerbated by ER stress.

A phase 1 study of a heterologous prime-boost vaccination involving a truncated HER2 sequence in patients with HER2-expressing breast cancer

A phase 1 clinical trial was conducted to assess the safety, tolerability, and preliminary efficacy of a heterologous prime-boost strategy involving plasmid DNA (pHM-GM-CSF, expressing truncated human epidermal growth factor receptor 2 (HER2) and granulocyte macrophage colony-stimulation factor (GM-CSF) as a bicistronic message) and an adenoviral vector (Ad-HM, containing the same modified HER2 sequence only), in patients with stage III–IV metastatic breast cancer expressing HER2. Nine eligible subjects were divided into three cohorts based on the dosages (2, 4, and 8 mg/patient/visit) of pHM-GM-CSF used as the primer, which was intramuscularly injected three times at weeks 0, 2, and 4. It was followed by a single injection of Ad-HM (3 × 10⁹ virus particles), used as a booster, at week 6. During the 6-month follow-up period, adverse events (AEs), pharmacokinetics and pharmacodynamics, and HER2-specific cellular and humoral immune responses were evaluated. Seven cases of minor grade 1 toxicities in four of nine subjects and no serious drug-related AEs were reported. HER2-specific cell-mediated or humoral immunity was produced in all (100%) or three subjects (33%), respectively. One subject showed a partial response, and seven subjects had stable diseases. However, there were no differences in clinical tumor response and HER2-specific immune responses among the cohorts. These results showed that intramuscular injections of pHM-GM-CSF and Ad-HM were well tolerated and safe.

Gene Gun Her2/neu DNA Vaccination: Evaluation of Vaccine Efficacy in a Syngeneic Her2/neu Mouse Tumor Model

Genetic vaccination using naked plasmid DNA is an immunization strategy both against infectious diseases and cancer. In order to improve the efficacy of DNA vaccines, particularly in large animals and humans, different strategies have been pursued. These vaccination strategies are based on different application routes, schedules, and coexpression of immunomodulatory molecules as adjuvants. Our mouse tumor model offers the possibility to investigate Her2/neu DNA vaccines in different settings, i.e., intramuscular or intradermal application with or without coexpression of adjuvants. Protection from tumor growth in tumor challenge experiments and both T cell and humoral immune responses against Her2/neu peptides are used as surrogate parameters for vaccine efficacy.

Serum amyloid A3 exacerbates cancer by enhancing the suppressive capacity of myeloid-derived suppressor cells via TLR2-dependent STAT3 activation

Myeloid-derived suppressor cells (MDSCs), which suppress diverse innate and adaptive immune responses and thereby provide an evasion mechanism for tumors, are emerging as a key population linking inflammation to cancer. Although many inflammatory factors that induce MDSCs in the tumor microenvironment are known, the crucial components and the underlying mechanisms remain elusive. In this study, we proposed a novel mechanism by which serum amyloid A3 (SAA3), a well-known inflammatory factor, connects MDSCs with cancer progression. We found that SAA3 expression in BALB/c mice increased in monocytic MDSCs (Mo MDSCs) with tumor growth. The induction of SAA3 by apo-SAA treatment in Mo MDSCs enhanced their survival and suppressive activity, while it inhibited GM-CSF-induced differentiation. Endogenous SAA3 itself contributed to the increase in the survival and suppressive activity of Mo MDSCs. We demonstrated that SAA3 induced TLR2 signaling, in turn increasing the autocrine secretion of TNF-α, that led to STAT3 activation. In addition, activated STAT3 enhanced the suppressive activity of Mo MDSCs. Furthermore, SAA3 induction in Mo MDSCs contributed to accelerating tumor progression in vivo. Collectively, these data suggest a novel mechanism by which Mo MDSCs mediate inflammation through SAA3-TLR2 signaling and thus exacerbate cancer progression by a STAT3-dependent mechanism.

Tumor microenvironmental conversion of natural killer cells into myeloid-derived suppressor cells

How myeloid-derived suppressor cells (MDSC) emerge in the tumor environment remains unclear. Here, we report that GM-CSF can convert natural killer (NK) cells into MDSCs. When transferred into tumor-bearing mice, adoptively transferred NK cells lost their NK phenotype and were converted into Ly6C(high)Ly6G(high) MDSC. This conversion was abolished by exposure to IL-2 either in vitro or in vivo. Notably, we found that of the 4 maturation stages based on CD11b/CD27 expression levels, only the CD11b(high)CD27(high) NK cells could be converted into CD11b(+)Gr1(+) MDSC ex vivo. Transfer of CD27(high) NK cells from tumor-bearing mice into tumor-bearing recipients was associated with conversion to MDSC in a manner associated with reduced numbers of CD11b(high)CD27(high) and CD11b(high)CD27(low) NK cell populations in the recipients. Our results identify a pathway of MDSC development from immature NK cells in tumor-bearing hosts, providing new insights into how tumor cells modulate their host immune microenvironment to escape immune surveillance.

Vaccination for the prevention and treatment of breast cancer with special focus on Her-2/neu peptide vaccines

Immunologic interventions in a subset of breast cancer patients represent a well-established therapeutic approach reflecting individualized treatment modalities. Thus, the therapeutic administration of monoclonal antibodies targeting tumor-associated antigens (TAA), such as Her-2/neu, represents a milestone in cancer treatment. However, passive antibody administration suffers from several drawbacks, including frequency and long duration of treatment. These undesirables may be avoidable in an approach based on generating active immune responses against these same targets. Only recently has the significance of tumors in relation to their microenvironments been understood as essential for creating an effective cancer vaccine. In particular, the immune system plays an important role in suppressing or promoting tumor formation and growth. Therefore, activation of appropriate triggers (such as induction of Th1 cells, CD8+ T cells, and suppression of regulatory cells in combination with generation of antibodies with anti-tumor activity) is a desirable goal. Current vaccination approaches have concentrated on therapeutic vaccines using certain TAA. Many cancer antigens, including breast cancer antigens, have been described and also given priority ranking for use as vaccine antigens by the US National Cancer Institute. One of the TAA antigens which has been thoroughly examined in numerous trials is Her-2/neu. This review will discuss delivery systems for this antigen with special focus on T and B cell peptide vaccines. Attention will be given to their advantages and limitations, as well as the use of certain adjuvants to improve anti-cancer responses.

Suppressive effects on the immune response and protective immunity to a JEV DNA vaccine by co-administration of a GM-CSF-expressing plasmid in mice

As a potential cytokine adjuvant of DNA vaccines, granulocyte-macrophage colony–stimulating factor (GM-CSF) has received considerable attention due to its essential role in the recruitment of antigen-presenting cells, differentiation and maturation of dendritic cells. However, in our recent study of a Japanese encephalitis virus (JEV) DNA vaccine, co-inoculation of a GM-CSF plasmid dramatically suppressed the specific IgG response and resulted in decreased protection against JEV challenge. It is known that GM-CSF has been used in clinic to treat neutropenia for repopulating myeloid cells, and as an adjuvant in vaccine studies; it has shown various effects on the immune response. Therefore, in this study, we characterized the suppressive effects on the immune response to a JEV DNA vaccine by the co-administration of the GM-CSF-expressing plasmid and clarified the underlying mechanisms of the suppression in mice. Our results demonstrated that co-immunization with GM-CSF caused a substantial dampening of the vaccine-induced antibody responses. The suppressive effect was dose- and timing-dependent and likely related to the immunogenicity of the antigen. The suppression was associated with the induction of immature dendritic cells and the expansion of regulatory T cells but not myeloid-derived suppressor cells. Collectively, our findings not only provide valuable information for the application of GM-CSF in clinic and using as a vaccine adjuvant but also offer further insight into the understanding of the complex roles of GM-CSF.

The restoration of myeloid-derived suppressor cells as functional antigen-presenting cells by NKT cell help and all-trans-retinoic acid treatment

Myeloid-derived suppressor cells (MDSCs), which accumulate during tumor progression, have been shown to function as important suppressor cells. In a previous study, we showed that immunosuppressive MDSCs could function as immunogenic antigen-presenting cells (APCs) with the help of activated natural killer T (NKT) cells. In the current study, however, we found that MDSCs harvested at a late time point after tumor injection (late MDSCs) were poorly immunogenic even when stimulated with activated NKT cells. As tumor growth progressed, the expression of MHC and costimulatory molecules on MDSCs was gradually down-regulated. Late MDSCs also had innate defects in activation and differentiation mediated by cytokine stimuli. Although late MDSCs treated only with all-trans-retinoic acid (ATRA), a stimulating agent for MDSC differentiation, could not become immunogenic, NKT ligand-loaded, ATRA-treated late MDSCs could be converted into immunogenic APCs to induce incremental immune responses. Furthermore, these effects were mediated by NKT cells secreting IFNγ, and ATRA-mediated increases in glutathione (GSH) levels. Thus, combined treatment with differentiating and activating agents is a prerequisite for the conversion of late MDSCs into immunogenic APCs. Collectively, these results suggest that combined treatments are required for the differentiation and activation of late MDSCs in late stage cancer.

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.

NKT ligand-loaded, antigen-expressing B cells function as long-lasting antigen presenting cells in vivo

We had previously shown that activated NKT cells licensed B cells to be immunogenic antigen-presenting cells and helped to elicit a wide spectrum of cancer targeted immune responses. In the current study, we sought to verify the safety of αGalCer-loaded, and adenovirus-transduced B cell-based vaccines, together with mechanism of action. Intravenously injected αGalCer-loaded, antigen-expressing B cells rapidly localized in the spleen and directly primed CD8(+) T cells in an antigen-specific manner. The transferred antigen was sustained for at least 30 days. While some injected B cells produced nonspecific IgG, the antigen-specific IgG response was completely dependent on endogenous B cells. The liver was one of the main tissues where injected B cells were retained; however, we could not find the signs of liver toxicity. Our results demonstrate that αGalCer-loaded, antigen-expressing B cells behave as "antigen-presenting" cells that stimulate endogenous antigen-specific T cells and B cells in vivo without significant toxicity.

Evaluation of a DNA vaccine candidate expressing prM-E-NS1 antigens of dengue virus serotype 1 with or without granulocyte-macrophage colony-stimulating factor (GM-CSF) in immunogenicity and protection

Dengue is one of the most important mosquito-borne viral diseases. In past years, although considerable effort has been put into the development of a vaccine, there is currently no licensed dengue vaccine. In this study, we constructed DNA vaccines that carried the prM-E-NS1 genes of dengue virus serotype 1 (DV1) with or without the granulocyte-macrophage colony-stimulating factor (GM-CSF) gene, an attractive DNA vaccine adjuvant. Immunization with the plasmid pCAG-DV1/E/NS1, which expresses viral prM-E-NS1, or the bicistronic plasmid pCAG-DV1-GM, which co-expresses viral prM-E-NS1 and GM-CSF, resulted in long-term IgG response, high levels of splenocyte-secreted interferon-γ and interleukin-2, strong cytotoxic T lymphocyte activity and sufficient protection in the DV1-challenged mice. This suggested that both humoral and cellular immune responses were induced by the immunizations and that they played important roles in protection against the DV1 challenge. Interestingly, the magnitude, quality and protective capacity of the immune responses induced by immunization with pCAG-DV1/E/NS1 or pCAG-DV1-GM seemed stronger than those induced by pCAG-DV1/E (expressing viral prM-E alone). Taken together, we demonstrated that prM/E plus NS1 would be a suitable solution for the development of a DNA vaccine against DV.

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.

Co-expression of Flt-3 ligand gene ablates tumor immunity elicited by HER-2/neu DNA vaccine in transgenic mice

Fms-like tyrosine-kinase 3 ligand (Flt-3L), is a powerful hematopoyetic growth factor, known to modulate the immune response against delivered antigens by acting either as an adjuvant or tolerogenic stimulus. In this study we evaluated the use of murine Flt-3 ligand plasmid (pFl) in combination with a DNA vaccine encoding rat-p185 oncoprotein extra cellular domain (pECD) in the prevention of mammary carcinogenesis in rat-neu HER-2 mutated (neuT) transgenic mice. We demonstrate that intramuscular (i.m.) co-immunization of pFl inhibits the production of anti-HER-2 antibody elicited by pECD vaccine, resulting in the development of spontaneous carcinomas in all co-immunized mice. The inhibitory effect on antibody production by mFlt3 gene appeared to be: dose-dependent, linked to the injection site and timing, and transient in nature. Additionally, we show that co-administration of pFI and pECD plasmids was unable to trigger cytotoxic T-cell immune response in neuT mice. On the other hand, we found that the combination of pFl with pECD had no impact on the ability of pECD to reject HER-2+ transplantable tumors in parental mice. In summary our results demonstrate that, depending on tumor model, co-administration of pFl gene can produce untoward effects to immune response, and thus its application as a vaccine adjuvant should be carefully evaluated.

Optimal induction of HPV DNA vaccine-induced CD8+ T cell responses and therapeutic antitumor effect by antigen engineering and electroporation

Since human papillomavirus (HPV) E6 and E7 are promising tumor antigens, we engineered E6 and E7 antigens to generate an optimal HPV DNA vaccine by codon optimization (Co), fusion of E6 and E7, addition of a tissue plasminogen activator (tpa) signal sequence, addition of CD40 ligand (CD40L) or Fms-like tyrosine kinase-3 ligand (Flt3L). The resulting constructs were investigated in terms of their antitumor activity as well as induction of HPV-specific CD8(+) T cell responses. When E6(Co) and E7(Co) were fused (E67(Co)), CD8(+) T cell responses specific for E6 or E7 antigen decreased, but the preventive antitumor effect rather improved, demonstrating the importance of broad immunity. Interestingly, Flt3L-fused HPV DNA vaccine exhibited stronger E6- and E7-specific CD8(+) T cell responses as well as therapeutic antitumor effect than that of CD40L linked HPV DNA vaccine. Finally, the optimal construct, tFE67(Co), was generated by including tpa signal sequence, Flt3L, fusion of E6 and E7, and codon optimization, which induces 23 and 25 times stronger E6- and E7-specific CD8(+) T cell responses than those of initial E67 fusion construct. In particular, inclusion of electroporation in intramuscular immunization of tFE67(Co) further enhances HPV-specific CD8(+) T cell responses, leading to complete tumor regression in a therapeutic setting. Thus, our results provide valuable insight on effective HPV DNA vaccine design and suggest that tFE67(Co) delivered with electroporation may be a promising therapeutic HPV DNA vaccine against cervical cancer.

Induction of T cell-mediated immunity using a c-Myb DNA vaccine in a mouse model of colon cancer

Overexpression of the proto-oncogene c-Myb occurs in more than 80% of colorectal cancer (CRC) and is associated with aggressive disease and poor prognosis. To test c-Myb as a therapeutic target in CRC we devised a DNA fusion vaccine to generate an anti-CRC immune response. c-Myb, like many tumor antigens, is weakly immunogenic as it is a "self" antigen and subject to tolerance. To break tolerance, a DNA fusion vaccine was generated comprising wild-type c-Myb cDNA flanked by two potent Th epitopes derived from tetanus toxin. Vaccination was performed targeting a highly aggressive, weakly immunogenic, subcutaneous, syngeneic, colon adenocarcinoma cell line MC38 which highly expresses c-Myb. Prophylactic intravenous vaccination significantly suppressed tumor growth, through the induction of anti-tumor immunity for which the tetanus epitopes were essential. Vaccination generated anti-tumor immunity mediated by both CD4+ and CD8+ T cells and increased infiltration of immune effector cells at the tumor site. Importantly, no evidence of autoimmune pathology in endogenous c-Myb expressing tissues was detected as a consequence of breaking tolerance. In summary, these results establish c-Myb as a potential antigen for immune targeting in CRC and serve to provide proof of principle for the continuing development of DNA vaccines targeting c-Myb to bring this approach to the clinic.

alpha-Galactosylceramide-loaded, antigen-expressing B cells prime a wide spectrum of antitumor immunity

Most of the current tumor vaccines successfully elicit strong protection against tumor but offer little therapeutic effect against existing tumors, highlighting the need for a more effective vaccine strategy. Vaccination with tumor antigen-presenting cells can induce antitumor immune responses. We have previously shown that NKT-licensed B cells prime cytotoxic T lymphocytes (CTLs) with epitope peptide and generate prophylactic/therapeutic antitumor effects. To extend our B cell vaccine approach to the whole antigen, and to overcome the MHC restriction, we used a nonreplicating adenovirus to transduce B cells with antigenic gene. Primary B cells transduced with an adenovirus-encoding truncated Her-2/neu (AdHM) efficiently expressed Her-2/neu. Compared with the moderate antitumor activity induced by vaccination with adenovirus-transduced B cells (B/AdHM), vaccination with alpha-galactosylceramide-loaded B/AdHM (B/AdHM/alpha GalCer) induced significantly stronger antitumor immunity, especially in the tumor-bearing mice. The depletion study showed that CD4(+), CD8(+) and NK cells were all necessary for the therapeutic immunity. Confirming the results of the depletion study, B/AdHM/alpha GalCer vaccination induced cytotoxic NK cell responses but B/AdHM did not. Vaccination with B/AdHM/alpha GalCer generated Her-2/neu-specific antibodies more efficiently than B/AdHM immunization. More importantly, B/AdHM/alpha GalCer could prime Her-2/neu-specific cytotoxic T cells more efficiently and durably than B/AdHM. CD4(+) cells appeared to be necessary for the induction of antibody and CTL responses. Our results demonstrate that, with the help of NKT cells, antigen-transduced B cells efficiently induce innate immunity as well as a wide range of adaptive immunity against the tumor, suggesting that they could be used to develop a novel cellular vaccine.

Immunogenicity and safety profiles of genetic vaccines against human Her-2/neu in cynomolgus monkeys

Her-2/neu is a well-characterized tumor-associated antigen, the overexpression of which in human carcinomas correlates with a poor prognosis. Here, we evaluated Her-2/neu-specific humoral and cellular immune responses in immunized monkeys after immunization with nonreplicating adenovirus (AdHM) expressing the extracellular and transmembrane domain of human Her-2/neu (HM) and/or naked DNA vaccine (pHM-hGM-CSF) expressing human granulocyte-macrophage colony-stimulating factor together with HM. Priming of monkeys with AdHM generated Her-2/neu-specific long-lasting antibody production. Furthermore, these Her-2/neu-specific antibodies produced by AdHM immunization, some of which shared epitope specificity with Herceptin, were able to induce antibody-dependent cellular cytotoxicity against Her-2-expressing target cells. Cellular immune responses were elicited in all monkeys immunized with Her-2/neu-expressing vaccine; interferon-gamma was secreted when these splenocytes were restimulated with Her-2/neu-expressing autologous cells, and immunization with AdHM induced Her-2/neu-specific lymphoproliferative responses. Further, immunization with pHM-hGM-CSF before AdHM immunization noticeably enhanced cytotoxic T-lymphocyte activity. In addition, we observed no abnormalities that would indicate that the genetic vaccines had toxic effects in the immunized monkeys. Thus, we can conclude that our genetic vaccines efficiently elicited Her-2/neu-specific humoral and cellular immune responses without causing severe adverse effects in nonhuman primates and that as such they warrant further clinical investigation.

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.

Coexpression of Flt3 ligand and GM-CSF genes modulates immune responses induced by HER2/neu DNA vaccine

DNA vaccine and dendritic cells (DCs)-based vaccine have emerged as promising strategies for cancer immunotherapy. Fms-like tyrosine kinase 3-ligand (Flt3L) and granulocyte-macrophage-colony-stimulating factor (GM-CSF) have been exploited for the expansion of DC. It was reported previously that combination of plasmid encoding GM-CSF with HER2/neu DNA vaccine induced predominantly CD4(+) T-cell-mediated antitumor immune response. In this study, we investigated the modulation of immune responses by murine Flt3L and GM-CSF, which acted as genetic adjuvants in the forms of bicistronic (pFLAG) and monocistronic (pFL and pGM) plasmids for HER2/neu DNA vaccine (pN-neu). Coexpression of Flt3L and GM-CSF significantly enhanced maturation and antigen-presentation abilities of splenic DC. Increased numbers of infiltrating DC at the immunization site, higher interferon-gamma production, and enhanced cytolytic activities by splenocytes were prominent in mice vaccinated with pN-neu in conjunction with pFLAG. Importantly, a potent CD8(+) T-cell-mediated antitumor immunity against bladder tumors naturally overexpressing HER2/neu was induced in the vaccinated mice. Collectively, our results indicate that murine Flt3L and GM-CSF genes coexpressed by a bicistronic plasmid modulate the class of immune responses and may be superior to those codelivered by two separate monocistronic plasmids as the genetic adjuvants for HER2/neu DNA vaccine.

Construction of recombinant attenuated Salmonella typhimurium DNA vaccine expressing H pylori ureB and IL-2

AIM: To construct a recombinant live attenuated Salm-onella typhimurium DNA vaccine encoding H pylori ureB gene and mouse IL-2 gene and to detect its immunogenicity in vitro and in vivo.

METHODS: H pylori ureB and mouse IL-2 gene fragments were amplified by polymerase chain reaction (PCR) and cloned into pUCmT vector. DNA sequence of the amplified ureB and IL-2 genes was assayed, then cloned into the eukaryotic expression vector pIRES through enzyme digestion and ligation reactions resulting in pIRES-ureB and pIRES-ureB-IL-2. The recombinant plasmids were used to transform competent E. coli DH5α, and the positive clones were screened by PCR and restriction enzyme digestion. Then, the recombinant pIRES-ureB and pIRES-ureB-IL-2 were used to transform LB5000 and the recombinant plasmids extracted from LB5000 were finally introduced into the final host SL7207. After that, recombinant strains were grown in vitro repeatedly. In order to detect the immunogenicity of the vaccine in vitro, pIRES-ureB and pIRES-ureB-IL-2 were transfected to COS-7 cells using Lipofectamine^TM2000, the immunogenicity of expressed UreB and IL-2 proteins was assayed with SDS-PAGE and Western blot. C57BL/6 mice were orally immunized with 1 × 10⁸ recombinant attenuated Salmonella typhimurium DNA vaccine. Four weeks after vaccination, mice were challenged with 1 × 10⁷ CFU of live H pylori SS1. Mice were sacrificed and the stomach was isolated for examination of H pylori 4 wk post-challenge.

RESULTS: The 1700 base pair ureB gene fragment amplified from the genomic DNA was consistent with the sequence of H pylori ureB by sequence analysis. The amplified 510 base pair fragment was consistent with the sequence of mouse IL-2 in gene bank. It was confirmed by PCR and restriction enzyme digestion that H pylori ureB and mouse IL-2 genes were inserted into the eukaryotic expression vector pIRES. The experiments in vitro showed that stable recombinant live attenuated Salmonella typhimurium DNA vaccine carrying ureB and IL-2 genes was successfully constructed and the specific strips of UreB and IL-2 expressed by recombinant plasmids were detected through Western blot. Study in vivo showed that the positive rate of rapid urease test of the immunized group including ureB and ureB-IL-2 was 37.5% and 12.5% respectively, and was significantly lower than that (100%) in the control group (P < 0.01).

CONCLUSION: Recombinant attenuated Salmonella typhimurium DNA vaccine expressing UreB protein and IL-2 protein with immunogenicity can be constructed. It can protect mice against H pylori infection, which may help the development of a human-use H pylori DNA vaccine.

Adjuvanticity of plasmid DNA encoding cytokines fused to immunoglobulin Fc domains

PURPOSE

Plasmid DNAs encoding cytokines enhance immune responses to vaccination in models of infectious diseases and cancer. We compared DNA adjuvants for their ability to enhance immunity against a poorly immunogenic self-antigen expressed by cancer.

EXPERIMENTAL DESIGN

DNAs encoding cytokines that affect T cells [interleukin (IL)-2, IL-12, IL-15, IL-18, IL-21, and the chemokine CCL21] and antigen-presenting cells [granulocyte macrophage colony-stimulating factor (GM-CSF)] were compared in mouse models as adjuvants to enhance CD8+ T-cell responses and tumor immunity. A DNA vaccine against a self-antigen, gp100, expressed by melanoma was used in combination with DNA encoding cytokines and cytokines fused to the Fc domain of mouse IgG1 (Ig).

RESULTS

We found that (a) cytokine DNAs generally increased CD8+ T-cell responses against gp100; (b) ligation to Fc domains further enhanced T-cell responses; (c) adjuvant effects were sensitive to timing of DNA injection; (d) the most efficacious individual adjuvants for improving tumor-free survival were IL-12/Ig, IL-15/Ig, IL-21/Ig, GM-CSF/Ig, and CCL21; and (e) combinations of IL-2/Ig+IL-12/Ig, IL-2/Ig+IL-15/Ig, IL-12/Ig+IL-15/Ig, and IL-12/Ig+IL-21/Ig were most active; and (f) increased adjuvanticity of cytokine/Ig fusion DNAs was not related to higher tissue levels or greater stability.

CONCLUSIONS

These observations support the potential of cytokine DNA adjuvants for immunization against self-antigens expressed by cancer, the importance of timing, and the enhancement of immune responses by Fc domains through mechanisms unrelated to increased half-life.

CD1d-restricted T cells license B cells to generate long-lasting cytotoxic antitumor immunity in vivo

Although resting B cells are known for being poorly immunogenic and for inducing T-cell tolerance, we have here attempted to test whether their immunogenicity could be enhanced by CD1d-restricted invariant T cells (iNKT) to a point where they could be used in cellular vaccines. We found that the addition of the iNKT ligand alpha-galactosylceramide (alphaGalCer) to peptide-loaded B cells overcame peptide-specific T-cell unresponsiveness and allowed for the generation of peptide-specific memory CTL immunity. This CTL was induced independently of CD4 T and natural killer cells but required iNKT and CD8 T cells. B cells directly primed CTL, and the alphaGalCer and the peptide must be presented on the same cell. Importantly, our B-cell-based vaccine is comparable in efficiency with dendritic cell-based vaccines, inducing similar CTL responses as well as providing an effective regimen for preventing and suppressing s.c. and metastatic tumors. Therefore, with the help of iNKT, peptide-pulsed B cells can establish long-lasting antitumor immunity and so show promise as the basis for an alternative cell-based vaccine.

DNA vaccines: successes and limitations in cancer and infectious disease

Vaccination with plasmid DNA is an active area of investigation that is being applied to diseases including cancer and microbial pathogens associated with infectious diseases. Since its discovery, great progress has been made with the administration of DNA vaccines to initiate specific and effective immune responses against targeted illnesses. However, many obstacles still face its use in prophylactic and therapeutic vaccination scenarios. The nature of these difficulties alongside the successes and future of plasmid DNA will be discussed.

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.

Combined therapy of an established, highly aggressive breast cancer in mice with paclitaxel and a unique DNA-based cell vaccine

Here, we describe the enhanced benefits of treating a highly aggressive breast cancer in mice with a combination of paclitaxel and immunization with a unique DNA-based cell vaccine. An adenocarcinoma was isolated from a spontaneous neoplasm that arose in the mammary gland of a C3H/He mouse (H-2(k)) (SB5b cells). The vaccine was prepared by transfer of genomic DNA-fragments (25 kb) from the breast cancer cells into a mouse fibroblast cell line (LM), modified to enhance its immunogenic properties. As the transferred DNA is integrated, and replicated as the recipient cells divide, the vaccine could be prepared from relatively small numbers of cancer cells (10(7) = 4 mm tumor). SB5b cells were injected into the mammary fat pad of naïve C3H/He mice, which are highly susceptible to the growth of the cancer cells. When the tumors reached 3 mm, the mice were injected s.c. with a noncurative dose of paclitaxel. Six days later, when immune competence returned, the mice received the first of 3 weekly s.c. injections of the vaccine. The combined therapy induced robust cellular immunity to the breast cancer, mediated by CD8+ and NK/LAK cells, which resulted in prolonged survival. The immunity was specific, as immunization with a vaccine prepared by transfer of DNA from B16 melanoma cells into the fibroblasts failed to induce immunity to the breast cancer. This type of vaccine raises the possibility that an analogous strategy could be used in the treatment of breast cancer patients at an early stage of the disease.

Hantaan/Andes virus DNA vaccine elicits a broadly cross-reactive neutralizing antibody response in nonhuman primates

At least four hantavirus species cause disease with prominent renal involvement-hemorrhagic fever with renal syndrome (HFRS); and several hantavirus strains cause disease with significant pulmonary involvement-hantavirus pulmonary syndrome (HPS). The most prevalent and lethal hantaviruses associated with HFRS and HPS are Hantaan virus (HTNV) and Andes virus (ANDV), respectively. Here, we constructed a DNA vaccine plasmid (pWRG/HA-M) that contains both the HTNV and ANDV M gene segments. Rhesus macaques vaccinated with pWRG/HA-M produced antibodies that bound the M gene products (i.e., G1 and G2 glycoproteins), and neutralized both HTNV and ANDV. Neutralizing antibody titers elicited by the dual-immunogen pWRG/HA-M, or single-immunogen plasmids expressing only the HTNV or ANDV glycoproteins, increased rapidly to high levels after a booster vaccination administered 1-2 years after the initial vaccination series. Memory responses elicited by this long-range boost exhibited an increased breadth of cross-neutralizing activity relative to the primary response. This is the first time that hantavirus M gene-based DNA vaccines have been shown to elicit a potent memory response, and to elicit antibody responses that neutralize viruses that cause both HFRS and HPS.

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.

Gene therapy for carcinoma of the breast

In view of the limited success of available treatment modalities for breast cancer, alternative and complementary strategies need to be developed. The delineation of the molecular basis of breast cancer provides the possibility of specific intervention by gene therapy through the introduction of genetic material for therapeutic purposes. In this regard, several gene therapy approaches for carcinoma of the breast have been developed. These approaches can be divided into six broad categories: (1) mutation compensation, (2) molecular chemotherapy, (3) proapoptotic gene therapy, (4) antiangiogenic gene therapy, (5) genetic immunopotentiation, and (6) genetic modulation of resistance/sensitivity. Clinical trials for breast cancer have been initiated to evaluate safety, toxicity, and efficacy. Combined modality therapy with gene therapy and chemotherapy or radiation therapy has shown promising results. It is expected that as new therapeutic targets and approaches are identified and advances in vector design are realized, gene therapy will play an increasing role in clinical breast cancer treatment.

Fusion to Listeriolysin O and delivery by Listeria monocytogenes enhances the immunogenicity of HER-2/neu and reveals subdominant epitopes in the FVB/N mouse

Five overlapping fragments of rat HER-2/neu have been expressed in recombinant Listeria monocytogenes. Each fragment of HER-2/neu is secreted as a fusion protein with a truncated, nonhemolytic form of listeriolysin O (LLO). Lm-LLO-EC1, Lm-LLO-EC2, and Lm-LLO-EC3 overlap the extracellular domain of HER-2/neu, whereas Lm-LLO-IC1 and Lm-LLO-IC2 span the intracellular domain. All five strains controlled the growth of established NT-2 tumors, a rat HER-2/neu-expressing tumor line derived from a spontaneously arising mammary tumor in a FVB/N HER-2/neu-transgenic mouse. The antitumor effect of each of these vaccine constructs was abrogated by the in vivo depletion of CD8(+) T cells, although only one known epitope has been defined previously and is present in Lm-LLO-EC2. Anti-HER-2/neu CTL responses were generated by each of the rLm vaccine constructs. With the use of a panel of 3T3 cell lines expressing overlapping fragments of HER-2/neu, regions of HER-2/neu with potential CD8(+) T cell epitopes have been defined. DNA vaccines expressing either a fragment or full-length HER-2/neu were constructed in LLO-fused and non-LLO-fused forms. CTL analysis of the DNA vaccines revealed a broadening in the regions of HER-2/neu recognizable as targets when the target Ag is fused to LLO. These studies show the efficacy of L. monocytogenes-based HER-2/neu vaccines in a murine model of breast cancer and also that the immunogenicity of self-Ags can be increased by fusion to LLO and delivery by L. monocytogenes revealing subdominant epitopes.

Optimization of codon usage enhances the immunogenicity of a DNA vaccine encoding mycobacterial antigen Ag85B

In spite of its many other benefits, DNA vaccine is limited in its application by its insufficient immunogenicity. One promising approach for enhancing its immunogenicity is to maximize its expression in the immunized host. In the current study, we investigated whether codon optimization of the mycobacterial antigen Ag85B gene could enhance the expression and immunogenicity of the Ag85B DNA vaccine. We generated a synthetic humanized Ag85B (hAg85B) gene in which codon usage was optimized for expression in human cells. DNA plasmids with codon-optimized hAg85B increased the level of protein expression in vitro and in vivo. DNA vaccine with hAg85B induced stronger Th1-like and cytotoxic T-cell immune responses in BALB/c mice and generated higher protective immunity in a BALB/c mouse model of Mycobacterium tuberculosis aerosol infection than did the DNA vaccine with wild-type Ag85B. Therefore, our results suggest that codon optimization of mycobacterial antigens (e.g., Ag85B) could improve protein expression and thereby enhance the immunogenicity of DNA vaccines against M. tuberculosis.

Characterization of immune responses induced by intramuscular vaccination with DNA vaccines encoding measles virus hemagglutinin and/or fusion proteins

Measles virus (MV) hemagglutinin (MV-H) and fusion (MV-F) proteins induce plaque reduction neutralizing (PRN) antibodies and cell-mediated immune responses that protect against clinical measles. DNA vaccines that encode MV-H and MV-F are being investigated as a new generation of measles vaccine to protect infants too young to receive currently licensed attenuated measles vaccines. However, it is unclear whether DNA vaccines encoding both MV-H and MV-F act synergistically to induce stronger immunity than immunization with plasmids encoding MV-H or MV-F alone. To address this question, we generated Sindbis virus-based pSINCP DNA vaccines that encode either MV-H or MV-F alone or bicistronic or fusion system vectors that encode both MV-H and MV-F (to mimic MV infection where both MV-H and MV-F proteins are expressed by the same mammalian cell). Mice immunized with DNA vaccine encoding MV-H alone developed significantly greater PRN titers than mice immunized with bicistronic constructs. Interestingly, the presence of MV-F in the bicistronic constructs stimulated serum MV-specific immunoglobulin G of reduced avidity. By contrast, mice immunized with bicistronic constructs induced equivalent or higher levels of MV-specific gamma interferon responses than mice immunized with DNA vaccine encoding MV-H alone. These data will help guide the design of DNA-based MV vaccines to be used early in life in a heterologous prime-boost strategy.

Coimmunization with an Optimized IL-15 Plasmid Results in Enhanced Function and Longevity of CD8 T Cells That Are Partially Independent of CD4 T Cell Help

DNA vaccines are a promising technology for the induction of Ag-specific immune responses, and much recent attention has gone into improving their immune potency. In this study we test the feasibility of delivering a plasmid encoding IL-15 as a DNA vaccine adjuvant for the induction of improved Ag-specific CD8(+) T cellular immune responses. Because native IL-15 is poorly expressed, we used PCR-based strategies to develop an optimized construct that expresses 80-fold higher than the native IL-15 construct. Using a DNA vaccination model, we determined that immunization with optimized IL-15 in combination with HIV-1gag DNA constructs resulted in a significant enhancement of Ag-specific CD8(+) T cell proliferation and IFN-gamma secretion, and strong induction of long-lived CD8(+) T cell responses. In an influenza DNA vaccine model, coimmunization with plasmid expressing influenza A PR8/34 hemagglutinin with the optimized IL-15 plasmid generated improved long term CD8(+) T cellular immunity and protected the mice against a lethal mucosal challenge with influenza virus. Because we observed that IL-15 appeared to mostly adjuvant CD8(+) T cell function, we show that in the partial, but not total, absence of CD4(+) T cell help, plasmid-delivered IL-15 could restore CD8 secondary immune responses to an antigenic DNA plasmid, supporting the idea that the effects of IL-15 on CD8(+) T cell expansion require the presence of low levels of CD4 T cells. These data suggest a role for enhanced plasmid IL-15 as a candidate adjuvant for vaccine or immunotherapeutic studies.

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.