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 anti-tumor efficacy of a GM-CSF-secreting tumor cell vaccine is not inhibited by docetaxel administration

Docetaxel has demonstrated therapeutic efficacy against breast, prostate, and ovarian cancer and other solid tumors. The tumoricidal activity of docetaxel is mainly attributed to its ability to block microtubule depolymerization, thus inducing G₂-M arrest and apoptosis. Mounting evidence indicates that docetaxel also possesses immunomodulatory activity such as augmenting macrophage and lymphokine activated killer activity and inducing pro-inflammatory cytokines, suggesting that docetaxel may be a good chemotherapeutic agent to combine with cancer immunotherapies, assuming that it does not inhibit the vaccine-induced immune response. The anti-tumor activity of the combination of docetaxel and a GM-CSF-secreting B16F10 tumor cell vaccine (B16.GM) was evaluated in the murine B16 melanoma model. Dose levels of docetaxel and the B16.GM vaccine known to be ineffective when used as single agents were selected. Three iv treatments of 6 mg/kg docetaxel per injection given on days 5, 9, and 13 after tumor challenge or a single vaccination with 2–3×10⁶ B16.GM cells on day 3 were ineffective at inhibiting tumor growth when used as single agents [median survival time (MST)=24 days in both treatment groups and in control animals]. However, combination of docetaxel and B16.GM vaccine significantly delayed tumor growth, increasing MST to 45 days. A similar improvement in anti-tumor efficacy was observed using multiple treatment cycles of the B16.GM vaccine/docetaxel combination. Administration of docetaxel every 4 days between bi-weekly B16.GM vaccinations increased the median survival of tumor-bearing mice from 31 to 52 days compared to multiple B16.GM vaccinations alone. In summary, these data demonstrate that rather than inhibiting the anti-tumor effects of a GM-CSF-secreting tumor cell vaccine, docetaxel combined with a whole cell vaccine significantly inhibits tumor growth, increases survival time and does not impede T-cell activation in the murine B16F10 melanoma tumor model. GM-secreting tumor cell vaccines in combination with docetaxel may represent a new strategy for combining chemo and immunotherapy for cancer.     

增强恶性疟原虫DNA疫苗免疫反应的研究

构建了含有恶性疟原虫抗原基因 ( AWTE)及白介素 2基因的重组质粒 p CMV- AWTE以及p CMV- IL2、p CMV- IL2 - AWTE、p RSV- AWTE。将纯化的质粒混合后免疫小鼠 ,3次免疫后比较其诱导机体产生的免疫应答的水平 ,发现 IL- 2可以明显地提高机体的细胞免疫 ,而对体液免疫的影响甚微。麻醉剂、蔗糖、免疫剂量等因素也可以不同程度地提高机体的免疫应答水平 ,RSV启动子与 CMV启动子对免疫应答水平无明显的影响     

Enhancement of the immunogenicity of a porcine circovirus type 2 DNA vaccine by a recombinant plasmid coexpressing capsid protein and porcine interleukin‐6 in mice

The development of effective vaccines against porcine circovirus type 2 (PCV2) has been accepted as an important strategy in the prophylaxis of post‐weaning multisystemic wasting syndrome; a DNA vaccine expressing the major immunogenic capsid (Cap) protein of PCV2 is considered to be a promising candidate. However, DNA vaccines usually induce weak immune responses. In this study, it was found that the efficacy of a DNA vaccine expressing Cap protein was improved by simultaneous expression of porcine IL‐6. A plasmid (pIRES‐ORF2/IL6) separately expressing both Cap protein and porcine IL‐6 was constructed and compared with another plasmid (pIRES‐ORF2) expressing Cap protein for its potential to induce PCV2‐specific immune responses. Mice were vaccinated i.m. twice at 3 week intervals and the induced humoral and cellular responses evaluated. All animals vaccinated with pIRES‐ORF2/IL6 and pIRES‐ORF2 developed specific anti‐PCV2 antibodies (according to enzyme‐linked immunosorbent assay) and a T lymphocyte proliferation response. The percentages of CD3⁺, CD3⁺CD8⁺, and CD3⁺CD4⁺ subgroups of peripheral blood T‐lymphocytes were significantly higher in mice immunized with pIRES‐ORF2/IL6 than in those that had received pIRES‐ORF2. After challenge with the virulent PCV2 Wuzhi isolate, mice vaccinated with pIRES‐ORF2/IL6 had significantly less viral replication than those vaccinated with pIRES‐ORF2, suggesting that the protective immunity induced by pIRES‐ORF2/IL6 is superior to that induced by pIRES‐ORF2.     

Intratumoral delivery of vector mediated IL-2 in combination with vaccine results in enhanced T cell avidity and anti-tumor activity

Systemic IL-2 is currently employed in the therapy of several tumor types, but at the price of often severe toxicities. Local vector mediated delivery of IL-2 at the tumor site may enhance local effector cell activity while reducing toxicity. To examine this, a model using CEA-transgenic mice bearing established CEA expressing tumors was employed. The vaccine regimen was a s.c. prime vaccination with recombinant vaccinia (rV) expressing transgenes for CEA and a triad of costimulatory molecules (TRICOM) followed by i.t. boosting with rF-CEA/TRICOM. The addition of intratumoral (i.t.) delivery of IL-2 via a recombinant fowlpox (rF) IL-2 vector greatly enhanced anti-tumor activity of a recombinant vaccine, resulting in complete tumor regression in 70–80% of mice. The anti-tumor activity was shown to be dependent on CD8⁺ cells and NK1.1⁺. Cellular immune assays revealed that the addition of rF-IL-2 to the vaccination therapy enhanced CEA-specific tetramer⁺ cell numbers, cytokine release and CTL lysis of CEA⁺ targets. Moreover, tumor-bearing mice vaccinated with the CEA/TRICOM displayed an antigen cascade, i.e., CD8⁺ T cell responses to two other antigens expressed on the tumor and not the vaccine: wild-type p53 and endogenous retroviral antigen gp70. Mice receiving rF-IL-2 during vaccination demonstrated higher avidity CEA-specific, as well as higher avidity gp70-specific, CD8⁺ T cells when compared with mice vaccinated without rF-IL-2. These studies demonstrate for the first time that the level and avidity of antigen specific CTL, as well as the therapeutic outcome can be improved with the use of i.t. rF-IL-2 with vaccine regimens.     

针对潜伏结核感染的 A39 DNA 疫苗构建及其免疫原性研究

选取结核分枝杆菌潜伏相关抗原Rv2029c、结核分枝杆菌优秀抗原Ag85A和Rv3425,构建针对潜伏感染的结核分枝杆菌DNA疫苗pVAX1／Ag85A-Rv3425-Rv2029c （A39）,并对其免疫原性进行研究。首先用聚合酶链反应（PCR）扩增Ag85A基因,构建重组质粒pVAX1／Ag85A （A）;PCR扩增 Ag85A-Rv3425连接片段,插入pVAX1载体,构建重组质粒pVAX1／Ag85A-Rv3425（A3）;PCR扩增Rv2029c基因,插入A3,构建重组质粒pVAX1／Ag85A-Rv3425-Rv2029c （A39）。将构建成功的重组质粒转入 HEK293T细胞,蛋白免疫印迹法验证质粒在真核细胞中得到表达。在大肠埃希菌BL21中成功表达和纯化去除信号肽的Ag85A、Rv3425和Rv2029c蛋白。用质粒免疫C57BL／6小鼠,共分为5组：PBS、pVAX1、A、A3和A39组,采用电脉冲导入免疫,每2周免疫1次,共3次,用酶联免疫斑点检测（ELISPOT）、酶联免疫吸附试验（ELISA）、流式细胞术等方法检测细胞免疫和体液免疫水平。结果显示,A39免疫小鼠后,能引发强烈的细胞免疫反应﹝γ干扰素（IFN-γ）、肿瘤坏死因子α（TNF-α）和白细胞介素2（IL-2）高水平分泌﹞,外周血CD4＋／CD8＋ T细胞比值增加,CD8＋穿孔素＋ T细胞比例增加。结果表明,构建的A39 DNA疫苗能引发强烈的免疫反应,显示出良好的抗结核潜力,可作为结核分枝杆菌新型候选疫苗。     

携带TGEV DNA疫苗减毒沙门氏菌的构建及安全性与免疫性分析

【目的】探讨以减毒沙门氏菌为载体,进行TGEV DNA疫苗口服免疫可行性。【方法】通过RT-PCR扩增TGEV四川株（SC-H）S基因5’端约2.1 kb的主要抗原位点片段,将其插入真核表达载体pVAX1,构建重组质粒pVAX-S,体外转染COS7细胞,间接免疫荧光检测S基因表达。通过电转化将pVAX-S转入减毒鼠伤寒沙门氏菌SL7207,构建SL7207（pVAX-S）重组菌,并在体外感染小鼠腹腔巨噬细胞,以RT-PCR、间接免疫荧光检测细胞内S基因的转录与表达情况。将SL7207（pVAX-S）重组菌以5×108、1×109、2×109CFU剂量口服接种BALB/c小鼠,分析其安全性,并以1×109CFU剂量的重组菌3次免疫BALB/c小鼠,通过间接ELISA检测免疫小鼠的血清IgG与肠道粘膜IgA抗体。【结果】成功构建重组质粒pVAX-S,且重组质粒能在COS7细胞中表达。重组菌SL7207（pVAX-S）感染巨噬细胞后检测到目的基因的转录、表达。小鼠口服接种不同剂量重组菌,具有良好的安全性。免疫小鼠于二免后两周可检测到针对TGEV S蛋白的特异性血清IgG与肠道粘膜IgA抗体,且三免后两周与SL7207（pVAX1）空载体免疫组间分别存在显著性差异（P<0.05）和极显著性差异（P<0.01）。【结论】携带TGEV DNA疫苗的减毒沙门氏菌小鼠试验显示了良好的免疫原性与安全性。     

Protective immunity conferred by porcine circovirus 2 ORF2‐based DNA vaccine in mice

Post‐weaning multisystemic wasting syndrome (PMWS) associated with porcine circovirus type 2 (PCV2) has caused the swine industry significant health challenges and economic damage. Although inactivated and subunit vaccines against PMWS have been used widely, so far no DNA vaccine is available. In this study, with the aim of exploring a new route for developing a vaccine against PCV2, the immunogenicity of a DNA vaccine was evaluated in mice. The pEGFP‐N1 vector was used to construct a PCV2 Cap gene recombinant vaccine. To assess the immunogenicity of pEGFP‐Cap, 80 BALB/c mice were immunized three times at 2 weekly intervals with pEGFP‐Cap, LG‐strain vaccine, pEGFP‐N1 vector or PBS and then challenged with PCV2. IgG and cytokines were assessed by indirect ELISA and ELISA, respectively. Specimens stained with hematoxylin and eosin (HE) and immunohistochemistry (IHC) techniques were examined histopathologically. It was found that vaccination of the mice with the pEGFP‐Cap induced solid protection against PCV2 infection through induction of highly specific serum IgG antibodies and cytokines (IFN‐γ and IL‐10), and a small PCV2 viral load. The mice treated with the pEGFP‐Cap and LG‐strain developed no histopathologically detectable lesions (HE stain) and IHC techniques revealed only a few positive cells. Thus, this study demonstrated that recombinant pEGFP‐Cap substantially alleviates PCV2 infection in mice and provides evidence that a DNA vaccine could be an alternative to PCV2 vaccines against PMWS.     

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.     

恶性疟原虫抗原表位的亚单位疫苗与DNA疫苗的联合免疫

构建了含有恶性疟原虫抗原基因 ( AWTE)的真核表达质粒 p CMV- AWTE,以及能在大肠杆菌中得到分泌性表达的原核表达质粒 p MC0 5 ,表达的蛋白 AWTE保持了疟原虫抗原的抗原性。将 p CMV- AWTE以及 AWTE两者混合各 1 0μg鼻腔免疫小鼠 ,一次后诱导机体产生了较高水平的体液免疫及细胞免疫     

Synthesis and evaluation of novel pyrimidine-based dual EGFR/Her-2 inhibitors

A structure-activity relationship study of 4-anilinopyrimidines for dual EGFR/Her-2 inhibitor has resulted in the identification of 4-anilino-5-alkenyl or 5-alkynyl-6-methylpyrimidine derivatives that have exhibited effective inhibitory activity against both enzymes. The presence of 5-alkenyl or 5-alkynyl moiety bearing terminal hydrophilic group played important role for inhibition of these enzymes. Selected compounds in the series demonstrated some activity against Her-2 dependent cell line (BT474).     

DNA疫苗研究进展

DNA疫苗是20世纪90年代初出现的一种新型疫苗,近年来发展迅速,在预防和治疗病毒性疾病及肿瘤等方面效果显著。同传统的疫苗相比,DNA疫苗具有免疫效果好、生产成本低、临床应用方便等优点,但同样存在安全性的担忧。对DNA疫苗的发展及其作用机制、优势进行了综述,并对DNA疫苗的安全性提出了自己的观点与看法,可供DNA疫苗的研究者参考。     

Epitope-driven DNA vaccine design employing immunoinformatics against B-cell lymphoma: a biotech's challenge

DNA vaccination has been widely explored to develop new, alternative and efficient vaccines for cancer immunotherapy. DNA vaccines offer several benefits such as specific targeting, use of multiple genes to enhance immunity and reduced risk compared to conventional vaccines. Rapid developments in molecular biology and immunoinformatics enable rational design approaches. These technologies allow construction of DNA vaccines encoding selected tumor antigens together with molecules to direct and amplify the desired effector pathways, as well as highly targeted vaccines aimed at specific epitopes. Reliable predictions of immunogenic T cell epitope peptides are crucial for rational vaccine design and represent a key problem in immunoinformatics. Computational approaches have been developed to facilitate the process of epitope detection and show potential applications to the immunotherapeutic treatment of cancer. In this review a number of different epitope prediction methods are briefly illustrated and effective use of these resources to support experimental studies is described. Epitope-driven vaccine design employs these bioinformatics algorithms to identify potential targets of vaccines against cancer. In this paper the selection of T cell epitopes to develop epitope-based vaccines, the need for CD4(+) T cell help for improved vaccines and the assessment of vaccine performance against tumor are reviewed. We focused on two applications, namely prediction of novel T cell epitopes and epitope enhancement by sequence modification, and combined rationale design with bioinformatics for creation of new synthetic mini-genes. This review describes the development of epitope-based DNA vaccines and their antitumor effects in preclinical research against B-cell lymphoma, corroborating the usefulness of this platform as a potential tool for cancer therapy. Achievements in the field of DNA vaccines allow to overcome hurdles to clinical translation. In a scenario where the vaccine industry is rapidly changing from a mostly empirical approach to a rational design approach, these new technologies promise to discover and develop high-value vaccines, creating a new opportunity for future markets.     

Co-administration of GP96 and Her2/neu DNA vaccine in a Her2 breast cancer model

Heat-shock proteins have biochemical and immunological roles in chaperoning/signaling and activation of innate and adaptive immune responses, respectively. Their effect on the immune response is due to a phenomenon known as cross-priming of antigen, in which exogenous antigens are presented via MHC class I by antigen presenting cells. GP96 exerts adjuvant activity with some viral and bacterial antigens when applied in the form of a DNA vaccine. In this study, animals with Her2-expressing tumors were vaccinated by co-administration of GP96+ Her2/neu DNA vaccines. Analyses of the immune response, 2 weeks after the last immunization revealed decreased CD4+ CD25+ Foxp3+ naturally occurring regulatory T cells (Tregs) at the tumor site and increased IFN-γ/IL-4 level. Nevertheless, the graph of tumor size demonstrated a bi-phasic pattern in which partial control of tumor progression initially occurred, but finally its effectiveness was inversely affected by tumor size.     

乙型肝炎病毒DNA疫苗的研究进展

预防与控制乙型肝炎发病的乙型肝炎病毒(HBV)疫苗,是有重大的社会和经济意义。HBV的持续感染可引起慢性肝脏疾患,并逐步发展为肝硬化和肝细胞癌(HCC)。目前的乙肝重组亚单位疫苗可以使90％的接种产生保护性抗体;但是对慢性HBV携带,由于其机体对HBsAg蛋白产生耐受,不能产生体液和细胞免疫,因此它只能作为一种预防性的疫苗。DNA疫苗(基因疫苗)是一种新的疫苗技术,通过向体内递送编码抗原的细菌质粒,刺激产生特异的体液和细胞免疫反应。在小鼠和其他的肝炎病毒感染动物模型中,HBV DNA疫苗可以特异性地引起体液和细胞免疫,清除HBV转基因动物血循环中的HBsAg颗粒和HBV DNA。如果加入各种免疫调节细胞因子的基因,可以进一步提高HBV DNA疫苗的免疫效果,因此它不仅可作为预防性疫苗,也可作为治疗型疫苗。     

Synergistic antitumor effect of a human papillomavirus DNA vaccine harboring E6E7 fusion gene and vascular endothelial growth factor receptor 2 gene

Human papillomavirus (HPV) has been identified as the primary etiological factor in cervical cancer as well as in subsets of anogenital and oropharyngeal cancers. The two HPV viral oncoproteins, E6 and E7, are uniquely and consistently expressed in all HPV‐infected cells and are therefore promising targets for therapeutic vaccination. In order to achieve a synergistic antitumor and anti‐angiogenesis effect, we designed and constructed a novel DNA vaccine that can express the HPV 16 E6E7 fusion protein and VEGFR2 in the same reading frame. A series of DNA plasmids encoding E6E7, VEGFR2 and their conjugates were constructed and injected into mice. The resultant humoral and cellular immune responses were detected by ELISA and enzyme‐linked immunospot (ELISPOT), respectively. To evaluate the antitumor efficacy of these plasmids, tumor‐bearing mice expressing the E6E7 fusion protein were constructed. After injection into the tumor‐bearing mouse model, the plasmid harboring the E6E7 fusion gene and VEGFR2 showed stronger inhibition of tumor growth than the plasmid expressing E6E7 or VEGFR2 alone, which indicated that the combination of E6E7 and VEGFR2 could exert a synergistic antitumor effect. These observations emphasize the potential of a synergistic antitumor and anti‐angiogenesis strategy using a DNA vaccine, which could be a promising approach for tumor immunotherapy.     

预防SARS病毒核酸疫苗的构建

本研究通过反转录-PCR获得了SARS冠状病毒辐条样蛋白、核衣壳蛋白和膜蛋白基因,将所获得的可能与免疫保护相关的基因克隆至核酸疫苗表达载体pcDNA-ThyA中,酶切及序列分析结果均表明载体构建正确,该候选DNA疫苗已用于动物免疫实验。     

DNA vaccine with discontinuous T‐cell epitope insertions into HSP65 scaffold as a potential means to improve immunogenicity of multi‐epitope Mycobacterium tuberculosis vaccine

DNA‐based vaccine is a promising candidate for immunization and induction of a T‐cell‐focused protective immune response against infectious pathogens such as Mycobacterium tuberculosis (M. tb). To induce multi‐functional T response against multi‐TB antigens, a multi‐epitope DNA vaccine and a ‘protein backbone grafting’ design method is adopted to graft five discontinuous T‐cell epitopes into HSP65 scaffold protein of M. tb for enhancement of epitope processing and immune presentation. A DNA plasmid with five T‐cell epitopes derived from ESAT‐6, Ag85B, MTB10.4, PPE25 and PE19 proteins of H37Rv strain of M. tb genetically inserted into HSP65 backbone was constructed and designated as pPES. After confirmation of its in vitro expression efficiency, pPES DNA was i.m. injected into C57BL/6 mice with four doses of 50 µg DNA followed by mycobacterial challenge 4 weeks after the final immunization. It was found that pPES DNA injection maintained the ability of HSP65 backbone to induce specific serum IgG. ELISPOT assay demonstrated that pPES epitope‐scaffold construct was significantly more potent to induce IFN‐γ⁺ T response to five T‐cell epitope proteins than other DNA constructs (with epitopes alone or with epitope series connected to HSP65), especially in multi‐functional‐CD4⁺ T response. It also enhanced granzyme B⁺ CTL and IL‐2⁺ CD8⁺ T response. Furthermore, significantly improved protection against Mycobacterium bovis BCG challenge was achieved by pPES injection compared to other DNA constructs. Taken together, HSP65 scaffold grafting strategy for multi‐epitope DNA vaccine represents a successful example of rational protein backbone engineering design and could prove useful in TB vaccine design.     

稳定携带H5亚型禽流感病毒候选DNA疫苗减毒沙门氏菌的构建及其免疫原性

采用PCR技术从重组质粒pVAX1-HA扩增出禽流感病毒JSGO(H5N1)株的血凝素(HA)基因,将其克隆入真核表达质粒pmcDNA3.1 中,获得重组表达质粒pmcDNA3.1-HA。通过电穿孔转化法将重组质粒转入减毒鼠伤寒沙门氏菌SL7207*,构建成功携带DNA疫苗的重组沙门氏菌SL7207*(pmcDNA3.1-HA)。经体内体外试验证实,重组质粒pmcDNA3.1-HA在沙门氏菌中的稳定性显著高于pcDNA3.1-HA。将重组菌SL7207*(pmcDNA3.1-HA)和SL7207*(pcDNA3.1-HA)分别以2×109CFU剂量两次口服免疫BALB/c小鼠,免疫小鼠可产生针对禽流感病毒HA蛋白的黏膜抗体。重组菌以5×109CFU剂量两次口服免疫试验鸡,免疫鸡的小肠样品中可测到针对禽流感病毒HA蛋白的黏膜抗体,且SL7207*(pmcDNA3.1-HA)免疫组的抗体效价高于SL7207*(pcDNA3.1-HA)免疫组。免疫保护试验结果显示,SL7207*(pmcDNA3.1-HA)和SL7207*(pcDNA3.1-HA)免疫组的免疫保护率均与空载体组之间存在显著性差异(P<0.05),且SL7207*(pmcDNA3.1-HA)免疫组的保护率较SL7207*(pcDNA3.1-HA)免疫组提高了22.6%,说明稳定携带H5亚型禽流感病毒DNA疫苗的减毒沙门氏菌具有良好的免疫原性和免疫保护性。