Zymosan enhances the immune response to DNA vaccine for human immunodeficiency virus type-1 through the activation of complement system

In the present study, the adjuvant effect of zymosan on human immunodeficiency virus type-1 (HIV-1)-specific DNA vaccine and the mechanism of this enhancement were studied in a murine model. We coinoculated zymosan with our candidate HIV-1 specific DNA vaccine (pCMV160IIIB) into skeletal muscles of BALB/c mice. Higher levels of both humoral immune response and HIV-specific delayed-type hypersensitivity (DTH) response were observed when zymosan was coinoculated with pCMV160IIIB compared with that obtained using pCMV160IIIB alone. HIV-specific cytotoxic T lymphocyte (CTL) activity was also enhanced. This enhancing activity was suppressed when coinoculated to the fifth complement (C5)-deficient DDD and AKR mice. The enhanced activity was also suppressed when anti-C3 antibody was inoculated to mice intramuscularly. There was significant induction of immunoglobulin G2a (IgG2a) and interferon-gamma (IFN-gamma) in pCMV160IIIB vaccine with zymosan. These results suggest that zymosan-mediated DNA vaccination enhances helper T cell (Th) 1-mediated immunity. The effect is suggested to be based on the consequences of its recruitment and activation of macrophages, dendritic cells or antigen-presenting cells (APC) through complement activation, especially through the alternative pathway. Taken together, these results suggest that zymosan can be an effective immunological adjuvant in DNA vaccination against HIV-1.     

Human immunodeficiency virus type-1-specific immune responses induced by DNA vaccination are greatly enhanced by mannan-coated diC14-amidine

Use of mannan-coated N-t-butyl-N′-tetradecyl-3-tetradecylamino-propion-amidine (diC14-amidine) as an adjuvant for a DNA vaccine encoding glycoprotein 160 of human immunodeficiency virus type-1 (HIV-1) enhanced the antigen-specific immune responses. The role of interferon-γ (IFN-γ) and interleukin-12 in the mechanism of adjuvant action was also evaluated. Coating of diC14-amidine with mannan significantly augmented the HIV-specific delayed-type hypersensitivity reaction induced by the immunogenic DNA. HIV-1-specific cytotoxic T lymphocyte activity was also markedly enhanced by the mannan-diC14-amidine cocktail. An immunomodulatory effect of this cocktail was inhibited by treatment with anti-IFN-γ monoclonal antibody in vivo, which suggests that IFN-γ plays an important role in inducing cell-mediated immunity by the DNA vaccine containing this adjuvant. The results of both antigen-specific immunoglobulin isotype analysis and cytokine measurement showed that the immunogenic DNA incorporated into mannan-coated diC14-amidine elicits Th1-biased immune responses.     

Robust HIV-specific immune responses were induced by DNA vaccine prime followed by attenuated recombinant vaccinia virus (LC16m8 strain) boost

Recombinant vaccinia virus-based vaccine combined with DNA vaccine has produced a protective immune response against HIV infection in non-human primates. In this study, we explored the immunogenicity of a recombinant vaccinia virus (LC16m8 strain), which has been used in children without severe side effects. The vaccinia virus expressing an HIV(89.6)env gene (vLC-Env) alone or combined with a DNA vaccine expressing the HIV(89.6)env gene (pCAG-Env) was characterized in BALB/c mice. Vaccination of vLC-Env induced much higher HIV-specific humoral and cell-mediated immune responses than that of pCAG-Env. Priming with pCAG-Env further enhanced vLC-Env induced immune responses, especially cell-mediated immune response. Moreover, efficient expression of Env protein was achieved following infection of bone marrow dendritic cells by vLC-Env in vitro. Administration of vLC-Env-infected dendritic cells to mice generated a high cell-mediated immune response. These results demonstrate that priming with pCAG-Env and boosting with vLC-Env represents a logical candidate for vaccination against HIV infection.     

Induction of specific immune responses by severe acute respiratory syndrome coronavirus spike DNA vaccine with or without interleukin-2 immunization using different vaccination routes in mice

DNA vaccines induce humoral and cellular immune responses in animal models and humans. To analyze the immunogenicity of the severe acute respiratory syndrome (SARS) coronavirus (CoV), SARS-CoV, spike DNA vaccine and the immunoregulatory activity of interleukin-2 (IL-2), DNA vaccine plasmids pcDNA-S and pcDNA-IL-2 were constructed and inoculated into BALB/c mice with or without pcDNA-IL-2 by using three different immunization routes (the intramuscular route, electroporation, or the oral route with live attenuated Salmonella enterica serovar Typhimurium). The cellular and humoral immune responses were assessed by enzyme-linked immunosorbent assays, lymphocyte proliferation assays, enzyme-linked immunospot assays, and fluorescence-activated cell sorter analyses. The results showed that specific humoral and cellular immunities could be induced in mice by inoculating them with SARS-CoV spike DNA vaccine alone or by coinoculation with IL-2-expressing plasmids. In addition, the immune response levels in the coinoculation groups were significantly higher than those in groups receiving the spike DNA vaccine alone. The comparison between the three vaccination routes indicated that oral vaccination evoked a vigorous T-cell response and a weak response predominantly with subclass immunoglobulin G2a (IgG2a) antibody. However, intramuscular immunization evoked a vigorous antibody response and a weak T-cell response, and vaccination by electroporation evoked a vigorous response with a predominant subclass IgG1 antibody response and a moderate T-cell response. Our findings show that the spike DNA vaccine has good immunogenicity and can induce specific humoral and cellular immunities in BALB/c mice, while IL-2 plays an immunoadjuvant role and enhances the humoral and cellular immune responses. Different vaccination routes also evoke distinct immune responses. This study provides basic information for the design of DNA vaccines against SARS-CoV.     

Intranasal administration of human immunodeficiency virus type-1 (HIV-1) DNA vaccine with interleukin-2 expression plasmid enhances cell-mediated immunity against HIV-1.

DNA vaccine against human immunodeficiency virus type-1 (HIV-1) can induce substantial levels of HIV-1-specific humoral and cell-mediated immunity. To develop more potent HIV-1 DNA vaccine formulations, we used a murine model to explore the immunomodulatory effects of an interleukin-2 (IL-2) expression plasmid on an HIV-1 DNA vaccine following intranasal administration of the combination. When the vaccine and expression plasmid were incorporated into cationic liposomes and administered to mice, the HIV-1-specific delayed-type hypersensitivity response and cytotoxic T lymphocyte activity were significantly increased. Restimulated immune lymphoid cells showed enhanced production of both IL-2 and interferon-gamma and reduced secretion of IL-4. The level of total antibody to HIV-1 antigen was not greatly changed by coadministration of the DNA vaccine and IL-2 expression plasmid. An analysis of serum HIV-1-specific IgG subclasses showed a significant drop in the IgG1/IgG2a ratio in the group that received the plasmid-vaccine combination. These results demonstrate that the IL-2 expression plasmid strongly enhances the HIV-1-specific immune response via activation of T helper type-1 cells.     

Safety and immunogenicity of a Gag-Pol candidate HIV-1 DNA vaccine administered by a needle-free device in HIV-1-seronegative subjects

OBJECTIVE: To evaluate the safety and immunogenicity of a candidate HIV DNA vaccine administered using a needle-free device. DESIGN: In this phase 1, dose escalation, double-blind, placebo-controlled clinical trial, 21 healthy adults were randomized to receive placebo or 0.5, 1.5, or 4 mg of a single plasmid expressing a Gag/Pol fusion protein. Each participant received repeat immunizations at days 28 and 56 after the first inoculation. Safety and immunogenicity data were collected. RESULTS: The vaccine was well tolerated, with most adverse events being mild injection site reactions, including pain, tenderness, and erythema. No dose-limiting toxicities occurred. HIV-specific antibody response was not detected in any vaccinee by enzyme-linked immunosorbent assay. HIV-specific T-cell responses to Gag or Pol as measured by enzyme-linked immunospot assay and intracellular cytokine staining were of low frequency and magnitude. CONCLUSIONS: This candidate HIV DNA vaccine was safe and well tolerated. No HIV-specific antibody responses were detected, and only low-magnitude HIV-specific T-cell responses were detected in 8 (53%) of 15 vaccinees. This initial product led to the development of a 4-plasmid multiclade HIV DNA Vaccine Research Center vaccine candidate in which envelope genes expressing Env from clades A, B, and C and a Nef gene from clade B have been added.     

Immunomodulatory effects of a plasmid expressing B7-2 on human immunodeficiency virus-1-specific cell-mediated immunity induced by a plasmid encoding the viral antigen

B7 co-stimulation is essential for activating resting T cells following antigen recognition by the T cell receptor. To determine whether B7 has adjuvant activities on human immunodeficiency virus type-1 (HIV-1)-specific immunity induced by inoculation of a plasmid encoding HIV-1 env and rev (DNA vaccine), B7-1 and B7-2 expression plasmids were co-inoculated with the DNA vaccine. The delayed-type hypersensitivity response and cytotoxic T lymphocyte (CTL) activity were significantly enhanced when B7-2 expression plasmid was co-inoculated with the DNA vaccine, but were unaffected when the B7-1 expression plasmid was used with the vaccine instead. The immunological response enhanced by B7-2 decreased below the level of mice immunized with the DNA vaccine in combination with CTLA4Ig, an inhibitor of the B7/CD28 co-stimulatory signal, suggesting that this signal is critical for the enhanced response induced by co-inoculation of the DNA vaccine and B7-2 expression plasmid. This enhancement appeared to occur via an interferon-γ (IFN-γ)-dependent mechanism, as combined administration of the B7-2 plasmid and neutralizing anti-IFN-γ antibody abrogated the virus-specific cell-mediated immunity. These results suggest that this gene-based co-inoculation strategy using HIV-1 viral antigen and B7-2 co-stimulatory molecule could be a powerful means of combating HIV-1 infection.     

Nonneutralizing Functional Antibodies: a New “Old” Paradigm for HIV Vaccines

Animal and human data from various viral infections and vaccine studies suggest that nonneutralizing antibodies (nNAb) without neutralizing activity in vitro may play an important role in protection against viral infection in vivo. This was illustrated by the recent human immunodeficiency virus (HIV) RV144 vaccine efficacy trial, which demonstrated that HIV-specific IgG-mediated nNAb directed against the V2 loop of HIV type 1 envelope (Env) were inversely correlated with risk for HIV acquisition, while Env-specific plasma IgA-mediated antibodies were directly correlated with risk. However, tier 1 NAb in the subset of responders with a low level of plasma Env-specific IgA correlated with decreased risk. Nonhuman primate simian immunodeficiency virus (SIV) and simian-human immunodeficiency virus (SHIV) challenge studies suggest that Env-mediated antibodies are essential and sufficient for protection. A comparison of immune responses generated in human efficacy trials reveals subtle differences in the fine specificities of the antibody responses, in particular in HIV-specific IgG subclasses. The underlying mechanisms that may have contributed to protection against HIV acquisition in humans, although not fully understood, are possibly mediated by antibody-dependent cell-mediated cytotoxicity (ADCC) and/or other nonneutralizing humoral effector functions, such as antibody-mediated phagocytosis. The presence of such functional nNAb in mucosal tissues and cervico-vaginal and rectal secretions challenges the paradigm that NAb are the predominant immune response conferring protection, although this does not negate the desirability of evoking neutralizing antibodies through vaccination. Instead, NAb and nNAb should be looked upon as complementary or synergistic humoral effector functions. Several HIV vaccine clinical trials to study these antibody responses in various prime-boost modalities in the systemic and mucosal compartments are ongoing. The induction of high-frequency HIV-specific functional nNAb at high titers may represent an attractive hypothesis-testing strategy in future HIV vaccine efficacy trials.     

Long-Term Antibody and Immune Memory Response Induced by Pulmonary Delivery of the Influenza Iscomatrix Vaccine

Pulmonary delivery of an influenza Iscomatrix adjuvant vaccine induces a strong systemic and mucosal antibody response. Since an influenza vaccine needs to induce immunological memory that lasts at least 1 year for utility in humans, we examined the longevity of the immune response induced by such a pulmonary vaccination, with and without antigen challenge. Sheep were vaccinated in the deep lung with an influenza Iscomatrix vaccine, and serum and lung antibody levels were quantified for up to 1 year. The immune memory response to these vaccinations was determined following antigen challenge via lung delivery of influenza antigen at 6 months and 1 year postvaccination. Pulmonary vaccination of sheep with the influenza Iscomatrix vaccine induced antigen-specific antibodies in both sera and lungs that were detectable until 6 months postimmunization. Importantly, a memory recall response following antigenic challenge was detected at 12 months post-lung vaccination, including the induction of functional antibodies with hemagglutination inhibition activity. Pulmonary delivery of an influenza Iscomatrix vaccine induces a long-lived influenza virus-specific antibody and memory response of suitable length for annual vaccination against influenza.     

乙型肝炎病毒DNA疫苗电转加强含S-PreS1颗粒的蛋白疫苗在小鼠中免疫效果的研究

目的探索新型有效的HBV治疗性疫苗研制的策略。方法构建含S与PreS1融合基因的HBVDNA疫苗,采用两次蛋白疫苗（含不同佐剂）肌内注射初免,一次DNA疫苗皮内电转免疫加强的联合免疫方式,在小鼠中分析比较了各疫苗所引起的体液与细胞免疫应答。结果HBVDNA疫苗皮内注射加电转可明显增强表面抗原（s）特异的细胞免疫应答（IFN-γ ELISpot分析）及PreS1特异性抗体水平,并以蛋白疫苗加铝佐剂初免组细胞免疫增强效果最明显。结论HBSS1 DNA疫苗结合皮内注射＋电转方式可明显加强含S-PreS1颗粒的蛋白疫苗在小鼠中免疫效果,明显高于蛋白疫苗单独应用。这些研究结果为新型HBV治疗性疫苗的研制与应用提供了依据。     

Enhancement of antibody responses to Bacillus anthracis protective antigen domain IV by use of calreticulin as a chimeric molecular adjuvant

The generation of protective humoral immune responses against the receptor-binding domain (domain IV) of protective antigen [PA(dIV)] of Bacillus anthracis represents a plausible approach against anthrax toxin. In the current study, we have developed a naked DNA vaccine encoding calreticulin (CRT) linked to PA(dIV) of Bacillus anthracis [CRT/PA(dIV)]. We transfected a human embryonic kidney cell line (HEK 293) with CRT/PA(dIV) DNA and performed Western blotting and confocal microscopy analysis. We found that linkage of CRT to PA(dIV) targets PA(dIV) to the endoplasmic reticulum, resulting in secretion of the chimeric CRT/PA(dIV) protein. We then evaluated the ability of CRT/PA(dIV) DNA to generate PA(dIV)-specific antibody responses and protective immunity against lethal anthrax toxin (PA plus lethal factor) challenge. We found that mice immunized with CRT/PA(dIV) DNA were capable of rapidly inducing significantly higher PA(dIV)-specific antibody responses than mice immunized with PA(dIV) DNA alone. Furthermore, we observed that this enhanced antibody response generated by CRT/PA(dIV) DNA was CD4 dependent, since CD4 knockout mice demonstrated a significant reduction in antibody responses. In addition, analysis of the titers and avidity maturation of the induced PA-specific antibodies revealed that vaccination with CRT/PA(dIV) DNA vaccine accelerated the avidity maturation of antibodies to PA(dIV) compared to vaccination with PA(dIV) DNA. Importantly, the enhanced antibody responses correlated to protective immunity against lethal anthrax toxin challenge. Thus, DNA vaccines encoding CRT linked to PA(dIV) may dramatically enhance PA-specific protective antibody responses. Our results have significant clinical applications for biodefense against anthrax toxin.     

Immunization of RANTES expression plasmid with a DNA vaccine enhances HIV-1-specific immunity.

Cytokines play important roles in regulating immune response. This study evaluated the adjuvant effect of an expression plasmid encoding RANTES (regulated on activation normal T-cell expressed and secreted) chemokine on the immunity induced by a DNA vaccine. This vaccine consists of expression plasmids encoding the env and rev genes of human immunodeficiency virus type 1 (HIV-1). DNA vaccination with RANTES plasmid induced significantly higher titers of serum HIV-1-specific IgG and IgG2a antibodies than DNA vaccination alone on both intramuscular and intranasal immunization. This combination also increased HIV-1-specific cytotoxic T lymphocyte activity and delayed-type hypersensitivity. Intranasal immunization induced a higher titer of fecal secretory IgA antibody than intramuscular immunization. These results demonstrate that coadministration of RANTES plasmid dominantly induced HIV-1-specific cell-mediated immunity.     

The use of layered double hydroxides as DNA vaccine delivery vector for enhancement of anti-melanoma immune response

Our previous studies have shown that Mg:Al 1:1 layered double hydroxides (LDH(R1)) nanoparticles could be taken up by the MDDCs effectively and had an adjuvant activity for DC maturation. Furthermore, these LDH(R1) nanoparticles could up-regulate the expression of CCR7 and augment the migration of DCs in response to CCL21. In current study, we have evaluated whether LDH(R1) as DNA vaccine delivery carrier can augment the efficacy of DNA vaccine immunization in vivo. Firstly, we found that LDH(R1) was efficient in combining DNA and formed LDH(R1)/DNA complex with an average diameter of about 80-120 nm. Its high transfection efficiency in vivo delivered with a GFP expression plasmid was also observed. After delivery of pcDNA(3)-OVA/LDH(R1) complex by intradermal immunization in C57BL/6 mice, the LDH(R1) induced an enhanced serum antibody response much greater than naked DNA vaccine. Using B16-OVA melanoma as tumor model, we demonstrated that pcDNA(3)-OVA/LDH(R1) complex enhanced immune priming and protection from tumor challenge in vivo. Furthermore, we showed that LDH(R1) induced dramatically more effective CTL activation and skewed T helper polarization to Th1. Collectively, these findings demonstrate that this LDH(R1)/DNA plasmid complex should be a new and promising way in vaccination against tumor.     

Safety and Immunogenicity of DNA Prime and Modified Vaccinia Ankara Virus-HIV Subtype C Vaccine Boost in Healthy Adults

A randomized, double-blind, placebo-controlled phase I trial was conducted in 32 HIV-uninfected healthy volunteers to assess the safety and immunogenicity of 3 doses of DNA vaccine (Advax) plus 1 dose of recombinant modified vaccinia virus Ankara (MVA) (TBC-M4) or 3 doses of TBC-M4 alone (groups A and B, respectively). Both vaccine regimens were found to be safe and well tolerated. Gamma interferon (IFN-γ) enzyme-linked immunosorbent spot (ELISPOT) assay responses were detected in 1/10 (10%) individuals in group A after three Advax primes and in 9/9 individuals (100%) after the MVA boost. In group B, IFN-γ ELISPOT responses were detected in 6/12 (50%) and 7/11 (64%) individuals after the second and third MVA vaccinations, respectively. Responses to all vaccine components, but predominantly to Env, were seen. The breadth and magnitude of the T cell response and viral inhibition were greater in group A than in group B, indicating that the quality of the T-cell response was enhanced by the DNA prime. Intracellular cytokine staining indicated that the T-cell responses were polyfunctional but were skewed toward Env with a CD4⁺ phenotype. At 2 weeks after the last vaccination, HIV-specific antibody responses were detected in all (100%) group B and 1/11 (9.1%) group A vaccinees. Vaccinia virus-specific responses were detected in all (100%) group B and 2/11 (18.2%) group A vaccinees. In conclusion, HIV-specific T-cell responses were seen in the majority of volunteers in groups A and B but with a trend toward greater quality of the T-cell response in group A. Antibody responses were better in group B than in group A.     

肺炎链球菌核酸疫苗在恒河猴体内的免疫原性研究

目的 研究肺炎链球菌溶血素(pneumolysin,PN)核酸疫苗在恒河猴体内的免疫原性.方法 将肺炎链球菌溶血素全长基因和切去羧基端33个核苷酸的基因分别插入到质粒pVAX1载体中,构建成Ppn和Ppnd两种核酸疫苗.采用体内电转染初免结合相应蛋白质抗原加强的策略免疫恒河猴.结果 切去肺炎链球菌溶血素基因羧基端33个核苷酸.表达的重组截短溶血素蛋白保留了抗原性但去除了溶血活性,从而保证了疫苗的安全性.给恒河猴肌肉内注射500μg核酸疫苗加电转染能诱导出特异性抗体免疫应答,用相应蛋白质加强免疫后血清抗体几何平均滴度提高了约4倍.结论 采用电转染技术结合蛋白质加强免疫的策略,能增强肺炎链球菌溶血素核酸疫苗在恒河猴体内的特异性抗体水平.     

Flt3 ligand enhances the immunogenicity of a gag-based HIV-1 vaccine

Liposomes and Flt3 ligand (Flt3L), a ligand for the fms-like tyrosine kinase receptor Flt3/ FLK2, can augment the immune response to an HIV peptide vaccine. The HGP-30 peptide used in these studies is a synthetic peptide that corresponds to a highly conserved region of HIV-1 p17 gag (amino acids 86-115). Mice were immunized with HGP-30 or HGP-30 conjugated to keyhole limpet hemocyanin (KLH) and delayed-type hypersensitivity (DTH) responses, antibody (IgG) amount and antigen-specific proliferative responses by spleen cells were used to monitor the immune response. Daily injections of Flt3L prior to HGP-30 administration enhanced significantly an antigen-specific lymphocyte proliferation response when compared with Flt3L, HGP-30 alone or HGP-30 containing liposomes. Intravenous administration of HGP-30 was superior to intramuscular (i.m.) immunization for the induction of DTH responses. The HGP-30/KLH containing liposomes enhanced both DTH and antibody responses, while liposomes containing HGP-30 peptide elicited only T cell responses. In these studies, either Flt3L or liposomes increased DTH responses compared with the i.m. injection of the HGP-30 vaccine alone.     

Enhanced murine respiratory tract IgA antibody response to oral influenza vaccine when combined with a lipoidal amine (avridine)

The adjuvant activity of avridine, a synthetic lipoidal amine, incorporated in liposomes, was studied in mice immunized orally with killed influenza virus vaccine (A/PR/8/34, H1N1). Coadministration of avridine-containing liposomes and viral antigen enhanced the remote-site IgA antibody response in the respiratory tract without a concomitant serum antibody response or side effects. The results support the possible use of mucosal adjuvants for oral immunization against respiratory pathogens.     

Induction of SARS-nucleoprotein-specific immune response by use of DNA vaccine

Induction of effective cytotoxic T lymphocyte (CTL) and/or a specific antibody against conserved viral proteins may be essential to the development of a safe and effective severe acute respiratory syndrome coronavirus (SARS-Cov) vaccine. DNA vaccination represents a new strategy for induction of humoral and cellular immune response. To determine the ability of SARS-Cov nucleoprotein (N protein) to induce antiviral immunity, in this report, we established a stable C2C12 line expressing SARS-Cov N protein, which was used as a target for specific CTL assay. We also expressed recombinant N proteins in Escherichia coli and prepared N protein-specific polyclonal antibodies. C3H/He mice were immunized with N protein-expressible pcDN-fn vector by intramuscular injections. We found that the DNA vaccination induced both N protein-specific antibody and specific CTL activity to the target. When C3H/He mice were immunized by three separate injections, high antibody titre (1:3200-1:6400, average titre is 1:4580) and high CTL activity (67.4+/-8.4% (E:T = 25:1), 69.6+/-6.7% (E:T = 50:1) and 71.8+/-6.2% (E:T = 100:1)) were observed. In the case of two vaccine injections, CTL activity was also high (56.6+/-12.7% (E:T = 25:1), 57.4+/-11.7% (E:T = 50:1) and 63.0+/-6.3% (E:T = 100:1)) However, antibody titres were much lower (1:200-1:3200, average titre is 1:980). Our results suggest that SARS-Cov nucleocapsid gene might be a candidate gene for SARS DNA vaccination.     

Trichostatin-A enhances adaptive immune responses to DNA vaccination.

BACKGROUND: The efficacy of DNA vaccines to date has overall been disappointing, especially in large animal models and in humans, which might be partially explained by the chromatinization of the administered foreign DNA. Trichostatin-A (TSA) is a specific inhibitor for histone deacetylase (HDAC) and a gene expression enhancer in in vitro DNA viral infection, including herpes simplex type 1 (HSV-1) and cytomegalovirus (CMV). OBJECTIVES: We sought to determine if increasing antigen expression of DNA vaccines through inhibition of HDAC-induced chromatin silencing using TSA would enhance DNA vaccine efficacy in vivo. STUDY DESIGN: A luciferase assay was used to detect effects of TSA on different promoters in vitro. The effects of TSA on DNA vaccination of mice were determined by neutralization assays for antibody production and interleukin staining for detection of specific T cell responses. RESULTS: Mice receiving TSA in combination with a DNA vaccine exhibited higher antibody responses to the vaccine than mice not given TSA. Co-administration of TSA also enhanced specific CD8 T cells response. CONCLUSION: Drugs such as TSA that reduce initial gene silencing by preventing histone deacetylation can increase immune responses to DNA vaccination.