DNA-based immunization by in vivo transfection of dendritic cells

Combined treatment of an intratumoral injection of dendritic cells and systemic chemotherapy (Paclitaxel) for murine fibrosarcoma

A novel combined treatment of conventional chemotherapy with an intratumoral injection of syngeneic dendritic cells (DCs) has emerged as a potent cancer treatment strategy. In this study, we evaluated the synergistic effect of an intraperitoneal (i.p.) injection of a chemotherapeutic drug, paclitaxel, and an intratumoral (i.t.) injection of syngeneic bone marrow-derived DCs for the treatment of pre-existing fibrosarcoma. Subcutaneous tumors were established using MCA102 fibrosarcoma cells in syngeneic C57BL/6 mice. The results demonstrated that the combined treatment of paclitaxel chemotherapy and the injection of DCs led to complete tumor regression, in contrast to only partial eradication of the tumors with chemotherapy or DCs alone. Furthermore, the tumor-free mice were able to resist a repeat challenge with the same type of tumor. These findings suggest that a combination therapy of systemic chemotherapy along with the intratumoral administration of DCs is a potent treatment strategy for fibrosarcoma.

Characterization of HPV-16 E6 DNA vaccines employing intracellular targeting and intercellular spreading strategies

Human papillomavirus (HPV) E6 and E7 are consistently expressed and are responsible for the malignant transformation of HPV-associated lesions. Thus, E6 and E7 represent ideal targets for therapeutic HPV vaccine development. We have previously used the gene gun approach to test several intracellular targeting and intercellular spreading strategies targeting HPV-16 E7. These strategies include the use of the sorting signal of lysosome-associated membrane protein (LAMP-1), Mycobacterium tuberculosis heat shock protein 70 (HSP70), calreticulin (CRT) and herpes simplex virus type 1 (HSV-1) VP22 proteins. All of these strategies have been shown to be capable of enhancing E7-DNA vaccine potency. In the current study, we have characterized DNA vaccines employing these intracellular targeting or intercellular spreading strategies targeting HPV-16 E6 for their ability to generate E6-specific CD8+ T cell immune responses and antitumor effects against an E6-expressing tumor cell line, TC-1, in C57BL/6 mice. We found that all the intracellular targeting strategies (CRT, LAMP-1, HSP70) as well as the intercellular spreading strategy (VP22) were able to enhance E6 DNA vaccine potency, although the orientation of HSP70 linked to E6 antigen in the E6 DNA vaccine appears to be important for the HSP70 strategy to work. The enhanced E6-specific CD8+ T cell immune response in vaccinated mice also translated into potent antitumor effects against TC-1 tumor cells. Our data indicate that all of the intracellular targeting and intercellular spreading strategies that have been shown to enhance E7 DNA vaccine potency were also able to enhance E6 DNA vaccine potency.

In vivo induction of cellular and humoral immune responses by hybrid DNA vectors encoding simian/human immunodeficiency virus/hepatitis B surface antigen virus particles in BALB/c and HLA-A2-transgenic mice

To improve the immunogenicity of epitopes derived from Gag proteins of simian immunodeficiency virus (SIV) and from the envelope (Env) protein of human immunodeficiency virus type 1 (HIV-1), we have designed hybrid DNA vaccines by inserting sequences encoding antigenic domains of SIV and HIV-1 into the hepatitis B virus envelope gene. This gene encodes the hepatitis B surface antigen (HBsAg) capable of spontaneous assembly into virus-like particles that were used here as carrier. Injections of hybrid vectors encoding B-cell epitopes from the gp41 and the gp120 envelope proteins of HIV-1 induced specific humoral responses in BALB/c mice. Furthermore, high frequencies of IFN-gamma-secreting CD8+ T cells specific for various antigenic determinants of SIV-Gag were observed after intramuscular injections of hybrid DNA vectors in BALB/c mice. Genetic immunization of HLA-A2.1-transgenic mice with HIV-Env/HBsAg-encoding DNA generated a strong CTL response and IFN-gamma-secreting CD8+ T lymphocytes specific for HIV-1 envelope-derived peptide. H-2d-restricted HBs-specific T-cell responses dominated over SIV-Gag responses in BALB/c mice whereas HLA-A2-restricted HIV-Env response was enhanced after fusion with HBsAg. These data demonstrate that different B and T-cell epitopes of vaccine-relevant viral antigens can be expressed in vivo as fusion proteins with HBsAg but that the optimal immunogenicity may differ strikingly between individual epitopes.

Enhancement of immunity by a DNA melanoma vaccine against TRP2 with CCL21 as an adjuvant

Tyrosinase-related protein-2 (TRP2) is a weak antigen expressed in murine and human melanomas. Induction of antibody (Ab) response and T-cell immunity toward TRP2 with DNA plasmid vaccines has not been efficient to date. Recent studies have suggested that a chemokine ligand for the CCR7 (CCL21) present on T-cells and dendritic cells is important in activating and regulating immunity. We investigated the effectiveness of CCL21 as an adjuvant with an HVJ anionic liposomal TRP2 DNA (plasmid) vaccine to enhance anti-TRP2 Ab, cytokines, delayed-type hypersensitivity, T-cell responses, and tumor protection against B16 melanoma cells. Induction of anti-TRP2 immunity depended mainly on cell-mediated immunity, which was regulated by timing and route of CCL21 administration with DNA vaccine. The optimum protocol was to administer CCL21 im 24 h before DNA vaccine at the same vaccination site. Two vaccinations (prime/boost) were essential for induction of strong anti-TRP2 cell-mediated immunity. CCL21 administration 3 days before or 24 h after DNA vaccine, simultaneous with DNA vaccine, or at different sites (iv, opposite leg) was not effective. This study demonstrated that CCL21 was an effective adjuvant to enhance TRP2-specific immunity induced by a plasmid DNA cancer vaccine.

Comparative evaluation of three different intramuscular delivery methods for DNA immunization in a nonhuman primate animal model

Although plasmid DNA vaccines induce potent cell-mediated immune responses and prime for antibody responses in experimental laboratory animals, their immunogenicity in humans has been less remarkable. A number of strategies have been proposed to improve the immunogenicity of these vaccines, including using novel means of vaccine delivery. In the present study, the immunogenicity of three different methods of intramuscular plasmid DNA administration was compared in cynomolgus monkeys: needle and syringe, Biojector 2000, and Mini-Ject. The elicited cellular and humoral immune responses were comparable in monkeys immunized using these different delivery techniques, suggesting that the needle-free approaches to vaccine administration do not significantly improve the immunogenicity of the plasmid DNA vaccine used in the study.

The role of particle-mediated DNA vaccines in biodefense preparedness

Particle-mediated epidermal delivery (PMED) of DNA vaccines is based on the acceleration of DNA-coated gold directly into the cytoplasm and nuclei of living cells of the epidermis, facilitating DNA delivery and gene expression. Professional antigen-presenting cells and keratinocytes in the skin are both targeted, resulting in antigen presentation via direct transfection and cross-priming mechanisms. Only a small number of cells need to be transfected to elicit humoral, cellular and memory responses, requiring only a low DNA dose. In recent years, data have accumulated on the utility of PMED for delivery of DNA vaccines against a number of viral pathogens, including filoviruses, flaviviruses, poxviruses, togaviruses and bunyaviruses. PMED DNA immunization of rodents and nonhuman primates results in the generation of neutralizing antibody, cellular immunity, and protective efficacy against a broad range of viruses of public health concern.

Initiation and regulation of CD8+T cells recognizing melanocytic antigens in the epidermis: implications for the pathophysiology of vitiligo

Antigen-specific CD8+T lymphocytes play an important role in defense against cutaneous microbial infection and skin cancer as well as in the pathophysiology of autoimmune skin disease such as lupus erythematodes and vitiligo. We have explored the role of CD8+ cytotoxic T lymphocytes (CTL) in an experimental mouse model of vitiligo, a pigmentation disorder characterized by focal loss of melanocytes in the skin. Using genetic immunization techniques we found that pigment cells in the epidermis can be destroyed by CD8+ T cells specifically recognizing a single H2-Kb-binding peptide derived from the model melanocytic self antigen tyrosinase-related protein 2 (TRP2), a melanosomal enzyme involved in pigment synthesis. Experimental evidence suggests that peripheral tolerance of pigment cell-specific cytotoxic CD8+T cells is regulated in two steps. In the induction phase, stimulation and expansion of these T cells in vivo strictly depends on CD4+ T cell help. In the effector phase, autoimmune destruction of melanocytes in the skin depends on local inflammation facilitating the migration of T cells into the epidermis and supporting effector functions. Our results suggest that accidental stimulation of CD8+ CTL recognizing MHC class I-binding peptides derived from melanocytic proteins in the context of an inflammatory skin disease may play an important role in the pathophysiology of vitiligo. Further investigations will address the role of chemokines, chemokine receptors and adhesion molecules in this experimental system and will reveal the role of keratinocytes and Langerhans cells in regulating cutaneous CD8+ T cell responses.

New developments in dendritic cell-based vaccinations: RNA translated into clinics

Dendritic cells (DCs) are the most powerful antigen-presenting cells that induce and maintain primary immune responses in vitro and in vivo. The development of protocols for the ex vivo generation of DCs provided a rationale for designing and developing DC-based vaccination studies for the treatment of infectious and malignant diseases. Recently, it was shown that DCs transfected with ribonucleic acid (RNA) coding for a tumour-associated antigen or whole tumour RNA are able to induce potent antigen and tumour-specific T-cell responses directed against multiple epitopes. The first RNA-transfected-DC-based clinical studies have shown that this form of vaccination is feasible and safe. In some cases, clinical responses were observed, but the preliminary data require further extensive investigations that should address the technical and biological problems of manipulating human DCs, as well as the development of standardised protocols and definitions of clinical settings.

Epidermal delivery of protein and DNA vaccines

Targeting vaccines to the skin epidermis results in the activation of an immune inductive site that is rich in antigen-presenting cells. The superficial location of the skin makes it accessible to vaccine delivery. However, it is difficult to access the epidermis using needle and syringe delivery, and vaccine antigens are too large to be effectively delivered using standard topical formulations. Needle-free vaccine delivery systems have been developed for efficient delivery of particulate vaccines into the epidermal tissue. Particle-mediated epidermal delivery of DNA vaccines is based on the delivery of DNA-coated gold particles directly into the cytoplasm and nuclei of living cells of the epidermis, facilitating DNA delivery and gene expression. Alternatively, protein vaccines can be formulated into a dense powder, which can be propelled into the skin epidermis by epidermal powder immunisation using similar delivery devices and principles, but in this instance the protein is delivered to the extracellular space. Preclinical and clinical data will be reviewed, demonstrating applications of epidermal vaccine delivery to a wide range of experimental infectious disease vaccines.

Anti-tumor effect of an intratumoral administration of dendritic cells in combination with TS-1, an oral fluoropyrimidine anti-cancer drug, and OK-432, a streptococcal immunopotentiator: involvement of toll-like receptor 4

The authors investigated the in vivo anti-tumor effect of intratumoral administration of bone marrow-derived dendritic cells (DCs) after chemotherapy using an oral fluoropyrimidine anti-cancer drug TS-1, and followed by immunotherapeutic agent OK-432, in two syngeneic tumor-bearing mouse models. Both in Meth-A fibrosarcoma-bearing BALB/c mice and in SCCVII-bearing C3H/HeN mice, 1 week of oral administration of TS-1 effected partial eradication of established tumors. Intratumoral injection of DCs and OK-432 caused only slight inhibition of the tumor growth. However, TS-1 administration followed by DCs and OK-432 resulted in a marked inhibition in the tumor growth and also contributed to a greater prolongation of survival. By the injection of DCs and OK-432 after TS-1 administration, a significant infiltration of immune cells, especially CD8+ T cells, was observed. Furthermore, the cytotoxic activities of tumor-infiltrating lymphocytes and draining lymph node cells against inoculated tumor cells were significantly increased by the therapy, while activities against nonspecific target cells were not. Cytotoxic memory T cells were also induced; the main effectors were MHC class I-restricted, CD8+ T cells. The same therapy was also applied to SCCVII-bearing C3H/HeJ mice in which the Toll-like receptor (TLR) 4 is mutated and its function impaired; no immunotherapeutic effect was observed in the TLR4-deficient mouse model. These findings suggest that the local DC therapy in combination with TS-1 and OK-432 may be a useful strategy for the treatment of solid tumors, and that TLR4 signaling is involved in the success of this therapy.

Allogeneic Dendritomas Induce Anti-tumour Immunity Against Metastatic Colon Cancer

Colon cancer (CC) is one of the most common malignancies in the Western world. Although surgical resection is the first choice worldwide, at this point an effective approach for the treatment of patients with metastasis and cancer recurrence post-operation has not yet been found. The aim of this study was to investigate the role of the allogeneic dendritomas from fusion of dendritic cells (DC) and metastatic CC cells in the activation of anti-tumour immunity against metastatic CC. Dendritomas were generated by fused allogeneic human peripheral blood DC with metastatic CC cells using 50% polyethylene glycol. The proliferation of the T cells and the toxicity of the cytotoxic T lymphocytes were observed after T cell pulsed with allogeneic dendritomas. The activated ratios of CD4+T helper 1 and CD8+Tc1 cells were about 51.55 and 65.60% after T cells were mixed with fusions for 24 h, which higher than those of controls. The proliferation of T cells were significantly higher than those of control after T cell pulsed with dendritomas (P < 0.01). Significantly, the activated CD8+ T lymphocytes effectively lysed the CC cells. These results demonstrate that allogeneic dendritomas activate T-cell responses against metastatic CC cells.

Cutaneous antigen priming via gene gun leads to skin-selective Th2 immune-inflammatory responses

It is becoming increasingly evident that the compartmentalization of immune responses is governed, in part, by tissue-selective homing instructions imprinted during T cell differentiation. In the context of allergic diseases, the fact that "disease" primarily manifests in particular tissue sites, despite pervasive allergen exposure, supports this notion. However, whether the original site of Ag exposure distinctly privileges memory Th2 immune-inflammatory responses to the same site, while sparing remote tissue compartments, remains to be fully investigated. We examined whether skin-targeted delivery of plasmid DNA encoding OVA via gene-gun technology in mice could generate allergic sensitization and give rise to Th2 effector responses in the skin as well as in the lung upon subsequent Ag encounter. Our data show that cutaneous Ag priming induced OVA-specific serum IgE and IgG1, robust Th2-cytokine production, and late-phase cutaneous responses and systemic anaphylactic shock upon skin and systemic Ag recall, respectively. However, repeated respiratory exposure to aerosolized OVA failed to instigate airway inflammatory responses in cutaneous Ag-primed mice, but not in mice initially sensitized to OVA via the respiratory mucosa. Importantly, these contrasting airway memory responses correlated with the occurrence of Th2 differentiation events at anatomically separate sites: indeed cutaneous Ag priming resulted in Ag-specific proliferative responses and Th2 differentiation in skin-, but not thoracic-, draining lymph nodes. These data indicate that Ag exposure to the skin leads to Th2 differentiation within skin-draining lymph nodes and subsequent Th2 immunity that is selectively manifested in the skin.

Transfection of a mouse dendritic cell line by plasmid DNA-loaded PLGA microparticles in vitro

Targeting of DC for DNA vaccination may be achieved by DNA-loaded poly(lactide-co-glycolide) (PLGA) biodegradable microparticles, since DC efficiently capture these microparticles in vitro and in vivo. DNA was encapsulated in PLGA microparticles by spray-drying. Various additives were tested and process parameters adjusted in order to prevent degradation of the DNA during encapsulation. The highest degree of supercoiled DNA was maintained by adding a strong buffering agent, such as PBS or NaHCO(3), whereas the cryoprotective lactose did not show a significant protective effect. DNA-containing PLGA microparticles were administered to a mouse DC line. Transfection efficacy was compared with commonly employed cationic transfectants and was visually assessed by green fluorescent protein expression. Transfection rate was very low in DC for all microparticle formulations and was comparable with commonly used cationic transfectants. It is concluded that the transfection of DC using PLGA microparticles is feasible, but efforts need to be undertaken to improve transfection efficiency in vitro, which may in addition lead to improved immune responses in vivo.

Pooled peptides from HER-2/neu-overexpressing primary ovarian tumours induce CTL with potent antitumour responses in vitro and in vivo

Unfractionated peptides (MW: up to 10 kDa), derived from HLA-A2.1 positive (+) HER-2/neu-overexpressing primary tumour cell acid cell extracts (ACE), were successfully used to generate in vitro cytotoxic T lymphocytes (CTL). Primary tumour cells were collected from peritoneal malignant effusions of patients with ovarian cancer. Acid cell extracts-induced CTL specifically lysed in an HLA-A2-restricted manner HER-2/neu+ autologous primary tumour cells as well as HER-2/neu+ tumour cell lines. In addition, adoptive transfer of such CTL significantly prolonged the survival of SCID mice xenografted with HLA-A2.1+, HER-2/neu+ human breast and ovarian tumour cell lines. Acid cell extracts collected from HLA-A2.1+ HER-2/neu negative (-) primary ovarian tumours induced HLA-A2.1-restricted CTL with weak in vitro and in vivo antitumour capacity, suggesting that HER-2/neu peptides within ACE from HER-2/neu-overexpressing primary ovarian tumour cells are immunodominant. The results presented herein serve as a rationale for the initiation of vaccination studies in patients with HER-2/neu-overexpressing ovarian tumours utilising autologous tumour-derived ACE.

Induction of RNA interference in dendritic cells

Dendritic cells (DC) reside at the center of the immunological universe, possessing the ability both to stimulate and inhibit various types of responses. Tolerogenic/regulatory DC with therapeutic properties can be generated through various means of manipulations in vitro and in vivo. Here we describe several attractive strategies for manipulation of DC using the novel technique of RNA interference (RNAi). Additionally, we overview some of our data regarding yet undescribed characteristics of RNAi in DC such as specific transfection strategies, persistence of gene silencing, and multi-gene silencing. The advantages of using RNAi for DC genetic manipulation gives rise to the promise of generating tailor-made DC that can be used effectively to treat a variety of immunologically mediated diseases.

Enhancement of DNA vaccine potency through linkage of antigen gene to ER chaperone molecules, ER-60, tapasin, and calnexin

DNA vaccines have emerged as an attractive approach for generating antigen-specific immunotherapy. Strategies that enhance antigen presentation may potentially be used to enhance DNA vaccine potency. Previous experiments showed that chimeric DNA vaccines utilizing endoplasmic reticulum (ER) chaperone molecules, such as Calreticulin (CRT), linked to an antigen were capable of generating antigen-specific CD8+ T cell immune responses in vaccinated mice. In this study, we tested DNA vaccines encoding the ER chaperone molecules ER-60, tapasin (Tap), or calnexin (Cal), linked to human papillomavirus type 16 (HPV-16) E7 for their abilities to generate E7-specific T cell-mediated immune responses and antitumor effects in vaccinated mice. Our results demonstrated that vaccination with DNA encoding any of these chaperone molecules linked to E7 led to a significant increase in the frequency of E7-specific CD8+ T cell precursors and generated stronger antitumor effects against an E7-expressing tumor in vaccinated mice compared to vaccination with wild-type E7 DNA. Our data suggest that DNA vaccines employing these ER chaperone molecules linked to antigen may enhance antigen-specific CD8+ T cell immune responses, resulting in a significantly more potent DNA vaccine.

Vaccines for human papillomavirus-associated anogenital disease and cervical cancer: practical and theoretical approaches

The association of genital warts, cervical dysplasia and cervical cancer with certain human papillomavirus (HPV) types indicates that vaccine strategies that target the virus could be effective in controlling disease onset and progression. Three vaccine strategies are available. Firstly, a prophylactic approach of immunisation with HPV virus-like particles to elicit neutralising antibody would prevent infection. Secondly, vaccination targeting replicating virus in suprabasal cells of infected anogenital epithelium would be an effective therapy for infection and early dysplasias. Thirdly, immunotherapy directed to the oncoprotein products of the HPV E6 and E7 open reading frames would be effective in the control of cervical carcinoma. We examine how these strategies may be augmented by contemporary vaccine technologies, in particular through the use of live recombinant vaccine vectors, specific targeting of antigen processing pathways, dendritic cell and 'polytope' approaches, to produce 'designer' vaccines of maximum specificity and efficacy. How these approaches are being exploited by vaccine manufacturers and in clinical trials is discussed.

Vaccination with helper-dependent adenovirus enhances the generation of transgene-specific CTL

Recombinant adenoviral vectors (AdV) have been used experimentally as vaccines to present antigenic transgenes in vivo. However, administration of first-generation vectors (FG-AdV) is often limited by their induction of antiviral immunity. To address this limitation, helper-dependent vectors (HD-AdV) were developed that lack viral coding regions. While the administration of HD-AdV results in long-term gene expression in vivo, their utility as immunogens has never been examined. Direct vaccination with 10(8) blue-forming units (BFU) of HD-AdV injected into C57BL/6 mice lead to superior transgene-specific CTL and antibody responses when compared to the same amount of a FG-AdV. The antibody responses to viral antigens were high in response to both the vectors. As a mechanism to reduce viral exposure, dendritic cells (DC) were transduced with HD-AdV in vitro and then used as a cell-based vaccine. DC transduced with HD-AdV expressed higher levels of transgene-specific mRNA and up to 1200-fold higher levels of transgene protein than did DC transduced with a FG-AdV. In addition, HD-AdV-transduced DC stimulated superior transgene-specific CTL responses when administered in vivo, an effect that was further enhanced by maturing the DC with LPS prior to administration. In contrast to direct immunization with HD-AdV, vaccination with HD-AdV-transduced DC was associated with limited antibody responses against the AdV. We conclude that HD-AdV stimulates superior transgene-specific immune responses when compared to a FG-AdV, and that immunization with a DC-based vaccine maintains this efficacy while limiting antiviral reactivity.

A DNA Vaccine Targeting Survivin Combines Apoptosis with Suppression of Angiogenesis in Lung Tumor Eradication

A novel strategy achieved the eradication of lung tumor metastases by joint suppression of angiogenesis in the tumor neovasculature and induction of tumor cell apoptosis. This was accomplished by CTLs induced by a DNA vaccine encoding secretory chemokine CCL21 and the inhibitor of apoptosis protein survivin, overexpressed by both proliferating endothelial cells in the tumor vasculature and tumor cells. Oral delivery of this DNA vaccine by doubly attenuated Salmonella typhimurium (dam− and AroA−) to such secondary lymphoid organs as Peyer's patches in the small intestine, elicited marked activation of antigen-presenting dendritic cells, and an effective CD8+T cell immune response against the survivin self-antigen. This resulted in eradication or suppression of pulmonary metastases of non–small cell lung carcinoma in both prophylactic and therapeutic settings in C57BL/6J mice. Moreover, the suppression of angiogenesis induced by the vaccine did not impair wound healing or fertility of treated mice. It is anticipated that such novel DNA vaccines will aid in the rational design of future strategies for the prevention and treatment of cancer.

Modification of Professional Antigen-Presenting Cells with Small Interfering RNA In vivo to Enhance Cancer Vaccine Potency

RNA interference using small interfering RNA (siRNA) is an effective means of silencing gene expression in cells. Intradermal administration of nucleic acids via gene gun represents an efficient method for delivering nucleic acids to professional antigen-presenting cells in vivo. In this study, we show that the coadministration of DNA vaccines encoding human papillomavirus type 16 E7 with siRNA targeting key proapoptotic proteins Bak and Bax prolongs the lives of antigen-expressing dendritic cells in the draining lymph nodes, enhances antigen-specific CD8+ T-cell responses, and elicits potent antitumor effects against an E7-expressing tumor model in vaccinated mice. Our data indicate that intradermal administration of siRNA to manipulate gene expression represents a plausible strategy for modification of the properties of professional antigen-presenting cells in vivo to enhance cancer vaccine potency.

DNA vaccines employing intracellular targeting strategies and a strategy to prolong dendritic cell life generate a higher number of CD8+ memory T cells and better long-term antitumor effects compared with a DNA prime-vaccinia boost regimen

We have previously shown that intradermal coadministration of DNA encoding Bcl-x(L), an antiapoptotic protein, with DNA encoding E7 antigen linked to the sorting signal of the lysosome-associated membrane protein type 1 (Sig/E7/LAMP-1) prolongs dendritic cell life and enhances antigen presentation through the MHC class I and II pathways. In the current study, we compared this approach with a conventional DNA prime-vaccinia boost protocol on the basis of their ability to generate antigen-specific CD8(+) memory T cells and longterm antitumor effects against an E7-expressing tumor. Mice primed and boosted with Sig/E7/LAMP-1 DNA mixed with Bcl-x(L) DNA generated significantly higher numbers of E7-specific CD8(+) memory T cells and a better long-term protective antitumor effect compared with mice primed with Sig/E7/LAMP-1 DNA and boosted with Sig/E7/LAMP-1 vaccinia (Vac-Sig/E7/LAMP-1). Furthermore, coadministration of Sig/E7 /LAMP-1 DNA mixed with Bcl-x(L) DNA also generated higher avidity E7-specific CD8(+) T cells than did vaccination with Sig/E7/LAMP-1 DNA followed by a Vac-Sig/E7/LAMP-1 booster. Our results indicate that coadministration of a DNA vaccine employing intracellular targeting strategies and a DNA encoding antiapoptotic proteins may potentially generate a higher number of memory CD8(+) T cells and better long-term protective antitumor effects compared with the conventional DNA prime-vaccinia boost regimen.

Altered intracellular sorting signals do not influence the efficacy of genetic melanoma vaccines incorporating helper determinants in mice

BACKGROUND

A genetic melanoma vaccine consisting of cDNA encoding the model self-antigen tyrosinase-related protein 2 (TRP2) fused in-frame to the immunogenic enhanced green fluorescent protein (EGFP) was able to break immune tolerance and stimulate CD8+ T cells in vivo. In the present study we investigated whether alteration of the intracellular antigen localization as a result of the linkage with immune-enhancing helper proteins affects the resulting immune response.

METHODS

Expression plasmids and recombinant adenoviruses were constructed encoding various fusion proteins with different intracellular sorting signals which direct the antigen to the cytosol, the endoplasmic reticulum or the endosomal compartments. Genetic immunization of C57BL/6 mice was performed with all constructs using particle-bombardment of the skin and injection of recombinant adenoviruses. The resulting immune response was analyzed using ELISPOT and tumor rejection assays.

RESULTS

Induction of TRP2-specific CD8+ T cells in vivo and autoimmune-mediated destruction of melanocytes in the bombarded area of the skin were observed with all constructs expressing fusion proteins between TRP2 and EGFP. Importantly, injections of the different recombinant adenoviruses all mediated protective immunity against transplanted B16 melanoma cells.

CONCLUSIONS

Altered intracellular sorting signals do not significantly influence the efficacy of genetic melanoma vaccines incorporating helper determinants in our model system. These results further support the concept that linkage of immunogenic helper sequences can be successfully applied for antigen-specific immunotherapy of melanoma and provide a scientific basis for the translation of this strategy in future clinical applications.

DNA vaccines against human immunodeficiency virus type 1

Development of a vaccine against human immunodeficiency virus type 1 (HIV-1) is the main hope for controlling the acquired immunodeficiency syndrome pandemic. An ideal HIV vaccine should induce neutralizing antibodies, CD4+ helper T cells, and CD8+ cytotoxic T cells. While the induction of broadly neutralizing antibodies remains a highly challenging goal, there are a number of technologies capable of inducing potent cell-mediated responses in animal models, which are now starting to be tested in humans. Naked DNA immunization is one of them. This review focuses on the stimulation of HIV-specific T cells and discusses in the context of the current 'state-of-art' of DNA vaccines, the areas where this technology might assist either alone or as a part of more complex vaccine formulations in the HIV vaccine development.

Strategies for improved formulation and delivery of DNA vaccines to veterinary target species

Interest in DNA immunization of animals continues, despite the fact that immune responses induced by DNA vaccines are generally lower than those elicited by conventional vaccines. In attempts to enhance the immune response to DNA vaccines, individuals have tried a variety of immune modulators, cytokines, and costimulatory molecules, but these only boost immune responses marginally. These results clearly demonstrate that the major challenge to improving DNA-based vaccines is to improve the transfection efficiency. Gene gun and electroporation can increase transfection and improve immune responses significantly, but these technologies have not yet advanced to the stage of routine use in livestock. Hopefully, transfection efficiency can be increased further in a user-friendly manner to ensure that the benefits of using DNA vaccines become a reality.

B lymphocytes as antigen-presenting cell-based genetic vaccines

Inoculation of plasmid DNA is a simple way to immunize, but it is characterized by low immunogenicity, which has hampered the development of effective DNA vaccines for human use. Here, we discuss how poor immunogenicity can be solved and present our proposal: genetically programmed B lymphocytes as antigen-presenting cell (APC) vaccines. First, we demonstrate that mature B lymphocytes take up plasmid DNA spontaneously, i.e., in the absence of any facilitating molecule or event, spontaneous lymphocyte transgenesis. Second, we demonstrate that transgenic B lymphocytes are easily and reproducibly turned into functional APCs with dual characteristics: upregulation of costimulatory molecules and endogenous synthesis of antigen. Used as immunogens in mice, transgenic B lymphocytes induce robust and long-lasting T-cell immunity after single intravenous injection. Surprisingly, immunity and protection against lethal virus challenge can be obtained with a single intravenous injection of 3 x 10(2) transgenic lymphocytes. The new approach is discussed relative to the advantage of targeting secondary lymphoid organs with genetically programmed B lymphocytes and the advantage offered with respect to low antigen dose. We suggest that these properties reflect on simple characteristics, such as time synchronization and initial localization to secondary lymphoid organs of APCs endowed with protracted synthesis and presentation of antigen to T cells.

Cross-presentation, dendritic cell subsets, and the generation of immunity to cellular antigens

Cross-presentation involves the uptake and processing of exogenous antigens within the major histocompatibility complex (MHC) class I pathway. This process is primarily performed by dendritic cells (DCs), which are not a single cell type but may be divided into several distinct subsets. Those expressing CD8alpha together with CD205, found primarily in the T-cell areas of the spleen and lymph nodes, are the major subset responsible for cross-presenting cellular antigens. This ability is likely to be important for the generation of cytotoxic T-cell immunity to a variety of antigens, particularly those associated with viral infection, tumorigenesis, and DNA vaccination. At present, it is unclear whether the CD8alpha-expressing DC subset captures antigen directly from target cells or obtains it indirectly from intermediary DCs that traffic from peripheral sites. In this review, we examine the molecular basis for cross-presentation, discuss the role of DC subsets, and examine the contribution of this process to immunity, with some emphasis on DNA vaccination.

A Library-Selected, Langerhans Cell-Targeting Peptide Enhances an Immune Response

The ability to deliver antigens and immunomodulators specifically to Langerhans cells (LCs) in the skin could impact vaccine development. However, cell-specific targeting of therapeutic molecules remains a challenge in biomedicine. Using phage display technologies, we have developed a protocol that identifies peptides that mediate uptake into target cell types. Employing this approach, we have isolated a 20-mer peptide that mediates specific uptake by immunopotent LCs. The peptide is functional outside the context of the phage and is able to deliver a nanoparticle to LCs in vitro. Although selected on cells in vitro, the peptide is able to direct antigens and genes to LCs in vivo. Liposomes bearing the LC targeting peptide are able to deliver a transcriptionally active gene to LCs in a mouse model. Furthermore, we demonstrate that a low-dose injection into mice of phage bearing the LC-targeting peptide yields faster and higher immune responses against phage-associated antigens than control-phage injections.

Alteration of T cell immunity by lentiviral transduction of human monocyte-derived dendritic cells

BACKGROUND

Dendritic cells (DCs) are professional antigen-presenting cells that play important roles during human immunodeficiency virus type 1 (HIV-1) infection. HIV-1 derived lentiviral vectors (LVs) transduce DCs at high efficiency but their effects on DC functions have not been carefully studied. Modification of DCs using LVs may lead to important applications in transplantation, treatment of cancer, autoimmune and infectious diseases.

RESULTS

Using DCs prepared from multiple blood donors, we report that LV transduction of DCs resulted in altered DC phenotypes and functions. Lentiviral transduction of DCs resulted in down-regulation of cell surface molecules including CD1a, co-stimulatory molecules CD80, CD86, ICAM-1, and DC-SIGN. DCs transduced with LVs displayed a diminished capacity to polarize naive T cells to differentiate into Th1 effectors. This impaired Th1 response could be fully corrected by co-transduction of DCs with LVs encoding interleukin-12 (IL-12), interferon-gamma (IFN-gamma), or small interfering RNA (siRNA) targeting IL-10.

CONCLUSIONS

DCs transduced with LVs in vitro displayed diminished Th1 functions due to altered DC phenotypes. Our study addresses an important issue concerning lentiviral infection and modification of DC functions, and provides a rational approach using LVs for immunotherapy.

Generation of human tumor-specific CTLs in HLA-A2.1-transgenic mice using unfractionated peptides from eluates of human primary breast and ovarian tumors

HER-2/neu oncoprotein is overexpressed in a variety of human tumors and is associated with malignant transformation and aggressive disease. Due to its overexpression in tumor cells and because it has been shown to be immunogenic, this protein represents an excellent target for T-cell immunotherapy. Peptide extracts derived from primary HLA-A*0201-positive (+) HER-2/neu+ human tumors by acid elution (acid cell extracts (ACEs)) were tested for their capacity to elicit in HLA-A*0201 transgenic mice, cytotoxic T lymphocytes (CTLs) lysing HLA-A*0201+ HER-2/neu+ tumor cells. Injections of ACE in transgenic mice induced CTLs capable of specifically lysing HER-2/neu+ tumor cell lines (also including the original HER-2/neu+ primary tumor cells from which the ACEs were derived) in an HLA-A*0201-restricted fashion. Adoptive transfer of ACE-induced CTLs was sufficient to significantly prolong survival of SCID mice inoculated with HLA-A*0201+ HER-2/ neu+ human tumor cell lines. Cytotoxicity of such ACE-induced CTL lines was directed, at least as detected herein, also against the HER-2/ neu peptides HER-2 (9(369)) and HER-2 (9(435)) demonstrating the immunodominance of these epitopes. HER-2 peptide-specific CTLs generated in the HLA-A*0201-transgenic mice, upon peptide immunization, lysed in vitro HER-2/neu+ human tumor cell lines in an HLA-A*0201-restricted manner and, when adoptively transferred, conferred sufficient protection in SCID mice inoculated with the same human tumor cell lines as above. However, CTLs induced by ACEs displayed enhanced efficacy in the therapy of xenografted SCID mice compared with the HER-2 peptide-specific CTLs (i.e., HER-2 [9(369)] or HER-2 [9(435)]). Even by administering mixtures of CTLs specific for each of these peptides, the prolongation of survival achieved was still inferior compared with that obtained with ACE-induced CTLs. This suggested that additional epitopes may contribute to the immunogenicity of such tumor-derived ACEs. Thus, immunization with ACEs from HER-2/neu+ primary tumor cells appears to be an effective approach to generate multiple and potent CTL-mediated immune responses against HER-2/neu+ tumors expressing the appropriate HLA allele(s). By screening ACE-induced CTL lines with synthetic peptides encompassing the HER-2/neu sequence, it is feasible to identify immunodominant epitopes which may be used in mixtures as vaccines with enhanced efficacy in both the prevention and therapy of HER-2/neu+ malignancies.

Preventative and therapeutic vaccines for cervical cancer

"High-risk" genotypes of the human papillomavirus (HPV), most commonly HPV genotype 16, are the primary etiologic agents of cervical cancer. Indeed HPV DNA is detected in 99% of cervical carcinomas. Thus, cervical cancer and other HPV-associated malignancies might be prevented or treated by the induction of the appropriate viral-antigen-specific immune responses. Transmission of papillomavirus may be prevented by the generation of antibodies to capsid proteins L1 and L2 that neutralize viral infection. HPV L1 virus-like particles (VLPs) show great promise as prophylactic HPV vaccines in ongoing clinical trials but L2-based preventative vaccines have yet to be tested in patients. Since the capsid proteins are not expressed at detectable levels by infected basal keratinocytes or in HPV-transformed cells, therapeutic vaccines generally target the nonstructural early viral antigens. Two HPV oncogenic proteins, E6 and E7, are critical to the induction and maintenance of cellular transformation and are co-expressed in the majority of HPV-containing carcinomas. Although other early viral antigens show promise for vaccination against papillomas, therapeutic vaccines targeting E6 and E7 may provide the best opportunity to control HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 are administered in live vectors, as peptides or proteins, in nucleic acid form, as components of chimeric VLPs, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. Should this new generation of HPV preventative and therapeutic vaccines function in patients as demonstrated in animal models, oncogenic HPV infection and its associated malignancies could be controlled by vaccination. Importantly, recent advances in HPV detection and continued improvements in screening further enhance our opportunities to systematically eradicate HPV-associated malignancy.

Expression of toll-like receptor 4 on dendritic cells is significant for anticancer effect of dendritic cell-based immunotherapy in combination with an active component of OK-432, a streptococcal preparation

A lipoteichoic acid-related molecule OK-PSA is an active component of OK-432, a Streptococcus-derived anticancer immunotherapeutic agent. In the present study, we first examined the effect of OK-PSA on the maturation of dendritic cells (DCs) in vitro by using the DCs derived from 5 healthy donors and 10 patients with head and neck cancer with or without expression of toll-like receptor 4 (TLR4) or MD-2 mRNA. OK-PSA treatment effectively increased the surface expression of MHC class II, CD80, CD83, and CD86. OK-PSA-stimulated DCs secreted the cytokines that can induce helper T-cell 1 (Th1)-type T-cell response, and stimulated allogeneic T cells to produce IFN-gamma and to elicit an allogeneic antigen-specific cytotoxicity. These activities almost depended on expression of TLR4 and MD-2 genes. We next investigated the in vivo anticancer effect of intratumoral administration of syngeneic DCs followed by OK-PSA against established tumors in mice. C57BL/6 mice, which express wild-type TLR4, and C57BL/6-derived TLR4-knockout (TLR4(-/-)) mice were used. Although OK-PSA accelerated the antitumor effect of intratumoral DC administration in wild-type mice bearing syngeneic tumors, the antitumor effect of OK-PSA as well as of the combination therapy with DCs and OK-PSA was not significant in TLR4(-/-) mice. Interestingly, an administration of wild-type-mouse-derived DCs followed by OK-PSA exhibited a marked antitumor effect even in the TLR4(-/-) mice. These findings suggest that OK-PSA may be a potent adjuvant for local DC therapy, and that DC therapy followed by OK-PSA is able to elicit anticancer activity even in a TLR4-deficient host when TLR4 is expressed only in DCs injected intratumorally.

Development of a DNA vaccine targeting human papillomavirus type 16 oncoprotein E6

Human papillomavirus (HPV), particularly type 16 (HPV-16), is present in more than 99% of cervical cancers. The HPV oncoproteins E6 and E7 are constantly expressed and therefore represent ideal targets for HPV vaccine development. We previously developed DNA vaccines encoding calreticulin (CRT) linked to HPV-16 E7 and generated potent E7-specific CD8(+) T-cell immune responses and antitumor effects against an E7-expressing tumor. Since vaccines targeting E6 also represent an important strategy for controlling HPV-associated lesions, we developed a DNA vaccine encoding CRT linked to E6 (CRT/E6). Our results indicated that the CRT/E6 DNA vaccine, but not a wild-type E6 DNA vaccine, generated significant E6-specific CD8(+) T-cell immune responses in vaccinated mice. Mapping of the immunodominant epitope of E6 revealed that an E6 peptide comprising amino acids (aa) 48 to 57 (E6 aa48-57), presented by H-2K(b), is the optimal peptide and that the region of E6 comprising aa 50 to 57 represents the minimal core sequence required for activating E6-specific CD8(+) T lymphocytes. We also demonstrated that E6 aa48-57 contains cytotoxic T-lymphocyte epitopes naturally presented by E6-expressing TC-1 cells. Vaccination with a CRT/E6 but not a CRT/mtE6 (lacking aa 50 to 57 of E6) DNA vaccine could protect vaccinated mice from challenge with E6-expressing TC-1 tumors. Thus, our data indicate that E6 aa48-57 contains the immunodominant epitope and that a CRT/E6 DNA vaccine may be useful for control of HPV infection and HPV-associated lesions.

Particle-mediated DNA vaccine delivery to the skin

Particle-mediated DNA vaccines employ a physical, intracellular delivery device to achieve the deposition of plasmid DNA-based expression vectors directly into the interior of cells of the skin. The resultant bolus of transient antigen expression in keratinocytes and trafficking dendritic cells results in the induction of humoral and cellular immune responses in various animal models and humans, mimicking characteristics of live or live-vectored vaccines. Ultimately, DNA vaccine success in the clinic will depend on both the successful intracellular delivery of a plasmid vector and an immunostimulator or adjuvant to maximise humoral and cellular immune responses to the encoded antigen(s). To this end, recent DNA vaccine clinical trials are confirming the importance of an intracellular delivery system, while preclinical studies in animal models are demonstrating the feasibility of augmenting responses through the use of DNA-encoded immunostimulators. Particle-mediated DNA vaccines represent a promising tool for developing candidate vaccines against some of the more difficult infectious, parasitic and oncologic disease targets.

Flt-3 ligand as adjuvant for DNA vaccination augments immune responses but does not skew TH1/TH2 polarization

Since transfection of dendritic cells (DC) plays a key role in DNA vaccination, in vivo expansion of DC might be a tool to increase vaccine efficacy. We asked whether Fms-like tyrosine kinase-3 ligand (Flt-3L), a growth factor for DC, can be used as an adjuvant for DNA vaccination. Beta-galactosidase (beta-gal) was used as a model antigen in C57BL/6 mice. Mice were immunized i.m. with DNA coding for beta-gal with or without additional injection of Flt-3L. In both cases, antigen-specific CD4+ and CD8+ T cells were detectable after vaccination. Compared with DNA alone, additional administration of Flt-3L led to a significant increase in the antigen-specific proliferative response. However, increased cytotoxicity by T cells was not observed. The cytokines secreted by splenocytes of immunized mice upon in vitro stimulation with antigen had a TH2 profile. Humoral responses against beta-gal preferentially consisted of IgG1 antibodies. Analysis of DC from Flt-3L-treated mice revealed an immature phenotype with low or absent expression levels of CD80, CD86 and CD40. We conclude that Flt-3L does not generally skew immune responses towards a TH1 type. More likely, factors determined by the antigen and/or the vaccination procedure itself are crucial for the resulting type of immune response. Flt-3L - under circumstances such as the one we have investigated - can also lead to suppression of TH1 T cell immunity, possibly by expansion of immature/unactivated DC.

DNA vaccine-encapsulated virus-like particles derived from an orally transmissible virus stimulate mucosal and systemic immune responses by oral administration

Delivery of foreign genes to the digestive tract mucosa by oral administration of nonreplicating gene transfer vectors would be a very useful method for vaccination and gene therapy. However, there have been few reports on suitable vectors. In the present study, we found that plasmid DNA can be packaged in vitro into a virus-like particle (VLP) composed of open reading frame 2 of hepatitis E virus, which is an orally transmissible virus, and that these VLPs can deliver this foreign DNA to the intestinal mucosa in vivo. The delivery of plasmid DNA to the mucosa of the small intestine was confirmed by the results of immunohistochemical analyses using an expression plasmid encoding human immunodeficiency virus env (HIV env) gp120. After oral administration of VLPs loaded with HIV env cDNA, significant levels of specific IgG and IgA to HIV env in fecal extracts and sera were found. Moreover, mice used in this study exhibited cytotoxic T-lymphocyte responses specific to HIV env in the spleen, Payer's patches and mesenteric lymph nodes. These findings suggest that VLPs derived from orally transmissible viruses can be used as vectors for delivery of genes to mucosal tissue by oral administration for the purpose of DNA vaccination and gene therapy.

Influence of polypeptide size and intracellular sorting on the induction of epitope-specific CTL responses by DNA vaccines in a mouse model

We have analysed the influence of size, intracellular localisation, and sorting of various human immunodeficiency virus type 1 (HIV-1)-derived Gag and Env polypeptides containing well defined H2(d)-restricted cytotoxic T lymphocyte (CTL) epitopes on the induction of a humoral and cellular immune response after DNA vaccination. Thus, expression vectors were generated based on RNA- and codon-optimised genes encoding (i). budding competent full-length Gag, (ii). a myristylation defect mutant GagMyr(-), (iii). the isolated p24 capsid moiety of Gag as well as variants of these proteins, which were C-terminally fused HIV gp120-derived V3 epitope (R10I), respectively. These constructs were compared to different minitopes each encoding one of the H2(d)-restricted Gag epitopes A9I and E10F or the V3 epitope R10I that were directly linked to the C-terminus of an Ad2-E3 protein-derived ER signal peptide. Immunological evaluation of these constructs in BALB/c mice revealed that both, the budding competent as well as the intracellular Gag proteins were-irrespective of their molecular weights-equally efficient in the priming of Gag-specific humoral and cellular immune responses. In addition, the capacity of these constructs to stimulate Gag-specific humoral as well as H2-K(d) and H2-L(d) restricted cellular immune responses was not influenced by C-terminal fusion of the immunodominant H2-D(d) restricted V3 epitope. Chimeric GagV3 polyproteins encoding all three major CTL epitopes within a continuous polyprotein were more efficient to stimulate epitope-specific cellular immune responses than the selected minitopes. In addition, the minitopes failed to induce epitope-specific antibody responses. These results clearly show the advantages of complex polypeptides over minitopes regarding the induction of strong humoral and cellular immune responses.

A DNA vaccine co-expressing antigen and an anti-apoptotic molecule further enhances the antigen-specific CD8+ T-cell immune response

We have shown that DNA encoding the anti-apoptotic protein Bcl-xL enhances E7-specific CD8+ T-cell responses and DNA encoding pro-apoptotic protein caspase-3 suppresses E7-specific CD8+ T-cell responses when co-administered intradermally via gene gun with DNA encoding human papillomavirus type 16 (HPV-16) E7 linked to the sorting signal of the lysosome-associated membrane protein type 1 (LAMP-1). E7 and LAMP-1 are linked to form the chimeric Sig/E7/LAMP-1 (SEL). Because co-administration does not ensure delivery of both constructs to a single cell, we used pVITRO, a mammalian expression vector with double promoters, to ensure expression of both molecules in the same cell. We vaccinated C57BL/6 mice with pVITRO-SEL-Bcl-xL, pVITRO-SEL-mtBcl-xL, pVITRO-SEL, or pVITRO-SEL-caspase-3 intradermally via gene gun and intramuscularly via injection. We demonstrated that vaccination with pVITRO achieved similar results to a co-administration strategy: that Bcl-xL enhanced the E7-specific CTL response and caspase-3 suppressed the E7-specific CTL response. In addition, we found intradermal vaccination elicited significantly higher numbers of E7-specific CD8+ T cells compared to intramuscular vaccination. Thus, intradermal vaccination with a pVITRO vector combining an anti-apoptotic strategy (Bcl-xL) and an intracellular targeting strategy (SEL) further enhances the E7-specific CD8+ T-cell response and guarantees co-expression of both encoded molecules in transfected cells.

DNA transfection of mononuclear cells in muscle tissue

BACKGROUND

Genes encoding non-self proteins may be injected into skeletal muscles in vivo to obtain induction of cellular and humoral immune responses against the encoded antigens (DNA vaccination). Bone marrow derived professional antigen-presenting cells (APCs) play a key role in the induction of immunity by DNA vaccination. In the present work we have investigated whether the APCs are transfected by DNA injection into muscle.

METHODS

DNA encoding green fluorescent protein (GFP) was injected into rat and mouse limb muscle and followed by electroporation. Whole mount muscle tissue with GFP-positive mononuclear cells (MNCs) were treated with immunocytochemical markers specific for leukocytes, and studied with fluorescent microscopy. To detect transfected cells migrating to peripheral lymphoid tissue RT-PCR was applied on RNA isolated from the draining popliteal lymph node and spleen. Lymphoid tissue was also analyzed with real-time PCR for distribution of the injected plasmid.

RESULTS

MNCs were transfected after intramuscular DNA injection, and, following DNA injection with electroporation, the number of GFP-positive MNCs increased 6-fold in rats and 14-fold in mice. None of the GFP-positive MNCs were stained with leukocyte-specific antibodies. Even though GFP encoding DNA was detected in the popliteal lymph node, no RNA encoding GFP was found in the lymph node or spleen. However, MHC II-positive cells in the muscle tissue appeared preferentially around the transfected MNCs.

CONCLUSIONS

Many MNCs in the muscle are transfected after intramuscular DNA injection. Electroporation significantly increases the number of transfected MNCs. None of the observed transfected MNCs however were leukocytes. MHC II-positive cells accumulated around transfected MNCs; this suggests that transfer of antigen from transfected MNCs to APCs may contribute to the immune response.

Targeting plasmid-encoded proteins to the antigen presentation pathways

The antigen presentation pathways constitute a fulcrum on which adaptive immunity is balanced, and their manipulation should allow us to induce designer immune responses. The ease and rapidity with which DNA vaccines can be constructed and altered make them ideal candidates with which to test the various targeting strategies that have been conceived to date. These approaches and the mechanisms that may (or may not) underlie their success are reviewed in this article.

Generation and characterization of DNA vaccines targeting the nucleocapsid protein of severe acute respiratory syndrome coronavirus

Severe acute respiratory syndrome (SARS) is a serious threat to public health and the economy on a global scale. The SARS coronavirus (SARS-CoV) has been identified as the etiological agent for SARS. Thus, vaccination against SARS-CoV may represent an effective approach to controlling SARS. DNA vaccines are an attractive approach for SARS vaccine development, as they offer many advantages over conventional vaccines, including stability, simplicity, and safety. Our investigators have previously shown that DNA vaccination with antigen linked to calreticulin (CRT) dramatically enhances major histocompatibility complex class I presentation of linked antigen to CD8(+) T cells. In this study, we have employed this CRT-based enhancement strategy to create effective DNA vaccines using SARS-CoV nucleocapsid (N) protein as a target antigen. Vaccination with naked CRT/N DNA generated the most potent N-specific humoral and T-cell-mediated immune responses in vaccinated C57BL/6 mice among all of the DNA constructs tested. Furthermore, mice vaccinated with CRT/N DNA were capable of significantly reducing the titer of challenging vaccinia virus expressing the N protein of the SARS virus. These results show that a DNA vaccine encoding CRT linked to a SARS-CoV antigen is capable of generating strong N-specific humoral and cellular immunity and may potentially be useful for control of infection with SARS-CoV.

Prevention of gastrointestinal tumors based on adenomatous polyposis coli gene mutation by dendritic cell vaccine

Here we describe the effect of immunization with dendritic cells loaded with syngeneic tumor cells (DC/Ts) by polyethylene glycol treatment, on tumor development in adenomatous polyposis coli (APC) gene mutant mouse models, APC1309 and APC(Min-/+), in which adenomatous polyps of the gastrointestinal tracts develop with a high incidence. Treatment with DC/Ts prevented the development of gastrointestinal tumors, and coadministration of DC/Ts and IL-12 caused a further reduction in tumor incidence. Splenocytes from APC1309 mice treated with DC/Ts and IL-12 showed no cytotoxic activity toward the tumor cells, but serum antibody specific to them was detected. IgG from the treated mice exhibited cytotoxic activity against the tumor cells in vitro. Predominance of Th2 cell response over Th1 response was also suggested by ELISPOT assays in the treated mice. Depletion in vivo of CD4(+) T cells, not CD8(+) T cells, by the intraperitoneal administration of corresponding mAb's decreased the antitumor effect of DC/T inoculation. Immunofluorescence microscopic studies showed that Ig was attached to tumor cells in mice treated with DC/Ts and IL-12. These findings indicate that DC/T vaccination prevents tumor development through APC gene mutation and that its preventive effects are mediated by humoral antitumor immunity.

Induction of cytotoxic T lymphocyte activity by immunization with recombinant Semliki Forest virus: indications for cross-priming

For the rational design of vaccines capable of inducing CD8+ T cell responses knowledge of the identity of the antigen-presenting cell (APC) and the mechanism of antigen presentation is very important. Here, we address these issues for alphavirus-based immunization, in particular immunization with recombinant Semliki Forest virus (rSFV). Studies with dendritic cells (DCs) from various origins revealed that rSFV has a very limited capacity to transfect this cell type in vitro. To further investigate in vivo whether rSFV transfects professional antigen-presenting cells directly or whether the antigens reach APCs via a mechanism of cross-priming we compared the immunological effects of three different SFV-constructs encoding the influenza nucleoprotein (NP). These constructs differ in the amount of NP produced per cell or in the stability of the NP, respectively. Induction of cytotoxic T lymphocytes (CTLs) appeared to benefit from a large amount of stable antigen. In contrast, rapid antigen degradation, and thus availability of antigenic peptides in the transfected cell, was found to be disadvantageous. Based on these in vitro and in vivo results, we hypothesize that antigen presentation after SFV-based immunization proceeds via a mechanism in which APCs are not transfected directly but acquire antigen from other transfected cells and present it to CTLs in a process of cross-priming.

In vitro antitumor immune response induced by fusion of dendritic cells and colon cancer cells

AIM

The prevention of recurrence of colon cancer (CC) after operation is very important for improvement of the prognosis of CC patients, especially those with micro-metastasis. The generation of fused cells between dendritic cells (DCs) and tumor cells maybe an effective approach for tumor antigen presentation in immunotherapy. In this study, we fused human colon caner SW480 cells and human peripheral blood - derived DCs to induce an antitumor activity against human CC.

METHODS

CC SW480 cells and human peripheral blood - derived DCs were fused with 500 mL/L polyethylene glycol (PEG).

RESULTS

The specific T cell responses activated by fusion cells (FCs), were observed. About 100 mL/L to 160 mL/L of the PEG-treated non-adherent cells with fluorescences were considered to be dendritomas that highly expressed the key molecules for antigen presentation in our five cases. In vitro studies showed that fusions effectively activated CD8(+) T lymphocytes to secrete interferon-gamma. The early apoptotic ratio of the colon cancer SW480 cells was higher than that of controls, which was affected by cytotoxic T lymphocytes (CTLs) stimulated by dendritomas.

CONCLUSION

The data indicate that fusion of tumor cells with DCs is an attractive strategy to induce tumor rejection.

Plasmid encoding interleukin-4 in the amelioration of murine collagen-induced arthritis

OBJECTIVE

To evaluate the therapeutic effect of the administration of plasmid encoding interleukin-4 (IL-4) via gene-gun delivery and via intradermal injection on collagen-induced arthritis (CIA).

METHODS

IL-4 plasmid was administered by gene-gun delivery and intradermal injection to DBA/1 mice immunized with type II collagen (CII). The therapeutic effect on the development of CIA was evaluated clinically with a visual scoring method for arthritis and serologically by enzyme-linked immunosorbent assays and polymerase chain reaction.

RESULTS

Treatment with IL-4-expressing plasmid significantly reduced the incidence and severity of CIA, including a reduction in the anti-CII antibody level. In particular, gene-gun delivery had a higher immunosuppressive effect on CIA compared with intradermal injection. As shown by in vitro stimulation assay, the spleen cells from mice immunized with CII and treated with IL-4 plasmid via gene gun exhibited higher Th2 cytokine responses compared with cells treated with control plasmid after in vitro stimulation with CII.

CONCLUSION

The results of this study suggest that treatment with IL-4 plasmid may constitute a new clinical use of cytokine gene therapy for rheumatoid arthritis.

DNA vaccines against human immunodeficiency virus type 1 in the past decade

This article reviews advances in the field of human immunodeficiency virus type 1 (HIV-1) and AIDS vaccine development over the last decade, with an emphasis on the DNA vaccination approach. Despite the discovery of HIV-1 and AIDS in humans nearly 20 years ago, there is no vaccine yet that can prevent HIV-1 infection. The focus has shifted toward developing vaccines that can control virus replication and disease progression by eliciting broadly cross-reactive T-cell responses. Among several approaches evaluated, the DNA-based modality has shown considerable promise in terms of its ability to elicit cellular immune responses in primate studies. Of great importance are efforts aimed at improvement of the potency of this modality in the clinic. The review discusses principles of DNA vaccine design and the various mechanisms of plasmid-encoded antigen presentation. The review also outlines current DNA-based vaccine strategies and vectors that have successfully been shown to control virus replication and slow disease progression in animal models. Finally, it lists recent strategies that have been developed as well as novel approaches under consideration to enhance the immunogenicity of plasmid-encoded HIV-1 antigen in various animal models.