Co-expression of granulocyte-macrophage colony-stimulating factor with antigen enhances humoral and tumor immunity after DNA vaccination

Effect of Multiple Vaccinations with Tumor Cell-Based Vaccine with Codon-Modified GM-CSF on Tumor Growth in a Mouse Model

Ectopic expression of codon-modified granulocyte-macrophage colony-stimulating factor (cGM-CSF) in TC-1 cells (TC-1/cGM-CSF), a model cell line for human papillomavirus (HPV)-infected cervical cancer cells, increased the expression level of GM-CSF and improved the efficacy of tumor cell-based vaccines in a cervical cancer mouse model. The number of vaccine doses required to induce a long-term immune response in a cervical cancer mouse model is poorly understood. Here, we investigated one, three, and five doses of the irradiated TC-1/cGM-CSF vaccine to determine which dose was effective in inducing a greater immune response and the suppression of tumors. Our findings showed that three doses of irradiated TC-1/cGM-CSF vaccine elicited slower tumor growth rates and enhanced survival rates compared with one dose or five doses of irradiated TC-1/cGM-CSF vaccine. Consistently, mice vaccinated with three doses of irradiated TC-1/cGM-CSF vaccine exhibited stronger interferon gamma (IFN-γ) production in HPV E7-specific CD8⁺ T cells and CD4⁺ T cells. A higher percentage of natural killer cells and interferon-producing killer dendritic cells (IKDCs) appeared in the splenocytes of the mice vaccinated with three doses of irradiated TC-1/cGM-CSF vaccine compared with those of the mice vaccinated with one dose or five doses of irradiated TC-1/cGM-CSF vaccine. Our findings demonstrate that single or multiple vaccinations, such as five doses, with irradiated TC-1/cGM-CSF vaccine suppressed the immune response, whereas three doses of irradiated TC-1/cGM-CSF vaccine elicited a greater immune response and subsequent tumor suppression.

Is sentinel node susceptibility to metastases related to nodal immune modulation?

Sentinel lymph nodes (SLNs), the initial site of regional metastases, directly receive lymph containing immune-modulatory cytokines and tumor cells from primary melanomas. Immune-suppressed SLNs are ideal for studies of tissue susceptibility to metastases. They show reduced antigen-presenting dendritic cells, activated T cells, high endothelial venules, and transvenular immigration of T cells. Tumor-induced immune suppression contributes to establishment of nodal metastases. SLNs may serve as an effective model to study reversal of tumor-induced immune suppression. We reviewed this topic in Nature Reviews of Immunology in 2006. We here summarize the Nature paper and provide additional results from ongoing studies and the recent literature.

Synergistic antitumor efficacy of combined DNA vaccines targeting tumor cells and angiogenesis

To further enhance the antitumor efficacy of DNA vaccine, we proposed a synergistic strategy that targeted tumor cells and angiogenesis simultaneously. In this study, a Semliki Forest Virus (SFV) replicon DNA vaccine expressing 1-4 domains of murine VEGFR2 and IL12 was constructed, and was named pSVK-VEGFR2-GFc-IL12 (CAVE). The expression of VEGFR2 antigen and IL12 adjuvant molecule in 293T cells in vitro were verified by western blot and enzyme-linked immune sorbent assay (ELISA). Then CAVE was co-immunized with CAVA, a SFV replicon DNA vaccine targeting survivin and β-hCG antigens constructed previously. The antitumor efficacy of our combined replicon vaccines was evaluated in mice model and the possible mechanism was further investigated. The combined vaccines could elicit efficient humoral and cellular immune responses against survivin, β-hCG and VEGFR2 simultaneously. Compared with CAVE or CAVA vaccine alone, the combined vaccines inhibited the tumor growth and improved the survival rate in B16 melanoma mice model more effectively. Furthermore, the intratumoral microvessel density was lowest in combined vaccines group than CAVE or CAVA alone group. Therefore, this synergistic strategy of DNA vaccines for tumor treatment results in an increased antitumor efficacy, and may be more suitable for translation to future research and clinic.

DNA vaccination for prostate cancer: key concepts and considerations

While locally confined prostate cancer is associated with a low five year mortality rate, advanced or metastatic disease remains a major challenge for healthcare professionals to treat and is usually terminal. As such, there is a need for the development of new, efficacious therapies for prostate cancer. Immunotherapy represents a promising approach where the host's immune system is harnessed to mount an anti-tumour effect, and the licensing of the first prostate cancer specific immunotherapy in 2010 has opened the door for other immunotherapies to gain regulatory approval. Among these strategies DNA vaccines are an attractive option in terms of their ability to elicit a highly specific, potent and wide-sweeping immune response. Several DNA vaccines have been tested for prostate cancer and while they have demonstrated a good safety profile they have faced problems with low efficacy and immunogenicity compared to other immunotherapeutic approaches. This review focuses on the positive aspects of DNA vaccines for prostate cancer that have been assessed in preclinical and clinical trials thus far and examines the key considerations that must be employed to improve the efficacy and immunogenicity of these vaccines.

GM-CSF-loaded chitosan hydrogel as an immunoadjuvant enhances antigen-specific immune responses with reduced toxicity

Background

The application of vaccine adjuvants has been vigorously studied for a diverse range of diseases in order to improve immune responses and reduce toxicity. However, most adjuvants have limited uses in clinical practice due to their toxicity.

Methods

Therefore, to reduce health risks associated with the use of such adjuvants, we developed an advanced non-toxic adjuvant utilizing biodegradable chitosan hydrogel (CH-HG) containing ovalbumin (OVA) and granulocyte-macrophage colony-stimulating factor (GM-CSF) as a local antigen delivery system.

Results

After subcutaneous injection into mice, OVA/GM-CSF-loaded CH-HG demonstrated improved safety and enhanced OVA-specific antibody production compared to oil-based adjuvants such as Complete Freund’s adjuvant (CFA) or Incomplete Freund’s adjuvant (IFA). Moreover, CH-HG system-mediated immune responses was characterized by increased number of OVA-specific CD4⁺ and CD8⁺ INF-γ⁺ T cells, leading to enhanced humoral and cellular immunity.

Conclusions

In this study, the improved safety and enhanced immune response characteristics of our novel adjuvant system suggest the possibility of the extended use of adjuvants in clinical practice with reduced apprehension about toxic side effects.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-014-0048-x) contains supplementary material, which is available to authorized users.

MAGE proteins regulate KRAB zinc finger transcription factors and KAP1 E3 ligase activity

Expression of Melanoma AntiGen Encoding (MAGE) genes, particularly MAGE-A3, has been correlated with aggressive clinical course, the acquisition of resistance to chemotherapy and poor clinical outcomes of melanoma and other malignancies. MAGE proteins bind to KAP1, a gene repressor and ubiquitin E3 ligase which also binds KRAB domain containing zinc finger transcription factors (KZNFs), and MAGE expression may affect KZNF mediated gene regulation. To investigate mechanisms for these effects, we tested the hypothesis that differences in KRAB domain composition affect KZNF poly-ubiquitination and determine whether MAGE expression increases, decreases, or has no effect on KZNFs mediated gene repression. Using an integrated reporter gene responsive to repression by KRAB domain fusion proteins, we found that MAGE-A3 relieved KZNF mediated repression and induced KZNF poly-ubiquitination and degradation in association with expression of the A+B box KRAB domain. In contrast, MAGE-A3 enhanced KAP1 mediated repression of KZNFs expressing A or A+b box KRAB domains but caused no increase in poly-ubiquitination or degradation. MAGE-A3 has no significant impact on KZNFs with KRAB domains containing the Scan box motif. These data support our hypothesis by showing that the effects of MAGE-A3 on gene repression depend on the type of KZNF KRAB domain involved.

Enhancement of antitumor immunity using a DNA-based replicon vaccine derived from Semliki Forest virus

A DNA-based replicon vaccine derived from Semliki Forest virus, PSVK-shFcG-GM/B7.1 (Fig. 1a) was designed for tumor immunotherapy as previously constructed. The expression of the fusion tumor antigen (survivin and hCGβ-CTP37) and adjuvant molecular protein (Granulocyte-Macrophage Colony-Stimulating Factor/ GM-CSF/B7.1) genes was confirmed by Immunofluorescence assay in vitro, and immunohistochemistry assay in vivo. In this paper, the immunological effect of this vaccine was determined using immunological assays as well as animal models. The results showed that this DNA vaccine induced both humoral and cellular immune responses in C57BL/6 mice after immunization, as evaluated by the ratio of CD4⁺/CD8⁺ cells and the release of IFN-γ. Furthermore, the vaccination of C57BL/6 mice with PSVK-shFcG-GM/B7.1 significantly delayed the in vivo growth of tumors in animal models (survivin⁺ and hCGβ⁺ murine melanoma, B16) when compared to vaccination with the empty vector or the other control constructs (Fig. 1b). These data indicate that this type of replicative DNA vaccine could be developed as a promising approach for tumor immunotherapy. Meanwhile, these results provide a basis for further study in vaccine pharmacodynamics and pharmacology, and lay a solid foundation for clinical application.

Protective Immunity againstBordetella pertussisby a Recombinant DNA Vaccine and the Effect of Coinjection with a Granulocyte-Macrophage Colony Stimulating Factor Gene

A recombinant pertussis DNA vaccine was described here with its immunogenicity and the ability to induce protection against B. pertussis infection in mice. Three immunodominant antigen gene fragments of pertussis, pertussis toxin subunit 1 (pts1), fragments of pertactin (prn) and filamentous hemagglutinin (fha), were recombined as fragment pts1-prn-fha named ppf, and it was cloned to plasmid pVAX1 as pVAX1/ppf. Compared to those injected with pVAX1, the mice injected with pVAX1/ppf significantly elicited more antigen specific antibody anti-PTS1, anti-PRN, anti-FHA and cytokine IL-10, IFN-gamma. When pGM-CSF was coinjected with pVAX1/ppf, the mice showed significantly increases of the three antibodies and cytokine IL-10, IL-4, IFN-gamma and TNF-alpha compared to those injected with pVAX1 only. The mice in group pVAX1/ppf & pGM-CSF, in particular; induced much more anti-PTS1, IL-4 and TNF-alpha than those in group pVAX1/ppf. In the intracerebral mouse protection test, the mice immunized with pVAX1/ppf or pVAX1/ppf & pGM-CSF induced protection to a lethal dose of B. pertussis. The results indicate that recombinant DNA vaccine and pGM-CSF coinjection can induce protective immunity against B. pertussis, demonstrating a valuable method to prevent pertussis.

Granulocyte-Macrophage Colony Stimulating Factor: An Adjuvant for Cancer Vaccines

Granulocyte-macrophage colony stimulating factor (GM-CSF) enhances immune responses by inducing the proliferation, maturation, and migration of dendritic cells, and the expansion and differentiation of B and T lymphocytes. There is significant data in pre-clinical animal models demonstrating the adjuvant effects of GM-CSF in a variety of cancer vaccine approaches, including cellular vaccines, viral vaccines, peptide and protein vaccines, and DNA vaccines. GM-CSF is an attractive vaccine adjuvant because of its immune modulation effects and low toxicity profile. The results in animal models have been confirmed in pilot clinical trials and several clinical trials are currently ongoing.

Enhancement of the immunogenicity of DNA replicon vaccine of Clostridium botulinum neurotoxin serotype A by GM-CSF gene adjuvant

Granulocyte-macrophage clony-stimulating factor (GM-CSF) is an attractive adjuvant for a DNA vaccine on account of its ability to recruit antigen-presenting cells to the site of antigen synthesis as well as stimulate the maturation of dendritic cells.This study evaluated the utility of GM-CSF as a plasmid DNA replicon vaccine adjuvants for botulinum neurotoxin serotype A (BoNT/A) in mouse model. In balb/c mice that received the plasmid DNA replicon vaccines derived from Semliki Forest virus (SFV) carrying the Hc gene of BoNT/A (AHc), both antibody and lymphoproliferative response specific to AHc were induced, the immunogenicity was enhanced by co-delivery or coexpress of the GM-CSF gene. In particular, when AHc and GM-CSF were coexpressed within the SFV based DNA vaccine, the anti-AHc antibody titers and survival rates of immunized mice after challenged with BoNT/A were significantly increased, and further enhanced by coimmunization with aluminum phosphate adjuvant.

A high-affinity T-helper epitope enhances peptide-pulsed dendritic cell-based vaccine

The NV epitope, a dominant helper determinant from the circumsporozoite antigen of Plasmodium falciparum, is strongly immunogenic and can provide help for cytotoxic T-lymphocyte (CTL) activation. In this study, we evaluated whether the addition of NV peptide can augment the efficacy of peptide-pulsed dendritic cell (DC) immunization in vivo. Using B16 melanoma as tumor model, we demonstrated that DCs pulsed with both NV and gp100 (a melanoma-specific antigen) peptide enhanced immune priming and protection from tumor challenge in vivo. Further, we showed the mechanisms of the NV epitope that help CTL activation; MHC-II-restricted NV peptide induced dramatically more effective helper cells, with a higher level of CD40L expression and IFN-γ production, which, in turn, more effectively conditioned DCs for CTL activation. The improved helper cells also induced greater IL-12 production by DCs, accounting for the reciprocal T-helper polarization to Th1, and increased the expression of costimulatory molecules. Collectively, these findings demonstrate that NV peptide in addition to tumor antigen-pulsed DC immunizations augment helper cell activation, which in turn promotes maturation of DC, and enhance in vivo antitumor activity.

GM-CSF and IL-2 as adjuvant enhance the immune effect of protein vaccine against foot-and-mouth disease

Background

Cytokines as molecular adjuvant play a critical role in differentiation of effector T cell subsets and in determination of the magnitude of the response after vaccination. In this study, we investigated the effects of GM-CSF and IL-2 as adjuvant on the immune responses of VP1 recombinant protein as a model antigen for foot and mouth disease.

Results

Six expression plasmids were constructed and expressed in E. coli BL21. In guinea pigs, the immunological and molecular effects of the fusion proteins were determined by ELISA, LPA, DTH and semi-quantitative Reverse Transcriptase PCR (RT-PCR). The data revealed that IL-2 and GM-CSF as adjuvant of VP1 could stimulate both humoral and cell-mediated immune response. Interestingly, IL-2 and GM-CSF, either as a co-expressed protein or as a mixture of two single proteins, showed much better adjuvant effects than that of single one.

Conclusions

IL-2 and GM-CSF could be used as a potential adjuvant for VP1 and had synergistic effect when co-expressed or mixed with VP1.

The dermis as a portal for dendritic cell-targeted immunotherapy of cutaneous melanoma

Complete surgical excision at an early stage remains the only curative treatment for cutaneous melanoma with few available adjuvant therapy options. Nevertheless, melanoma is a relatively immunogenic tumor type and particularly amenable to immunotherapeutic approaches. A dense network of cutaneous dendritic cells (DC) may account for the reported efficacy of vaccination through the skin and provide an attractive target for the immunotherapy of melanoma. Several phenotypically distinct DC subsets are discernable in the skin, among others, epidermal Langerhans cells and dermal DC. Upon appropriate activation both subsets can efficiently migrate to melanoma-draining lymph nodes (LN) to prime T cell-mediated responses. Unfortunately, from an early stage, melanoma development is characterized by strong immune suppression, facilitating unchecked tumor growth and spread. Particularly the primary tumor site and the first-line tumor-draining LN, the so-called sentinel LN, bear the brunt of this melanoma-induced immune suppression-and these are exactly the sites where anti-melanoma effector T cell responses should be primed by DC in order to prevent early metastasis. Through local immunopotentiation or through DC-targeted vaccination, the dermis may be utilized as a portal to activate DC and kick-start or boost effective T cell-mediated anti-melanoma immunity, even in the face of this immune suppression.

DNA vaccination: using the patient's immune system to overcome cancer

Cancer is one of the most challenging diseases of today. Optimization of standard treatment protocols consisting of the main columns of chemo- and radiotherapy followed or preceded by surgical intervention is often limited by toxic side effects and induction of concomitant malignancies and/or development of resistant mechanisms. This requires the development of therapeutic strategies which are as effective as standard therapies but permit the patients a life without severe negative side effects. Along this line, the development of immunotherapy in general and the innovative concept of DNA vaccination in particular may provide a venue to achieve this goal. Using the patient's own immune system by activation of humoral and cellular immune responses to target the cancer cells has shown first promising results in clinical trials and may allow reduced toxicity standard therapy regimen in the future. The main challenge of this concept is to transfer the plethora of convincing preclinical and early clinical results to an effective treatment of patients.

Comparative measurement of cell-mediated immune responses of swine to the M and N proteins of porcine reproductive and respiratory syndrome virus

The principal objectives of this study were to develop autologous antigen-presenting cells (APCs) and to characterize the antigen-specific T-cell responses to the M and N proteins of porcine reproductive and respiratory syndrome virus (PRRSV) by using those APCs in outbred pigs. The orf6 and orf7 genes fused with porcine granulocyte-macrophage colony-stimulating factor (GM-CSF) were cloned into the mammalian expression vector to generate two plasmid DNAs, namely, pcDNA3.1-GM-CSF-PRRSV-M and pcDNA3.1-GM-CSF-PRRSV-N. Three of six pigs in two groups were repeatedly immunized with either plasmid DNA construct, and four pigs were used as controls. The recombinant M and N proteins fused with the protein transduction domain (PTD) of the human immunodeficiency virus type 1 transactivator of transcription protein were employed to generate major histocompatibility complex-matched autologous APCs from each pig. The levels of T-cell proliferation and gamma interferon (IFN-gamma) synthesis were compared between pigs immunized with the two plasmid DNAs after stimulation of the peripheral blood mononuclear cells (PBMCs) of each pig with the autologous antigen-presenting dendritic cells and PBMCs. Higher levels of T-cell proliferation and IFN-gamma synthesis were identified in PBMCs isolated from the pigs immunized with pcDNA3.1-GM-CSF-PRRSV-M than in those isolated from the pigs immunized with pcDNA3.1-GM-CSF-PRRSV-N. By way of contrast, serum antibodies were detected only in pigs immunized with pcDNA3.1-GM-CSF-PRRSV-N. However, no T-cell response or antibody production was detected in the control pigs. These results suggest that the M protein of PRRSV is a more potent T cell-stimulating antigen than the N protein. Nevertheless, it should be emphasized that the N protein substantially induces both cellular and humoral immune responses. The newly developed protocol for generating self APCs may prove effective in further efforts to characterize additional PRRSV proteins involved in the induction of cell-mediated immunity.

A cytokine-cytokine interaction in the assembly of higher-order structure and activation of the interleukine-3:receptor complex

Interleukine-3 (IL-3) binds its receptor and initiates a cascade of signaling processes that regulate the proliferation and differentiation of hematopoietic cells. To understand the detailed mechanisms of IL-3 induced receptor activation, we generated a homology model of the IL-3:receptor complex based on the closely related crystal structure of the GM-CSF:receptor complex. Model-predicted interactions between IL-3 and its receptor are in excellent agreement with mutagenesis data, which validate the model and establish a detailed view of IL-3:receptor interaction. The homology structure reveals an IL-3:IL-3 interaction interface in a higher-order complex modeled after the dodecamer of the GM-CSF:receptor complex wherein an analogous GM-CSF:GM-CSF interface is also identified. This interface is mediated by a proline-rich hydrophobic motif (PPLPLL) of the AA' loop that is highly exposed in the structure of isolated IL-3. Various experimental data suggest that this motif is required for IL-3 function through receptor-binding independent mechanisms. These observations are consistent with structure-function studies of the GM-CSF:receptor complex showing that formation of the higher-order cytokine:receptor complex is required for signaling. However, a key question not answered from previous studies is how cytokine binding facilitates the assembly of the higher-order complex. Our studies here reveal a potential cytokine-cytokine interaction that participates in the assembly of the dodecamer complex, thus linking cytokine binding to receptor activation.

Melanoma vaccines

Over the last century, vaccine studies have demonstrated that the human immune system, with appropriate help, can limit or prevent infection against otherwise lethal pathogens. Encouraged by these results, success in animal models and numerous well-documented reports of immune-mediated melanoma regression in humans, investigators developed melanoma vaccines. However, despite considerable laboratory evidence for vaccine-induced immune responses, clinical responses remain poor. Recent studies have elucidated several mechanisms that hinder or prevent the creation of successful vaccines and suggest novel approaches to overcome these barriers. Unraveling the mechanisms of autoimmunity, dendritic cell activation, regulatory T cells and Toll-like receptors will generate novel vaccines that, when used in conjunction with standard adjuvant therapies, may result in improved clinical outcomes. The objective of this review is to provide an overall summary of recent clinical trials with melanoma vaccines and highlight novel vaccine strategies to evaluate in the near future.

The structure of the GM-CSF receptor complex reveals a distinct mode of cytokine receptor activation

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic cytokine that controls the production and function of blood cells, is deregulated in clinical conditions such as rheumatoid arthritis and leukemia, yet offers therapeutic value for other diseases. Its receptors are heterodimers consisting of a ligand-specific alpha subunit and a betac subunit that is shared with the interleukin (IL)-3 and IL-5 receptors. How signaling is initiated remains an enigma. We report here the crystal structure of the human GM-CSF/GM-CSF receptor ternary complex and its assembly into an unexpected dodecamer or higher-order complex. Importantly, mutagenesis of the GM-CSF receptor at the dodecamer interface and functional studies reveal that dodecamer formation is required for receptor activation and signaling. This unusual form of receptor assembly likely applies also to IL-3 and IL-5 receptors, providing a structural basis for understanding their mechanism of activation and for the development of therapeutics.

In vivo responses to vaccination with Mage-b, GM-CSF and thioglycollate in a highly metastatic mouse breast tumor model, 4T1

Metastatic breast cancer is an important contributor to morbidity and mortality. Hence, new therapies are needed that target breast cancer metastases. Here, we focus on Mage-b as a possible vaccine target to prevent the development of breast cancer metastases, through activation of Mage-b-specific cytotoxic T lymphocytes (CTL). The syngeneic cell line 4T1, highly expressing Mage-b, was used as a pre-clinical metastatic mouse breast tumor model. BALB/c mice received three preventive intraperitoneal immunizations with Mage-b DNA vaccine mixed with plasmid DNA, secreting granulocyte-macrophage colony stimulating factor (GM-CSF). In addition, antigen-presenting cells were more efficiently recruited to the peritoneal cavity by the injection of thioglycollate broth (TGB), prior to each immunization. Immunization with Mage-b/GM-CSF/TGB significantly reduced the number of metastases by 67% compared to the saline/GM-CSF/TGB and by 69% compared to the vector control/GM-CSF/TGB. Also, tumor growth was significantly reduced by 45% in mice vaccinated with Mage-b/GM-CSF/TGB compared to the saline/ GM-CSF/TGB and by 47% compared to the control vector/ GM-CSF/TGB group. In vivo, the number of CD8 T cells significantly increased in the primary tumors and metastases of mice vaccinated with Mage-b/GM-CSF/TGB compared to the saline/GM-CSF/TGB and the control vector/ GM-CSF/TGB group, while the number of CD4 T cells significantly decreased. The combination of Mage-b, GM-CSF and TGB did not only induce significantly higher levels of IFNgamma in the lymph nodes of vaccinated compared to control mice, but also induced significantly higher expression levels of Fas-ligand (FasL) in the primary tumors (expressing Fas protein constitutively), compared to the control mice. Whether the interaction between Fas and FasL may have contributed to the smaller tumors needs to be further analyzed.

Granulocyte-macrophage colony-stimulating factor DNA prime-protein boost strategy to enhance efficacy of a recombinant pertussis DNA vaccine

AIM

To investigate a new strategy to enhance the efficacy of a recombinant pertussis DNA vaccine. The strategy is co-injection with cytokine plasmids as prime, and boosted with purified homologous proteins.

METHOD

A recombinant pertussis DNA vaccine containing the pertussis toxin subunit 1 (PTS1), fragments of the filamentous hemagglutinin (FHA) gene and pertactin (PRN) gene encoding filamentous hemagglutinin and pertactin were constructed. Balb/c mice were immunized with several DNA vaccines and antigen-specific antibodies anti-PTS1,anti-PRN, anti-FHA,cytokines interleukin (IL)-10, IL-4, IFN-gamma,TNF-alpha,and splenocyte-proliferation assay were used to describe immune responses.

RESULTS

The recombinant DNA vaccine could elicit similar immune responses in mice as that of separate plasmids encoding the 3 fragments, respectively. Mice immunized with DNA and boosted with the corresponding protein elicited more antibodies than those that received DNA as boost. In particular, when the mice were co-immunized with murine granulocyte-macrophage colony-stimulating factor plasmids and boosted with proteins, all 4 cytokines and the 3 antigen-specific antibodies were significantly increased compared to the pVAX1 group. Anti-PTS1, anti- FHA, IL-4 and TNF-alpha elicited in the colony stimulating factor (CSF) prime-protein boost group showed significant increase compared to all the other groups.

CONCLUSION

This prime and boost strategy has proven to be very useful in improving the immunogenicity of DNA vaccines against pertussis.

Tumour-induced immune modulation of sentinel lymph nodes

Sentinel lymph nodes (SLNs), being the first nodes to receive lymph from a primary tumour and the preferential site of initial tumour metastases, are intensively exposed to the bioactive products of tumour cells and other associated cells. This makes them ideal for studies of the factors that determine selective tissue susceptibility to metastases. We postulate that tumour-induced immune modulation of SLNs facilitates lymph-node metastases by inhibiting the generation of tumour-specific cytotoxic T cells that are active against tumour cells of primary and metastatic melanomas. Immune modulation of the lymph nodes can be reversed by granulocyte/macrophage colony-stimulating factor (GM-CSF), a finding that has implications for the future therapy of lymph-node metastases.

Select cancer testes antigens of the MAGE-A, -B, and -C families are expressed in mast cell lines and promote cell viability in vitro and in vivo

MAGE antigens are proteins that are normally expressed only in gametes but are often aberrantly expressed in melanomas, hematopoietic malignancies, and other "cancers". The functions of most MAGE proteins are unknown. Data have accumulated suggesting expression of MAGE proteins by malignant cells may contribute to advanced disease or resistance to chemotherapy, but direct evidence supporting this hypothesis is lacking. We show here that small interfering RNA (siRNA) suppression of MAGE-A, -B, and -C gene expression slows proliferation and induces caspase independent apoptosis in human and murine mast cell lines. Furthermore, treatment with MAGE specific siRNA suppresses growth of malignant cells in an in vivo murine model of mastocytosis. These observations demonstrate that MAGE protein expression can contribute to the development of tumors by permitting proliferation and prolonging the survival of malignant cells. We suggest a shift of the current clinical paradigm from one that envisions MAGE proteins solely as targets for immunologic attack to one in which MAGE genes and proteins are also targets for functional manipulation.

Intramuscular immunization with plasmid coexpressing tumour antigen and Flt-3L results in potent tumour regression

Dendritic cells (DC) are professional antigen-presenting cells capable of initiating a potent primary immune response, making them an attractive target for cancer immunotherapy. Flt-3 ligand (Flt-3L) is a haematopoietic growth factor that efficiently induces DC expansion in vivo. To achieve a more efficient and effective method of priming tumour-specific, DC-mediated immune response, we generated a DNA vaccine comprising both human Flt-3L and the tumour antigen, MUC-1 (pNGVL-hFLex-MUC-1). We report that pNGVL-hFLex-MUC-1 is able to induce antigen-specific CTL immunity in vivo, resulting in a potent anti-tumour response, and that the Flt-3L component is essential to the efficacy of the DNA vaccine. Moreover, the route of immunization is critical in determining the type of immune response generated; intramuscular (i.m.) immunization with pNGVL-hFLex-MUC-1 conferred tumour protection in contrast to poor response with hydrodynamic-based intravenous delivery. Post-i.m. immunization, we observed a massive infiltration of mononuclear cells to the injection site, comprised predominantly of CD11c(+)/CD8alpha(-) DC. Therefore, we propose that Flt-3L acts as an adjuvant to recruit DC, thereby priming the anti-tumour response. However, systemic expansion of DC prior to immunization did not enhance the specific cellular response, suggesting that it is in situ recruitment or expansion of DC that is critical for pNGVL-hFLex-MUC-1 potency.

Experimental frontiers for clinical applications: Novel approaches to understanding mechanisms of lymph Node metastases in melanoma

Sentinel lymph nodes are the first nodes to receive lymph from primary tumors and are the preferential site of initial metastases. Sentinel nodes show morphology changes that suggests immune modulation with reduced antigen-presenting dendritic cells, activated T lymphocytes, high endothelial venules and transvenular migration of T lymphocytes. Tumor cells generate down-regulatory molecules. We postulate that tumor-induced immune dysfunction facilitates establishment of nodal metastases. Nodal immune modulation can be reversed by granulocyte macrophage colony-stimulating factor (GMCSF), a finding with implications for future therapy to prevent or reverse these nodal metastases.

Cytokine GM-CSF genetic adjuvant facilitates prophylactic DNA vaccine against pseudorabies virus through enhanced immune responses

Granulocyte/macrophage colony-stimulatory factor (GM-CSF) is an attractive adjuvant for a DNA vaccine on account of its ability to recruit antigen-presenting cells (APCs) to the site of antigen synthesis as well as its ability to stimulate the maturation of dendritic cells (DCs). This study evaluated the utility of GM-CSF cDNA as a DNA vaccine adjuvant for glycoprotein B (gB) of pseudorabies virus (PrV) in a murine model. The co-injection of GM-CSF DNA enhanced the levels of serum PrV-specific IgG with a 1.5-to 2-fold increase. Moreover, GM-CSF co-injection inhibited the production of IgG2a isotype. However, it enhanced production of an IgG1 isotype resulting in humoral responses biased to the Th2-type against PrV antigen. In contrast, the co-administration of GM-CSF DNA enhanced the T cell-mediated immunity biased to the Th1-type, as judged by the significantly higher level of cytokine IL-2 and IFN-gamma production but not IL-4. When challenged with a lethal dose of PrV, the GM-CSF co-injection enhanced the resistance against a PrV infection. This suggests that co-inoculation with a vector expressing GM-CSF enhanced the protective immunity against a PrV infection. This immunity was caused by the induction of increased humoral and cellular immunity in response to PrV antigen.

DNA immunization of dairy cows with the clumping factor A of Staphylococcus aureus

Blocking the primary stages of Staphylococcus aureus infection, specifically the bacterial adhesion to cell and the colonization of the mucosal surface, may be the most effective strategy for preventing infections. Clumping factor A (ClfA) is considered to be one of the most important adhesions factors of S. aureus to host cells. The present study describes the immune response of dairy cattle to a DNA vaccine against ClfA and evaluates the ability of specific genetic adjuvants, targeting sequences (granulocyte macrophage colony-stimulating factor and cytotoxic T lymphocyte antigen-4) and transporter molecules (chitosan and copolymer) to modify the immune response of cows. The results show that vaccination of cows with fibrinogen-binding region A induced a strong and specific antibody response to ClfA in comparison with a control group injected with the pCI vector alone. Although the co-expression of both genetic adjuvants and the addition copolymer transporter did not augment the overall antibody response, these approaches decreased the number of non-responsive cows. Chitosan was the only factor that did not enhance the immune response. Three months after the last DNA immunization, three cows from each of the pGM-CSF, internal ribosomal entry site (IRES), pCTLA and pCI groups were injected with 200 microg of recombinant ClfA protein in incomplete Freund's adjuvant. A strong humoral response was observed in all groups following this protein boost, with the response occurring slightly earlier in DNA-primed protein boost cows. Sera and milk samples taken from cows after the second DNA injection or after the protein boost (sera only) were analyzed for their ability to block adherence and increase phagocytosis. Pre-incubation of S. aureus with sera or milk from vaccinated cows significantly reduced the pathogen's ability to adhere to MAC-T cells relative to the sera and milk samples from the pCI-injected control cows. Similarly, pools of sera and milk from vaccinated cows increased phagocytosis of S. aureus by neutrophils. After the protein boost, sera were more efficient promoters of phagocytosis, reflecting the higher anti-ClfA antibody level of these sera. DNA-prime/protein boost regimes combined with molecular adjuvants appeared to be effective in generating a strong immune response to S. aureus antigens in cattle.

Immunization with a gene encoding granulocyte-macrophage colony-stimulating factor inserted with a single helper T-cell epitope of an intracellular bacterium induces a specific T-cell subset and protective immunity

We evaluated here the effect of immunization with a gene encoding granulocyte-macrophage colony-stimulating factor (GM-CSF) inserted with a helper T cell (Th) epitope, listeriolysin O (LLO) 215-226 derived from Listeria monocytogenes on induction of a specific Th by gene gun bombardment. Immunization of C3H/He mice with pGM215m plasmid encoding murine GM-CSF inserted with LLO 215-226 Th epitope gave the epitope-specific proliferative responses of CD4(+) T lymphocytes. In addition, specific interferon-gamma production from the splenocytes was observed. Concomitantly, pGM215m-immunized mice showed significant protective immunity against lethal listerial challenge. These results suggest that immunization of a gene for GM-CSF inserted with a Th epitope is useful for eliciting a specific Th subset in vivo.

Granulocyte-macrophage colony-stimulating factor does not increase the potency or efficacy of a foot-and-mouth disease virus subunit vaccine

Foot-and-mouth disease (FMD) is one of the most feared diseases of livestock worldwide. Vaccination has been a very effective weapon in controlling the disease, however a number of concerns with the current vaccine including the inability of approved diagnostic tests to reliably distinguish vaccinated from infected animals and the need for high containment facilities for vaccine production, have limited its use during outbreaks in countries previously free of the disease. A number of FMD vaccine candidates have been tested and a replication-defective human adenovirus type 5 (Ad5) vector containing the FMDV capsid (P1-2A) and 3C protease coding regions has been shown to completely protect pigs against challenge with the homologous virus (FMDV A12 and A24). An Ad5-P1-2A+3C vaccine for FMDV O1 Campos (Ad5-O1C), however, only induced a low FMDV-specific neutralizing antibody response in swine potency tests. Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been successfully used to stimulate the immune response in vaccine formulations against a number of diseases, including HIV, hepatitis C and B. To attempt to improve the FMDV-specific immune response induced by Ad5-O1C, we inoculated swine with Ad5-O1C and an Ad5 vector containing the gene for porcine GM-CSF (pGM-CSF). However, in the conditions used in this trial, pGM-CSF did not improve the immune response to Ad5-O1C and adversely affected the level of protection of swine challenged with homologous FMDV.

The mouse chorionic gonadotropin beta-subunit-like (muCG beta l) molecule produced by tumor cells elicits the switch of T-cell immunity response from TH2 to TH1 in mice immunized with DNA vaccine based on rhesus monkey homologous CG beta (rmCG beta)

BACKGROUND

CG beta is expressed not only in placenta, but also in a wide range of tumors. To study DNA vaccine based on xenogeneic CG beta for cancer immuno-therapy, we investigated whether rhesus monkey CG beta (rmCG beta) DNA vaccine could induce protective T-cell responses and humoral responses in mouse.

METHODS

We constructed a plasmid containing the rmCG beta coding sequence. Two cloned syngeneic SP2/0 myeloma cell lines that stably express muCG beta l (SP2/0-muCG beta l) and HN (SP2/0-HN) protein were established. Inoculation of these cell lines was made into mice that had been immunized with DNA vaccine. Specific IgG and IgG type were measured by ELISA and the cytokine expression was detected with RT-PCR. To measure the lymphocyte metabolic activity, the MTS assay was used.

RESULTS

After injection of SP2/0-muCG beta l into mice that had been immunized with DNA vaccine, a significant increase in the IgG2a specific to the antigen (p < 0.05) and a decrease in the specific IgG1 (p < 0.05) were measured. The expression of T(H)1 but not T(H)2 cytokines, including IFN-gamma and IL-2, were detected in the splenocytes. However, injection of tumor cells expressing irrelevant or mock molecules into immunized mice could not induce these changes. The survival rate of vaccine-immunized mice injected with SP2/0-muCG beta l was as high as 58.3% after 55 days.

CONCLUSIONS

The rmCG beta DNA vaccine has proved to be a potential strategy for protection against tumors with homologous molecules. The muCG beta l produced by tumors is able to elicit an immunity switch from T(H)2 to T(H)1 in vaccinated mice.

Antigen epitope-expressing cytokines for DNA immunization

Strategies to enhance the efficacy of DNA vaccination against malignancy remain to be established. In this study, a plasmid expressing a tumor antigen incorporated into the signal peptide of human IL-2 was tested as a DNA vaccine in a murine model system. Results showed that antigen-specific CTL responses were elicited by intramuscular injection of these plasmids. Importantly, compared with a minigene vector expressing the same epitope, the OVA epitope-incorporated, IL-2 expression plasmid vaccination was more effective in protecting mice from OVA-expressing tumor challenge. The improved efficacy appears to result from enhanced antigen presentation as well as the immunostimulatory activity of IL-2. This approach may provide new perspectives in designing cytokine-adjuvant DNA vaccines for clinical applications.

A DNA vaccine encoding genetic fusions of carcinoembryonic antigen (CEA) and granulocyte/macrophage colony-stimulating factor (GM-CSF)

The anti-tumor immunologic effects of plasmid DNA vaccines encoding human carcinoembryonic antigen (CEA) fused to mouse granulocyte/macrophage colony-stimulating factor (GM-CSF) were examined. Immunization of C57BL/6 mice with the CEA-GMCSF fusion plasmids in a three injection, high-dose immunization schedule led to T cell and antibody responses specific for CEA. Mice injected with CEA-GMCSF fusion plasmids also developed IgG autoantibodies to GM-CSF. Tumor challenge with the CEA-expressing syngeneic mouse adenocarcinoma line, MC38-CEA-2, showed delayed tumor growth in mice immunized with the CEA-GMCSF fusion plasmids but complete protection in mice immunized with plasmid encoding CEA alone. In contrast, a single low-dose immunization with CEA-GMCSF fusion plasmids provided better tumor protection than low-dose CEA plasmid alone and resulted in lower titers of GM-CSF antibodies.

TLR9-/- and TLR9+/+ mice display similar immune responses to a DNA vaccine

Plasmid DNA continues to attract interest as a potential vaccine-delivery vehicle. However, the mechanisms whereby immune responses are elicited by plasmids are not fully understood. Although there have been suggestions regarding the importance of CpG motifs in plasmid immunogenicity, the molecular mechanisms by which CpG motifs enhance immune responses to DNA vaccines are not well understood. As Toll-like receptor 9-deficient (TLR9-/-) mice fail to respond to the adjuvant effects of CpG oligonucleotides, we used these mice to determine the effect of CpG motifs in plasmids used for DNA immunization. In the study described below, we report that DNA immunization was as effective in eliciting antigen-specific antibody and at stimulating antigen-specific interferon-gamma (IFN-gamma)-secreting cells in TLR9-/- mice as in TLR9+/+ mice. This study illustrates that DNA vaccines elicit immune responses by multiple mechanisms and demonstrates that TLR9 is not essential for the induction of immune responses following DNA immunization.

Heat shock protein 70 / MAGE-1 tumor vaccine can enhance the potency of MAGE-1-specific cellular immune responses in vivo

The cancer-testis antigen encoded by the MAGE-1 gene is an attractive antigen in tumor immunotherapy because it can be processed as a foreign antigen by the immune system and generate tumor-specific cellular immune response in vivo. However, increase of the potency of MAGE-1 DNA vaccines is still needed. The high degree of sequence homology and intrinsic immunogenicity of heat shock protein 70 (HSP70) have prompted the suggestion that HSP70 might have immunotherapeutic potential, as HSP70 purified from malignant and virally infected cells can transfer and deliver antigenic peptides to antigen-presenting cells to elicit peptide-specific immunity. In this research, we evaluated the enhancement of linkage of Mycobacterium tuberculosis HSP70 to MAGE-1 gene of the potency of antigen-specific immunity elicited by naked DNA vaccines. We found that vaccines containing MAGE-1-HSP70 fusion genes enhanced the frequency of MAGE-1-specific cytotoxic T cells in contract to vaccines containing the MAGE-1 gene alone. More importantly, the fusion converted a less effective DNA vaccine into one with significant potency against established MAGE-1-expressing tumors. These results indicate that linkage of HSP70 to MAGE-1 gene may greatly enhance the potency of DNA vaccines, and generate specific antitumor immunity against MAGE-1-expressing tumors.

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.

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

Certain types of malignant tumors overexpress Her-2/neu, a transmembrane glycoprotein of the class I receptor tyrosine kinase erbB family. To develop an effective Her-2/neu vaccine for selective immunotherapy of these malignancies, we prepared Her-2/neu DNA plasmid encoding the transmembrane and extracellular domain (pHM) and tested the ability of this construct to induce antitumor immunity in animal models. In addition, we investigated the effects of cytokine used as a genetic adjuvant. Modulation by factors that affect T-cell function or hematopoiesis, including interleukin-12, interleukin-15, interleukin-18, interleukin-23, Eta-1, Flt3L and GM-CSF, was studied in the forms of monocistronic and bicistronic plasmid. Our results demonstrated that vaccination of pHM could induce successful antitumor immunity against Her-2/neu-expressing murine tumor cells in BALB/c mice. We also showed that the antitumor activity of pHM was augmented by coadministration and coexpression of different cytokines. Despite the similar levels of gene expression, the antitumor effects of bicistronic plasmids coexpressing Her-2/neu antigen and cytokine were improved in comparison with coadministration of separate monocistronic plasmid. In particular, coexpression of interleukin-18 or GM-CSF with Her-2/neu increased antitumor activity in both preventive and therapeutic experiments. These findings can help in the decision concerning which of the various cytokine adjuvants should be used for the development of a Her-2/neu DNA vaccine. In addition, our results from a large panel of cytokine adjuvants in the various tumor models may provide an insight into the important immune components of antitumor immunity.

Resiquimod is a modest adjuvant for HIV-1 gag-based genetic immunization in a mouse model

DNA vaccines have been effective at generating useful immune responses in many animal species. However, it is clearly desirable to increase their potency. The identification of adjuvants that increase their cell-mediated immune (CMI) response is therefore an important goal. Resiquimod is an imiquimod analog proven to activate dendritic cells through TLR-7. The adjuvant capacity of resiquimod has not, to our knowledge, been studied in the context of genetic immunization. Here, we studied resiquimod as an adjuvant for plasmid vaccine therapy by intra-muscular immunization of BALB/c mice with HIV-1 gag DNA vaccine without and with several concentrations of resiquimod (ranging from 5-100nM). We observed that resiquimod moderately enhanced IFN-gamma production as measured by a peptide-based ELISPOT assay compared to that obtained in mice immunized with DNA gag only. Antigen-specific T-cell proliferation studies showed a several-fold increase in the stimulation index in mice immunized with DNA gag +50 nM of resiquimod as compared to mice receiving DNA gag alone. Antibody titer also increased, while the antibody isotyping data showed a strong Th1 biased type response. Analysis of cytokine production in serum samples demonstrated a stronger Th1 cytokine bias in the presence of resiquimod. Furthermore, relevant increase in IL-4 production, as measured by ELISPOT assay, was not observed. Our results show that resiquimod can have modest adjuvant activity, in a DNA formulation, driving the immune system towards a cell-mediated immune response. Additional studies involving this adjuvant for DNA vaccines are underway.

Immobilisation of GM-CSF onto particulate vaccine carrier systems

Physical connection of vaccine carriers with immunostimulating cytokines may provide an interesting possibility to enhance the immune response of protective or therapeutic vaccines. As a first evaluation, various aluminium hydroxide adjuvants and poly(D,L-lactide-co-glycolide) (PLGA) microparticulates with modified positively and negatively charged surfaces were prepared to adsorb granulocyte-macrophage colony-stimulating factor (GM-CSF) under different pH conditions. Negatively charged surfaces were chosen to resemble physiological binding of GM-CSF to extracellular glycosaminoglycans, while modified positively charged surfaces may enhance GM-CSF adsorption due to electrostatic interaction. Release of GM-CSF was checked in vitro in a simulated interstitial environment. Anionic and cationic surfaces efficiently attracted GM-CSF to the carrier surface independently of the pH, while the composition of the carrier largely influenced the release of GM-CSF over time. Thus, the adsorption of GM-CSF to aluminium hydroxide adjuvants and PLGA microparticulates provides a simple and efficient possibility to physically connect the cytokine with these commonly used and potential vaccine carriers and may enable its localised delivery to the side of action.

Induction of protective immunity against Schistosoma mansoni via DNA priming and boosting with the large subunit of calpain (Sm-p80): adjuvant effects of granulocyte-macrophage colony-stimulating factor and interleukin-4

Considerable morbidity and mortality result from schistosomiasis, an affliction affecting an estimated 200 million people. Although schistosomicidal drugs and other control measures (including public hygiene and snail control) exist, the advent of an efficacious vaccine remains the most potentially powerful means for controlling this disease. We have targeted a vaccine candidate (large subunit of calpain, Sm-p80) because of its consistent immunogenicity, protective potential, and integral role in surface membrane biogenesis of schistosomes. Since surface membrane renewal appears to be one of the major phenomena employed by schistosomes to evade the host's immune system; an immune response directed against Sm-p80 should render the parasite susceptible to immune clearance from the host by both providing a focus of attack and by potentially impairing the membrane repair process. In the present study, we have employed DNA immunization protocols using Sm-p80 with plasmids encoding granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). Sm-p80 by itself provided 39% protection (P = < or =0.0001) against challenge infection in C57BL/6 mice. This protection was increased to 44% (P = < or =0.0001) when the plasmid encoding GM-CSF was coadministered with Sm-p80 DNA. Coinjection of plasmid DNA encoding IL-4 with Sm-p80 DNA yielded a protection level of 42% (P = < or =0.0001). Statistically, the protection conferred by including GM-CSF, but not IL-4, was significantly greater than that when only Sm-p80 was used. Sm-p80 DNA by itself elicited strong responses that include IgG2A and IgG2B antibody isotypes. The introduction of GM-CSF DNA with Sm-p80 DNA led to distinct increases in total IgG and IgG1 titers, whereas the coadministration of IL-4 DNA with Sm-p80 DNA resulted in a slight elevation of IgG1 and IgG3 titers and in some reduction of IgG2A and IgG2B titers. Our data again indicate that Sm-p80 can be an excellent candidate for a schistosomiasis vaccine.

Immunotherapy of malignant melanoma

Several areas of immunotherapeutic research may ultimately improve the effectiveness of active specific immunotherapy for melanoma and other malignancies. Identification of the most relevant tumor antigens will continue to be a vital component of vaccine design. Optimizing delivery of these antigens by use of adjuvants, dendritic cells, or heat shock proteins will enhance the immunogenicity of vaccines. The use of DNA vaccines to deliver nucleotides that encode relevant antigens and immunologic molecules, such as costimulatory molecules, and the use of targeted therapy with immunocytokines have yielded promising results in animal studies. Finally, cutting-edge techniques such as quantitative polymerase chain reaction and gene/protein microarrays will be used to monitor the response to a vaccine and thereby guide management decisions. Although IFN-alpha 2b is the only FDA-approved adjuvant treatment for AJCC stage IIB/III melanoma, recent data failed to show a benefit in overall survival. For patients with AJCC stage IV melanoma, chemotherapy with dacarbazine is currently the standard of care, with modest response rates of 15% to 20%. The encouraging response rates and low toxicities that were reported in phase I/III trials suggest that active immunotherapy may prove to be the most effective adjuvant therapy. At present, there are no FDA-approved cancer vaccines for malignant melanoma, and the results of ongoing randomized phase III clinical trials are greatly anticipated.

Molecular assembly of the ternary granulocyte-macrophage colony-stimulating factor receptor complex

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hematopoietic cytokine that stimulates the production and functional activity of granulocytes and macrophages, properties that have encouraged its clinical use in bone marrow transplantation and in certain infectious diseases. Despite the importance of GM-CSF in regulating myeloid cell numbers and function, little is known about the exact composition and mechanism of assembly of the GM-CSF receptor complex. We have now produced soluble forms of the GM-CSF receptor alpha chain (sGMRalpha) and beta chain (sbetac) and utilized GM-CSF, the GM-CSF antagonist E21R (Glu21Arg), and the betac-blocking monoclonal antibody BION-1 to define the molecular assembly of the GM-CSF receptor complex. We found that GM-CSF and E21R were able to form low-affinity, binary complexes with sGMRalpha, each having a stoichiometry of 1:1. Importantly, GM-CSF but not E21R formed a ternary complex with sGMRalpha and sbetac, and this complex could be disrupted by E21R. Significantly, size-exclusion chromatography, analytical ultracentrifugation, and radioactive tracer experiments indicated that the ternary complex is composed of one sbetac dimer with a single molecule each of sGMRalpha and of GM-CSF. In addition, a hitherto unrecognized direct interaction between betac and GM-CSF was detected that was absent with E21R and was abolished by BION-1. These results demonstrate a novel mechanism of cytokine receptor assembly likely to apply also to interleukin-3 (IL-3) and IL-5 and have implications for our molecular understanding and potential manipulation of GM-CSF activation of its receptor.

DNA-encoded fetal liver tyrosine kinase 3 ligand and granulocyte macrophage-colony-stimulating factor increase dendritic cell recruitment to the inoculation site and enhance antigen-specific CD4+ T cell responses induced by DNA vaccination of outbred animals

DNA-based immunization is a contemporary strategy for developing vaccines to prevent infectious diseases in animals and humans. Translating the efficacy of DNA immunization demonstrated in murine models to the animal species that represent the actual populations to be protected remains a significant challenge. We tested two hypotheses directed at enhancing DNA vaccine efficacy in outbred animals. The first hypothesis, that DNA-encoding fetal liver tyrosine kinase 3 ligand (Flt3L) and GM-CSF increases dendritic cell (DC) recruitment to the immunization site, was tested by intradermal inoculation of calves with plasmid DNA encoding Flt3L and GM-CSF followed by quantitation of CD1(+) DC. Peak DC recruitment was detected at 10-15 days postinoculation and was significantly greater (p < 0.05) in calves in the treatment group as compared with control calves inoculated identically, but without Flt3L and GM-CSF. The second hypothesis, that DNA encoding Flt3L and GM-CSF enhances immunity to a DNA vector-expressed Ag, was tested by analyzing the CD4(+) T lymphocyte response to Anaplasma marginale major surface protein 1a (MSP1a). Calves immunized with DNA-expressing MSP1a developed strong CD4(+) T cell responses against A. marginale, MSP1a, and specific MHC class II DR-restricted MSP1a epitopes. Administration of DNA-encoding Flt3L and GM-CSF before MSP1a DNA vaccination significantly increased the population of Ag-specific effector/memory cells in PBMC and significantly enhanced MSP1a-specific CD4(+) T cell proliferation and IFN-gamma secretion as compared with MHC class II DR-matched calves vaccinated identically but without Flt3L and GM-CSF. These results support use of these growth factors in DNA vaccination and specifically indicate their applicability for vaccine testing in outbred animals.

Update on cancer vaccines

The development of vaccines to induce tumor-specific immunity in patients with cancer has as emerged as a major area of investigation. The identification of antigens uniquely expressed by tumor cells and a heightened understanding of tumor immunology have resulted in efforts to activate host immunity to recognize and reject tumor cells. Tumor-associated antigens and peptides, genes encoding tumor antigens, and modified whole tumor cells have been used in preclinical studies with provocative results. Potent antigen-presenting cells, known as dendritic cells, have also been modified using peptides, genetic material, or whole tumor cells to present tumor antigens in the context of co-stimulation to overcome tolerance and induce tumor-specific cell killing. Promising data generated from the preclinical evaluation of cancer vaccines have resulted in the initiation of clinical trials to define the associated toxicity profile, immunologic response, and clinical impact of this treatment approach. We summarize the preclinical and clinical experience in this expanding area of investigation. Cancer vaccines hold much promise; however, many unresolved questions remain in the effort to generate a clinically meaningful treatment strategy.