Vaccination with dendritic cells pulsed in vitro with tumor antigen conjugated to cholera toxin efficiently induces specific tumoricidal CD8+ cytotoxic lymphocytes dependent on cyclic AMP activation of dendritic cells

Choice and Design of Adjuvants for Parenteral and Mucosal Vaccines

The existence of pathogens that escape recognition by specific vaccines, the need to improve existing vaccines and the increased availability of therapeutic (non-infectious disease) vaccines necessitate the rational development of novel vaccine concepts based on the induction of protective cell-mediated immune responses. For naive T-cell activation, several signals resulting from innate and adaptive interactions need to be integrated, and adjuvants may interfere with some or all of these signals. Adjuvants, for example, are used to promote the immunogenicity of antigens in vaccines, by inducing a pro-inflammatory environment that enables the recruitment and promotion of the infiltration of phagocytic cells, particularly antigen-presenting cells (APC), to the injection site. Adjuvants can enhance antigen presentation, induce cytokine expression, activate APC and modulate more downstream adaptive immune reactions (vaccine delivery systems, facilitating immune Signal 1). In addition, adjuvants can act as immunopotentiators (facilitating Signals 2 and 3) exhibiting immune stimulatory effects during antigen presentation by inducing the expression of co-stimulatory molecules on APC. Together, these signals determine the strength of activation of specific T-cells, thereby also influencing the quality of the downstream T helper cytokine profiles and the differentiation of antigen-specific T helper populations (Signal 3). New adjuvants should also target specific (innate) immune cells in order to facilitate proper activation of downstream adaptive immune responses and homing (Signal 4). It is desirable that these adjuvants should be able to exert such responses in the context of mucosal administered vaccines. This review focuses on the understanding of the potential working mechanisms of the most well-known classes of adjuvants to be used effectively in vaccines.

Subcutaneous cholera toxin exposure induces potent CD103⁺ dermal dendritic cell activation and migration

CD103⁺ dermal dendritic cells (dDCs) are a recently described DC subset of the skin shown to be the principal migratory DCs capable of efficiently cross-presenting antigens and activating CD8⁺ T cells. Harnessing their activity would promote vaccine efficacy, but it has been unclear how this can be achieved. We tested a panel of adjuvants for their ability to affect dDCs. In comparison to the other adjuvants tested, the capacity of cholera toxin (CT) to induce the migration of dDCs was unique. Within 24 h of CT injection, large numbers of highly activated dDCs (including CD103⁺ dDCs) migrated to the draining lymph nodes and cross-presented coinjected antigens, potently activating naïve CD8⁺ T cells. Peptide vaccines adjuvanted with CT induced T-cell responses uniquely characterized by dynamic cytokine responses including the production of IL-2, and such vaccines were protective in situations reliant on CD8⁺ T-cell responses, including liver-stage Plasmodium challenge, or tumor challenge. This study is the first to examine the effects of adjuvants on CD103⁺ dDCs and identifies CT as a prototypical adjuvant for the activation of CD103⁺ dDCs, opening the way to development of vaccines and adjuvants that specifically target dDCs and generate effective CD8⁺ T-cell responses.

Conjugation of HPV16 E7 to cholera toxin enhances the HPV-specific T-cell recall responses to pulsed dendritic cells in vitro in women with cervical dysplasia

We have evaluated whether cholera toxin (CT) as a carrier/adjuvant can enhance human T-cell responses to a viral oncoprotein in vitro using dendritic cells (DCs) as antigen-presenting cells. Monocyte-derived DCs obtained from women with cervical dysplasia were pulsed with the HPV16 oncoprotein E7, either alone or conjugated to CT, and tested for their ability to induce antigen-specific activation of autologous T cells in vitro. CT-conjugation of E7 significantly improved the capacity of pulsed DCs to activate antigen-specific CD4+ T-cell proliferation and IFN-gamma secretion. The CT-E7-pulsed DCs also produced significantly more of the Th1-inducing cytokine IL-12 compared to DCs pulsed with E7 or CT alone. Furthermore, DCs pulsed with CT-conjugated HPV16 E7 caused a response in T cells from women with advanced disease (CIN III) as well as in T cells from women that were currently not infected with HPV16. These data show the potential of using CT-conjugated viral oncoproteins for DC-induced T-cell activation in humans.

Reduction of major histocompatibility complex class I expression on bladder carcinoma following tumor antigen-pulsed dendritic cell vaccine: Implications for immunoresistance in therapy

OBJECTIVES

To clarify the relationship between a decreased major histocompatibility complex class I (MHC-I) expression on bladder tumors and decreased immunological efficacy of tumor antigen-pulsed dendritic cell vaccine in a rat bladder carcinoma model induced by N-methyl-N-nitrosourea irrigation.

METHODS

Enzyme-linked immunosorbent assay was used to evaluate interferon-gamma concentration in the serum and colorimetric lactate dehydrogenase release assay in vitro was used to test the cytotoxicity capability of T lymphocytes. MHC-I expression on tumor cells was detected by flow cytometry and analyzed with CellQuest software.

RESULTS

The tumor antigen sensitized dendritic cell vaccine group showed decreased hyperplastic formations, lower pathological stages in rat bladders and more potent cytotoxicity activity (P < 0.001) than the dendritic cell vaccine group. Additionally, immunization with pulsed dendritic cell vaccine induced higher specific cytokine production of interferon-gamma. Nevertheless, a decreased MHC-I expression on bladder tumors was tested after immunotherapy by pulsed dendritic cell vaccine on week 15. As expected, the cytotoxic activity of T lymphocytes from rats on tumor cells with low MHC-I expression was also decreased to 19.70 +/- 4.82% as compared with tumor cells with high MHC-I (52.10 +/- 8.66%, P = 0.005).

CONCLUSIONS

Tumor antigen sensitized dendritic cell vaccine has beneficial activity on N-methyl-N-nitrosourea-induced bladder cancer in situ in rats, but therapeutic responses are accompanied by decreased MHC-I expression on tumors, possibly suggesting poor long-term therapeutic outcomes.

Reciprocal effects of Th1 and Treg cell inducing pathogen-associated immunomodulatory molecules on anti-tumor immunity

We have addressed the hypothesis that pathogen-associated immunomodulatory molecules may influence anti-tumor immunity through their pro- and anti-inflammatory activities and abilities to induce effector and regulatory T (Treg) cells. We found that CpG oligonucleotides (CpG) and cholera toxin (CT), which promote Th1 or Th2/Treg cell biased responses, respectively, had differential effects on tumor growth. Therapeutic peritumoral administration of CpG significantly reduced subcutaneous tumor growth and prolonged survival, whereas CT enhanced tumor growth and reduced survival. Peritumoral administration of CpG enhanced the frequency of IFN-gamma-secreting and reduced IL-10-secreting CD4(+) and CD8(+) T cells, in the tumor and in the draining lymph nodes, whereas, CT significantly enhanced the frequency of CD4(+)CD25(+)Foxp3(+) Treg cells, but reduced IFN-gamma-secreting T cells infiltrating the tumor. In contrast to the beneficial effect of CpG in mice with subcutaneous tumors, CpG or CT had no protective effect against tumor growth in the lungs when given therapeutically by the nasal route. However, prophylactic intranasal administration of CpG significantly reduced the number of lung metastases and this was associated with an enhanced frequency of IFN-gamma-secreting CD8(+) T cells in the draining lymph node and enhanced tumor-specific CTL responses. Our findings demonstrate that pathogen-associated molecules can either inhibit or enhance anti-tumor immunity by selectively promoting the induction of effector or regulatory T cells, and that the environment of the growing tumor influences the protective effect.

Recent developments in mucosal vaccines against prion diseases

Bovine spongiform encephalopathy in cattle is highly suspected to be orally transmitted to humans through contaminated food, causing new variant Creutzfeldt-Jakob disease. However, no prophylactic procedures against these diseases, such as vaccines, in particular those stimulating mucosal protective immunity, have been established. The causative agents of these diseases, termed prions, consist of the host-encoded prion protein (PrP). Therefore, prions are immunologically tolerated, inducing no host antibody responses. This immune tolerance to PrP has hampered the development of vaccines against prions. We and others recently reported that the immune tolerance could be successfully broken and mucosal immunity could be stimulated by mucosal immunization of mice with PrP fused with bacterial enterotoxin or delivered using an attenuated Salmonella strain, eliciting significantly higher immunoglobulin A and G antibody responses against PrP. In this review, we will discuss these reports.

The mucosal immune system: from control of inflammation to protection against infections

The IV meeting of the European Mucosal Immunology Group, held October 8-10, 2004, in Lyon, gathered fundamental and clinical research scientists to discuss the most recent updates on basic and clinical aspects of mucosal immunology. The meeting was focused on innate and acquired immune mechanisms underlying handling and immune recognition of commensals, allergens, and pathogens by the mucosal immune system and its outcome in health and disease as well as for vaccine development. The scientific program featured five topics of growing interest for fundamental research scientists and clinicians, including the role of commensal bacteria in mucosal immunity; function of dendritic cells in infection, inflammation, and tolerance; control of mucosal inflammation by regulatory T cells; novel routes and adjuvants for mucosal vaccines; and mucosal immunity against HIV infection and vaccination strategies.

Mucosal adjuvants and anti-infection and anti-immunopathology vaccines based on cholera toxin, cholera toxin B subunit and CpG DNA

Mucosal immunisation may be used both to protect the mucosal surfaces against infections and as a means for immunological treatment of peripheral immunopathological disorders through the induction of systemic antigen-specific tolerance ('oral tolerance'). The development of mucosal vaccines, whether for prevention of infectious diseases or for oral tolerance immunotherapy, requires efficient antigen delivery and adjuvant systems that can help to present the appropriate vaccine or immunotherapy antigens to the mucosal immune system. The most potent (but also toxic) mucosal adjuvants are cholera toxin (CT) and the closely related Escherichia coli heat-labile enterotoxin (LT), and much effort and significant progress have been made recently to generate toxicologically acceptable derivatives of these toxins with retained adjuvant activity. Among these are the non-toxic, recombinantly produced cholera toxin B-subunit (CTB). CTB is a specific protective antigen component of a widely registered oral cholera vaccine as well as a promising vector for either giving rise to mucosal anti-infective immunity or for inducing peripheral anti-inflammatory tolerance to chemically or genetically linked foreign antigens administered mucosally. CT and CTB have also recently been used as combined vectors and adjuvants for markedly promoting ex vivo dendritic cell (DC) vaccination with different antigens and also steering the immune response to the in vivo-reinfused DCs towards either broad Th1 + Th2 + CTL immunity (CT) or Th2 or tolerance (CTB). Another type of mucosal adjuvants is represented by bacterial DNA or synthetic oligodeoxynucleotides containing CpG-motifs, which especially when linked to CTB have been found to effectively stimulate both innate and adaptive mucosal immune responses. The properties and clinical potential of these different classes of adjuvants are being discussed.