Therapeutic efficacy of a tumor cell–based vaccine against experimental B16 melanoma requires the disruption of either of two immunoregulatory mechanisms that control autoreactive T cell responses: the cytotoxic T lymphocyte–associated antigen (CTLA)-4 pathway or the CD25+ regulatory T (Treg) cells. Combination of CTLA-4 blockade and depletion of CD25+ Treg cells results in maximal tumor rejection. Efficacy of the antitumor therapy correlates with the extent of autoimmune skin depigmentation as well as with the frequency of tyrosinase-related protein 2180–188–specific CTLs detected in the periphery. Furthermore, tumor rejection is dependent on the CD8+ T cell subset. Our data demonstrate that the CTL response against melanoma antigens is an important component of the therapeutic antitumor response and that the reactivity of these CTLs can be augmented through interference with immunoregulatory mechanisms. The synergism in the effects of CTLA-4 blockade and depletion of CD25+ Treg cells indicates that CD25+ Treg cells and CTLA-4 signaling represent two alternative pathways for suppression of autoreactive T cell immunity. Simultaneous intervention with both regulatory mechanisms is therefore a promising concept for the induction of therapeutic antitumor immunity.

Objective. Regulatory T cells play an important role in the prevention of autoimmunity and have been shown to be effective in the treatment of experimental colitis, a T cell-mediated and organ-specific disease. We previously demonstrated that intrinsic CD25؉ regulatory T cells modulate the severity of collagen-induced arthritis (CIA), which, in contrast to colitis, is a systemic antibody-mediated disease and an accepted model of rheumatoid arthritis. We undertook this study to determine whether regulatory T cells have the potential to be used therapeutically in arthritis.Methods. We transferred CD4؉,CD25؉ T cells into mice exhibiting arthritis symptoms, both immunocompetent mice and mice subjected to lethal irradiation and rescued with syngeneic bone marrow transplantation.Results. A single transfer of regulatory T cells markedly slowed disease progression, which could not be attributed to losses of systemic type II collagenspecific T and B cell responses, since these remained unchanged after adoptive transfer. However, regulatory T cells could be found in the inflamed synovium soon after transfer, indicating that regulation may occur locally in the joint. Conclusion.Our data indicate that CD25؉ regulatory T cells can be used for the treatment of systemic, antibody-mediated autoimmune diseases, such as CIA.

Objective. CD4؉,CD25؉ T regulatory cells may offer opportunities to intervene in the course of autoimmune disease. We wished to evaluate their potential for influencing systemic and chronic joint inflammation by investigating their involvement in collagen-induced arthritis (CIA).Methods. We depleted DBA/1 mice of CD25؉ regulatory cells by injection of a depleting monoclonal antibody specific for CD25 14 days before a single immunization with type II collagen (CII) in Freund's complete adjuvant. CD4؉,CD25؉ T cells were adoptively transferred to some groups of mice during immunization. Mice were then scored for signs of arthritis, and blood was taken periodically to measure the amounts of CII-specific antibodies. Splenocytes of treated mice were examined in vitro to determine the effects of depletion on proliferation to CII and control antigens.Results. CD25؉ cell-depleted DBA/1 mice had significantly more severe disease than control mice following collagen immunization. The magnified severity was also accompanied by higher antibody titers against collagen, and in vitro tests showed increased proliferation of collagen-specific T cells. Adoptively transferring CD4؉,CD25؉ T cells into depleted mice was shown to reverse the heightened severity. Control mice, which were depleted and immunized with the neoantigen keyhole limpet hemocyanin (KLH), had neither an increased antibody response toward KLH nor an augmented proliferative response, indicating that CD25؉ cell depletion preferentially affects immunity against self antigen.Conclusion. These results establish a link between CD4؉,CD25؉ regulatory cells and CIA and provide a rationale for investigating CD4؉,CD25؉ T regulatory cells in the treatment and prevention of arthritis.

Dendritic cells (DCs) are specialized APCs with an important role in the initiation and regulation of immune responses. Immature DCs (iDCs) reportedly mediate tolerance in the absence of maturation/inflammatory stimuli, presumably by the induction of regulatory T cells. In this study, we show for the first time that repetitive iDC injections trigger the expansion of a novel regulatory population with high immunomodulatory properties, able to protect mice from collagen-induced arthritis. These regulatory T cells are characterized by the expression of the CD49b molecule and correspond to a CD4+ α-galactosylceramide/CD1d-nonrestricted T cell population producing IL-10. Adoptive transfer of <105 TCRβ+CD49b+ cells isolated from the liver of iDCs-vaccinated mice, conferred a complete protection against arthritis. This protection was associated with an attenuation of the B and T cell response associated with a local secretion of IL-10. Thus, together these data demonstrate that iDCs can expand and activate a novel regulatory population of CD49b+ T cells, with high immunosuppressive potential able to mediate protection against a systemic autoimmune disease.

Although merozoite surface protein 1 (MSP-1) is a leading candidate vaccine antigen for blood-stage malaria, its efficacy in clinical trials has been limited in part by antigenic polymorphism and potentially by the inability of protein-in-adjuvant vaccines to induce strong cellular immunity. Here we report the design of novel vectored Plasmodium falciparum vaccines capable of overcoming such limitations. We optimized an antigenic insert comprising the four conserved blocks of MSP-1 fused to tandemly arranged sequences that represent both allelic forms of the dimorphic 42-kDa C-terminal region. Inserts were expressed by adenoviral and poxviral vectors and employed in heterologous prime-boost regimens. Simian adenoviral vectors were used in an effort to circumvent preexisting immunity to human adenoviruses. In preclinical studies these vaccines induced potent cellular immune responses and high-titer antibodies directed against MSP-1. The antibodies induced were found to have growth-inhibitory activity against dimorphic allelic families of P. falciparum. These vectored vaccines should allow assessment in humans of the safety and efficacy of inducing strong cellular as well as cross-strain humoral immunity to P. falciparum MSP-1.

These data indicate that vaccination with oxLDL-pulsed mDCs provides a novel and powerful strategy for the immunomodulation of atherosclerosis.

Dendritic cells (DCs) are professional APCs which have the unique ability to present both foreign and self-Ags to T cells and steer the outcome of immune responses. Because of these characteristics, DCs are attractive vehicles for the delivery of therapeutic vaccines. Fully matured DCs are relatively well-defined and even used in clinical trials in cancer. DCs also have the potential to influence the outcome of autoimmunity by modulating the underlying autoimmune response. To gain a better appreciation of the abilities and mechanisms by which immunomodulatory DCs influence the outcome of T cell responses, we studied several immunomodulatory DCs (TNF-, IL-10-, or dexamethasone-stimulated bone marrow-derived DCs) side by side for their ability to modulate T cell responses and autoimmune diseases. Our data show that these differentially modulated DCs display a different composition of molecules involved in T cell activation. Although, all DC subsets analyzed were able to inhibit the induction of collagen-induced arthritis, the modulation of the underlying immune response was different. Vaccination with TNF- or IL-10-modulated DCs altered the Th1/Th2 balance as evidenced by the induction of IL-5- and IL-10-secreting T cells and the concomitant reduction of the IgG2a-IgG1 ratio against the immunizing Ag. In contrast, DCs modulated with dexamethasone did not affect the ratio of IL-5-producing vs IFN-γ-producing T cells and tended to affect the Ab response in a nonspecific manner. These data indicate that distinct mechanisms can be used by distinct DC subsets to change the outcome of autoimmunity.

Objective. Dendritic cells (DCs) are crucial for the initiation of T cell immunity and therefore play an important role in the initiation and regulation of immune responses in arthritis. Full mobilization of effector T cells depends on the proper maturation of DCs. Current evidence indicates that the type of T cell response induced is crucially dependent on the activation status of the DCs. In this study, we explored the immunologic effects of differentially matured DCs on the development of collagen-induced arthritis (CIA).Methods. Bone marrow-derived DCs were cultured in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF). Before immunization with bovine type II collagen (CII) protein, mice were repeatedly injected with DCs that had been pulsed with CII. Immature, semimature, or fully mature DCs were injected. Mice were boosted on day 21 after CII immunization, and the disease course was monitored.Results. While vaccination with immature or lipopolysaccharide-activated DCs had no significant effect on the disease course, administration of antigenloaded, tumor necrosis factor (TNF)-modulated DCs propagated in GM-CSF with or without interleukin-4 resulted in a delayed onset of arthritis and a lower clinical score. The response was antigen-specific, since TNF-treated DCs pulsed with a control antigen did not modify the disease course. A specific decrease in the collagen-specific "Th1-associated" IgG2a response was observed, whereas IgG1 titers were unaffected.Conclusion. CIA can be prevented through vaccination with TNF-matured DCs in an antigen-specific manner. These findings provide a rationale for immunotherapy using DCs in rheumatoid arthritis.