Cabrera, Rosalyn

Abstract Failures in tolerance mechanisms cause autoimmunity. Self reactive cells in the periphery are kept in check by peripheral tolerance. Mice expressing a neoself antigen, called BALB-neuT, were used as a model for delineating mechanisms of peripheral tolerance. Two questions were addressed: Are BALB-neuT tolerant to neoself antigen? Can BALB-neuT tolerance be broken? We first established that BALB-neuT are tolerant to Her2/neu peptide while parental BALB/c mounted a significant response after immunization with Her2/neu peptide in CFA and repeated CpG stimulations. Next we depleted CD25+ cells and used the immunomodulating antibody B7-DC XAb to study the mechanism involved. CD8+ T cells from treated BALB-neuT generated a potent response when compared to untreated BALB-neuT or BALB/c, as measured by IFNγ secretion. Interestingly, IL-10 secretion from BALB-neuT T cells was high after incubation with murine breast cell lines, irrespective of expression of BALB-neuT antigen. After depletion of CD4+CD25+ T cells, secretion of IL-10 was diminished, suggesting that the IL-10 is being secreted by T regulatory cells. In conclusion, BALB-neuT are tolerant to neoself antigen. Tolerance can be broken by depleting Tregs or using B7-DC Xab to modulate immunity. Future studies are aimed at identifying mechanisms regulating IL-10 secretion to unravel pathways important in regulation of autoimmunity.

Abstract Dendritic cells (DC) initiate and shape an adaptive immune response. DC can be stimulated with B7-DC XAb, a novel immunomodulatory IgM that crosslinks B7-DC/PDL2 on the DC surface. Previously, we have shown that B7-DC XAb treated DC (DCXAb) reprogram Foxp3+ Tregulatory cells into IFNgamma+, IL-17+ effectors. Adoptive transfer of neoself antigen (OVA)-pulsed DCXAb induces destruction of OVA-bearing pancreatic islets and autoimmune diabetes in RIP-OVA mice. We hypothesized that DC-derived molecules involved in Th1 or Th17 polarization would be important in autoreactive T cell activation by DCXAb. In spite of their ability to induce a CTL response against OVA-bearing targets, we found that DCXAb deficient in either Tbet, IFNgamma (Th1 polarizing) or CD40, IL-6 (Th17 polarizing) fail to cause autoimmunity. In conclusion, both Th1 and Th17 polarizing molecules on DC are needed to stimulate an autoimmune response.

We developed a novel model to study peripheral tolerance using mice expressing chicken ovalbumin under a rat insulin promoter. In contrast to previous RIP‐OVA mouse models, we induce autoimmune diabetes by activating the natural T cell repertoire; not by transfer of high affinity TCR T cells. Our treatment, DCXAb + OVA, employs adoptive transfer of dendritic cells (DC) pulsed with neoself antigen OVA and monoclonal therapeutic antibody (MTAb) B7‐DC XAb. This immunomodulatory MTAb crosslinks B7‐DC (PD‐L2) and activates DC. In our model, Tg mice develop severe hyperglycemia and loss of islet beta cells in 7 days. Adoptive transfer of IL‐6 KO DC, a cytokine involved in suppression of Treg, fails to cause diabetes. Also, nondiabetic splenocytes suppress proliferation of diabetogenic T cells, suggesting Treg are involved. DCXAb + OVA induces a specific break in tolerance that is beneficial when targeting tumors. In this light, splenocytes from diabetic mice specifically kill B16‐OVA targets but not B16. DCXAb treatment allows specific activation of the natural T cell repertoire and will help elucidate effectors important in autoimmunity and cancer therapy.

Abstract Lymphocyte differentiation from naive CD4+ T cells into mature Th1, Th2, Th17, or T regulatory cell (Treg) phenotypes has been considered end stage in character. In this study, we demonstrate that dendritic cells (DCs) activated with a novel immune modulator B7-DC XAb (DCXAb) can reprogram Tregs into T effector cells. Down-regulation of FoxP3 expression after either in vitro or in vivo Treg-DCXAb interaction is Ag-specific, IL-6-dependent, and results in the functional reprogramming of the mature T cell phenotype. The reprogrammed Tregs cease to express IL-10 and TGFβ, fail to suppress T cell responses, and gain the ability to produce IFN-γ, IL-17, and TNF-α. The ability of IL-6+ DCXAb and the inability of IL-6−/− DCXAb vaccines to protect animals from lethal melanoma suggest that exogenously modulated DC can reprogram host Tregs. In support of this hypothesis and as a test for Ag specificity, transfer of DCXAb into RIP-OVA mice causes a break in immune tolerance, inducing diabetes. Conversely, adoptive transfer of reprogrammed Tregs but not similarly treated CD25− T cells into naive RIP-OVA mice is also sufficient to cause autoimmune diabetes. Yet, treatment of normal mice with B7-DC XAb fails to elicit generalized autoimmunity. The finding that mature Tregs can be reprogrammed into competent effector cells provides new insights into the plasticity of T cell lineage, underscores the importance of DC-T cell interaction in balancing immunity with tolerance, points to Tregs as a reservoir of autoimmune effectors, and defines a new approach for breaking tolerance to self Ags as a strategy for cancer immunotherapy.

Abstract IL-17-producing CD8+ T cells (Tc17) appear to play a role in a range of conditions, such as autoimmunity and cancer. Thus far, Tc17 cells have been only marginally studied, resulting in a paucity of data on their biology and function. We demonstrate that Tc17 and Th17 cells share similar developmental characteristics, including the previously unknown promoting effect of IL-21 on Tc17 cell differentiation and IL-23-dependent expression of IL-22. Both STAT1 and STAT4 are required for optimal development of Tc17 cells and maximal secretion of cytokines. Tc17 cells are cytotoxic, and they can be either pathogenic or nonpathogenic upon adoptive transfer in the model of autoimmune diabetes. Tc17 cells treated with TGF-β1 plus IL-6 are not diabetogenic, whereas IL-23-treated cells potently induce the disease. IL-17A and IL-17F are necessary but not sufficient for diabetes induction by Tc17 cells. Tc17 cells treated with TGF-β1 plus IL-6 or IL-23 likely differ in pathogenicity due to their disparate capacity to attract other immune cells and initiate inflammation.