@phdthesis{Tiurbe2006,
  author    = {Tiurbe, George Christian},
  title     = {Characterization of immature rat bone marrow-derived dendritic cells : Evaluation of their phenotype and immunomodulatory properties in vitro and after organ transplantation},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-21429},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2006},
  abstract  = {Solid organ transplantation is an established therapeutic approach in modern medicine to extend and to improve the life of patients in the final stages of organ failure. Transplantation between genetically non-identical individuals leads to the activation of the transplant recipient's immune system. This alloimmune response is a consequence of the recognition of foreign MHC molecules by alloreactive host T cells. To prevent their activation and the subsequently induced activation of further cell subsets (e.g. B cells, cytotoxic T cells, macrophages)immunosuppressive drugs are absolutely necessary in the clinic. However,permanent immunosuppression leads to severe side effects such as nephrotoxicity, diabetes and hyperlipidaemia, and a reduced immunity to infections and malignant diseases. At the moment, there is no real alternative to immunosuppression. The purpose of this study was to analyse the importance of rat dendritic cells with immune inhibitory properties to prevent the immune activation after experimental transplantation. The rat is one of the most important animal models for experimental organ transplantation in a clinic-relevant procedure. In order to modulate the immune response after transplantation in an antigenspecific manner, the strategy should include the alloantigens. These antigens have to be presented by immature dendritic cells in the absence of costimulatory signals in order to turn alloreactive T cells into anergic or regulatory T cells instead of effector T cells. For a certain rat model of allograft rejection,the immunodominant peptide P1 was identified as an important alloantigen which accelerates graft rejection. Such a model offers an attractive and practical approach to analyse the potential of host tolerogeneic dendritic cells pulsed with P1 to suppress the allograft-induced immune response in an antigen-specific manner without the need of chronic immunosuppression. A homogenous population of rat immature dendritic cells was generated from bone marrow precursors cultured with GM-CSF and IL-4 (= IL-4 DCs) or GM65 CSF and IL-10 (= IL-10 DCs). These cells with an identical immature phenotype showed no or a very low surface expression of costimulatory molecules like CD80 and CD86 and a 10-fold reduced expression of MHC class II molecules in comparison to mature splenic DCs. No obvious difference was observed between the phenotype of the IL-4 DCs and the IL-10 DCs. Neither IL-4 DCs nor IL-10 DCs were able to activate na{\"i}ve T cells or to restimulate antigen-specific T cells. This strong inhibitory effect, mediated within 24 hours, was dependent on the number of immature dendritic cells added to the proliferation assay. Antigen-specific T cells pre-incubated with IL-4 DCs and IL-10 DCs, respectively, were not able to proliferate in the presence of P1-pulsed mature DCs. This anergic state was reversible with the addition of exogenous IL-2. T cells incubated with IL-4 DCs (= IL-4 DC-Ts) were able to inhibit the T cell proliferation in a cell number dependent manner. In contrast, antigen-specific T cells pre-incubated with P1-pulsed IL-10 DCs (= IL-10 DC-Ts)showed no effect on the proliferation assay. This was the unique difference between IL-4 DCs and IL-10 DCs found in the present study. Immature DCs influenced also the immune response after transplantation. Different numbers of P1-loaded immature IL-4 DCs and IL-10 DCs were transferred intravenously into Lewis rats one day before transplantation. The best results were obtained with 30 million P1-pulsed immature DCs which prolonged the survival time to a median of 11.2 ± 1.6 days. In addition, the antigen specificity of this effect was demonstrated with a third-party graft from Brown Norway donors. These findings suggest that an antigen-specific modulation of the immune response is possible using immature dendritic cells loaded with the allogeneic antigens. Even more, the protocols described in the present study show that the immune system can be, at least temporarily, controlled after transplantation without the use of immunosuppressive drugs.},
  language  = {en}
}
@phdthesis{Sitaru2003,
  author    = {Sitaru, Ana Gabriela},
  title     = {Modulation of the T cell response with MHC class I peptides and their analogues},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-4561},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2003},
  abstract  = {Transplantation is now firmly established as a therapeutic approach to extend and improve the life of patients in the final stages of organ failure. It has been demonstrated that transplantation between genetically non-identical individuals leads to the activation of the recipient's alloimmune response as a major determinant of transplant outcome. T cell recognition of foreign MHC molecules plays a key role in initiating and sustaining allograft rejection. To prevent the risk of rejection, patients are given immunosuppressive drugs, which are non-specific and have major side-effects (infections, malignancies). It has been shown that the alloreactive T cells specifically recognize donor MHC-derived peptides. This implies that it may be possible to develop antigen-specific strategies in order to modulate the alloimmune response by peptide analogues and specifically altered peptide ligands. The purpose of this study was to explore the potential of "recipient-adapted" analogues from the dominant MHC class I peptide to modulate the alloimmune response. Beside the significant role of donor dominant determinants in the rejection process, we tested seven 13-to-24-mer peptides from the Wistar-Furth MHC class I molecule (WF, RT1.Au) for their possible immunogenicity in a fully MHC-mismatched WF to Lewis (LEW, RT1l) rat strain combination. Secondly, the immunodominant allopeptide was selected to generate analogues in order to investigate their modulatory capacity. All peptides were tested in vitro in a standard proliferation assay and in vivo using a heterotopic heart transplantation model. Our findings show that five peptides (P1-P5) were able to induce specific T cell proliferation in LEW responders. Furthermore, we found a hierarchical distribution of the determinants: peptide P1 as a good candidate for the immunodominant determinant, while P2, P3, P4, and P5 as subdominant epitopes and the other two peptides, P6 and P7, as non-immunogenic determinants of WF MHC class I molecule. Furthermore, the dominance of P1 was confirmed by the strong proliferation induced after immunization with a mixture of peptides in the presence of P1. This hierarchical distribution of the proliferative response correlated with the cytokine production. Peptide P1, comprising only 3 allogeneic amino acids (L5, L9, and T10) induced the strongest T cell proliferation and produced high levels of cytokines, especially IL-2 and IFN-g. In addition, the immunodominance of peptide P1 was confirmed by the significant reduction in the allograft survival time in comparison to the non-immunized control animals. Since the TCR Vß repertoire of rejected graft-infiltrating cells in rejected allografts was similar to the profile observed after in vitro restimulation of P1-primed T cells, we concluded that peptide P1 is able to activate the alloreactive T cell population. Our results demonstrate the particular role of the dominant peptide P1 (residues 1-19) in the allograft rejection in WF to LEW rat strain combination. In the second set of experiments, we investigated the fine specificity of the dominant peptide P1-activated T cells using peptide analogues from P1. The "recipient-adapted" analogues were designed by changing the allogeneic RT1.Au amino acids (L5, L9, T10) one-by-one with the correspondent syngeneic RT1.Al amino acids (M5, D9, I10) in the sequence of peptide P1. The six peptide analogues (A1.1-A1.6) consisting of either one or two allogeneic amino acids were able to induce a specific T cell proliferative response and cytokine production. Analogue A1.5 with only one allogeneic amino acid (L5) was of particular interest because it induced a low T cell proliferation and high cytokine levels, especially IL-4 and IL-10. In addition, immunization with A1.5 did not influence the allograft survival time in comparison to the non-immunized LEW recipients. A1.5 was the only analogue able to down-regulate the proliferation of P1-primed T cells. Our results reveal that A1.5 is an MHC competitor as confirmed by the in vitro MHC competition assay and the inhibition of the negative effect of P1 on the allograft survival time when recipients were immunized with a mixture of P1 and A1.5. These findings suggest that it is possible to design peptide analogues, such as A1.5, which do not stimulate the dominant peptide P1-specific T cell population and even more, are able to block its presentation in the MHC molecule. In all, the results indicate that the specific suppression of indirect allorecognition can be achieved by using peptide analogues of the dominant allopeptide.},
  language  = {en}
}