@phdthesis{Stuehler2010,
  author    = {St{\"u}hler, Claudia},
  title     = {Strategies to prevent graft-versus-host disease and augment anti-fungal immunity in allogeneic hematopoietic stem cell transplant recipients},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-51957},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {Allogeneic hematopoietic stem cell transplantation (HSCT) is often the only effective treatment for patients with hematological malignancies, but its curative potential is often limited by the development of acute or chronic graft-versus-host disease (GvHD). Although extensive immunosuppressive therapy is highly efficient in the prevention or treatment of GvHD, it greatly increases the risk for life-threatening opportunistic fungal or viral infections and the recurrence of malignant disease. The possibility to selectively deplete alloreactive T cells from donor grafts prior or after transplantation would greatly diminish the need for immunosuppressive therapy in the transplant recipient and thereby greatly improve its clinical outcome. The molecular chaperone heat shock protein of 90 kDa (Hsp90) has been previously shown to stabilize many signal transduction proteins involved in T lymphocyte activation and proliferation and is furthermore able to exert anti-apoptotic effects in different cell types. The aim of this study was therefore to investigate the possibility to selectively target activated, proliferating T cells in lymphocyte populations by inhibition of Hsp90, without compromising viability and function of non-reactive T cell populations including pathogen-specific T lymphocytes. It could be shown in this work, that activated T cells are indeed more prone to apoptotic cell death in the presence of Hsp90 inhibitors than resting cells and that treatment of mixed lymphocyte cultures with such inhibitors eliminates the proliferation of alloreactive cells. In contrast, T cells remaining in a resting state during inhibitor treatment remain viable and also display functional virus-specific responses after inhibitor removal. These data suggest, that Hsp90 could represent a novel target for selective depletion of alloreactive T cells and that application of Hsp90 inhibitors could be a potential approach to prevent or treat GvHD without impairing pathogen-specific T cell immunity. In the second part of this work, the immune responses to strictly defined antigens of the opportunistic pathogenic fungus Aspergillus fumigatus were characterized. Opportunistic fungal infections are highly prevalent in immunocompromized and immunosuppressed individuals, especially in HSCT recipients suffering from GvDH. Although antifungal treatment is permanently improved, invasive fungal infections are still often fatal. In healthy individuals clinical disease is rare, because innate and adaptive immunity act in conjunction to protect the host. Therefore one possible strategy to prevent and treat life-threatening fungal infections in immunocompromized patients is to improve host resistance by augmenting the antifungal functions of the immune system, for example by vaccination or adoptive transfer of antigen-specific T cells. Based on previous findings, the objective of this dissertation was to identify and characterize distinct immunogenic A. fumigatus antigens that could be used for clinical application like vaccination or ex vivo generation of antigen-specific T cells and to characterize the interaction of this antigen-specific lymphocytes with cells of the innate immune system. First, memory T cell responses to different recombinant A. fumigatus proteins in healthy individuals were evaluated. The majority of tested donors displayed stable CD4+ TH1 responses to the Crf1 protein, whereas responses to the other antigens tested could only be detected in a limited number of donors, qualifying Crf1 as potential candidate antigen for clinical use. It was also possible to identify an immunodominant MHC class II DRB1*04-restricted epitope of Crf1 and to generate T cell clones specific for this epitope. This Crf1-specific T cell clones could be specifically activated by dendritic cells fed with synthetic peptide, recombinant protein or germinating A. fumigatus conidia or outgrown hyphae. Interestingly, these A. fumigatus-specific T cell clones also responded to stimulation with Candida albicans, which likewise causes opportunistic infections in immunocompromized patients and encodes for a glucosyltransferase similar to A. fumigatus Crf1. It was also possible to show that supernatant harvested from activated Crf1-specific T cell cultures was able to significantly increase fungal killing by monocytes. These data indicate that the specified FHT epitope of the A. fumigatus protein Crf1 could be potentially used as antigen for vaccination protocols or for the generation of Aspergillus-specific effector T cells for adoptive transfer.},
  subject      = {Transplantat-Wirt-Reaktion},
  language  = {en}
}