Self-tolerance to p53 is a major potential limitation for the activation of the endogenous T-cell repertoire. So far, p53 specific CD8+ and CD4+ T-cell immunity has been described in cancer... Show moreSelf-tolerance to p53 is a major potential limitation for the activation of the endogenous T-cell repertoire. So far, p53 specific CD8+ and CD4+ T-cell immunity has been described in cancer patients and healthy individuals. However, the restrictions of tolerance on the recruitment of p53 specific T cells have thus far not been completely elucidated. In this thesis we have studied several basic mechanisms that underlie the availability of p53 specific T-cell immunity and how this repertoire can be employed for immunotherapy against tumors. In chapter 2 we have compared the presence and quality of the p53 specific T-helper cell repertoire in p53 deficient (p53-/-) mice and p53 wt (p53+/+) mice. By direct vaccination with p53, in a viral vector and as 30-mer peptides, we were able to determine the specificity and avidity of T-helper cell populations in the two mouse strains. We show that, unlike the repertoire to other tumor specific antigens such as CEA (88), the p53 specific T-helper cell repertoire in these mouse strains is not blunted by self-tolerance and therefore completely available for immunotherapy of cancer. In chapter 3 we studied the correlation between intracellular accumulation and immunogenicity of several well-described frameshifted colon tumor antigens. Accumulation alone is not a sufficiently indicative marker for the immunogenic properties of a tumor antigen. By comparing intracellular accumulation, direct presentation and cross-presentation in vivo we were able to categorize several tumor antigens and to predict their potency as antigen targets for T helper cells or CTL. In chapter 4 we analyzed the potential beneficial and harmful effects of p53 specific CD8+ T cells in detail. We generated a p53¹⁵⁸⁻¹⁶⁶ specific TCR transgenic mouse and studied the effects of self-tolerance on p53 specific CD8+ T cells in chapter 4.1. We show that thymic selection has a drastic effect on the differentiation of p53 specific CD8+ T cells in p53 +/+ and p53 +/- mice. Education of p53 specific CD8+ T cells in the absence of p53 (in p53-/- mice) leads to a potent population of peripheral p53 specific CD8+ T cells. We studied the in vivo effects of these p53 specific CD8+ T cells in chapter 4.2. In an supplemental chapter 4.3 we show the expression and capacities cells expressing the p53 TCR after retroviral gene transfer. Our data in chapter 4 indicate that immunotherapy with p53 specific CD8+ T cells can lead to acute and severe hematopoietic ablation. These data stress the importance of meticulous pre-clinical research when targeting ubiquitously expressed self-antigens, before starting clinical application. Successful cancer immunotherapy in the absence of any toxicity could nevertheless be achieved by combination of p53 CD8+ T cell transfer and hematopoietic reconstitution with non-sensitive (allogeneic) bone marrow stem cells. A general discussion of this thesis in chapter 5 describes the caveats, challenges and pitfalls of the findings portrayed in this thesis and places them in the context of recent literature. The past decade our understanding of molecular and cellular mechanisms of T-cell mediated anti-tumor responses has taken a leap. Nevertheless, due to improved TCR engineering techniques, the diversity of tumor antigens in (pre) clinical trials is increasing. Despite the differences between models or species the results in the results in this thesis urge for targeting of well-chosen tumor antigens and great caution when targeting ubiquitously expressed self-antigens. Show less
Skin carcinomas develop at a high rate in organ-transplant recipients who are kept on immune suppressive drugs to prevent graft rejection. The present study dealt with a broad range of aspects of... Show moreSkin carcinomas develop at a high rate in organ-transplant recipients who are kept on immune suppressive drugs to prevent graft rejection. The present study dealt with a broad range of aspects of this elevated carcinoma risk, starting from the earliest oncogenic events to the ultimate therapy. Advancements on any of these aspects may be of significant benefit to the patient and his/her physician in the management of multiple and progressive skin carcinomas. The studies presented in Chapter 2 - 4 focused on the early pathogenesis of skin cancer in organ-transplant recipients to gain a better understanding of the underlying mechanism(s) of the increased skin cancer risk in these patients. We specifically focused on the role of p53 and beta-PV in early skin carcinogenesis. The clinical studies in Chapter 5 - 7 investigated the management of skin cancer in organ-transplant recipients. Show less
