Preclinical evaluation of human T lymphocytes in RAG2-/-γc-/- mice

This thesis describes the development and application of a new model for the preclinical study of human T cells by transfer of huPBMCs into RAG2 -/- γc -/- immunodeficient mice. The ultimate goal of treating patients with a malignancy is to eradicate the malignant cells, while keeping hold of damage to the healthy cells of the body. Therefore, the treatment has to be specific for only the malignant cells. Chemotherapy is often not specific enough, especially if high doses are needed to control the disease. A promising new treatment option is adoptive immunotherapy. Adoptive immunotherapy concerns the administration to a patient of immunogeneic cells (T cells) from a donor, that have the ability to track down and kill the malignant cells. To make the donor-derived T cells more specific for only malignant cells, a certain period in the laboratory (in vitro) is necessary for manipulation of the cells before administration to the patient. During this manipulation certain subsets of T cells can be selected, made more active or even genetically transformed. The results of the first clinical trials with adoptive immunotherapy are promising, but a lot of work still has to be done to improve the in vivo functionality of manipulated T cells. It is therefore necessary to test the functionality of manipulated human T cells in an animal model (in vivo) before application to patients. However, a preclinical model for in vivo evaluation of human T cells is not available. Initially, the huPBMC-RAG2-/-gc-/-model was developed as a new model for sensitive engraftment of human T cells. Engraftment levels of T cells were so high that at a relatively low dose of 15x106 human T cells all mice died of acute xenogeneic graft-versus-host disease. Histopathologically there were striking similarities of xenogeneic graft-versus-host disease in the mice and human graft-versus-host disease following allogeneic stem cell transplantation. Interestingly, when mice survived acute graft-versus-host disease, about 50% of mice developed chronic xenogeneic graft-versus-host disease. Further experiments demonstrate the huPBMC-RAG2-/-gc-/-model to be the first model that can be used for a quantitative evaluation of in vivo functionality of human T cells following in vitro manipulations. In mouse models, murine CD4+CD25+ regulatory T cells have been shown to influence the extent of graft-versus-host disease. Therefore, manipulating regulatory T cells may be a new tool to improve outcome of allogeneic stem cell transplantation for patients with hematological malignancies. Results of additional experiments in this model for the first time show the effect of depletion and reinfusion of human regulatory T cells on xenogeneic graft-versus-host disease. In conclusion, this thesis describes the development and application of a new preclinical model for the in vivo study of human T cells. For a safe and effective application of adoptive immunotherapy, this model can be considered an important step forward towards clinical application.