In this PhD thesis the potential of T-cells as therapy for disease are explored. The applications of genetically modified T-cells for treatment of cancer and autoimmune disease; the functionality and optimal activation of T-cells are discussed. Successful treatment of cancer with T-cell receptor (TCR)-modified T-cells was first reported in 2006, and is based on recognition of a specific peptide by the TCR in the context of the MHC molecule. As antigen presentation in tumors is often defective and to avoid MHC-restriction, chimeric antigen receptors (CAR) molecules containing an antibody part for recognition of cell surface antigens and TCR and co-receptor signaling domains have been developed. Activated T-cells mount an efficient immune response resulting in the killing of the cancer cell and initiating T-cell proliferation. The rationale for using genetically modified T-cells instead of isolating tumor infiltrating lymphocytes from the tumor and expanding them (TIL therapy) is that it is often very difficult to obtain viable lymphocytes that are able to expand enough in order to use them for therapy. This thesis explores the possibility of using prostate-specific antigens to target T-cells towards prostate cancer. The prostate has many unique tissue antigens but most patients with metastatic prostate cancer have undergone prostatectomy and consequently have “prostate antigen” expression only in cancer cells. We targeted the prostate antigens TARP and PSCA with a HLA-A2 restricted TCR and a CAR respectively. In both cases the tumor-specific T-cells were able to generate potent proliferative and cytotoxic responses in vitro. The PSCA CAR-modified T-cells delayed subcutaneous tumor growth in vivo. It is evident from our in vivo experiments that the PSCA CAR T-cells were unable to completely cure the mice. Therefore, we aimed to improve the quality of the transferred T-cells and their resistance to the immunosuppressive tumor microenvironment. Stimulation with allogeneic lymphocyte-licensed DCs improved the resistance to oxidative stress and antitumor activity of the T-cells. We further investigated the potential of genetically modified regulatory T-cells (Tregs) to suppress effector cells in an antigen-specific manner. Using a strong TCR we hypothesize that the phenotype of the TCR-transduced Tregs may be affected by antigen activation of those cells. We found that the engineered Tregs produced cytokines consistent with Th1, Th2 and Treg phenotypes.