Conventional cancer therapies are limited by their toxicity and lack of specificity. To achieve targeted immunotherapy of cancer, we have chosen Wilm's Tumour antigen (WT1) as a target as it is over-expressed in most leukemia and many solid cancers. Using sophisticated WT1-TCR retroviral constructs, we have performed in vivo engraftment studies with CD34+ leukemic progenitor cells. In our model, treatment with WT1-TCR engineered patiens' T cells had cleared patients own leukemic cells. As the analysis of bone marrow indicated that control group showed evident engraftment of human leukemia cells, while the WT1-TCR treated group had none detectable