Gene Transfer into Hematopoietic Cells: From Basic Science to Clinical Application Christopher Baum 1. The Potential of Gene Transfer into Hematopoietic Vectors with the potential for stable transgene integration are Cells widely used in basic hematology and clinical trials of gene me- cine. In basic research, both gain-of-function and loss-of-fu- tion situations of individual genes can be created by gene transfer, leading to a wide range of applications in developmental biology, stem cell biology, immunology, leukemia research, and human genetics. With the first evidence of successful modification of murine hematopoietic cells using retroviral gene vectors (1, 2), researchers have also explored the therapeutic potential of this approach. To date, the emerging discipline of gene therapy is a highly diversified field that offers entirely novel approaches to treat a great variety of human diseases (3). All hematopoietic cell types are of major interest in this context, since the modification of the hematopoietic stem cell population may potentially give rise to a completely transgenic hematopoiesis with the potential to cure genetic disorders or fight severe chronic infections, and the targeting of mature cells such as lymphocytes or antigen-p- senting dendritic cells offers all types of transient and semiper- nent modifications of the immune system. The unifying principle of gene medicine is the need to transfer complex nucleic acids cells that do not contribute to the germline (somatic cells).