DESCRIPTION (Applicant's Description): The development of gene therapy for hematopoietic cells is very important in order to treat human disorders that are incurable today using standard medical procedures. Primarily, these are genetic disorders and malignant diseases (leukemia and solid tumors) within and outside the hematopoietic system. During the past 10 years there have been considerable advances in developing gene therapy approaches for murine hematopoietic cells and for hematopoietic progenitor cells of humans. However, fundamental problems remain in the development of gene therapy for hematopoietic stem cells. This has been demonstrated in multiple preclinical and clinical studies where gene marking of stem cells has been demonstrated but at very low efficiency. This meeting will bring together experts in virology, vectorology and molecular and cellular hematopoiesis to present the latest scientific results and discuss how new fundamental approaches can be used to develop effective gene transfer strategies for hematopoietic ells, in particular hematopoietic stem cells. Particular emphasis will be put on the development of vectors that can transduce quiescent (nondividing) stem cells. Similarly, site-specific integration of transferred genes will be discussed. A special section will be devoted to the interaction between viral envelope proteins and receptors on mammalian cells, both to discuss targeted delivery to particular cells and also to explore the use of hybrid vectors with components from various viral systems in order to broaden host range and facilitate vector uptake. Similarly, the leading experts in hematopoiesis will present data and discuss possibilities of increasing the understanding of [how] the genetic control of hematopoiesis is regulated to increase understanding of how it could be possible to manipulate stem cell division in vitro or in vivo in order to increase the proportion of primitive hematopoi-etic cells that have been genetically modified. In addition, gene expression in specific compartments of the hematopoietic hierarchy will be addressed, in particular regulation of gene expression in the stem cell compartment. How can genes that control stem cell specific expression be isolated and how can the ability to isolate and "purify" human hematopoietic stem cells be increased? These are the fundamental issues and questions that will be discussed by scientific leaders in the fields of vectorology and hematopoie-sis.