Many of the experimental protocols for the projects in this program rely on retroviral transduction of primary or cultured cells. Because the techniques of retroviral preparation and transduction require a high degree of technical expertise, a central facility where these techniques are performed would significantly enhance the progress of all projects. A central facility for retroviral preparation and transduction would offer multiple advantages to the group. These include: 1) uniform procedures for preparing high titer retroviral supernatants, 2) regular availability of high titer retroviral supernatants, 3) periodic monitoring of retroviral supernatants to insure that they are mycoplasma-free and do not contain replication competent retrovirus, and 4) expertise in transduction of fetal liver and bone marrow hematopoietic stem cells, Because of the collaborative nature of the research program, availability of high titer retroviral supernatants and procedures for transduction, together with standardization of protocols and reagents would be of great benefit to everyone in the program. The retroviral core will be housed in Dr. Pear's research space. The Core will purchase and maintain equipment necessary for these procedures. Additionally, consumables will also be purchased in bulk by the Core to ensure standardization of materials and bulk purchase discounts.