This project studies peripheral blood hematopoietic progenitors (PBHP) as a target for gene therapy of inherited diseases affecting the function of human phagocytic cells such as neutrophils, monocytes and eosinophils. Some aspects of this work are also directed toward studying the mechanisms by which phagocytic cells provide host defense against infection. There were three major directions of study that were the focus of this project over the past year. 1. During the past year we have developed several new methods and materials which improve our ability to get new genes into human blood stem cells. The specific goal was to develop a system of gene therapy to correct the genetic defect in the X-linked genetic form of chronic granulomatous disease (CGD). The results of this development could then be used in a clinical trial of gene therapy for CGD. That clinical trial and the results from that clinical trial will be discussed in the report for Project Z01-AI-00645-07. Specifically, we developed a retrovirus vector producer cell line that secretes high titers of the MFGS vectors containing the gp91phox cDNA that will correct the functional defect in X-linked CGD neutrophils. We demonstrated that the fibronectin fragment CH-296 coated on culture vessel surfaces will greatly augment the gene transfer correction of stem cells from patients with CGD. 2. We have studied the biological differences in stem cells derived from the bone marrow compared to stem cells which can be induced to enter the circulation by treatment with granulocyte colony stimulating factor (G-CSF). Specifically we demonstrated that the stem cells that are recruited to the peripheral blood by G-CSF treatment have more cells in the G-1 phase of the cell cycle and less in G-0 than similar cells from resting bone marrow. We also showed that the G-CSF recruited cells have a higher level of expression of receptor for the amphotropic retrovirus envelope. These properties make the peripheral blood stem cells an excellent target for gene therapy.