This is an application to purchase a Becton-Dickinson FACS Vantage high speed fluorescence cell sorter. The instrument will be housed in the Cell Sorter Facility of the Albert Einstein College of Medicine. The operating budget for this facility is derived from an NCI grant and supplemented by university funds and user charges. It is staffed with an operations director who has over 2 decades experience in flow cytometry and a technician. There is a faculty supervisor and a steering committee to set policy and ensure quality performance. The FACS Vantage permits high reliability, high speed sorting of defined cell populations. Cell populations can be characterized using parameters of forward and side scatter and fluorochrome staining; 8 parameters can be simultaneously analyzed. Less advanced instruments permit the simultaneous analysis of only 4 parameters and sort populations at one tenth the speed. The increased potential of this instrument will permit the isolation of rare cells for functional studies, more comprehensive characterizations of cell cycle and phenotypic properties of cell populations, the analysis of molecular interactions occurring within cells (FRET) and kinetic studies of activation profiles. Similar studies can be performed on microorganisms as well. The major user group for this instrument consists of investigators studying cells in the immune system, examining lineage commitment, immune cell activation and death, and alterations of immune function in disease states. The instrument will also be used by a large number of investigators studying oncogenesis, cell cycle regulation and differentiation, investigators studying microorganisms to identify virulence factors and investigators involved in drug design, analyzing the phenotype and function of drug exposed cells.