The key aims that we seek to address through the current protocol are related to objective (1) listed above: To develop improved methods for fractionating breast milk into epithelial cell rich and liquid components. Given that Dr. Arcaro has an IRB approved open protocol to collect fresh milk at University of Massachusetts, NCI can only pursue this collaborative aim (effectively within the timeframe of the bench-to-bedside award) in the context of this ongoing study. Specifically, the collaborative project that is the subject of this IRB application will assess the following aims through in vitro manipulation of fresh liquid milk collections: 1) the effects of modifying the initial rinse of epithelial pellets (rinse solution: saline vs. media; centrifugation speeds, temperature); 2) yields of cells and nucleic acids achievable via fractionation of milk using different types of immunomagnetic beads (coated with antibodies to remove leukocytes ( negative selection ) vs. coated with antibodies to remove epithelial cells ( positive selection ); 3) the relative preservation at room temperature at 24, 48 and 72 hours of milk suspended in cellular fixatives (e.g. formalin, Proclin) as compared to fresh milk without fixation; 4) the possibility that strategies 1 and 2 be combined. This project brings together specific experience and expertise at University of Massachusetts with regard to milk processing with technical knowledge from NCI, provided by Drs. Kopp, Heckman, Yang and Sherman. In particular, NCI Frederick and Dr. Heckman have successfully used immunomagnetic bead technology to purify epithelial cells from blood products and lactating mouse glands by removing leukocytes.