Mobilized peripheral blood mononuclear cells (PBMC) are collected from healthy human volunteer donors under IRB approved informed consent by leukapheresis using the COBE® Spectra Apheresis System MNC collection protocol. Donors are injected with G-CSF (Neupogen® - FDA approved), which stimulates the bone marrow to produce a large number of hematopoietic and progenitor stem cells and mobilizes them into the peripheral blood stream.