PBMCs secrete higher levels of immunostimulatory cytokines than do pure NK cells in response to Herceptin-coated human breast cancer cells and IL-12. The SKBR3 cell line was cultured with purified NK cells or a whole PBMC population in our in vitro coculture assay. Standard controls were also included. Culture supernatants were harvested after 72 hours and analyzed for (a) IFN-γ (b) TNF-α (c) GM-CSF, and (d) MIP-1α.