How can I separate mouse cells from a mouse/human cell mixture grown in a cell culture dish as a monolayer? 

You can use the Mouse Cell Depletion Kit for this application. Do not use trypsin for passaging the cells because it would destroy important epitopes, and as a result, the depletion would be incomplete.

Follow our detailed application protocols "Isolation of xenografted cells from tumors by depletion of mouse cells".