The present invention relates in essence to a method for detecting a subset of cells with a binding domain which is specific for a target which characterizes said subset of cells which method comprises detecting ex vivo said subset of cells wherein said binding domain is to be administered to a subject which comprises or is assumed to comprise said subset of cells prior to the removal of said subset of cells. The present invention also relates to the use of a binding domain as defined herein in a method defined herein. The use of a binding domain as defined herein for the preparation of a diagnostic composition to be used in a method defined herein is also envisaged. In another aspect the present invention relates to the binding domain as defined herein to be used in a method defined herein. Kits comprising a binding domain as defined herein and means to administer said binding domain to a subject and optionally means to detect said binding domain with a method defined herein are also disclosed. In another aspect the present invention relates to the use of a binding domain preferably a therapeutically effective antibody like for example alemtuzumab apolizumab cetuximab epratuzumab galiximab gemtuzumab ipilimumab labetuzumab panitumumab rituximab trastuzumab nimotuzumab mapatumumab matuzumab rhMab ICR62 rhMab B Ly1 and pertuzumab etc including combinations thereof for the preparation of a pharmaceutical composition for the treatment of patients disposed to respond favorably to said binding domain as identified by a method defined herein.
