Therapeutic and drug delivery systems are provided in the form of medical devices with coatings for capturing and immobilizing target cells such as circulating progenitor or genetically-altered mammalian cells in vivo. The genetically-altered cells are transfected with genetic material for expressing a marker gene and a therapeutic gene in a constitutively or controlled manner. The marker gene is a cell membrane antigen not found in circulating cells in the blood stream and therapeutic gene encodes a peptide for the treatment of disease, such as, vascular disease and cancer. The coating on the medical device may be a biocompatible matrix comprising at least one type of ligand, such as antibodies, antibody fragments, other peptides and small molecules, which recognize and bind the target cells. The therapeutic and/or drug delivery systems may be provided with a signal source such as activator molecules for stimulating the modified cells to express and secrete the desired marker and therapeutic gene products.