Compositions and methods for enhanced transepithelial and transendothelial transport or active agents

A method for enhancing transcellular or transmembrane transport of an active agent, said method comprising:

• forming a conjugate of said active agent with a cell-surface receptor ligand for a transferrin receptor;
• and
• administering said conjugate and a transfer enhancing amount of a transfer enhancement agent which enhances transcytosis of a cell-surface receptor/ligand complex.