Provided herein are conjugate molecules containing a substrate for a nucleoside transport pathway linked to an active agent, wherein the conjugate can be transported into a cell or into the nucleus of a cell via a cellular nucleoside transport pathway. Further provided are methods of delivering a conjugate molecule to a target cell expressing a nucleoside transport pathway, wherein the conjugate contains a substrate for the nucleoside transport pathway linked to an active agent. Also provided are methods for screening for conjugates that are transported by nucleoside transport pathways. Further provided are methods of treating a patient having a disease or disorder affecting tissues expressing nucleoside transport pathways, in which a conjugate containing an agent effective in treating the disorder is administered to the patient. Also provided are methods of treating a patient having an autoimmune disorder involving administering to the patient a compound that inhibits a nucleoside transport pathway.