A method including delivering to a treatment site within a lumen of a blood vessel (1) a cellular component including at least one of endothelial cells and endothelial progenitor cells and/or (2) a conjugate having a first site having affinity to or capable of conjugating with the blood vessel and a second site having affinity to a cellular component or capable of conjugating with a cellular component. A method including coating a treatment site within a lumen of a blood vessel with a polymeric biomaterial including (1) molecular moieties with affinity to cells or a treatment agent and (2) a treatment agent. A composition including a cellular component including endothelial cells or endothelial progenitor cells and modified to increase the potential for retention at a treatment site. A composition including a polymeric biomaterial including (1) molecular moieties with affinity to cells or a treatment agent or (2) a treatment agent.