Disclosed herein are materials and methods suitable for treating and managing plaque disease, including vulnerable plaque. An implantable material comprising cells, such as but not limited to endothelial cells, and a biocompatible matrix can reduce progression or deterioration of a plaque-associated lesion situated on the interior lumen of said blood vessel. The implantable material is implanted directly on an exterior surface of a blood vessel at or adjacent or in the vicinity of the site of a lesion on an interior lumen. Alternatively, the implantable material is deposited on an exterior surface at or adjacent or in the vicinity of the site of a lesion on an interior lumen by an intraluminal delivery device which traverses or penetrates the vessel wall or by a percutaneous delivery device which enters the perivascular space. Both modes of administration can be preceded by or coincident with an imaging step. The present invention can treat hemorrhage, erosion, fissure, plaque-associated thrombosis and occlusion, rupture, displacement and/or dislodgement of a plaque lesion.