Correspondence Response to Letter Regarding Article, “CC Chemokine Receptor-1 Activates Intimal Smooth Muscle–Like Cells in Graft Arterial Disease” To the Editor:

The comments by Lee are well taken. Our study on graft arterial disease has primarily emphasized that the intimal smooth muscle cells (SMLCs) are distinct from medial smooth muscle cells.1 Indeed, we believe that SMLCs likely consist of multiple lineages instead of a single cell source. As we showed previously, candidate precursor cells of the intimal SMLCs include medial smooth muscle cells, bone marrow–derived cells, endothelial cell transdifferentia-tion, fibroblasts, tissue-derived stem cells, or hematopoietic inflam-matory cells.2 We also agree that fibrocytes may contribute to the SMLC population. We have not formally explored whether fibro-cytes can differentiate into intimal SMLCs, but this possibility merits consideration. Regardless, SMLC precursors of bone marrow origin (eg, fibrocytes) constitute 20 % of the total intimal SMLC popula-tion in the graft arterial disease lesion of murine aortic transplanta-tion without immunosuppression.