Bone marrow cells contribute to neointimal formation after stent implantation in swine

Background Recent studies suggest that neointimal cells in atherosclerotic lesions are partly derived from bone marrow (BM) cells. However, studies with large animal models have not yet clarified how BM cells contribute to neointimal formation in restenotic lesions. We examined the expression of CD34, a hematopoietic stem cell marker, in the neointima after coronary stent implantation in porcine. Methods Pigs underwent balloon injury in the coronary arteries followed by stent implantation. The arteries were harvested at 3, 7, and 28 days after the stenting. The samples were used for immunohistochemistry for CD34, smooth muscle embryo (SMemb), α-smooth muscle cell actin (α-SMA), macrophage, c-kit, and AC133 antibodies. In morphometric analysis, each layer of vascular wall was calculated in the sections. Results At 3 days, the expressions of CD34 and SMemb were minimal, and many macrophages were seen around the stent struts. At 7 days, co-expression of CD34 and SMemb was observed around the struts, and 11.5% of the neointimal cells were stained by CD34. In addition, c-kit positive cells and AC133 positive cells are detected in neointimal area. At 28 days, the neointima had thickened and expressed α-SMA rather than SMemb, and a few CD34-positive cells were detected. In morphometric analysis, luminal area/total vascular area was significantly smaller and intimal area/total vascular area was significantly bigger in 7 and 28 days than in the day of implantation. Conclusion BM cells of possibly hematopoietic origin partially contributed to neointimal formation after coronary stent implantation in a large animal model.