Circulating endothelial cells after transplantation ; author's reply

Sir,

The presence of recipient cells wasassociated with graft rejection, especially with vascular rejection. We speculated that bloodborne endothelial precursor cells could repair vascular damagecaused by rejection. 

Eberhard Gunsilius and colleagues suggest that the process we note in transplanted kidneys is similar to maintenance angiogenesis. We fully agree with this idea. Their data that bone-marrow-derived endothelial cells cause maintenance angiogenesis is in line with our hypothesis, that bloodborne cells lead to endothelial-cell chimerism. They propose that bloodborne endothelial cells, derived from the passenger leucocytes in the graft, home into the blood vessels outside the graft. This mechanism might result in a state of microchimerism.

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Endothelial chimerism could, however, induce abnormal interactions between allogeneic cell types that could lead to endothelial-cell activation, cytokine secretion, and an inflammatory reaction resulting in endovasculitis and vascular rejection. We could not investigate whether the infiltrate precedes or follows endothelial chimerism, but this is an important issue that needs further investigation.