VANIN-1, A NOVEL GPI-LINKED PERIVASCULAR MOLECULE INVOLVED IN THYMUS HOMING

Migration of hematopoietic precursor cells to the thymus is shown to d epend upon a novel molecule called Vanin-1 expressed by perivascular t hymic stromal cells. An anti-Vanin-1 antibody blocks the binding of pr o-T cells to thymic sections in vitro, the in vivo accumulation of bon e marrow cells around cortical thymic vessels, and long-term thymic re generation. Thus, it interferes with the entry, and not the differenti ation, of hematopoietic precursor cells. The Vanin-1 gene codes for a GPI-anchored 70 kDa protein that shows homology only with human biotin idase. Transfection of thymic stromal cells with the Vanin-1 cDNA enha nces thymocyte adhesion in vitro. These data suggest that vanin-1 regu lates late adhesion steps of thymus homing under physiological, noninf lammatory conditions.