7E3 MONOCLONAL-ANTIBODY DIRECTED AGAINST THE PLATELET GLYCOPROTEIN IIB IIIA CROSS-REACTS WITH THE LEUKOCYTE INTEGRIN MAC-1 AND BLOCKS ADHESION TO FIBRINOGEN AND ICAM-1/

Recent clinical trials suggest that blockade of integrins is a promisi ng strategy for the treatment of acute coronary syndromes. Administrat ion of 7E3 monoclonal antibody (mAb) Fab fragment (c7E3 Fab) directed against platelet integrin IIb/IIIa (alpha IIb beta 3, CD41/CD61) reduc es acute ischemic complications of coronary angioplasty and clinical r estenosis at 6 months. However, 7E3 mAb is not selective for platelet IIb/IIIa but also cross-reacts with the leukocyte integrin Mac-1 (alph a M beta 2, CD11b/CD18) and the vitronectin receptor (alpha v beta 3, CD51/CD61). Information regarding how this mAb may affect other cells important in vascular repair is scant. Potential interactions of c7E3 Fab with inflammatory (ie, monocytes and neutrophils), vascular smooth muscle, and endothelial cells may contribute to the in vivo actions o f c7E3 Fab. In this study we explored the binding of 7E3 to monocytic cells and the functional effect of 7E3 and c7E3 Fab on Mac-1-mediated adhesion to fibrinogen (FGN) and intercellular adhesion molecule-1 (IC AM-1), ligands abundant in the injured vessel wall. Flow cytometry dem onstrated that 7E3 bound to THP-1 monocytic cells and identified a sub population (approximate to 10%) of Mac-1 that was qualitatively simila r to that recognized by CBRM1/5, a mAb directed to an activation-speci fic neoepitope present on a subset of Mac-1 molecules. mAb 7E3 bound t o K562 cells transfected with just the alpha subunit (CD11b) of Mac-1 but not to nontransfected cells, confirming a direct interaction betwe en 7E3 and Mac-1. mAb 7E3 and c7E3 Fab blocked the adhesion of Mac-1-b earing cells to FGN (80+/-11% and 78+/-9% inhibition, respectively) an d ICAM-1 (62+/-14% and 62+/-17%). Both 7E3 and c7E3 Fab significantly inhibited (70+/-6% and 62+/-26%) soluble FGN binding to human peripher al blood monocytes. Thus, c7E3 Fab cross-reacts with the CD11b subunit of Mac-1 and interrupts cell-extracellular matrix and cell-cell adhes ive interactions and may thereby influence the recruitment of circulat ing monocytes to sites of vessel injury. Given the recent evidence tha t adherent and infiltrating monocyte number directly correlates with t he extent of neointimal hyperplasia, inhibition of Mac-1-dependent adh esion and IIb/IIIa-dependent function by c7E3 Fab may jointly contribu te to the regulation of vascular repair and to the sustained clinical benefits observed with c7E3 Fab after angioplasty.