A CD66A-SPECIFIC, ACTIVATION-DEPENDENT EPITOPE DETECTED BY RECOMBINANT HUMAN SINGLE-CHAIN FRAGMENTS (SCFVS) ON CHO TRANSFECTANTS AND ACTIVATED GRANULOCYTES

Antibodies to CD66 recognize at least five members (CD66a-e) of the ca rcinoembryonic antigen (CEA) family. Recombinant human single-chain Fv fragments (scFvs) that bind specifically to CD66a (biliary glycoprote in) were obtained from a naive human scFv library, The scFvs bound to the N-domain of CD66a on Chinese hamster ovary (CHO) transfectants but did not bind to freshly isolated peripheral granulocytes or to dimeth ylsulfoxide-treated HL-60 cells. In contrast, scFvs bound web to granu locytes that were short-term activated with N-formyl-Met-Leu-Phe or ph orbol 12-myristate 13-acetate and to human IL-60 cells that were treat ed with all-trans-retinoic acid to induce granulocytic differentiation . Quantification of antigenic sites showed that the activation-depende nt CD66a epitopes were expressed on nearly all of the CD66a molecules on CHO-biliary glycoprotein transfectants, but they were detected only on a portion of the molecules on activated polymorphonuclear neutroph ils and differentiated HL-60 cells, Binding of CD66a scFvs to their ne oepitopes on prestimulated PMNs induced respiratory burst, suggesting that CD66a is capable of delivering transmembrane signals in these cel ls.