Apoptosis of human naive NK cells mediated by a rat IgG2b anti CD2 mAb through a fractricidal ADCC reaction

LO-CD2a/BTI-322, a rat anti human CD2 mAb, shows in vitro and in vivo immun osuppressive properties and induces T-cell depletion resulting partially fr om an antibody dependent cellular cytotoxicity (ADCC) mediated by NK cells. The aim of this paper is to study the in vitro effect of LO-CD2a/BTI-322 o n NK cells, the majority of them also expressing the CD2 molecule. The addi tion of the mAb to purified naive NK cells induces apoptosis of CD2(+) cell s. The apoptosis is rapid, Fas ligand independent and completely inhibited by the calcium chelator EGTA, suggesting a fractricidal ADCC reaction and i mplying that NK cells are not resistant to lysis when used as target cells. At the end of the reaction, the CD2(-) remaining cells are still capable o f natural cytotoxicity against K562 cells, but at a lower rate than untreat ed cells. (C) 1999 Elsevier Science B.V. All rights reserved.