MONOCLONAL antibodies are potentially useful therapeutic agents in a variety of immunologically mediated diseases, offering the theoretical advantage of selective attack on cells implicated in the immunopathogenesis of these disorders. Antibodies to surface markers on lymphocytes, particularly T cells, have already demonstrated efficacy both in animal models and in clinical allograft rejection.1 2 3 For this purpose, monoclonal antibodies can be used either to block vital receptors for antigen, adhesion, or growth factors or to block target cells by harnessing the various natural effector systems (complement and accessory cells) that are activated by the Fc regions of cell-bound antibodies. The optimal use… © 1990, Massachusetts Medical Society. All rights reserved.