AN ANTI-CD2 MAB INDUCES IMMUNOSUPPRESSION AND HYPORESPONSIVENESS OF CD2(-CELLS IN-VITRO() HUMAN T)

We describe here the potent specific immunosuppression obtained in vit ro by LO-CD2a, a rat mAb directed against the human CD2 molecule. Addi tion of low dose LO-CD2a (40 ng/ml) at the time of mixed lymphocyte cu lture (MLC) initiation inhibits 80% of the proliferation and, more imp ressive, addition of the mAb 4 days after culture initiation at a simi lar concentration still suppresses 50% of the MLC. When responder T ce lls previously treated with LO-CD2a are challenged a second time by th e same donor or third party allogeneic cells, hyporesponsiveness occur s in both cases, although reactivity to T cell mitogenic stimulation p ersists. Finally, the low production of cytokines such as tumor necros is factor-alpha and IFN-gamma after incubation of human T cells with L O-CD2a suggests the absence of T cell activation. These results demons trate that LO-CD2a mAb has a significant immunosuppressive effect and induces hyporesponsiveness in vitro, thereby suggesting potential effi cacy in vivo for the treatment of acute rejection and for the inductio n of tolerance in allotransplantation.