In vitro separation of host specific graft-versus-host and graft-versus-leukemia cytotoxic T cell activities.

The association of graft-versus-host disease (GVHD) with lower relapse rates following allogeneic bone marrow transplantation (BMT) in humans led us to analyse post HLA-identical BMT derived anti-host cytotoxic T cells (CTL) for their putative anti-leukemic activity. To establish whether graft-versus-host (GVH) and graft-versus-leukemia (GVL) activities are separate, CTL lines were generated at different time points post-BMT from three patients suffering from acute GVHD. These CTL lines, which exhibited lysis of host normal lymphocytes and neoplastic cells, were analysed at the clonal level. Three functionally different types of clones were characterized: clones directed at host specific minor Histocompatibility (mH) antigens which are shared by patient's peripheral blood lymphocytes (PBL) and leukemic cells; clones recognizing only host PBL but not host leukemic cells; and putative GVL clones directed at patient's neoplastic cells only. These data could explain the long controversies on dissection of GVH and GVL activities. Our results demonstrate that GVH and GVL activities can be dissected, while non-separable effector cells which exhibit both activities do exist as well.