Anti LFA1 monoclonal antibody for the prevention of graft rejection after T cell-depleted HLA-matched bone marrow transplantation for leukemia in adults.

A mouse IgG monoclonal antibody (MoAb) directed against the human LFA1 molecule (25.3 MoAb) was used in nine adult leukemic patients to prevent graft rejection after T cell-depleted HLA matched bone marrow transplantation. Based on the results of a previous study in children 0.1 mg/kg of 25.3 was given on days -3, -1, +1, +3, +5 in addition to a standard conditioning regimen with cyclophosphamide (120 mg/kg) and fractionated total body irradiation. The marrow transplant was T cell-depleted using T101 Fab immunotoxin ricin A chain. Seven patients received post-graft immunosuppression with methotrexate and cyclosporine A; two patients received no immunosuppression post-graft. A mean T cell depletion of 98.3% (80-100%) was achieved. Tolerance to the infusions of 25.3 MoAb was excellent. No patient developed any form of graft-versus-host disease. However two patients failed to engraft and three patients had delayed graft failures. These results show that this regimen of anti LFA1 MoAb, which was extremely good at permitting engraftment of HLA mismatched T cell-depleted transplant in children with constitutional diseases, is not able to prevent graft failure and rejection of T cell-depleted HLA matched transplants in adults with leukemia. Further efforts are needed to overcome graft failures in this clinical situation.