COMBINED IN VITRO AND IN VIVO T LYMPHOCYTE DEPLETION FOR THE CONTROL OF GRAFT-VERSUS-HOST DISEASE FOLLOWING HAPLOIDENTICAL MARROW TRANSPLANT

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Abstract
Most patients requiring allogeneic bone marrow transplantation (BMT) lack a human leukocyte antigen genotypically identical sibling and require an alternative donor. This carries an increased risk of graft failure and acute graft-versus-host disease (GVHD). We sought to overcome these problems with transplants by using grafts obtained from the most readily available source: the haploidentical, partially mismatched, related donor. This study of 40 patients used a novel approach combining in vitro and in vivo T cell depletion with T lymphocyte targeted monoclonal antibodies (mAb) and intensified conditioning therapy, including fractionated total body irradiation before etoposide, cytoside arabinoside, cyclophosphamide, and methylprednisolone. Grafts were treated with T10B9·1A-31 mAb, directed against the αβ heterodimer of the T cell receptor, and rabbit complement. In vivo depletion was attempted with an anti-CD5 mAb-Ricin A-chain (H65-RTA) immunotoxin (IT). Study patients were compared with a historical control group of 17 patients not given H65-RTA. Rates of engraftment were not significantly different (93% vs. 100%, P=0.12), although patients receiving IT engrafted more rapidly. The incidence of > grade I GVHD was significantly lower in the study group (36% vs. 100%, P=0.0001), as well as for severe grade III-IV GVHD (19% vs. 92%, P=0.0001). Five-year survival tended to be improved in the study group (40% vs. 18%, P=0.21). Transplant from haploidentical family members is indicated for patients without a matched sibling in whom allogeneic BMT offers the best opportunity to achieve cure.