A new marrow T cell depletion method using anti-CD6 monoclonal antibody-conjugated magnetic beads and its clinical application for prevention of acute graft-vs.-host disease in allogeneic bone marrow transplantation: results of a phase I-II trial.

We established a simple method of T cell depletion using anti-CD6 monoclonal antibody-conjugated immunomagnetic beads. Preliminary experiments using this method demonstrated that CD3+ T cells could be partially depleted without depleting CD56+ NK cells. A phase I-II clinical study was performed to assess the safety and efficacy of this partial T cell depletion method for the prevention of acute graft-vs.-host disease (GVHD) in 10 leukemia patients at high risk for GVHD (defined as 1) unrelated transplant from MLC-positive or HLA-DRB1 mismatched donor or 2) related transplant from serologically HLA-A, -B, or -DR one-locus mismatched donor). Cyclosporine (CSP) and methotrexate (MTX) were used for additional prophylaxis against GVHD in all cases. Sustained engraftment occurred in 9 of the 10 patients. Although acute GVHD developed in 6 of the 9 evaluable patients, none developed more than grade III severe acute GVHD. Five patients were alive in remission at a median follow-up of 32 months after bone marrow transplantation, and no relapse of leukemia was observed. We conclude from this pilot study that selective T cell depletion with anti-CD6 monoclonal antibody coupled with CSP and MTX posttransplant immunosuppressive therapy is safe. Further analysis of the phase II-III study is needed to confirm the effectiveness of this protocol.