EX-VIVO PURGING OF ALLOGENEIC MARROW WITH L-LEUCYL-L-LEUCINE METHYL-ESTER - A PHASE-I STUDY

L-Leucyl-L-leucine methyl eater (LLME) is a lysosomatropic compound th at is converted by dipeptidyl peptidase I to metabolites that are memb ranolytic for cytotoxic T cells, NK cells, and LAK cells. Ex vivo trea tment of murine marrow with LLME ameliorates acute graft-versus-host d isease (GVHD), which led to consideration of a clinical study. A phase I study design was initiated to evaluate the effects of ex vivo purgi ng of allogeneic marrow on engraftment, since LLME also suppresses hum an progenitor cells. All patients received a preparative regimen of cy clophosphamide plus total body irradiation. GVHD prophylaxis consisted of cyclosporine +/- corticosteroids. This study included 19 patients with high risk disease undergoing allogeneic transplantation from an H LA-identical sibling (n = 12) or a partially HLA-matched family donor (n = 7). Marrow mononuclear cells were treated ex vivo in a dosage esc alation study with LLME concentrations of 0.25 mM, 0.375 mM, and 0.5 m M. Marrow NK and LAK activities were essentially eliminated at con cen trations greater than or equal to 0.375 mM LLME. CD8(+) cells were als o reduced. Granulocyte macrophage colony-forming unit recovery was 3% at 0.5 mM LLME. The median time to an absolute neutrophil count of 500 /mu l was 17 days after transplantation (95% confidence interval = 14- 18 days). One patient that received marrow treated with 0.5 mM LLME di ed of secondary graft failure. Complete donor chimerism was documented in each evaluable case. NK recovery was delayed at LLME concentration s greater than or equal to 0.375 mM LLME, Grade II/IV GVHD occurred in 4/18 evaluable patients. Ex vivo treatment of human marrow with LLME diminishes NK activity, LAK activity, CD8(+) cells, and granulocyte ma crophage colony-forming units, but does not totally prevent acute GVHD .