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Ex vivo purging of allogeneic marrow with L-Leucyl-L-leucine methyl ester. A phase I study
C S Rosenfeld1, D L Thiele, R K Shadduck
1Texas Oncology, P.A., Stem Cell Transplant Unit, University of Texas Southwestern Medical Center, Dallas 75235-8887, USA.
Abstract:
L-Leucyl-L-leucine methyl ester (LLME) is a lysosomatropic compound that is converted by dipeptidyl peptidase I to metabolites that are membranolytic for cytotoxic T cells, NK cells, and LAK cells. Ex vivo treatment of murine marrow with LLME ameliorates acute graft-versus-host-disease (GVHD), which led to consideration of a clinical study. A phase I study design was initiated to evaluate the effects of ex vivo purging of allogeneic marrow on engraftment, since LLME also suppresses human progenitor cells. All patients received a preparative regimen of cyclophosphamide plus total body irradiation. GVHD prophylaxis consisted of cyclosporine +/- corticosteroids. This study included 19 patients with high risk disease undergoing allogeneic transplantation from an HLA-identical sibling (n = 12) or a partially HLA-matched family donor (n = 7). Marrow mononuclear cells were treated ex vivo in a dosage escalation study with LLME concentrations of 0.25 mM, 0.375 mM, and 0.5 mM. Marrow NK and LAK activities were essentially eliminated at concentrations > or = 0.375 mM LLME. CD8+ cells were also reduced. Granulocyte macrophage colony-forming unit recovery was 3% at 0.5 mM LLME. The median time to an absolute neutrophil count of 500/microliters was 17 days after transplantation (95% confidence interval = 14-18 days). One patient that received marrow treated with 0.5 mM LLME died of secondary graft failure. Complete donor chimerism was documented in each evaluable case. NK recovery was delayed at LLME concentrations > or = 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 macrophage colony-forming units, but does not totally prevent acute GVHD.
Insights
L-Leucyl-L-leucine methyl ester (LLME) purging of marrow reduced immune cells and improved engraftment time in transplant patients. However, it did not fully prevent graft-versus-host disease (GVHD) and carried a risk of graft failure.
Area of Science:
- Hematology
- Immunology
- Transplantation
Background:
- Allogeneic stem cell transplantation is a potential cure for hematologic malignancies.
- Graft-versus-host disease (GVHD) remains a significant complication, necessitating effective prophylaxis strategies.
- Ex vivo purging of donor marrow aims to reduce GVHD while preserving engraftment.
Purpose of the Study:
- To evaluate the safety and efficacy of ex vivo L-Leucyl-L-leucine methyl ester (LLME) purging of allogeneic marrow in a phase I clinical trial.
- To assess the impact of LLME on immune cell recovery, engraftment, and GVHD incidence.
- To determine optimal LLME concentrations for ex vivo marrow treatment.
Main Methods:
- A phase I dosage escalation study of ex vivo LLME treatment on allogeneic marrow.
- 19 high-risk patients received cyclophosphamide, total body irradiation, and cyclosporine +/- corticosteroids for GVHD prophylaxis.
- LLME concentrations ranged from 0.25 mM to 0.5 mM, with subsequent transplantation and monitoring for engraftment and GVHD.
Main Results:
- LLME concentrations ≥ 0.375 mM eliminated NK and LAK cell activity and reduced CD8+ cells.
- Granulocyte-macrophage colony-forming unit recovery was 3% at 0.5 mM LLME.
- Median time to neutrophil engraftment was 17 days; 4/18 patients developed Grade II-IV GVHD. One patient receiving 0.5 mM LLME died of graft failure.
Conclusions:
- Ex vivo LLME marrow purging reduces key immune cell populations and progenitor cells.
- While LLME can impact engraftment kinetics and GVHD, it does not completely prevent acute GVHD and carries a risk of graft failure.
- Further investigation is needed to optimize LLME use in allogeneic transplantation.