L-Leucyl-L-Leucine Methyl Ester (LLME) Treated Non-Myeloablative Allogeneic Hematopoietic Stem Cell Transplantation (HSCT) for Patients With Hematological Malignancies

GVHD remains an obstacle for allogeneic HSCT. While T cell depletion of donor grafts results in much lower incidences of GVHD, rejection and poor immune recovery are often associated with this approach. To address these issues, we developed a transplant approach using LLME to test the hypothesis that the selected depletion of T cells containing cytotoxic effector granules would result in less significant GVHD while at the same time preserving GVT effects and infectious immunity. LLME preferentially kills cytotoxic effector granule bearing lymphocytes including most NK and CD8 T cells with relative sparing of CD4 T cells. Fourteen patients, with a median age of 57 years with high risk disease were transplanted from related or unrelated donors after a conditioning regimen of flu/cyclo/ara-C. Prior to the infusion of the donor inoculum, we performed CD34 selection using the Isolex® system to separate the graft into CD34+ and CD34- fractions. The CD34- fraction was then treated with LLME to selectively deplete the cytotoxic effector granule containing subsets, thus avoiding stem cell exposure to LLME. Patients received the CD34 selected stem cell product (median CD34 dose 4.13 x 106/kg). This HSC product contained 5 x 104 untreated CD3 cells/kg in the initial 6 patients treated, but due to significant GVHD, the final 8 patients received 2.5 x 104 untreated CD3 cells/kg. One day later, the LLME treated CD34- fraction (median CD3 dose 8.74 x106 /kg) was infused. One patient died shortly after the stem cell infusion from infectious complications. All 13 evaluable patients engrafted WBC by day 14. Two patients experienced late rejection. One of these patients is still alive 3 years later with evidence of recurrent disease and the other patient eventually died of relapsed disease. Of the remaining 11 patients, 3 patients developed grade III-IV GVHD and 1 patient developed cGVHD. All 4 of these patients died of GVHD related causes. Three patients died of complications from relapsed disease and 1 additional patient died of infectious complications. Four patients are alive at a minimum of 3 years post transplant. Two of these patients have relapsed disease, 1 patient is disease free with 100% donor chimerism and one patient is disease free with a persistence of 5% host cells. This study shows that LLME can be used to treat lymphocytes without affecting initial engraftment, but relapse and GVHD remain significant barriers in this high risk population.