The role of thiotepa in allogeneic stem cell transplantation in patients with leukemia

Graft versus host disease (GVHD) and recurrence of basic disease are major obstacles to a successful allogeneic bone marrow transplantation (BMT) outcome. One of the possibilities of maintaining the therapeutic potential of marrow allografting in the absence of GVHD is to intensify the conditioning regimen administered pre-T-cell depleted BMT in order to compensate for the loss of GVH related graft versus leukemia (GVL) effect. In order to do so we used a preparative regimen consisting of three alkylating agents-Busulfan (BU), Thiotepa (TTP) and Cyclophosphamide (CY)-for T-cell depleted allogeneic stem cell transplantation (SCT) instead of the standard BU-CY protocol. The effect of this intensified regimen was investigated in 30 consecutive leukemia patients who underwent T-cell depleted SCT from HLA identical siblings. Sixteen of the patients were males and 14 females, of median age 24 (5-43) years. Fourteen patients had acute myelogenous leukemia (AML), ten acute lymphoblastic leukemia (ALL), four chronic myelogenous leukemia (CML) and two myelodysplastic syndrome. The conditioning regimen consisted of BU 4 mg/kg x 4 days (-8 to -5), TTP 5 mg/kg x 2 days (-4 and -3), and CY 60 mg/kg x 2 days (-2 and -1). Engraftment was normal, with WBC >1.0x10(9)/l at day +18 (10-32), ANC >0.5x10(9)/l at day +21 (9-33) and platelets >25x10(9)/l at day +30 (14-69). Regimen related toxicity (RRT) was moderate and transplant related complications comparable to other conventional conditioning protocols. Overall survival and disease free survival (DFS) at 60 months follow up was 50%. Only three patients (10%), with ALL, relapsed and subsequently died. From the current data it would appear that TTP does not significantly improve BMT outcome in patients with leukemia, when compared to the standard BU-CY conditioning. However, our results with the BU-TTP-CY combination followed by T-cell depleted allogeneic SCT could provide the basis for a prospective randomized study comparing this protocol with the standard BU-CY regimen.