Randomized phase III trial of haploidentical HCT with or without an add back strategy of HSV-TK donor lymphocytes in patients with high-risk acute leukemia.

Abstract

6541 Background: Suicide gene therapy applied to allogeneic stem cell transplantation has been tested in several trials. When exposed to ganciclovir, donor lymphocytes expressing herpes simplex thymidine kinase suicide gene (TK cells) are selectively eliminated. In a phase I-II trial (Ciceri, Bonini, Lancet Oncology 2009,489-500), TK cells were infused in patients after haploidentical transplantation. Of 50 patients enrolled, 28 received transduced-TK cells and 22 achieved rapid immune reconstitution, with a non-relapse mortality of 14%. GvHD after DLI-TK infusion was reported in 30% of patients and in all cases was fully controlled by ganciclovir treatment. Methods: High risk leukemia patients in first or subsequent complete remission are currently randomized in a 2-arm (3:1 ratio) phase III trial with or without the add-back strategy of HSV-TK donor lymphocytes in patients underwent T-depleted haploidentical stem cell transplant. Primary end point is disease-free survival (DFS), while secondary end points included overall survival, non-relapse mortality, immune reconstitution, acute and chronic GvHD incidence, and relapse incidence. For the primary analysis of DFS 170 patients (127 patients in the experimental group and 43 patients in the control) are required to detect an hazard ratio of 0.55 with at least 80% power for 2-sided 0.05 level test. Patients are eligible for the study if they are older than 18 years-old, absence of timely and suitable HLA matched family or unrelated donor, and have a ECOG performance status < 2. Patients are stratified by state of disease, ECOG PS and country before randomization. Results: Transduced lymphocytes are given to patients between day +21 and day +49 after haploidentical HCT in the absence of spontaneous immune reconstitution and/or development of GvHD. In absence of immune reconstitution and GvHD after the first TK-cells add-back further 3 infusions could be administered 30 days after the last infusion. TK lymphocytes dose is 1 x10^7 CD3/Kg. Conclusions: The study (TK008) is currently open to accrual in EU, US, Israel (clinicaltrials.gov:00914628).