TRANSFER OF THE HSV-TK GENE INTO DONOR PERIPHERAL-BLOOD LYMPHOCYTES FOR IN-VIVO MODULATION OF DONOR ANTITUMOR IMMUNITY AFTER ALLOGENEIC BONE-MARROW TRANSPLANTATION

The infusion of donor lymphocytes after allogeneic bone; marrow transp lantation is a promising therapeutic tool for achieving a graft versus leukemia (GvL) effect in case of leukemic relapse (1-7), and for the treatment of other complications related to the severe immunosuppressi ve status of transplanted patients, such as Epstein Barr virus-induced lymphoproliferative disorders (EBV-BLPD) (8) or reactivation of CMV i nfection (9). Although the delay in the administration of T lymphocyte s is expected to reduce the risk of severe GVHD, this risk is still pr esent at higher doses of donor T-cells. The transfer of a suicide gene into donor lymphocytes could allow the in vivo selective elimination of cells responsible for severe GvHD. Additionally, under appropriate conditions, it may allow in vivo modulation of donor anti-tumor respon ses, and to separate GvL from GvHD. Finally, crucial questions concern ing survival and function of donor lymphocytes could be answered by th eir gene marking. Previous studies documented that T lymphocytes are s uitable targets for gene transfer through retroviral vectors (10,11). This protocol has been designed to evaluate in the contest of allogene ic BMT: 1-the safety of increasing doses of donor lymphocytes transduc ed with a suicide retroviral vector; 2--the efficacy in terms of survi val and immunologic potential of donor lymphocytes after in vitro acti vation, gene transduction, and immunoselection; 3-the possibility of i n vivo down regulation of GvHD by the administration of ganciclovir to patients treated by tk-transduced donor lymphocytes. Patients will be enrolled in three groups: A-patients in complete remission after a T depleted allo-BMT, in order to prevent disease relapse; B-patients wit h relapse of hematologic malignancies after allo-BMT, in order to achi eve a GvL effect; C-patients with an EBV-BLPD after allo-BMT, in order to provide donor EBV-specific T-cells. For this purpose, donor periph eral blood lymphocytes (PBL), will be transduced with a suicide retrov iral vector containing two genes: the first coding for the thymidine k inase of the herpes simplex virus (HSV-tk) and the second coding for t he low affinity receptor for NGF(12) truncated of its intracellular do main (Delta NGFR). The HSV-tk confers ganciclovir sensitivity (13), th us allowing in vivo selective downregulation of all transduced allogen eic cells in case of severe GvHD. The Delta NGFR will be used as a cel l surface marker allowing rapid in vitro immunoselection of transduced cells, and ex vivo detection and characterization of the transduced c ells after infusion.