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A graft-versus-leukemia (GVL) effect has been considered a concentrations of 20 to 50 mmol/L, induced ı90% killing of major factor responsible for cures in patients with hemato-G418-selected cells without affecting nontransduced cells. logic malignancies undergoing allogeneic bone marrow Correlation of the extent of T-cell kill and the proportion of transplantation; however, associated graft-versus-host dis-TK-gene-transduced cells is consistent with the absence of ease (GVHD) results in significant morbidity and mortality. a bystander effect. Transduced cells were CD3 " and either T-cell depletion reduces the incidence and severity of GVHD CD8 " or CD4 " and retained functional properties of untransbut eliminates, at least partially, the GVL effect. Reinfusion duced cells. In vivo administration of GCV prevented tumor of donor T lymphocytes at relapse posttransplantation can development after subcutaneous injection of TK-transduced induce a potent antitumor response, but GVHD still occurs in murine myeloma cells (MOPC-11), whereas such an effect the majority of patients. Prior transduction of T lymphocytes was not observed on injection of untransduced cells into the with the suicide gene, the viral thymidine kinase (TK), peropposite flank. Our studies provide critical information that mits specific cell kill on administration of ganciclovir (GCV).(1) adequate numbers of TK-transduced lymphocytes can Therefore, infusion of TK-transduced T lymphocytes may inbe selected efficiently with ı90% purity, (2) selected cells duce GVL effect and allow for their subsequent selective remain functional, (3) 24 hours of exposure to GCV at clinielimination in case GVHD develops. To evaluate the efficacy cally achievable concentration effects ı90% killing of seand feasibility of this promising approach, anti-CD3-stimulected cells, and (4) GCV is effective in vivo in killing TKlated primary human lymphocytes cultured in interleukin-2 transduced cells. Based on these data, a clinical study has were TK-transduced by a retroviral vector carrying both TK been initiated in patients with multiple myeloma with perand neomycin-resistance genes. After selection in G418, sistent or relapsing disease after T-cell-depleted allogeneic more than 90% of the cells contained the TK gene as shown transplants. by a semiquantitative polymerase chain reaction. In addi-᭧ viral Herpes simplex thymidine kinase gene (TK) is a suit-Supported in part by a grant from USPHS National Heart Blood able candidate for such an approach because it will selecduced cells in case GVHD develops, possibly without abro-Rock, AR 72205.gating the GVL effect. This assumption is based on observa-The publication costs of this article were defrayed in part by page tion in murine leukemia, in which the GVL effect precedes charge payment. This article must therefore be hereby marked the onset of GVHD. 22 In this model, the antitumor effect is ''advertisement'' in accordance with 18 U.S.C. section 1734 solely to accomplished in mice within 6 to 7 days after administration indicat...

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