THYMIDINE KINASE (TK) GENE-TRANSDUCED HUMAN-LYMPHOCYTES CAN BE HIGHLYPURIFIED, REMAIN FULLY FUNCTIONAL, AND ARE KILLED EFFICIENTLY WITH GANCICLOVIR

A graft-versus-leukemia (GVL) effect has been considered a major facto r responsible for cures in patients with hematologic malignancies unde rgoing allogeneic bone marrow transplantation; however, associated gra ft-versus-host disease (GVHD) results in significant morbidity and mor tality. T-cell depletion reduces the incidence and severity of GVHD bu t eliminates, at least partially, the GVL effect. Reinfusion of donor T lymphocytes at relapse posttransplantation can induce a potent antit umor response, but GVHD still occurs in the majority of patients. Prio r transduction of T lymphocytes with the suicide gene, the viral thymi dine kinase (TK), permits specific cell kill on administration of ganc iclovir (GCV). Therefore, infusion of TK-transduced T lymphocytes may induce GVL effect and allow for their subsequent selective elimination in case GVHD develops. To evaluate the efficacy and feasibility of th is promising approach, anti-CD3-stimulated primary human lymphocytes c ultured in interleukin-2 were TK-transduced by a retroviral vector car rying both TK and neomycin-resistance genes. After selection in G418, more than 90% of the cells contained the TK gene as shown by a semiqua ntitative polymerase chain reaction. In addition, 1 to 5 days of GCV e xposure, at clinically achievable concentrations of 20 to 50 mu mol/L, induced greater than or equal to 90% killing of G418-selected cells w ithout affecting nontransduced cells. Correlation of the extent of T-c ell kill and the proportion of TK-gene-transduced cells is consistent with the absence of a bystander effect. Transduced cells were CD3(+) a nd either CD8(+) or CD4(+) and retained functional properties of untra nsduced cells. In vivo administration of GCV prevented tumor developme nt after subcutaneous injection of TK-transduced murine myeloma cells (MOPC-11), whereas such an effect was not observed on injection of unt ransduced cells into the opposite flank. Our studies provide critical information that (1) adequate numbers of TK-transduced lymphocytes can be selected efficiently with greater than or equal to 90% purity, (2) selected cells remain functional, (3) 24 hours of exposure to GCV at clinically achievable concentration effects greater than or equal to 9 0% killing of selected cells, and (4) GCV is effective in vivo in kill ing TK-transduced cells. Based on these data, a clinical study has bee n initiated in patients with multiple myeloma with persistent or relap sing disease after T-cell-depleted allogeneic transplants. (C) 1997 by The American Society of Hematology.