Objective-Limited clinical trials have validated the hypothesis of controlling graft-versus-host disease (GVHD) arising from stem cell transplant utilizing suicidal T-lymphocytes that have been transduced to express the HSV-TK gene. However, clinical utility has been limited by diminished T-cell function arising from the production process. To evaluate strategies for harnessing the graftversus-leukemia (GVL) effect while improving the safety and function of suicidal lymphocytes, we have developed techniques to produce fully functional, retrovirally transduced, HSV-TKpositive murine T cells (TK + TC).Methods-Utilizing a murine major histocompatibility complex-matched transplant model, we evaluated the ability of TK + TC to generate a GVL effect and the ability to control GVHD in experiments where we varied the dose of TK + TC, ganciclovir (GCV) dose, the start of GCV administration (day 4, 7, 10, 13, 15, or 19) posttransplantation, and the GCV administration route (osmotic pump versus intraperitoneal).Results-At TK + TC doses in excess of the standard lethal dose (SLD) of unmanipulated T-cells, GCV administration completely (2 × SLD) and partially (4 × SLD) controlled GVHD. Additionally, GVHD remained reversible despite delaying administration of GCV for a week after GVHD developed. Importantly, GVHD was controlled with a 1-log but not 2-log reduction in GCV dose, and this "partial suicide" preserved more circulating TK + TC compared with standarddose GCV. Survival of leukemia-positive mice receiving TK + TC and GCV was significantly increased compared with control cohorts not receiving GCV or transplanted with unmanipulated T cells, thereby demonstrating a GVL effect. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptConclusion-Retrovirally transduced suicidal lymphocytes generate a potent GVL effect while simultaneously enabling control of GVHD, which results in improved leukemia and GVHD-free survival.The risk of graft-versus-host disease (GVHD) in patients with leukemia who undergo allogeneic bone marrow transplantation necessitates finding a suitably matched donor so that these patients can benefit from the graft-versus-leukemia (GVL) effect [1,2]. However, the inability to identify such donors is a barrier to transplantation for most leukemia patients. Although both prophylactic therapeutic strategies and strategies to manipulate the graft are used to prevent GVHD, as many as 40% of patients who receive HLA-matched transplants develop GVHD that requires systemic therapy [2,3]. The interventions required to treat GVHD further compromise an already impaired immune system, and fatal infections are common during GVHD therapy. Consequently, the risks associated with GVHD decrease the curative potential of allogeneic transplantation by either preventing patients from undergoing transplantation in the first place or complicating the course of those who do.Selectively removing the GVHD-initiating T cells after grafts are established and T cells have been activated might control GVHD...

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