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Kinetics of In Vivo Elimination of Suicide Gene-Expressing T Cells Affects Engraftment, Graft-Versus-Host Disease, and Graft-Versus-Leukemia after Allogeneic Bone Marrow Transplantation

Performed in collaboration with John DiPersio's Lab.
Suicide gene therapy is one approach being evaluated for the control of graft-vs-host disease (GVHD) after allogeneic bone marrow transplantation (BMT). We recently constructed a novel chimeric suicide gene in which the entire coding region of HSV thymidine kinase (HSV-tk) was fused in-frame to the extracellular and transmembrane domains of human CD34 (ΔCD34-tk). ΔCD34-tk is an attractive candidate as a suicide gene in man because of the ensured expression of HSV-tk in all selected cells and the ability to rapidly and efficiently purify gene-modified cells using clinically approved CD34 immunoselection techniques. In this study we assessed the efficacy of the ΔCD34-tk suicide gene in the absence of extended ex vivo manipulation by generating transgenic animals that express ΔCD34-tk in the peripheral and thymic T cell compartments using the CD2 locus control region. We found that ΔCD34-tk-expressing T cells could be purified to near homogeneity by CD34 immunoselection and selectively eliminated ex vivo and in vivo when exposed to low concentrations of GCV. The optimal time to administer GCV after allogeneic BMT with ΔCD34-tk-expressing transgenic T cells was dependent on the intensity of the conditioning regimen, the leukemic status of the recipient, and the dose and timing of T cell infusion. Importantly, we used a controlled graft-vs-host reaction to promote alloengraftment in sublethally irradiated mice and provide a graft-vs-leukemia effect in recipients administered a delayed infusion of ΔCD34-tk-expressing T cells. This murine model demonstrates the potential usefulness of ΔCD34-tk-expressing T cells to control GVHD, promote alloengraftment, and provide a graft-vs-leukemia effect in man.
GVL effect obtained by delaying GCV administration after day 10 DLI of ΔCD34-tk Tg T cells. Lethally irradiated (900 cGy) BALB/c recipients were given TCD B6 BM (CD45.1+) with (A20; n = 10) or without (BMT only; n = 6) added A20-luc/egfp cells (1-2 x 104 cells). Donor lymphocytes (CD45.2+; 2 x 106 ΔCD34-tk Tg T cells) were administered 10 days post-BMT. Animals receiving T cells were then either left untreated (A20 + DLI; n = 10) or were treated with GCV (50 mg/kg/day i.p.) as indicated (days 1-7, n = 10; days 4-10, n = 12; days 10-16, n = 10). Surviving animals were bled at 30 and 100 days post-BMT and analyzed by FACS. Tumor growth was assessed at various time intervals by BLI using a cooled CCD optical system (Xenogen IVIS). (A) BLI of Luc activity. Representative images of mice transplanted with BM only or treated with GCV from days 10-16 post-DLI. Photon flux is indicated in the color scale bars. Mice 1 and 2 in the day 10-16 GCV treatment group had tumor signal above background. Mouse 3 did not exhibit significant tumor signal and is representative of the remaining seven mice in the day 10-16 GCV treatment group. (B) Kaplan-Meier survival curve.
References:	Rettig MP, Ritchey JK, Prior JL, Haug JS, Piwnica-Worms D, DiPersio JF. Kinetics of in vivo elimination of suicide gene expressing T cells affects engraftment, graft-versus-host disease, and the graft-versus-leukemia effect after allogeneic bone marrow transplantation. J Immunol 2004; 173(6): 3620-30.	PubMed Link

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