Ganciclovir-mediated elimination of HSV-Tk+ T cells and cure of graft-vs-host disease in an allogeneic bone marrow transplantation model in the rat.
OBJECTIVE
Suicide gene therapy for leukemia aims to benefit from T cells in the BM graft, by reducing the probability of leukemia relapse (GVL), while severe complications of graft-vs-host disease (GVHD) may be avoided. In an allogeneic rat BMT model we defined the conditions to induce a lethal GVHD with HSV-Tk gene-transduced T cells. We studied the feasibility to rescue the animals by conditional elimination of the T cells with ganciclovir (GCV) treatment.


METHODS
Allogeneic T cells transduced with a retroviral vector encoding the HSV-Tk suicide gene were added in varying numbers to a BM graft. Expression of HSV-Tk strongly increases the cytolytic effect of GCV, thereby allowing elimination of overreactive T cells at will. Various experimental conditions were tested in the rat model.


RESULTS
A relation between the number of HSV-Tk(+) T cells added to the BM graft and GVHD development was found. GCV treatment resulted in selective HSV-Tk(+) T-cell elimination in blood and tissues but not in abrogation of GVHD due to persistence of HSV-Tk(-) T cells. T cells in unmanipulated rat BM normally have a low risk to induce GVH but when they are administered in combination with high numbers of HSV-Tk(+) T cells there is an apparent increase in their GVH-inducing potential. When HSV-Tk(+) T cells are added to T cell-depleted BM a consequently developing GVH can be controlled by GCV treatment with 60-70% of the animals surviving.


CONCLUSIONS
We show that T cell-mediated suicide gene therapy within the context of allo-BMT can be applied with success. The apparent limitation in the number of transduced as well as nontransduced T cells that can be safely added to the BM graft should be taken into consideration when designing human suicide gene therapy protocols.
Weijtens
Mo
M
Jordan Laboratory of Hemato-Oncology, Department of Hematology, University Medical Center Utrecht, 3508 GA Utrecht, The Netherlands.
van Spronsen
Anke
A
Hagenbeek
Anton
A
de Weger
Roel
R
Martens
Anton
A
D000818:Animals; D016026:Bone Marrow Transplantation / Q000379:methods*; D015774:Ganciclovir / Q000494:pharmacology*; D041722:Genes, Transgenic, Suicide; D015316:Genetic Therapy / Q000379:methods*; D006086:Graft vs Host Disease / Q000209:etiology / Q000628:therapy*; D008212:Lymphocyte Depletion / Q000379:methods; D023421:Models, Animal; D051381:Rats; D011919:Rats, Inbred Strains; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism* / Q000637:transplantation; D014161:Transduction, Genetic; D014184:Transplantation, Homologous
D015774:Ganciclovir