Graft-versus-host disease (GVHD) is a major complication of allogeneic bone marrow transplantation. One strategy to treat GVHD is to equip donor T cells with a conditional suicide mechanism that can be triggered when GVHD occurs. The herpes simplex virus thymidine kinase (HSV-tk)/ganciclovir system used clinically has several limitations, Including immunogenicity and cell cycle dependence. An alternative switch based on chemically inducible apoptosis was designed and evaluated, A chimeric human protein was expressed comprising an extracellular marker (Delta LNGFR), the Pas intracellular domain, and 2 copies of an FK506-binding protein (FKBP), Primary human T lymphocytes retrovirally transduced with this construct could be purified to homogeneity using immunomagnetic beads. Genetic integrity of the construct was ensured by redesigning repetitive sequences. Transduced T cells behaved indistinguishably from untransduced cells, retaining the ability to mount a specific; antiallogeneic immune response, However, they rapidly underwent apoptosis with the addition of subnanomolar concentrations of AP1903, a bivalent "dimerizer" drug that binds FKBP and induces Pas cross-linking, A single P-hour treatment eliminated approximately 80% of T cells, and multiple exposures induced further apoptosis. T cells were eliminated regardless of their proliferation state, suggesting that the AP1903/Fas system, which contains only human components, is a promising alternative to HSV-fk for treating GVHD, (Blood, 2001; 97:1249-1257) (C) 2001 by The American Society of Hematology.
