Cell surface tagging and a suicide mechanism in a single chimeric human protein

Many therapeutic uses of gene-modified cells could benefit from inclusion of a surface marker for immunoselecting transduced cells. Another desired feature is a failsafe mechanism to ablate engineered cells if required. We describe here a system that combines a cell surface tag and an inducible apoptosis mechanism in a single protein. Spencer et al, (Curr, Biol, 1996;6:839-847) described an inducible cell suicide gene containing a myristoylation sequence, the human protein FKBP12, and the intracellular domain of Pas, Cells expressing this protein apoptose on treatment with a cell-permeable chemical dimerizing agent that binds two FKBP domains and cross-links the chimeric Fas proteins. We modified this system by anchoring a Fas-FKBP construct to the membrane with the extracellular and transmembrane domains of the low-affinity nerve growth factor receptor (LNGFR), thereby uniting cell surface tagging with the inducible apoptosis mechanism, Cells retrovirally transduced with this construct apoptosed on exposure to a chemical dimerizer, AP1903 (Clackson et al., Proc, Natl, Acad, Sci, U.S.A. 1998;95: 10437-10442), The LNGFR-tagged construct showed an unpredicted clear advantage over the myristoylation-anchored construct in its efficiency of signaling in HT1080 cells. This linked marker and failsafe mechanism may have particularly attractive safety properties for gene therapy.