DeltahGHR, a novel biosafe cell surface-labeling molecule for analysis and selection of genetically transduced human...

We describe a new selectable marker for retroviral transduction and selection of human and murine cells. The molecule expressed on the cell surface of the transduced population is a truncated version of human growth hormone receptor (deltahGHR), capable of ligand (hGH) binding, but devoid of the domains involved in signal triggering. We demonstrate that the engineered molecule is stably expressed in the target cells as an inert protein unable to trigger proliferation or to rescue the cells from apoptosis after ligand binding. This new marker will probably have a wide application spectrum, since hGHR in the human adult is highly expressed only in liver cells, and lower levels have been reported in certain lymphocyte cell populations. The deltahGHR label has high biosafety potential, as it belongs to a well-characterized hormonal system that is nonessential in adults, and there is extensive clinical experience with hGH administration in humans. This record allows us to hypothesize the lack of relevant clinical consequences resulting from massive transgene expression caused by successful replacement of a large tissue with genetically transduced cells. We take advantage of the differential binding properties of several monoclonal antibodies (MAbs) in describing a cell rescue method in which the antibody used to select deltahGHR-transduced cells is eluted by competition with hGH or, alternatively biotinylated hGH is used to capture tagged cells. In the latter system, the final purified population would be recovered free of attached antibodies in hGH (a substance approved for human use)-containing medium, providing additional biosafety relative to currently existing methods that rely on the use of murine MAb to rescue genetically labeled cells.