Delta hGHR, a novel biosafe cell surface-labeling molecule for analysis and selection of genetically transduced human cells

We describe a new selectable marker for retroviral transduction and selecti on of human and murine cells, The molecule expressed on the cell surface of the transduced population is a truncated version of human growth hormone r eceptor (Delta hGHR), capable of ligand (hGH) binding, but devoid of the do mains involved in signal triggering. We demonstrate that the engineered mol ecule is stably expressed in the target cells as an inert protein unable to trigger proliferation or to rescue the cells from apoptosis after ligand b inding. This new marker will probably have a,vide application spectrum, sin ce hGHR in the human adult is highly expressed only in liver cells, and low er levels have been reported in certain lymphocyte cell populations. The De lta hGHR label has high biosafety potential, as it belongs to a well-charac terized hormonal system that is nonessential in adults, and there is extens ive clinical experience with hGH administration in humans. This record allo ws us to hypothesize the lack of relevant clinical consequences resulting f rom massive transgene expression caused by successful replacement of a larg e tissue with genetically transduced cells, We take advantage of the differ ential binding properties of several monoclonal antibodies (MAbs) in descri bing a cell rescue method in which the antibody used to select Delta hGHR-t ransduced cells is eluted by competition with hGH or, alternatively biotiny lated 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 mu rine MAb to rescue genetically labeled cells.