CELL-SURFACE ENGINEERING WITH GPI-ANCHORED PROTEINS

Protein engineering of cell surfaces is a potentially powerful technol ogy through which the surface protein composition of cells can be mani pulated without gene transfer, This technology exploits the fact that proteins that are anchored by glycoinositol phospholipids (GPIs), when purified and added to cells in vitro, incorporate into their surface membranes and are fully functional, By substituting 3'-mRNA end sequen ce of naturally GPI-anchored proteins (i.e., a sequence that contains the signals that direct GPI anchoring) for endogenous 3'-mRNA end sequ ence, virtually any protein of interest can be expressed as a GPI-anch ored derivative, The GPI-anchored product then can be purified from tr anfectants and the purified protein used to ''paint'' any target cell, Such protein engineering or ''painting'' of the cell surface offers s everal advantages over conventional gene transfer, Among these advanta ges are that 1) GPI-anchored proteins can be painted onto cells that a re difficult to transfect, 2) cells can be altered immediately without previous culturing, 3) the amount of protein added to the surface can be precisely controlled, and 4) multiple GPI-anchored proteins can be sequentially or concurrently inserted into the same cells, Emerging a pplications for the technology include its nse for the analysis of com plex cell-surface interactions, the engineering of antigen presenting cells, the development of cancer vaccines, and possibly the protection against graft rejection.