Discovery of Aptamers Against Cell Surface Markers Using Ligand-Guided Selection

Oligonucleotide ligands (DNA, RNA, or XNA), also known as aptamers, are selected against various target molecules using an iterative, evolutionary process called systematic evolution of ligands by exponential enrichment (SELEX). To select aptamers against complex cell surface proteins in their native state, a variant of SELEX termed ligand-guided selection (LIGS) was recently introduced. The significance of LIGS is rooted in its strategy of exploiting the selection step in SELEX to identify highly specific aptamers against known cell surface markers. Thus, in LIGS, a higher-affinity secondary ligand, such as a monoclonal antibody (mAb) to a whole-cell bound to an evolved SELEX library, is introduced to outcompete sequences against the mAb targeting cell surface protein or induce a conformational switch to destabilize the aptamer-surface cell surface protein resulting in elution of the sequences. Here, we describe the detailed method of LIGS utilized in identifying aptamers against T-cell receptor cluster of differentiation three complex (TCR-CD3) expressed in human T-cells and T-cell leukemia.