Synthetic Antibodies for Reversible Cell Recognition

Antibody-mediated cell recognition plays a critical role in various biological and biomedical applications. However, strong antibody-cell interactions can lead to the difficulty of separating antibodies from the bound cells in a simple and non-destructive manner, which is often necessary to numerous applications such as cell sorting or separation. Thus, this thesis research is aimed to create an antibody-like nanomaterial with the function of reversible cell recognition. ^ It was hypothesized that nucleic acid aptamer and dendrimer could be used as fundamental structural components to develop an antibody-like nanomaterial. The aptamer functions as the binding site of an antibody; the dendrimer is used as a robust, defined nano-scaffold to support the aptamer and to carry small molecules (e.g., fluorophores). To test this hypothesis, a novel method was first developed to discover the essential nucleotides of full-length aptamers to mimic the binding sites of antibodies. The essential nucleotides were further conjugated with a dendrimer to synthesize a monovalent aptamer-dendrimer nanomaterial. The results clearly showed that the essential nucleotides could maintain high affinity and specificity after tethered on dendrimer surface.^ To further test the hypothesis that antibody-like nanomaterials can be rationally designed to acquire the capability of reversible cell recognition, an aptamer that was selected at 0 °C was used as a model to synthesize a Y-shaped nanomaterial by conjugating two aptamers to the same dendrimer. The results showed that the nanomaterial-cell interaction could be affected by the distance between two binding aptamers. In addition, the Y-shaped antibody-like nanomaterial could bind target cells more strongly than its monovalent control. Importantly, the strong cell-nanomaterial interaction could be rapidly reversed when the temperature was shifted from 0 °C to 37 °C.^ In summary, we developed a synthetic antibody that can not only mimic the functional structure and cell recognition capability of antibodies, but also possess specific features that natural antibodies do not possess. This study has opened a new avenue for developing synthetic antibodies and has also advanced the understanding of the functionality of multivalent nanomaterials. This novel synthetic antibody holds great potential for various biological and biomedical applications such as cell separation.