Cell-selective bioorthogonal labeling.

In classic bioorthogonal labeling experiments, the cell's biosynthetic machinery incorporates bioorthogonal tags, creating tagged biomolecules that are subsequently reacted with a corresponding bioorthogonal partner. This two-step approach labels biomolecules throughout the organism indiscriminate of cell type, which can produce background in applications focused on specific cell populations. In this review, we cover advances in bioorthogonal chemistry that enable targeting of bioorthogonal labeling to a desired cell type. Such cell-selective bioorthogonal labeling is achieved in one of three ways. The first approach restricts labeling to specific cells by cell-selective expression of engineered enzymes that enable the bioorthogonal tag's incorporation. The second approach preferentially localizes the bioorthogonal reagents to the desired cell types to restrict their uptake to the desired cells. Finally, the third approach cages the reactivity of the bioorthogonal reagents, allowing activation of the reaction in specific cells by uncaging the reagents selectively in those cell populations.