oYo-Link HyperBright: antibody fluorescent labeling reagents - Fluorescently labeled antibodies are indispensable tools for a wide range of biological applications, including flow cytometry, immunofluorescence microscopy, and high-content screening. Despite their widespread use, existing antibody labeling strategies present significant limitations. Traditional methods rely on random conjugation of fluorophores to lysine residues via amine-reactive chemistries, which results in a heterogeneous degree of labeling (DOL), unpredictable labeling efficiency, and variable assay performance. Over-labeling can lead to fluorescence quenching, while under-labeling reduces signal intensity. Because the conjugation can occur near or within antigen-binding regions, these modifications can also interfere with antibody affinity and specificity, reducing the reliability of experimental results. Batch-to-batch variability in DOL often necessitates costly and time-consuming optimization for each new antibody, further complicating workflows. Site-specific labeling strategies—designed to overcome some of these issues—have emerged in recent years but are typically complex, multistep protocols that require antibody engineering or enzymatic modification, long reaction times, high antibody concentrations, and often fail to work in the presence of common buffer additives like BSA or Tris. These constraints have limited their widespread adoption for everyday use. Meanwhile, labeling strategies that rely on larger dye-carrying platforms, such as fluorescent polymers and nanoparticles, offer the potential for increased brightness but suffer from their own drawbacks. These include low conjugation yields, polydispersity, increased hydrophobicity, and unpredictable steric effects on antibody binding. As a result, their use has been largely restricted to secondary antibodies, severely limiting flexibility and utility in applications requiring primary antibody labeling. AlphaThera's oYo-Link® technology addresses these limitations by enabling site-specific, covalent labeling of off-the-shelf IgG antibodies at the Fc region through a photoreactive antibody-binding domain that forms a stable covalent bond upon brief exposure to 365 nm light. This platform allows for efficient conjugation in a one-step reaction that is compatible with virtually all buffers and storage conditions, with no impact on antigen-binding regions. Building on this foundation, we propose to develop oYo-Link HyperBright, a plug-and-play, bright, but compact fluorescent platform that enables any primary antibody to be transformed into a high-performance fluorescent probe, dramatically simplifying workflows and expanding the utility of flow cytometry and immunofluorescence assays. The specific aims of this proposal are: Aim 1. Generate and characterize oYo-Link HyperBright constructs; Aim 2. Quantify the brightness and specificity of antibody-HyperBright constructs via flow cytometry.
