Han, Hee-SunNiemeyer, ElisabethHuang, YuhuiKamoun, WalidMartin, JohnBhaumik, JayeetaChen, YunchingRoberge, SylvieCui, JianMartin, MargaretFukumura, DaiJain, RakeshBawendi, MoungiDuda, Dan2019-10-052015Han, Hee-Sun, Elisabeth Niemeyer, Yuhui Huang, Walid S. Kamoun, John D. Martin, Jayeeta Bhaumik, Yunching Chen, et al. 2015. “Quantum Dot/Antibody Conjugates for in Vivo Cytometric Imaging in Mice.” Proceedings of the National Academy of Sciences 112 (5): 1350–55. https://doi.org/10.1073/pnas.1421632111.0027-84240744-28311091-6490http://nrs.harvard.edu/urn-3:HUL.InstRepos:41483017Multiplexed, phenotypic, intravital cytometric imaging requires novel fluorophore conjugates that have an appropriate size for long circulation and diffusion and show virtually no nonspecific binding to cells/serum while binding to cells of interest with high specificity. In addition, these conjugates must be stable and maintain a high quantum yield in the in vivo environments. Here, we show that this can be achieved using compact (similar to 15 nm in hydrodynamic diameter) and biocompatible quantum dot (QD) -Ab conjugates. We developed these conjugates by coupling whole mAbs to QDs coated with norbornene-displaying polyimidazole ligands using tetrazine-norbornene cycloaddition. Our QD immunoconstructs were used for in vivo single-cell labeling in bone marrow. The intravital imaging studies using a chronic calvarial bone window showed that our QD-Ab conjugates diffuse into the entire bone marrow and efficiently label single cells belonging to rare populations of hematopoietic stem and progenitor cells (Sca(1+) c-Kit(+) cells). This in vivo cytometric technique may be useful in a wide range of structural and functional imaging to study the interactions between cells and between a cell and its environment in intact and diseased tissues.en-USJournal Article2019-10-0510.1073/pnas.1421632111