Single-molecule localization microscopy reveals the molecular organization of endogenous membrane receptors.

Super-resolution microscopy in combination with genetic labeling methods allows imaging of single proteins in cells. However, visualizing endogenous proteins on primary cells remains challenging due to the use of sterically demanding antibodies for labeling. Here, we demonstrate how immunolabeling conditions and antibody cross-linking influence the quantification and identification of membrane receptor stoichiometry on cells using single-molecule localization microscopy. We developed an optimized immunolabeling and analysis protocol and demonstrate the performance of the approach by resolving the molecular organization of endogenous CD45, CD69, and CD38 on Jurkat T cells. To demonstrate the usefulness of the method for immunotherapy applications, we investigated the interaction of primary multiple myeloma cells with the therapeutic monoclonal antibodies daratumumab and isatuximab and a polyclonal anti-CD38 antibody. Our approach might lay the foundation for improved personalized diagnostics and treatment with therapeutic antibodies.