Fluorosomes: a convenient new reagent to detect and block multivalent and complex receptor‐ligand interactions

Abstract

We describe for the first time fluorescent virus‐like particles decorated with biologically active mono‐ and multisubunit immune receptors of choice and the basic application of such fluorosomes (FSs) to visualize and target immune receptor‐ligand interactions. For that purpose, human embryonic kidney (HEK)‐293 cells were stably transfected with Moloney murine leukemia virus (MoMLV) matrix protein (MA) GFP fusion constructs. To produce FSs, interleukins (ILs), IL‐receptors (ILRs), and costimulatory molecules were fused to the glycosyl phosphatidyl inositol anchor acceptor sequence of CD16b and coexpressed along with MoMLV group‐specific antigen‐polymerase (gag‐pol) in MA:GFP + HEK‐293 cells. We show that IL‐2 decorated but not control‐decorated FSs specifically identify normal and malignant IL‐2 receptor‐positive (IL‐2R + ) lymphocytes by flow cytometry. In addition to cytokines and costimulatory molecules, FSs were also successfully decorated with the heterotrimeric IL‐2Rs, allowing identification of IL‐2 + target cells. Specificity of binding was proven by complete inhibition with nonlabeled, soluble ligands. Moreover, IL‐2R FSs efficiently neutralized soluble IL‐2 and thus induced unresponsiveness of T cells receiving full activation stimuli via T‐cell antigen receptor and CD28. FSs are technically simple, multivalent tools for assessing and blocking mono‐ and multisubunit immune receptor‐ligand interactions with natural constituents in a plasma membrane context.—Kueng, H. J., Manta, C., Haiderer, D., Leb, V. M., Schmetterer, K. G., Neunkirchner, A., Byrne, R. A., Scheinecker, C., Steinberger, P., Seed, B., Pickl, W. F. Fluorosomes: a convenient new reagent to detect and block multivalent and complex receptor‐ligand interactions. FASEB J. 24, 1572–1582 (2010). www.fasebj.org