Multiplexed Pan Soluble Ligandome Assaying via OASIS

Screening soluble protein ligands is essential for understanding signaling interactions and enabling drug discovery. Currently, screens require arrayed formats because ligand diffusibility causes non-cell-autonomous effects. To enable multiplexed pooled assaying, we developed Obligate Autocrine Signaling In situ Screening (OASIS). Using lentiviral delivery of genetically barcoded ligands fused to a tethering domain, we anchor proteins to the expressing cells outer membrane, exclusively enforcing autocrine signaling. Validation using IFNA2 and EGF demonstrated uncompromised autocrine signaling with significantly reduced paracrine activity. We leveraged OASIS to perform a pan-ligandome fitness screen of all 770 validated human ligands in KOLF2.1J hiPSCs, identifying potent self-renewal factors, including FGF family ligands, which we experimentally validated in soluble form. Finally, we performed single-cell Perturb-Seq to map the transcriptional remodeling induced by the pan-ligandome library. OASIS provides a generalizable framework to accelerate functional interrogation of the human ligandome and novel peptide binders within live cells and diverse lineages. SUMMARYWe present Obligate Autocrine Signaling In situ Screening (OASIS), a platform enabling pooled assaying of soluble ligands by tethering genetically barcoded proteins to the surface of their expressing cells, enforcing autocrine signaling. We demonstrate OASIS by assaying all verified human ligands in hiPSCs, measuring fitness and transcriptional impacts. Our results recapitulate canonical interferon and FGF mediated signaling, validating the application of OASIS for rapid interrogation of ligands and engineered binders.