Abstract
CD28 is an essential costimulatory receptor required for full T cell activation, and its dysregulation contributes to multiple immune-mediated pathologies. Despite its central immunological role, CD28 remains largely unexplored as a target for small-molecule modulation, primarily due to the shallow and large interface of its ligand-binding site. Here, we applied a fragment-based high-throughput screening (HTS) strategy to identify low molecular weight chemotypes capable of engaging with human CD28. A 3,200-member library composed of structurally diverse fragments, enriched for scaffolds designed to target protein-protein interaction (PPI) interfaces, was screened in single-dose format using temperature-related intensity change (TRIC) technology, yielding 36 primary hits (1.13% hit rate). Follow-up surface plasmon resonance (SPR) validation confirmed two fragments as direct CD28 binders. Molecular docking analysis revealed a plausible binding orientation for PPIF3 within the CD28 extracellular domain, suggesting potential interaction hotspots that may be exploited during future optimization. Together, these findings provide the first demonstration that fragment-based screening can successfully identify chemotypes capable of engaging with the CD28 PPI interface. This work establishes a scalable, biophysics-driven workflow for CD28 ligand discovery and lays the foundation for subsequent hit-to-lead development of small molecule CD28 modulators.
Full Text Availability
The license terms selected by the author(s) for this preprint version do not permit archiving in PMC. The full text is available from the preprint server.
