Development of conformation-selective antibodies targeting human SLC15A4

SLC15A4, an endolysosomal solute carrier family transporter, plays a critical role in TLR7/8/9-induced immune responses through assembling a complex with the downstream adaptor TASL in a conformation-dependent manner. Despite its close functional association and promising therapeutic potential in infections, tumors, and autoimmune diseases, the development of conformation-specific antibodies for human SLC15A4 (hSLC15A4) remains challenging. Here, using a systematic screening and validation approach, we identify a pair of conformation-selective antibodies, clones 107 and 235, targeting the endolysosomal lumen surface of hSLC15A4 with opposite conformation-regulatory activities. Specifically, clone 107 selectively binds to hSLC15A4 in a TASL binding-incompetent luminal-open state; whereas clone 235 stabilizes hSLC15A4 in a TASL binding-competent cytoplasmic-open state. Our research identifies antibodies that recognize distinct conformations of hSLC15A4, potentially enabling modulation of the TLR7/8/9 pathway and contributing to the development of targeted therapies and research tools selectively targeting hSLC15A4.