SummaryPoorly antigenic small molecules pose challenges for the production of clinically efficacious antibodies. To address this, we have developed an immunization platform derived from the antigenic surface coat of the African trypanosome. Through sortase-based conjugation of antigens to the trypanosome surface coat protein variant surface glycoprotein (VSG), we created the VAST (VSG-immunogen Array by Sortase Tagging). We used VAST to elicit protective immunity to the effects fentanyl. Immunizing mice with fentanyl-VAST generated serological memory and protection from fentanyl challenge. Employing single-cell RNAseq, we then developed a streamlined method that synergizes with the VAST to identify immunization-elicited memory B cells and the antibodies they encode. All antibodies selected by this method displayed picomolar affinities for fentanyl. Passive immunization protected animals from fentanyl, while crystallography revealed that the mAbs bind fentanyl in an unusually deep pocket suited to small molecules, demonstrating the ability of the VAST to elicit high-quality therapeutic antibodies.
