Abstract
Polypeptide vaccines effectively activate human T cells but suffer from poor biological stability, which confines both transport logistics and in vivo therapeutic activity. Synthetic biology has the potential to address these limitations through the generation of highly stable antigenic “mimics” using subunits that do not exist in the natural world. We developed a platform based on D–amino acid combinatorial chemistry and used this platform to reverse engineer a fully artificial CD8+ T cell agonist that mirrored the immunogenicity profile of a native epitope blueprint from influenza virus. This nonnatural peptide was highly stable in human serum and gastric acid, reflecting an intrinsic resistance to physical and enzymatic degradation. In vitro, the synthetic agonist stimulated and expanded an archetypal repertoire of polyfunctional human influenza virus–specific CD8+ T cells. In vivo, specific responses were elicited in naive humanized mice by subcutaneous vaccination, conferring protection from subsequent lethal influenza challenge. Moreover, the synthetic agonist was immunogenic after oral administration. This proof-of-concept study highlights the power of synthetic biology to expand the horizons of vaccine design and therapeutic delivery.
Highlights
CD8+ T cells recognize short peptide fragments presented by MHC class I (MHC-I) molecules on the surface of nucleated cells [1,2,3]
Influenza A virus was selected as an expedient model for this purpose, because antigen-specific memory T cell populations are commonly present in adult humans, and pathogen challenge experiments are feasible in humanized mice
Based on previous reports of occasional crossrecognition, we initially examined the ability of a retroinversion of the GILGFVFTL epitope ltfvfglig to activate an archetypal TRBV19+ [24] HLA-A2–GILGFVFTL–specific CD8+ T cell clone (ALF3)
Summary
CD8+ T cells recognize short peptide fragments presented by MHC class I (MHC-I) molecules on the surface of nucleated cells [1,2,3] These peptide–MHC-I (pMHC-I) molecular arrays are scanned by clonotypically distributed αβ T cell receptors (TCRs) [4], which trigger T cell activation beyond a preset monomeric TCR/pMHC-I affinity threshold [5,6,7,8]. D–amino acids are mirror image stereoisomers of L–amino acids with identical chemical and physical properties, the corresponding proteins are intrinsically resistant to protease-mediated hydrolysis [13] Immunogens designed from these building blocks may allow the production of stable vaccines with enhanced bioavailability and in vivo efficacy. The data validate what we believe to be a novel and systematic approach to the design of nonnatural immunogens that offers substantial advantages over current vaccine formulations
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