Synthetic Peptide Nanofiber Adjuvants Engage Mechanisms of Autophagy in Antigen Presenting Cells

Abstract

A crucial challenge in subunit vaccine development is to minimize adjuvant-associated toxicity and balance immunogenicity with safety. Due to the chemical heterogeneity and toxicity associated with most plant- or pathogen-derived adjuvants, those clinically approved in the U.S. are limited to alum and AS04 (alum combined with MPLA). Therefore, there is a compelling clinical need for new adjuvant strategies that potentiate strong immune responses and are chemically defined and minimally toxic. We have previously demonstrated that supramolecular peptide nanofibers are potent adjuvants that elicit protective antibody and cellular immune responses in animal models of infectious diseases, cancer, and addiction. Critically, the adjuvant potential was non-inflammatory and the exact mechanism of action was unknown. Here, we report that self-assembling peptide nanofibers bearing CD4+ or CD8+T cell epitopes are processed through mechanisms of autophagy in antigen presenting cells (APCs). Using in vitro antigen presentation assays, we confirmed loss and gain of adjuvant function using pharmacological modulators of autophagy and APCs deficient in multiple autophagy proteins. Incorporation of microtubule associated protein 1A/1B-light chain 3 (LC3-II) into the autophagosomal membrane, a key biological marker for autophagy, was confirmed using microscopy. Our findings indicate that autophagy plays an essential role in the mechanism of adjuvant action of supramolecular peptide nanofibers.