2, University of Texas Health Science Center, Houston, Texas, United States
3, Rutgers Cancer Institute of New Jersey, New Brunswick, New Jersey, United States
4, Houston Methodist Research Institute, Houston, Texas, United States
Biomaterials constructed from de novo designed peptides and peptidomimetics that assemble into β-sheet rich peptide nanofibers and hydrogels have enormous potential for applications in biology and medicine. Self-assembling peptide biomaterials have been used as multivalent scaffolds for applications in tissue engineering, regenerative medicine, and drug delivery due to their biocompatibility, ease of synthesis, and the rich chemistry with which the primary sequence can be manipulated to impart structure or function. In recent years, supramolecular peptide nanofibers have attracted considerable attention as immune adjuvants for applications in vaccine development and immunotherapy due to their ability to induce strong antibody and cellular responses to conjugated antigens. Unlike traditional depot forming adjuvants (alum or Freund’s), peptide nanofibers are non-inflammatory and do not elicit inflammation at the injection site (recruitment of neutrophils, eosinophils, monocytes, etc.). Several studies have confirmed the efficacy of peptide nanofiber-based vaccines in animal models of infectious and non-infectious diseases; however, the immunological mechanisms that drive the inflammation-free adjuvant potential have not yet been elucidated.
An evolutionarily conserved mechanism that cells use to homeostasis is ‘autophagy’. Autophagy is crucial for the clearance of fibrillar protein aggregates implicated in neurodegenerative diseases such as Alzheimer’s and Huntington’s and a component of innate immunity that is involved in host defense elimination of pathogens. Autophagy has been identified as a route by which cytoplasmic and nuclear antigens are delivered to MHC class II molecules for presentation to CD4+T cells and MHC class I cross-presentation of tumor antigens to CD8+T cells. 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 standard 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 in APCs plays an essential role in the mechanism of adjuvant action of supramolecular peptide nanofibers.