Patterned substitution of d -amino acids into the primary sequences of self-assembling peptides influences molecular-level packing and supramolecular morphology. We report that block heterochiral analogs of the model amphipathic peptide KFE8 (Ac-FKFEFKFE-NH 2 ), composed of two FKFE repeat motifs with opposite chirality, assemble into helical tapes with dimensions greatly exceeding those of their fibrillar homochiral counterparts. At sufficient concentrations, these tapes form hydrogels with reduced storage moduli but retain the shear-thinning behavior and consistent mechanical recovery of the homochiral analogs. Varying the identity of charged residues (FRFEFRFE and FRFDFRFD) produced similarly sized nonhelical tapes, while a peptide with nonenantiomeric l - and d -blocks (FKFEFRFD) formed helical tapes closely resembling those of the heterochiral KFE8 analogs. A proposed energy-minimized model suggests that a kink at the interface between l - and d -blocks leads to the assembly of flat monolayers with nonidentical surfaces that display alternating stacks of hydrophobic and charged groups.

Bacillus Calmette-Guerin (BCG) is the only vaccine against TB and has limited protection efficacy, which wanes past adolescence. Multifunctional CD8+ T cells (IFN-γ+/TNF-α+/IL-2+) are associated with lower reactivation risk and enhanced control of active Mtb infection. Since boosting with BCG is contraindicated, booster vaccines that augment T cell immunity in the lungs of BCG-vaccinated individuals are urgently needed. We developed a vaccination strategy based on self-assembling peptide nanofibers presenting Mtb-specific CD8+ or CD4+ T cell epitopes that induce high frequency and antigen-specific effector memory T cells producing IFN-γ and IL-2. Intranasal immunization with peptide nanofibers was well tolerated in mice leading to increased antigen-specific CD8+ T cell population in the lungs. Co-assembled nanofibers of CD8+ T cell epitopes and toll-like receptor 2 (TLR2) agonists induced a 8-fold expansion in multifunctional CD8+ T cell populations in the lungs of vaccinated mice. Aerosol challenge with Mtb in BCG-primed and nanofiber-boosted mice provided an additional 0.5-log CFU reduction in lung bacterial load and indicating enhanced protection compared to BCG alone. Together, these data suggest that heterologous prime-boost with BCG and peptide nanofiber vaccines induces cell mediated immunity in the lung, reduces bacterial burden, and is a potentially safer alternative for boosting BCG-primed immunity.

Supramolecular peptide nanofibers are attractive for applications in vaccine development due to their ability to induce strong immune responses without added adjuvants or associated inflammation. 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 the adjuvant function using pharmacological modulators of autophagy and APCs deficient in multiple autophagy proteins. The 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.

Heterologous vaccine regimens could extend waning protection in the global population immunized with Mycobacterium bovis Bacille Calmette-Guerin (BCG). We demonstrate that pulmonary delivery of peptide nanofibers (PNFs) bearing an Ag85B CD4+ T cell epitope increased the frequency of antigen-specific T cells in BCG-primed mice, including heterogenous populations with tissue resident memory (Trm) and effector memory (Tem) phenotype, and functional cytokine recall. Adoptive transfer of dendritic cells pulsed with Ag85B-bearing PNFs further expanded the frequency and functional repertoire of memory CD4+ T cells. Transcriptomic analysis suggested that the adjuvanticity of peptide nanofibers is, in part, due to the release of damage-associated molecular patterns. A single boost with monovalent Ag85B PNF in BCG-primed mice did not reduce lung bacterial burden compared to BCG alone following aerosol Mtb challenge. These findings support the need for novel BCG booster strategies that activate pools of Trm cells with potentially diverse localization, trafficking, and immune function.

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.