Supramolecular Strategies for Generating Therapeutic Immune Reponses to HIV-1

Human Immunodeficiency Virus (HIV) is a vaccine target that has remained elusive for decades. In 2015, 1.1 million people died of HIV-related causes and 2.1 million new infections occurred. Although an effective HIV vaccine has long been a major goal of the World Health Organization (WHO), HIV has been an extraordinarily challenging vaccine target. This challenge is due to several compounding factors including the evolution of the virus within individuals and across geographic regions. This evolution makes it difficult to develop a universal HIV vaccine that will neutralize all strains of the virus. Furthermore, the virus is exceptionally efficient at mutating to evade the immune systems of infected individuals. The outer surface of the virus is densely glycosylated, making it difficult for the immune system to make effective antibodies against such a shielded structure. Consequently, most antibodies generated against the virus are either non-neutralizing or only partially neutralizing and are ineffective at clearing HIV infection. Thus, alternative strategies to direct the immune system towards making neutralizing antibodies are required for an effective HIV vaccine. Attempts at creating an effective HIV vaccine have centered around stimulating high-affinity antibodies that effectively bind genetically diverse strains of the virus. Through protein engineering, variable dosing regimens, and creation of new antigens, HIV researchers have identified the key factors required for the human immune system to raise functional anti-HIV antibodies. Primarily, the immune system must be directed towards the highly conserved and functional antigenic regions of HIV surface proteins to make protective antibodies. To steer the immune system towards specific, neutralizing epitopes from HIV-1, the repertoire of B cells activated by HIV vaccines must be altered from those elicited by natural infection or traditional immunization approaches. Two ways to alter the B cell populations activated upon immunization are explored in this dissertation. Firstly, lowering the activation threshold of activated B cells by arraying antigens on materials allows for a shift of antibody repertoires toward more epitope specificities and potentially broader binding of antibodies to mutated viral strains. Secondly, the immune system can be focused toward specific epitopes using heterologous immunization regimens where antibodies are selected toward a certain specificity, then evolved to bind native antigens, such as those that would be displayed on HIV virions. Though both of these approaches have been explored in other systems, the unique impact of self-assembling peptides in this space has yet to be explored. Peptide biomaterials with fibrillar morphologies such as β-sheet peptides, worm-like micelles, and peptide amphiphiles have been explored towards numerous biomedical applications including scaffolds for tissue repair, immunotherapies for infectious diseases, cancer, or inflammatory conditions, and depots for sustained drug delivery. Although these materials have shown promise in preclinical applications, the immunological effects of their length and ligand valency are poorly understood. Because both of these features can be utilized to tune immune responses, optimizing them in the context of HIV immunization has the potential to improve the magnitude and quality of antibodies elicited by nanofiber immunogens. To examine the impact of antigen valency and nanofiber size in HIV immunization, structural tools to control these features were developed. The ability to control nanofiber length was achieved in this body of work be engineering a set of peptides we have designed and characterized to stabilize self-assembling interfaces. This newfound control over nanofiber length allows size-based targeting of materials which was not previously possible. In addition to studying size-dependent immunogenicity, the role of glycans in immune responses to nanoscale are a newfound area of interest amongst the biomaterials community. Though some glycans can be readily conjugated to peptide and polymer assemblies, many carbohydrates, such as sialic acids are extremely difficult to functionalize chemically. To overcome this, glycomimetic peptides which resemble diverse glycans have been designed, but are implemented in few therapeutic contexts. This system capitalizes upon the synthetic advantages of utilizing glycomimetic peptides in peptide-based immunogens and represents a broadly applicable strategy to impart lectin-binding properties to peptide materials. Although it is appreciated that multivalency and nanomaterial shape and size can influence immunogenicity, these aspects have yet to be fully exploited in the context of a specific disease. To meet these challenges, we have designed a self-assembling peptide system with control over the lengthwise assembly of nanofibers and have studied the effect of antigen valency on immune responses to these materials in the context of HIV. As immunogens, peptide nanofibers have a unique ability to activate low-affinity B cells, such as those which react to autologous targets, will likely be advantageous for HIV vaccination, where low-affinity B cells are precursors to the induction of broadly neutralizing antibody (bnAb) responses. To determine the utility of peptide nanofibers as platforms for HIV vaccination, We first constructed nanofibers that are covalently linked to the HIV envelope antigen gp120 which demonstrated their ability to raise antibodies with broad binding profiles. As an alternative approach for raising immune responses against HIV antigens, we have explored the use of peptide nanofibers displaying short, linear HIV epitopes as priming immunogens. This approach capitalizes on the ability of nanofibers to generate antibodies against short epitopes and tailors the accumulation of nanofibers in lymph nodes to prime epitope-focused antibodies against HIV virions. Taken together, the studies described here utilize supramolecular control over antigen valency and immunogen size to generate antibody responses to HIV with high affinity and high binding breadth. The supramolecular tools described here provide morphological controls for spontaneously assembling materials which have not yet been utilized for these types of platforms. This tight control over morphology allows us to ask questions with levels of immunological precision that are not common in biomaterials literature.