PROJECT SUMMARY/ABSTRACT A resurgence of research interest in bacteriophages, viruses that infect bacteria, is driving the development of engineered phages for biomedical applications, including antimicrobial therapy and phage-based vaccination. As antimicrobial agents, phages have significant advantages over conventional antibiotics: they are well- tolerated, pathogen-specific, and replicate at the site of infection. Phages are also promising as vaccine platforms because they can be precisely engineered to deliver multiple foreign antigens. However, phages are immunogenic and both applications are susceptible to interfering immune responses. Antimicrobial phages, for example, can elicit neutralizing antibodies that prevent infection of the bacterial target. This immunogenic nature is advantageous for vaccine development, since the phage acts as its own adjuvant, but it comes at a price: off-target responses to immunodominant phage antigens can distract from intended protective responses to foreign antigens. Unfortunately, data on phage immunology are limited, confounding routine biomedical applications of phage. This proposal outlines basic experiments to elucidate the basis of phage immunogenicity and evaluate methods of modulating it. Aim 1 will develop a structural map of antibody binding to three therapeutic mycobacteriophages. Structure- guided engineering and directed evolution will be used to generate mutant phages that escape antibody binding. The ability of these mutants to evade established immune responses to their wild-type counterparts in vivo will be evaluated in a mouse model. In Aim 2 the same phages will be used as platforms for a therapeutic bacterial vaccine. Leveraging both phage display and phage DNA vector technologies, the vaccine candidates will defend and protect against bacteria with three mechanisms: 1) phage infection and killing, 2) generation of bacterium-binding antibodies, and 3) activation of helper and cytotoxic T cells. Aim 3 will evaluate a method to suppress interfering immune responses: co-administration of phage with rapamycin-loaded nanoparticles. This will down-regulate phage-specific helper T cells and upregulate regulatory T cells, training the immune system to recognize phage as ‘self’. These Aims will expand our understanding of phage immunogenicity and assess the potential to improve phage-based medicine with principles from immunoengineering. Furthermore, Aim 1 is a training vehicle for the candidate, who has developed immunology experience in the lab but requires mentored training and formal education to establish independence in this field. Aim 1 also provides additional mentored training in structural biology, specifically asymmetric reconstructions of phage-antibody complexes. With the planned scientific training, practice in publishing and grant writing, and the support of her mentors throughout an academic job search, the candidate is expected to establish and sustain an independent research career focused on immunoengineering phage to improve their biomedical applications.

PROJECT NARRATIVE Bacteriophages, viruses that infect bacteria, can defend against emerging pathogens when deployed as targeted antimicrobials or vaccine platforms. However, the human immune response to bacteriophage administration can interfere with efficacy. The proposed research will improve our understanding of bacteriophage immunogenicity and establish novel methods of modulating it to improve phages for biomedical applications.