Phage Interactions with Immune Cells in 3D Microgels

• Ansolei Taliaferro, Biological Sciences, Delaware State University

• Catherine Fromen, Chemical and Biomolecular Engineering, University of Delaware
• Victoria Muir, Chemical and Biomolecular Engineering, University of Delaware

Bacteriophages, or “phages” for short are viruses that kill bacteria and are found everywhere in the biosphere. Phage therapy has been developed to fight bacterial infections because of the rise of antibiotic resistance and the need for other ways to treat infections. Local therapy is beneficial compared to systemic treatment because it allows increased drug concentration at the intended site and reduces side effects. Phage therapy could be delivered locally through the delivery of granular hydrogels. Granular hydrogels are packed micro-sized hydrogel particles. When delivered into the body, phages and microgels will interact with host immune cells. However, the effect of phages on mammalian immune cells is not often studied. It is important to research these interactions as immune cells are at high concentration at the site of infection. Our central objective is to better understand how immune cells respond to bacteriophages delivered from granular hydrogels. The microgels used for our experiments were made from GelMA, a gelatin polymer with a methacrylate group added. The methacrylate group allows us to covalently crosslink the gelatin together to form a stable hydrogel network. The microgels must be crosslinked by UV light to stay linked in the temperature needed for cell incubation (37°C). We found that uncrosslinked microgels impacted the morphology of immune cells without being added in a transwell, but microgels added with a transwell did not impact immune cell morphology. We also found that a high dosage of phage negatively affected the metabolism of RAW immune cells, while a low dosage was more like our positive control. However, macrophages seem to endocytose both high and low amounts of phages. We investigated the dynamics of phage-immune cell interactions with and without granular hydrogels. We found that phages diffuse throughout cells and microgels and have more fluorescence over time. As a proof of concept, we also showed that granular hydrogels loaded with phages could be bioprinted into stable structures. This highlights the potential for creating bioprinted models of phage-immune cell interactions. These studies influence new insights into phage therapy and ways to study phage-immune cell interactions.