(229g) Macrophage Internalization of PEGDA Nanoparticles Drives Secretion of Pro-Survival Signals

Antigen presenting cells (APC), such as macrophages and dendritic cells, are phagocytic cells that internalize foreign objects and bridge innate and adaptive immune functions. These phagocytic cells naturally interact with engineered nanoparticles (NP) and receive a plethora of information during the phagocytic process that dictates the downstream response. Despite this knowledge, the full extent to which physiochemical cues from the NP drive changes to APC response is not fully understood, in large part due to the complexity of the phagocytic immune synapse. Prior work from the Fromen lab has shown that delivering model NPs comprised of poly(ethylene glycol) diacrylate (PEGDA)-based chemistries to primary macrophages enhances their survival, even in the absence of a therapeutic or stimulating cargo. Herein, we further investigate this phenomenon and study how this extended survival influences cell-cell communication. We first fabricate anionic PEGDA NPs ~200 nm in hydrodynamic diameter and evaluate cellular lifespan of two primary-like APC populations: murine bone marrow derived macrophages (BMM) and bone marrow derived dendritic cells (BMDC), both differentiated from C57BL/6 female mice. Expanding prior results, we demonstrate that a single dose of 100 µg/mL anionic PEGDA NPs significantly enhances ex vivo survival of both BMM and BMDCs; this effect is further modulated through repeated NP administration. Interestingly, we find that following NP-internalization, BMMs secrete an as-of-yet unidentified pro-survival signal that enhances survival of other BMM cells. Using either a single supernatant transfer or a non-contacting co-culture using transwells, exposure to supernatants of NP-dosed BMMs increases the survival of adjacent, NP-free BMMs to a significantly greater extent than those exposed to untreated BMM supernatants. Bioinformatics approaches evaluating both cellular RNAseq and supernatant mass spectrometry proteomic datasets have revealed a list of possible secreted factors accounting for this effect, lending important insight into the signaling cascade that is downstream of NP internalization. Fully characterizing the implications of phagocytosis on APCs such as BMMs builds important groundwork for a wide range of NP-based therapeutics and vaccines, where controlling the duration of survival and antigen presentation may offer an important, untapped engineering design parameter.