Saturday, September 7, 2024
9/7/2024
Project Summary Volumetric muscle loss (VML) is a debilitating injury caused by trauma or disease to skeletal muscle that leads to incapacitating fibrosis and loss of limb function. We and others have identified delayed clearance of apoptotic neutrophils as a primary mediator of fibrosis via detrimental effects on satellite cell and macrophage behavior. Because macrophages are critical regulators of wound healing and also the primary cell type that clear apoptotic neutrophils in a process called efferocytosis, macrophage cell therapy is a promising therapeutic approach, but is limited by two main challenges: 1) Macrophages are highly plastic cells that rapidly shift phenotype in response to microenvironmental cues. Therefore, a strategy is needed to control their phenotype in situ following administration, to prevent them from changing phenotype in response to pro-inflammatory cues at the site of injury. 2) High manufacturing costs and regulatory hurdles prevent the use of autologous (patient- derived) macrophages, especially because very high numbers are required, but allogeneic (donor-derived) macrophages elicit a strong T cell-mediated adverse immune response. We developed an innovative biomaterial-mediated macrophage cell therapy strategy that simultaneously addresses both of these challenges. In this strategy, referred to as Particle-Assisted Control over Macrophage-Neutrophil interactions (Pac-Man), the macrophages are first loaded ex vivo with polymeric biodegradable microparticles that slowly release dexamethasone intracellularly, thus controlling macrophage phenotype from the inside out following their administration to sites of injury. Dexamethasone was selected because it causes an anti-inflammatory/pro- regenerative phenotype in macrophages, increases their efferocytosis of apoptotic cells, and suppresses their ability to activate T cells. Thus, the intracellular release of dexamethasone following administration of the macrophages to sites of injury is expected to make them clear detrimental neutrophils, resolve inflammation, and suppress T cell activation to prevent rejection of allogeneic cells. In Aim 1, the functional phenotype of the adoptively transferred Pac-Man macrophages will be rigorously characterized over time in vitro and in vivo using flow cytometry, gene expression profiling, and analysis of their interactions with apoptotic neutrophils. Effects on muscle repair will be assessed using histology and functional mechanical testing. In Aim 2, the potential to use an allogeneic cell source will be tested in vitro and in vivo using primary human immune cells from mixed donors and mice from different strains. This project will advance an innovative off-the-shelf, translational cell therapy to enhance clearance of apoptotic cells, which would be transformative for the treatment of fibrotic injuries such as VML and many others.
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