PLGA particle size as a critical modulator of immune tolerance via ⍺vβ3 mechano-sensor engagement

Abstract

The increasing prevalence of inflammatory and autoimmune conditions underscores the critical need for novel therapeutic strategies that modulate inflammation without impairing the capacity to mediate protective immunity against infection and cancer. In recent years, there has been growing interest in the use of biodegradable particles to modulate immune responses for therapeutic purposes, spanning from vaccine adjuvants to drug delivery vehicles. Notably, size was found to be a crucial physicochemical property that regulates the capacity of particulates to modulate the activation of innate immune cells. This study investigated the capacity of poly(lactic-co-glycolic acid) (PLGA) particles to induce anti- inflammatory immune responses and explored the mechanisms by which innate immune cells can respond to PLGA particles differentially based on size. This work identified that particles in the 0.5–2 μm size range can reprogram innate immune cells toward immunosuppressive phenotypes. Specifically, PLGA particles within this narrow size range were found to induce the secretion of transforming growth factor β (TGFβ), IL-1 receptor antagonist (IL-1Ra), and IL-10 from key antigen- presenting cells (APCs). Incubation of dendritic cells (DCs) with these particles resulted in an enhanced capacity to prime and expand CD4+ regulatory T-cell (T- reg) in an in-vitro co-culture model and vaccination with antigen and particles induced enhanced antigen-specific T-reg numbers. Investigations into the mechanism by which APCs respond to particles based on size revealed significant changes in cell morphology and membrane fluidity, particularly in response to 0.5– 2 μm PLGA particles. Furthermore, surface expression of the mechanosensory integrin ⍺vβ3 was markedly upregulated by particles within this size range. A critical role for ⍺vβ3 was identified in regulating the transduction of mechanical stimuli from the cell membrane into biochemical signalling, resulting in the observed anti-inflammatory responses. Importantly, ⍺vβ3 was essential for the ability of DCs to activate antigen-specific T-regs by mediating the mechanical activation of latent TGFβ, providing crucial pro-tolerance signals during antigen presentation. These findings demonstrate the potential of biodegradable 0.5-2 μm PLGA particles as adjuvants for ‘inverse vaccines’ to promote immunological tolerance in a manner independent of biologic agents or potent immunosuppressants. Furthermore, these findings exhibit the importance of mechanical cues in driving immune responses and how these can be harnessed to improve existing particle-based immune-therapies.