Mechanisms and Engineering of Polymeric Nanoparticles for Modulating Innate and Adaptive Immune Responses

Abstract

The delivery of disease-relevant antigens by nanoparticles is a promising strategy for selectively inhibiting pathogenic autoreactive cells while maintaining a protective immune repertoire. This process, known as antigen-specific immune tolerance, would be a curative treatment for patients with autoimmune disorders. Currently, symptoms are managed by broad-acting immunosuppressive therapies that increase the risk for opportunistic infection and cancer. This dissertation describes the mechanistic insights and engineered improvements made toward the application of polymeric nanoparticles (NPs) to the modulation of innate and adaptive immune responses. A new method for loading antigen into poly(lactide-co-glycolide) (PLG) particles was engineered using PLG-antigen polymer conjugates to incorporate antigen into the bulk of the particle’s polymer matrix. This method was a significant improvement compared to formulations that couple antigen to the particle surface or encapsulate antigen within the particle. By comparison, these antigen-polymer conjugate NPs significantly increased the range and precision of antigen-loading, eliminated uncontrolled payload release, and reduced the exposure of antigen on the particle surface. This loading strategy enabled the delivery of multiple immunodominant antigens within a single particle formulation, which induced tolerance to multiple antigens simultaneously, a significant advancement toward developing treatments for heterogeneous disease pathologies. The tolerogenic ability of these polymer conjugate particles was augmented by conjugating the anti-inflammatory cytokine transforming growth factor beta (TGF-β) to the particle surface. Both antigen and TGF-β were bioactively co-delivered and these TGF-β-coupled particles were able to enhance tolerance induction at decreased nanoparticle doses compared to antigen-only particles, demonstrating the therapeutic potential for influencing Ag presentation by co-delivering cytokines. Mechanistic studies demonstrated a significant role for the liver in particle-induced tolerance. Specifically, the Kupffer cells and liver sinusoidal endothelial cells contributed to tolerance induction by collectively presenting antigen, secreting inhibitory IL-10 and prostaglandin E2, and expressing inhibitory surface molecule PD-L1. Interestingly, Kupffer cells contributed to, but were not necessary for, particle-induced tolerance. The cellular mechanisms of particle-induced tolerance were evaluated in the context of antigen presentation to T cells. Dendritic cell transcription factor activity and T cell secretion of IL-2 and IFNγ were positively regulated by NP antigen loading. In mice, tolerance induction by antigen-containing particles was dependent on both particle dose and antigen loading. Specifically, tolerance induction required a minimal antigen loading of 8 μg/mg and could not be rescued at lower loadings by increasing the NP dose. A minimum NP dose of 0.5 mg was required for tolerance, even at the high antigen loading of 128 μg/mg. PLG and poly(lactic acid) (PLA) NPs were found to be inherently immunomodulatory and inhibited the macrophage production of inflammatory cytokines induced by bacterially-derived lipopolysaccharide (LPS). This inhibitory effect was influenced by polymer composition and surface charge. In the sepsis mouse model of lethal LPS-induced endotoxemia, prophylactic and therapeutic treatment with PLA NPs increased the survival rates to 63% and 14%, respectively. Collectively, this work has advanced the design, abilities, and understanding of antigen-loaded and cargo-free nanoparticles which have demonstrated the potential for clinically modulating pathological adaptive and innate immune responses.