Combinatorial, Microparticle-Based Delivery of Immune Modulators Reprograms the Dendritic Cell Phenotype and Promotes...

Safe, effective, antigen-specific therapy for rheumatoid arthritis (RA) remains an elusive clinical goal with a few lasting, viable options on the horizon. Existing therapeutic interventions are indiscriminate and inconsistently immunosuppressive, often leaving patients susceptible to infection. Herein, we investigate the use of a dual-sized, microparticle "regulatory vaccine" (REGvac) that passively targets dendritic cells for antigen-specific biomaterial-based immunotherapy of RA. This REGvac employs poly(d,l-lactic-co-glycolic-acid) (PLGA) microparticles (MPs) encapsulating (i) a dendritic cell chemoattractant, (ii) potent immunosuppressive molecules, (iii) and an RA-relevant autoantigen to provide a multifaceted approach for the treatment of collagen-induced arthritis (CIA), the primary mouse model of RA. Subcutaneous administrations of the REGvac after mice had developed moderate clinical symptoms markedly diminished overt inflammation in the paws, halted cartilage degradation, and restored gait parameters within 56 days after initial treatment. Positron emission tomography imaging corroborated reduction of inflammation in the paws of REGvac-treated mice. In-depth immunological assessments showed a decreased expression of CD80, CD86, and MHC II on CD11c⁺ dendritic cells in joint-associated lymph nodes. Further, we observed significant increases in conventional regulatory CD25⁺FOXP3⁺ T cells, as well as programmed cell death protein-1 (PD-1)-expressing CD4⁺ T cells in joint-proximal lymph nodes and the spleen. Real-time PCR analysis of joint tissues from treated mice revealed significant decreases in inflammatory cytokine expression (IL-6), while IL-10 mRNA levels were significantly increased. These observations strongly hint toward the induction of multiple tolerogenic mechanisms by administration of this MP regulatory vaccine. With regards to antigen specificity, ex vivo antigen recall assays revealed a lack of response to collagen by CD4⁺ T cells from the popliteal and inguinal lymph nodes of REGvac-treated mice, contrasting with the proliferative response of CD4⁺ T cells from CIA+ mice. Taken altogether, our results strongly support the application of this MP regulatory vaccine as a potent, biomaterial-based, antigen-specific therapy for RA.