Srinivasan, Sangeetha ; Babensee, Julia E. Biomedical Engineering (Joint GT/Emory Department) Champion, Julie A. Thomas, Susan N. Botchwey, Edward A. Roy, Krishnendu ; Babensee, Julia E.
Pivotal discoveries in the field of immunology over the last five decades have changed the way new therapies are designed for applications as varied as organ transplantation, autoimmune diseases or even cancer. In this regard, dendritic cells (DCs) were identified to play an important role in the orchestration of the adaptive immune response. Importantly, the phenotype of DCs is a powerful indicator of their downstream effector functions. In the recent years, parallel advancements made in biomaterial design and biocompatibility considerations are being directly translated into developing improved immunotherapies. Interestingly, biomaterials also elicit differential effects on the host immune response and the phenotypic state of DCs. The first objective of this doctoral thesis was to validate the role of DCs in supporting antigen presentation for a proliferative antigen-specific T cell response in the presence of PLGA, consistent with the previously observed adjuvant effect of PLGA. Herein, by conditionally ablating DCs in a murine CD11c-DTR model, the adjuvant effect of PLGA towards co-delivered OVA was revisited. The diminished proliferation of adoptively transferred OVA-reactive T-cells in these mice was suggestive of mitigated antigen presentation due to the absence of CD11c+ DCs; thereby we demonstrated that the effect of PLGA in vivo on the antigen-specific proliferative T-cell response, a likely early precursor to antibody response, was indeed due to its effects on DC presence and phenotype. The second objective of this thesis was to design, develop and validate a multicomponent, multifunctional immunomodulatory (MI) scaffold comprised of macroporous agarose as the base scaffold material into which were embedded crosslinked gelatin microparticles (MPs), pre-loaded with immunomodulators, for their controlled release to mimic tolerogenic human or murine DC culture conditions. Aided by empirical modeling, using the Weibull equation, of experimental data using ‘model’ proteins, we identified parameters of gelatin MP crosslinking density and number of embedded MPs in agarose to achieve prescribed temporal controlled release of immunomodulators for induction of tolerogenic DCs. The prescribed MI scaffold aimed to release granulocyte monocyte colony-stimulating factor (GM-CSF; delivered within 0-3 days) to induce differentiation of monocyte precursors into DCs after dexamethasone (DEX, delivered within 3-6 days) addition would induce regulatory properties to these cells as well as peptidoglycan (PGN, delivered on days 5-6) to induce an alternative activated phenotype in DCs. Such alternatively activated DCs (aaDCs), are endowed with immunosuppressive as well as directed lymph node migratory properties to effectively exert their tolerogenic effect. Ability of this MI scaffold to induce tolerogenic phenotype in human blood-derived as well as murine bone marrow-derived cells was demonstrated upon in vitro treatment using a large cadre of immunological assessments. In summary, the work in this thesis documents the importance of DCs in the effect of PLGA in enhancing antigen-specific adaptive immunity in vivo and provides a construct formulation that can be used to generate aaDCs with tolerogenic and migratory properties that are highly relevant in designing future immunotherapies targeting autoimmune diseases as well as in alleviating allograft rejection.
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Conditioning dendritic cell responses using engineered biomaterials for immunotherapy
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