This thesis serves to explore engineering mechanisms by which dendritic cells and their interactions are capable of modulating immune responses. In this, I explore the generation, characterization, and use of a novel cytokine fusion, Flt3L-SA, to therapeutic ends involving both the innate and adaptive immune system. Chapter 1 defines the major players of the immune system. Herein I also explore how these cellular and soluble factors interact and play off of one another to generate beneficial immune responses (pro- and anti-inflammatory) as well as characterize when an immune response malfunctions and the issues it may cause. Finally, I review past and future protein- based technologies involved in immunomodulation to skew immune responses back in an appropriate direction in instances such as pushing inflammation forward to generate anti- tumor immunity, or skewing away from pathogenic inflammation to an inert form. In Chapter 2, I introduce my novel engineered-cytokine. The fusion of Flt3L to serum albumin (called Flt3L-SA), is then rigorously characterized for binding, activity, and pharmacokinetics and dynamics. We here explore how treatment impacts players of both the adaptive and innate systems with an obvious focus on Dendritic Cells, but also how this expansion of DCs impacts the T cell compartments, primarily that of Tregs. Following the general characterization of treatment with Flt3L-SA, Chapter 3 explores the utility of such a treatment in many settings. The first setting this is characterized in is the use of Flt3L-SA with an immunogenic protein drug as a model of enzyme replacement therapy and the prevention of antibodies to the foreign drug. Furthermore, as we note a major immune skewing in the immune system related to the gut, we also explore how oral antigen treatment in combination with Flt3L-SA changes the context in which immune education occurs. Finally, Chapter 4 discusses future works involving this fusion protein in tolerance and wound healing.