We present a translational method for developing a tolerogenic vaccine to drastically decrease the burden of patients with multiple sclerosis (MS) by using nanotechnology. We hypothesize that nano/microparticles fabricated from the polymer acetalated dextran (Ac-DEX) that encapsulate the active form of vitamin D, and myelin basic protein (MBP) will initiate the formation of MBP specific inducible T-reg cells (iT-regs) capable of suppressing MS in an antigen specific manner. Our project is innovative because: 1.) Passive in vivo targeting: Previous methods to develop tolerogenic DCs to treatment MS require ex vivo manipulation. Phagocytic dendritic cells (DCs) allow passive targeting since the nanoparticles are too large to be taken up by non-phagocytes. Passive targeting leads to in vivo delivery of tolerogenic agents to the DCs, such as the active form of vitamin D (calcitriol). Currently, calcitriol is ineffective at treating MS because at the concentrations necessary to ameliorate the disease, whole tissue calcification is prominent. 2.) Dose sparing: Our preliminary studies indicate that encapsulation of immunomodulatory agents leads to dose sparing. We hypothesize that we will be able to target DCs in vivo and deliver payload intracellularly, thus decreasing the amount of calcitriol needed, thereby preventing tissue calcification. The targeted DCs will become tolerogenic, which will then be capable of inducing the formation of MS suppressing iT-reg cells. 3.) Acid sensitive nanoparticles: Acid sensitive nanoparticles exposed to the acidic environment of the phagocyte lysosome will degrade, releasing the encapsulated antigen and initiating an immune response. We have previously shown that using our pH sensitive polymer Ac-Dex, we can drastically increase both CD4 and CD8 presentation compared to free protein, and protein encapsulated in other common polymeric carriers. 4.) Specific immune dampening: Current methods of MS treatment require non-specific systemic immune suppression. We present a method in which we can generate a MBP specific iT-reg population that can suppress against MS without suppressing the entire immune system. We present preliminary data that shows encapsulation of dexamethasone and MBP peptide results in increased formation of MBP specific iT-regs in the CNS and reduced disease progression with treatment before experimental autoimmune encephalomyelitis (EAE) onset in mice. In order to develop these nanoparticles and test their efficacy we present the following three specific aims: Specific Aim 1 will focus on calcitriol and MBP peptide encapsulation in nanoparticles. Specific Aim 2 will focus on evaluating calcitriol encapsulated nanoparticles in inducing tolerogenic DC and iT-regs in vitro. Specific Aim 3 will be testing the formation of iTregs in vivo by the immunization with co-encapsulated MBP and calcitriol. Finally, by using the EAE model of MS, we will treat mice with our nanoparticles. If successful, we will take the data generated in this grant and apply for an R01. In addition, our nanoparticle system could be applied to other autoimmune diseases such as Type 1 diabetes and rheumatoid arthritis.