Suppressive DNA vaccination in experimental autoimmune encephalomyelitis

Abstract: This thesis describes the development of a novel method to suppress an organ-specific autoimmune disease, experimental autoimmune encephalomyelitis (EAE), by vaccination with DNA encoding autoantigenic peptides. DNA vaccination can produce long-term immunity and generate antigen-specific CD8+ and CD4+ T cells. EAE is an autoimmune disease of the central nervous system (CNS), and an animal model for multiple sclerosis (MS). We used myelin basic protein (MBP)-EAE, in which Lewis (LEW) rats are immunized with MBP or encephalitogenic MBP-peptides. The disease is considered to be T1-mediated. We vaccinated LEW rats with DNA encoding the irnmunodominant T cell epitope MBP-peptide 68-85 (MBP68-85) targeted to IgG, before challenge with MBP68-85. The clinical and histopathological signs of EAE were reduced in the DNA vaccinated group, compared to controls. We observed a reduced production of IFN-[gamma] in the vaccinated group, compared to controls, but we measured no induction of type 2 immunity. DNA sequences in DNA vaccine constructs may function as immunomodulators, such as immunostimulatory DNA sequences (ISS). ISS are non-coding, unmethylated CpG motifs of bacterial or viral origin that promote type 1 immunity. Treatment with a DNA vaccine encoding MBP68-85 and containing three ISS suppressed clinical signs of EAE, while a corresponding DNA vaccine without such ISS had no effect. Furthermore, coinjection of IL-4 or IL-10-coding cDNA with the ISS-positive DNA vaccine, inhibited the suppressive effect of the vaccine. We studied the requirements for dominant expression of TCRBV8S2 in LEW rats, after immunization with MBP63-88. The preferential recruitment of TCRBV8S2+ T cells was strictly dependent on MHC haplotype and heterologous MBP-peptide. Then, we demonstrated that a single aminoacid exchange in position 79 from serine (non-self) to threonine (self) in MBP68-85 dramatically altered the protective effect of DNA vaccine encoding MBP68-85. Furthermore, the DNA vaccine encoding MBP68-85 did not protect against MBP89-101-induced EAE and vise versa. Thus, the protective effect was highly specific. To study if DNA vaccination also is feasible with other important encephalitogenic peptide autoantigens, we used myelin oligodendrocyte glycoprotein (MOG)-EAE. Vaccination with DNA encoding MOG91-108 suppressed clinical signs of EAE, after MOG91-108-challenge. In conclusion, vaccination with DNA encoding autoantigenic peptides suppresses EAE. Presence of ISS and a local type 1 cytokine milieu is decisive for specific, protective DNA vaccination in EAE, and the effect is highly specific.