Presence of CpG DNA and the local cytokine milieu determine the efficacy of suppressive DNA vaccination in experimental autoimmune encephalomyelitis

We here study the adjuvant properties of immunostimulatory DNA sequences (I SS) and coinjected cytokine-coding cDNA in suppressive vaccination with DNA encoding an autoantigenic peptide, myelin basic protein peptide 68-85, aga inst Lewis rat experimental autoimmune encephalomyelitis (EAE), EAE is an a utoaggressive, T1-mediated disease of the CNS, ISS are unmethylated CpG mot ifs found in bacterial DNA, which can induce production of type 1 cytokines in vertebrates through the innate immune system. Because ISS in the plasmi d backbone are necessary for efficient DNA vaccination, we studied the effe ct of one such ISS, the 5'-AACGTT-3' motif, in our system. Treatment with a DNA vaccine encoding myelin basic protein peptide 68-85 and containing thr ee ISS of 5'-AACGTT-3' sequence suppressed clinical signs of EAE, while a c orresponding DNA vaccine without such ISS had no effect. We further observe d reduced proliferative T cell responses in rats treated with the ISS-conta ining DNA vaccine, compared with controls. We also studied the possible imp act of coinjection of plasmid DNA encoding rat cytokines IL-4, IL-10, GM-CS F, and TNF-alpha with the ISS-containing DNA vaccine. Coinjection of IL-4-, IL-10-, or TNF-alpha-coding cDNA inhibited the suppressive effect of the D NA vaccine on EAE, whereas GM-CSF-coding cDNA had no effect. Coinjection of cytokine-coding cDNA with the ISS-deficient DNA vaccine failed to alter cl inical signs of EAE, We conclude that the presence of ISS and induction of a local T1 cytokine milieu is decisive for specific protective DNA vaccinat ion in EAE.