Modulation of immunostimulatory activity of CpG oligonucleotides by site-Specific deletion of nucleobases

The effect of nucleobase deletion in the 3′- or the 5′-flanking sequence to a CpG-motif on immunostimulatory activity of CpG-containing oligonucleotides was examined by cell proliferation, secretion of IL-12 and IL-6 in mouse spleen cell cultures, and by spleen enlargement in mice. Deletion of one or two nucleobases in the 3′-flanking sequence to a CpG-motif at certain positions did not affect immunostimulatory activity, while similar deletions in the 5′-flanking sequence increased immunostimulatory activity compared with the parent oligo.