The present invention provides compositions comprising synthetic non-DNA base- containing polynucleotide sequences of 3 to 30 bases in length comprising one or more non- DNA bases wherein the bases are nebularine, hypoxanthine, or uracil, or combinations of nebularine, hypoxanthine and uracil bases, in combination with a pharmaceutically acceptable vehicle, particularly one or more adjuvant vehicle, and one or more antigen. The present invention relates to the use of these compositions in methods for inducing or modulating an immune response in vitro or in vivo, and particularly for activating antigen presenting cells.
