Nucleic acid molecules and compositions comprising: a nucleic acid sequence that encodes IL-12 p35 subunit or a functional fragment thereof and/or a nucleic acid sequence that encodes IL12 p40 subunit or a functional fragment thereof, are disclosed. The nucleic acid molecules and compositions further comprising a nucleic acid sequence that encodes an immunogen are also disclosed. Method of modulating immune response and methods of inducing an immune response against an immunogen are disclosed. Therapeutic and prophylactic vaccination methods are also disclosed.