The present invention relates to improved methods to immunize / vaccinate or stimulate the immune system of animals, including humans, using vectors containing expression cassettes that encode for the DNA of one or more protein / peptide antigens and / or adjuvants, in particular, cytokines like GMCSF, Flt3L, interleukins, and the like, which can be encoded by DNA as well, also recombinase mediated integration. Adjuvants known to increase immune responses following DNA vaccination. In addition, the vectors contain one or more sites recognized by a recombinase / transposase, which catalyzes the insertion of the vector into the genome of transfected cells. Stable integration of the plasmid vector into the genome of transfected cells results in higher and longer-lasting expression of the encoded protein(s), and increases the immune response in the vaccinated animal. The present invention also relates to adjuvant compositions comprising the novel polypeptide, rabbit GMCSF, for boosting antibody production in rabbits.