Immunological memory after somatic transgene immunization is positively affected by priming with GM-CSF and does not require bone marrow-derived dendritic cells.

Inoculation of plasmid DNA is a promising vaccination approach but optimal regimes and ways to enhance immunogenicity remain to be established. Among natural immunological adjuvants, granulocyte-macrophage colony-stimulating factor (GM-CSF) was shown to increase the potency of immunization against tumor cells and protein antigens. Here we studied the effect of GM-CSF on memory responses against a 12-mer B cell epitope in mice primed with a single DNA inoculation. The results show that GM-CSF given at priming as a DNA/GM-CSF chimeric vaccine enhances the magnitude of the anamnestic response irrespective of the form of antigen used subsequently in the booster immunization. Using mice lacking bone marrow-derived dendritic cells we also determined that the enhancing effect is not strictly dependent on these cells. These results expand our understanding of the activity of GM-CSF in vivo as a modulator of the immune response including immunological memory.