The GD2 ganglioside expressed on neuroectodermal tumor cells is weakly 
immunogenic in tumor-bearing patients and induces predominantly IgM antibody 
responses in the immunized host. Using a syngeneic mouse challenge model with 
GD2-expressing NXS2 neuroblastoma, we investigated novel strategies for 
augmenting the effector function of GD2-specific antibody responses induced by a 
mimotope vaccine. We demonstrated that immunization of A/J mice with DNA vaccine 
expressing the 47-LDA mimotope of GD2 in combination with IL-15 and IL-21 genes 
enhanced the induction of GD2 cross-reactive IgG2 antibody responses that 
exhibited cytolytic activity against NXS2 cells. The combined immunization 
regimen delivered 1 day after tumor challenge inhibited subcutaneous (s.c.) 
growth of NXS2 neuroblastoma in A/J mice. The vaccine efficacy was reduced after 
depletion of NK cells as well as CD4(+) and CD8(+) T lymphocytes suggesting 
involvement of innate and adaptive immune responses in mediating the antitumor 
activity in vivo. CD8(+) T cells isolated from the immunized and cured mice were 
cytotoxic against syngeneic neuroblastoma cells but not against allogeneic EL4 
lymphoma, and exhibited antitumor activity after adoptive transfer in 
NXS2-challenged mice. We also demonstrated that coimmunization of 
NXS2-challenged mice with the IL-15 and IL-21 gene combination resulted in 
enhanced CD8(+) T cell function that was partially independent of CD4(+) T cell 
help in inhibiting tumor growth. This study is the first demonstration that the 
mimotope vaccine of a weakly immunogenic carbohydrate antigen in combination 
with plasmid-derived IL-15 and IL-21 cytokines induces both innate and adaptive 
arms of the immune system leading to the generation of effective protection 
against neuroblastoma challenge.