Immunogenicity and efficacy of a DNA vaccine in aged mice

The immunogenicity and protective efficacy of a DNA vaccine encoding the circumsporozoite protein of the Plasmodium yoelii malaria parasite was evaluated in young (2 months) versus aged (>26 months) BALB/c mice. The primary and secondary humoral immune response of aged mice was 19- and 7-fold lower, respectively than that of similarly treated young animals (p <.01). Cytotoxic T lymphocyte activity in aged mice, was also lower than ill younger animals. The vaccine response of aged animals was characterized by a 6-fold increase in interleukin-4 and a 3-fold increase ill interferon-gamma (IFN-gamma) secreting cells, whereas in :young animals immunization only stimulated the production of the type I cytokine IFN-gamma. Overall, 80% of young vaccinated mice were protected from subsequent challenge with live malaria sporozoites whereas only 40% of aged mice were protected. These results are the first to demonstrate that DNA vaccination induces less effective immunity in aged than young animals.