IMMUNOGENICITY AND EFFICACY OF A DNA VACCINE IN AGED MICE

The immunogenicity and protective efficacy of a DNA vaccine encoding t he 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 1 9- and 7-fold lower, respectively than that of similarly treated young animals (p <.01). Cytotoxic T lymphocyte activity in aged mice, was a lso lower than ill younger animals. The vaccine response of aged anima ls was characterized by a 6-fold increase in interleukin-4 and a 3-fol d increase ill interferon-gamma (IFN-gamma) secreting cells, whereas i n :young animals immunization only stimulated the production of the ty pe I cytokine IFN-gamma. Overall, 80% of young vaccinated mice were pr otected from subsequent challenge with live malaria sporozoites wherea s only 40% of aged mice were protected. These results are the first to demonstrate that DNA vaccination induces less effective immunity in a ged than young animals.