CpG DNA functions as an effective adjuvant for the induction of immune responses in aged mice

The present studies demonstrate that the immunization of aged mice with Diphtheria toxoid in formulations containing unmethylated immunostimulatory CpG motifs, promotes the successful development of immune responses that are qualitatively and quantitatively comparable to those induced in young animals vaccinated in a similar manner. Aged mice given vaccines containing CpG oligodeoxynucleotides (ODNs) expressed primary and secondary systemic humoral immune responses having isotype profiles consistent with an enhancement in Th-1 type immunity. The ability to generate common mucosal immunity was also restored in aged animals given CpG ODN-containing vaccines. Dendritic cells (DCs) were determined to represent one of the cellular targets of CpG ODN activities in aged mice since restoration of immune function was observed when DCs from aged donors were pulsed with antigen and CpG ODNs, prior to injection into syngeneic young adult or aged recipients. Interestingly, antigen-pulsed DCs from young donors were fully capable of stimulating immune responses following their injection into syngeneic young adult or aged hosts, without a need for exposure to CpG ODNs. Although the mechanism(s) by which CpG DNA exerts its beneficial adjuvant effects on the aged immune system remains unclear, our findings suggest that the incorporation of CpG ODNs into vaccine formulations provided to the aged could prove useful in the development of more effective vaccines for the elderly.