Potential advantages and risks of nucleic acid vaccines for infant immunization.

Infant antibody responses are impaired due to defective B cell activation by bacterial polysaccharides, slow B cell responses to protein antigens and reduced T cell helper activities. These features result in a 'greater susceptibility to severe infections by encapsulated bacteria and the requirement for repeated doses of vaccines during the first years of life. Nucleic acid vaccines could optimize infant antibody responses by allowing the identification of novel protective antigens, by supplying missing cytokines, by the achievement of sustained immune responses or by the design of novel combination vaccines allowing a reduction of required injections. The deficient infant cellular immune responses, responsible for their susceptibility to infections with intracellular pathogens, could possibly benefit from the potential of nucleic acid vaccines to trigger strong TH1-like responses. Last, a major contribution to infant immunization would be achieved if nucleic acid vaccines proved able to circumvent maternal antibody-mediated inhibition of infant responses to vaccine antigens.