Antigen delivery systems ii. development of live recombinant attenuated bacterial antigen and dna vaccine delivery vector vaccines

The development of safe, efficacious recombinant attenuated bacterial antigen delivery systems requires attention to some desired attributes. The vaccine design should be focused on-enhancing immunogenicity and the magnitude and duration of the immune response to the expressed protective antigen, and on diminishing the potentially competing immune responses to antigens of the attenuated bacterial antigen delivery vector. Depending upon the disease to be prevented and the nature of the pathogen causing that disease-it may be necessary to make genetic modifications of the antigen delivery system, to maximize a Th2 response important for inducing mucosal and systemic antibody responses or, in other cases, a Th1 response to enhance the cellular immunity. It is potentially desirable to introduce biological containment features into vaccines to prevent their survival and persistence in environments into which they might be introduced as a consequence of immunization. The magnitude of protective immunity to an expressed protective antigen in regard to mucosal and systemic antibody responses, is more or less dependent on the amount of protective antigen delivered to the immunized host.