Durable immunity and immunologic memory to a parasite antigen induced by somatic transgene immunization.

Somatic transgene immunization (STI) is an alternative approach to immunization mediated by inoculation of plasmid DNA. In the experiments presented here we show that inoculation of plasmid DNA carrying an immunoglobulin heavy chain gene under the control of tissue-specific regulatory elements, leads to immunity and persistent immunologic memory against a peptide epitope encoded in the third complementarity-determining region. The epitope consists in three repeats of the tetrapeptide Asn-Ala-Asn-Pro (NANP) and is the immunodominant B cell epitope expressed at the surface of Plasmodium falciparum malaria parasite. When inoculated directly in the spleen the plasmid DNA initiated a specific anti-NANP response which lasted for 2 years. During the initial phase of priming the anti-NANP response was higher than that induced by immunization with recombinant protein in immunologic adjuvants. The establishment of immunologic memory was probed by single booster injection at various times after priming. We found that STI induces persistent immunologic memory up to 2 years. The immunologic characteristics of this new model are examined with respect to the requirement for the induction of B cell memory.