SOMATIC TRANSGENE IMMUNIZATION WITH DNA ENCODING AN IMMUNOGLOBULIN HEAVY-CHAIN

A plasmid DNA containing a chimeric immunoglobulin heavy-chain gene wi th tissue-specific promoter and enhancer elements was used as a model system to study the events triggered by a single intraspleen DNA inocu lation in adult C57BL/6 mice. A single intraspleen inoculation was fol lowed in a week by secretion of transgene immunoglobulins and producti on of immunoglobulin M (IgM) anti-immunoglobulins. Their kinetics of s erum appearance were almost superimposable. While anti-immunoglobulin antibodies remained detectable for over 6 months, transgene immunoglob ulins disappeared after 3-4 weeks, However, transgene mRNA was detecte d in the spleen for 4 months. A multiplex polymerase chain reaction (P CR) analysis on splenic genomic DNA 17 days after inoculation demonstr ated that the transgene was integrated in the host chromosomal DNA, Th e nucleotide sequence of the rearranged VDJ region from splenic genomi c DNA was identical to that of the parental plasmid DNA, hence ruling out that hypermutation had occurred, A booster injection of immunoglob ulin encoded by the transgene on day 200 elicited a typical secondary immune response with IgG(1) and IgG(2b) antibodies. These results demo nstrate that a single inoculation of an immunoglobulin heavy-chain DNA targeted to spleen lymphocytes leads to spontaneous integration of th e transgene into the host DNA, and that this is sufficient to initiate immunity and establish immunologic memory, Our data also show that mi nute amounts (<100 ng/ml) of an endogenously produced protein secreted in the microenvironment of a lymphoid tissue generate immunity and es tablish immunologic memory rather than tolerance.