INFLUENCE OF CELLULAR LOCATION OF EXPRESSED ANTIGEN ON THE EFFICACY OF DNA VACCINATION - CYTOTOXIC T-LYMPHOCYTE AND ANTIBODY-RESPONSES ARE SUBOPTIMAL WHEN ANTIGEN IS CYTOPLASMIC AFTER INTRAMUSCULAR DNA IMMUNIZATION

We examined the role of the cellular localization of antigen on the im mune response after DNA immunization of mice with three forms of ovalb umin (OVA), DNA encoding OVA which was secreted (sOVA) generated 10- t o 100-fold higher IgG responses with 50- and 100-fold higher levels of IgG1 than the cytoplasmic (cOVA) or membrane bound (mOVA) forms. An I gG2a predominance was seen only in cOVA and mOVA immunized mice. Altho ugh the antibody response was CD4(+) T cell dependent, the differences in the antibody response could not be compensated for by provision of excess CD4(+) T cell help in TCR transgenic mice. Together with our h apten-carrier studies, this would indicate that membrane or intracellu lar localization limits the availability of antigen for B cell priming which affects the magnitude and form of the antibody response. Surpri singly, stronger cytotoxic T lymphocyte (CTL) responses were generated for sOVA or mOVA than for cOVA via intramuscular (i.m.) injection. Si nce a cytoplasmic antigen should have best access to the canonical cla ss I pathway for antigen presentation, our results indicate that primi ng of CTL responses after i.m. DNA immunization is probably by cross-p resentation of antigen by nontransfected professional antigen-presenti ng cells. In contrast, intradermal immunization with cOVA produced opt imal CTL responses but, as with mOVA, suboptimal antibody responses. T his, together with our ex vivo RT-PCR analysis showing similar mRNA le vels from all three constructs 7 days post-immunization, argues agains t the differential CTL response for i.m. injection to be due to dose.