NUCLEIC-ACID VACCINE-INDUCED IMMUNE-RESPONSES REQUIRE CD28 COSTIMULATION AND ARE REGULATED BY CTLA4

Immunization with plasmids expressing specific genes (DNA or nucleic a cid vaccination (NAV)) elicits robust humoral and cell-mediated immune responses, The mechanisms involved in T cell activation by NAV are in completely characterized, We have examined the costimulatory requireme nts of NAV, CD28-deficient mice did not mount Ab or CTL responses foll owing i.m. immunization with eukaryotic expression plasmids encoding t he bacterial gene beta-galactosidase (beta gal). Because these mice re tained their ability to up-regulate the CTLA4 receptor (a negative reg ulator of T cell activation), we examined CTLA4's role in the response of wild-type BALB/c mice to NAV, Intact anti-CTLA4 mAb but not Fab fr agments suppressed the primary humoral response to pCIA/beta gal witho ut affecting recall responses, indicating CTLA4 activation inhibited A b production but not T cell priming, Blockade of the ligands for CD28 and CTLA4, CD80 (B7-1) and CD86 (B7-2), revealed distinct and nonoverl apping function, Blockade of CD80 at initial immunization completely a brogated primary and secondary Ab responses, whereas blockade of CD86 suppressed primary but not secondary responses. Simultaneous blockade of CD80 + CD86 was less effective at suppressing Ab responses than eit her alone, Enhancement of costimulation via coinjection of B7-expressi ng plasmids augmented CTL responses but not Ab responses, and without evidence of Th1 to Th2 skewing. These findings suggest complex and dis tinct roles for CD28, CTLA4, CD80, and CD86 in T cell costimulation fo llowing nucleic acid vaccination.