DNA IMMUNIZATION OF MICE AGAINST SIVMAC239 GAG AND ENV USING REV-INDEPENDENT EXPRESSION PLASMIDS

Simian immunodeficiency virus (SIV) structural gene expression, includ ing gag and env, strictly depends on the interaction of the viral post transcriptional regulator Rev with its target RNA, the Rev-responsive element (RRE), A small RNA element, termed the constitutive transport element (CTE), located in the 3' portion of simian retrovirus 1 (SRV-1 ) mRNA, can efficiently substitute for the human immunodeficiency viru s (HIV Rev-RRE interaction, and thus render HIV expression and replica tion Rev independent, We tested the ability of the SRV-1 CTE to drive the expression of SIVmac239 env and gag from subgenomic constructs des igned for possible use in vaccine trials, In vitro, expression studies showed that when the SRV-1 sequence is coupled to the SIV gag and env mRNAs, it functions in an orientation-dependent fashion, and leads to strong expression of SIV Gag and Env in human anti monkey cell lines; levels of CTE-mediated protein expression were similar to those obtai ned with a functional Rev-RRE system, On the other hand, in murine fib roblast-like cells, SIV Gag and Env were expressed from constructs at relatively high levels even in the absence of Rev-RRE; nevertheless, t heir expression was increased by the presence of the SRV-1 CTE, As rep orted previously for HIV, the murine cell lines appeared to be defecti ve for Rev-RRE activity, and required overexpression of Rev to induce a Rev response, Intramuscular injection of the gag-CTE and env-CTE con structs in BALB/c mice resulted in the expression of the corresponding mRNAs, and the production of anti-Gag and anti-Env antibodies, thus s uggesting that these vectors might be used for genetic immunization ap proaches.