Gene gun DNA vaccination with Rev-independent synthetic HIV-1 gp160 envelope gene using mammalian codons

DNA immunization with HIV envelope plasmids induce only moderate levels of specific antibodies which may in part be due to limitations in expression i nfluenced by a species-specific and biased HIV codon usage. We compared ant ibody levels, Th1/Th2 type and CTL responses induced by synthetic genes enc oding membrane bound gp160 versus secreted gp120 using optimized codons and the efficient gene gun immunization method. The in vitro expression of syn .gp160 as gp120 + gp41 was Rev independent and much higher than a classical wt.gp160 plasmid. Mice immunized with syn.gp160 and wt.gp160 generated low and inconsistent ELISA antibody titres whereas the secreted gp120 consiste ntly induced faster seroconversion and higher antibody titres. Due to a hig her C + G content the numbers of putative CpG immune (Th1) stimulatory moti fs were highest in the synthetic gp160 gene. However, both synthetic genes induced an equally strong and more pronounced Th2 response with higher IgG1 /IgG2a and IFN gamma/IL-4 ratios than the wt.gp160 gene. As for induction o f CTL, synthetic genes induced a somewhat earlier response but did not offe r any advantage over wild type genes at a later time point. Thus, optimizin g codon usage has the advantage of rendering the structural HIV genes Rev i ndependent. For induction of antibodies the level of expression, while impo rtant, seems less critical than optimal contact with antigen presenting cel ls at locations reached by the secreted gp120 protein. A proposed Th1 adjuv ant effect of the higher numbers of CpG motifs in the synthetic genes was n ot seen using gene gun immunization which may be due to the low amount of D NA used. (C) 1999 Elsevier Science Ltd. All rights reserved.