OLIGONUCLEOTIDE-MEDIATED INHIBITION OF CD28 EXPRESSION INDUCES HUMAN T-CELL HYPORESPONSIVENESS AND MANIFESTS IMPAIRED CONTACT HYPERSENSITIVITY IN MICE

Ligation of CD28 provides a costimulatory signal essential for Ag-medi ated T cell activation via the TCR, Blocking CD28 ligation can inhibit cytokine expression and elicits a state of T cell hyporesponsiveness, In this study, we examined the effect of inhibiting CD28 expression o n in vitro and in vivo T cell responses. To address this, we have synt hesized a series of G-rich phosphorothioate oligonucleotides that inhi bited activation-induced transcription and cell surface expression of CD28 on human T cells. CD28 blockade was selective, as expression of o ther activation-induced receptors was unaffected by oligonucleotide tr eatment, Using strategic changes to base composition, we identified a minimal 12-mer sequence, containing two sets of four contiguous guanos ines separated by 3 to 5 bases, which conferred activity in vitro, Fur thermore, inhibition of CD28 expression mediated by one representative active oligonucleotide, GR1, resulted in a concomitant dose-dependent diminution of anti-CD3/PMA-induced cytokine (IL-2, IFN-gamma, IL-8) p roduction. Inhibition of IL-2 synthesis was dependent on CD28 expressi on, as GR1 failed to abrogate activated IL-2 production in a CD28-defi cient T cell line, HUT 78, The inhibitory activity of GR1 reduced T ce ll proliferative responses in MLR and induced Ag-specific T cell hypor esponsiveness to alloantigens. Finally, s.c. administration of GR1 imp aired in vivo contact hypersensitivity responses in mice and was assoc iated with substantially decreased CD28 and IFN-gamma mRNA expression in lymph node cells. Collectively, our studies show the tolerogenic po tential of oligonucleotide-mediated CD28 inhibition on T cell activati on, in vitro and in vivo.