SEQUENCE-SPECIFIC TARGETING OF THE INTERLEUKIN-2 RECEPTOR P55 CHAIN GENE-EXPRESSION BY ANTISENSE OLIGONUCLEOTIDES

Others have documented that anti-sense oligonucleotides (AS ONs) block the expression of the early, transiently transcribed oncogenes. Expre ssion of the interleukin-2 receptor (IL-2R) p55 gene involves delayed, prolonged gene activation in activated T-cells. Given our interest in IL-2 receptor directed immune-suppression, we sought to determine if AS ONs could provide a new tool for blocking the expression of the IL- 2R p55 chain. An 18 mer AS ON was specifically designed to target exon 3 of the IL-2R p55 chain. AS ON to exon 3 reduced the level of IL-2R p55 transcripts, i.e. 49% in phytohaemagglutinin (PHA)-stimulated peri pheral blood mononuclear cells (PBMC) and 52% in cultures treated with sense (S ON) as controls versus 29% in cultures treated with AS ON as assessed by semiquantitative polymerase chain reaction (PCR) using be ta-actin as a standard (100%). Nonetheless, the AS ON targeted at the IL-2R p55 gene did not block the full-length IL-2R p55 protein of PHA- stimulated PBMC on the cell surface as assessed by flow cytometry. PHA -induced proliferation of PBMC determined by TdR uptake was diminished from 123865 +/- 4927 cpm to 55915 +/- 1829 cpm with AS ON (5.25 mu M) as compared to nonspecific inhibition of 99234 +/- 6070 cpm with the S ON (5.25 mu M) as a control. Hence, the effect of the AS ON on speci fic IL-2R p55 expression and lectin-stimulated proliferation was modes t. We attribute this modest effect, which contrasts with the rigorous effect on early activated genes, to rapid degradation of unmodified AS ONs prior to expression of the IL-2R gene. Transcription of the targe t gene is delayed and persistent. To extend the spectrum of genes whos e transcripts are reduced by AS ON to later-activated genes with a pro longed expression such as the IL-2R, chemically modified AS ONs with a greater stability are required.