The present invention provides the cyclic dinucleotide compound 2'2'-RR-(3'F-A)(3'F-A) as a highly active immune stimulator that activates DCs via the cytoplasmic receptor known as STING (Stimulator of Interferon Genes), and compositions and uses thereof.本發明提供作為高度活性免疫刺激劑之環二核苷酸化合物2'2'-RR-(3'F-A)(3'F-A),其可經由稱為STING (干擾素基因之刺激劑)之細胞質受體活化DC;以及其組合物及用途。