TLR9 and cancer: Oligodeoxynucleotides (ODNs) containing unmethylated cytosine–phosphate–guanosine (CpG) motifs, which are highly abundant in bacterial DNA, are readily recognized by Toll-like receptor 9 (TLR9) on immune cells, trigger an immunomodulatory cascade, and induce a Th1-biased immune milieu, which makes CpG ODNs have great potential to treat cancer, infections, and allergies [10].