TLR7 agonist 20 (compound 23) is an imidazoquinoline analogue. TLR7 agonist 20 is a potent TLR7 specific agonist, with an EC 50 value of 0.23 μM for hTLR7. TLR7 agonist 20 shows strong adjuvant activity on spike antibody levels which induces a strong T helper 1 (Th1) response with increase in IgG2b and IgG2c , in addition to IgG1.