CDN-A is a cyclic di-nucleotide, it can be used to synthesis antibody-drug conjugate (ADC). Cyclic di-nucleotides are potent stimulators of innate and adaptive immune responses. In humans, cyclic di-nucleotide, which are either produced endogenously in response to foreign DNA or by invading bacterial pathogens, trigger the innate immune system by activating the expression of interferon genes.