The ADC supply chain (antibody, payload-linker, conjugation, fill)

An ADC is assembled from a monoclonal antibody made by CHO culture and purified like any biologic, a cytotoxic payload-linker made by small-molecule chemistry in high-containment suites because a few micrograms can harm a worker, and a conjugation step in which the two are joined (through lysines, reduced interchain cysteines or engineered sites), the excess payload removed, and the drug-to-antibody ratio and free payload measured. The conjugated drug substance is then filled and usually lyophilised at a sterile fill-finish site with the same containment. Each of the four steps is typically at a different site, often a different company and country, and the intermediates are frozen and shipped between them, so lead times add up to a year or more and a slip at any node delays the whole product.

The pattern is visible in the licensed products. Trastuzumab deruxtecan combines an antibody, an exatecan-derived payload and Daiichi Sankyo's own conjugation, with contract manufacturers added as demand outran the launch capacity; sacituzumab govitecan's first approval attempt ended in a 2019 complete response letter over chemistry, manufacturing and controls findings before approval in 2020; brentuximab vedotin and enfortumab vedotin depend on MMAE payload-linker supplied by a small number of high-potency API makers. Because so much ADC conjugation capacity was built at WuXi XDC in China, Western sponsors have moved to add Lonza, Samsung Biologics, Abzena, Piramal, Sterling and Merck KGaA capacity, and the manufacturing map on this site tracks those sites. The existing records on conjugation CDMOs, payload synthesis and site-specific chemistry hold the detail on each node.