Merck & Co. Inc. partnered with Ambrx Inc. because the pharma hopes to build upon the biotech's near-decade of experience in site-specific peptide modification to move antibody-drug conjugates beyond oncology.

Last month, Merck agreed to pay Ambrx $15 million up front and up to $288 million in milestones to use this technology to develop antibodies against an undisclosed number of pre-defined targets. The deal marks Ambrx's third antibody partnership in three years.