TE-1146

First‐line treatment of multiple myeloma, a prevalent blood cancer lacking a cure, using anti‐CD38 daratumumab antibody and lenalidomide is often inadequate due to relapse and severe side effects. To enhance drug safety and efficacy, an antibody‐drug conjugate, TE‐1146, comprising six lenalidomide drug molecules site‐specifically conjugated to a reconfigured daratumumab to deliver cytotoxic lenalidomide to tumor cells is developed. TE‐1146 is prepared using the HighDAR platform, which employs i) a maleimide‐containing “multi‐arm linker” to conjugate multiple drug molecules creating a drug bundle, and ii) a designed peptide with a Zn2+‐binding cysteine at the C‐termini of a reconfigured daratumumab for site‐specific drug bundle conjugation. It is shown that TE‐1146 remains intact and effectively enters CD38‐expressing tumor cells, releasing lenalidomide, leading to enhanced cell‐killing effects compared to lenalidomide/daratumumab alone or their combination. This reveals the remarkable potency of lenalidomide once internalized by myeloma cells. TE‐1146 precisely delivers lenalidomide to target CD38‐overexpressing tumor cells. In contrast, lenalidomide without daratumumab cannot easily enter cells, whereas daratumumab without lenalidomide relies on Fc‐dependent effector functions to kill tumor cells.