This study also reported the generation and isolation of mAb 15A7.5, an anti–nectin-4 mAb chosen due to its observed selectivity toward nectin-4–expressing tumor cells in comparison with skin keratinocytes, as we hypothesized that less binding to keratinocytes would lead to less in vivo–associated clinical signs of skin toxicity. The gene discussed is NECTIN4; the disease is dermatological toxicity.