Although B16-F10 murine melanoma cells were less sensitive to maytansine in vitro (EC50: 47.7 nM) compared to EL4 murine T cell lymphoma cells reported previously (EC50: 3.9 nM),30 the DM1-modified A12-VHHkappa showed comparable cytotoxicity (EC50: 48.1 nM) as free maytansine after a three-day incubation with B16-F10 cells with high PD-L1 expression (Figure S17A). Here, CD274 is linked to melanoma.