Anti-ICOS ADCs have a specific in vitro efficacy in ICOS-expressing cell lines. (A) Immunophenotyping of CTCL cell lines using flow cytometry. Note that ICOS expression was higher in MyLa and MJ cells than in HUT78 cells. (B-F) Percentage of cell viability in increasing ADC concentrations, assessed with alamarBlue (mean of 16 replicates), on MyLa cells (B), MJ cells (C), HUT78 cells (D), Jurkat cells (E), and Jurkat-ICOS cells (F). Anti-HER2 ADCs were used as a negative control, whereas anti-CD30 ADCs (BV) were a positive control. (G) Summary table of IC₅₀ values expressed in ng/mL of all ADCs. ***P < .001. ns, not significant. PBD, pyrrolobenzodiazepine.