²¹¹At-CD38 selectively binds and kills CD38⁺ MM cells. (A) CD38⁺ or CD38⁻ cell lines were incubated with either anti-CD38 OKT10 mAb, or OKT10 conjugated with amine-reactive B10, or OKT10 conjugated with yttrium chelator DOTA. Cells were then washed twice, incubated with anti-mouse IgG Fc-APC, washed twice, and analyzed by flow cytometry. (B) CD38⁺ cells were preincubated with buffer or CD38 mAb, then ²¹¹At-OKT10-B10 or isotype control ²¹¹At-BHV1-B10 was added and cells incubated, washed twice, cell-associated radioactivity measured in a γ counter, and ²¹¹At uptake calculated as a percentage of applied ²¹¹At. N = 4 replicates per treatment; error bars = 1 standard error of the mean (SEM). (C) CD38⁺ or CD38⁻ cells were incubated in media (control) or serial dilutions of OKT10-B10 or ²¹¹At-OKT10-B10 at 37°C for 60 hours. Cytotoxicity was then assessed using CellTiter-Glo. N = 3 replicates per treatment; error bars = 1 standard deviation (SD).