Epcoritamab eliminates CLL cells in PDXs. (A) PBMCs from patients who were TN (n = 3, triangles) and RES (n = 4, squares) were injected into NSG mice on experimental day 0. Cell engraftment was confirmed on day 2 via flow cytometry. Mice were then treated once weekly with either epcoritamab or B12 control (0.5 mg/kg). Four or 5 mice were included for each patient and divided between the 2 treatment groups (n = 7 patients; n = 31 mice). (B) Representative flow cytometry dot plots of peripheral blood from mice treated with either epcoritamab (EPCO) or B12 control (B12) on day 2 (top, before treatment), day 10 (middle, after 1 injection), and day 17 (bottom, after 2 injections). (C) Comparison of the mean CLL cell count in the peripheral blood between EPCO-treated (blue) and B12-treated (red) groups on experimental days 10 and 17. (D) Percentage of CLL cells among nucleated cells in the spleen on experimental day 17 between the EPCO-treated (blue) and B12-treated (red) groups. The median and interquartile ranges are indicated. Asterisks indicate statistical significance using Mann-Whitney test. ∗∗P< .01; ∗∗∗∗P< .0001.