In vivo efficacy of VAY-736 in the Eμ-Tcl1 mouse model of CLL. (A) Histogram flow cytometry analysis of VAY-736 binding over isotype to CD5⁺ CD19⁺ double-positive Eμ-TCL1 mouse splenocytes. (B) Representative FACS of CD5⁺ CD19⁺ percent double-positive leukemia lymphocyte population in peripheral blood samples from a leukemia-burdened Eμ-TCL1 transgenic mouse. Mice were injected weekly for 2 weeks total with 100 mg/kg of VAY-736. Blood was collected 1 day after treatment and weekly. (C-D) Peripheral blood from Eμ-TCL1 mice were collected 24 hours before (Pre tx) and 24 hours after (Post tx) injection of VAY-736 at 100 mg/kg or phosphate-buffered saline (PBS) vehicle control, and CD5⁺ CD19⁺ double-positive leukemic cells were counted (C) and percentages were analyzed (D) by using flow cytometry. (E) Survival analysis of SCID mice engrafted with leukemia-burdened Eμ-TCL1 splenocytes from a single donor. SCID mice were enrolled in the study when CD5⁺ CD19⁺ percent lymphocytes from peripheral blood reached >20% within 9 weeks of engraftment. Mice received weekly injections of VAY-736 (10 mg/kg) or PBS vehicle control for 6 weeks (P = .0169: VAY-736; n = 3, vs vehicle, n = 4). (F) Eμ-TCL1 splenocytes from a highly leukemic burdened mouse were adoptively transferred into NOTAM mice. Peripheral leukemic percentages were monitored by using flow cytometry before engraftment, pretreatment, 24 hours posttreatment, and at 12 days posttreatment with either VAY-736 injection (10 mg/kg) or vehicle (PBS). (G) Mice from panel F were euthanized at day 12 posttreatment, and the leukemic burden of the spleen and bone marrow were analyzed according to percent CD5⁺ CD19⁺ by using flow cytometry.