CLL cells expand faster in vivo in the presence of constantly elevated levels of CD257. (A) Splenocytes from TCL1×BAFF-Tg mice were labeled with CD3 and CD5 antibodies and CD3⁻CD5⁺ were enriched by cell sorting. Sorted leukemic cells (10⁶) were injected into either BAFF-Tg or WT recipients (n = 6 each group) and their expansion was analyzed 30 days later by flow cytometry. (B) Expansion of transferred CD3⁻CD5⁺ cells transduced with a luciferase-expressing lentivirus before injection was measured by bioluminescence at the indicated time points. (C) Representative autopsy and flow cytometry of splenocytes from a BAFF-Tg mouse 5 months after adoptive transfer (n = 6). Camera: Nikon COOLPIX 995. (D) Representative flow cytometry of cells obtained from inguinal lymph nodes from WT or BAFF-Tg mice 5 months after adoptive transfer (n = 6 mice each group).