Temporary sequestration of T cells in secondary lymphoid organs in which they undergo activation during the priming phase of T-BsAb treatment. (A) huCD3/20 double transgenic mice received IV injection of CD3 × CD20 T-BsAb. At the indicated time points after injection, blood samples were obtained. Percentage of B cells, T cells, and the expression of T-cell activation markers were analyzed by flow cytometry. Upper panel: gate on all CD45⁺ cells. Lower panel: gate on CD8⁺ T cells. (B) Mice and treatment were the same as described for panel A. Mice were euthanized 24 hours after treatment, and the lymph nodes, spleen, and bone marrow were removed. Percentage of B cells, T cells, and the expression of T-cell activation markers were analyzed by flow cytometry. Upper panel: gate on all CD45⁺ cells. Lower panel: gate on CD8⁺ T cells.