Effects of CD137 mAb on naive T-cell homeostasis in lymphopenic mice. CFSE-labeled naive OT-1 × RAG1 KO T cells (1 × 10⁶) were adoptively transferred into sublethally irradiated B6 mice. Then, 100 μg rat IgG or 2A was injected intraperitoneally on day 0 (upper panels) or day 7 (lower panels) after cell transfer. Spleen cells were prepared at day 6 after antibody treatment and analyzed by flow cytometry. Histogram plots of CFSE intensity of transferred OT-1 cells (gated on CD8⁺ OT-1 tetramer-positive cells) in the spleen are shown. The results are from one representative of 3 independent experiments with similar results.