Antitumor immunity visualized by A20HA-Luci imaging. (A) Experimental outline. Donor mice received 2.5 × 10⁶ CD4⁺-enriched HA-specific T cells with or without a tumor challenge (10⁶ A20HA-Luci intravenously 9 days before T-cell transfer). At 18 days after T-cell transfer, donor mice were killed, and their spleens and LNs were harvested and T cell–enriched to be transferred into transplant recipients. Recipients were challenged with or without 10⁶ A20HA-Luci intravenously 10 days prior to transplantation. Recipients underwent transplantation as described in “Methods.” A total of 3 tumor-bearing and 3 non–tumor-bearing mice were randomly removed from the donor pool and received plus or minus 10⁷ pfu VaccHA (subcutaneously). They were killed 6 days later to assess HA-specific T-cell function. (B) Percentage of HA-specific T-cell expansion in vivo and (C) IFNγ production in response to HA peptide in vitro in these non–tumor-bearing (NT) and tumor-bearing (T) mice are shown. Data represent mean plus or minus SE. (D,E) Photon emission was used as an indication of tumor size and dissemination. Images of 4 ear-tagged mice per group at the indicated time points are shown.