In vitro uptake assay of [3H]DDG in cells obtained from mice treated with anti-4-1BB. Cells were extracted on day 14 post-tumor implant from mice bearing CT26 tumors treated with 4-1BB mAb, which showed an 8-fold increase in non-adherent CD45+ cells extracted from tumors (TI_CD45+; a) and draining lymph nodes (DLN; b) of mice treated with 4-1BB mAb compared to untreated mice. The TI_CD45+ and DLN cell populations are represented in bar graphs (c, d). e) In vitro co-culture of CT26 cells and splenocytes extracted from the CT26 tumor bearing mice, also showed a significant 2-fold increase in uptake of [3H]DDG in splenocytes isolated from the treated mice compared to the untreated mice. CT26 tumor cell uptake did not show a significant difference between the group treated with 4-1BB mAb and the untreated group (f). ** p < 0.01 and *** p < 0.0001 by t-test.