Figure 3. T cells enriched for high EGFRt expression are efficiently depleted by cetuximab in vivo.

(A) GFP/EGFRt-transduced CD45.1⁺ OT-I cells were sorted into GFP/EGFRt-high and -low populations using EGFR Fab Streptamers on day 5 after transduction. Unsorted and FACS-sorted samples were stained with an EGFR-specific mAb. Numbers indicate frequencies of GFP/EGFRt-high (top right gate) and GFP/EGFRt-low (bottom right gate) cells. (B) 1 × 10⁶ sorted OT-I cells were transferred into separate mouse groups, called EGFRt-high and EGFRt-low, and expanded in vivo by MVA-OVA vaccination. Cetuximab was administered to both mouse groups. Blood samples were obtained after MVA-OVA challenge and after mAb infusions. GFP versus EGFR staining of CD45.1-pregated cells is shown. Frequencies of GFP/EGFRt-high and -low cells are indicated in the top row, frequencies of GFP⁺ cells in the bottom row. (C) Blood samples were obtained from 2 mouse groups that received EGFRt-high or -low cells; time points of MVA-OVA challenge and cetuximab infusions are indicated. The control group received mock-transduced OT-I cells and similar infusions. Transferred cells among total living lymphocytes were detected with a CD45.1-specific mAb. Number of CD45.1⁺ cells per microliter blood was plotted over time for each mouse group. (D) Numbers of GFP⁺ cells per microliter blood are plotted over time. (E) A section of the graph in D that refers to days 17–64 is shown on a different y axis scale. Means ± SD are shown in all graphs; n = 3 for EGFRt-high, n = 6 for EGFRt-low, n = 2 for mock.