CD177 and neoplasm: To substantiate the value of CD4-directed PET imaging as a decision-making approach, we applied additional α4-1BB mAbs, which have been shown to deplete Treg cells (74), to standard-of-care αPD-1–treated MC38 tumor-bearing animals, which presented increased 64Cu-CD4-Nb1 PET tracer uptake in the tumor periphery.