Next, we focused on 89Zr-hCD4-Mb and 89Zr-mCD4-Mb uptake within the TME and detected significantly enhanced 89Zr-hCD4-Mb uptake in αPD-1/α4-1BB-treated PyMT tumor-bearing hCD4-KI mice when compared to WT mice (3.22 ± 0.23 vs. 2.51 ± 0.06 %ID/ml, Figure 4A, B). Here, MB is linked to neoplasm.