The Programmed cell death protein 1 (PD1)/Programmed death-ligand 1 (PD-L1) axis is an important immune checkpoint for T cell activation that is used by tumors to evade the host immune response. Blocking signaling with the PD-L1 antibody MPDL3280A results in ongoing T cell activity and can induce durable tumor regression across numerous solid tumor types. PD-L1 is not only expressed by tumor cells but also by immune cells, activated vascular endothelial cells and in immune privileged sites such as the eye. An obstacle to using PD-L1 expression as predictive biomarker might be its potential heterogeneous expression and fast dynamics. For PD1/PD-L1 pathway inhibition PD-L1 tumor surface expression, positive in 40-100% of all melanoma patients and 35-95% of all non-small-cell lung cancer (NSCLC) patients, was proposed as a potential biomarker. In early clinical trials, PD-L1 expression has been associated with response to PD1/PD-L1 inhibition. However, other clinical trials reported response to PD1/PD-L1 checkpoint inhibitors in up to 47% of PD-L1-negative melanomas assessed by a single biopsy. In bladder cancer weak to strong PD-L1 expression has been reported in 30% of the patients, however also response in PD-L1-negative patients has been seen. For triple-negative breast cancer (TNBC) little is known, but early response data are also very promising.~Radio-labeling of MPDL3280A with the positron emission tomography (PET) radionuclide Zirconium-89 (89Zr) enables non-invasive imaging and quantification of PD-L1 distribution in cancer patients. By performing a 89Zr-MPDL3280A-PET scan prior to treatment with MPDL3280A, the uptake of the tracer in the primary and metastatic tumor lesions and normal organ distribution can be evaluated, as well as the use of a 89Zr-MPDL3280A-PET as a complementary tool for patient selection in the future. There is currently no information with regards to tumor saturation or inflammation induced by checkpoint inhibitors. This can be measured with SUV of 89Zr-MPDL3280A PET changes during a therapeutic dosing with MPDL3280A.
By performing a 89Zr-MPDL3280A-PET scan prior or during treatment with MPDL3280A, the uptake of the tracer in the primary and metastatic tumor lesions and normal organ distribution can be evaluated, as well as the use of a 89Zr-MPDL3280A-PET as a complementary tool for patient selection and MPDL3280A- target saturation during treatment.