PET imaging facilitates antibody screening for synergistic radioimmunotherapy with a 177Lu-labeled αPD-L1 antibody

Rationale:The low response rate of immunotherapy, such as anti-PD-L1/PD-1 and anti-CTLA4, has limited its application to a wider population of cancer patients.One widely accepted view is that inflammation within the tumor microenvironment is low or ineffective for inducing the sufficient infiltration and/or activation of lymphocytes.Here, a highly tumor-selective anti-PD-L1 (αPD-L1) antibody was developed through PET imaging screening, and it was radiolabeled with Lu-177 for PD-L1-targeted radioimmunotherapy (RIT) and radiation-synergized immunotherapy.Methods: A series of αPD-L1 antibodies were radiolabeled with zirconium-89 for PET imaging to screen the most suitable antibodies for RIT.Mice were divided into an immunotherapy group, a RIT group and a radiation-synergized immunotherapy group to evaluate the therapeutic effect.Alterations in the tumor microenvironment after treatment were assessed using flow cytometry and immunofluorescence microscopy.Results: Radiation-synergistic RIT can achieve a significantly better therapeutic effect than immunotherapy or RIT alone.The dosages of the radiopharmaceuticals and αPD-L1 antibodies were reduced, the infiltration of CD4 + and CD8 + T cells in the tumor microenvironment was increased, and no side effects were observed.This radiation-synergistic RIT strategy successfully showed a strong synergistic effect with αPD-L1 checkpoint blockade therapy, at least in the mouse model.Conclusions: PET imaging of 89 Zr-labeled antibodies is an effective method for antibody screening.RIT with a 177 Lu-labeled αPD-L1 antibody could successfully upregulate antitumor immunity in the tumor microenvironment and turn "cold" tumors "hot" for immunotherapy.