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Background  Programmed death-ligand 1 (PD-L1) regulates immune homeostasis by promoting T-cell exhaustion. It is involved in chronic infections and tumor progression. Nuclear imaging using radiolabeled anti-PD-L1 antibodies can monitor PD-L1 tissue expression and antibody distribution. However, physiological PD-L1 can cause rapid antibody clearance from blood at imaging doses. Therefore, we hypothesized that inflammatory responses, which can induce PD-L1 expression, affect anti-PD-L1 antibody distribution. Here, we investigated the effects of three different infectious stimuli on the pharmacokinetics and tumor targeting of radiolabeled anti-PD-L1 antibodies in tumor-bearing mice.    Materials/Methods  Anti-mouse-PD-L1 and isotype control antibodies were labelled with indium-111 ([ 111 In]In-DTPA-anti-mPD-L1 and [ 111 In]In-DTPA-IgG2a, respectively). We evaluated the effect of inflammatory responses on the pharmacokinetics of [ 111 In]In-DTPA-anti-mPD-L1 in RenCa tumor-bearing BALB/c mice in three conditions: lipopolysaccharide (LPS), local  Staphylococcus aureus , and heat-killed  Candida albicans . After intravenous injection of 30 or 100 µg of [ 111 In]In-DTPA-anti-mPD-L1 or [ 111 In]In-DTPA-IgG2a, blood samples were collected 1, 4, and 24 h p.i. followed by microSPECT/CT and  ex vivo  biodistribution analyses. PD-L1 expression, neutrophil, and macrophage infiltration in relevant tissues were evaluated immunohistochemically.    Results  In 30 µg of [ 111 In]In-DTPA-anti-mPD-L1 injected tumor-bearing mice the LPS-challenge significantly increased lymphoid organ uptake compared with vehicle controls (spleen: 49.9 ± 4.4%ID/g versus 21.2 ± 6.9%ID/g, p &amp;lt; 0.001), resulting in lower blood levels (3.6 ± 1.6%ID/g versus 11.5 ± 7.2%ID/g; p &amp;lt; 0.01) and reduced tumor targeting (8.1 ± 4.5%ID/g versus 25.2 ± 5.2%ID/g, p &amp;lt; 0.001). Local  S. aureus  infections showed high PD-L1 +  neutrophil influx resulting in significantly increased [ 111 In]In-DTPA-anti-mPD-L1 uptake in affected muscles (8.6 ± 2.6%ID/g versus 1.7 ± 0.8%ID/g, p &amp;lt; 0.001). Heat-killed  Candida albicans  (Hk- C. albicans ) challenge did not affect pharmacokinetics. Increasing [ 111 In]In-DTPA-anti-mPD-L1 dose to 100 µg normalized blood clearance and tumor uptake in LPS-challenged mice, although lymphoid organ uptake remained higher. Infectious stimuli did not affect [ 111 In]In-DTPA-IgG2a pharmacokinetics.    Conclusions  This study shows that anti-PD-L1 antibody pharmacokinetics and tumor targeting can be significantly altered by severe inflammatory responses, which can be compensated for by increasing the tracer dose. This has implications for developing clinical PD-L1 imaging protocols in onco-immunology. We further demonstrate that radiolabeled anti-PD-L1 antibodies can be used to evaluate PD-L1 expression changes in a range of infectious diseases. This supports the exploration of using these techniques to assess hosts’ responses to infectious stimuli.

PD-L1 Antibody Pharmacokinetics and Tumor Targeting in Mouse Models for Infectious Diseases