1022 Purpose: The programmed death-ligand 1 (PD-L1) immunohistochemistry correlates moderately with the response to PD-L1 immunomodulatory therapy. Here we present the initial results from the studies to assess the feasibility of non-invasive PD-L1 imaging with 68Ga-WL12 (a 12-mer anti-PD-L1 peptide) radiotracer from animal experiments to the first-in-human study. Methods: PD-L1 binding peptide, NOTA-WL12, was synthesized by custom services with >95% chemical purity. , we generated 68Ga-WL12 with high specific radioactivity and radiochemical purity. We select human non-small cell lung cancer cells ( HCC827) , which with moderate expression of PD-L1. To demonstrate PD-L1-specific binding of 68Ga-WL12, both binding affinity test and cell uptakes were carried out with excess WL12. Normal Mice were used for PET/CT imaging and biodistribution study. Finally, we recruited a patient ( 80 years old female ;ethical approval No.2019KT) with non-small cell lung cancer who was positive for PD-L1(>80%) and performed PET/CT imaging with 68Ga-WL12 before and after immunomodulatory therapy. Results: To demonstrate PD-L1 specificity and cell uptake, we generated 68Ga-WL12 with radiochemical purity >99% after purification, specific activity 27.8-111.2 GBq/umol. High 68Ga-WL12 uptake was observed in PD-L1-positive HCC827 cells. TO confirming radiotracer specificity, we observed a significant reduction in bound 68Ga-WL12 in the presence of the excess unmodified peptide, indicating that 68Ga-WL12 binding to PD-L1 is specific. We performed PET imaging of the tumor model with 68Ga-WL12. The uptake value was consistent with tracer biodistribution. Finally, in this first-in-human assessment of 68Ga-WL12, we show that the imaging signal corresponds to PD-L1 expression at sites of the primary tumor and metastatic focus. The SUVpeak of different tumor lesions ranged from 2.0 to 6.0. The SUV value of PD-L1 positive tumors decreased significantly after immunomodulatory therapy. Conclusions: In this study, we demonstrated that 68Ga-WL12 exhibited a high affinity to PD-L1 in the Cell uptake experiment in vitro. 68Ga-WL12 demonstrated PD-L1 specific uptake first-in-human study. Therefore, 68Ga-WL12 PET/CT imaging may be a useful tool to assess PD-L1 expression in lesions. Future clinical studies are needed to confirm our findings in a larger patient population, to comprehensively assess different 68Ga-WL12 uptake features in combination with other clinical data to optimize therapy response prediction, and to evaluate whether 68Ga-WL12 PET could also be used as a response predictor for treatment with other monoclonal antibodies targeting the PD-1/PD-L1 axis.