Knockdown of Programmed Death 1 Inhibited Progression of Papillary Thyroid Carcinoma in Mice

Background: PD-L1 and PD1 mainly focused on melanoma, lung cancer and other tumors, while the related studies on early lymph node metastasis of papillary thyroid carcinoma were rarely reported. Objective: For elucidating the role of programmed death 1 (PD1)/programmed death ligand 1 (PD-L1) pathway in tumor growth of papillary thyroid carcinoma (PTC). Methods: Human thyroid cancer cell line and human normal thyroid cell line were obtained and transfected with si-PD1 or pCMV3-PD1 for the construction of PD1 knockdown or overexpression models. BALB/c mice were purchased for in vivo studies. Nivolumab was implemented for in vivo inhibition of PD1. Western blotting was performed for determining protein expression, while RTqPCR was used to measure relative mRNA levels. Results: The PD1 and PD-L1 levels were both significantly upregulated in PTC mice, while the knockdown of PD1 downregulated both PD1 and PD-L1 levels. Protein expression of VEGF and FGF2 was increased in PTC mice, while si-PD1 decreased their expression. Silencing of PD1 using si-PD1 and nivolumab both inhibited tumor growth in PTC mice. Conclusion: Suppressing PD1/PD-L1 pathway significantly contributed to the tumor regression of PTC in mice.