ObjectiveTo investigate the mechanism by which Haizao Yuhu Tang regulates the nuclear receptor subfamily 4 group A member 1 （NR4A1）signaling pathway to modulate CD8-positive T lymphocyte （CD8⁺T） cell exhaustion-mediated immune escape in transgenic mice with papillary thyroid carcinoma （PTC）. MethodsSixty C57BL/6J mice carrying the conditional BRAF^V600E point mutation were randomly assigned to five groups （n=12）： Model， low-dose （7.28 g·kg^-1·d^-1） Haizao Yuhu Tang， medium-dose （14.56 g·kg^-1·d^-1） Haizao Yuhu Tang， high-dose （29.12 g·kg^-1·d^-1） Haizao Yuhu Tang， and vemurafenib （PLX4032， 0.02 g·kg^-1·d^-1）. In addition， 12 BRAF^V600E-negative mice were selected as the control group. All the groups received continuous intervention for 8 weeks. After treatment， the thyroid tumor weight and volume of mice in each group were measured. Hematoxylin and eosin （HE） staining was performed to observe the morphological characteristics of thyroid tumors. Enzyme-linked immunosorbent assay （ELISA） was adopted to quantify the serum levels of interferon-γ （IFN-γ）， interleukin-2 （IL-2）， tumor necrosis factor-α （TNF-α）， C-X-C motif chemokine ligand 9 （CXCL9）， and C-X-C motif chemokine ligand 10 （CXCL10）. Flow cytometry was employed to determine the proportion of cytotoxic CD8⁺T cells in the tumor tissue. Western blot and real-time PCR were employed to determine the protein and mRNA levels， respectively， of molecules related to the NR4A1 signaling pathway. ResultsCompared with the control group， the model group showed significantly increased thyroid tumor volume and weight （P<0.01）. Compared with the model group， the low-dose， medium-dose， and high-dose Haizao Yuhu Tang groups and the vemurafenib group exhibited varying degrees of reduction in thyroid tumor volume and weight （P<0.05， P<0.01）， with the medium-dose Haizao Yuhu Tang group and the vemurafenib group showing the most pronounced therapeutic effects （P<0.01）. Compared with the model group， the low-dose， medium-dose， and high-dose Haizao Yuhu Tang groups and the vemurafenib group showed increased serum levels of IFN-γ， IL-2， TNF-α， CXCL9， and CXCL10， decreased mRNA and protein levels of NR4A1， Programmed cell death-1 （PD-1）， and Programmed cell death-ligand 1 （PD-L1）， and enhanced cytotoxic activity of CD8⁺T cells （P<0.05， P<0.01） Among these groups， the medium-dose Haizao Yuhu Tang group exhibited the optimal therapeutic effects. In addition， compared with that in the model group， T-cell factor-1 （TCF-1） expression was increased in the low-dose， medium-dose， and high-dose Haizao Yuhu Tang groups （P<0.01）， whereas no significant change in TCF-1 expression was observed in the vemurafenib group. ConclusionHaizao Yuhu Tang may restore the cytotoxic function of CD8⁺T cells by inhibiting the NR4A1 signaling pathway， thereby suppressing immune evasion in PTC and delaying PTC growth.