Objective To study the expression of kynureninase(KYNU)in pancreatic cancer tissue and its relationship with immune invasion and prognosis.Methods A total of 49 patients with resectable pancreatic cancer who underwent surgical treatment in Department of General Surgery,Wuxi Fifth People's Hospital from January 2019 to June 2021 were selected as the study subjects.All patients were diagnosed with resectable pancreatic cancer by pathology and imaging,and their TNM stagings of tumors were stages Ⅰ-Ⅲ,which received neoadjuvant therapy before surgery.Cancer tissue and corresponding paracancer tissue samples(≥4cm from the cancer focus)of all patients were collected.Immunohistochemical staining was used to detect the expression of KYNU protein in pancreatic cancer tissues and corresponding adjacent tissues,and the infiltration of CD8+TILs,CD103+TILs,CD68+TAMs,CD204+TAMs,and CD11c+DCs in cancer tissues.Real-time fluorescence quantitative PCR was used to detect the relative expression of KYNU mRNA.The relationship between KYNU mRNA expression and immune infiltration and prognosis was analyzed by Pearson correlation analysis,Kaplan Meier survival curve,and COX proportional hazards regression model.Results The positive rate of KYNU protein(77.6%)and mRNA expression(2.9±0.7)in pancreatic cancer tissues were higher than those in adjacent normal tissues(38.8%,0.8±0.5),and the differences were significant(χ2=15.138,t=17.088,all P<0.05).The infiltration number of CD8+TILs,CD103+TILs,CD68+TAMs,CD204+TAMs and CD11c+DCs in KYNU high expression group was higher than those in KYNU low expression group,and the differences were significant(t=2.533～5.806,all P<0.05).The expression of KYNU in pancreatic cancer was positively correlated with the invasion numbers of CD8+TILs,CD103+TILs,CD68+TAMs,CD204+TAMs and CD11c+DCs(r=0.514,0.502,0.319,0.415,0.438,all P<0.05).The cumulative OS and DFS of high KYNU expression group were lower than those of low KYNU expression group(20.0%vs 42.9%,14.3%vs 35.7%),and the differences were significant(Log Rank χ2=4.358,4.273,P = 0.039,0.042).Multivariate COX regression analysis showed that TNM stageⅢ(HR:1.653,95%CI:1.294～1.937),low differentiation(HR:1.671,95%CI:1.284～2.003),lymph node metastasis(HR:1.582,95%CI:1.117～1.896)and KYNU high expression(HR:1.591,95%CI:1.106～1.902)were independent risk factors for pancreatic cancer prognosis(all P<0.05).Conclusion KYNU was highly expressed in pancreatic cancer tissues,which was closely related to immune infiltration and clinical prognosis of pancreatic cancer.It may be a potential biomarker for predicting prognosis of pancreatic cancer.