Background: The aim of this study is to evaluate whether the combination of the ImmuKnow assay (IMK) and cytochrome P450 3A5 (CYP3A5) genotype assay is useful for identifying the risk of morbidity and mortality in living donor liver transplantation (LDLT) patients, and also to investigate the optimal cutoff value of IMK level of immune status. Material/Methods: Sixty six LDLT patients, who were randomly screened by using IMK between March 2002 and June 2011, were divided into 2 groups: patients in whom at least 1 IMK value was <175 ng/mL (Group A, n=16) and patients in whom all IMK values were >175 ng/mL (Group B, n=50). Both donors and recipients were evaluated for the CYP3A5 genotype. Results: The frequencies of cytomegalovirus and bacterial infection in Group A were significantly higher than those in Group B (P<0.001). The short term mortality was 4 (25.0%) in Group A and none in Group B, and the IMK level in all four cases became <100 ng/mL at least one time before death. The rate of CYP3A5*1 allele (expressors) among recipients was significantly higher in Group A than in Group B (63.6% vs. 22.2%, P=0.0147). The rates of CMV infection and bacterial infection, and the IMK levels was significantly higher in recipients with expressors (p=0.0216, p=0.0332, and p=0.0433, respectively). Conclusions: The combination of the IMK and CYP3A5 genotype assay is useful for monitoring immune status after LDLT, and the IMK level <100 ng/ml might be the critical level to make a recovery from the severe immunesupressive condition.
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