Quantification of a low cellular immune response to aid in identification of pediatric liver transplant recipients at high-risk for EBV infection

Objective: Uncontrolled EBV infection leading to lymphoproliferative disease is a significant cause of morbidity in pediatric orthotopic liver transplant (OLT) recipients. Herein, we describe the use of a novel immune assay, which quantifies the lymphocyte immune response and correlates the value to risk for EBV infection. Methods: All patient data were prospectively collected between 2003 and 2005. The study included 18 pediatric liver transplant recipients, seven males and 11 females with a mean follow-up of 47 months post-OLT. Patient EBV load was monitored using real-time quantitative PCR (qPCR). The ATP release (ng/mL) of CD3⁺ lymphocytes after mitogenic stimulation with phytohemagluttinin (PHA; Cylex Corporation) was used to quantitate patient immune response. Patients were stratified by EBV load: low (< copies/μg DNA), medium (1000-4000 copies/μg DNA), and high (>4000 copies/μg DNA). Results: Patients with low EBV loads had a significantly (p < 0.04) stronger immune response to PHA than patients with EBV load >1000 copies/μg DNA. Further analysis demonstrated that patients with ATP level <125 ng/mL had 100% probability of an EBV titer >4000 copies/ μg DNA, when compared with 22% if the ATP level was between 125 and 400 ng/mL or only 15% if >400 ng/mL (p < 0.05). When immunosuppression was reduced, we observed an increase of the ATP release that correlated with a decrease of the EBV viral load. Conclusion: In conclusion, this study investigates the use of a lymphocyte activation assay to closely measure the immunosuppression status of pediatric liver transplant recipients. Because measurement of EBV DNA load as a single parameter has a poor positive predictive value for development of PTLD, the association of these assays may be of help in the identification of patients at risk for PTLD.