Establishing pediatric immune response zones using the Cylex® ImmuKnow™ assay

For all transplant patients, the transplant physician must balance the risk of rejection caused by under-immunosuppression against the risk of drug toxicity, secondary infections and post-transplant lymphoproliferative disorder with over-immunosuppression. A Food and Drug Administration (FDA)-approved in vitro assay, the Cylex® ImmuKnow™ assay, provides a global assessment of cellular immune function to help monitor the immune status of immunosuppressed patients. This assay uses the plant lectin phytohemagglutinin to stimulate lymphocytes; an ATP assay is then used to measure the degree of activation of CD4⁺ T cells. However, the normal values for this assay were developed with healthy adult patients. In this study, we determined the normal ranges for the ImmuKnow™ assay in healthy children and compared those values to levels obtained in healthy adults and in stable pediatric renal transplant patients. We found that healthy children 12 yr of age and older showed immune function levels indistinguishable from adults, while healthy children under 12 had significantly lower immune function levels than adults. For adults, the ImmuKnow™ assay zones (in ng/mL ATP) of strong, moderate and low immune function correspond to > 525, 225 to 525, and < 225. In children under 12, we found the corresponding zones to be > 395, 175-395 and < 175 ng/mL. The median value for normal adults is 415, whereas it is only 295 for children < 12 yr of age and this value decreases to 165 in stable renal transplant patients < 12 yr of age (compared with 258 for stable adult renal transplant patients). Thus, this study provides critical information necessary to utilize the ImmuKnow™ assay with pediatric patients. In adults, the degree of immune function as assessed by the ImmuKnow™ assay helps to predict patients at risk for infection or rejection. If further studies in pediatric patients document the same and is true for children, then the ImmuKnow™ assay will provide a useful adjunct tool to prevent over- or under-immunosuppression as newly developed drugs are utilized or drug treatment is altered because of drug side effects, toxicity, concurrent illnesses or rejection.