Background Long-term use of immunosuppressants is associated with significant morbidity and mortality in transplant recipients A simple whole blood assay that has US Food and Drug Administration clearance directly assesses the net state of immune function of allograft recipients for better individualization of therapy A meta-analysis of 504 solid organ transplant recipients (heart, kidney, kidney-pancreas, liver and small bowel) from 10 US centers was performed using the Cylex ImmuKnow assay Methods Blood samples were taken from recipients at various times posttransplant and compared with clinical course (stable, rejection, infection) In this analysis, 39 biopsy-proven cellular rejections and 66 diagnosed infections occurred Odds ratios of infection or rejection were calculated based on measured immune response values Results A recipient with an immune response value of 25 ng/ml adenosine triphosphate (ATP) was 12 times (95% confidence of 4 to 36) more likely to develop an infection than a recipient with a stronger immune response Similarly, a recipient with an immune response of 700 ng/ml ATP was 30 times (95% confidence of 8 to 112) more likely to develop a cellular rejection than a recipient with a lower immune response value Of note is the intersection of odds ratio curves for infection and rejection in the moderate immune response zone (280 ng/ml ATP) This intersection of risk curves provides an immunological target of immune function for solid organ recipients Conclusion These data show that the Cylex ImmuKnow assay has a high negative predictive value and provides a target immunological response zone for minimizing risk and managing patients to stability

Assessing relative risks of infection and rejection: a meta-analysis using an immune function assay.

The Changing Face of Heart Transplantation

Infectious complications remain a leading cause of morbidity and mortality after solid organ transplantation (SOT), and largely depend on the net state of immunosuppression achieved with current regimens. Cytomegalovirus (CMV) is a major opportunistic viral pathogen in this setting. The application of strategies of immunological monitoring in SOT recipients would allow tailoring of immunosuppression and prophylaxis practices according to the individual's actual risk of infection. Immune monitoring may be pathogen-specific or nonspecific. Nonspecific immune monitoring may rely on either the quantification of peripheral blood biomarkers that reflect the status of a given arm of the immune response (serum immunoglobulins and complement factors, lymphocyte sub-populations, soluble form of CD30), or on the functional assessment of T-cell responsiveness (release of intracellular adenosine triphosphate following a mitogenic stimulus). In addition, various methods are currently available for monitoring pathogen-specific responses, such as CMV-specific T-cell-mediated immune response, based on interferon-γ release assays, intracellular cytokine staining or main histocompatibility complex-tetramer technology. This review summarizes the clinical evidence to date supporting the use of these approaches to the post-transplant immune status, as well as their potential limitations. Intervention studies based on validated strategies for immune monitoring still need to be performed.

https://onlinelibrary.wiley.com/doi/pdf/10.1038/cti.2014.3

Clinical immune-monitoring strategies for predicting infection risk in solid organ transplantation.

Background Current monitoring systems of immunosuppression in solid-organ transplant recipients are typically focused on prevention of clinical toxicities of immunosuppressive drugs. Unfortunately, these strategies are often not tailored to the individual and do not determine the optimal level of immunosuppression for these patients. Recently, the Cylex Immune Cell Function Assay (ImmuKnow; Cylex, Inc., Columbia, MD) was approved by the U.S. Food and Drug Administration (FDA) to measure global immune response in solid-organ transplant patients receiving immunosuppressive therapy. We sought to identify the level of functional immunity as measured by the ImmuKnow assay in lung transplant recipients and to correlate these values with the dose and trough levels of immunosuppression as well as other clinical parameters in lung transplant recipients. Methods We assessed the functional immune response by the ImmuKnow assay in 143 sequential blood samples from 57 lung transplant recipients from Loyola University Medical Center. Results The average ImmuKnow assay in stable lung transplant recipients was 244 ± 138 adenosine triphosphate (ATP) ng/ml and the median level was 236 ATP ng/ml (range 5 to 669 ATP ng/ml), approximately 703 ± 695 days after lung transplantation. There was no correlation between ImmuKnow levels and tacrolimus trough levels. Stepwise multiple regression analysis identified African American race as an independent predictor of ImmuKnow assay levels when age, gender and underlying diagnosis were taken into account ( p p = 0.0001). Sixteen of the remaining 42 patients had low ImmuKnow assay values ( Conclusions The Cylex ImmuKnow assay levels were lower in infected lung transplant recipients compared with non-infected recipients and increased with treatment of these infections. It remains unclear whether the ImmuKnow assay reflects over-immunosuppressed individuals at risk of infection or bone marrow suppression by infectious agents. Further investigation will determine the role of the ImmuKnow assay in tailoring immunosuppression in lung transplant recipients.

Cylex ImmuKnow assay levels are lower in lung transplant recipients with infection.

Background Balancing immunosuppression to prevent rejection while minimizing infection or drug toxicity risk is a major challenge in heart transplantation. Therapeutic drug monitoring alone is inadequate to measure the immune response. An immune monitoring (IM) assay (ImmuKnow; Cylex, Columbia, MD) performed on peripheral blood measures adenosine triphosphatase (ATP) release from activated lymphocytes and may predict the immune state. Therefore, we sought to determine the utility of IM in heart transplant recipients. Methods Between November 2005 and July 2008, 296 heart transplant recipients had a total of 864 IM assays performed at 2 weeks to 10 years post-transplant and were correlated with infection and rejection events that occurred within 1 month after IM testing. All patients received standard triple-drug immunosuppressive therapy with tacrolimus, mycophenolate mofetil and corticosteroids, without induction therapy. Results There were 38 infectious episodes and 8 rejection episodes. The average IM score was significantly lower during infection than steady state (187 vs 280 ng ATP/ml, p p = 0.35). Interestingly, 3 of 8 rejection episodes were antibody-mediated rejections and had hemodynamic compromise and, for these, the mean IM score was significantly higher than for steady-state patients (491 vs 280 ng ATP/ml, p Conclusions The non-invasive IM test appears to predict infectious risk in heart transplant patients. The association between high IM scores and rejection risk is inconclusive due to the small number of rejection episodes. Further studies with larger sample sizes for rejection episodes are required.

Benefit of immune monitoring in heart transplant patients using ATP production in activated lymphocytes.

Each year, 55 000 organ transplants are performed worldwide. Cumulatively, the number of living organ recipients is now estimated to be over 300 000. Most of these transplant recipients will remain on immunosuppressive drugs for the remainder of their lives to prevent rejection episodes. Controlled doses of these drugs are required to prevent over-medication, which may leave the patient susceptible to opportunistic infection and drug toxicity effects, or under-dosing, which may lead to shortened graft survival because of rejection episodes. This paper describes the result of a multicenter study conducted at the Universities of Pittsburgh, Alabama and Maryland to evaluate an in vitro assay (CylexTM Immune Cell Function Assay) for the measurement of global immune response in transplant patients receiving immunosuppressive therapy. The assay uses a whole blood sample to maintain the presence of the drug during incubation. Following overnight incubation of blood with phytohemagglutinin (PHA), CD4 cells are selected using paramagnetic particles coated with a monoclonal antibody to the CD4 epitope. The CD4-positive cells are targeted as major immunosuppressive drugs are designed to specifically inhibit T-cell activation which has been implicated in rejection. The data generated at these three sites were submitted in support of an Food and Drug Association (FDA) application for the use of this assay in the detection of cell-mediated immunity in an immunosuppressed population. The assay was cleared by the FDA on April 2, 2002. This cross-sectional study was designed to establish ranges for reactivity of this bioassay in the assessment of functional immunity for an individual solid organ recipient at any point in time.

Mary C Schneider

Papers

Immune cell function testing: an adjunct to therapeutic drug monitoring in transplant patient management.