Comparison of two IGRA assays exploring cell-mediated immunity against CMV, BKV, and EBV in kidney transplant patients

Monitoring cellular immune responses (CMIs) appears to be a new biomarker in managing immunocompromised patients, especially kidney transplant recipients. This study compared the performance of two interferon-gamma (IFN-γ)-based assays-enzyme-linked immunosorbent spot assay (ELISpot) and VIDAS-IGRA-for detecting T-cell responses against cytomegalovirus (CMV), Epstein-Barr virus (EBV), and polyomavirus BK (BKV). Twenty-eight blood samples from kidney transplant recipients were analyzed using both assays. CMV-specific CMI was assessed using overlapping peptide pools from pp65 and IE-1 proteins (JPT Peptide Technologies GmbH) and a CMV lysate (bioMérieux). All patients were monitored for opportunistic viral replication through qPCR for up to 6 months after blood sampling. For CMV-CMI, the agreement between both assays was 91.7%, 100%, and 80% after stimulation by pp65 peptide pool, pp65 + IE-1 peptide pools, and CMV lysate, respectively. Positive responses were consistent with CMV serology, especially for the VIDAS-IGRA assay and after activation by JPT's PepMix. For EBV-specific responses, positive assay agreement was 92.3%, whereas the positive agreement with BKV was 80.7%. For EBV and BKV, responses were generally weaker than those for CMV (positive response if >10 spots/250,000 PBMC for EBV and >10 spots/350,000 PBMC for BKV in ELISpot or level of IFN-γ >0.08 IU/mL in VIDAS). This study highlights the importance of standardizing interferon-gamma release assays (IGRA). While VIDAS-IGRA RUO offers an open, automated, and standardized solution, responses were in agreement with ELISpot-T assay and even more when using JPT's PepMIX. However, the cellular response to BKV is weaker, and no link with viral replication has been found. This raises the question of the value of these IGRA assays in assessing the cellular response to BKV and the need to optimize these tests. A longitudinal study to observe the evolution of the cellular response could be interesting.IMPORTANCEThis original article, a proof of concept, is the first study comparing a new interferon-gamma release assay, performed on whole blood and based on an enzyme-linked immunofluorescent assay detection technique, with a homemade enzyme-linked immunosorbent spot assay using activation by the same peptides. These results were also analyzed in relation to serology results. The inclusion of these tests in clinical guidelines for monitoring cytomegalovirus, Epstein-Barr virus, and polyomavirus BK infections requires studies to evaluate their robustness and compare them.